# Thread: The nature of time

1. ## The nature of time

I am a biologist with a very limited physics background, but I was standing in my kitchen today and it occurred to me to wonder if time is flowing toward equilibrium with itself. It seems like an idiotic idea because that would imply that time can occur in differing concentrations.

I tried to google it, but any search that has "time," "flow," and "equilibrium" is cluttered with a million irrelevant things, and it sounds like there are people here with a higher concentration of physics knowledge than I. (Luckily your own expertise concentrations will not deplete if some of it flows my way, even though it will require an expenditure of energy, for which I thank you in advance.)

2. More thoughts:
The directionality of the flow of time is dependent on
A. Our perception.
or
B. A relative measure of the entropy in the universe or the amount of expansion in the universe.

But absent our perception and these relative measures, there is no way to determine if the flow of time really exists except as a perceptional construct.

The question in my head goes something like this. When entropy has reached it's maximum and all matter in the universe is at equilibrium, and therefore gravity is at equilibrium, will time still flow?

3. First... I'm not familiar enough with the concept of entropy. my understanding is that it's movement towards chaos. Given this understanding, I'm not sure I understand what gravitational equilibrium is, unless it means things have fallen apart so much that everything is spread everywhere, cancelling out all the gravity. I could probably look up these things, but it's more fun to discuss them.

I can't really answer that question until I know that part of it, at the very least.

4. The idea is that at some point, all matter and energy will be evenly distributed throughout the universe, and as such there will be no more potential energy. If all matter is equally distributed, then should that not also apply to gravitational forces since they are dependent on a concentration of mass?

Now here's the big if...the part I'm purely conjecturing on...based on my non-verified hypothesis that time is flowing toward equilibrium in the same way that energy is, and the second assumption, that the uneven distribution that causes time to need to seek equilibruim is somehow dependent on gravity, that once matter and therefore gravity is equally distributed, time will also be equally distributed, and will therefore cease to flow.

5. When entropy is maximum, time will flow but the future won't be distinguishable from the past the way it is now.

6. Originally Posted by P-O
When entropy is maximum, time will flow but the future won't be distinguishable from the past the way it is now.
So time will flow, but will have no discernible direction. Is that not the same thing as time itself being at maximum entropy?

7. Originally Posted by Sistamatic
So time will flow, but will have no discernible direction. Is that not the same thing as time itself being at maximum entropy?
FYI, I can see and am aware of a great degree of circularity in my reasoning here...and that is what I'm trying to break out of...

8. Originally Posted by Sistamatic
More thoughts:
The directionality of the flow of time is dependent on
A. Our perception.
or
B. A relative measure of the entropy in the universe or the amount of expansion in the universe.

But absent our perception and these relative measures, there is no way to determine if the flow of time really exists except as a perceptional construct.

The question in my head goes something like this. When entropy has reached it's maximum and all matter in the universe is at equilibrium, and therefore gravity is at equilibrium, will time still flow?
I'd say A is a philosophical and psychological issue about the phenomenology of time, which whilst reliant on B as a phenomena is in some ways a separate issue to B. The phenomenology of time is less tied to entropy as it is to observing sequences of events as past and present, either categorising them as such, or stating that one time is specifically 'before' another time, or 'after' another time. Given the debate surrounding whether time in this sense actually 'exists' as a coherent entity, rather than a figment of our mental process of reconstructing causality - it doubtful question what kind of conception of time could coherently be linked between our perception and some instrumental variable like entropy anyway, at least insofar as we use it to reconstruct our common language of events.

I think this is especially worth bearing in mind when one considers that both with the application of quantum mechanics and and the relativity of simultaneity dictate that time is illusionary in some sense - albeit it in the latter case replacing it with a different variable in the form of absolute time, that emerges as a result of classical approximations.

Which is to say this might not necessarily be the right question to be asking in the first place. The heat death of the universe (if the concept of total entropy of the universe is coherent in itself - also debatable) could result in a loss in the direction of time - because of the lack reversibility - but would remain as a variable of kinematics, in so far as positions of particles vary as a function of something. And if, as is statistically inevitable, a patch of the universe does reverse itself into a lower entropy state again, or say triggers another inflation epoch, the same variable could reproduce the flow of time in the sense we are used to.

9. I mean, well it's just semantics once you understand that point. Plenty of people would agree with the sentiment.

edit: @syst

10. Originally Posted by Sistamatic
So time will flow, but will have no discernible direction. Is that not the same thing as time itself being at maximum entropy?
Well, in some ways that is dependent what you feel the answer is to the Loschmidt paradox. What you say is correct... if the initial conditions of the universe are the cause of the asymmetry of the universe, then yes... (starting from a statistically low probability state and evolving to which in a family of higher probabilities, but there are problems with this that make physicists loathe to accept it), or something else that breaks time symmetry like CP asymmetry, quantum measurements or the expansion of the universe which would therefore still exist even in a maximum entropic state.

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