Why Going Faster-Than-Light Leads to Time Paradoxes

Is faster-than-light (FTL) travel possible? In most discussions of this, we get hung up on the physics of particular ideas, such as wormholes or warp drives. But today, we take a more zoomed out approach that addresses all FTL propulsion - as well as FTL messaging. Because it turns out that they all allow for time travel. Join us today as we explore why this is so and the profound consequences that ensue.
Written & presented by Prof David Kipping. Special thanks to Prof Matt Buckley for fact checking and his great blog article that inspired this video (www.physicsmatt.com/blog/2016/....
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::References::
► Alcubierre, M., 1994, The warp drive: hyper-fast travel within general relativity, Classical and Quantum Gravity, 11 L73: arxiv.org/abs/gr-qc/0009013
► Alcubierre & Lobo (2021), Warp drive basics, arxiv.org/abs/2103.05610
► Pfenning, M. & Ford, L., 1997, The unphysical nature of Warp Drive, Classical and Quantum Gravity, 14, 1743: arxiv.org/abs/gr-qc/9702026
► Finazzi, S., Liberati, S., Barceló, C., 2009, Semiclassical instability of dynamical warp drives, Physical Review D., 79, 124017: arxiv.org/abs/0904.0141
► McMonigal, B., Lewis, G., O'Byrne, P., 2012, Alcubierre warp drive: On the matter of matter, Physical Review D., 85, 064024: arxiv.org/abs/1202.5708
► Everett, A., 1996, Warp drive and causality, Physical Review D, 53, 7365: journals.aps.org/prd/abstract...
► For a more rigorous breakdown of the axis flipping in Minkowski spacetime, see Chapter 3 of "Special Relativity" by Valerio Faraoni (williamsgj.people.cofc.edu/Mi...)
::Music::
Music licensed by SoundStripe.com (SS) [shorturl.at/ptBHI], or via Creative Commons (CC) Attribution License (creativecommons.org/licenses/..., or with permission from the artist
► Hill - An Interesting Retirement [open.spotify.com/album/3S2hu2...]
► Joachim Heinrich - Stjärna
► Falls - Life In Binary
► Chris Zabriskie - Cylinder Two
► Chris Zabriskie - Cylinder Five
► Chris Zabriskie - Cylinder Four
► Falls - Ripley
► Caleb Etheridge - Always Dreaming
► Joachim Heinrich - Y
► Indive - Trace Correction
::Film/TV clips used::
► Interstellar (2014) Paramount Pictures
► Contact (1997) Warnes Bros.
► The Imitation Game (2014) The Weinstein Company
► Star Trek: Generations (1994) Paramount Pictures
► Cosmos: Possible Worlds (2020) National Geographic Fox
► Stephen Hawking's Favorite Places (2016) Curiosity Stream
► Star Wars: The Empire Strikes Back (1980) 20th Century Fox
► Star Trek: Deep Space Nine (1993-1999) Paramount Television
► The Day The Earth Stood Still (2008) 20th Century Fox
► Stargate (1994) MGM/UA Distribution Co.
► Star Trek: Beyond (2016) Paramount Pictures
► Star Trek IV: The Voyage Home (1986) Paramount Pictures
► The Expanse (2015-2022) Legendary Television Distribution
► Star Trek: The Next Generation (1987-1994) Paramount Television
► Avengers: Endgame (2019) Walt Disney Studios Motion Pictures
► Star Trek: Enterprise (2001-2005) Paramount Television
► Back To The Future (1985) Universal Pictures
► Passengers (2016) Sony Pictures Releasing
► The Time Machine (Dreamworks)
► Alien: Covenant (2017) 20th Century Fox
► Star Trek (1966-1969) Paramount Television
► Tenet (2020) Warner Bros. Pictures
► Loki (2021-) Marvel Studios
► Somewhere In Time (1980) Universal Pictures
► The Assassination of Jesse James by the Coward Robert Ford (2007) Warner Bros. Pictures
► Star Trek: Into Darkness (2013) Paramount Pictures
► Logan (2017) 20th Century Fox
► Star Trek: First Contact (1996) Paramount Pictures
::Subtitles::
► German by Frischholz Christian
::Chapters::
00:00 Introduction
06:52 Space Time Diagrams
12:51 Causality Violations
17:01 Paradoxes in Time
24:28 Outro and Credits
#FasterThanLight #Alcubierre #CoolWorlds

[@realbrickbread]

I like to imagine that as soon as we discover FTL and break spacetime, the simulation crashes and the higher beings are annoyed they have another bug to fix

[@MarcyTheKindaCoolWizard]

"God damn it i didnt think they would actually get to it! Now i gotta program a whole new enviorment and items"

[@lucasmoers]

“There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.” ― Douglas Adams, The Restaurant at the End of the Universe

[@insidejob8309]

Na no crashes (But i like the thought) I'm thinking just level 2 of the sim. It does not crash until 999,980 like the old arcade defender game.

[@MetalFan10101]

@@lucasmoers Can confirm. Same thing happened with my father.

[@noti7510]

human scientists are the higher beings who put a sim into effect at a higher speed than their own reality to see the future, then when paradoxes occur, they have to wind back to when it happens, and figure out what's meant to happen then, and to do that they have to study the sciences which the sim people developed, but they can't figure it out, so one frustrated technician just removes the people who did the faster than light stuff, and resumes the sim.

[@bachelorchownowwithflavor3712]

"The universe is not required to be in perfect harmony with human ambition." -Carl Sagan

[@duran9664]

Our physical bodies live in physical dimension out of many. ⚡️⚡️⚡️In multi-dimensions existence, causality wouldn’t be violated. Abrahamic secret texts of Jews, Christians & Muslims have hinted that “instantaneous” travel is indeed possible if we live within multiple dimensions. Each dimension has its own speed limit. When u reach certain speed, u jump into a deferent dimension & u loose direct connection to ur initial one until u slow down to within its speed limit. 🤔

[@letsbehonest4221]

Thats kind of a Captain Obvious thing for Carl to say..🤣🤣

[@tylerdurden3722]

@@letsbehonest4221 You'll be surprised how many there are who don't understand something so obvious.

[@user-uu9vl2qx9r]

Then for who is it

[@letsbehonest4221]

@ΝΙΚΟΛΑΟΣ ΗΛΙΑΚΟΠΟΥΛΟΣ not who..what .. For its self ...

[@MechDragon108]

If FTL does exist, the universe might have some way of blocking any information/matter from interacting with the ship/crew travelling FTL. Similar to how the event horizon of a black hole stops any information from escaping it where time and space flip beyond it ( which would also break causality if information could escape ).

[@sentientglitch]

Why would it break casuality?

[@MechDragon108]

@@sentientglitch Because space and time flip past the event horizon of a black hole, the only way to escape the event horizon after previously entering it would be to use Backwards Time Travel which by nature would create time paradoxes just by its existence. This video explains why time and space flip inside a black hole if you want to know. kzbin.info/www/bejne/fYK9ZIVuZs6se5I&ab_channel=ScienceClicEnglish

[@GAURAV_RANA_]

But why are we perceiving things from the perspective of the STL ship when things happened at FTL ships pace. The STL didn't know about anything. When they finally visit vega everything would had already happened. So how is causality broken? And anyways the FTL ship will anyways break the space time laws so how can people even think of explaining it with our known knowledge?

[@odinson4184]

@@sentientglitchwatch the video

[@robinfrost5439]

@Mech...you mean the universe may find some way of blocking messages to the crew of the STL ship..am I right here ?

[@thebladerunner744]

What if the solution is a combination of two rules? 1. Anything that is going FTL cannot physically interact with anything going STL. 2. When exiting FTL, your world line is also precisely what it was before you engaged FTL. For example, an FTL ship cannot instantly travel to an STL ship, and exit out of FTL with zero relative velocity to the STL ship. This would make the STL ship intercepting an FTL message impossible. The only way to send messages FTL is by way of literally sending a physical ship that exits out of FTL at the destination. A message that simply travels through space and can be arbitrarily intercepted by any observer is just not possible. The FTL ship could also fly out to the STL ship at FTL, but in order for it to ever get back to Earth earlier than it left, it would have to accelerate to have a zero relative velocity to the STL ship from this example. But then that acceleration would take time, preventing it from getting to Earth before it left. I dunno, I’m no physicist, so I feel like I have to be missing something here, because that type of restriction doesn’t feel too arbitrary to me. This could just be me not yet picturing some other diagram following those two rules that still break causality. Seems like the isolation within FTL, and your relative velocity from your departure being conserved in the jump, both feel like they might be more of like natural consequences of how an FTL drive might actually work.

[@this_dood_right_here]

I agree with you and just said something similar in response to another. I think we collectively miss the fact that radio messages are transmitted absurdly slower than any speeds we are trying to achieve physically. So we wouldn’t “know” what happened to a vessel on the other side of successfully achieving FTL speeds unless that vessel signaled back. And how long would that take? “God only knows” as they say. That’s assuming we couldn’t return the vessel home with its findings. All wild thoughts. But science and logic tells us it’s possible. Still solving the “how”

[@thejoshuahatcher]

Was just thinking about this concept of world line alterations as I was (re)watching this video. The notion of intercepting an STL message while in FTL somehow confused me/didn't seem like it should be possible in that reference point.

[@krishp1104]

Does anyone realize how crazy it is that we can even theorize something like this

[@randomcubing7106]

Thanks to Einstein

[@Vort_tm]

I mean, on a certain level it's completely intuitive. You can't shine a light at something and then arrive before the light hits it, or conversely the light we see from stars has been traveling X light years to reach us, so to travel faster than light we would travel to the source before it was sent. But I will agree that it's crazy that we have actual equations and models for it, thanks to the work of giants (upon whose shoulders we stand).

[@masteur]

If you think about it, maybe it is just a breach of the time line where earth after the ship send the reply to turn off the ftl transmitter, so you have a time line where the crew reply and a other where the don't receive any message because earth did not send it. So in the end 2 time line exist and no loop or paradox.

[@AboveEmAllProduction]

It's just the brain being brain lol, so smart it had to name himself

[@eddycolon1986]

We usually dream bigger as humans with the knowledge we have. Just think about Egyptians about death.

[@JACK_TheAllSeeingEye]

There once was a young lad named Mike. Who could run faster than the speed of light. He took off one day, In a relative way, And returned on the previous night!

[@dudew.5272]

6.67 out of 10

[@MastaShredduh]

@@dudew.5272 How about "11/10" because a score greater than 10 is impossible.

[@ophysic2861]

@@MastaShredduh ackchtaly 🤓🤓☝️☝️☝️☝️

[@vanillaicecream2385]

what we gotta do is rip open a hole into hell itself and travel through in these giant bubbled ships so we aren't eaten by demons

[@BPJJohn]

@@MastaShredduh Spinal Tap says otherwise

[@MHGFTW]

I watched the entire video, and I get the sense you broke the rules of your own diagram. You drew two diagonal lines at the start, indicating the speed of light. You set the premise that any line between the time axis and this diagonal line is something moving slower than light (STL). Any line between the diagonal line and the space axis are faster than light (FTL). You then start speculating about FTL transmitters able to send a message instantaneously, meaning horizontally to the right. I'm with you so far. This is where you break every rule that has been set. You draw a line that goes downward. We've not established any reason why a line would do that. Your made up transmitter can only go up to a limit of a horizontal line (instantaneous messaging). These paradoxes start popping up because you've suddenly decided this message is being sent to the past. The FTL transmitter is now a time machine for no reason. Like I said there might be some physics I don't understand. However in the diagram you've been using, there has been zero explanation of why any line would ever go down. The established rules were that lines could only be in the STL or FTL directions. Once you start going downward you break your own rule set.

[@digammaf7060]

Indeed, why is the first message drawn according to earth's POV but the second one is drawn according to the ship's POV? There's no explanation for that

[@tb3099]

​@@digammaf7060it's sent from the ships pov because that's where that particular message was coming from. However the original comment is correct that it doesn't make sense on this graph as if you map out time/ space for the the ships pov the line going downward would indicate that the message is sent faster than instantly from the ship back to earth. However if you send the message ftl but not faster than instantly than I don't think any causality is broken

[@digammaf7060]

@@tb3099 Take 3 points, the first one being the emission of signal, the second one being the relay of the signal on the ship, and the last one being the reception of the signal on earth. Place those three points in a similar configuration as in the video. From earth's POV there is a downward worldline, but if you apply the Lorentz' transform on all three points to obtain the ship's POV there is no downward worldline anymore. In fact, the downward worldline becomes an horizontal worldline, relevant with the idea that the message is transmitted instantaneously from the ship's POV. I just checked that using a graphing calculator, the original comment is not correct about that, and you are not correct about that either. I would gladly share the Geogebra file but I don't know how.

[@tb3099]

@@digammaf7060 interesting I was trying to figure out how to do it but I don't have a graphing calculator or know what app to use on my phone. On your graph is there a point at which the ships the ships transmitter can send something faster than light but not break causality.

[@digammaf7060]

I will explain it to you so you can reproduce it exactly. It's not complicated. The Earth's worldline is the line defined by x = 0 (vertical line perpendicular with the x axis). The Ship's worldline is the line defined by y = 1.18x (arbitrary speed close to the speed of the light). The light's worldline is the line defined by y = x (45deg line). The Signal emission Ma is located at (0; 4), the Signal relay Mb is located at (3.38; 4), the Signal reception Mc is located at (0; 1.14). Now you have the world from Earth's POV. To get the Ship's POV, we will apply the Lorentz transform on Ma, Mb and Mc. First, the speed of the referential we are using is 1/1.18 (we are using the natural units in which c = 1). According to the wikipedia page of the Lorentz transform, we should first compute a factor called Gamma which in our case is about 1.884 (remember to take c = 1 and v = 1/1.18). Then, for each point Ma', Mb' and Mc' which are the equivalent of Ma, Mb and Mc from the Ship's POV, we can compute the coordinates like this: Mx' = Gamma * (Mx - v*My) My' = Gamma * (My - (v*Mx)) (I simplified the equations seen on the wikipedia page because c = 1) We are left with: Emission' = (-6.39; 7.54) Relay' = (0, 2.14) Reception' = (-1.82, 2.15) As you can see, Relay' to Reception' is not a downward worldline from the Ship's POV, the only downward worldline is Emission' to Relay', which is a direct consequence of breaking the speed of light and not relevant. This is not worth discussing because the real issue is not the shape of the worldline: that wouldn't be a problem for causality if both message worldlines were drawn from the same perspective, and that's why I'm telling you that you are not on the right path. The real issue here is that EVERYTHING on the diagram is drawn from Earth's POV, everything BUT that one message reply which is drawn from the Ship's POV, which doesn't make any sense at all. When you are drawing a spacetime diagram, you draw everything from the same POV. Imaging drawing the inside of a house, but for some reason that one couch is drawn as seen from the outside. This is non sensical. When drawn correctly, the diagram is Emission = (0; 4) Relay = (3.38; 4) Reception = (0; 4) As you can see, Emission-Relay and Relay-Reception are the same line segment, which is relevant with the idea that the communication is instantaneous. When switching to the Ship's POV, both Emission-Relay and Relay-Reception are downward worldlines (since we broke the rule of the light speed then it's not surprising to see other funky things happen) but both are the same line segment, breaking no causality at all.

[@nativesugarshack9328]

It's very rare and special when someone can explain such a complicated topic in an easy to understand and follow way. Thank you.

[@jgunther3398]

favorite channel on 'tube. needs to have as many subscribers as real academically estimated by columbia star count

[@user-kb6mj7zq8t]

In a way thats easy to understand and follow*

[@user-kb6mj7zq8t]

​@@jgunther3398whatever

[@prestonwaters1088]

Except you can find a good explanation for just about anything on KZbin.

[@nathanwhitmore3980]

Alcubierre drive Krasnikov tube Worm hole

[@mw2zorzest]

Well, I don't know about time travel, but a fascinating thing to think about is that if you could travel FTL and have a way to look at earth from any distance, you could go far enough away from earth to see the past.

[@jakecutter1487]

​@@rodrigues.iVery easy point to understand. We're here on Earth looking out into space. If we look at the sun we're all seeing the sun in the past, as it was 8 minutes ago because that's how long light from the sun takes to reach our eyes. So likewise, if we could instantly transport to a point next to the sun and then looked at Earth we'd be seeing Earth as it was 8 minutes ago in the past. If we could instantly transport to Alpha Centauri and stare back at Earth we'd be seeing Earth as it was over 4 years ago because that's how long it takes light to reach our eyes from that star system. Get it?

[@paulshlasko3608]

Not only that, if you then turned around and went back, you would BE in the past, and that is a simpler way to show the FTL violated causality, right?

[@davidkatzenbach7189]

No... Wrong

[@mw2zorzest]

@@davidkatzenbach7189 If you mean me, how exactly is it wrong? If you move at FTL speeds you would see 'old' light once you stopped, therefore you would see the 'past' of the planet, which is why we see stars not as they are, but as they were many years ago, some stars already died, but we still see them because they're so far away that light from the time of their death has yet to reach us, same way we see planets, which reflect the light from stars. Light speed isn't instant, it's just really really fast. Thats what Lightyears are, we see a star 1 lightyear away as what it was like 1 year ago, because that's how long it takes for light to travel to our visible space. If I'm wrong, feel free to correct me, I am not omniscient, I can make mistakes, but I don't think I did here.

[@mw2zorzest]

@@paulshlasko3608 No, because as you would get closer to earth you would see less and less into the past, @philgiffin1487 explained it perfectly, the closer you are to a planet the less the time difference would become. I explained it in my other reply more thoroughly.

[@shinysheepy6311]

"It almost seems like a cruel cosmic joke that the universe be arranged such a way that we are able to look out and glimpse its wonders and yet are trapped here by the speed of light." So well said

[@foxtayle683]

Like God said "You can look but you can't touch".

[@AKa-qi2ov]

Blind people have eyes yet they can not see. Be grateful for what you have.

[@STho205]

It is only a cruel joke, due to human avarice. The concept of continuing to climb stairs to silver level, gold level, platinum level, diamond level luxury and status ...and be temtped by yet another staircase. The fire door locks behind you and you're trapped on a dirty roof with a noisy AC compressor.

[@chemplay866]

@@AKa-qi2ov Some don't have eyes.

[@AKa-qi2ov]

@@chemplay866 some don’t have brains and like their own comments 😂

[@Alex-dh2cx]

There's a great scifi series on a subreddit where humans are using C+ canons that send projectiles using something akin to "slipspace" to travel faster than light to target, and in universe from the target's perspective they get hit before the canons are even fired.

[@wehrewulf]

Cannons, not canons.

[@Alex-dh2cx]

@@wehrewulf bud, im typing on a phone, v relax

[@elliotvanhijfte]

​@Alex-dh2cx what is the series called? On the hfy subreddit i assume?

[@Alex-dh2cx]

@@elliotvanhijfte HFY, First Contact by Ralts Bloodthorne. That particular bit is a good ways into the story, which is over 2 million words. I THINK it was in one of the historical flashback chapters, but I'm currently in the Nova Wars series set far in the future from that part, i can't quite remember where in the story that came up, was just a small thing mentioned. They use some sort of special temporal tech to even be able to target things at great distances. It's probably the best long running series on the subreddit. The story of how it all got started is pretty amazing as well, the first few chapters are part of an introductory anthology, and the first chapter he wrote while serving in desert storm back in the 90s.

[@AlmightyDude420]

The greatest explanation so far. I've been trying for months to understand this by reading forums and watching youtube videos. None were able to explain this. I still need to understand it more intuitively instead of through looking at lines, but this definitely opened my eyes. This is by far the best and most simply explained video so far on this. Thank you

[@kenny.speaks]

Imagine a yellow star 10 light years away If you were to travel at the speed of light, it would take 10 years to get there right? lets say your friend is watching it in a telescope, 24/7 [LIGHT SPEED] - fly to star at light speed (10 years) - turn star purple - fly back home - (10 years later) you and your friend see in the telescope that the star turned purple [FTL] - instantly travel to star - arrive at star 10 years in the past - turn star purple - you might say, well the friend would see it instantly change - think about if instead of instant-travel, you travel with the speed of light back. toearth.. shouldnt it be purple the moment you land since you were traveling with the purple light? - also.. what happened to all the light that was traveling to earth? think about a middle-planet only 5 light years away from. the star instead..what do they see? -- at least how I understand it I think haha, but. who knows maybe there is infinite universes and you just jump to some alt dimension that is 99.9999999% the same except that the star turned purple at one moment instead of the other

[@dmitriimalikov6437]

Wrong right away. Why do you travel in the past when travelling instantly? Just zero time passes. You arrive there at the same moment you left, not in the past. You turn the star purple, instantly go back and then 10 years later photons reach Earth and you see the star purple.

[@caitlyn9972]

Omg this diagram finally explained why and how space and time are connected. Thank you so much. I always thought I understood this concept but I was just repeating info not fully grasping it.

[@w0tch]

You need to look at curved spacetime diagrams (this one is flat) to understand the link between space and time :)

[@caitlyn9972]

@@w0tch thanks, I will.

[@caitlyn9972]

@@N3KRoM3KHANIKaL Yes, I completely agree. We do not have enough information and may never get it. And relying only on math is most likely not the answer. It's a very "human" way of trying to solve things.

[@dlayman101]

Even then it's still a massive stretch, we don't even know it time is linear, parallel, or circular, we can observe evidence of what we experience as the passing of time, but quantum physics seems to be bending our undersanding of the rules of time, energy and matter. Remember 3rd law of thermodynamics, entropy "TENDS", why the word tend? Because at this point it is outside the realm of our current paradigm of awareness as well as the technological capabilities as it relates to se sensory data acquisition to be able to define that theory with a more resolute likely useful definition. Aka our current level of understanding is the first black and white television. Imagine, give it colour and increase its resolution to 8k, I'll bet its a picture you can draw a more detailed understanding from. Crude metaphore I know, but there is no such thing as the best answer, only the "currently knowable" best answer. Don't act like it's a doorway to a new world of understanding, but all the knowledge you learn is simple a small stepping stone for you to leap from into the universe of the unknown, for the purpose of stumbling upon new unseen, unknown, and untouched wonders. Big and small. Seen and currently unseeable. The final frontier is not the beginning of the last mission, but the beginning of the first mission, that never ends.

[@SkywalkerSamadhi]

@@N3KRoM3KHANIKaL maybe so.. but that doesn’t mean we give up trying. Ever. The only real failure that exists is in not trying at all. Otherwise every attempt to find FTL or unlock the mysteries of the universe bears fruit in the end, even if ultimately that fruit is just another way in which we learned how not to make a lightbulb.

[@gabe9125]

In the Halo extended lore (books and etc), their use of slipspace creates time paradoxes like, constantly. It's not uncommon for a ship to arrive at it's destination hours, days, or WEEKS before it left. And everyone's collective reaction to the existence of these paradoxes is just to kinda shrug, say "hey man, don't worry about it too much," and move on

[@deephorizon1365]

That's great, i fucking love it

[@brandenmarcum430]

“Hey if we keep doing this the universe might break” “Cool”

[@nickmalachai2227]

Every time I learn something about Halo lore it sounds completely tonally dissonant from the games I played. "John Halo is a brainwashed child soldier alongside every other Spartan, and the people who commissioned the Spartan Project belong in the Hague." "The use of slipspace at all is an existential threat to all the universe." "the UN created the Spartans to suppress rebellions with legitimate grievances" this is a space marine game about fighting aliens and being badass, what the fuck is all this genuinely horrifying secondary lore?

[@HorseDe-luxe]

@@nickmalachai2227 I'm glad to see someone else say this, I feel basically the same way. The deep lore fans irk me bad, it just sucks all the wind out of the sails for one of the most fun series of games I played as a kid. Like, I actually used to enjoy wiki diving and reading some of that lore- some of it was cool- but then every time I see people get up on a pedestal about how the UNSC are some evil Nazi-equivalent authoritarian regime, "the real baddies" (Compared to the Covenant? Those genocidal maniacs? Seriously?) and the spartan child soldier stuff, it makes it feel like none of it was worth it. Like, way to ruin a series; not only are the games after Bungie moved on arguably kind of mediocre, but then the books and other secondary lore retroactively hurt the Bungie games too. There's just nothing left to enjoy. It makes me so sad.

[@nickmalachai2227]

@@HorseDe-luxe I actually like the secondary lore, for the most part, I just wish the games were tonally consistent with it. Granted, I'm a Star Wars and Transformers fan. I'm used to worse bullshit than this.

[@joshuagharis9017]

Revisting this. Professor, I just saw an article featuring your terrascope idea, featuring you, of course 😊. I was so excited for you

[@CalamitousJonathan]

I enjoy that you are actually including the possibility of breaking the universe in this video. That is why we stopped increasing speed, in my warp engine space ship.

[@zadrik1337]

I like how Terry Pratchett said it better than the way Hawking did: Everything that happens, stays happened.

[@JROD082384]

I wouldn’t even bet my lunch on that smug assumption.

[@mkohlhorst]

I like Jim Butcher's version Law For the Conservation of History. Postulating that there is a force similar to inertia for temporal events. Essentially after an event has occurred a strong force will ensure that it remains unchanged

[@Itherageli]

Yeah it might be a bit naive or misunderstanding some implications of our current understanding of quantum mechanics, but it always seemed more intuitive to me that the future is set and that "change" is just a matter of viewing the universe from a different position within the spacetime and there is no need to "invent" a force preventing causality to break when the universe was already set (though this being true would probably make closed causal loops impossible).

[@elmoteroloco]

​@@mkohlhorst The "Good Doctor" Isaac Asimov described the inertia of the time stream in "The End of Eternity", an interesting read even today.

[@elmoteroloco]

So... "Everything that happens, try to stays happened"

[@tayzonday]

The speed of light should really be taught as the speed of causality. The speed of light is an incidental stenographer of the speed of causality.

[@CoolWorldsLab]

Yes! It’s not the right name but sadly we’re sort of stuck with it

[@alecdacyczyn]

Let's adopt Asimov's interpretation and say that light, gravity, and causality all travel at "Celeritas", a special speed that is an innate property of the universe.

[@OnlyLyricsMatter]

Tay wtf you got some varied interests. Taught me economics and now you're prepping a physics song?

[@w0tch]

And the speed of light is a top limit in the Lorentz transformation of spacetime diagrams that cannot be exceeded ! Using FTL info transmission breaks the maths of the spacetime diagrams (square roots of negative numbers), so the conclusions of this videos do not stand :)

[@stewiesaidthat]

@@CoolWorldsLab light travels faster than sound and doesn't break casuality for a blind man. Light travelling faster than light doesn't break casuality either. The universe operates on universal time, not local time. If you want to do a video about casuality, do one on the two different speeds of sound on Mars.

[@matzefly]

This video is amazing. Thank you for this simple explanation of such complex issues. I have discussed your diagrams with a couple of colleagues last night and we had an amazing time 😊

[@Dr.scottcase88]

What I love here in the commentary is everyone having the freedom to express their thoughts in either direction or in neither direction. Where I stand, the whole thing is a big mind F - - K. I want “want” to believe we can break the Ftl barrier, but any basis for that desire does not include any scientific knowledge or fact at this point in time. But, it’s fun to talk about. Peace.

[@JwebGuru]

The more I learn about it the more pessimistic I get, for example the Alcubierre drive is only a "solution" if it only is ever allowed to move in one direction (to avoid the light cone) and there isn't a second drive going in the opposite direction. For that to be somehow mandated by the universe would violate another fundamental tenet of relativity--that there is no preferred reference frame (i.e. among other things, the laws of physics are not different in one direction than another). People might be fine with giving that up but these kinds of symmetries are very fundamental and form the foundation of science as we know it (and have been tested to death in other regards). IMO, the impossibility of FTL causing time travel makes other stuff make *sense* too. Because what is travel into the past, really? Another way to look at is that it's a way of *changing the entire universe* (because you have to wipe out all evidence of the real past). How much energy would that take? Infinite sounds like a good answer! And how much energy does it take to accelerate matter to the speed of light (or decelerate a tachyon to the speed of light)? Infinite energy! It all just kind of works *and* provides a neat physical explanation for why we don't see time paradoxes. Whereas every attempt to justify FTL immediately runs into a whole host of problems. At some point, you just have to accept that FTL just probably isn't real. And one final thing... not being able to go FTL doesn't mean not being able to explore the stars in your lifetime! Theoretically, you can still get as close as you like to FTL and reach anywhere you want (modulo cosmic inflation) in any finite amount of time *from your own perspective*. You just can't do it and expect things to be the same when you get there. How would that look from your perspective? As you travel faster and faster, it's like the universe shrinks in your direction of travel--everything looks "short" in that direction. By using insane amounts of energy, we can compress the whole universe (or at least the small part of it where we travel) and cheat the cosmic speed limit! The universe gets so small, having to travel below light speed really doesn't seem like that big a deal anymore. Or like someone said, "the universe is a cramped place for a neutrino." To me, that's at least as cool as any proposed FTL mechanism, and it's 100% real.

[@yufansa]

"The cosmic speed limit, the speed of light is so diminutive compared to a galaxy. It almost seems like a cruel cosmic joke that the universe be arranged in such a way that we are able to look out and glimpse its wonders and yet are trapped here by the speed of light. Fated to only ever peer through the bars of our cosmic prison and dream." -- This is so beautifully spoken...

[@obothehobo173]

That's a carl sagan quote right?

[@buioso]

But isn't true. You don't need FTL to visit the Galaxy, as long as your speed is very close to the speed of light, your proper time slows down a lot. For example, at 299,792,456 m/sec (just 2m/sec less than c) you can reach a destination 720 Light years away in just one month at your clock. But for the rest of mankind, so your family, relatives and friends you are disappeared forever and no communication is possible. This is the real problem.

[@ProfShibe]

@@buiosoyeah that’s why it’s basically useless. The few people on board the ship or w/e is traveling would get to experience it, but upon returning the civilization probably wouldn’t even exist

[@davidt8087]

I'm sorry but I.dont see a paradox here for the ftl ship. There's so much trickery and perspective here. Imagine you are on the other side of earth and you discover the country you're in has learned of an atomic bomb strike coming at them, then you see the atomic.bomb on its way, it doesn't mean the warning came first. It's just the order of information you received that's changed, not the ORDER of ACTUAL events. Why do physicists put MORE emphasis and make EM WAVES the MOST fundamental aspect of the universe but not the ACTUAL mass and energy aka atoms which emit them in the first place? Think of em waves as Carrier waves. They don't matter at all. So what if i travel faster than light and I arrive at another planet, stop, and then someone using a telescope sees the light from my body arriving later starting from near the end (where light is closest) and appearing to go back. We would know the light is just an illusion. The ACTUAL FUNDAMENTAL ATOMIC MATTER AND MASS MATTERS MORE THAN ITS EM RADIATION IT OUTPUTS. But we instead only focus on the atomic OUTPUT aka em waves and base ENTIRE THEORIES AND PHYSICAL LAWS around THE EM WAVE. Who cares about light? We've seen that atoms can "communicate" at "infinite speed" via the double split experiments. If particles can communicate faster than light they are MORE fundamental than light. Now sure information can only travel faster than light but why focus on information as if it's more fundamental than the MASS energy? Particles can communicate instantly at infinite distance, and while the information is limited at light speed, so what. Light is just em waves with no mass. Could we make life out of em waves? No. So who cares. If we did travel faster than light THEN saw the light of our travel arrive, I'm sure NO ONE would say "wait how come you're here but yet I see you still on the way?". Everyone would know that it's just an illusion. So I don't see any paradox

[@Icedragon256]

I landed at the same "strict rules" conclusion back in 2007 when designing a sci-fi setting with FTL. I borrowed a bit from Douglas Adams and ended up with a version similar to one you hinted at. That any attempts to perform an action which would result in a paradox would be met with increasingly unlikely events to prevent it from occurring in the first place. Thus, before sending any FTL comms, or engaging in certain kinds of travel, you have to draw the light cones and think through the implications as shown in your video. Thanks for putting this together. It was nice to see someone think through the same things and tie it into a neat package.

[@just_me2797]

I am doing a copy and paste from a quick thought I had. "Just spitballing here, because I am not a physicist nor time traveler, but perhaps it needs to be viewed in other dimensions rather than with a 2d graph. Say for example someone makes a device that in theory can send an FTL message. They turn it on and send a message, but nothing happens so they think it didn't work. However thinking in the infinite universes model the senders universe continued on it's time line, but the message was received in a multitude of parallel universes. They have zero clue as to where the message came from, but they received it none the less. Or perhaps the universes have a way of keeping things tidy, so too speak. So when the FTL message is sent, how do I say this, the entire universe is sent and is no longer where it was in time. Thinking in terms of infinite universes perhaps there are as many, call them anti universes (empty spaces) in the big empty. So the universe itself where the FTL message originated instantly fills the space where the message is received thus avoiding some weird entanglement of timelines. Sure there might be some side effects such as the Mandela effect, but that is price we pay in order to have FTL."

[@W0NK042]

This is why I only travel on Bad News. 😉

[@RoyalPomegranate]

I have proven that even if you ignore all paradoxes with time travel it still violates the 1st law if thermodynamics.

[@raymondturner6784]

This is what I was thinking. I'm glad to see somebody else thought the same. I even hypothesized that that causing a paradox, that section of time is broken off and takes that space with it, like ALL of that universe at that exact time, essentially causing what would be parallel universe. Sting Theory mathematically checked out, and postulates that a multiverse exists, along with at least 11 dimensions. I think something like this videos scenario paradox happened in the Mark Wahlberg Planet of the Apes. I remember there being a video transmission they received in the beginning of the movie that was actually sent years later...

[@gatekeeping8528]

But I don’t understand, the problem seems to be STL not FTL but STL are totally possible

[@yapdog]

The universe doesn't care if it makes sense to us.

[@rajm5022]

This is perhaps one of the best explanations I’ve seen so far! Visual representation of this concept at its best!

[@Cxntrxl]

respect to all the cameramen who time travelled into the past to bring us footage of all their FTL ships for use in this video

[@daytradersanonymous9955]

Disrespect to spam ty comments👎

[@AashishK1993]

i love you

[@MetalFan10101]

Oh look an original joke...

[@durcheinanderme]

@@daytradersanonymous9955 Phd

[@durcheinanderme]

@@MetalFan10101 phd

[@curiousgemini]

If FTL is impossible, the upside is that the possibility of aliens attacking would be quite low.

[@ProfShibe]

That also includes the possibility of meeting them :( The world could be littered with civilizations, just they might be far apart, or some might even be next to each other, and we’d never know.

[@paulshlasko3608]

If hostile aliens became aware of us through telescopes much more advanced than ours and wished, for instance, to take over this wonderful piece of "real estate", they could possibly, with their advanced technology, attack us with a virus. The virus is so small that it could be accelerated to near the speed of light without breaking any rules. Said virus could be designed to make us really smart, smart enough to change our ecosystem in their favor, and so aggressive as to cause our own downfall through constant conflict. They could then send their STL vessels with colonizers to eventually clean up the mess and take over the place. Its not really far-fetched, in my opinion!

[@200fpsASH]

Alien 👽 of some types can bring souls witches % for the record player ✨!? Lol it's not of today because Mars&darWtfts planet a moon to Mars!

[@tobencoombs5750]

if aliens existed the first thing i would show them is a baja blast from taco bell

[@pierreo33]

@@200fpsASH Take your meds

[@BenjWarrant]

Thank you Professor, very interesting. I myself think that the only reason we even discuss FTL travel is because SF writers had to 'invent' it in order to write space travel stories. One thing: I believe you pronounced the word *albeit* as 'al-bite'. Actually albeit is simply a contraction of 'although be it' or 'although it be', and so is correctly pronounced *all-be-it*.

[@fickjosh]

at 17:00, the video illustrates how the "STL ship's time axis" should be vertical (plus, then FTL works again, according to this model)

[@adamhsu8247]

Hiya, aerospace engineering grad student here! This seems really well-researched, and yes, this _is_ an effect that happens exactly as you say - and it's also not time travel. Not in the way we conventionally think of it, anyway. This model is actually referring to _information_ travel, which is surprisingly pretty different! And no, even if you switched the FTL signal to, say, a person traveling FTL to tell the Vegans (lol vegans XD), everything still holds up to how we understand relativity. This is because this thought experiment doesn't factor in the *quantum effects of information.* Take a pair of electrons, for example - let's make these two electrons quantum-entangled (something that can actually happen!), which is a fancy way of saying that their properties are connected and shared - when one electron does something, so does the other. We have experimentally proven that, when one electron's spin flips, so does the other - _instantaneously._ Which shouldn't be possible, so long as we assume everything is capped at the speed of light. AND this happens regardless of the electron pair's distance from one another. So in theory, if we separated these two entangled electrons across the entire Milky Way, then flipped one, the other would also flip at the exact same moment as the first. This is because with _information_ travel, there's no light-speed limit to be found - no speed limit at all, really. So when one electron flips, the information of that flip _instantly_ travels to the other electron, and so it flips at the exact same time. Crazy, right? All this just to say that, according to quantum physics, information is not bound to the rules of relativity, in regards to both space AND time. This is exactly what happens in this thought experiment - due to the nature of the different axes of space, the information onboard the STL ship comes in all jumbled and in the wrong order, but because information doesn't actually have a given speed limit (the entangled electrons are proof of this), nothing in relativity is broken! The rest of the universe follows the horizontal axis (mostly), and causality remains unbroken - since the space axis is relative to the observer, the *perspective of the order of events can change* because _information has no given speed limit,_ it's only limited by how it's perceived - so the events themselves still happen exactly in the order they happen. The line parallel with the space axis, traveling up and down, is really an _information perception line._ Think about it this way - forget the signal. What if you had a ship that traveled at exactly the speed of light? Both its time and space axis would be at 45 degrees, and thus its perception line would also be at 45 degrees. In that frame of reference, all three events - supernova X, Earth observation of X, and Vega observation of X - would happen at the exact same time. And what if we add back in the signal, and the ship was an FTL ship? Flip the STL ship line and the STL space axis line at 14:47, and we're FTL! The perceived (note: _perceived_ ) order gets _really_ janky with this example - first, the Vegans receive the warning from Earth; then the Vegans see X; then Earth sees X; then X happens. It's almost backwards! But that's okay, because *information - and thus our perception of that information - can arrive in whatever order it wants, or rather, in the order that the frame of reference allows.* No time travel, just information travel. Just thought I should mention that, to alleviate the confusion! Physics, sadly, just _really_ doesn't like actual, real time travel. (My inner Doctor Who fan is crying) Edit: Whoopsie, so I brought this post by my thesis advisor, aaand turns out I may be just a _wee_ bit absolutely incorrect about how transmission of information via quantum entanglement works. Say you have a pair of entangled electrons that you've measured to have a net spin of 0. If you measure one electron's spin to be some value x, due to quantum entanglement, the other electron's spin must be -x. Simple enough, right? All entanglement says is that mutually shared info is conserved. _Technically_ it means you also instantly know that the other electron's spin is some value -x once you measure the first electron to be spin x, but the pitfall for many people (including myself, sadly) is extending this logic to the _transmission_ of information. Just because an electron is entangled with another doesn't mean flipping that electron will have an instant effect on the other. Transmission of information is, much like everything else in the universe, bound to the speed of light. Physically flip an electron, and the other electron will flip after an appropriate amount of time, NOT instantly. (Note that this also is in an ideal setting, where spin only happens along a single axis - normal electrons can have spin along any axis they want, which has all sorts of brain-breaking issues that I will NOT try and summarize for both your and my sanity.) Having said that, though, the logic of the information perception line still holds true to a degree. Proper FTL travel doesn't yet exist, so we can't properly test the effects that FTL might have on causality. The thought experiment proposed in this video calls into question some of the issues FTL might have, but this post is more calling into question the claim that what's happening is time travel. An error I made was assuming the information in this setting was quantum information, which makes no sense since this isn't really a quantum system! You find quantum info in a quantum system, which this isn't, so the information perception line is really just the perception of normal, tangible information. (And again, quantum info like everything else is bound to the speed of light. Just pointing out another error I made.) And yes, it still looks like causality is being broken, but still only from an information standpoint. Events still carry on as they do, it's just the order of _detection_ of events that's getting weird. Which is totally fine! Harking back to the entangled electrons, if we separate the pair far enough and make enough observations in a second, communication via the speed of light would take longer than the interval between observations, meaning you can find out the other entangled electron's spin faster than the other side could tell you what that spin is. So in a bit of a backwards way to what I said earlier, information _still_ finds cheeky ways of "beating" the speed of light without actually beating the speed of light. If information can do that, then there's no reason why this doesn't extend further ie. to this thought experiment. Information gets wonky, but we already know that's okay. No time paradoxes here! To be fully honest here, I ain't an expert in this field - I'm a hands-on build stuff kinda guy, the stuff discussed in both what I've said as well as in this video are only tangentially related to what I study. Thanks so much to all the people who've (politely) criticized my errors - y'all were the reason why I brought this to my thesis advisor in the first place. Science is all about correcting incorrect assumptions, so thanks to all of y'all for setting me straight! And feel free to point out any other errors I've made in this edit - there's only so far proofreading will get you lol

[@Bullshitvol2]

I wanted to write something similar, but you explained it much better than I ever could. TLDR: Paradoxons are always a human brain child. If they actually happen they are resolved on their own.

[@jadenwalker6713]

This implies a device can be constructed to determine absolute speed of an object. The idea of an information order can be used to distinguish the angle of a given objects space axis and the information axis. Take two ships in space, they start off docked, moving through space at some unknown fraction of the speed of light. they exchange entangled electrons and set timers for an hour. both ships then accelerate away from one another so their separation speed is .5c after an hour of observed time on one ship they flip their electron, but the on the other ship they see the electron has already flipped. they can conclude that because the electron flipped on their ship, they must have been moving at a higher lower angle to the information plane. Assuming they can observe and be alerted to the flip as you suggest, they could even calculate their angle to the information plane. Now lets say after each ship observed an hour pass they turned around and reunited. After their rendezvous they will be on the same course and speed as before but now know what that speed is compared to the information plane. They can then decelerate together to be at zero absolute universal speed. At this point our duo can do all kinds of naughty things like shine around the emittance spectrum of helium at any other observers in the universe while transmitting a signal declaring their speed as zero absolute. Of course this would allow any observer to determine their absolute speed by comparing red shift of the helium spectrum. Or our stationary ships could observe the redshift of equidistant galaxies billions of light years away and determine were the center of the universe is. The ability to take such actions is highly cursed and Einstein would not approve. The fundamental problem here is the information axis. The universe does not actually suffer this problem or we would have declared Einstein's theory of relativity dead the moment QE electrons were observed. With accurate enough clocks we could have already determined the absolute speed of earth by using earth's rotation to generate the velocity difference. The flawed assumption here is that QE can relocate information. QE cannot do this. Yes, the changes in a particles are instant BUT you could not differentiate the change from random chance without observing BOTH particles and comparing the results. So far as we know this observation must happen at luminal speeds. Example: some process, call it radioactive decay, simultaneously generates two entangled electrons. these electrons have an a spin sum of zero but each one has an unknown spin. you then separate these electrons from each other. you take one electron and put it threw some spin flipping machine. Now you pass your electron through a filter that sends an electron with an up spin into detector A and a down spin electron into detector B. The moment the electron hits a detector it breaks its entanglement due to the act of observation. if your electron hits the up spin detector you can know with certainty the other electron would have hit the down spin detector but the observer of the other electron would have no clue your electron was passed through the flipping machine unless you told them. Fundamentally the information of the spin the electron does not exist until observed, changing the spin state before hand changes nothing and observing the electron breaks the connection. No FTL information. Its actually comical how far entangled pairs go to generally troll anyone trying to do FTL communication with them.

[@adamhsu8247]

@@jadenwalker6713 Neat - didn't know that! And now I do, thanks friend! I guess there's still plenty of gaps in my knowledge for now lol

[@JROD082384]

You literally wasted a mile of comment space being wrong.

[@jdove6883]

Physicist here, well done engineer. However, again, there is no "flow" of time as if it is a river. Einstein postulated that all matter has it's own time clock and that it can, and does, tick at different rates for different velocities.

[@terra2965]

Cosmological and chronological paradoxes are so interesting, rather enjoyed listening to this more than I'd expected.

[@fullercrane1795]

the hack is to listen to it like your life depends on it.

[@user-ml8oq5dh9n]

Great video. Speed of “thought” as form of FTL travel? Perhaps currently the only way. Also, love Hawkings ideas that time paradox’s are impossible.

[@adalwulfsnow201]

What if for the reply signal that gets sent back (for the Supernova FTL Warning example), could we potentially just calculate the point in time/space where Earth would be, and send a signal with a specified frequency to travel the exact speed needed to meet that calculated point?

[@tom4ivo]

15:18 If we are looking at things from the ship's crews' perspective, how can you say that the first thing the crew perceives is Vega receiving the message from Earth? How did that information get from Vega to the ship? Was it instantaneous? Doesn't this information take time to travel to the ship from Vega? Yes, the time line has reached Vega, but it hasn't reached the ship yet. In fact, it appears that the ship learns about the message from Earth to Vega when the ship arrives at Vega (this might be an artifact of the speed of the ship, and might not be true for a different speed). More importantly, according to your timeline, the STL ship thinks Vega has received the message from Earth BEFORE THE SHIP HAS LAUNCHED. 18:11 Justify the world line for the return message from the ship. No matter how I look at it, the message from the ship back to Earth arrives later, not earlier. I don't see any way to get your reply world line from any of the other lines you've drawn.

[@jackie.p6891]

I was feeling stupid for not understanding that part of the video, but my reasoning is the same as yours. I went back and forth in the video trying to understand why the STL ship would see that vega was warned before earth even sent the message. wouldn't that require that ship to see faster than light? on the other hand, I find it far more likely that I just don't understand the use case and I'm missing something that smarter people than me have thought of xD

[@salbrismind]

@@jackie.p6891 The time slice isn't about seeing events it's about them "happening" on that world line. The video is missing some crucial explanation of the STL ship and how it travels. The close to speed of light you are travelling (without FTL) time for you actually slows down and your observations of the world outside are also slowed down. Which seems paradoxical but it's what relativity tells us. So when we talk about what the ship experiences it's really just a question of it's perspective of the outside world. A transformation into the perspective of the ship would produce a diagram where the events happening on Eartth are slowed down.

[@danielross7983]

@@salbrismind The STL ship's space line should be an S shaped curve to account for acceleration to relativistic speeds and deceleration. That would change it's position on the overall chart.

[@sirdeadlock]

If time is a constant in the equation, then no amount of space warping, special relativity, can make anything go back in time, or can make something happen before it starts. It can slow down subjective perception or slow down objective perception, but time proceeding forward, cannot go backward.

[@ozasco]

I am with you guys I am either too dumb or a message can never travel back in time

[@Heretbg]

Yet again you combine scientific explanation with a thoughtful and beautiful message. Thanks for one day deciding to start doing these videos, they mean a lot to me.

[@miaokuancha2447]

Same。

[@duran9664]

Why not also mix it with spiritual & religious thoughts?! ⚡️⚡️⚡️In multi-dimensions existence, causality wouldn’t be violated. Abrahamic secret texts of Jews, Christians & Muslims have hinted that “instantaneous” travel is indeed possible if we live within multiple dimensions. Each dimension has its own speed limit. When u reach certain speed, u jump into a deferent dimension & u loose direct connection to ur initial one until u slow down to within its speed limit. 🤔

[@the-guy-on-your-moms-couch]

I see what you did there. Or maybe what you will do there

[@miaokuancha2447]

@@the-guy-on-your-moms-couch Well played!

[@onlyonewhyphy]

I like Carl Sagans son too

[@MK.__]

Phenomenal job of explanation & presenting in a minimalistic way 👏🏻👏🏻👏🏻👏🏻👏🏻

[@erykbrzozowski2087]

I wish every video was so capturing and beautifully made - just epic

[@victorcurysimionato6412]

Congratulations, you had my complete attention to the entire 25 minutes. Very well done video and explanation. Super interesting

[@daMillenialTrucker]

He's an interesting man, I'm the same way. I can get deep into my own thoughts while listening to a video but like you, listened to it in its fullness.

[@KhaiGK]

I use this video to sleep

[@marilynkozak17]

Always a GREAT day when KZbin dings you because there is a new Cool Worlds!! 🛎 👍

[@MrJuxone]

Absolutely 💯

[@stevenclark7453]

Yesss

[@tomcha75]

Ok. I'm no scientist or mathematician so please excuse my clumsy effort. But there seem to be a few problems with this logic/diagram/explanation. Maybe someone can point out my errors. 1. Using the ship's space axis line or its angle as the base to measure the sequence of events seem false. While it may seem to the crew that the order is different, it doesn't change it in the "outside" world where they are not moving at the speed the ship is traveling. This seems like someone traveling in a bullet train looking out the window saying the world is so blurry. While it may appear that way to the person on the train, the objective world outside doesn't change to fit that observation. When measuring the effect of change or sequence of events in the outside world, you must use their own space axis, which is still horizontal in this diagram model. Then, the sequence of events still make sense. 2. Reply from the ship back to earth seems completely wrong. Assuming the speed of the FTL message is constant, why is the line from the ship to earth at a different angle? Yet, another even bigger problem is the flow of time. Based on the diagram, the time flows upwards along the Y-axis. Then, the message from the ship to earth should also go upward at an angle reflected about the horizontal line. So if the original FTL from earth to ship was at an 30 degree angle (indicating it is faster than the speed of light at 45 degrees) measured from horizontal line on the right side, then the FTL from ship to earth should be 30 degrees (again indicating it is faster than the speed of light at 45 degrees) from the horizontal but from the left side. This is because again, the objective time still flows upward along the Y-axis. The line drawn in the diagram noting the message from the ship to earth literally says the message is traveling backward in time.

[@tomcha75]

I wasn't sure how to explain the gut feeling I had for #1. Maybe this is a better explanation. Imagine you are sitting the bullet train. As you zip by, you observe someone throwing the ball up in the air and catching it repeatedly. As you pass by him, you focus on the tossed ball's trajectory. To you it traces an arch. However, this is just your perception from the movement. It does not change or affect in anyway the objective reality of the ball outside of your train or the vehicle of influencing your perception. Likewise, the crew of the ship may indeed perceive the order of events in different order. However, it does not alter the objective reality or passage of time.

[@KrazyTrumpeter05]

My mind is blown. When you switch the communications to "instantaneous" and re-explained the diagram, everything started making sense. I have had so much trouble trying to conceptually understand these potential issues with FTL travel/communication and this has helped so much. Still hope we figure out a way around it, though! Like you said, it's criminal to be able to see all this cool stuff out there and not actually be able to go see it ourselves.

[@nellkellino-miller7673]

I think as soon as something like FTL is achieved, we'll soon learn that there is some other, infinitely stranger arbitrary limitation way beyond our grasp that we could never have even conceived of before. I have dreams about it all the time, since I was a child in fact.

[@griseld]

Same! I think it's just a question of science. As much as i believe in science, we make a lot of hypothesis and assumptions, we are also able to calculate stuff precisely(think gravity) without actually understanding how it works exactly or at the quantum scale. We can measure stuff and make accurately predictions on things because they follow rules, even if we don't understand them at their core. With our understanding advancing we will eventually find out that there's much more hidden stuff in the universe, much more detail to the laws of physics as we know them. I'm pretty sure with time everything we deem impossible will eventually unravel itself with technology. Think about our understanding of gravity or molecules or whatever has evolved, from thinking that something doesn't allow you to leave the ground, to thinking there might be a force, to formulating an explanation to that force, to finding actual data on it and doing research. We will eventually end up finding that gravity is an illusion and happens for other reasons than we think 🤣

[@stefanschleps8758]

I like the way you think!

[@optimuseprime7887]

@@griseld As much as I like your enthusiasm, and would love for FTL and other fancy tech to happen, wanting it to happen won't make it so. The reason science is so scientific is because of intrinsic scientific value; skepticism. Being skeptical is probably a key to being a scientist. So it isn't really healthy as a scientist to start thinking that everything you know now is completely wrong because something else that people thought was right turned out to be wrong. That kind of thinking can lead you to certain biases that can have a lot of effect on your research. Of course, pretty much all scientists and people want FTL to be possible and would love for it to be so, but also most of them know that as it stands right now, FTL is likely impossible, and, assuming they aren't researching something that could change that, they are probably working according to that. Scientific/technological progress could hit a wall tomorrow, and any advancement could freeze. Of course, that's unlikely to happen, but it is possible. It's good to be optimistic, and enthusiastic, but knowing where the potential limits are is good. I would love for FTL to be possible as I already said, but as far as we know it's either impossible or requires incredibly advanced technology that we won't have for hundreds, or maybe even thousands of years. And our current best theories suggest it's the former, but who knows? Maybe someone will create a theory of quantum gravity that will be proven, and that will allow for FTL.

[@procrastinathor4594]

What would that be like?

[@JeffTheHippo]

I wonder how much faster you would have to go to reach that barrier

[@kurtisengle6256]

It's amazing how slow you plan to go faster than light. I have other things to do. If I have time, when I'm finished goofing off, I might check in to see if you made it to light speed.

[@radekpanek9524]

you can't turn ftl message wordline to stl ship frame refference(because ftl message is still absolute to the universe time-space frame) so when stl ship receive message its reply is inverse to receiving line so reply is receive at earth after. And that dashed line of stl is only time reference for in-ship time so it is moveable(alongside time axis) and that way, where it cross ship's full line is when something happens in crew perspective time. So when they arrive on vega and get the information from ftl ship it appears on dashed line on crossing with vega's full line. So no paradox occure!!

[@stanjohns348]

Am always amazed at how confidently people are wrong. Especially in science and medicine. But hey, I’m the same way.

[@Jane-gq8xo]

The direction of the return ftl message from the stl ship is unexplained here. I would love to know the reason for that, seems like the most important part. Wonderful vid, very informative and easy to follow!

[@ApostleO]

It had something to do with the local reference time line being tilted, which also felt unexplained. If the diagram is drawn based on Earth's perspective, or even some sort of objective third perspective, why would the timeline tilt at all?

[@tbunreall]

It's because for the message to be ftl, it has to be under the yellow line, if the message went up, it would go over the yellow line and thus not be ftl

[@dennis-o]

@tbunreall is correct. To elaborate, we’ve measured the speed of light to be the same no matter what your velocity is, i.e., the yellow line stays put for both Earth and the ship. The only way that can happen is by time slowing down as your velocity increases. So from Earth’s perspective, time has slowed down for the ship and vice versa. That is equivalent to saying that if two objects are traveling at different velocities, their time axes will be different. Now to get the space axis, you have to flip the time axis around the yellow line. So their space axes will also be different. An instantaneous message has to be parallel to the space axis of the sender. The instantaneous message from Earth to the ship is parallel to Earth’s space axis while the *_RETURN_* message is parallel to the _ship’s_ space axis. Anything slower that’s still FTL has to have an angle between the yellow line and the space axis of the sender. Please let me know if anything is unclear, it helps me learn too!

[@badrkhan]

This video is incorrect and gives wrong conclusion. Draw a 45 degree from STL towards earth. You can still do FTL lower than 45 degrees but it will be above the moment when original transmission was made. Logic in this video is false

[@TonyVallad]

I agree it's the most important part of the video and yet it doesn't seem correct to me either. It really does need an explaination because the whole video depends on it ! xD And no offence but the replies you got don't convince me. Hoping for a better representation ;)

[@madzangels]

What is most beautiful about this video - is actually what it has done to the comments section. Look at all the wonder, the questions, the curiosity, the debate. All these wonderful human beings trying to discover - this is what I love most about humanity, we're all in this thing together :)

[@pansepot1490]

Have a look at the comments on some conspiracy videos. The moon landing deniers, or the flat earthers for instance.

[@gamingcreatesworlddd2425]

@@pansepot1490 no don't your brain will hurt badly

[@AJ-qv9yo]

Isn't the STL line off? The slower it goes the more vertical it will be, right? But then, the mirroring at the speed of light would be more extreme, to a point where the angle becomes zero, if the STL ship does not move at all, hence the time slice would be horizontal too. The message back, seems to travel backward in time in any reference system. Why? Just because it is drawn this way? Shouldn't it be angled up, and everything is restored? Looks to me, that in addition like the space/time coordinates of the STL ship are confused with that of Earth and Vega. Or vice versa and this causes the paradox. Confused.

[@ReynosoJD]

By far best explanation compared to all others. Great job. Could be perfect if at 14:30 (most frequently played viewer likely replying because it was a bit confusing) if you just explained more why the 45 degree flip dotted line for STL rather than mention to refer to a previous video for that understanding. Still good job.

[@gtd9536]

Well this is the best explanation I've seen that explains why FTL will break causality. Every other show or channel just mentions that a violation will happen; you actually break it down and explain it clearly step-by-step. Amazing. You deserve a much wider audience. I will start referring others to your channel.

[@CoolWorldsLab]

Thanks! This is a really challenging topic to explain in understandable terms

[@vferrei2]

Do you have any of those other shows or channels? I’ve been looking for anything that explains well why FTL would break causality, and I didn’t find this video to be any better than any other one I’ve seen. This video still doesn’t make any sense to me. But I’m hoping I can find one that does.

[@Twister_with_your_sister]

Blames "every other show or channel" for "paying lip service" Makes whole comment that "pays lip service" to this channel Speaks in hyperboles and hypocrisies. Well done 👏...👏...👏...

[@Ketchup.Bottle.Fart.Noise.]

@@vferrei2 Destiny Astrum Hybrid Librarian Sabine Hossenfelder SciShow Space Scott Manley SEA Strange Mysteries The above listed channels all have at least 1 episode on this very same topic. Also, you could look up lectures by Prof. Brian Cox , or Prof. Brian Greene. Brian Greene has very good lectures with power point, and models that will break this down much more thoroughly, and with visuals for you. In fact, some parts of this video, are taken directly from Brian Greene's lecture and power point. This channel even used his explanation word for word in some parts. You could start there TBH (If you don't mind lectures) @gtd is really just paying "lip service" himself to this channel, by devaluing "every other channel" . Especially since, as I said, some parts of this specific video are taken directly from Brian Greene's power point. Hope that gives you a good start.

[@angrymokyuu9475]

@@vferrei2 The simplest possible explanation I can give is that relativity mandates superluminal things go back in time(just as it demands you experience "less" and "less" time the closer you get to light speed and that anything at light speed experiences no time at all). This might not seem like a problem at first, but if you were to then travel back to where you started, you would arrive before you left(thus violating causality).

[@thevaticanbikers1535]

I'm no expert, but, it seems that the ultimate paradox of sending the messages back in time before the event happened only appears if you switch between the two frames of reference. Which you do (we are talking about material around 19 min of video). To explain, you mark the signal of supernova travelling from earth to the stl ship instantaneously as observed from the earth and then mark how the signal to switch the FTL transmitter travels from the stl ship to earth as observed by the stl ship. If you were to draw the signal lines corresponding to single observer only, they will almost overlap and be parallel. Given a slight time delay in the machine that receives and interprets the signal and sends the signal back (a computer constrained by the speed of light for example) the signal to switch off will be always slightly later. Causality violation will never occur from a point of view of a single observer and no-one would ever be able to experience it, including the machine that sends out the supernova signal and receives the switch off signal, unless they can be in two places at the same time and be able to switch between the two frames of reference freely.

[@naveedrehman6083]

This is exactly what I 100% believe. The line at 18:12 drawn down-left is impossible even if you send message at 1 million x speed of c. The lowest it can go is horizontal (right to left). Thanks for sharing!

[@Amehdion]

Yeah this confused me as the message back from the ship from earths perspective should be traveling upward and left instead of downward and left. In which case no paradox happens. Earth will always send the message before the ship sends the reply.

[@jordancook8511]

It's because this is all wrong and your velocity has nothing to do with altering space time. Relativity proves this but everyone likes to misinterpret Einsteins findings. The epxlanation with the clock moving slower the faster you go to lightspeed was not an example of altering time. It was just an example of how the light behind you would react if you approached light speed.

[@SpaceCitizenFaye]

THHHIIIIIIISSSS

[@xkinsey3831]

​@@naveedrehman6083the horizontal line is earth's reference frame, not the universal one (there isn't a universal one). That line is possible given the space line and the null line of the STL ship.

[@user-sm4ms8cx1m]

What a fantastic misunderstanding of the subject. Glorious video, classic KZbin.

[@xtear0]

Considering that the ship is an observer and does not affect either the fact that the event happened or that it had been received I don’t see a problem with them receiving the warning before they see earth send the message. Remember, it’s the light traveling, not the actual event taking place.

[@seattleitefpv]

Let's start perhaps with a more modest goal: Alcubierre-style drive that targets STL flight instead of FTL. Even that would be a tremendous step forward for our civilization.

[@galaxya40s95]

.

[@robertharvilla4881]

That seems like it would be more difficult than actually achieving FTL. I would think that simply creating the warp bubble is going to be hard enough, and generating the energy levels and creating the exotic matter required is a monumental achievement in and of itself.

[@rarebeeph1783]

I disagree. What we should actually focus on is achieving relativistic STL flight directly. By my understanding, the closer the ship gets to c, the less time they experience throughout their trip (as the length between their origin and destination contracts, or as time dilation, depending on reference frame). Assuming STL travel close enough to c, one could get to almost any location within the cosmic event horizon, while only experiencing the amount of time it takes the ship to speed up and slow down from its own perspective. The only problem this results in is that all those who aren't also travelling relativistically will be left in the past by the crew of this ship by a number of years equal to the number of light years travelled (this is the effect that would be solved by FTL travel, for what it's worth). It seems to me that an STL Alcubierre drive would remove the length contraction / time dilation effects from the crew, since they aren't actually moving, which would paradoxically possibly make the trip longer for them than if they had travelled traditionally at the same rate as their warp bubble travelled.

[@robertharvilla4881]

@@rarebeeph1783 I don't think that relativistic speeds are going to be possible for humans due to the often overlooked relativistic effect of mass dilation, not time dilation. The faster you go, the heavier you become, and there's no telling what that is going to do to the ship itself, much less its crew.

[@robertharvilla4881]

But the possible negative effects of relativistic travel might only be dealt with by warping space itself rather than accelerating to higher and higher speeds. That makes warping the most likely of ways forward, or at least the least problematic. But then there's the question of what that's going to do to the universe itself when such a warp bubble is created. Seems to me it would result in a singularity or something even worse. ;)

[@Calvinxc1]

I'm having a lot of difficulty wrapping my head around some things here. For example, why is the space axis a mirror-flip across the null line of the world line? For the "stationary" earth I get that it would look like a mirror-flip, but why is it? Also, when the transmission is sent from the STL ship after receiving the earth transmission, why is the slope negative? I feel like having this side-by-side with a similar diagram for the STL ship's perspective (with its world line being vertical, and the others being angled) would help clear things up... Like, I get that there's some consideration here for time dilatation, but wouldn't that be bypassed too, as using something like the Alcubierre drive, the object is not actually moving FTL, just the space it resides in is, so it wouldn't suffer time dilatation... I'm just getting confused.

[@jdshi6693]

This is where I'm stuck as well. I feel like the mirror line is the most critical aspect of the problem, but is also the least explained. He says, "Now, adding the null line back on we can note the relationship that the space axis is really just a flip of the time axis around the null." This statement is just kinda thrown out there like it might as well just be a coincidence rather than a requirement. But he's a smart guy, so I'm sure there is more to it that gets lost in the explanation. Here is what I really don't understand. FTL travel is obviously impossible if what he's saying is true. So then why are people spending years of their lives working on possible FTL ship designs? Is it not a complete waste of time?

[@rhorho2]

yep, the 'obvious' mirror flip across the null line was just thrown in there without any real explanation. I'm confused.

[@theOrionsarms]

Whole this explanation is a little bit wrong, straight lines are from special relativity theory, but relativistic slower than light ship need to have curved lines from general relativity, so space lines of the ship is only local oriented, and not apply to the whole universe, but(to be fair) the general relativity theory allows close temporal lines that breaks causality.

[@CoolWorldsLab]

If you want to a deeper explanation, check out Section 3.3 of williamsgj.people.cofc.edu/Minkowski%20Spacetime.pdf. It really comes down to Lorentz transforms. That the FTL ship is isolated during its trip doesn’t really matter, it departs and arrives in regular space time and is able to reach its destination faster than a beam of light (a beam of “causality”) can.

[@miaokuancha2447]

@@CoolWorldsLab Beam of causality ... Those are words to conjure with.

[@geraldkenneth119]

Even if FTL is impossible things like Alcubierre drive and wormholes could , hypothetically, still be used for slower-than-light or light-speed travel. STL or light-speed wormholes might also be useful as makeshift pocket dimensions, since the throat would have to be longer or the same length as the distance between the two mouths in normal space. They could also be used for uninterceptable communication

[@CaritasGothKaraoke]

All wormhole travel would be limited to light speed. The difference is that the shape of space itself is bent.

[@istvantoth7431]

Great vid bud, very much enjoyed it! 👍

[@Iron-Bridge]

Your written script and voice work is top class, man. Documentary level for me, especially for a subject matter that I find intriguing.

[@Zakini]

It would've been useful to see that diagram from the STL ship's perspective, since it's not very clear why their reply travels at that angle

[@isavedtheuniverse]

I also agree, although after a few times of piecing it together, I think this is what I came to. Under relativity, the speed of light is constant, therefore is that 45º line between the vertical of time and horizontal of space. Any observer is always going to have their own time line vertical and their own space line horizontal and the null line or speed of light line halfway between them at a 45º angle. So as someone else speeds up on your graph, their line will tip towards the right. This is their time line but their space line is also tipping up, both getting closer and closer to the null or speed of light line. I think it gets easier to comprehend once he switches over to instantaneous messages because those are parallel to the space line. So its easy to see why a line leaving the STL ship leaves parallel to what its space line is. I think the part that I don't understand is why one instantaneous or FTL message gets placed parallel to the earth's space line and yet the return message from the STL ship is parallel to its own space line. So I get the math of why the line is that angle, but I don't understand why 2 instantaneous messages don't have lines that are themselves parallel.

[@danielebowman]

Indeed. Given the diagram, isn't their reply being sent backwards? Surely their message to earth would be in a diagonal going up and left. This is because time is going forward so the path of any action should always point upwards except the instantaneous lines which are flat ? (In an angle that mirrors the light speed line).

[@MagicScorpio]

@@danielebowman this is exactly what I’m having trouble with. Their time line is going upward, so sending or receiving should be higher from where they started. I wish I understood this better, but the paradox didn’t make sense on that graph, or could have been drawn better. I don’t know why it’s angled down.

[@danielebowman]

@@MagicScorpio Time should always go up on the context of the graph. The author made a bad mistake.

[@dansmith4132]

@@MagicScorpio I think it's easiest to see it when you actually tip the graph to the angle of the STL ship's space angle. The time access for the ship was shown moving up and to the left through the graph. The STL ship using FTL communication back to Earth sends on it's space angle, which intersects with Earth in the past.

[@its_lucky252]

you didn't explain why the STL ships signal would go back in time.

[@Delibro]

19:19 What you conclude here is that there is a paradox at the earth, so then you must draw all lines in the reference frame of the earth. Then there is no paradox. You can also draw all lines from the reference frame of the STL ship, then there is no paradox too. The fault is the mixing of reference frames.

[@Delibro]

It is right that the pink arrows can be drawn horizontally and diagonal, both is valid, but observed from earth both arrows must be horizontally, whereas observed from STL both must be diagonal.

[@LineOfThy]

All reference frames are equally important meaning if one frame receives a paradox, you’ve broken the universe.

[@Delibro]

@@LineOfThy Yea that's right, but as I wrote no frame receives a paradox, its consistent from either way.

[@calebkimm325]

I have an affinity for how this gentleman explain science jargon in elucidating terms to the lay person and makes it also both profoundly educational and entertaining. He's never ever boring.

[@jeffvincent4827]

That was awesome,, answered a question I've had a difficulty conceiving for so long.. it now makes sense and as always opens the door to more questions. Great video and thankyou very much..

[@chadparks7553]

If you’ve ever listened to people’s near death experiences they’ll often times describe going to the light and then time no longer being a concept, as if everything is happening all at once.

[@SkullyYouTube]

it explains why some "religions" say that our soul/consciousness is not "time-bound" or "space-bound", that it actually is a 4D thing actually trapped in a 3D body

[@davsaltego]

Being high sometimes feels the same way. Maybe what both have in common is the properties of our mind that create the passage of time-creates the arrow. Because without our minds, is there an arrow?

[@BrianKarmo]

Numbers 14:21 is a verse from the Bible, specifically from the Old Testament. The verse is from the book of Numbers, chapter 14, verse 21 (Numbers 14:21). The exact wording may vary depending on the translation, but a common English translation (New International Version) reads: "But as surely as I live and as surely as the glory of the Lord fills the whole earth," This verse is part of the account of the Israelites' disobedience and lack of faith when they were on the verge of entering the Promised Land. The context includes God's pronouncement of judgment and Moses' intercession on behalf of the people.

[@user-wl2px9on8l]

Have you done the math with the actual Lorentz Transform equations? In the case of instantaneous travel, there are 3 events that occur at different locations and different times according to the two different reference frames. A message is sent from Earth the the STL ship and then back to earth both via FTL. It is absolutely vital in this situation to define the first two controls: The Earth time + location the message was sent, and the STL time + location the message was received. Once these controls are put in place, the diagram as shown no longer works (FTL breaks the rules of this diagram). However, the underlying Lorentz Transform equations are still valid. You will find an observer at a distance can witness events that are out of place, but NO message can be sent by any means before the origin, even with instantaneous travel! I have done the math several times with the correct controls, and Sabine Hossenfelder released a video that agrees with this finding.

[@mzrmozar]

can you send the video..... i think the dashed line of the STL space ship is wrong

[@Atomicsuplex]

​@@mzrmozarah, I thought so too. . . But assumed I was missing some important information.

[@johnks6733]

If the message to earth was instantaneous, then wouldn’t the space line for that message be horizontal & arrive in earths future This makes me think that the space line of a FTL massage to earth would take longer than an instantaneous message, which makes me believe that the space line would be upwards rather than downwards as shown in the diagram and arrive in the future.

[@andrewguitarnoob8440]

I’m not a physicist to check the math, but had the same conceptual concerns. I don’t see why it would point back in Earth’s relative time.

[@okaythisisfuckingrid]

exactly@@mzrmozar , @user-wl2px9on8l

[@allenhonaker4107]

Attempting the impossible almost always brings great discoveries even if it's not the one that is being sought

[@MyKharli]

Also leads you to fall off a cliff

[@allenhonaker4107]

@@MyKharli As a former rock climber I can tell you that as long as you are properly belayed go for it

[@brokedolph]

what even is an "impossibility?"

[@TechExpanse]

well in this case there is nothing to attempt, speed of light is fundamental part of spacetime .. going faster follows same logic as lifting chair up while sitting on it

[@greenpumpkin172]

18:44 This paradox will never happen. Thats the point, it will always be a closed loop. Similar to Delayed Choise Quantum Eraser experiment. It is the same thing... I know it is hard to understand, but yeah, FTL is possible, time travel as well and it does not lead to paradoxes ! U can imagine it as those events are linked in time and they always happen (forming a closed loop), no matter what you will do between those events. Also on quantum level in very short times, the causality breaks down... You can apply this to whole universe. And yes, time paradoxes are not possible :-) as Steven Hawking said. Also, what do you think about the UAPs ? I would say they use FTL travel without a problem and some nonsence about causality does not bother them :D.

[@MU-oi1su]

This subject always makes me think about the One Electron hypothesis. Just one brave little electron getting it done... at all times... at all places.

[@LiteraIIy_Nobody]

I wonder what this would imply when you take into account the fact that light might not travel the same speed in all directions.

[@Luna-wt9oy]

I like how he predicted every point where I got confused or skeptical and delivered a good answer without me ever asking anything lol About the talk in the end about exploration without FTL, it was quite poetic, but individuals can actually experience it one day and travel to many stars, considering there is no barrier in the laws of physics that say living things can't last for billions of years. More than that, the way in which time is perceived can be drastically modified, where a million years travel can feel like a mere hour. Just imagining human-like consciousness in a digital substrate is enough to see how this things are possible

[@cassandravonpohl942]

Same. I'd have a question pop into my head, and two sentences later, he was explaining it!

[@toromontana8290]

One problem. The Universe really doesn't like computers either.

[@youtubeforcinghandlessucks]

Even if we stay our squishy selves, we can cross our galaxy in under 25 years (traveler's time, because of time dilation) going at a comfortable 1g halfway and decelerating at the same rate the other half. Even going to the edge of the universe will take under 50 years in these conditions. Maintaining that acceleration that long will require insane amounts of fuel of course (i.e. the annihilation of 600 million tons of matter and antimatter as fuel for crossing the galaxy for a 100kg payload), but it's nice to think it's "possible" in some ways.

[@pinnacleexpress420]

you must not have even tried to look at the "graphs"

[@valkyriefrost5301]

Looking at my cat, I cannot really fathom what she is truly thinking as she stares back at me. With this in mind, I truly have no way to imagine what a "human-like consciousness in a digital substrate" would ever feel like. I suppose it would be as alien as comparing my consciousness to that of an ant...

[@nicholasiverson9784]

If you moved instantaneously from earth to vega, and then told someone - to instantaneously go to earth, and tell them to shut off the instantaneous transporter, they'd arrive essentially the moment you left. That's significantly faster than light speed and there's no causal issue. The whole reason the space line is the time line reflected by the null line is Because we assume the fastest speed is the speed of light, that's an emergent property of the assumption, and any relativistic effects assumed to also be reflected are affected by that original assumption. If you bend or break space itself to accomplish moving subluminally from point A to point B in a shorter time than light could travel that's fine - if difficult, but it wouldn't allow for paradoxes to arise, you're moving slower than light in your own reference frame, from the reference frame of your starting and ending locations - it's as if they are closer not as if you are faster. If you traveled through space more traditionally as you got close to the speed of light your physical and nuclear properties slow until you reach light speed and they halt, you couldn't perceive a message arriving at your location at this speed and even if you kept a record it wouldn't be reacted to until you reached your destination, upon which even sending the message back at the same absurd speed wouldn't arrive back to earth before it was sent. There's also the issue of spreading out if you behave like a wave at that speed, becoming red shifted as space expands with you moving through it, and if fermions and bosons behave the same way through space at those speeds - you might arrive out of sync in a catastrophic way, unless your beginning and ending points are specific distances away - regardless of how long it took you'd eventually find such a place, and even then they'd need some marvel of engineering to slow you down or put you back together once you arrived. Your mechanical interactions would stop entirely as two objects moving in the same direction at the same speed never collide, no nuclear interaction beyond perhaps making you more or less energetic in difficult to predict ways, the magnetic components would just cycle as you travel hopefully arriving in the right orientation and not becoming a tangled mess. If Everything lined up Just right, you'd arrive after experiencing no time pass yourself, it feels instantaneous to the traveler, and that's only moving At the speed of light. If you moved somehow faster - which is as absurd as constructing a machine Out of photons to propel photons faster - you can't experience less than nothing happening.

[@zerepmoto4402]

Very well written, thank you.

[@joannefitzpatrick992]

Maybe maybe travel at the speed of thought or smell?

[@possum4403]

You did not need the other two large paragraphs. Your first paragraph is correct in all respects, well done Human.

[@insertnamehere2746]

I agree with this comment far more than I do with the dude making the non-sensica graphs in the video

[@olegruss]

This is a cool argument, but I think it contains a mistake. You start considering this exchange of signals in the Earth reference system, but when the FTL signal comes to the STL ship and the latter sends it back, you switch to the STL reference system, so the signal basically starts moving back in time from the Earth's view point. You should either continue considering it in the Earth system and it would go back horizontally, or consider the whole picture in the STL ship system from the very beginning, and there would be no paradox either. Actually, these dashed lines assume the constancy of the light speed, so they can't be used with the FTL signals.

[@user-nc4rs5xm1u]

Don’t take this wrong but the style of this video’s cover is really like 3b1b which is one of my favorite channel, and also thank you to make contribution to spread the knowledge and explaining everything to us😂

[@Jacxel]

From the messages point of view, even if it was travelling instantly it still has to travel "through" all the light emitted from the destination. If its destination is 1 light year away, while travelling towards it it will see the destination experiencing a full year. If it then turns around and looks at the source it will be a year in the past from when it left but if it immediately heads back it will not arrive a year in the past it will see the source experiencing a year in an instant and arrive at or after the time it originally left.

[@norbertlauret8119]

Well, you're describing what would happen to a message travelling at the speed of light. The whole point of the video is to look what would happen IF the message was travelling FTL, or intantaneously in the part you're refering to... Imagine a message that would be sent right into a wormhole and directly to the ship. It wouldn't have to travel "through" anything.

[@Vort_tm]

@@norbertlauret8119 The message doesn't move at all, it just moves the universe around it.

[@Jacxel]

@@norbertlauret8119 no, I was describing instantaneous travel. If the message was moving at the speed of light it would have taken a year to get to the destination. During that year it would see the destination experience 2 years worth of time, I.e its time moving at double speed, and then it arrived and turned around and looked at its source it would see it still at the same time when it left. If a wormhole goes to the past then it breaks causality naturally but that's a completely different thing and makes the graphs in the video irrelevant anyway.

[@norbertlauret8119]

@@Jacxel Oh, I'm sorry. I didn't understand what you actually meant by "travelling through" and "see the destination experiencing x year(s)". My bad.

[@cptblood1981]

I would posit that it is possible it's just all about frames of reference. You would not be able to affect anything in your personal referential past. You could observe it, but not change it. I think the diagram is off in using the frame of reference for the STL ship as the "speed" of their FTL message would be significantly "faster" than the message from Earth. The correction for this means that their message would NOT arrive prior to that of the sent message. (On the graph their message would appear to them (could they see the graph) to curve upward past the message point. Using star trek terms if you fired off a message at warp 1 its not going to travel at (warp 1 + full impulse) simply because you were going at full impulse. Basically this graph "forgets" that for all of the pink FTL lines, the straight "space" line is not straight. For them it is a curve, so if you factor that in and the flatten it back out it shouldn't violate causality. I am probably wrong somewhere, it's 2 in the morning...

[@GAURAV_RANA_]

Ah thank you. I was thinking that this seems very off but couldn't put it in words.

[@Johninatorful]

It doesn't make sense to me that the stl ship exists on a line based on the space axis...

[@Snow_Fire_Flame]

Saying that "the line is not straight" and implying it should be straight is basically equivalent to saying "relativity is incorrect." Now, you can have FTL travel AND causality if you scrap relativity, but unfortunately, relativity looks highly likely to be true based on our current assumptions. And relativity means those strange angled paths through spacetime, where by going really fast in a frame of reference time will pass differently (seems to be experimentally true for satellites with clocks in orbit!). (And yes, I know that the video seems to claim that relativity isn't the problem, but... it totally is, I disagree with the video on that.)

[@cptblood1981]

@Peter Ingraham no, what I am implying is that this graph is uses a straight line (thus treating it linearly) vis a vis space whereas the whole concept discussed involves bending or folding space. I do not think relativity presents a problem as I have discussed as I believe it sorts itself put if you discount momentum and the standard rules that apply to speed and motion as you would have to when folding space itself. Similarly to how the rules change when you approach a black hole they would change when you folded space. As such, this graph assumes that if they are traveling at (using star trek references just for ease of discussion) warp 1 and fire of a beacon at warp 1 it will be traveling at warp 2. It will not. I posit that folded space travel is a definite limiter such that you cannot increase the speed simply by initiating a launch from something going at speed. As such it would APPEAR to curve away from the perspective of the FTL ships view on the graph IN ACCORDANCE WITH RELATIVITY. Whereas it's not actually making a curve on the graph because the graph treats space as linear and FTL travel does not.

[@garconek712]

It may be right or wrong but the fact that it is showing 4 dimensional space-time on a 2 dimensional graph, it's like trying to show a 3D cube in 1D, it's simply not doable or at least it seems to me. From what I learned we are able to show a cube on a 2d sheet just because we are able to visualize the depth of the image and draw a "line behind the lines" that how we create 3d in short we are able to circumvent one dimension by imagining it so 4d can be shown in 3d, 3D in 2D, 2D in 1D, jumping from 4D to 2D doesn't make much sense and many things may not match like they should. That I think is the main problem here that there is just no way that he could show what he wants on 2D sheet. Rather than FTL I am more convinced by Einstein-Rosen bridges theory beacuse from what I know they go through additional 4th dimension of space there for not creating this paradox if its true. (sorry for mistakes if any english isn't my first language)

[@isaiahtimothylacaba5985]

I'm confused. Why did the STL ship start at the bottom of the Earth's time axis instead of starting at the point when Earth saw X?

[@riichobamin7612]

Same.

[@iLikeMelk]

Because it left the planet before Earth observed the supernova. And probably to keep the visualization/graph relatively condensed for the sake of the video lol

[@OreOscar]

If a system like an FTL communication system did exist, you could probably avoid the paradoxes by having unique communication "channels" where only certain references frames could interact with it, or just not have FTL communication between STL ships and main communication systems. You could also probably analyse what ships are travelling based on missions you're running and you could analyse possible paradox creating courses of events and avoid them. What would happen if you ran the same thought experiment but with an FTL ship?

[@davemoore5222]

Surely the ‘paradox’ stems from the problem that your graphical representation ‘calculated’ the outgoing ‘instantaneous transmission’ from the Earth’s frame-of-reference, but the incoming ‘instantaneous transmission’ from the STL ship’s frame-of-reference. I would have thought that two instantaneous transmissions from A to B and from B to A (both sent at exactly the same time) have to follow the same path through space-time when modelled in a single frame-of-reference. Which would mean that both transmissions lines should either be parallel to the Earth’s time axis or to the STL ship’s time axis, depending upon which observer is measuring the path through space-time.

[@SagarThorat]

This makes sense. It’s feels like just that the STL observers may “think” that there message to earth has been received by earth before it was sent. But from earths perspective, in Earths frame of reference, Earth to STL and STL to Earth will be instantaneous. So probably like as earth receives response as soon as it sends!! Which now that I think of it, is actually close to breaking casualty.

[@davemoore5222]

@@SagarThorat Breaking causality? Assuming that it were possible to travel at twice the speed of light (2c, and without relativistic effects) to a star that was 100 light years away. You arrive there 50 years after you left Earth. You make an instantaneous transmission back to Earth. That transmission is received 50 years after you left. Causality remains. As the travel time tends to zero, the required multiplier of c tends to infinity. Causality cannot be broken that way…

[@rhapsody4025]

exactly you are right ! ihad the exact same doubt ! thanks for your comment ! so no casualityy is broken. right?

[@cavemanraveman1]

I'm pretty mixed up here but doesn't the idea of instantaneous transmission inherently violate relativity? The paradox is in trying to reconcile these two concepts.

[@davemoore5222]

@@cavemanraveman1 Yes. Trying to explain that nothing can move faster than the speed of light by using a ‘sub-light’ spacecraft and a transmission travelling at ‘c times infinity’ (an instantaneous transmission) is, I believe, where the problem lies (Too many uncontrollable variables). As far as I was aware, none of the ‘Warp-drive’ hypotheses allow a spaceship inside a ‘Warp Bubble’ to send any transmission (information) to the space time outside of the Bubble, and no one outside would be able to transmit in. If the Bubble was collapsed, the spacecraft would then be exactly as it was inside the Bubble and not moving relative to it’s starting point (remember that with all of the current Warp-drive hypotheses it is the Bubble of ‘Space Time’ that is moving, and not the ship). If the ship is not moving relative to the Earth, they are both in the same frame-of-reference and hypothetical instantaneous transmissions would not destroy causality anymore than saying “good morning” to a co-worker standing next to you would. Also: Imagine three galaxies in a straight line, A, M (our Milky Way) and B. A is to the left of M and B is to the right, such that A & B are receding at 0.75c in opposite directions, due to the universe’s expansion of Space-Time. How fast are they receding from each other? Remember, General Relativity puts a speed limit on moving things, but not on the expansion of Space-Time itself. These two galaxies are not actually ‘moving’ with respect to each other (even though they might move relative to their local group by gravitational attraction) - it is Space-Time that is expanding that is causing the increasing separation. Also, as A will never be able to view (and hence know of the existence of) B and vice-versa, there can be no causality problems (people rarely send messages to others that they are unaware of).

[@becyk_du_quebec]

Best explanation of time travel paradoxes I've seen in a long time, thank you for this! I feel so amazed that on one hand we can theorize and explain stuff like this yet a lot of people will still doubt that we ever went to the moon.

[@kritizismmusics9737]

For sure. It's like a hideo Kojima metal gear story lmao he'd right a story about some shit like this. Make a good one crew falls out time

[@joehopkins6724]

I don't think we went to the Moon, too many variables and orbit and where it's going to be and how do we get there if you look at Apollo 13 movie with Tom Hanks they talk about the 8-ball bubble how do you get orientation when you're not on Earth

[@mowvu5380]

@@joehopkins6724 dude, there's a decent shout for never breaching LEO. but your argument is instantly null and void when you're bringing up hollywood movies lol.

[@ayaankhan-vt5jy]

Yeah man. I love this guy

[@whichgodofthousandsmeansno5306]

There are still people who think the earth is flat. Even though the first circumnavigation of the earth was completed 500 years ago. The problem with time travel is if it were conventionally possible we should already have had evidence of time travelers and it would be very easy for anyone from the future to prove it. From a theoretical standpoint, M-theory is the only possible solution to the paradox I can imagine but still seems impossible to prove regardless.

[@VintageCR]

the other option or direction is that we assume "time" travels at the same speed in every corner of the universe which indeed can cause paradoxes. if we don't assume time is equal everywhere, it means sending FTL messages to the fictional Vega planet about X can either arrive before or after the event happened depending on how fast time travels in that corner of the universe or system. However, my knowledge only goes so far.. if you disagree with this i fully understand but explain to me why this is not possible when FTL is?

[@LeAdri1du40]

I think the problem is simply with the FTL going backwards in time in the graph, the thing is the FTL message would be traveling inside space itself, what we could call a fourth dimension where time is absolute, why would it be bound by general relativity, if it's breaking it in the first place?. Then on your graph you can trace it without the time dilation of the ship, thus it would be relative to the earth again and not the ship, so for the ship, their 'FTL' is actually slower than light but for the earth it's traveling faster than light It's the only way to have possible FTL without creating time paradoxes

[@thelusciousgamer1547]

Could someone explain to me why the message went back in time from the ship? It was kind of glossed over on the WHY and we went straight to the What it did.

[@colinharrington5303]

Sir, I only found out about you less than a month ago but have almost instantly became obsessed with your content. Keep it up man, I love everything you put out.

[@prod-tkat]

U should b a multi-million subscriber channel! Some of the best content on KZbin 🎉

[@DarkThomy]

18:09 why would the STL ship's message answer go back that way on the diagram? I don't get it at all. It's very confusing because there were no example of someone answering back without FTL shenanigans.

[@stealthyshiroean]

I always love the very grounding and philosophical thoughts proposed in these videos along with the theory. Really helps to place the science and the importance of these studies in a broader sense and why or why not humanity should pursue them.

[@johnnynitetrain32379]

Well said.

[@sarge9733]

I love watching this channel. I have such a longing for knowledge of the universe, space and all the theoretical studies and possibilities they potentially propound. I feel like I'm learning with every video, yet after each one ends, I feel more stupid than before I started.

[@meapyboy12345]

this reminds me of a VSauce quote where he said "The more you are enlightened the more you realize how in the dark you have been." Which basically means the more you learn the more you realize how much you didn't know. I feel you with feeling stupider every video i feel the same way. But i am still very happy to be learning all that i have learned from this channel.

[@___jd]

15:38 Okay but how does that sequence of events actually manifest itself from the crew's perspective? They won't "know" that Vega received the warning before X even happens, and by the time they arrive at Vega it will be _after_ the warning was received, just as it is for Veg's timeline. And they are now _on_ Vega's timeline at that point so it shouldn't matter..?

[@Enthai21]

I think it's because in that scenario at 15:38 the crew inside the STL ship is not interfering yet like he illustrates later on, so yeah if the crew doesn't interfere then nothing of consequence will happen, however in their reality the chronological timeline of events is already messed up even though they don't know it. Like if they continue their journey normally then nothing will seem out of order, however during their journey some things happened that they don't know of that broke causality

[@davidschaftenaar6530]

I'm probably just not understanding this properly, but: Shouldn't the reply from the STL ship _always_ travel *up* every possible Worldline, no matter how quickly it gets back to Earth? Drawing the reply the way you're drawing it, means that _all_ replies back to Earth (even STL ones) will break causality, because you're sending them backwards through time rather than forwards. While Earth, the ship and Vega are all moving through time at different rates, time is still passing for all three; In your example, you're drawing the reply line back to Earth as though Earth were stationary in time from the moment it sent it's message.

[@morgan0]

doesn’t this assume the FTL system functions within and is warped by spacetime? if it were to be outside it, like a wormhole, would it not be a line that moves up at 45 degrees for some time, jumps over, and then 45 degrees again until hitting the other stationary observer? it seems to me it would create a light cone that has multiple center points, but with some shift up to account for some non-zero distance to travel to get there. this seems like it would be much better behaved, but i’m not a theoretical physicist.

[@theneonwarriors3794]

It’s actually really easy to go faster than light, just make a big ball of light and attach a couple rockets to it

[@lukesgoldies]

Genius

[@bhedgepig9653]

I try to do it by hitting the light switch while simultaneously jumping under the ceiling light bulb fitting. after 9 years practice it feels like I'm about there. also I got those 9 years back just because its kind of magnets

[@nicholusshadursky9512]

I actually just imagined myself as light going around the world in an instant and turns out I succeeded. It felt instantaneous and there were no measurable details of the event, but it was still awesome because it happened.

[@mmheti]

I have an even cheaper option. Get a mirror, then walk towards it. You are trevelling in the opposite direction the fotons reflected from the mirror, so you are travelling FTL from that light's point of view.

[@bhedgepig9653]

​@@mmhetikzbin.info/www/bejne/kKXcqX2JfLJmrpI

[@thaflowie]

What if the acceleration after light speed rather than adds more speed causes a bigger time dilation that preserves causality by from your prespective making everyone elses time pass faster?

[@generalvikus2138]

Isn't saying, 'if I had an Alcubierre drive, I could go back in time,' equivalent to saying, 'if I had a genie in a bottle, I could use one of my three wishes to go back in time?' This 'drive' requires negative energy - that is, at least one logical impossibility, correct? You could accept the axiom that genies are real and then wonder how causality could be preserved in that universe, but what would be the point?

[@cjc363636]

Thank you for this lesson! I finally have a slightly better grasp of 'world line' diagrams. I did't realize, or remember, that all "C"/ Light Speed lines are 45degrees. That helps. Now, I'm gonna look at a nice sunset to rest my brain!!

[@housetheunstoppablessed4846]

Spacetime itself can exceed this speed limit, by stretching and contracting space which itself is the concept behind the warp drive and the wormhole. This video is mostly hogwash that only deals in purely in physics currently testable by current means and not in theoretical physics. Here is a paper that deduces that FTL can be achieved: arxiv.org/pdf/2201.00652.pdf

[@primaerr]

Edit: Cleaned it up. As others have mentioned, the only constraint necessary for a vector to have a >= T (Time) value. The problem is that T and S axis are different for different frames of reference. The one frame can have a vector with positive T (maintaining a dot product == C), but be a negative T vector (or dot product C) when translated to a different frame of reference. I think then the problem, all vectors having a positive T (and vector dot product == C), would be solved if there was an absolute frame of reference. A possibility frame would be the expansion of the universe. If all vectors are then constrained to having a positive T (and dot product of C) on the universal frame, regardless if a vector from one frame translates into a negative T vector in another. The universal constraints would then not be violated. That also means that "time travel" would really only be within a local frame, not the universal frame. Local paradoxes resolve on the Universal Frame. I think that makes sense. And hopefully I used the correct terms; my math is old and shaky. IANAP (I am not a physicist)

[@amorencinteroph3428]

A universal frame by it's nature would disproof relativity, however. But many scifi shows do use it as as explanation for why FTL is possible but doesn't break causality (hyperspace, subspace, etc). There's an adage in scifi circles, "Relativity, Causality, FTL, pick any two".

[@PukitisLaunitis]

Hyperspace does not break causality, it just abolishes relativity. Even Hawking once admitted that in sci fi interstellar travel can be made fast if the author so wishes, as FTL travel would allow an astronaut to travel many times in his career instead of max. 1 expedition. And even if that cancels relativity, so be it. By the way, even Herbert Wells' Time Machine does not break causality. A 19th century man goes to the future, sees it and comes back to tell the story, no causality broken. Some sci fi authors do break causality to create intellectual puzzles (Harry Harrison's Time Machine Saga or William Tenn's Discovery of Morniel Mathaway) but that is a different theme altogether.

[@PukitisLaunitis]

FTL does not break causality, at least in sci fi. In fact, hardly any sci fi writer breaks causality, except for a couple of authors breaking causality as intellectual puzzle (Harry Harrison's Time Machine Saga or William Tenn's Discovery of Morniel Mathaway - by the way, none of them has anything to do with space travel). FTL just abolishes relativity. Edmond Hamilton, Isaaac Asimov, you name it.

[@fickjosh]

maybe I'm just not getting it, but the "STL ship's time axis" isn't a diagonal line - that's the trajectory of the 'current present' of its "world/time-line/axis" as it moves across the X-Axis "Space"... But the "STL ship's time axis" is still a vertical line to its own position in "Space" which should be drawn as a perpendicular/vertical line; therefore, it's movement through "Space" should be a zone whose boundary is what is depicted as the current "STL ship's time axis" and the entire section of the graph beneath that line should be colored in. The reason it is more appropriate to "color this region in" is because you have the "STL ship's time axis" MOVING along the X-axis, "Space" and thus must represent its potential position through "space" - this would be a quantum field! That is to say, a variable field (of positioning) which has various potential data points/states (notice the doubling of the root word 'vary' - that's 100% intentional by mathematicians and physicists, as they are saying, "it depends" w/ a shrug)! This means the "STL ship's space axis" would actually be what's labeled as the "STL ship's time axis" - as this line represents the amount of time/distance it took to actually cross the space, and definitely -not- the Ship's perception of time (aka, the "world/time-line/axis" or "STL ship's time axis")... Note that the perception of time is the same for all observers (see Einstein) - so the ACTUAL "STL ship's time axis" is still a vertical line... what you actually see during that time is completely inconsequential, hence why you can represent different items in different parts of space as having their own "Time Lines" or whatever label we decide to employ

[@fickjosh]

yea... the whole thing falls apart (or together?), once you realize the inherent error

[@esbuenodun]

Outstanding! FTL was always a dream since watching Star Trek as a kid. The fact that we can glimpse these wonders of the universe as water filled meat sacks is truly amazing. Even if it isn’t possible, I appreciate that logic as to why is isn’t possible. Space is big. We’re living in an age of high definition discovery.

[@k.lisaswensen9877]

Water filled meat sacks, lol 😂

[@mateonikolic6984]

Wouldn't call humans just water filled meat sacks. We are an outstanding species that just appeared shortly on earth. Our intelligence and consciousness is a God's given gift truly. In the future I believe we'll be able to change universe to our fit

[@charleslong7815]

@micaiah middleton kzbin.info/www/bejne/a6LCq2t4n86MpMk - Starship Congress 2017: Miguel Alcubierre, "Faster Than The Speed Of Light"

[@ZacharyBurr]

I have a few questions: 1. Why is the instantaneous message from the STL ship parallel to the ship's space axis and not perpendicular to its time axis? Because in this frame those two are not the same. A line perpendicular to the ship's time axis would arrive at the Earth after it sent the first message, thus not breaking causality. 2. Furthermore, why doesn't the message travel perpendicular/parallel based on the "global" space/time axes? I get this might cause some issues as relativity shows that it is essentially impossible to define a true inertial reference frame, but the choice of which axes we draw the line based on seems a bit arbitrary to me. Why do we use the sender's frame and not the receiver's? In the Earth reference frame, wouldn't the reply arrive immediately after the first message was sent? 3. Light-speed will always correspond to a line with 45 degree slope yes? Because if so, drawing a line at 45 degrees from a point on the ship's worldline back to the Earth worldline shows that the light arrives after an instantaneous message sent by Earth. Therefore, there is a region in-between when Earth sent the message and when light from the ship returns back to Earth. Can't a message from the ship follow a trajectory such that it arrives in between those two events? Then the message would travel FTL, but it still would not break causality. 4. What if we consider the FTL ship is communicating with Vega instead? Let's say Vega sends an instantaneous message to the ship as it is on its way there. If we assume that the instantaneous message does travel parallel to the ship's space axis as described in the video (and not perpendicular to the time axis as I asked about above), then a message traveling instantaneously from the ship would arrive after the initial message from Vega, thus not breaking causality. In fact this would also be true for any ship traveling toward the observer it's communicating with. What's up with this? Does space/time behave differently in different directions? Is it not possible then that the ship could then send an FTL message in the forward spatial direction but not the backward? (However, interestingly we now have the opposite problem wrt my first question. A message traveling perpendicular to the ship's time axis would go back in time!)

[@kudr66]

BINGO! IMO your point 2. is the solution. He draws the message sent back in ship's frame and shows us that message arrives too early, but in Earth's frame. The line of the Message sent back has to be: a) either drawn in the Earth's frame b) or transformed back to the earth's frame Both a) and b) are in fact identical and don't show any paradox.

[@johannageisel5390]

Huh, yes, that's weird. One would assume that observed from Earth, the FTL message arrives at the ship instantaneously (perpendicular to Earth's time axis), goes with the ship's time axis for a short little bit (the time that's passing while they prepare the answer) and then the instantaneous return message ALSO moves perpendicular to Earth's time axis. It would then arrive at Earth after a different timespan has passed than has passed for observers on the ship, but still AFTER the sending of the original message. Very confused.

[@thekrymax]

Thanks you summarised my questions, i see some issues in this video. I dont think that relativity works that way. Why should the message frome the stl ship move backwards, because of ftl? It could and would just going forward on the time line in a smaller angle. You can't just draw the vector in the opposite direction against universal time direction, because of the law of entropy.

[@AverageAlien]

1. Because it's not travelling through time alone. The message is travelling through space, which means it has to sacrifice speed through time

[@ZacharyBurr]

@@AverageAlien but the message from earth travels perpendicular to the Earth's time axis. Which means it doesn't move through time at all, which is the definition of instantaneous. It just happens that for the Earth the space and time axes are perpendicular, so perpendicular to the time axis is parallel to the space axis.

[@anatolimitkov3976]

My interpretation of traveling faster than the speed of light is that if you fly alway in a ship going just enough faster than the speed of the light and you reach let's say Saturn 15 min faster than the light. Then you look back at earth and try to preserve what happened. You will see yourself taking of from earth. Something like that I could not calculate exactly the timing right now, but you got the idea.

[@TurdFerguson43]

My conjecture is that when you are moving faster than the speed of light, regardless of the means of doing so, you are not actually moving along a spacial path that enables time travel paradoxes. The equations of relativity actually solve to show you are moving along an imaginary (think the number i) time axis if you were somehow moving locally faster than the speed of light. That said, if you are moving space faster than the speed of light, you, yourself, are not moving faster than light. Space time is not actually distorted for you enabling time travel paradoxes due to your locally subliminal speeds. In fact, I would go so far as to say that if time travel paradoxes happened due to spacial distortions that happen faster than light speed, then the universe would already be experiencing paradoxes, given that universal expansion happens faster than light speed. We literally *observe* it happening FTL. Notably, the universe does not contain time travel paradoxes right now. That alone should tell us that relativity, albeit is a smart idea, is clearly lacking the proper answers at extreme conditions such as FTL (not to mention inside of black holes). If time travel paradoxes are to exist, it’s possible that the universe simply “overwrites” both states into existence at the same time enabling a universal memory of both states, which would locally enable humans to realize that the time travel “paradox” exists and simply do the effect that enables the cause. That is, for the transmitter message, the universe would enable it to happen but it would simply ignore its effect on itself. So the message would still transmit because the universe ignores the effect of the message to shut itself off before it even started. Another possibility is that since the FTL message would not be continuously actually tied to the spatial line of the STL ship, it would simply “readjust” to move along its proper spatial line as determined by a non-inertial frame of reference and would just move diagonally towards the earth into the future. The only people who would perceive it as reaching earth first would be the people aboard the ship, and they would simply be observing something they cannot logically determine or they would simply actually observe the FTL travel happening along the non-inertial path and thusly reaching earth in the future. As to why that would mathematically happen? I refer back to Einstein’s equations not properly working in extreme situations, just like Newton’s didn’t work in another set of extreme situations leading to Einstein’s equations.

[@MitchJohnson0110]

We could go the "Three Body Problem" route and say that maybe time paradoxes do exist, we just lack the ability to see and/or understand what they are from our limited perspective. Like the shooter and turkey theories.

[@avinashreji60]

General relativity perfectly explains the universe’s expansion being FTL, you’re wrong

[@Designed1]

the expansion of the universe is the expansion of space itself, so it doesn't need to be slower than light. but then again, there's like, no way that FTL can cause time travel paradoxes lol

[@opliko]

@@avinashreji60 If you don't explain why, there is no point of speaking.

[@TurdFerguson43]

@@avinashreji60 I mean, it doesn’t, since there aren’t time travel paradoxes stemming from objects universally traveling FTL in expanding space. Accordingly, moving FTL in the universal frame of reference while traveling slower than light in the local frame would actually enable us to avoid time travel paradoxes. Meanwhile, the current general relativity model postulates that such movement would cause backwards time travel and thus paradoxes. That’s plainly not been observed.

[@benjtheo414]

This is the first video I watch of you and I am amazed by the quality of the edit and the way you explain these concepts. Thank you so much :)

[@yolochicken1236]

You take the words out of my mouth

[@MENAMEJUMFOORD]

@@yolochicken1236 I'll substitute those words with something else in your mouth 😋