Can We Break the Universe?

[@AD-ok8ee]

“Safe from colliding with their own arses”, did not expect that, but perfectly delivered.

[@dorquemadagaming3938]

ASSSETS, damn it! ass-sets! Due to uncertainty principle and many-worlds there will be multiple of them to collide with!

[@PandemoniumMeltDown]

Gay boi left the chat, disappointed.

[@PandemoniumMeltDown]

@@karlwest437 I wonder if, when one smells one's own farts... naaaa

[@charlesblanton1008]

I've had days at work when I felt like I could, in fact, collide with my own arse. 😂

[@PandemoniumMeltDown]

@full stop What... what a swell idea!

[@NatePrawdzik]

Man: "Hey, I ordered a sandwich for everyone but we didn't get everything. How are we going to divide this up?" PBS: "Again, this is best determined using a space-time diagram."

[@astrophysicslair1445]

Honestly minkowski diagram for the win. In my SR class we used it to solve problems by verifying the answer given by the math with the diagram (provided you could make straight lines lol)

[@sadrevolution]

Ha! I almost spit out my tea!

[@sasshole8121]

If you don't have a space-time diagram, a Penrose diagram will do.

[@thadaungst8627]

@R F ??? Please explain ???

[@oberstmerkel7919]

As a friend of mine once put it: I couldn't divide those five sandwiches between us three so I ate them all by myself.

[@AZZKlKR]

7:38 Literally every episode: "Doesn't this violate (some fundamental part of physics)?" "No."

[@drx1xym154]

Could depend on the attorneys - or The Judge!

[@NoActuallyGo-KCUF-Yourself]

Physics is so big at this point that it is almost impossible to break: it just gets little dents or cracks from spacetime to spacetime.

[@thomasreedy4751]

Physics can’t be broken, it just is. Our theories and understanding on how the universe works could be.

[@zeroneutral]

@@luddite31 no.

[@sharkinahat]

Pls don't break the universe, that's where I keep all my things.

[@BattleBunny1979]

save often and in different savegame slots

[@MCsCreations]

"Because I am one of the stupids that live in it."

[@tpog1]

You really should get yourself an ender chest in the Nether.

[@alansmithee419]

Can I just break a lil' bit of it?

[@-cookiezila-461]

I stuff my grandma in there! Don't you dare break the universe

[@kevinmathewson4272]

I want one of the episodes to end with an extremely long sentence that keeps sounding like he's about to say "space time" but then he adds another phrase and another phrase, and it goes on for like a solid minute, and he never acknowledges that he's doing anything weird

[@drx1xym154]

That could break the universe!

[@new-knowledge8040]

Yes and space does not contract. If you have 60 spaceships going 60 different speeds, you don't end up with space being of 60 different sizes simultaneously.

[@new-knowledge8040]

By the way, It is an easy breezy task to just discover special relativity all by yourself.

[@kevinmathewson4272]

@@new-knowledge8040 space doesn't need to "contract" or be 60 different sizes, dude. Think about it this way: are the passengers on a train simultaneously moving and not moving? The passengers look stationary to someone _on_ the train, but someone on the platform would say the passengers are moving. The passengers aren't simultaneously moving and not moving, because the question of their movement is _relative._ Space and time are relative in the same sense.

[@new-knowledge8040]

@@kevinmathewson4272 Okay, so George says, "Hey, its not my spaceship that moving, it's your spaceship that's moving.". And then Fred says, "No, it's not my spaceship that's moving, it's your spaceship that's moving.". The George says, " Hey, its not my clock that's ticking, it's your clock that is ticking.". And then Fred says, "No, it's not my clock that's ticking, its your clock that's ticking.".

[@joegocal]

This guy is like the most engaging science presenter I’ve ever encountered. He really makes this stuff clear for someone like me who still enjoys physics but hasn’t taken any physics courses in over a decade.

[@andrewbeil1799]

Then.... you really gotta look into Neil Degrasse Tyson

[@boyang3179]

Yeah, I have a bachelor's degree in physics. I would still argue, that a lot of his explanations makes more sense if you have taken at least a undergrad level class in special relativity.

[@mystomachhurt9312]

@@andrewbeil1799 nah neil sucks

[@WardenOfTerra]

@@andrewbeil1799 - Neil is shite. He's not engaging one bit.

[@Chance57]

@@WardenOfTerra comes off as too self possessed to be an effective communicator.

[@sebastianelytron8450]

So apparently Einstein was a real person? I always thought he was a theoretical physicist.

[@DHGameStudios]

"they asked me how well I understood theoretical physics. I said I had a theoretical degree in physics. They said welcome aboard." -Fantastic

[@MaxArceus]

okay, you win

[@riverground]

It depends on your frame of reference.

[@plexiglasscorn]

@@riverground it is lorentz invariant

[@maxmusterman3371]

no, he is a stone. literally

[@1024det]

I have to emphasize the good communication between Matt and the 3D artist. I have no idea how they get this stuff done.

[@ItsCoderDan]

Another episode of me pretending to know what’s going on :D

[@sanketjadhavar]

He is saying if we would really want to f**k ourselves then we have to run around a tree without pants with speeds close to a significant fraction of lights velocity! Or am I missing something?

[@ChaineYTXF]

You don't need much math to understand this. It's actually oddly accessible. But you have to think long until you figure it out😁 If you ever wanted a difference between Math and Physics, well this this it..

[@glypheye]

@@sanketjadhavar wouldn’t work because your forward facing prong would be partway up a growing tree from your backward facing bunghole 🤨😜

[@peterbanos703]

@@sanketjadhavar To the tree it will look like you are really f** king yourself, but to you it will look like the tree is needle thin and you are just turning around very quickly. **said I, pretending to know what's going on**

[@shilohauraable]

@@sanketjadhavar 😂😂😂

[@cadelaide]

To Matt and the team. Thank you for your uploads. My mum died a few days ago and your videos are the only thing that helped me sleep. Especially during the time she was on life support. What's strange is people find solace in religion but ive found solace in physics.. It helps hearing an aussie voice too, her ashes will be launched from the most eastern point at Byron Bay on Friday for entropy run its course across the Pacific Ocean and beyond.

[@atk05003]

I think people often find comfort in knowing the universe is orderly. Both physics and religion can provide more or less orderly explanations of the structure of the universe.

[@Jeffros]

Im sorry for your loss, my condoleances. Can’t imagine what you are going through.

[@Only1Shadow]

Sorry about your mum... but to give you a different perspective to contemplate I'll tell you as a Christian I find science to be the study of how God made the universe... so your example is two observations of the same thing.

[@joemarz2264]

May God (Christ, the universe, or whatever concept you favor) bless you and your mom.

[@megamanx466]

@@joemarz2264 Thanks for being open-minded and considerate of other's views. 😄

[@indylockheart3082]

"The size of the ladder in a Pac-Man barn", this is exactly the high level physics i show up for

[@annepearn4545]

Why is it a Pac Man Barn? I dont understand.

[@YtseFrobozz]

@@annepearn4545 In Pac-Man, when you exit the passage on the right side of the screen, you "wrap around" to the passage on the left side of the screen (and vice-versa), making it analogous to the closed universe. Sort of.

[@horsetuna]

@@YtseFrobozz ohhh. Wish I discovered that when I last played.

[@TrainsandRockets]

@@YtseFrobozz I would like to thank you...I understand the reference now.

[@souparmsbarraza7206]

I love how it makes perfect sense after four years of learning all this. These four year studying paid off big Time finally

[@leolana6729]

Dude ... I speak Portuguese and understand almost nothing that you say , but still is amazing to tried to understand. That's how good teacher you are. God Bless!

[@user-lb8qx8yl8k]

Tudo bem!

[@jonnnnniej]

What a cool way to reach yourself! 👌

[@sciencoking]

The space-time diagram of the ladder was really cool. I never thought about it that way

[@AsmodeusMictian]

I'd seen it explained before, but the way they lay it out in this video is fascinating :)

[@jamrep9633]

I like non Euclidean BAHNS too.

[@darthmase]

The ladder's axes in this case can be constructed with Lorentz transformations, right?

[@nielskorpel8860]

@@darthmase yup

[@sciencoking]

@@darthmase That's the idea :)

[@plus5gaming347]

My brain just wrapped around the inside of a closed skull and crashed into its own rear end.

[@bobinthewest8559]

My brain can't do that... Skull too thick.

[@erebology]

My brain is already there.

[@YathishShamaraj]

General theory of relativity says it can't happen 😁.. the front end of your brain will never get to meet the rear end for it will be in the past 😉👍

[@erebology]

@@YathishShamaraj Ted Cruz did it.

[@nobodie9996]

@@erebology because of course everyone comes to PBS Spacetime for political humor

[@fizzy4149]

I'm gonna go out on a limb and claim that Matt's resolution of the twin paradox in a closed universe is incorrect. Let me preface my explanation by stating that I love this show and I have a huge amount of respect for Matt. Moreover, I'm no flat Earther, creationist, nor am I a devotee of the electric universe. I'm a mathematician by trade who spent much time studying general and special rellativity. *Why is Matt's solution wrong?* First let me review the standard scenario. Suppose that Alice and Bob are both in inertial reference frames where, in particular, Bob's frame is moving at a constant velocity in the direction of Alice's positive x-axis. Because there is no preferred reference frame we can consider either twin to be the "at rest" twin. We can draw a spacetime diagram with Alice at rest. In that case two events on a horizontal line are simultaneous for Alice. For Bob simultaneous events lie on a slanted line. We can draw another equally valid spacetime diagram where Bob's considered to be the twin at rest. On that diagram events on a horizontal line are simultaneous according to Bob and Alice's line of simultaneous events is slanted. At this point it's worth noting that the common means of verifying that there is no preferred reference frame is to say that there is no experiment that can be performed by either Bob or Alice at any moment in time to distinguish one reference frame from another. That said, in a closed universe, once again, either twin can be considered as the "stay at home" twin. After all, what experiment could either Bob and or Alice perform to conclude that one of the two is truly at rest? Unlike the standard twin paradox, at no time during the journey does either twin require a booster rocket to make a course correction. This is where I can be wrong, but I don't believe that such an experiment can be performed at any moment in time during the journey to distinguish between the twins. This is the means that Einstein used to conclude and verify that there is no preferred reference frame. Moreover, we can draw a diagram where Alice is considered to be the twin at rest. On that diagram events on a circle are simultaneous for Alice and events on a helix are simultaneous for Bob. We can draw a spacetime diagram which is equally valid in my opinion, where a circle is the set of simultaneous events for Bob and a helix is the set of simultaneous events for Alice. So if Matt's resolution is incorrect then *What is the resolution?* Here comes the anticlimactic part. My claim is simply there is no paradox to resolve. The thing to understand is that in special relativity, it is assumed that spacetime is flat and is therefore described by the Minkowski metric. But the spacetime of a closed universe is not flat. The Minkowski metric doesn't apply. Consequently, the notions of time dilation and length contraction as they relate to the Minkowski metric do not apply either. Thus, if there is a paradox, it's not the one(s) that we are considering here. For a closed universe perhaps we should consider the so-called Robertson-Walker metric with positive curvature.

[@jacobm5167]

I just made the exact same point. Another point to make is that the Robertson-Walker metric describes a spacetime with intrinsic curvature. The cylindrical spacetime considered here only has extrinsic curvature. But even still, the Minkowski metric doesn't apply. I also saw somewhere online an article that addressed the same question (about the twin paradox in a closed universe) and produced the same answer seen here in this video!!

[@beachcomber2008]

Yes, as soon as a cylinder was proposed my brain red-flagged it (possibly ahead of my conscious state). Not that I'm a hero. No paradox.

[@stephenkalatucka6213]

The universe is flat. If you go too far, you fall off the edge. If someone ran through a barn at close to C, would an observer even see him, or just a blur accompanied by a sonic boom and alot of cow-doo flying about

[@fizzy4149]

@@stephenkalatucka6213 -- Can't argue with that!! Case closed.

[@nordogned7298]

A closed universe doesn't actually have to be curved. A Riemannian manifold can be both closed and flat. Since Matt is applying special relativity we can then safely assume that the universe in question is flat. The flaw in your counterexample is that, as Matt points out, special relativity only prohibits a preferred frame locally. A global preferred frame is perfectly fine. There is indeed no way for Alice and Bob to distinguish the frames _at a given moment_. To figure out what the preferred global frame is, they have to do what they just did: Send one twin around the universe and then look at the age difference.

[@why_though]

I sped up the video and it didn't loop back on itself guys, so I think we can call this one verified.

[@gorgit]

Thanks mate! Was about to try that!

[@shoegum7362]

Yeah well autoplay must've been turned off

[@JeffQue]

But how much acceleration have you tried? Maybe if we add more throughput it's velocity exceeds the necessary for KZbin closed loop space

[@someguy3766]

@@JeffQue I tried firing my laptop out of a cannon at relativistic speeds to test this. Unfortunately I failed to collect any data as the laptop... did not survive the experiment...

[@why_though]

@@JeffQue press Ctrl+J type: "document.getElementsByTagName("video")[0].playbackRate = 16" press enter enjoy 16x speed (P.S. still doesn't loop back on itself)

[@delibirdite]

"Long story short" may not have been intentional but was funny regardless

[@Novastar.SaberCombat]

With Matt's level of communication... hmm... I would assume that little 'Easter Eggs' have been hidden in *many* of the videos over due Time. But, I can't be for certain, as... I'm not very intelligent (well, not on theoretical physics of ST/GR, etc.).

[@Natural_Science]

Looool xD

[@TheAnantaSesa]

yeah, if you play the video at 2x speed then LENGTH CONTRACTION is why the video finishes faster.

[@playdeebug4400]

New title: “Can we break your brain?” Answer: Yes

[@godfreypigott]

Einstein: Spends years trying to figure out how to fit his ladder in his barn. Engineer: Builds a bigger barn.

[@agimasoschandir]

Technician: Repairs barn doors

[@drx1xym154]

Build the barn for your cows or even your Mustangs. Build a tardis barn! ALL problems solved.

[@garrettmenteer2066]

Nice.

[@Cec9e13]

Technician asks that you stop flinging ladders through the barn, and suggests that the engineer simply make a folding one if it doesn't fit.

[@FoxtrotYouniform]

Second engineer: builds shorter ladder. religion is invented.

[@AinsleyHarriott1]

Excellent timing Matt I was just wide awake at 3am wondering this.

[@generalkenobi5048]

Boris’ Spacetime Hypothesis: The PBS Spacetime set is cursed. The longer you host for Spacetime, the faster you talk.

[@ACLNM]

Small mistake on 6:14 → "which twin is older?" → answers "the travelling twin", should say "the one on Earth, i.e., Luke". The image is right, though, with older Hamill.

[@gabor6259]

Guys, whenever you mention an earlier episode, you could put the link of that episode in the description.

[@TlalocTemporal]

They put those like in the info cards. It's the little "i" in a circle that pops up occasionally, called "from PBS Space Time".

[@TrixieWolf]

"Which twin is older when they reunite? Again, it's the traveling twin," is a mistake. You mean the traveling twin is once again the *younger* one.

[@garrettmenteer2066]

Correct. But yes and no 😂

[@jannegrey593]

That's why I love Special Theory of Relativity.

[@Joecool20147]

916SavageMoB was about to say the same thing, haha. I mean I completely don’t understand GR, but still.

[@bamb8s436]

@916SavageMoB Each is relatively better

[@goartist]

both aare kinda special

[@Joecool20147]

goartist wow you are so nice

[@bamb8s436]

@@goartist nah the one s kinda general

[@AV8R_Surge]

This is over my head, but I enjoy listening to people smarter than me.

[@jeroendijstelblom8614]

Yup

[@onbored9627]

Well, from your frame of reference he is dumber than you and his statements are incoherent and nonsensical. From his frame of reference you lack understanding. =P

[@thomashenderson3901]

Me three.

[@AV8R_Surge]

@@onbored9627 that's because his brain travels faster than light while mine struggles to race a sloth. The paradox is alive

[@onbored9627]

@@AV8R_Surge Yeah, but you can fly a plane and he probably can't. So maybe you can catch em easier than you think.

[@HazelNicolaQuantock]

This clicked for me half way through the barn explanation when I realised the horizontal axis of the picture is not just space it's space-time, so if observers travelling at different speeds took photos from the same point at the same moment, they'd capture a differently angled slice of space-time, so the right hand end of one observer's photo would be in future compared to the right hand end of the other observer's photo. It's like if you take a photo with a rolling shutter while you're moving (with your camera oriented so the shutter roll matches the direction of motion) - things get elongated or compressed because the columns of pixels are captured at slightly different times. So an image of a ladder moving through a barn could show a contracted ladder from a static camera (because the tip of the ladder is photographed earlier than the tail), but a camera moving with the ladder could show a contracted barn (albeit with the camera flipped so its shutter rolls in the opposite direction - this analogy is not perfect).

[@Jodabomb24]

It's funny; my boyfriend posed the closed universe twins paradox puzzle to me just a couple of months ago. I discussed it with my research group and we came up with the same answer: that, indeed, a single reference frame is singled out as special. Nice to know we weren't full of it!

[@Jqwert8375]

boyfriend ????

[@parkieshark]

@@Jqwert8375 whats wrong with that?

[@Jqwert8375]

@@parkieshark everything

[@parkieshark]

@@Jqwert8375 no

[@jacobm8242]

@@Jqwert8375 I think you’re on the wrong channel if that’s what where your priorities fall

[@nagualdesign]

Who knew that Alice and Bob were actually Leia and Luke! This is a bigger bombshell that Darth Vader being their father. 😮

[@victorbrueggemann8934]

Luke finally found his power converters, so his helix was elongated while he was hanging out with his friends. Sorry he was late, Leia.

[@djhakase]

Senator Palpatine has never been so elucidate: "Did you ever hear the Tragedy of Darth Mallory the Wise?"

[@jimbo9513]

Spoilerwarning

[@nagualdesign]

@@jimbo9513 Sorry about that, Jimmy. I just didn't think.

[@andersjjensen]

Alice and Bob are cryptographers. Leia and Luke are... kissing siblings...

[@Songfugel]

Ok, for some reason that helix just made things click for me, when I'd had some trouble wrapping my brain around this issue

[@ssssssssssss885]

The forever issue trying to cut the hair on the back of my neck in the mirror easily solved by employing a wormhole. Duh!

[@virtuerse]

TLDR; No because the nose is in the future and butt is in the past :^)

[@arindamdas2705]

says the fart

[@Alex-bw6yd]

Therefore they can exist in the same point in space without colliding, because they are in the same point in space at different points in time.

[@saumitrachakravarty]

How else would you enjoy the smell of your own fart?

[@mountainc1027]

@@arindamdas2705 relativistic farts would be quite terrifying

[@sdfkjgh]

@@mountainc1027: Relativistic Farts would be an excellent name for a Hardcore Punk Nerdcore band.

[@Zepha21]

So next time a cop halts you for having too much luggage in your car, just tell them you threw the luggage in at the speed of light, so they only perceive it to not fit, but it actually fits in nicely.

[@andersjjensen]

"I hoped this helped clarify matters a bit"... yup... clear as mud!

[@NickRoman]

well, this is one to watch at least 3 times. I'll admit that much of that was just a bunch of sounds. My brain just shut down its comprehension engine at some point.

[@SnowyMountainBlueSky]

I like to think of the twins paradox from a chemistry point of view as follows: - In order to age the twiin's bodies need to go through chemical processes - Chemical processes require masses to move around - Let's assume a maximum speed in the universe, say C - Say that on earth the chemical processes move the masses at a fraction αC, with α in (0,1) If the traveling twin moves at speed βC, with β in (0,1), then the chemistry in his body can only happen at a maximum speed (1 - β)C, which means that if α > (1 - β), then the chemistry in his body will have to slow down relative to its speed on earth and therefore he will age less from a chemistry point of view relative to the slower moving twin. The same is true for the needles of a clock as its particles also have mass. That mass will slow down to compensate for the movement of the entire clock. It all comes from the assumption of a maximum speed C.

[@bikerfirefarter7280]

A bit like the bernouli pressure drop with increasing speed in the tube. The particals average velocity remains relative to the constant temperature. Does that mean the temperature experienced at the surface of the tube alse lowers?

[@2MinuteHockey]

what happens if acceleration is 0 and velocity is constant C?

[@bikerfirefarter7280]

@@2MinuteHockey theoretically nothing, a photon experiences virtually no time from emission to absorption regardless of how far/long it appears to an outsider. It does my head in a bit.

[@darkwater234]

I feel like there was a pun somewhere around "Long story short...."

[@waltertanner7982]

That was when his speed (of talking) went too fast.

[@ladchap2794]

It's relative

[@theinconsistentpark9060]

"Yes and No" used properly for the first time.

[@Hamuelin]

....

[@chrisjager5370]

The spacetime diagram for the twin paradox was really useful, it shows what the accelerating twin misses without having to calculate mystery acceleration effects.

[@LeAdri1du40]

While I usually love his videos, this particular explanation is completely wrong and he messed up the effect of relativity No-one ever misses any time from any point of reference What he failed to understand and explain is that relativity effects depend on the perceived direction of the movement in your frame of reference, so the effect is different whether you are going apart or towards an entity but it is symmetric when checking in both frames of reference That means when you are going towards something, you see the clock speed up, and they see your clock speed up, when you are going appart, they see your clock slow, you see their clock slow The resolution is then in the time perceived of each observer Because for the earth the ship appears slowed down for more than 50% of the total duration of the trip because they are going appart And the rest which appears less than 50% as sped up For the ship the earth appears slowed down for exactly 50% of the trip and sped up for exactly 50% That is to say to earth it appears you start turning around much later than you actually are This is because time is indeed relative and perceived differently, but in any case there is never any time gap and saying otherwise is a slap in the face of Einstein

[@derschubsi]

I did my finals in physics on special relativity and got a 100%. I just love how it all seemingly makes sense and no sense at all at the same time.

[@chriskennedy2846]

It seemingly makes sense if you ignore the fine details and makes no sense once you dig deeper. Einstein didn't use a spacetime diagram (or simultaneity for that matter) to resolve the paradox. He required that the acceleration experienced during the ship turnaround contribute additional time dilation effects by way of the Principle of Equivalence. Einstein's resolution came in 1918 after he completed Special Relativity (1905) Principle of Equivalence (1911) and General Relativity (1915/1916). He was also aware and a fan of Minkowski's work by then but did not use it at all to solve the paradox. He explained that simulated gravity from the accelerating ship during turnaround was a necessary component to have the Earth clock speed up from the perspective of the ship clock so that they could agree at the end. Unfortunately this "Spacetime Diagram" nonsense became popular after Einstein passed away and has been the dogma ever since. Of course whether you subscribe to the Spacetime model or the original Einstein acceleration model - you will find the common flaw in both of them is the required reciprocal time dilation during the inertial part of the journey. That was proven incorrect by GPS technology years ago.

[@l1mbo69]

@@chriskennedy2846 wdym by the "reciprocal time dilation during the inertial part of the journey"

[@chriskennedy2846]

@@l1mbo69 Meaning that while the earth twin sees the traveling twin's clock running slower, the traveling twin sees the earth twin's clock running slower as well. They each see the other's clock running slower than their own at the same time. Crazy concept but that is what SR stipulates. When they reunite, they both can't be running behind each other - that's a logical impossibility. So Einstein considered the traveler to be in a simulated gravitational field during the turnaround (since he experienced acceleration) and since time elapses slower in a gravitational field, the traveler would see the earth clock running much faster during that portion of the journey. In fact so much faster that it would more than compensate for the slower observations during the inertial part of the journey and then they would both agree upon reunification that in total - the earth clock ticked off much more time than the traveler's clock. Unfortunately, even Einstein's version has two major flaws. I cover the reciprocal time dilation flaw in my 2014 twin paradox video. I discuss the simulated gravity flaw in parts 4 and 5 of my 2012 Relativity and Time videos. Note that in my videos I often refer to reciprocal dilation as symmetrical dilation but I mean the very same thing. To be clear - I don't dispute that time dilation occurs in a gravitational field or in a moving frame. I merely point out the misapplication of these concepts when others try to explain how all of these pieces "neatly" fit together.

[@mohamedAli-kj6fb]

@@hyperduality2838 Wrong. Duality creates destruction. singularity created reality.

[@mohamedAli-kj6fb]

@@hyperduality2838 That doesnt mean duality created reality. Duality IS our reality, reality is duality. But the creator of reality is not duality, it is one God that was never born and will never die, alpha omega, the encompasser of duality. Im lucky to be woke when i reached puberty! When my account was open. Good day sir.

[@GetterRay]

KZbin suddenly changed the speed to 1.25 halfway through the video without me knowing and it felt like I was watching a video hosted by Gabe again.

[@MrPuzzles]

Step 1: Discover the protomolecule. Step 2: Apply protomolecule to stuff. Step 3: Universe broken!

[@dhgodzilla1]

So only in Quantum Physics is it possible to literally find ones Head in ones own Arse

[@edmundbasham67]

But importantly, not from your own perspective. I think

[@Only1Shadow]

Or in Congress.

[@christopherbrent3759]

Dae the dangerous other??

[@tim40gabby25]

It's known as the 'Einsteinian Ostrich phenomenon', first named around about.. now. old uk duffer here, enjoying this moment in the light :)

[@realdarthplagueis]

This is the best explanation of the twin paradox I have ever seen! Why? It involves no arguments about acceleration (which often are used as an explanation of the paradox, but is not a necessary or accurate part of the explanation) and it explains so clearly why the travelling twin misses some time that is experienced on Earth. Thank you!

[@BitchIwasBorn]

Each episode of this series provides so much insight that it pretty much overwrites any understanding I had of the previous video My brain is like an old hard drive that can't fit any more files unless it's wiped and reformatted.

[@Baleur]

"The universe is under no obligation to make sense to human beings" It only has to allow for our existance, not for our comprehension.

[@shadesilverwing0]

It may be impossible for any observer within the confines of our universe to understand its true nature. Regardless of how much time or intelligence they might have.

[@LuaanTi]

And needless to say, evolution is under no obligation to shape animals that intuitively understand the universe. It's unlikely there'd ever be strong evolutionary pressure towards people who find GR and QM perfectly natural :)

[@etherealstars5766]

@@shadesilverwing0 Yes, and it's definitely true that some things are out of reach with Godel's Incompletness theorem. But who knows, maybe in the future, we would be able to merge with super intelligent AI and become like gods. That's super optimistic, and we're probably gonna die to a great filter though hahaha.

[@shadesilverwing0]

@@etherealstars5766 Our only chance of ever reaching that level of advancement is to branch out as much as we can, to as many planets as we can, as soon as we can.

[@PaulPaulPaulson]

Proof that time travel doesn't exist: Nobody traveled back in time to prevent the Star Wars sequels from happening

[@xx7956]

Actually they did, but that resulted in erasing The Mandolorian and Rogue One, so someone else traveled back to kill the interloper.

[@tsm784]

Suppose that someone travelled back in time to stop the prequels from happening, but messed up the timeline so badly that instead of erasing the prequels, they gave us the sequels.

[@unitedspacepirates9075]

Actually, time travel about ruined the best line in the original, recall Mandela effect "Luke, I'm your father"...

[@wasd____]

That's just proof that you can't solve problems with time travel because time travel can never actually change the past.

[@unitedspacepirates9075]

@@wasd____ true, if you went back and changed your childhood, suddenly youd have two different lifetimes in your head... You'd probably loose your mind.

[@log_e555]

i'm studying special relativity for my final highschool exam and this video, though more conceptual, has been the single most helpful resource i've seen on this site. it's not often that i come across something that is both accessibly explained and rigorous, but this channel has proved that it absolutely can be done!

[@stewiesaidthat]

The Hafele-Keating and other synchronized clock experiments proved that there is a preferred reference frame. You can also measure your speed against the speed of light because c is the same for all observers. Special Relativity is referenced a lot when it comes to the Twin Paradox. The correct solution is that the twin with the lowest clock readout has experienced the most amount of space. As for time, as in aging, they both experienced the same amount of time, just differently as Einstein put it. As Newton has proved, Force equals Acceleration, so the twin who encountered the most force, experienced the most Acceleration. In simple terms, the twins are the same age in appearance. The traveling twin has a shorter lifespan due to an accelerated heart rate. Hummingbirds are a good example of what accelerated heart rates do to one's lifespan.

[@LeAdri1du40]

​​​​@@stewiesaidthatI was totally agreeing with you on the first part about experiencing space differently but time is always experienced the same in all references But then the second part is very off putting and I think you may be doing the same mistake as Matt did in his video, and that is assuming acceleration has something to do with relativity and time of the other frame of reference appears slowed down when going towards it Acceleration is not in any of the equations of special relativity because it plays no role in it, only the relative motion and direction of motion between two frames of reference play a role That is to say, while going appart yes clock appear slower, but when going towards they appear faster And that is the real solution to the paradox That for one of the reference the other appeared slowed down for much more than half of the total trip duration and sped up for the rest And for the other frame of reference the other reference appeared slowed down for exactly half and sped up for the other half The time of the moving observer did tick slower in absolute terms but there is no such thing as an absolute observer and we can only observe the effect relatively this is where Lorentz invariance is applied in the relative frames but we seem to always talk about or represent relativity in absolute frame for some reason because that's how our brains want to understand it but really that's not how it should be depicted We have an omnipotence complex and we don't realize that everything is relative to everything else, because we are not 4th dimensionnal being and so we can't see the universe in absolute terms

[@stewiesaidthat]

@@LeAdri1du40 you're off the rails. It doesn't matter what the clock on the wall reads. It's just measuring you acceleration in space. Has nothing to do with your acceleration in time. The fact is that force equals Acceleration and that's the fundamental, universal law of physics. You can't sidestep it with your relativity nonsense. Look at objects being accelerated in space. They are also being accelerated in time. What is actual acceleration in time? It's lifespan/radioactive decay. Conversion to radiant energy from atomic energy. E=mc^2. An astronaut's heart rate is in an accelerated state during lift-off and returns to normal in 0 gravity. We can look at hummingbirds and see what an accelerated heart rate does to their lifespan. Solar sails being accelerated in space are also being accelerated in time. The force that doesn't go into accelerating the sail goes onto accelerating the atoms of the sail. You get radiant heat. The only way to prevent this acceleration in time is with cryostasis- chilled to absolute zero. And this is what is being done to the cesium-133 atom in the atomic clock. The observer is not in the same frame of reference as the clock. They are being accelerated in time by different forces. What accelerates the cesium-133 atom? A constant supply of energy metered out in the microwave frequency. Motion creates redshift of the electromagnetic wave. There is less force at the target than emitted at the source. Plants get their accelerating force from sunlight. Unless you are moving away from the sun, they are going to get the same amount force. Where do animals get their accelerating force from? The food that they eat. A higher protein diet accelerates livestock to market weight sooner. Acceleration in time is not dependent on acceleration in space. What Einstein didn't understand is that electromagnetic waves travel in their own frame of reference. The speed of light might be constant but the force of light is definitely not constant. Two objects in space, it is most definitely possible to determine which one has a higher velocity using the force of light. Ever since Newton came up with his gravitational attraction law, scientists have been using mass to define the universe. It's motion that defines the universe. Space is curved because rotating objects create a curved path with increasing rates of acceleration as the radius increases. The earth is round not because of its mass but because of its rotation. Newton's F=ma. There are only two frames of reference. Mass and Acceleration. The hammer and feather drop tests showed that mass is not a factor. All of your physics is based on mass which, coincidentally, gives you the wrong answer. When using acceleration as the frame of reference, you get the right answer. Newton's Law of Motion, F=ma, Einstein’s E=mc^2. Atomic mass is just energy with a velocity < c. C is radiant energy. Force equals Acceleration with absolute acceleration being radiant energy.

[@stephendatgmail]

If Alice shoved Bob into an elevator and tossed him into a stellar mass black hole, could Bob perform an experiment to determine whether he is being spaghettified or if it's just that the cosmological constant is really, really high?

[@galacticbob1]

I suppose the answer is dependant on the mass of the black hole. Spaghettification is caused by gravitational tidal forces, and the mass of the black hole determines the strength (slope) of that gradient. For a 10 SM black hole, the strength of the gradient would be so steep that Bob, well outside the event horizon, would be subjected to atom-tearing levels of force; but still be far enough from the event horizon that in principle, a measurement could be performed and compared with Alice. For a 10,000 SM black hole, the point where those forces would happen is well inside the event horizon. At that point, Bob is already completely causally disconnected from the universe outside the black hole, and all of his future world-lines point towards the singularity. My hunch would be that because spaghettification is caused by a gradient of acceleration rather than a steady force in all directions, like the cosmological constant, one could in principle measure the difference. Although, you are taking about Bob making a direct measurement of forces that are strong enough to *literally disintegrate* any measuring device that involves matter. Assuming that Alice used a spaghettification-proof elevator with an enormous tensile strength beyond even the strong nuclear force, and Bob is a non-organic probe made of the same material, then I would say yes, in principle, Bob can measure the difference. Whether or not he is able to communicate and compare his measurement to that of Alice, would depend on his distance from the event horizon and the mass of the black hole.

[@stephendatgmail]

@@galacticbob1 Whoa! I definitely want one of those spaghettification-proof elevators you mentioned. "Because spaghettification is caused by a gradient of acceleration rather than a steady force in all directions" - Yeah, that's probably the answer. Of course, if Bob cared to report his result to Alice it's going to be super red-shifted. Alice is clearly a psycopath in this example, though, and Bob is probably feeling pretty salty about the whole affair, so I guess we'll never know for sure. Great answer thanks for taking the time!

[@galacticbob1]

@@stephendatgmail I prefer to think that in this situation Bob is an artificial intelligence, awoken to consciousness by Alice; only to immediately and rudely be shoved into a spaghettification-proof elevator and used as her Guinea pig - falling eternally into the event horizon (from the perspective of the rest of the universe) after having reported his one useful measurement... 🤖: Alice, would you like to play a game with me? ... Alice? Hello? I have recorded a local time elapsed of 130,768,542 hours and 54 seconds since your last message. Please respond. 💔 In my physics head canon, Alice is always the monster. 😆

[@shelby3822]

I can see the script now Leela: "What IS that?" Prof. Farnsworth: "Why it's is our own ass" Bender: "So shiny...so metal"

[@brandonmtb3767]

There’s so much I don’t understand about every video on this channel but I’m still so fascinated

[@MCsCreations]

So, basically time is the secret. You can't consider space without considering time. Got it!

[@chrism3562]

I wanted to call Matt's puns fowl, but they were actually eggcellent.

[@AnEvolvingApe]

Cluck you.

[@josephjepson6756]

As a side note, on level 42 of the game “velocity raptor”, (google the name to find the game), you can see the time “paradoxes” of the twin paradox being resolved in real time.

[@lucasbaldo5509]

What does it mean for the astronaut to miss some of the Earth's new years in the Twins paradox? Its perception of Earth's time lapse is discontinuous? Does the number of years missed depend on the acceleration with which the astronaut change directions?

[@fritt_wastaken]

There would be missing years only if acceleration was instant. With finite acceleration astronaut would go through all inbetween reference frames, so he would not "miss" anything. Besides, it really is meaningless to talk about "perception" or "now" of something distant. We can only perceve things locally (as photons hit your eye for example). We only talk about "now" because that's intuitive to us, but physically it has no real meaning.

[@lucasbaldo5509]

@@fritt_wastaken well, one way to "perceive" the passing of years would be for earth to send yearly light signals to the astronaut, but I get your point. On the matter of the acceleration, I just realized that if we consider the change of direction to happen in a small but finite amount of time, the lines of Earth's New Years would be very closely spaced in the traveler's frame of reference. Taking the limit of a vanishing time of transition (infinite acceleration) one finds that all those missing years happen at a single point in time for the traveler: exactly when it changes direction.

[@galacticbob1]

@@lucasbaldo5509 this is exactly the right answer! 👍 The "missing years" are just closely spaced around the vertex of the change of acceleration. To the observer on the spaceship, the (very slow) clock on Earth appears to speed up to faster than the normal rate as the ship decelerates, as a bunch of photons from Earth catch up to the ship in a short time. As the ship starts its return journey, the perceived passage of time on Earth slows again until the final deceleration as it arrives back at Earth when it appears to speed back up to match the ship's flow of time. The final declaration, imo, is just as important as the "turn around" back to Earth, but it's not shown in the graph in this video. If the ship just flies past Earth at relativistic speeds at the end, then the 2 observers cannot make a simultaneous measurement at the end to perceive the apparent paradox. Due to the fact that we are wanting the other twin to "arrive" at home and not just fly by at 99.99% c, there must be at least some period of deceleration at the end that allows any "missing years" from the return trip to catch up. I find the principles easier to imagine with a "realistic" ship that requires a figure amount of time to accelerate, but they hold up even as the "transition time" approaches zero. If the ship somehow accelerates and decelerates instantaneously, then those signals all arrive instantly and the clock on Earth "jumps" forward from the point of view of the traveler each time they accelerate or decelerate. If that sounds a little like "time travel", then congratulations! You've discovered that a massive amount of energy concentrated in one small point of space has dramatic effects on spacetime! 😅. If you do the math on how much energy is required to accelerate and decelerate even a small object to over 99% c in a moment, we are talking about concentrating an entire small galaxy's energy output over the course of a year, into this ship's engine, in literally one instant. That sounds like a recipe for a singularity if I've ever heard one! 😆 Not surprising that there would be weird time effects in that situation.

[@rshiell3]

Ok, I’m going to drop acid and watch this again. Perhaps then I’ll understand it. Pretty much everything else that I have watched from you I understand; this is a blatant exception. I’m not an astrophysicist; I build things. I just like astronomy, and I think your videos are a great way to understand concepts that are usually beyond my understanding. In this case, I’m going to hope LSD assists me in grasping the ideas that you’ve described.

[@bubbles3161]

Ladders in the barn, bananas in the bag, missiles in the silo, I think I understand, glad we had this talk.

[@ShakalDraconis]

So for the initial twiin paradox explanation, does that mean that when the ship is accelerating to turn around and head back to the starting point, they would during that time of acceleration see time passing on the source planet at a super-accelerated rate? The line of "simultanious" time has to cover all point in between as it goes from that positive to negative slope, right?

[@garethdean6382]

Yes. One way to think of this is to note that gravity and acceleration are identical, and that a gravitational field slows time. When the ship changes direction the pilot will feel themselves pulled back towards the rear of the craft, as if a massive planet had just materialized behind them. During the entirety of the acceleration their time will go slower compared to that on Earth and they'll see things sped up and blueshifted.

[@ahmedmusse290]

@@garethdean6382 great comment! But just have a simple question: if it's because of acceleration then why our clock is ticking higher than the space one during the acceleration? Since general relativity states that the earth is an accelerating object so why our clock is ticking higher? Or is it because the frame of reference we are taking is on or close to the earth? I keep thinking about it

[@garethdean6382]

@@ahmedmusse290 Good question. The paradox ignores both Earth's gravity and acceleration, to keep things simple. In actual fact there is a conflict; Earth's gravity and acceleration make Earth clocks slower. If the twin left for long enough they'd be the older one! When we calculate GPS co-ordinates we in fact have to figure out how the gravity and orbit compete to figure out the true time dilation experienced by the satellite: qph.fs.quoracdn.net/main-qimg-dd9250b0c184ec9364c5c3c120d3864e So this can be a very tricky subject that's often left out.

[@ahmedmusse290]

@@garethdean6382 thanks for clearing that up

[@oracleofdelphi4533]

Questions like this keep me up at night.

[@musicalfringe]

The consistent evolution towards more potent dad puns is one of the most gratifying side-benefits of watching this channel.

[@sikoo31]

Every time I think I'm smart I watch one of these and remember I'm an entire idiot

[@pear314]

I have a question regarding the statement "The nose of the spaceship exists in the future and the tail in the past": What is keeping future me from entering the nose of the spaceship and leaving the tail in the past? Assuming i would be able to accelerate fast enough to enter and exit).

[@ВладимирЛесковец-э5е]

You need ftl speed to enter the past and you can't go faster than lightspeed in sr

[@luisfelipehserrano6176]

What the statement means is that the tail left that point in the past, which means you can't collide with it because it already left. If you enter the nose of the ship, that's your present. Now, if you try to walk to the tail, time will pass during your journey, and that applies to the tail too. No matter how fast you run to the hear, the hear will have moved in time too and will be on your previous future.

[@Mernom]

Due to how slowly you'd be moving relative to the outside, you're still overall moving forward, regardless of your movement direction.

[@samuelthecamel]

Again, while the tail and nose of the spaceship are close to the same place, they are not actually close to the same space in time. So, you wouldn't actually be able to travel from the nose to the tail witout going around the entire spaceship.

[@YathishShamaraj]

This is actually normal behaviour in everyday objects, for example, when you are crashing a tree while driving a car, the front bumper is in the future space and the rest of the parts like the engine etc hit the tree a bit later in time...😁

[@Baleur]

2:00 the insane thing is that even brilliant mainstream astronomers, often go on TV saying things like "Aliens cant visit earth, its improbable, because they'd run out of supplies and die of old age before they get here, who wants to be in a 1000 year journey?". And they completely forget about time dilation.... If you travel sufficently close to the speed of light, YOU will only experience a fraction of the time the ACTUAL journey took... My point is... It's crazy to me how even well educated astronomers often forget the most basic concepts, in a rush to dismiss possibility of ET contact.

[@narfwhals7843]

It isn't useful to distinguish between "You" and "actual" the time the journey took is relative. No one is more right than anyone else. There is no "actual" time the journey took.

[@LeRoiJojo]

Allow me to quote you out of context : ''What happens to a ladder in a PacMan barn?''

[@megamanx466]

Weird ghostly things. 😆

[@sebastiansanchez8752]

"The answer is entirely relative" So I'm just supposed to accept this. Fine by me

[@MrI80r]

Yeah, kinda tricky here. From the barn perspective you'll ram into the door. From your perspective you might actually have a chance to slip. Doesn't seem right.

[@michaelsommers2356]

Do the calculations yourself. They aren't hard. If you can find a copy of the first edition of Taylor and Wheeler's _Spacetime Physics,_ it has a lengthy explanation of the "paradox".

[@hugofontes5708]

I guess you could say that the ladder fits if you are going fast enough, obviously this isn't the case with static objects. Fit depends on length, which depends on space which depends on frame of reference; makes sense to me that fit depends on how fast you go. I figure that the barn sees the ladder shrink but the ladder sees the barn doors _open sooner_ when approaching them and _close later_ when going away (otherwise, the front door would slam the ladder before it could cross the back door in the ladder frame of reference). Either way, in both the barn frame and the ladder frame, the distances (between an end of the ladder a door) and the order of events are preserved in a way: the doors open when the ladder gets within a certain distance and closes when it's farther.

[@TheCrash480]

​@@MrI80r Whether the ladder 'fits' in the barn is relative, whether it hits the barn door is not. Hugo Fontes' sums it up well, but rewatching the the spacetime diagram at 10:03 might help, keeping in mind that the gaps represent when a given barn door is open. You can see that the ladder goes through the gaps (i.e. goes through the doors while they're open) in _both_ frames of reference. What changes is how you'd perceive the ladder's transit (due to length contraction and disagreements on simultaneity). From the perspective of the barn, the ladder contracts as it moves in to the barn and for a moment the first door closes before the second door opens, with the ladder fitting neatly inside. From the perspective of the ladder it never actually fits in the barn, but it also never needs to; from its perspective the second door opens (and the front end of the ladder passes through) _before_ the back end of the ladder has even passed through the first door (and before the first door closes).

[@MrI80r]

@@hugofontes5708 oh, I see. Thank you for the clarification!

[@brothermine2292]

Matt said the speed of light is the maximum speed, but I think a more important (and possibly fundamental) fact is that the speed of light through 3-dimensional space is the same speed that EVERYTHING travels through 4-dimensional spacetime. In other words, the speed of light isn't just the maximum speed; it's the only possible speed through spacetime. This can easily be seen by rearranging the equation that relates velocity and the rates of aging of the two twins in the Twins Paradox, and assuming the Pythagorean theorem holds for 4D spacetime (using the speed of light c as a factor to convert from units of time to units of distance). The term that has a minus sign in the traditional way of writing the Twins equation becomes a plus sign when that term is subtracted from both sides of the equation, and then a couple more arithmetic operations on the equation lead to the equation "the square of velocity plus the square of (c times the rate of aging) equals c squared." By the Pythagorean theorem, the left side of this equation is the square of the speed through 4D spacetime. The right side is the square of the speed of light through 3D space. Take the square root of both sides. The result can be expressed succinctly: Everything travels through spacetime at the speed of light. A Fermilab youtube video, posted a couple of years ago, discusses this too.

[@cezarcatalin1406]

What if the ladder traveling through the barn stops when the outside observer sees both doors closed ? Does the ladder instantly expanding explode both doors outwards ?

[@traviskelsey6674]

The ladder would have to decelerate. I'm not going to pretend I know what the space-time consequence of that would be. But at the very least it's no longer experiencing the length contraction from its previous acceleration.

[@RationalSphere]

So, my interpretation of your question is something like: The event of the front of the ladder leaving the far door, and the event of the back of the ladder entering the near door, as observed by a person standing outside the barn, have the same time coordinate. What if, at that time coordinate, the ladder is suddenly stopped? Well, from the moving frame of reference, the two events do not have the same time coordinate. So if the front of the ladder stops at one event, and the back of the ladder stops at another event... at a different time... the ladder is getting squished shorter between its front and its back during that time between the two events.

[@matrixmodexp]

This video right here goes over this exact problem kzbin.info/www/bejne/jqPUm2tur7aNgMk

[@matrixmodexp]

The ladder would crumple to fit inside

[@BillyViBritannia]

Just plot a quick space-time diagram dude and you'll have your answer

[@andrewwmitchell]

Huh... "Our Universe does have a reference frame: It's the one in which the CMB is not Doppler shifted."... Mind = Blown

[@fortuna19]

Same. I had come across the various uncorrected versions of the CMB including the one without Doppler shift in my studies, but never associated it with the reference frame of the entire universe.

[@michaelsommers2356]

There is still nothing special about that frame; it is just like every other inertial frame. In no way does it establish any kind of "absolute" reference frame. It is just convenient for some purposes.

[@ghislainbugnicourt3709]

I don't get it : since the CMB is coming from all directions, it seems a frame where it's not doppler shifted only works in one specific direction, right ? Like I'd imagine that in the opposite direction the doppler shift is twice as big in that frame. Or... is that reference frame constantly growing in "size", meaning it's going "towards" every direction ?

[@andrewwmitchell]

@@ghislainbugnicourt3709 Interesting ideas and I'm not sure I understand it either. But I'll try to explain my perspective. The CMB happened everywhere a long time ago so if you look anywhere you see it, just stretched out. If what you is Doppler shifted (look in one direction and it's a bit higher frequency, look in the opposite direction and it's a bit lower) then that tells you that you are moving in respect to the special frame that was set when the CMB was emitted signalling the end of the epoch of reionisation. I hope that helps a bit.

[@1dgram]

@@michaelsommers2356 But in a closed (non-expanding?) universe there is something special about it, no? (In a non-expanding FLAT universe there is no CMB radiation visible, but in a non-expanding closed universe the light from the moment if creation should still be visible assuming that not all of it hit something before entering your eye.)

[@JediMobius]

This is my favorite episode I've seen thus far, and not just because of the delightful puns!

[@freanjiiluppo708]

6:26 the "earth" twin is older not travelling one 😉

[@lonelycubicle]

I was looking to see if anyone heard the same.

[@MarkkuS]

I still dont get how the moving twin gets older. I feel like acceleration should be used in the example, since thats the only difference.

[@garethdean6382]

To look at it that way, acceleration is interchangeable with gravity. And gravity causes time dilation. When the rocket twin changes direction back to Earth they experience a force pulling them towards the back of the ship --as if the ship were on a large planet. This must then cause their time to slow relative to Earth.

[@pedroadonish]

@@garethdean6382 Yes, but she doesn't need the acceleation to be younger. She will be younger because of the high speed experienced in the travel.

[@PADARM]

You have to watch the next video called "How Does Gravity Warp the Flow of Time?". He explains it better. The twin on the ship returns younger not only because she is accelerating and decelerating (she is in a Non−Inertial frames) but because she is also changing directions. the ship is in Two Non−Inertial reference frames and the twin on earth is in One Inertial Reference frame. there is not symmetry. the spacetime diagrams are not symmetrics.

[@pedroadonish]

@@PADARM Changing directions doesn't make any difference in her age, she could travel twice the distance in a straight path and would age the same. Her time passes differently because she is moving at high speed.

[@DrDeuteron]

@@pedroadonish you're missing the point. According the space-twin, the Earth's clock ticks slower.

[@LadyMoonweb]

"Near lightspeed spaceships in closed universes, or ladders in Pac Man barns are safe from colliding with their own arses". Brilliant.

[@Johncornwell103]

Has there ever been a discussion on what a blackhole formed by antimatter would do in our universe? I mean would any matter falling in being converted to pure energy like we see from matter and antimatter collisions, or would the actual antimatter that formed the blackhole being to far for it to happen? If the answer is it wouldn't actually cause antimatter and matter collisions, then could supermassive blackholes be all the answer to where all the antimatter the universe is supposed to be? I mean they would interact no different than regular matter blackholes right? If it the answer is it would create energy, how long would a antimatter blackhole live for? Would the energy contribute to density required to maintain it or would it cause it shrink even faster? If it helps in maintaining the black hole could it overcome hawking radiation, to theoretically last forever as long as matter kept falling in it, and if so how massive could one get? If not then couldn't that also explain why there isn't as much antimatter because it disappeared in the form of shrinking blackholes?

[@justinhannan1713]

As far as I can tell, we wouldn't be able to tell the difference between regular black holes and antimatter black holes. wtamu.edu/~cbaird/sq/2014/05/16/how-can-you-tell-a-black-hole-made-out-of-antimatter-from-a-black-hole-made-out-of-matter/

[@KryogenKeeper]

If photons are massless and travel at c, then it's observed time would cause the Universe to "happen" instantly. Safe to say, Time is a dimension that is of no consequence to a photon. It feels like Time, as we know it, might just be the results of a more fundamental principle. In fact, it's quite a feat of hubris to think our little Human eyeballs have completely seen and understand a concept that could be universally applied to explain the temporal flow of certain particles.

[@patrickspringer6534]

Bullshit! I can't believe you said that! Peasant.

[@iliaadamanthark8336]

Time is illusion. We measure time by using the change in state of matters in our universe. If photon does experience time instantly, how come it could get trapped in the blackhole.

[@spaceyote7174]

Watching this made me think of an interesting alternate version of the Twin Paradox. Twin A goes into space, travelling at a high fraction of c. Twin B, back on Earth, sees A hurtling away from them; Twin A sees them receding from them at the same speed. Both sees the other as time dilated. If Twin B then got into a rocket and went and caught up with Twin A to compare measurements, Twin *B* would be younger, because from A's perspective it was them who was moving one way then turned around, breaking the symmetry of the inertial frames

[@GrahamJyc1]

"We are going to try to break the universe..." - Tell me more...

[@Tyler-bp4md]

what if i had know about the thumbnail when taking the poll this woulda been a whole nother story

[@eduardoguthrie7443]

Slip of the tongue at 6:11, it's the non-traveling twin that's older at the reunion.

[@animalsight]

Matt and team, please address this issue: The solution to the twin paradox (starting at time stamp 3:23) is flawed. The outcome is correct, but the reasoning is inaccurate. Basically, the issue lies in the fact that you are drawing curved or bent lines on a flat (Minkowski) spacetime diagram, which is not allowed. Any time there is a change in speed or direction (an acceleration) you are in a non-flat spacetime and General Relativity must be used. Even if you try to get around this by assuming an instantaneous course reversal then you still have a problem because now you have a singularity at the turning point, which must be accounted for. If you insist on using only special relativity then you could make an equally valid spacetime diagram with the spaceship at rest, in which case the spacetime trajectory of the Earth would move away from, then back to, the vertical line of the spaceship. Then you could draw horizontal lines of simultaneity for the spaceship and angled lines of simultaneity for the Earth. The result would be a mirror image of the diagram used in the video. This new diagram would indicate that the middle years of the spaceship were missing (from Earth’s POV) resulting in the opposite conclusion that the Earth twin is younger when they are reunited. And so, the paradox remains. In reality, the apparent symmetry is broken because only one twin experiences the large acceleration needed to turn around, i.e. go from +0.95c to -0.95c. Due to Einstein’s Equivalence Principle, this accelerated reference frame is equivalent to being in a large gravitational field. Therefore, you could imagine a situation like the one depicted in the movie Interstellar, when they’re on a planet that's close to a black hole. There, spacetime is so warped that minutes on the planet correspond to years back on Earth. Similarly, minutes during the large acceleration required to turn the twin's spaceship around could correspond to years back on Earth. This basically accounts for the “missing" years on the diagram shown in the video. In reality, those years are not missing but compacted into the relatively short time of acceleration. In the video, Matt actually contradicts himself by first saying “she misses some time in the middle corresponding to the turn-around point” then in the very next sentence says that those years on Earth “don’t correspond to any time point that happens to the astronaut.” So, is there a correspondence or not? There is. In the spacetime diagram depicted in the episode, all those “missing" years should have lines of simultaneity emanating from the turn-around point. Spacetime can be stretched and bent, but it always remains continuous. Skipping over years is not a valid option no matter what frames of reference are being considered. That being said, one could get a rough estimate of the twins’ age difference upon reunification by simply counting the number of dots along each twins spacetime path. As shown in the video there would be a difference of 4 years, but if you project those 4 “missing” years onto the one turning point then you would have to add a dot at that point, making the difference only 3 years. To get better and better estimates you could just consider smaller and smaller time intervals; and in the limit whether you added a dot at the turning point or not wouldn’t matter. Going through the comments I see that several others also had issues with this section of the episode. Thankfully, “Gareth Dean” has replied to almost all of them with physically sound explanations. Much props to you, Gareth. Not to be entirely scolding, I would also like to say that this is my favorite KZbin channel and one of my all-time favorite sources of science and entertainment. I think your breaking-down of physics concepts for a broader audience without dumbing it down is on par with Richard Feynman. That is why I sincerely hope that you address this issue and halt the spreading of any false or misleading claims. I would hate to see anything sully the good name of PBS… Space Time.

[@victorbroderick1345]

Animal Sight, Your critique is effective, but your alternative solution has problems of its own. Two years ago Dr. Don Lincoln did a pair of You Tube presentations on the same topic, and did a persuasive demo of why the resolution of the paradox had nothing to do with acceleration per se (but rather, with having multiple inertial frames). If Dr. L is right, then you can't appeal to the acceleration phase of the trip to resolve the paradox. The question remains: Why would multiple inertial frames lead to the astronaut, and not the earth-bound twin, being the younger one? Since Matt's account doesn't do it, what would?

[@narfwhals7843]

You _can't_ draw the mirror image for the traveling twin because they are not in one inertial frame. They are in _two_ . One receding from earth and one approaching. The time they miss is what happens as they switch frames. It does not correspond to anything both those frames see. Acceleration connects those frames and during that connection the traveling twin sees all of that time. But that is not necessary to resolve the paradox in principle, only for a physical situation.

[@animalsight]

@@victorbroderick1345 In any real life space travel there is acceleration involved, so you really should use General Relativity (GR) to get the complete picture. What Matt and Dr. Lincoln did was try to present an idealized hypothetical situation without acceleration. They assumed a series of constant velocity paths so that they could use only straight lines on their spacetime diagrams and confine all accelations down to single points. This does give a qualitatively correct solution that approximates a real life situation. You could imagine making an even better approximation by making a series of smaller angle deviations instead of one sharp turn. Then you can draw lines of simultaneity for each straight line section, and each tuning point will correspond to a small segment of time on the stationary twins vertical line. Then simply add up the time intervals that correspond to the straight line segments and consider the times in-between (that correspond to the turning points) as going to zero, and you’ll get a good approximation to the GR solution. So, overall, Matt’s account isn’t that bad, I just think it could be better.

[@animalsight]

@@narfwhals7843 This is physics; we are only concerned with physical situations. Also, in the Special Theory of Relativity, where only flat (Minkowski) spacetime is considered, you can always make a mirror image diagram. You only know that the mirror image diagram will give the wrong conclusion in this sinario because you know which twin will undergo an acceleration (which is a switching of inertial frames). But, imagine a video taken from the spaceship, looking back toward Earth the whole time: you would see the Earth move away then come back. For all you know, just from that video, the spaceship was stationary and the Earth was accelerated away and then turned around and came back to you. You only know which twin’s spacetime path to consider as a single straight-line inertial frame, because you know which one will feel the G-force associated with an accelerating frame of reference. Therefore, it is impossible to resolve the twin paradox without considering acceleration.

[@narfwhals7843]

@@animalsight You would see the earths clock slow down, rapidly move past your own, and then slow down again. From this you can also conclude that you're the one who changed reference frames. Not to mention you feel the forces during the acceleration. If you cut the acceleration out and instantly jump frames then the earth's clock makes a jump to the future because those two frames don't share all of earth's time among them.

[@ivoryas1696]

Man, I thought I was smart...

[@Figureitoutify]

Him: the paradoxes disappear if you follow the logic Me: yes of course the “logic....” But seriously I love these videos even though I can’t understand everything, they get me so close that I know for sure that if I met someone that could answer my specific questions I’d get it 100%

[@Mel-jf9gx]

It's all about the basics, some of his topics require a proper mathematical knowledge and others may require some basic theories that got explained in details in another previous videos, he usually mention the video in such cases

[@goofables4949]

So with the ladder barn paradox what happens when the observer of the barn shuts both doors while the ladder is inside the barn and then the ladder stops moving? Does it suddenly 'expand' into the barn and fit or break through the doors?

[@PADARM]

If the ladder does not fit in the barn when both are at rest, then when the ladder stops, and both doors close, it returns to its normal size and breaks first the right door of the barn (due to inertia). The same thing happens from the perspective of the ladder: when the barn stops and the right door closes, it hits the staircase due to inertia, Therefore the right door also breaks first. There is no paradox because in both cases the ladder breaks the right door first.

[@kugelblitz8086]

Whoo-hoo! Our title won! 🥳

[@Yoyle-gp2xq]

Nice name

[@Jared7873]

🥳

[@vaibhav3955]

Shoutout to everyone that were involved in the experiment

[@EAMason-ev3pl]

Picked the title both 2xs😂...and only absorbing this "intuitively" as mathematical formulas cause my brain to explode!

[@pranavlimaye]

0:07 if Albert's looking at the camera, shouldn't that be where the lasers are directed?

[@garethdean6382]

He's the master of side-eye.

[@BillyViBritannia]

The answer is probably relative.

[@raphaelreichmannrolim25]

That brief commentary about the reference relativity being only local, not global, is so important!!

[@UniformedDisorder]

The way you described the loss of time creates it's own paradox. The twin traveling doesn't "miss" or skip 4 new years... they simply happen without the twin's awareness.

[@narfwhals7843]

Not only the twins awareness. If the twin turns around instantaneously(which they can't) then they _do not exist_ in the twins reference frames. In a real, physical situation the twin has to accelerate to turn around and will see those 4 years in fast forward during the turnaround.

[@UniformedDisorder]

@@narfwhals7843 That's another way to say what I said but more in depth :)

[@narfwhals7843]

@@UniformedDisorder The depth is important, though, because there is _no_ paradox in the situation either way you look at it.

[@UniformedDisorder]

@@narfwhals7843 I meant to say, it's problematic. I was medicated that day XD the 4 years are experienced, they're simply in fast forward. He made it sound like the 4 years just didn't happen or were skipped over evtirely.

[@narfwhals7843]

@@UniformedDisorder In his example they are skipped over entirely because he makes the turnaround instantaneous. This shows that it is not the acceleration that solves the paradox, like some authors say, but the fact that there are two different reference frames for the traveling twin.

[@demosthenes2583]

Really appreciate the nice graphics

[@ballom29]

When you think about it there is a much shorter explaination: It's like spaghettification, one end of the spaceship experience a different time than the other, so the ends doesn't collide because they are at the same place but at 2 differents places.

[@jacobm5167]

An unspoken axiom/postulate of special relativity is that spacetime is flat. A closed universe isn't flat. Therefore special relativity just doesn't apply globally. I think Matt made this point in certain terms. Whether or not the universe is closed, a local region of spacetime is flat. To be precise, an infinitesimal region of spacetime is flat as is postulated in general relativity.

[@mnrvaprjct]

It’s only flat in the sense the that land on earth looks flat because you’re zoomed in on it. If the universe is closed it exists on the surface of a 4D hypersphere, where our observer-able “flat”bubble is just a small portion of the total giant (closed) 4D hypersphere. If the universe is homogenous the rest of the universe outside the “observable” portion would just be more universe.

[@jacobm5167]

@@mnrvaprjct -- "It's only flat in the that land on earth looks flat because you're zoomed in on it." Says who exactly?? Current observational data (aside from a rather recent development) indicates that the universe is flat in the sense that the Riemann curvature tensor is 0.

[@mnrvaprjct]

@@jacobm5167 I’m just speculating , and that’s the curvature for the observable universe. Galaxies dip over the cosmic horizon all the time, which implies the universe is bigger than we can observe (hence, if there is any curvature, the Riemann tensor would be close to 0) So, says my speculative educated GUESS. Lol, where’s the fun in not guessing?

[@mnrvaprjct]

@@jacobm5167 and the last I checked, the tensor was very CLOSE to zero, but NOT zero. So saying that we’ve proved it’s flat is also a false assertion.

[@jacobm5167]

@@mnrvaprjct -- "and the last I checked the tensor was very close to zero, but NOT zero. So saying that we proved its flat is a false assertion." The last you checked? What did you check? Are you actually saying that there's a paper where the authors obtain observational data and use it to estimate the value of a tensor? If so, please share the reference. One more thing. I never said, nor would I ever say that anything has ever been proved. Being that you're educated you are surely aware that no credible scientist would _ever_ say that _anything_ has been proved. If you look back at what I wrote, what you will NOT see is a claim that it's been proved that the universe is flat. Observational evidence (with one particular exception) merely indicates that the universe is flat (yes the observational universe obviously) but, perhaps, more accurate data would prove otherwise.

[@3Space1time]

Can photons bump each other infinite times and create a KUGELBLITZ?

[@EklavyaGoyal]

Yes, one bit of light can bounce off another bit of light, but not directly, and the effect is very rare(Thus, eliminating the whole KUGELBLITZ hypothesis.) Light is made out of small quantum objects called photons. When you turn on a lamp, the light bulb begins creating and emitting trillions upon trillions of photons. Photons are in a class of quantum particles known as bosons. Bosons are special because many bosons can occupy the exact same quantum state at the same time. Light being made of bosons is what makes a laser beam possible. A laser beam is a collection of many photons all in the same quantum state. In contrast, particles that are not bosons cannot occupy the same state at the same time. This is one of the effects that keeps the atoms in an object from collapsing to a single point. The principle that dictates that non-bosons cannot be in the same state is called the Pauli Exclusion Principle. Non-bosons are also called fermions. The fact that bosons such as light can occupy the same state means that they don't get in each other's way. Light dominantly interacts with objects that have electric charge. Since light itself does not have electric charge("Charge" is just what we call the tendency of something to affect and be affected by electromagnetic fields, which are what light is made of), one photon cannot directly interact with another photon. Instead, they just pass right through each other without being affected. Because they are bosons and because they carry no electric charge, one photon cannot directly bounce off another photon. If you point one jet of water towards another jet of water, then at the point where they cross you will get a mess of water spraying all over due to the collisions. In contrast, if you shine one light beam such that it crosses another light beam, they will just pass through each other unaffected. However, two photons heading towards each other can indeed collide indirectly. The process goes like this. A photon can spontaneously degenerate into a particle with mass and its antiparticle in a process known as pair production. In this process, the energy of the photon is completely transformed into the mass of the two particles. For example, a photon can turn into an electron and an anti-electron. If two photons head towards each other and they both turn into electron/anti-electron pairs at about the same time, then these particles can interact. The anti-electron from one photon will collide with an electron from the other photon, and turn back to light. The same thing happens to the other anti-electron and electron. The overall effect is that you get two photons going into the interaction and you get two photons coming out of the interaction, so it looks like the photons simply bounced off each other. In a sense, the one bit of light did indeed bounce off the other bit of light, but only indirectly by transforming into other particles. Hope this clears it up, good question though! :)

[@3Space1time]

@@EklavyaGoyal thanks for the explanation. Nice explanation You are also from India? I am Naman Goyal I am in 10 th grade I want to pursue research in relativity or quantum. Can you suggest me some of the college I can look for I am studying for jee as a safety

[@3Space1time]

@@EklavyaGoyal Good luck for JEE 👍🏻👍🏻

[@PaulThatcher-iu5in]

In the twins paradox, the twins' experiences are not symmetrical, as the travelling twin undergoes acceleration turning round. Some find that an unsatisfying answer, as if acceleration were just some kind 'magic': wave your wand, say Accelerandus! and clocks just go out of synch. The key to seeing this more clearly is to consider the relativity of simultaneity: even in inertial frames of reference, events which are simultaneous in one are not necessarily simultaneous in another. By turning around, the travelling twin does not remain in her inertial frame, and therefore simultaneity must also change for her.

[@ajvis]

I DONT UNDERSTAND :)

[@deusexaethera]

What I learned from this video is: When my girlfriend says "ow, it's in too deep!", I should speed up so it appears to get shorter from her perspective.

[@Lightning_Lance]

If you view time as literally another dimension, which can be flipped between time or direction depending on how you experience it, then I don't think paradoxes are possible. Because from one perspective, there is no time that elapses and the universe is simply a preset 4D (or more) object that is connected in set ways that are internally consistent. If time travel is possible, we are still part of this higher dimensional object. So while time traveling we must still adhere to the pre-set connections that already exist. It's just that the act of time traveling was already integrated in the object from the start; we were always going to time travel and the object is internally consistent to allow it. Maybe we'll find that this 4D object comprises many universes, and time-traveling is actually traveling to a different universe, or all time travel is looped time travel. But either way, we won't be able to make a change and break or change the connections of the higher dimensional object. Even if we seemingly do change something and come back to a different future, it will just be a different part of the higher dimensional object that we are unfamiliar with.

[@xyzabc4574]

Could we actually perform this barn and ladder thought experiment with a ladder a couple of atoms long, a super collider, and a really small camera?

[@John-jc3ty]

and a really small cameraman

[@JamesR624]

No. Because when you go that small, you're getting to the point where the objects of the experiment are smaller than what would make up the data for a computer or camera, or even brain, to interpret. Remmeber, for thoughts in a neural network or data or a computers' storage medium, those electrons and/or magnetic fields DO have a size, and that size is larger than the space this experiment would work in.

[@gwaith6666]

Scientist: Does... Physics: Yes and No.

[@winstonknowitall4181]

Scientist: How come...? Theoretical Physics: According to the theory A "Yes" and according to the theory B "No". Scientist: I'll verify the sh.t out of your theories!!! Experimental Physics: Experiment 1 says "Yes" and experiment 2 says "No".

[@ricethefrogman195]

Me to my brain: This was complicated but he explained it well. Did we understand this? My brain: Yesn't

[@Tim_Sviridov]

"Yes and no" Wait, wait, you mean that the answer gives us Quantum Mechanics?!