The Arrow of Time and How to Reverse It
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- Опубліковано 2 чер 2024
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Ever wish you could travel backward in time and do things differently? Good news: the laws of physics seem to say traveling backward in time is the same as traveling forwards. So why do we seem to be stuck in this inexorable flow towards the future? It's time to begin our journey towards really understanding time.
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Written by Matt O'Dowd
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"Alles hat ein Ende, nur die Wurst hat zwei." - Everything has an end, yet the sausage has two.
yum
🤣
Actually, the slingshot has three.
Wurst was supposed to be "Welt?"
Hey I was able to understand that. I guess my four semesters of German in the University didn't go to waste after all, LOL
Und der Donut hat keine. - And the donut has none. LOL
Timeless topic.
Duck
Duck
Duck
Duck
Duck
Okay this episode’s last line ‘space... time” was epic
It was witty.
I really like the mentioned definition of entropy as "a measure of how randomly spread is the energy in a closed system"
The Star Wars Prequels are still horrible
"Time flies like an arrow,
Fruit flies like a banana."
--Unknown author
Oldie but a goodie 😁
-Einstein probably
"Time flies; you can't - they go too fast". Probably the same anonymous author.
Actually, this one is due to Groucho Marx.
Time flies like fruit flies.
As a kid I always used to do a thought experiment that if time completely stopped around us we wouldn't even know because our perception of time would stop as well, so we would not feel it at all.
I want to assert that I also had those thoughts.
I always think I'd turn into a black hole
I also had that thought this means our genetic material is very close still we all human are very close in thinking
Yes I also from child to uptill as a teenage
Time never Moved, You had a perception that you're moving but you're watching yourself in a frame
I don’t understand a single thing here but it’s so fascinating
Me too, unfortunately! 😁
Christopher Nolan: Hold my inverted bullet
his worst movie to be honest... the reversed people were walking forward but driving cars backwards...
@@thulyblu5486 - backward car motion is from the other direction perspective,
@Xandrog Zodbolt He's not entirely wrong - the car crash is a mistake in the movie. From the perspective of the people going forward in time, the car seems to be crashing and tumbling inverted, then driving backwards - except the car never went through the turnstile - it's just a regular car moving forward in time with an inverted person inside it. The crash should have looked totally normal in the first scene. The movie aint exactly consistent with its rules.
@@SuperTurboCrash the car was inverted. we just didn't see it get inverted.
Loved the QED joke at the end, and the way he still managed to end the first segment with "Space Time".
yeah the QED joke got me good hahaha. you can tell the writing team has been busy lately!
I sensed a joke, but as a non native English speaker I can't understand what it is
Chan Captain Obvious save me?
@@thenasadude6878 QED = "quantum electrodynamics" and also initialism for the Latin saying "quod erat demonstrandum" ("that which needed to be proven")
@@thenasadude6878 QED is the acronym for Quantum Electrodynamics, but as the guy above me pointed out it's also the acronym for a Latin phrase which is commonly used at the end of mathematical proofs to tell the reader the proof is complete.
Yeah the writing in this one was on point, I loved both of those
"space: time." A novelty of an ending, well played.
Whomever wrote it must be exceedingly proud of that final line.
in description: written by mat o'dowd
*whoever
@@twincast2005 Whomstvwd've?
@@eriks8382 Wut?
For the record, I love "whom" (and "thou") and mourn their loss. But hypercorrected misuse is worse than just letting them die.
Someone send this to Christopher Nolan, he should make a movie about this!
Wait...
Tenet
JJ ABRAMS BABY!!! THAT'S MY VOTE!
TENET RULES 👏
Fun 'fact': Christopher Nolan actually reversed his entropy in order to move backwards through time and make TENET after reading this comment, even though- from our temporal perspective- this comment was posted after TENET was released.
Apperantaly in a parallel universe :
EMIT ECAPS SBP : How to make time move forward .
@Cyril but atleast you'll know that you're 80 at birth and now you are 24 .
(I know it seems crazy but try understanding the point(•))
@@NihilistEmier for them forward will be the backward
@@chinesevirus7139 yep dude
BTW pls stop spreading !!
Humble request from the world .
@@NihilistEmier virus lives matter!
You should’ve written this backwards
"Why do we not remember the future?"
Normal person: "Go home you drunk."
Physicist: "Good question! I gonna need three hours and a giant white board. Btw, do you know quantum physics?"
You probably are going to need a neurologist who is also a physicist to properly answer this. Add an additional 3 hours for that side.
Not personally ,,,study dreams,,keep a note pad and pen beside you when you sleep and write your dreams the best you can upon waking,,the vale you pass between awake and asleep will lessen,,the answers are in the memory
And a mathematician to tell if that's even possible to achieve in finite time
@@chinmaykrishna6485 a "neurophysicist" just kidding. But seriously add like 3yrs to to that work and 3 more scientists.
Troll: "It because you move through time backwards."
I like the idea that the Big Bang is the entropy minimum point and that a universe before it was essentially reversing time. To that universe, that opposite direction of time is their forward and we are reversing time in their eyes since the time dimension supposedly works exactly the same way in both directions with entropy increasing. This idea is so elegant and beautiful. Not only that, but from the perspective of the origin point, there's essentially two timelines with no preference of one or the other since both directions increase entropy. So the previous universe is like a sibling Universe, or rather an alter ego since it's essentially the same energy. And I call it previous because they would call us previous as well.
One day one smart man will tell us what time is and how it works and we all will say “I can’t believe it was that simple”
That day will be special indeed.
"Sir, you were speeding, sir!"
"No, I'm not. I was driving at -200km/h. That's way below the maximum 100km/h."
"Damn those backwards drivers."
Length of vectors are not the same as vectors, mind you! ;)
"I said speeding, sir, not velociting."
Hahaha you nearly got me you were reversing at 200km/h im taking your liscence
My car wasn’t moving, however, the road was going quite fast.
_laughs in T E N E T_
"We're going to need more episodes... Hey guys we're taking a short release break"
oooof
Just ride the wave of entropy to the next episode, man.
I will always adore this channel for diving deeper into complex physics topics in such a way that is digestible for people unable to get into the math behind it. Never stop being amazing.
The next 100 Years will probably decide what wins:
Science or Anti-Science.
To affect this, i even go so far as to ask random strangers like you: Want some
recommendations? Some Science-UA-camrs to check out, cause the Learning never ends?
@@nenmaster5218 wtf is anti-science?
@@pragalbhvashishtha7711 COVID-deniers, for one
My favorite part of that "Another universes behind/(before?) the big bang flowing the opposite direction" is that, due to CPT-symmetry, it has the most delightfully satisfying solution to the matter-antimatter asymmetry problem I've ever come across. All the antimatter is just on the other side of the big bang!
Me: it's time to sleep
Phone: PBS Spacetime just uploaded
Me: sleep can wait
"But its timely to spend time on that fascinating dimension that deserves more space: time."
I see what you did there!
I saw the Game of Life animation and I pondered: "But that is not time-reversible like electron collisions are!" And that lead me to discover reversible cellular automata on the wikipedia. Cool stuff, thanks for the inspiration! :D
This Christmas was great. Looking forward to last Christmas, where I give my new socks back and start wearing my worn out ones again
@The UA-cam Comment King They tried so hard to stop him. He was pretty dead set on it for many many years prior to him succeeding.
“It's a poor sort of memory that only works backwards,' says the White Queen to Alice.”
Nice one.
don’t surround yourself with yourself,move on back a square
That is actually a truth
Example: 'Arrival' movie.
Except that Lewis Carroll was experimenting with LSD when he came up with the plot for his book. That doesn't count as science.
UA-cam has better teachers than an average private school. Lmao
You get to touch the same wall as the great minds,I hope they hurry up with the math
As a school teacher, I would say that any lesson where you don't have to deal with the behaviour of your audience in order to get your knowledge across is always going to be better. That's currently the beauty of online teaching with a mute button!
We experience things as we go forwards in time. We Un-experience them if entropy is reversed. It might have happened before the big bang, or it might "un"happen to us if we consider time reversal. The trouble is we can't remember when we "UN-experience" things.
So glad you guys are spending more time on Time, my favorite subject.
I remember in one of Stanisław Lem's book - they were able to locally reverse entropy - which increased probability of Atoms coming together and making more "structured" things. At one point Dinosaurs started appearing - they cranked it up so high.
I have to read it again. Lem was a genius.
@@chemicalfrankie1030 Without knowing the English titles, I think it was from "Memoirs of Ijon Tichy" - story was called "Dragons of Probability". They went to create Dinosaurs/Dragons. I've read it 25 years ago, so it was some time.
Or rather "Cyberiad". I am confused.
In a certain way, the people who profess "healing frequencies" exist are really suggesting this sort of phenomenon.
@@Kowzorz BTW I've seen weird things Medicine-wise that Doctors said were impossible. Does someone know a channel were they explain this sort of stuff? With my background, I can guess a little, but this would be good source to debunk those "healing" methods.
For example my colleague had a burn through their arm, so you could see bone and veins easily and tendons if you looked really well. It was basically open to the outside. It didn't change for 3 years. Than that colleague started attending Teta (or Theta) - Healing and it started to close. They still have a mark, but area is closed and apart from the mark healed. I tried to think of possible triggers of cellular regeneration, but 1. I lack knowledge that deep. 2. I also don't have every detail. I've seen the wound before, I've seen it after (took 2 years to heal properly, after those 3 years of doing nothing) - but the only thing I could think of was basically Placebo effect and maybe this person started treating the wound in correct way, so it could regenerate? Because no, Teta-Healing didn't do anything apart from being very costly and making that person feel better.
@@jannegrey593 Cyberiad is great! I have a copy. Totally different from most sci fi and it makes you think deeply about things.
This UA-cam channel finally finds some time to discuss time. Yes, I think it's more than time to discuss time.
Love you Matt! This show has gotten me through some hard times over the past several years.... nothing like some abstract physics and cool graphics and your sense of humor to take mind off of things
How does it not make you spiral? It’s interesting to me, and i want to learn more but whenever my mind really sets in on this stuff I spiral lol
I always begin these videos with the best of intentions, and with a positive outlook on understanding these concepts. And, I'm good, until about 4 minutes in, and then I begin to doubt my intelligence as I get terribly lost and confused. 🤷🏾
You aren’t on your own
That's good. It means they're not deceiving people by creating an illusion of understanding. (As it typically happens in physics education.)
If you could rewind time, would a black hole repel particles? Or is the black hole a fixed point in space time?
It would be a white hole
Yeah, what I was going to say is that it would emit matter & light, which isn't exactly the same repelling particles.
Also, I think reverse hawking radiation would mean that its event horizon is a kind of acts as something that summons particles from far away, just to get annihilated by another particle that it emitted.
I think it would become a white hole
Now I'm trying to imagine reversing everything in the universe, and realizing that there's a problem involving the "moment" in time when the direction of everything reverses. Because that requires simultaneity. Does the warping of spacetime around a black hole allow for it to behave the same way in any time "direction?" After all, space becomes timelike beyond the event horizon, so maybe in a black hole, time just goes sideways.
I"m uncomfortable with the idea of all black holes becoming white holes when you reverse the direction of time. How does entropy change over time for a white hole? Does it increase or decrease when it emits matter and light? For that matter, how does entropy change over time for a black hole? I mean, I guess that's sort of the same question in reverse, but I'm not sure...
clicks on the video hoping to get another shot at childhood
You already had two if you include the backwards universe.
Even though it’s a lot more work than I imagined,the vision was worth it
skOsH,, Steven Kings Langolier
@skOsH telomeres don't affect aging directly. They're more like lightning rods for the errors involved in replication (or outright mutation) that aren't caught by the proofreading mechanism. Lengthening or restoring them would slow the onset of senescence, however.
@skOsH or rather it would mitigate the effects, since ageing in itself is inevitable.
I wan to thank you guys for the last few ep. in particular the Free will one. I have seen a few science channels get stuck in one concept that they view as correct but you tackled them from a very neutral position and explained multiple possible explanations
I remember reading about the reverse time universe suggestion a few years ago and didn't fully get it but you explained it really well, thanks!
My background is maths, not physics, but something seems to be missing here:
If physics is completely invertible (as in quantum theory without collapse) then forward evolution generates many worlds, and recovering the past from the present requires all those decohered worlds as input. If you start with only "our branch", then presumably running things backward also generates many worlds, most of which do grow in entropy - space still contracts, but you get lots of black holes etc.
On the other hand, if physics is not invertible (e.g. if true "collapse" occurs) then information about the past is completely lost, and generating the past from the present is impossible even in principle.
As far as I know the weak nuclear force breaks time symmetry as it interacts with matter and antimatter differently.And antimatter is also considered to be time reversed matter, in which case physics shouldn't be invertible.
Absolutely. In a quantum world, you need the full multiverse correlations to actually wind back the clock, and wave function collapse is absolutely irreversible. That could actually be a good thing, if you take the view that Copenhagen "explains" the arrow of time, but I've not heard anyone actually make that argument.
@@mikeflowerdew7877 However we don't know if the many world or the multiverse concept is true or not.
It might be that all other possibilities gets destroyed after a wave function collapse and only one reality persists.
This is what I prefer btw.Either way the process of wave function collapse doesn't seem reversible.
@@makisekurisu4674 Exactly. The very fact that this depends on which interpretation of QM you use should be raising alarm bells, as this really is a matter of philosophy not observation. I was simply stating what you need to assume to make the universe truly reversible, and you are perfectly entitled to reject that. I do think it's interesting there's a difference however, and one that isn't usually discussed.
@Makise Kurisu physics can be time-invertible without being time-symmetric: it just means that when time is reversed, things behave as though their charge and parity have been flipped (as you said, matter behaves like antimatter). But that still leads to everything rewinding, if we can take all those other worlds into account.
As a kid, when I used to dream of future events and told my mum, she used to lecture me on using the past tense for describing things that I remember happening. So I stopped talking about it, to avoid lectures. Eventually those dreams stopped too.
same here i use to "Sense" the future when i was younger. Like really in tune and aware almost psychic. Hard to explain but i feel you.
Intuition is a gift,
So... was she a physicist or a grammarian?
Happy thank's giving. I wish you all the best for 2021...
Understanding this is the key to understanding life
Inside black holes, time and space kind of swap places. Once inside the event horizon, going 'forward' inevitably means going towards the center of the singularity.
So what would happen if you reversed the flow of time?
Would black holes all turn into a white holes, which randomly spews out matter?
(by 'randomly', I mean in a completely unpredictable way, since black holes seem to break entropy)
Yes; that's actually the *definition* of a white hole. It's a time-reversed black hole. Hope that helps!
Its about time one direction got its space time video. They are only the most important and most influential band of our time. Possibly any time.
Um, sorry... do the Spice Girls and the Backstreet Boys mean nothing to you??
This is my favorite subject. I am increasing my excitement for the increase of entropy.
Finally. I have waited so long for this show to discuss this. Looking forward to the expanded topics.
I actually laughed out loud on how you worked in “space...time” into that segment. Well done.
0:59 I see Jupiter surface getting smashed by giant asteroid.
Great observational capability dude.
One of the best arguments in time travel, I've thought: if you went back in time, how would you know? When SciFi talks time travel, it really means traveling forward in time to some point "back" in time.
Thanks, this resolved one of the last understanding issues I had with entropy
All physical processes have a certain "unfolding" speed, that is what creates the illusion of time. For example, time slowing down the faster you go, simply means that the faster you go, the slower all chemical and physical processes tend to happen. We call this time dilatation. But in this way, time is not a real "entity" but just a measurement of movement and change, a mind construct. Removing all things would mean the end of time, because there would be nothing to measure. That means time does not actually slowdown the closer you get to the speed of light, but chemistry and physics are simply slowing down. That is why you can't go back in time, because it would mean reversing chemical and physical processes.
We need to get to the root of the problem - us - or our "consciousness". Still can't rule out if time is a human construct or not.
How can anything have an unfolding speed if time is an illusion. Speed is defined as a change in distance over a change in time so speed requires time.
So you mean "the passage of time" is rather "the occurrence of change" itself and not its cause? And time dilation is a variation of the "rate of change"?
If we travel back in time then there's no new episodes of Space Time, and I dont want to live in that kind of agony.
Fantastic description of the utility and limitations of specialist terminology!
That ending. Well done.
“The creatures can see where each star has been and where it is going, so that the heavens are filled with rarefied, luminous spaghetti. And Tralfamadorians don’t see human beings as two-legged creatures, either. They see them as great millepedes-“with babies’ legs at one end and old people’s legs at the other,” Kurt Vonnegut Slaughter House Five
Deeply unprofound
"The living often don’t appreciate how complicated the world looks when you are dead, because while death frees the mind from the straitjacket of three dimensions it also cuts it away from Time, which is only another dimension. So while the cat that rubbed up against his invisible legs was undoubtedly the same cat that he had seen a few minutes before, it was also quite clearly a tiny kitten and a fat, half-blind old moggy and every stage in between. All at once. Since it had started off small it looked like a white, cat-shaped carrot, a description that will have to do until people invent proper four-dimensional adjectives."
Terry Pratchet, Mort
@@Eternalentropy Thanks, anonymous internet stranger
@@christopherbrent3759 Most welcome :)
@@Eternalentropy dont do my boy kurt like that
I love how at the end he's wearing a heat death T-shirt.
I'm SO into all the fun you guys are having with the final "space time" line!
The next 100 Years will probably decide what wins:
Science or Anti-Science.
To affect this, i even go so far as to ask random strangers like you: Want some
recommendations? Some science-youtubers to check out, cause the Learning never ends?
I just love the endings of these episodes, "Space-Time", very nice and informative as always...
Doesn’t the collapse of the wave function also break time symmetry as well?
Not according to _Objective Collapse theory_ (certain conditions dictate when collapse happens), _superdeterminism_ (all collapses predetermined and traceable all the way to big bang) or information based approaches where the whole wave function could be considered an informational, statistical field rather than a some actual thing that collapses (if I understand it correctly... which i probably don't).
@@Nuclearcx my understanding of objective collapse theory is that the wave function collapses when something objective happens, this varies by version. For example according to Penrose when the gravitational differences becomes larger than some value. According to others there is a probability distribution when a wave function will spontaneously collapse etc. However for each of these the wave function collapse into one particular state, and I believe that is time irreversible.
In Many Worlds / the relational interpretations, there is coherence and decoherence and WE call the direction in which there happens to be more decoherence the future.
I'm having trouble seeing how quantum mechanical principles such as the uncertainty principle can be reconciled with the view that the laws of physics are independent from time. Could you elaborate on the relationship between entropy and quantum mechanics in future videos? It makes sense from the classical view of the universe described in the video though
I admit I don't involve myself as intricately as I should but I do respect and enjoy the knowledge you share , thank you.
I'm so excited for upcoming episodes.
Two questions: First off, what are the implications of this understanding of entropy and the current mainstream assumptions about dark energy on one another? Is the phenomenon of dark energy potentially responsible for entropy, or caused by entropy?
Second, is it possible that time is just an illusion caused by our imperfect human minds? If the functioning of our brains relies upon the phenomenon of entropy in some way, is it possible for the objective universe to not "care" about the directionality of time while our experience of the universe is limited to perceiving only one direction of time? If that were potentially the case, how could we experimentally test that?
Once again PBS Spacetime, thank you for making another delightful video! Looking forward to the next :)
1.) Dark energy increases entropy but we don't have any special link between it and entropy. One might as well ask if radioactive decay is responsible for entropy. (Though one could definitely argue that everything that happens is caused by entropy, dark energy included.)
2.) Our current understanding of physics suggests that the universe does indeed not care about the direction of time. That said there must be laws in place preventing us from remembering the future, limiting our perspective. Remembering the future (and being powerless to change it) seems physically possible but might just be very unlikely in a block multiverse. Our current tests involve testing 'time symmetry' by creating exact opposites of regular physical interactions and seeing if they indeed progress the exact opposite of their counterparts.
T-symmetry has indeed been broken but not so far in a way that would prove a universal arrow of time. (en.wikipedia.org/wiki/T-symmetry )
@@garethdean6382 What about cause and effect. Effect have an tendency to be after (in time) cause. Don't know how that works with quantum physics.
As I said on another comment, I think the human mind only works forwards, because it is not exactly "located" somewhere in spacetime, it is "embedded" in the sequence of brain states from initial to final. Even if time in our universe actually moves in reverse, I believe we would still experience time moving forwards. We can probably only test this after we figure out consciousness first.
If you magically reversed the direction of every particle's motion, then maybe some things will reverse, like unbreaking a glass or uncooking an egg. However mass+KE+PE is still preserved and identical, so at cosmic scales, the universe would still be expanding due to the presence of energy and would not reverse back to a big bang.
Nicely explained.
One postulates if: entropy increasing (on average) is the forward direction of time. Therefore if one rewinds the universe to before the Big Bang and extrapolates to another expanding universe, this may not be the reversal of time but in fact time running forward. Just as in the space-time slices, looking back through time to the entropy minimum and then continuing - it is in fact a forwards travel of time.
Apply this to the entire universe and on has the entropy minimums and maximums being the beginnings and endings of time for that universe (or cycle of it).
One further postulates that it may be possible to apply an arrow of time on the quantum scale, due to quantum fields spreading.
That was a nice play on words.
I got into physics by watching these videos but as an end result I believe I worked out exactly how time works... amongst other things. I’m not going to explain it but I will tell you, time is very simple. No matter which direction it goes in you will experience it in exactly the same way. In the sense that people like to imagine “going back in time” that is simply impossible. The direction that time travels in makes no difference at all to matter until you reach the singularity.
The next 100 Years will probably decide what wins:
Science or Anti-Science.
To affect this, i even go so far as to ask random strangers like you: Want some
recommendations? Some Science-UA-camrs to check out, cause the Learning never ends?
The question is fundamentally wrong, were we to actually move backwards through time, our consciousness would also run in reverse. The challenge is to BE AWARE you're travelling back in time, because that demands that your awareness continue to travel forward in time in order to record the new experience of travelling backwards sequentially AFTER your experience of the present. So, for all we know we could go back in time and it would be like a video being rewound, without us ever knowing it.
Yup, you're right our consciousness works because everytime we observe or store information in our brain entropy increases, so if we reverse it we will be never aware of inverse flow of time
Even when you rewind a video,you still play it forward,,and your memory,remembers accordingly,,using the same logic,traveling to the future would be more interesting and you would still be traveling backwards to your moment and remembering,remembering is a past thought of the future,,,good practice for manifestation,,focus is a powerful ingredient in visualization,, imagine all the people living for today 🎶
Imagine if we could find a neutron star, magnetar, white dwarf, anything that curves and magnifies space around itself, to bounce our proverbial ball of eyesight to another ball continually bending until we come back to the point in space where the earth was xxxx years ago and see what was going on?
It would take some very clean space, insane calculations, and likely three bodies well aligned in space and a very finely tuned space instrument to hit every curve just right to get to the next curving point.
Also, could a great solar eclipse with a diffraction star operate as a natural telescope with immense power? Just some thoughts.
@@bobleclair5665 I'm not talking about watching a video being rewound, I'm talking about being in the video which is being rewound. If you play the universe backwards, then you go backwards too because you are part of the universe. To consciously rewind time you'd need to insulate yourself from the effect, to remain travelling forwards in your own time while the universe rolled backwards around you.
Stuart Round: I apologize that I can only read part of your message,I’m still learning this phone
You have once again succeeded in thoroughly blowing my mind.
Keep up the great episodes. I'm back to promoting this channel because it's so good.
There's a little lever in the back you gotta turn...I had to do that when daylight savings time ended
we remember the past until the great alien in his mom's basement says to his friends "ok watch this" and flips the switch to "backwards"
Matt is so cool. He should have a reunion episode with Gabe!
That in the increasing entropy of our universe, our solar system and our Earth and all of the life on it, formed---is startling!
Hi, Matt. Great episode!
I would like to point out something which is very confusing to me in the way the standard argument (which you used here) of the reversibility of time at the microscopic level is carried out. It certainly works out if one restricts oneself to classical physics and quantum mechanics only. However, in our current best microscopic theory, the Standard Model which is a QFT, the chiral electroweak interaction explicitly breaks CP and hence time reversal. For instance this means that the scattering of 2 electrons shown in the video will not actually look the same under time reversal. Yes, this is a very small correction in this particular example, but it is very real. So doesn't this mean that the time-reversal symmetry is actually broken at the microscopic level? If this breaking has anything to do with the cosmological or thermodynamic time asymmetry would be another very interesting question.
What my friends watch on yt: memes
What I watch on yt: _how to reverse time_
friends r dumb lol
You describe how you watch videos to reverse time in a meme. MINDFREAK!!
this is wonderful. please make more episodes.
That’s the most brilliant way to end with “space: time”
Sounds like Panic at the Disco song, I'm in.
Bruh, you are the chosen one to teach us this.
One physics God watches another
Nice to see you here
Wait which song???
(ツ)_/¯[ ! ] u forgot this
I think it’s interesting to note that if “time” could be reversed in this way (the exact reversal of the direction of motion of every particle), for our actual universe, that our experience of time, or anything for that matter, would remain unchanged. Memories would simply be undone going one way, as opposed to being created going the other. The latter way being the way we would think we’re going regardless of which way we were actually going. That is, the way we do think we’re going.
P.S. that is of course, provided that specific experiences and memories depend on patterns of subsets of those configurations of particles...
@Thomas Shelby I just wanted to be explicit about an underlying assumption. I’m not hung up on subjective experience, but, I’m not about to pretend I can explain it either. And the point of my comment does depend crucially on what it really is.
@Thomas Shelby being clear about your assumptions and open to the possibility that it is incorrect is good actually. We don't know how qualitative experiences appear to emerge from quantitative matter. It's best to be open to whatever the data and philosophy come to
Great video! You guys do a fantastic job.
Perfect ending segment.
I'm always looking forward to seeing how you are gonna smuggle in "space-time" in the end, but this one was fantastic! :D
Isn't there another cause of the arrow of time, with a combination of CPT symmetry and the domination of matter over antimatter?
“Time’s arrow neither stands still nor reverses. It merely marches forward.”
I'm glad I made time to watch this.
So excited for time!
Flash is gonna be so mad at you for reversing time.
And yet people with stocks in Macromedia will be chuffed. Will have been chuffed. Are going to be chuffed. Are looking forward to past gains. gotoAndPlay(1).
He can moonwalk real fast then :D
HEHEEE!
Just a thought pertaining to us not experiencing time backwards: If the block universe idea is correct and "all time exists all the time" then it might be like this; a 'brain backwards in time' wouldn't be aware (if at all) the same way a 'brain forwards in time' would be. A brain (or person/conscious awareness) going backwards in time would be losing information instead of gaining it, becoming less and less complex. There would be no perceivable change in the universe from that viewpoint and there would be no awareness of the information that is lost going backwards in time since it 'hasn't happened yet' from that viewpoint. We can't analyze/experience a life that exists in reverse, there's no "new" information to build an understanding of it. So perhaps we do exist in time in both directions but can only be aware of one direction. :P
@@kirkhamandy True, true. I just want to point out that I'm in no way an expert in theoretical or particle physics or any other area of science for that matter, just a fan (before we get flamed for thinking outside of the box lol). If the block universe is real and all time exists all the time, then space-TIME is just a structure and every point in time is always being experienced. No matter where you start it always unfolds one way. OR, maybe consciousness is more fundamental like some scientists/philosophers think (shoutout to David Chalmers). Maybe it 'moves' through the structure that is spacetime, like a wave over the beach.
@@kirkhamandy Lol, I'm sure even Einstein rambled before he came up with the most well known equation. These are fun topics to speculate/ramble about. If we liken the record and record player to the block universe then technically the stylus is interacting from the outside and we could call that consciousness. I've always thought that consciousness was a fancy way of saying awareness and at the most basic meaning of that word even fundamental particles are "aware" of each other or they wouldn't react to one another. Sort of like the one-electron universe idea, I've wondered if consciousness was the same way. It's 'all one'. I mean most people agree that consciousness is a first person experience of the world. The lenses we experience the world through are unique but that first person viewpoint isn't. It's just awareness, made more or less complex based on the thing that's aware. So if the stylus is an analogy for consciousness then perhaps it's a single thing moving over the unique groves of the record. The stylus doesn't experience the entire record at once, just the point on the surface of the record it touches. So "one moment at a time".
@@kirkhamandy @Creamy Pasta I think, in this analogy, there is no stylus on the record. No point in the block universe, or point along the record, is a special "present". A consciousness that traces a path backwards through the universe, unthinking thoughts and unmaking memories as time proceeds backwards, seems like it's just another, kind of trippy way of looking at our forwards-facing existence. And I'm not sure what it would even mean to look at a consciousness in the present, if we decide to pick a slice of the block universe as our present. Seems like a question for someone more educated on the subject than me.
@@kirkhamandy yeah, it is enough of a hard question already, what the heck is the present to start with.
I guess it might not have anything to do with consciousness because, at least so I think, we don't need to be aware of two events in space-time for them to be either able to interact with each other or not. Perhaps it's similar to electric potential and you need to pick a region in the block universe, within a certain distance from a point within the region it's "the present/past/future" and it doesn't make sense otherwise.
I can't think experience it how we do, though.
Let's not get too worried on how educated we are on the subject as people are replying. Not remembering the future because it hasn't "happened" yet is the question. If time was reversed we would be "flinging away memories" but through what mechanism? It seems that causality has a definite arrow to me. If time ran backwards what cause would there be to un-write a letter for instance? Or the pen to float up on to the desk after it was dropped? I'm probably missing something but tendency for nature to find things "energetically favourable" like apples falling from trees shows a clear prefence for an arrow of time to me at least. Love to hear what you guys think?
I LOVED what you said about creating an illusion of understanding. I've seen so many people use words they don't understand to create a total BS argument....
Finally, a video that mentions that entropy increases in both directions of time. The good old explanation of "entropy is more likely to be higher on the next time instant" did not explain the arrow of time; the explanation was rather circular.
I feel like a distinction should be made between “travelling back in time” and “experiencing reverse time”. It’s safe to say that a majority would understand the first statement as “you start from point A in time (your present) and then you somehow magically get transported to a point in the past (let’s say ancient Egypt), allowing you to experience the universe from that point on, however, you are still experiencing time flowing in a *forward* direction”. The second statement implies that some magical force happens and you now start living your life “time-reversed”; like the egg un-splattering, but for everything in existence. The question which then comes to mind (or came to mind, or *will* come to mind?) is this: would we notice any difference?
"What if we are the time reversed universe, maaaaaan?"
I think the human mind only works forwards, because it is not exactly "located" somewhere in spacetime, it is "embedded" in the sequence of brain states from initial to final. Even if time in our universe actually moves in reverse, I believe we would still experience time moving forwards.
The spacetime closeout was fantastic this time guys. A+ Stay well out there everybody, and Jesus Christ be with you friends.😊
Very eloquent explanation for ism avoidance!
I understand the QED joke now!!!
Thanks, Calc III professor, for telling us how to end a proof.
If we consider antimatter as matter going backwards in time and add it to the symetric universe you talked about at the end of the video. Could't we deduce that there's where all the missing antimatter went? A perfectly symmetrical universe made out of antimatter.
Antimatter isn't matter going backwards in time though. It's just fermions with the exact same properties with one difference: the charge is opposite. It is a possible explanation, but it also wouldn't really describe why we still observe antimatter (albeit in small quantities) in our universe today if all of it has gone to the mirror universe nor would it explain why some of it is left behind.
@@ThatCrazyKid0007 I guess it wouldn't answer everything related to the topic as is but nevertheless it's an intresting way to answer the matter to antimatter disparity.
@@facundosciacca4456 There was a recent study that suggested that there is more asymmetry between neutrinos and antineutrinos than was initially expected and it hinted at a possibility that the discrepancy is thanks to asymmetries in neutrinos in the early universe. An article is up on Quanta magazine. So it is one of possible solutions yes, but there are others as well.
Love the old Matt for 1 second. Imagine how much that Matt will know. Time invariance is one of the most fascinating concepts. I think many answers lie here but so difficult, if not impossible to probe.
The point about entropy flow actually being independent of the direction of time in the block model was a fascinating clarifier I was not aware of. Mind boggling.
I've never heard such a succinct explanation of the reasons for using "labels" to describe something. They are useful if everyone understands what the label represents, and not so useful in describing the variations of that label. It's similar in that way to any other word with one or more complex definitions.
This is truly codified as a fascinating, scintillating, and ultimately engaging video. One could say it is timeless in its effect. Kudos to PBS Space Time again!
Off topic a bit, but here's a question for anyone to ponder.
When black holes and neutron stars merge, their mass goes down due to gravity waves carrying away some of it. But if two neutron stars have a certain number of neutrons, then how does 1 + 1 not equal 2??? Where do some of the neutrons go? And how? It seems that matter is made of gravity waves.
December 4th, 2020. Consider this my scientific paper on the nature of all matter.
And the time was 1:04 AM Central Time.
And electromagnetic waves would also be made of tiny gravity waves, though they would not just be micro versions of the macro-scale gravity waves.
Hey, quick question:
If the arrow of time can be reversed, and the equations work exactly the same to describe a universe in rewind - being this true for quantum mechanics to general relativity, doesn't this mean that we are stating that the universe is subject to absolute causality? And extending this to the maximum, doesn't this mean that ultimately there is no free will (thoughts are chemistry at the end of the day, and chemistry is subject to physics)?
It would be great if anyone could help me understand :)
Thanks!
They just did a video on this! ua-cam.com/video/RY7hjt5Gi-E/v-deo.html
Also, he answers a question from the mentioned video at the end. And that should answer your question too.
In short: yes, then the universe can be considered fully determined, but it doesn't matter because from inside the universe one can't find a universal* pattern to predict what happens next, so there always remain things that appear random from inside.
*universal meaning that you can predict everything at infinite precision.
@@userNULL Missed it, thanks!
Here's what I think is a plausible (though admittedly far-out) hypothesis related to this based more in a theory of mind than physics: There is, in fact, no free will. The universe is completely deterministic. And the perception of time's unidirectional flow is a result of the ego's need to preserve its sense of agency. If we were able to perceive time all-at-once like the other three dimensions, the ego couldn't possibly survive. It is dependent on the premise that it is in charge, that it is directing its own actions. This may be why people under the influence of psychedelics or in deep meditative states where the ego's defenses are compromised if not completely overrun experience time in very different ways than people experience it otherwise.
@toaritok If we're going into this territory, I'd like to suggest a couple refinements:
First, I think we need to be careful about distinguishing "mind" from "brain." You are your mind. (Or rather a product of your mind, I'll come back to this.) Increasingly I think experts on cognition are finding the mind isn't just situated in your brain. The brain is a huge (and likely most important) part of your mind. But cognition may well be distributed across (and even externally to) your nervous system. (See the 4E model of cognition for more.)
Second I think we also need to establish that "you" are not your mind. "You" are a product of your mind. Our sense of self, of being something distinct from the rest of the universe, our ego, arises from the mind. It is not the mind itself. Peak experiences (either spiritually or chemically induced) can obliterate the sense of self while the mind continues to operate at very high levels. To paraphrase some Buddhist wisdom, "you" are an emergent property of the mind. Not the mind itself.
This is the most fascinating one yet. Pls continue! Maybe will explain why when no longer 'tied to fabric of space-time' one can take on form of youth. So many questions.
Absolutely Epic. This is a fantastic meeting place.