What is the Grandfather Paradox? | Neil deGrasse Tyson Explains…

[@StarTalk]

Where would you go if you had the ability to travel back in time?

[@upsjetmechanic5647]

Pangaea.

[@blackmage999]

If i could reverse entropy id id create an infinite power source.

[@craigscott2315]

a bit of a divergent, yet still within the realm of paradox. Here Mr Tyson, do you fear flat earth theory is a systemic threat to the fundamental propositions of astrophysics?

[@damon81981]

Ancient Alexandria. See the lighthouse, the library, and the culture. Time travel to the past is not possible. Its just fun to think about.

[@blackmage999]

@UCLOrDf-QvrtlfDwpSMFH17A i dont believe that time as we know it actually exists. I believe what we perceive as time is just a measurement of change within a system (entropy). The idea of traveling backwards in time would be a reversal of entropy which would have greater impacts than visiting the past.

[@meisterthephilosopher6498]

“The road you take to avoid fate, is often the one that leads you to it” … one of my favourite quotes

[@miakg7571]

That Turtle from That Panda movie.

[@racingfuel28]

Or as Oogway said, “one often meets his destiny on the road he takes to avoid it.”

[@KingsleyIII]

That sounds like something Uncle Iroh would say in Avatar: The Last Airbender.

[@carfo]

like oedipus rex

[@MarioSellars-pg7rm]

“Only dead fish go with the flow” I feel is the contradictory quote to that quote lol.

[@igel9316]

Everyone is so scared of changing the past a little because it would change the present, yet no one cares changing the present even though it'll change the future! 🤯

[@R3_dacted0]

How can the future be changed if it wasn't set yet? For that matter, how can you be sure choice even exists in the present if you can only ever make one decision at any one point in time? If tomorrow at exactly 12:00:00 noon you are given a choice between A and B, and you pick A, how can you ever be certain that option B ever existed at all? You can never go back to 12:00:00 and select option B to check. The most you can do is go back at 12:00:01 and check... but at that point you can no longer be certain that either of those options are the same anymore. 🤔

[@abenitez34]

igel..... most intelligent argument I have heard in the past 12 minutes. Bravo.

[@Vioblight]

Man, the thinks I could accomplish if I read this everyday 😮😊

[@balakrishnakesani4289]

We have a lot of information about past, so it makes sense to go back and use that info to our advantage, for example you failed in a test but now u know the questions so u can find answers, go back and clear it but what if you have a test tomorrow, what can u change?????

[@sirdropbeartv]

The future can’t change as it hasn’t happened yet lol

[@tim0n4life]

The Netflix show “Dark” presented the best time travel story i ever saw.

[@fiusionmaster3241]

I heard it was an ok show. Is it m8? I just wandering

[@CrashBashL]

@@fiusionmaster3241 It's the best time travel series in TV history.

[@MrRowntree27]

Yes! I was thinking about that while they were talking about the inevitability stuff

[@omaritojf]

Yes! Its amazing and puzzling!

[@Thescrantondude]

Oh this show made my brain melt so bad

[@collinwilson2671]

You probably hear this all the time, but… you make learning fun. Coming from someone who hates to learn after listening to you I can’t get enough of wanting to learn more about our solar system and planters and and all the wild exciting and even scariest things about our galaxy. so mesmerizing and you help make it that mesmerizing

[@68SSCAM]

I always thought that if you can travel back in time, you can easily prevent or change things from happening, but then that creates a parallel universe where both outcomes are possible and you stay in the one that you changed.

[@dylanhughes572]

I always envisioned time travel this way.. The amount of power you'd need to time travel has got to be insane.. so I presume that such an event would pluck you completely out of the time stream and dump you at your intended location. This in turn would break causality but in essence the original you disappears and in the OG you'd be a missing person. Say you travelled back to 1899.. you would arrive and your arrival would branch the timeline. The original would still be there but from your perspective it would no longer exist. The new split would have you paradoxless.. even if you killed your great great grandparents, you would stay existing because in this time line your existence "started" when you arrived in 1899. You would be completely separate to those sort of consequences.

[@alexmcneel8931]

Yes

[@parttimetrader007]

The moment you travel back in your past that past become your present the one which you came from becomes the future but wait the future you will have from that moment onwards will be very much different from the future you came from .

[@Wiseman108]

That just a theory as well, nobody knows for sure what would happen.

[@jefftaylor3559]

What if people have traveled back in time, and the reality we see now is the result.

[@woodrobin]

The thing with "Supreme Strange," as the alternate version of Doctor Strange in "What If?" is referred to colloquially, is that he "lost his heart instead of his hands." In the main universe, he has horrible injuries to his hands in a car accident. In this alternate timeline, he convinces Christine Palmer to go to the award dinner with him (in the movie, she turns him down). Instead of the horrible hand injuries, he loses Christine in the accident. He spends his fortune researching time travel instead of experimental surgeries. He still ends up in Kamar-Taj and becomes a Master of the Mystic Arts, but he is definitely the *worst* person to entrust with the Time Stone. He goes back in time and tries to save Christine over and over, but because her death is what caused him to encounter the Time Stone in the first place, undoing her death undoes his ability to undo her death: Paradox! He finally accrues enough power to warp reality itself to his will by consuming the lives and powers of numerous extradimensional entities and even an alternate version of himself. But when he uses that power to save Christine, the laws of space and time snap under the pressure. He bent reality beyond its tensile limit. His universe, and every being in it other than himself and a small sphere he is able to preserve, dissolves into nothingness. He is (until the Watcher recruits him and brings him into the Multiverse) doomed to exist within a crystal sphere a few meters in radius, forever. His entire universe is essentially the saddest snow globe ever conceived.

[@fiusionmaster3241]

Bruh...

[@aunemartinsen6905]

Also if you could travel back in time it would mean we have no free will lol

[@tenadefiant]

Damn🤯

[@Visalputh99]

An absolute point

[@woodrobin]

@@aunemartinsen6905 If you can alter the past, it does nothing to contradict free will. In fact, it does little to contradict free will if you can't alter the past. You had free will to make the choices you made in your present. Now that that present has become the basis for events subsequent to it, you cannot alter the choices you originally freely made. In a universe where you can alter the past, free will is even stronger, in that your subjective present self can freely choose to change anything, even the actions of your subjective past self. Other people thwarting your will doesn't disprove free will in general. It just means they have an advantage over you in seeing their will implemented, whether that advantage is privilege, power, money, influence, or time travel.

[@bruceneeley1724]

The old Simpson's Halloween show where Homer time travels is the best "I wish I wish I hadn't stepped on that fish". Regarding the paradoxes, what about the many worlds theory creating different branches of timelines.... Your arrival in the past would create a different universe... not affecting the one you came from. Just thinking out loud... great episode!!!

[@StarTalk]

That’s a good point!

[@jeremiahgarza812]

There's an episode of Rick and Morty in the most recent season that explores this idea as well (Morty has Rick create essentially a "quick save/respawn device" that instead of moving him back in time to before something bad would happen it moves him into a separate reality and his "respawn" would destroy the morty in said dimension to make room for the original) meaning he never really travels back but only into another reality to the point before he (in that reality) would die

[@aprylvanryn5898]

There's also the perspective that if you travel back on your own timeline theres nothing you couldn't do that wasn't already done because you were already there in the past. You just don't know it in the present

[@rt329]

What’s the point of changing the past if your own timeline is not affected. I believe time travel is possible but interaction in the past or future is not. Everything happens for a reason, some might call that destiny.🤔😉

[@NothinButGame]

@@aprylvanryn5898 why wouldn’t you know in the present if it’s your life that you’re going back in time as? Right now you remember your past….

[@Strugglebaddy616]

I just imagine Neil DeGrasse Tyson shaking me awake, then says "Did you know..." **cue video**

[@fiusionmaster3241]

That would be interesting

[@MrLee43]

😂

[@12major18]

I’d probably just get up and follow that n**ga 😂

[@buck_maize111]

God that made me laugh 🤣

[@ponderosacal1218]

HAHAHAHA

[@erikwestervelt6083]

Groundhog Day also gives us a good example of inevitability/destiny. The little subplot there of Phil Connors (Bill Murray) helping out the old homeless man numerous times - getting him meals, bringing him in out of the cold, taking him to the hospital, etc. - but no matter what he does the old man dies each time. I think I remember the filmmakers touching on this and what they wanted to show is that no matter how much Phil knew and how much he could predict and control having relieved the same day over and over again, that he still wasn't omnipotent. Some things were beyond his control & power no matter how hard he tried or how many scenarios he played out. Comforting thought in a way...

[@FloydRinehart]

Or a movie I saw a long time ago called the Time Traveler’s Wife, if I remember correctly… …and then they mention “the movie from the 90s” shortly after I make this text. Ha!

[@emsleywyatt3400]

To quote Lost: The universe course corrects.

[@ronkempke6673]

@@FloydRinehart I guess the question is, "Are future life-changing events already determined long before they happen?" And what about our concept of free choice? Is it really "free" or do we just prefer to think it is?

[@pepesilvia7527]

I don't think I can ever get tired of the concept of time travel

[@DSanto-bk6oq]

That "stepping on a butterfly" story mentioned toward the end of this video came from the excellent Ray Bradbury short story "A Sound of Thunder" that was first published in the early 50's which was, in my opinion, one of the greatest sci-fi short stories every written.

[@Otokichi786]

...And a movie that was on the edge of greatness before falling into the MST3K pile: kzbin.info/www/bejne/aanEfKmJpNOVfZo

[@zacherade1541]

Came to the comments to make sure someone said the name of that story. I remember having to read that in Middle school. Great short story.

[@sadeeanselment1210]

I remember reading this in jr high. It still is one of my favorite short stories ever

[@ryanbutlerartcolorist651]

Two things I've always thought might vastly change time travel the way it is usually depicted: 1. If from now to end of the universe, time travel is invented, could we possibly already be living in a world that is the final product of every change made by a traveler? 2. If changes in a timeline did cause it to branch and become a different universe, then if you changed your own ancestry by accident you would still exist. Only the new universe you would be compromised.

[@UDubFootballFan]

1. No. 2. You wouldn't be aware.

[@ryanbutlerartcolorist651]

@@UDubFootballFan Any reasoning would be appreciated in your rebuttal against my rebuttal of the potentially fictional representation of time travel in media 🤣

[@steezymiguel2393]

I like to think thats how time travel would work, going back and changing something doesnt affect your timeline but branches out into a new one.

[@mikehoncho2640]

​@@ryanbutlerartcolorist651He's the time traveler who doesn't want you to know lol exposed ‼️

[@guypursin]

I’ve always been of the mindset that “what is meant to be will be”. That everything that has happened or will happen is that way because of AND in spite of time travel effects. If I interact with someone/something in the past, it doesn’t change the future, because it’s my action that sets that future thing into motion.

[@inlinechris]

Lazy way to think about it tbh

[@NecroWolfExPaladin]

Sending messages back in time is basically the Plot of Stien's Gate. That game also deals with the concept of "attractor fields" which are macro scale events that can only be changed if you alter the past enough to escape the pull of them. It's kind of like some kind of causality gravity. Grandfather paradox only really matters in a universe with a single flow of time. In a multiverse kind of scenario you can go back in time, which will automatically create a new branching point, and anything you do creates a new branch to a new future. In that situation it becomes basically impossible for you to ever return to the universe you left. If you broke ancestry, it wouldn't matter because the reality where you didn't and were born would still exist. Nothing gets broken, you just create and follow a new time stream into a new separate universe.

[@RuggedPanther]

AAAAH another steins;gate enjoyer in the wild! We're a rare breed (at least outside of the anime community).

[@NecroWolfExPaladin]

@@RuggedPanther It isn't the most popular game in the world, but I loved every moment. I watched NicoB play it.

[@AdityaRaj-hp8tn]

I watched the anime but all I was thinking was this was shown in Steins Gate, that's the first thing that came to mind while watching this video

[@dekmikasa4366]

Finally someone mention Steins Gate. I'm not playing the game, only watch the anime. I think it's one of the most interesting take on time travel ever.

[@melly1432]

A comic with an appreciation of science and an aptitude for it plus an astrophysicist with a great sense of humor equals me hooked. And thank you Mr Tyson for clarifying that it need not be called the grandfather paradox.

[@BillyBoyGenius]

I could watch these guy's talk forever, man.

[@dreamdjarin]

The banana peel scenario reminded me of the star wars ep.3 scenario with Anakin when he had a dream of the future with Padme and tried hard to prevent it, going so far as to joining the dark side, but it turned out that him doing all that, was the reason why she died.

[@dekmikasa4366]

Watch Steins Gate

[@frocat5163]

I agree that the more interesting approach to time travel stories is that events in the past can't be changed. Because the past has already happened, if at some future point time travel becomes possible and someone travels into the past, they were _already in the past,_ so nothing can be changed.

[@Honeybee9630]

Yeah, certainly. And they make sense in a way (not from a scientific stand point as I am pretty sure closed time loops are already disproven, are close to being disproven)

[@dangernba]

Not really. Quantum physics have already predicted and proved that the observation of really small particles change their behavior even in the past. Really mind-blowing.

[@tonimartins5066]

Thanks!

[@Twilighttank]

Neil basically describing the premise of stines gate was a great addition to my day

[@andrewjustice210]

It’s funny, because there is also a short story called “the sound of thunder“ that ends the same way… A guy stepped on a butterfly and it is on his boot… Also, he comes back and the Nazis won the war… So, Chuck made a joke, but he actually predicted the outcome of this 40 year old short story… It is actually a really good read! I encourage everybody to check it out

[@StarTalk]

Thanks for the recommendation!

[@Fizzer99]

There is also a movie with the same name. It's pretty interesting.

[@lukion27]

@@Fizzer99 The movie sucked compared to the short story. Very little similarity between the two.

[@IMAX]

I didn't see your comment before commenting about the movie "A Sound Of Thunder" in mine. I love that movie. I didn't know the short story included the Nazi's won WW2. That's scary alternative universe I glad I don't live in.

[@garybell81]

@@Fizzer99 it is a NOTORIOUSLY awful movie. The title is solely a reference to a gunshot in the story. Yet the movie did not include this event; thus, the title makes no sense for the film. This is not even scratching the surface of how and why it was a truly dreadful movie. Huge budget slashing after production had started, severe weather related issues with the location shooting, etc.

[@FeoAmante]

Back in the 1980s - and believe me I read tons of Science Fiction in magazines to anthologies - I read a time travel story, possibly in Omni magazine, where a Rescue time traveler went back to find out what happened to a previous time traveler. In short, the time traveler he found wasn't the one he searched for. This "First" time traveler couldn't return because he inadvertently made a change that stopped him from being born. So the machine he traveled in couldn't return to First traveler's time, because that "time" doesn't exist. Why? Because time isn't simply a number like the arbitrarily designated year of 2022. For his time machine, time exists as a coordinate and that didn't exist for Future First. That's all the detail I want to give in case someone else remembers the story. I don't want to spoil it for others. Still, I like the idea that we are too insignificant to the universe for cosmic time to "concern" itself over whether we go back and create a paradox for ourselves or not. So Physics doesn't stop First or create the Samara conundrum. First didn't Marty McFly fade or disappear. He simply kept living in the coordinate he arrived at - unable to return to the coordinate he came from. Rescue traveler has to figure out if he can solve the problem for First traveler.

[@1973vanguard]

Man did you bring back memories for me when you mentioned Omni magazine. Boss 😎

[@ossiedunstan4419]

Its all also FICTION, not NON FICTION.

[@natalyamartirosyan]

What was the name of that story, do you remember? Or maybe the author’s name? Sounds very interesting

[@FeoAmante]

@@natalyamartirosyan I was hoping someone here would remember. 😀👍

[@alicedawnphelan293]

The molecular displacement thing is possibly the closest I’ve come to explaining my reservations about time travel. Though my understanding is that it’s probably not possible to begin with.

[@justtosharefiles678]

That’s not true I made a time machine next month

[@cosmicwarrior1562]

@@justtosharefiles678 it didn’t work

[@louisrobitaille5810]

Fun fact: time travel does exist, we're all doing it right now. Time travel to the past is kinda possible, but it's impossible for anyone or anything to travel to their **own** past. Look up "cones of light" to understand why.

[@jf2369af]

I travel backwards through my time-line all the time. You ever remember your younger years? I do...

[@DavidBChannel]

Yeah, as far as I know, we don't even know if time is actually a thing or just a human concept. There might just be "now" and we may not be travelling forward through time at all.

[@RoyThe4th]

I think the 2 timelines would just merge. While your grandfather would cease to exist, you would still exist.

[@rebaz7256]

I love listening to Neil. He's a breath of fresh air

[@ThatAnArchyDude]

5:00 The final bits of Steins;Gate. Keep trying to save someone from dying, but they just die in a different way each time...at the same point in time...every time. 7:10 Literally the basis of Steins;Gate. lol

[@tomsadler4049]

I was looking and hoping to find a steins;gate comment haha

[@Josh-Casey]

Hi Neil! I believe, that if time travel ever is possible, it will be in a sort of "read only" mode. You would be an invisible viewer, with no ability to interact or affect anything. I suppose that's essentially what we're doing when we look up at the stars. 😀 If you instead could travel back and affect things, physics would either prevent a paradox from ever happening, as you more or less said with eventuality, or physics would just completely break down. Or, perhaps, if a paradox is created when traveling back in time, physics might only affect the traveler by instantly correcting the paradox or creating an alternative universe. Fun to think about, maddening to come up with a solution. 🤣 CHEERS! EDIT (7/15/22): People keep wanting to think of a Time Machine or Time Travel as being a more physical experience, of course how movies represent it, and I believe that the laws of physics simply will not allow any form of Time Travel to be a fully physical experience. Time Travel = Time Viewing. It will have to be some sort of virtual, or READ ONLY, experience. Something constructed out of inspecting the light, from the desired time, that has left the area of interest. Slap a telescope on Pluto, point it at Earth, record the footage, send it back to Earth, and you are now "Time Viewing" from 4.7 Hours in the past (+ another 4.7 Hours old sending back the data). If that telescope were powerful enough to record the planet in Uber Ultra MEGA HD [version 99.0], like Google Satellite view as a playable video, and you wanted to know where someone was 4 hours ago, BINGO, you can now get that info. Now push that telescope a light year away from earth, or further, and you now have the ability of Time Viewing further in the past, though no further back than when the telescope was implemented. One rebuttal was "that light has already passed that telescope by", referring to being able to go/view even further back into the past, which is an excellent point. But... Scientists don't believe you can travel faster than light, this is what people think prevents us from being able to view further back into the past in this scenario, and I agree with that speed limit. However, Scientists do believe it may be possible to travel through wormholes or bend space somehow that instantly, more or less teleports you, to other areas in the universe. You're not traveling through space, you're bending space to find a shortcut, to get around the speed limit. With the technology of traveling through wormholes, and being able to precisely inspect light from hundreds, thousands, hopefully millions of light years away, we will one day be able to inspect the light that left Earth when the City of Atlantis may have existed (12,000 light years away), when Dinosaurs roamed (66 million ly away, finally answering the question of how they died; we're pretty confident it was an asteroid impact, but what a sight that would be), or possibly even when the earth was formed (4.5 billion ly away). Even without the precise view using our "UberScope", the instant we discover wormhole, or similar, travel, we've essentially also invented "Time Viewing" just looking out a porthole. The sun may only be a spec, but that speck of light you're seeing from X light years away is from X years ago. Keep this in mind when you're doing things visible from a birds eye view! Someday one of your descendants might see you. 🤣 But, who knows, maybe there'll be another gadget that somehow detects photons through objects (a sort of X-Ray vision), then there's no escape. Granted these would have to be EXTREMELY high tech gadgets, but what's the limit to our technology? Only TIME... will tell. I think Harry Potter's trip into the Pensive is the best representation of "Time Travel/Viewing". It's nothing more than just VR experience, really, but you can see how Harry manages to view the past without affecting anything in the past (the observer effect), but with the information of the past he has the ability to change the future. CHEERS to you and thanks to everyone that's contributed below.

[@JasonB808]

You watching read only time travel right now. KZbin is a time machine, especially when the recommended algorithm shows you a vid from 10 years ago.

[@1973vanguard]

@@JasonB808 dude, good observation 👍

[@pacmonkruz9846]

I wonder if this is just death

[@JasonWW2000]

@@pacmonkruz9846 No, death is lights out.

[@JasonWW2000]

The invisible viewer theory is my idea as well. If you were to travel backwards in time it would be like your in another dimension. You can see and hear everything, but your slightly out of phase and can not interact. Of course that has its limitations like how are you breathing, hearing sound waves, etc... if your not able to interact? Still, that's the way I prefer to see it.

[@galactic-gumbo9911]

I love that Chuck watched the “What If ?” Series also 😂🔥

[@Moraenil]

I know this video's 2 years old, but I just had to mention that when I saw the title for this, it brought to mind a song called "I'm My Own Grandpa" that actually relates in a way to this video by more than just the title. It's also amazing how much stuff in this video is represented in Marvel stuff. There's a whole story about time travel and tachyon fields and particles in Marvel's Avengers video game. In the MCU, they address how those changes in the past (changing how someone died for example) spawn new timelines as a branch off the original. It's just amazing how much science is in Marvel comics/shows/movies/games.

[@forthenight3265]

Working on a story featuring time travel. So glad one of the greatest minds of our time can break it down this simply

[@dal3767]

I'm just watching this before I go to work. I've never laughed so much and learned so much at the same time🤣 You guys rock. You have made my day 😊

[@StarTalk]

This comment made ours!

[@bakkila99]

I like the idea that every time something changes in the timeline, it doesn’t change the future of the original timeline, it just creates a parallel branching timeline

[@Andres-cd6lr]

Did you watch Loki?

[@xombi213]

I agree. This is also a long standing theory. Multi dimensional aspects of the 4th dimension. How could you possibly change the past in the same timeline, it does not make sense as it already happened.

[@hmmmmm6056]

Ok avengers

[@tylerdurden5359]

Neil debunked his own debunking of Terminator. He said, "all the machines have to do is disrupt any part of Sarah's genetic line." But the actions of the machines is the catalyst that creates the revolutionary leader. So could the machines use time travel to prevent themselves from inventing time travel, thereby creating a divergent timeline where Kyle Reese was never sent back. Despite the advantages of the machines they failed because they focused on changing external variables when they could have looked inward and realized they had the technological lynchpin that facilitated the very premise. Or......would this divergent timeline spawn 'John Connor' machine counterpart to prevent the machine saboteur from preventing the invention of time travel so the machine race can defeat the human rebellion?

[@ossiedunstan4419]

really its a movie, script writers are not constrained bye reality or the scientific method, the hubrus on science fiction is a waste of time.

[@yt.personal.identification]

He also mentioned the plot of Terminator 2 - where they thought they stopped the creation of the Sky-Net but it continued anyway without the original primary creator - and didn't realise it.

[@FloydleeAtkins]

Hello!

[@StarTalk]

You’ve thought about this one!

[@BushidoBrownSama]

I'm thinking Sarah Connor would have a son named John Connor anyway except he'd have a different father & he wouldn't have been raised to be a revolutionary leader he'd merely come in to that naturally

[@SKITT7ES]

I love how they can make the most serious and complicated things so simple and funny.

[@WilliamBrownMBA]

Okay, so you and Kyle Hill have talked about World Cones, and the explanation seems to suggest that all past and future events conspire to bring you to the present moment. So, if we go back in time and change things, would the concept of world cones be a self correcting mechanism for such an event?

[@johnduffy62164]

Would to see Kyle do a show with Neil !

[@PWNHUB]

This is a great paradox except you've already defeated the paradox by going back in time. The fact you exist prior to your birth literally means you would still exist if you killed your grandfather before you would've been born. There is only really 2 options here, one being simply you exist in a different timeline that was created by your actions, or two being reality itself would come undone before peoples very eyes. There is no way you suddenly just fade out of existence like Back To The Future. The truth is once you time travel you've stepped out of time so there for the interactions within time would not apply to you anymore. This is also saying our understanding of time is correct and not completely wrong. We take time as passage of moments or chain of events, where as it's really a measurement of distance time as it's explained began with the big bang expansion etc. The only real time is how far particles have traveled since the initial expansion. So it might actually be theoretically possible to warp time and space but it may never be possible to go back to specific moments because that isn't what time even is.

[@jimrello7878]

you come back an have no parents

[@bencarey243]

@@jimrello7878 lol

[@pkkilla2]

TLDR

[@StarTalk]

Woooaaaah

[@michaelmadaio4128]

I do not think so because you are born and you are not reversing anything so you should still exist

[@toastedbread8774]

Love you Neil! Keep up the amazing work!

[@fiusionmaster3241]

Yes

[@MD-nt9nv]

In the movie Final Destination, I think there is the idea that even if you do somehow prevent certain events that were supposed to happen from happening, fate will eventually find you and have its way.

[@shauntempley9757]

Doctor Who said that to. It also said that if a time traveller sees his or her own grave, then either he or she will get one free trip before the events that make the grave, or a trip straight in to those events. 11's last three stories at the end of his era where all this played out.

[@mRendyIrawan]

I wish they would do an episode diving more into Marvel's multiverse theory which states that if you travel back in time, you're not traveling back in time, you're just creating an alternate timeline. I wonder what Neil's take would be on this theory, and how close it would be to the real thing if we ever created a way to time travel.

[@justgoodies]

I would like Neil to watch and comment on the movie Frequency (2000), where a radio would be the Tachyon the main character uses to literally talk with his late father 30 years in the past. It's a very good movie.

[@lordnul1708]

8:10 sometimes referred to as a "stable time loop" or "a break in rule #0 of time travel" depending on whether or not you intended to become the origin point (another example is the Song of Storms from Legend of Zelda Ocarina of Time, in which the time travel was more "sending your consciousness into the past/future" than physically traveling... And another would be the Goron Vase from Legend of Zelda Oracle of Ages, which despite being more physical here, is just as impossible as the aforementioned song).

[@lydiafaye494]

Would love to hear your take on time travel creating alternate time loops, kinda like in the TV show 'Dark'. I thought that was a refreshing take on it. Or in 'Travellers' where they send consciousness back in time into the bodies of people moments before they were meant to die. Or even something like 'Interstellar' where we essentially can only be an observer and not interact/ghostly like interactions. Would love to hear these thoughts 😊

[@XScorpio123X]

I've watched both the series you mentioned and it would indeed be very interesting to hear Neil's breakdowns of those alternate forms of time travel or unraveling.

[@realbadger]

I loved a moment in one of Isaac Asimov's novels where time agents would prevent negative events, at one point preventing a massive interplanetary war simply by _moving a bottle_ from one storage room shelf to another, causing a momentary delay. My favourite time travel novel is _The Man Who Folded Himself_ by David Gerrold, in which the first person narrator is given a Time-Belt. He learns not only how to observe history, but due to infinite timelines, he literally can "edit" events to such an extent he can forget the original. He even finds he can strangle _himself as an infant,_ and yet not vanish from existence... he'd just created a new timeline in which he'd not existed. Even your referencing Ray Bradbury's _A Sound of Thunder,_ from which we get the Butterfly Effect, the guy's mistake of falling from the designated path causing the dead butterfly demonstrates an alternate timeline.

[@1973vanguard]

Nice! Which Asimov novel is it?

[@realbadger]

@@1973vanguard _The End of Eternity_

[@1973vanguard]

@@realbadger awesome. Many thanks!

[@ossiedunstan4419]

Yes and their is a very large partition to reality from science fiction. Especially Isaac, yes i have read his books, entertaining but nothing of the scientific method , just one man's imagination, John of arc had imagination, look where it got her. Thought experiment's do not require imagination. It is constrained bye the condition of reality, Imagination is not.

[@MorliHolect]

Read the short story "All You Zombies" by Robert A. Heinlein (or watch the movie Predestination based on it). It's the ultimate time travel paradox story.

[@IRONHEAD12701]

Chuck Nice makes this video so much better. Great comic ❤️🤙🏻

[@alistairgrey5089]

I've always heard the inevitability if time described as a stream or river. The river (representing time) flows along like it's supposed to. You can interact with it in limited ways. For example, you can throw a stone into the river. This will cause ripples and a splash but the river itself will still continue on mostly unchanged. I'm not sure I agree with it but it's an interesting analogy.

[@skullfracture3870]

There is a small degree of truth to this, the change you make to the river or the pond may not be immediately apparent, but there is something called the Butterfly Effect, a butterfly can flap its wings in San Francisco, and in Central Park you get rain instead of sunshine, thank you Jurassic Park. The idea is that you may not see the change that pebble makes to the river, but over hundred’s, thousands, or even millions of years that river changed its course, but we will never know if it was or was not because of that pebble you threw. Any change you make to the past can have drastic repercussions in the present. A good example of that is Back to the Future II.

[@alistairgrey5089]

@@skullfracture3870 oh yeah. I agree completely. I think the idea that we can change the time we are in or the time we came from is false. I believe that if time travel is possible the moment you go back, regardless of what you do, you've already changed that timeline to one that no longer matches yours. Unless there is some way to time travel without effecting a single molecule in the past just the presence of someone will change things. The changes may be very small and have no real effect or they could be small changes that become massive changes. Am example of this actually came for a TTRPG that I once played. There was a magic that could predict probabilities to the point where a character with this ability could toss a penny out of the window and over the course of a couple days caused a nuclear war. It's an interesting concept and if someone had enough knowledge it could theoretically be done.

[@SolarisBali]

If we go back in time, we assume the earth is in a different position in the universe, so the most likely scenario is that we just materialize in space somewhere and suffocate immediately. Or rematerialize in the center of the earth? Or at 30,000 feet in the air? Time is one thing, but space (location) is another confounder...

[@pzych0p4th]

This is the exact thing I am always thinking about talking time travel, whether you travel back or forth, you would not be able to navigate to the exact same spot/space in the universe, because earth at any given time moves through space and is never in the exact same location and will never be until the end of the universe- To calculate where the travel from-to point on Earth would be in the dimensions of the entire universe would also be completely impossible, Earth moves through the solar system, the solar system moves through the Milky Way and the Milky Way moves through the universe, what does the universe move through? Space? 🤔😅

[@SpongeWorthy76]

I think people mean travel back in spacetime (world line) when they say travel back in time.

[@lisear2926]

And that's why we need a TARDIS

[@dashiefiles]

yeah you'd have to do a calculation of the earths position and materialize in space in the right place

[@RakeshMalikWhiteCrane]

There's another even more obvious paradox in both the Time Machine and in The Terminator, though Wells got it right -- if the protagonist travelled back in time because his wife died, so to save his wife would be to rewrite the history in which his reason to travel back in time ceases to exist. So in any timeline where he travels back in time, his wife is already dead. The Terminator has the same problem. If the terminator succeeds in killing its reason for being sent back in time, it won't be sent back. And T2 repeated that -- Sarah Connor could not stop Judgement Day, because it's now her past... Her son would no exist of judgement day didn't happen, and if judgement day doesn't happen, she doesn't get warned about it, so she wouldn't stop it, therefore allowing it to happen. It seems like they figured that out for T3 though 😁

[@Riftsrunner]

The whole problem with Terminator is it starts out a Grandfather Parodox, but eventually becomes a Bootstrap Paradox. The whole reason for SkyNet to send a Terminator into the past was to prevent John Connor's birth. However, by sending the Terminator actually led to its creation. If Sarah hadn't have killed the Terminator like she did, she would not have left the arm that was used in T2 to reverse engineer the technology that lead to SkyNet. At this point, it becomes counter productive to prevent John Connor's survival as its own creation is now irrevocably attached to his existence. And that is besides the fact that in the first movie, sending the Terminator was a last ditch effort on SkyNet's part. The John Connor led humans were on SkyNet's door step and were about to defeat the machines. Now the question becomes why send the T-800 to stop Sarah Connor, but not either of the other two Terminators in T2 and T3? This is because SkyNet has a limited window to send Terminators back in time before the humans gain control and send their own timetravelers. So why not send a T-X or even a T-1000 to do all your John Connor assassinations? Those options had to be available because it doesn't get a second chance to send more Terminators later once the human shut it down and gain control of the time travel machine.

[@ClarkKent2011]

Small correction: The "trying to save his fiancée Emma" happens only in the 2002 movie. Not in the original H.G.Wells book, nor the 1960 movie.

[@iamlordapollo]

im going to blow your mind with the solution for the hg wells dead wife paradox. all he has to do is trick his past self into believing shes dead while preventing her from actually dying. by ensuring his motivation as the time traveler (and therefore the quantum mechanical "observer" *see schrodinger) he is free to save his wifes life and return to the present he initially left where he will find her alive and well. anything that contradicts his own initial experience is what fuels the paradox, so he has to maintain the initial experience where he finds her and assumes her dead. therefore he will time travel, and once he leaves the timeline he wakes up his wife and actually doesnt even have to travel a couple minutes into the future because there is only 1 verson of him again since his past self left already.

[@ShawnRavenfire]

What if every moment in time, the universe is splitting into an infinite number of alternate timelines? That would mean that any person travelling back in time would have to arrive at a point before a divergence, which would mean that from his own point of view, all the random variables are reset. So I might flip a coin, see it come up heads, then go back in time and watch myself flip the same coin, but have it come up tails the second time around.

[@DimitriMoreira]

There's already a hypothesis for this. I'm just not remembering the name of the study.

[@1973vanguard]

It's the Hugh Everett many worlds hypothesis. He posited that new timelines are created with each and every single interaction of all the particles, something like nanosecond to nanosecond.

[@erick_falker]

@@1973vanguard I even think this hypothesis is pretty 'cause time fission wouldn't be an extraordinary event, but a natural one, like everyday stuff.

[@MiddleAgedBob]

Yeah, I have heard this hypothesis before. But while that would feel like time travel, wouldn't it actually "just" be traveling between parallel/alternative universes?

[@louistrinnaman7344]

Pretty sure in H.G Wells book the answer to why he couldn't save her was that his grief from her death is what motivated him to build the time machine so if he saved her he would not had made the machine hence he couldn't go back in time to save her. Meaning he created his own paradox in that moment that it forces the timeline to always flow in that direction in order for him to build his time machine. I find time travel to be a fascinating concept but to ensure you can't mess with the timeliness I would love to build a Tachyon Telescope and Binoculars giving us a window to look into the past and observe our history unfold. That would be amazing.

[@ClarkKent2011]

Small correction: The "trying to save his fiancée Emma" happens only in the 2002 movie. Not in the original book, nor the 1960 movie. With everything else, I think, yopu are completely right.

[@55555konman55555]

Man I wish this dude was my science teacher. Something about having this knowledge come from a black man hits different. Being mixed myself it’s joyful to see this level of knowledge. Praise to you bro.

[@scottmilosch4]

#StarTalk So Neil, as I’m listening I came across a question. In a previous show you talked about the universe expanding at a faster and faster rate, faster than light. In this episode you stated that traveling faster than light you can go back in time. Does this mean as our universe and all galaxies are expanding then we are seeing the formation of everything in reverse?

[@driftwood9705]

Actually in “ The time machine” The head of the Morlocks, which is the old wise being Explains to the professor the reason his fiancé kept dying is because he would’ve never spent the rest of his time and drive building the time machine had she not died so the fact that he has the time machine and keeps trying to save her he cannot.

[@Philzney]

The tachyon enhanced smartphone and banana peel message alert that Neil talked about perfectly describes the plot of Stein's Gate, a very popular sci-fi anime series. The plot is about changing word lines and also employs the idea of minor changes and their effects on inevitable events in the timeline that Neil also mentioned

[@draroking]

EL PSY CONGROO

[@arsal.07]

EL PSY CONGROO

[@alessandromangiapia7082]

Hey! Loved this one! I wish you could do an episode on the many-worlds interpretation of quantum physics 🥰🥰🥰

[@kiddprofit2500]

It was this one movie on netflix where the guy went back in time so much he became his Husband,Wife, and Son all while being protagonist & villain at same time

[@scottdebruyn7038]

2013 movie 'About Time' with Domhnall Gleeson, Rachel McAdams and Bill Nighy is a movie that very much touches on the 'what if you change anything prior to your child being born' aspect Neil talks about. Do catch this movie as it is very much a time travel movie with humor and touching romance. One of the best I've seen of the time travel genre... And I love this genre! :) Great video guys!

[@JimNicholls]

Another time travel paradox: All the atoms in your body were somewhere else before they were in you. Tomorrow there will be some new ones, and some of the old ones will be gone, there is constant change. Travel far enough back in time, to before you were conceived, and every one of those atoms will be somewhere else. Since atoms cannot be in two places at once, even travelling back a week or a month will mean some parts of your body fading away, and the further you go the less of you will remain, until you're completely gone. Exactly the same applies to the machine you travel in - just a short time earlier, all of its atoms would be still be in minerals in the ground or whatever. I'm not buying a ticket for that!

[@erick_falker]

That's why whenever I open I time travel portal, I send a drone with a camera first. LOL

[@TheCosmicGuy0111]

String theory

[@brianstrutter1501]

That makes no sense

[@MrDDiRusso]

What determines what is a major or minor historical event in the context of time travel?

[@fiusionmaster3241]

Good question. I have a better one. How says we are important enought to the universe, that it splits itself into peaces (diferent universes), because of out minimal action in the bigger picture (AKA decisions)?

[@thehermitman822]

@@fiusionmaster3241 why is Gamora?

[@spellbinder3113]

Legends of Tomorrow dealt with the fact that you could change little details in history, but larger points in history were frozen and unavoidable.

[@RPIdemon]

Aside from forgetting the name Back To The Future, Chuck was on point with the jokes and the pop culture references. I thought of the What If? episode with Doctor Strange too

[@jcIIXVIIIVII]

Since no one has actually invented time travel, as we've seen depicted in film and shows, we really DON'T know exactly how it would work...BUT I've always been intrigued by the, what you now termed, Ancestral Paradox lol But my REAL question is about branched timeline time travel, like the one discussed in Avengers: Endgame, and the show Loki, where you go back in time, but instead of affecting the past of the future you came from, you, instead, create an alternative timeline that deviates from the one you came from, however, the events that happened in your original timeline still happen the same way. Do you think that THAT type of time travel is possible? Where going back in time doesn't change anything in your timeline, but creates an alternative one instead. That could technically and effectively get around the whole Ancestral Paradox

[@royalecrafts6252]

Since we dont know for sure, we cannot even know if such paradoxes will unfold in the case of time travel, maybe no paradox at all happens

[@maraudershields283]

You should look up Minute Physics and their time travel video. They explore all the different ‘rules’ presented in different movies, and the logics behind them. Interesting stuff.

[@ФилипВасилевски]

@@royalecrafts6252 no paradox at all? U think this is possible?

[@royalecrafts6252]

@@ФилипВасилевски yes, we cannot really assume anything since we barely know anything about time, so yeah I think is possible for the universe to not have time paradoxes

[@ФилипВасилевски]

@@royalecrafts6252 giving me hope thank u

[@bernieburton6520]

Unless multiple worlds is correct. In which case, you couldn't change the past of your universe, but you could go back and create a separate universe that leads to a different future.

[@RLomoterenge]

I would love to see a serious Terminator movie where they try to scientifically try to foil the future from happening using crazy antics like introducing Sara Conner to Chuck or having the terminator learn some exceptional coffee making skills and get a job at a coffee shop where Sara and Kyle are gonna be right before they conceive just so they can order a second cup. That’d be hilarious!

[@ronkempke6673]

If I'm not mistaken, Star Trek's, "The Guardian of Forever" episode addresses this.

[@PaulShadwell]

The movie you're referring to regarding the different baby being born was called "It's about time". One of my favourite time travel series was in "The Flip Side of Dominic Hide" released in 1980.

[@incognito3620]

I have never had so much fun watching a science video. You guys make science fun.GREAT!

[@wissamhouchaime4984]

Great episode as always. You guys should really consider adding movie spoiler alerts though!

[@kn1ghtRipper7]

Chuck mentioning "What If?" Super! 😊

[@ArmughanJalil]

What about Futurama where Fry travels back in time and mates with his grandmother thus becoming his own grandfather? Which paradox is that?

[@makinawake9178]

Wow I never felt like I know Tyson really appreciated this video 👍

[@suonoblu6650]

If we consider travel back in time as possible, then Novikov's principle of self-consistency would be the only solution to the grandfather paradox to have a logical coherence, as the multiverse-based solution generates grandfather paradoxes in turn.

[@noneYAbidnusORIGINAL]

"Predestination" is a sleeper time travel movie 10/10

[@ManDinqa]

Chuck Nice always cracks Neal up.

[@csabafacsar5562]

I love these two!!! They are so goooood together !!! :)

[@theicephoenix]

You incredibly described how premonitions work with the taquion device LOL

[@michaelccopelandsr7120]

Neil and Chuck for 2024

[@isatousarr7044]

The time travel paradox, particularly the grandfather paradox, raises intriguing questions about causality and the nature of time. If a time traveler were to go back and prevent their grandfather from meeting their grandmother, would they still exist to make that journey? This paradox challenges our understanding of time and the interconnectedness of events. Could it be possible that altering the past creates alternate timelines instead of erasing the original one?

[@DrMario-su6xj]

Nearly everyone knows this paradox but if it's Neil and Chuck it's worth having a revision.

[@rizo1176]

The smartphone “time machine” (sending messages in the past) example, is amazing to hear from Neil say it’s possible after watching steins gate. 🤯🤯🤯

[@jacobwhite9551]

I’m glad he brought up the what if series cause that’s exactly what I was thinking about when they were talking about the Time Machine

[@sherievangelene9045]

Great conversation! Loved this one

[@Thumbs1101]

I’d love to hear him discuss the Hyperion series

[@Dizma_Music]

05:30 - Tyson mentions that it would be cool for there to be a fiction regarding time travel where big events can't be changed. There's a Twilight Zone audio drama episode where someone tries to go back to stop the assassination of Lincoln and the major event cannot be changed, just the small details.

[@SoupedUpCustoms]

I love Neil's example of banana and cellphone with texting from the past. Really reminds me of a great time-travelin' theme anime called Steins;Gate. Hope you guys Neil and Chuck check it out I wanna hear your thoughts on it and maybe it's time to revisit again this time travel episodes....

[@scotthodgins7975]

Just a quick note about "forces of time stopping specific things from happening" ... Stephen King wrote a really cool book about that idea called '11/22/63', in which a man tries to go back and prevent JFK from being assassinated and all the problems that this man encounters. Another interesting series of books dealing with time travel and its inherent problems is Simon Hawke's "Time Wars" series. In which he takes actual events from history and introduces future soldiers. It is a very difficult storyline to explain, but I will try to be very brief: Basically in the far future, if any country/company/opposing ideologies have a dispute, rather than fighting with each other, you hire "time soldiers" to go back in time to any battle and whoever has the most people come back to the current time is the winner. Those 'time soldiers' don't necessarily have to fight each other, they could be on the same side, or in two completely different battles. Very interesting read.

[@gloriousexceptionalism2346]

Really REALLY enjoy these chats 🥰🤣😂

[@DieCastoms]

And then there's this paradox: People -believe- that if they go back in time -any- distance, and step on a single butterfly/moth/ant/mosquito/etc., if they change a single fiber of the universe, it will irreparably change the future, and yet they do not believe that they can do anything NOW, here, in the present, to change the future!

[@karensmith1832]

Thank you both! Always learn and laugh 😆

[@hariboddeeti]

Science is fun to learn with Neil DeGrasse Tyson

[@SamuelTheCoello]

We need to understand the deeper underlyings of this paradox. The two begin to discuss it towards the end of their discussion, my favorite example being the one when the text message. The anime Steins;Gate has journeyed into this aspect of time travel. And also, the inevitability of constantly causing the outcome in which you are trying to prevent. So bravo to you two for talking about time travel in this sense, I really enjoy the idea of it. I imagine at times my thoughts today are able to be pulled from the future up to the boundary of infinity, sometimes I wonder if it can go beyond the boundary. Anyway, if that’s the case, it does feel like there’s some time confederation suppressing these ideas. My favorite easily testable example is. Learning about Physics to try to counteract nuclear warfare. The learning of Physics LEADING to nuclear warfare. You two should do a review on SpinLaunch by the way I’m not sure that you have. It’s an interesting concept.

[@slowpoke101_]

I wish they knew of that anime...

[@SamuelTheCoello]

@@slowpoke101_ They need to watch it!!!

[@slowpoke101_]

@@SamuelTheCoello I don't know man they don't strike me as the anime type

[@thapureheart]

" Make the train come a little later " is just perfect in that context 😂😂

[@tyrellchibvongodze3566]

Chuck is hilarious! In the series Fringe there are multiple time travel references. One equivalent to the butterfly effect is about a boy who caught a firefly, therefore a little girl got lost looking for fireflies ... and another son got into a car accident and died! The Observers future were not supposed to interfere in events and just Observe!. I think I am going to watch Fringe again LOL!

[@thetotalwarrior]

At about 5:01 Neil talks about the idea that maybe the forces of nature care about major events in spite of you changing minor events and says it would make a cool Sci-fi movie. This was done in the T.V show Lost. In that show at least one person goes back in time and tries to change the course of events leading to a life changing incident and no matter what he does "time has a way of correcting the course"

[@MrEmotional33]

Those guys are so funny and entertaining. That's by far the best way to understand science ;-)

[@shaneriley4411]

Now I get it my friend!!! For the most part. Got me thinking 🤔 alwayz

[@darkpilsen]

I think Dr. Tyson may have been talking about the movie "About time" which is amazing.

[@flurng]

Going back to the banana peel scenario, we can't ignore the "oscillation effect" - this is where you successfully prevent your friend from slipping, but since he never slips, you don't bother sending the text, therefore he gets no warning and he DOES slip, so you DO send the text, and on & on & on.....

[@eternalfizzer]

Great hook "It's seems like we've done this before ..."

[@skullfracture3870]

Sometimes, I think of the C&E Paradox (cause and effect), where the Effect actually happens before the Cause. The age old question: what came first, the chicken or the egg? A perfect example is The Terminator. In the movie John Conner, Skynet, and the Terminators already exist in Kyle Reese’s reality, but essentially they are the effect and the cause at the same time. Skynet sends a Terminator to 1984 to prevent the birth of John Conner, who in the future miraculously knows how to fight the machines. In the process of sending the Terminator back in time Skynet actually set that future in motion, ensuring both the birth of John Conner and it’s own creation.

[@MondoLeStraka]

Great as usual. As mentioned in another thread, could you please do a video on pseudoparticles? TIA.