Nobody Knows What TIME Really Is. But it might be this...

A good definition of information in physics: "information contained in a physical system = the number of yes/no questions you need to get answered to fully specify the system."

References:

Chapters:
0:00 - Why is time one way but physical laws are not?
2:19 - What is Entropy? Disorder and information
5:29 - Does entropy cause time?
7:12 - What is time? Recorded past vs future possibilities
8:07 - Lee Smolin's theory of time
10:31 - Will time always flow forward? heat death & big freeze
12:33 - Best online course on time

Summary:
In quantum mechanics, it’s just as natural to go forward in time as going backwards. And if you look at a typical Feynman diagram, you can turn the diagram either way. Where does this transition from time symmetry at the quantum level, to time asymmetry at the macro level occur?

To understand its irreversibility, we have to look for other irreversible processes in nature to see if there is any correlation - such as in thermodynamics, Entropy.

Entropy is a measure of disorder, but a more rigorous definition has to do with information. Entropy is related to the amount of information necessary to describe a system. Thus, information is directly tied to entropy. And if entropy of the universe is always increasing, it means that the information necessary to describe the universe must also be increasing.

If we have two gases on the two sides of a chamber and allow the gases to mix, they'll mix together and not unmix. This is a one way process, from an ordered state of two separate gases, to a disordered state of a mixtures. The process evolves from one state to the other, and you cannot go back to the prior state. This is similar to the one way direction of time.

It's important to point out that it is not impossible for the mixture of gases to go back to the prior ordered state. It is a statistical impossibility but not a physical impossibility.

Does increasing entropy cause the forward flow of time? Time and entropy seem to be related. But how do we know one is the cause of the other? If you could reverse time, you would see a scrambled egg going back to being unscrambled.

If increasing entropy was directly responsible for the forward flow of time, it would be logical to presume that decreasing entropy would cause the backward flow of time. The inside of your refrigerator decreases entropy by removing heat. But time does not run backwards inside your refrigerator.

The best definition of time in physics is that time is the process that brings the unknown future into a recorded past via the present. This requires an increase in information because every moment that goes by is recorded as a definite past which are events that have definitely happened. This was not knowledge until it happened. When it happened, it became new information and thus added to the total information in the universe. More information is more entropy.

Physicist Lee Smolin suggests that what distinguishes the past from the present is a kind of knowledge that is gained once indeterminate quantum events consisting of only probabilities in the present, become a classical definite past.

So what seems to separate the past from the present is whether it is knowable or not.The change from quantum indefinite present to a classical definite past is what defines the arrow of time. This points always in the forward direction as the quantum present constantly churns out a classical past.

Note that although it is established that information is related to entropy, both Smolin’s paper and my extrapolation of his paper to information are not established theories, but conjecture.

This means that entropy must have been much lower earlier in time, near the big bang. How did the universe get to this low entropy state at the beginning? If entropy only increases, one hypothesis is that one day the universe will be in a state with no useful energy, only radiation and heat. Then nothing can happen - no physical movement, no chemistry, not even thoughts in brains.
#entropy
#time
#whatistime
If nothing happens in the entire universe, and not even thoughts or consciousness can exist, does time still continue to move forward? I’m not so sure.

[sodea]

my boss explained to me that somehow time is money

[darrellseike]

This is the first I have seen where time, entropy and information have all been tied together into something that makes real sense! Thank you!!!

[HawthorneHillNaturePreserve]

I love how Alvin says he hopes someone watching this video will come up with a new theory of time. That’s cool to think a bright mind anywhere might be able to do this! The possibilities!

[AnthonyCandaele]

From all the physics videos I'v seen on Youtube, Arvin really gives the best explanation on physics!

[nikokoro]

Select your difficulty:
Easy - Arvin Ash
Medium - Sabine Hossenfelder
Hard - PBS Space Time
INSANE - Your lazy college professor

[antonystringfellow]

When you break it down to its fundamentals, everything in the Universe is information.

Gravity, it appears, is not a force, in a field, carried by a particle, but is an emergent phenomenon caused by the fact that time advances more slowly near a massive object. In this situation, you must move downwards in order to be in an inertial frame of reference. From the surface of a massive object, this movement is not possible because the object is in the way (pauli exclusion principle). This resistance is the same as constant acceleration and we feel this as weight. Gravity is an effect, not something fundamental in the same way that there is no such thing as a centrifugal force, rather there is a centrifugal effect.

Seems to me that space and time (or spacetime) are also emergent (effects) with their underlying causes emerging from information. Maybe something like this:

Time: The transformation of a probability into a certaintly (knowledge).

Space: The degree of quantum entanglement or propagation of information.

Just wild speculation on my part but I can't escape the feeling that the only thing that is fundamental in this Universe is information and everything else is just emergent.

[nikokoro]

12:25 "My dream is that a someone watching this video right now, comes
up with such a theory, and changes the world."

Just you wait, Arvin. Just you wait.

[Debanil]

You are the best expository speaker I have encountered ever. Also the passion that oozes out of your expression is really motivating. Keep it up. ♥️

[craigo]

Arvin you are my favourite 'gangsta' science educator. You always stay open minded and never arrogant, and always clearly explain the sides to any scientific debate, rather than taking a dogmatic position. I experience this as very respectful. Thanks for another great video.

[Crescent_Audio]

In the 4d “block universe” model, all instances of time exist simultaneously in a sort of loaf of bread where a particular instant would be represented by a slice. We live inside the loaf and experience out 3d reality second by second but a being who could see the entire loaf at once could see our entire timeline at once.

[missinformed]

I watch a lot of videos about physics and very few express ideas with such clarity and patience. Thank you Arvin for all you do to help people get it. In addition to quality productions you are gifted as a presenter. Well done, excellent and appreciated!

[eric-jandenooyer]

My current explanation/belief about 'time' is that it's simply a measurement of change (absolute change, local change). Because all methods of measuring time involves some means of measuring a physical object that has a changing position in 'space' (e.g., the sun, a pendulum, the resonance induced by an oscillating field). And so that would mean that 'time' cannot exist without also having a 'space' for things to move through; ergo, 'spacetime'.

Further, my belief is that there's only one current moment in time (though things that happen non-locally do take their time to be communicated to other locations). And so, this present single moment is the result of all prior cause-and-effects, and also carries information forward that brings upon some new cause-and-effects (though some events can have their causes chosen, which then offers a different outcome than would have been otherwise predestined). So then, as change happens, the previous circumstances become history/information, and that historical fact cannot really be erased/reversed (though it can be forgotten). Simply stated, a bell cannot be un-rung, and so time behaves somewhat like an absolute value function.

But yet, if we don't move through space, we are still moving through time. So, are we falling through time? Or, is something always moving/changing even when it doesn't look like it? And then, if something moves through space fast enough, time actually stops and it becomes as thin as zero, but not negative (to the external observer anyway, if they can measure it). Essentially, dimensionless and timeless. In between these extremes, whenever we move through space, we're effectively taking a shortcut through space & time. The faster we go, the shorter the path becomes (both in space and time). It's like seeing every movement as traveling through a wormhole, particularly when you think about those muons coming in from the upper atmosphere.

[VedanthB]

This explanation satiated my curiosity. I was quite discontent with entropy being equated with time. But this explanation clears it. Thank you for making this video!

[danhaire]

Three thoughts.
1: What if time does run backwards and we don't know it? Time could be switching directions all the time, and if everything runs backwards, including our thoughts and memories, then we would never know it was running backwards at all.
2: I really like the idea that increasing entropy is what defines time. 'Time', as a human word, really represents our perception of this constantly changing state of the universe. It is only because we have consciousness and memory that we can perceive the change from one state of the universe to another state a moment later, and it is only because of our intelligence that we can reconstruct what past states of the universe have been.
3. I agree with your conclusion that in the end, when all energy in the universe has been equalised (so there is no more stored potential energy anywhere, be that gravitational, electrical, heat vs cold or whatever, then there would be no more energy exchange anywhere in the universe. Then, all future states would be the same as the present state, so time would be irrelevant.

So I guess my conclusion on this one is that the universe is constantly moving from one state to another, and overall entropy is increasing. But time itself, is an intelligent being's perception of this change facilitated by consciousness and memory. Time only matters because we are here to witness it. If we weren't here to witness it, what would it matter?

[atribhattacharyya]

You are a wonderful teacher..Thanks for all the brilliant knowledge you pass by towards your viewers..Keep up the great work..

[Xeexie]

Love your videos Arvin, you really do have a special talent for explaining really complex topics in a clear and understandable way.

[AfricanLionBat]

I'm glad you mentioned entropy reversal isn't technically impossible but rather statistically unlikely.

[bobblacka]

Arvin Ash is an absolute genius. Best explanation of time ever. The reason Newton's laws of motion work at all is because they describe what happens after the collapse of the wave function. Stated another way, Newton's laws describe the position of a particle accurately only when the probability wave function is tightly squeezed together, i.e. with little variation. Where Newton's laws fall apart is when the probability function flattens out, so the probability function is now spread out and not as well defined, for example where there are competing gravitational fields. And that is why Newton's laws predict the future in some systems pretty well, but fail in other instances. Time has nothing to do with it. The probability function is everything.

[lmiones]

... and there is more: concept of Time depends on the Theory we are considering ... We sometimes omit saying that entropy is a probabilistic average of the quantity of information (like "mass of structure")... We should not worry thermic death: The Universe gets more complex (networks, vibration and resonance are key concepts to understand the quantum world) A stimulating presentation, thank you!

[jatinbangar]

I think your channel is the BEST. I follow multiple physics channel but you have this insane ability to explain everything so very clearly. Fantastic channel!