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Curious to know if time is fundamental to nature, or just an illusion?

We measure time by observing physical changes, increasing or decreasing disorder.When there is no change, there is no perceived time.

UPDATED QUESTION at request of moderator to make it more specific: Is time an independent field, perhaps attributable to specific particles, like mass or electromagnetic forces, or time 'simply' a way we track changes in matter (entropy?) relative to each other? - best I can do.

I am not a physicist. Layman's terms please. Thanks.

devoton
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  • This isn't a question that is answered in physics unfortunately. – Charlie Mar 08 '21 at 00:44
  • "Well they were wrong then, weren't they!" - Igor / Young Frankenstein – devoton Mar 08 '21 at 01:03
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    Can You define illusion in terms of physics? If so add in the question and you will get an answer I guess. – Creator Mar 08 '21 at 01:06
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    Time is fundamental to nature, and there are many questions about it on this site. The nature of time is different than you would expect. See What is time, does it flow, and if so what defines its direction? – mmesser314 Mar 08 '21 at 01:30
  • Certainly the question of whether we have one less dimension ("illusory time") is as relevant to contemporary physics as whether we have more (eg: Kaluza Klein)? By down voting and closing, an opportunity was lost to sharpen up the language and answer a relevant question from a perceptive "non-physicist". – Gary Godfrey Mar 08 '21 at 19:25
  • @GaryGodfrey Not being relevant to physics was not the closure reason. – BioPhysicist Mar 08 '21 at 19:55
  • @creator - The "illusion" being the experience of the passage of time if there is no independent field of time, like electromagnetism. Clocks convey time (intervals) but really they measure physical changes. So question is - does "time" really exist, or is it just a way to measure changes in matter. If the latter, then one could imagine infinite duration between discrete moments experienced as brief by a local observer subject to the same local effects. Just a question. – devoton Mar 14 '21 at 03:51
  • I understand illusion but not in terms of "physics".Before illusion you need to define experince in "physics". Even before that you need to define mind in "physics". Humanity is very from there so far. Hope we get their soon. – Creator Mar 14 '21 at 03:53
  • This question pertains to Time as understood in physics, nothing less or more. Experience = the effects of time. Mind is irrelevant because we want to know how time applies to matter, and not how it is experienced or understood philosophically. For sake of argument, consider only the pieces on a chessboard. No humans, no organisms, no minds. – devoton Mar 14 '21 at 04:06

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As near as we can tell, time passes even though we might not be present to observe it i.e., the stratigraphic record and radioactive decay both record deep time which passed long before humans were present to study them. In addition, our best knowledge of the structure of the observable universe indicates that the light now reaching our telescopes from the farthest reaches of the universe has been in transit towards us for billions of years.

If the passage of time is an illusion, it is an intricately contrived one, requiring the active intervention of something so clever as to create fake evidence of its passage convincing enough to fool our best minds for hundreds of years.

niels nielsen
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  • @nielsen - not questioning measured age of universe, but whether "time" is a fundamental component of the universe, regardless of observers. Does the universe need a field called "time" to construct the irreversible pattern of causality that we observe as time? – devoton Mar 14 '21 at 03:56
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Yes, time is necessary to our perception of nature, but to see this I will use a more quantum mechanical view of time.

Historically, 3-dimensional space (or since relativity 4-dimensional space-time) has been the playground for physics. Particles, densities, fields, events all exist at coordinate locations in space-time. After all, you see this vast space with your own eyes and can reach out into it. Many questions follow from this picture. Perhaps there are more than 4 dimensions, perhaps space/time is emergent from "events", and your question of perhaps time being illusory?

However, quantum mechanics is not about objects in space-time. Instead it is about objects (kets) that stand for particles and are in a very large dimensional Hilbert space. The Hilbert space is not "space-time". Representations of the Poincare group act on the kets in the Hilbert space to rotate, boost, and translate the kets by the Lie group parameters $\vec{\theta},\vec{\lambda},\vec{x},t$. The Poincare group acts on its own generators by conjugation such that under its rotation subgroup, $\vec{\theta},\vec{\lambda},\vec{x}$ rotate like 3-vectors, and under its Lorentz subgroup, $(\vec{x},t)$ transforms like a 4-vector. It is the space of the Lie Group parameters $(\vec{x},t)$ that is called "space-time".

Now, suppose you decided to do all the physics transformations $\vec{\theta},\vec{\lambda},\vec{x}$ but no time translation t (ie: no waiting). In other words, there is a subset t of Poincare group transformations you decide not to do. Unfortunately, eliminating time transformations from the Poincare Group does not leave a closed subgroup. For example, if you do a sequence of small translations ($x<<1$) and boosts ($\lambda <<1$) in the same direction, you would discover that you had done a little bit of time translation $t=\lambda x$.
$$ e^{\lambda K}e^{x P}e^{-\lambda K}e^{-x P}=e^{\lambda x E}=e^{t E} $$
So even if you thought you got rid of time translation, the product of other group elements would bring it back.

Here is a less mathematical argument. Suppose you have the object "muon". If you wait about 2.2 usec, it decays (changes into other stuff). If instead of waiting, you did the single transformation of rotation, boost, or spatial translation to the muon, it would not have decayed. Waiting is essential to explain our perception of the muon decaying and is therefore not illusory.

Gary Godfrey
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  • This is way over my head. I have no physics background. But it would be nice to get a general idea why a physicist would think time does or does not exist.

    For example -- if space-time is relative, why not consider that time is perception of relative change. If you and your environment do not change, then there is no time. OR, maybe there is infinite time between changes which can only be experienced as discrete events in a continuum. Analogy: chess pieces are only aware of changes on the board, not the external clock ticking nearby.

     – devoton Mar 09 '21 at 00:27
  • Yes, change indicates time has passed. If you and your environment do not change, then no time has passed ... you have not done the action of waiting. You shouldn't conclude that there no such thing as time. Also, changes in the chess board or movement of the hands of a clock do not cause the chess piece to age and turn to dust. Instead, all things age together as you do the action of waiting. Physicists are also very aware of times arrow. The action of negative waiting can't be done. You can't unwait and watch the dust turn into a chess piece. – Gary Godfrey Mar 09 '21 at 20:11
  • @godfrey - these are good arguments, but the analogy of the chess board refers to state of everything, meaning all constituent pieces of the universe, including conscious observers. By "no change", we mean no changes to observers as well. So my question is whether or not time as fundamental and independent component or construct even exists? The Arrow of Time (irreversability) would refer to the inability to revert matter/energy to its previous state, and not some movement through an independent field we call time. – devoton Mar 14 '21 at 03:27
  • @godfrey - in relativistic terms, wouldnt moving close to speed of light relative to decaying muon go beyond 2.2 usec. Does that say more about relative changes in matter between observer and muon, or more about time? – devoton Mar 14 '21 at 04:20
  • If the chess piece and everything else (including the observer) do not change, then no time has passed. Since change is occurring (as demonstrated by us writing each other), it is useful to have a number that follows the change. Entropy is one such number. Time is another such number that changes as the state of the chess piece and everything else changes. So time "exists" in the sense that it is a useful and needed way to parameterize change ... even better than rotations, boosts, and spatial translations which sometimes don't change when the universe changes. – Gary Godfrey Mar 14 '21 at 19:48
  • @godfrey - thank you - "useful way to parameterize change". I will have to look up those terms: rotations, boosts, translations to get some inkling of how time manifests (or not) at the quantum level. If "no change = no time", then what does that say about approaching speed of light? We are unable to observe change at relativistic speeds due to universal speed limit? – devoton Mar 15 '21 at 00:08
  • Physics text books just start using time without a discussion like we are having. The text book may explain time as what a clock reads. Our "useful way to parameterize change" is a bit philosophical. The Lorentz transformation in Special Relativity explains why the observer on earth sees the spaceship clock going slower as the spaceship approaches the speed of light (but never reaches it, so the clock never appears stopped). – Gary Godfrey Mar 15 '21 at 01:19