In terms of the "big freeze" predicted as the end of the universe....

It may not be the "end".... time may keep going.....

19 minutes ago, julius2 said:

In terms of the "big freeze" predicted as the end of the universe....

It may not be the "end".... time may keep going.....

Is there any credible discussion of time stopping in the heat death scenario?

30 minutes ago, swansont said:

Is there any credible discussion of time stopping in the heat death scenario?

Well ... possibly.
Once maximal entropy is reached, and the universe is essentially at equilibrium, no processes can go forward or backward.
Sure, there will be some small oscillations about the equilibrium state, because of QM, but how would you measure the passage of time ?
( if this wasn't off topic, it would make an interesting discussion )

Edit - I see you fixed that problem. Thanks.

Edited June 10Jun 10 by MigL

4 minutes ago, MigL said:

Well ... possibly.
Once maximal entropy is reached, and the universe is essentially at equilibrium, no processes can go forward or backward.
Sure, there will be some small oscillations about the equilibrium state, because of QM, but how would you measure the passage of time ?
( if this wasn't off topic, it would make an interesting discussion )

I can see how you couldn’t measure time in that case, but is time dependent on that? Does time pass if there’s nothing around to experience it?

Interesting question.
But keeping in mind that ALL processes would be halted, and QM oscillations could go backwards or forward, there would be absolutely no way to detect the passage of time.
If time is redundant, would it still exist indepenently ?

2 hours ago, MigL said:

Interesting question.
But keeping in mind that ALL processes would be halted, and QM oscillations could go backwards or forward, there would be absolutely no way to detect the passage of time.
If time is redundant, would it still exist indepenently ?

Are quantum oscillations well understood?

If so ,is the nature of quantum oscillations a key to any question as to whether or not "time" might cease to exist and , like Samsung pull down all of "creation" with it and prevent its reemergence in any form at all-copper fastening a certified "death" of everything that was or could be ?

I have read that quantum fluctuations can be visualized collectively as a kind of "foam:.

Is there any structure of any kind to this foam or are we talking about a never ending vista of randomness?

I wasn't thinking of Quantum fluctuations as typically understood, but rather fluctuations around the final equilibrium of the maximal entropy universe.
But you do bring up a good point.
The Quantum fluctuations due to the Uncertainty Principle cannot be ignored as they are a necessity of Quantum systems.
The energy-time uncertainty dictates that their deltas must be greater than , or equal to, h-bar/2.
IOW, 'borrowed' energy for the fluctuation must be re-paid within a specific period of time.
As this is a process that even maximal entropy cannot stop, time IS still needed.

5 hours ago, julius2 said:

In terms of the "big freeze" predicted as the end of the universe....

It may not be the "end".... time may keep going.....

I just don't buy the famous Second Law "Heat Death" scenario which is what I assume you mean by big freeze.

This was originally introduced long before we had even a proper idea of molecules let alone sub atomic particles and quanta.

It requires a continuous distribution of energy, which cannot be achieved with our current table of particles and forces.

3 hours ago, MigL said:

fluctuations around the final equilibrium of the maximal entropy universe.

Unless you're suggesting that growth of the scale factor will decelerate to zero, can there ever be a maximal entropy? (IIRC, AOTBE, entropy grows proportionally to ln a)

Ultimately, matter and energy may become so thinly spread out that particle interactions rarely occur, and each particle tends towards its own isolated little ground-state universe of entropy zero (in its own frame of reference). But then, many if not most of these will be photons which don''t experience time anyway.

As for the leptons, while they are able to oscillate between their various flavours/states, they must still be little clocks ticking away for eternity, aren''t they? Which suggests that time will at least continue somewhere. Even when their nearest neighbours have been accelerated away to such an extent that their light cones no longer intersect.

It all begins to sound a bit Hilbert's Hotelish, but I've yet to see anything paradoxical in an asymptotic approach to zero local entropy density at infinite time/global entropy.

Not sure that 'equilibrium' has any meaning at such infinitessimally low densitities. No collisions: no equilibrium.

It is interesting to know about the "heat death"....... but what will happen to "living things".............

1 hour ago, julius2 said:

It is interesting to know about the "heat death"....... but what will happen to "living things".............

Once protons start decaying at a minimum of 10³⁴ years, I can't imagine any living things to be around ...

16 hours ago, sethoflagos said:

Unless you're suggesting that growth of the scale factor will decelerate to zero, can there ever be a maximal entropy?

Omce our galaxy is the only gravitationally bound system in the observable ( causal ) universe, how would you determine growth of the scale factor ?
No, I've already had second thoughts about the situation in a previous post.
Oscillations between energy levels of fundamental particles ( no decay ) would be governed by the energy/time uncertainty relation, making time an essential factor.

3 hours ago, julius2 said:

It is interesting to know about the "heat death"....... but what will happen to "living things".............

They will suffer an ''absence of heat" death. No more stars (or radioactivity etc.) to keep local temperatures much above absolute zero. Chemistry ceases to be a thing. Or at least chemical reactions grind to a halt. No food; no respiration; no metabolism.

2 hours ago, MigL said:

Omce our galaxy is the only gravitationally bound system in the observable ( causal ) universe, how would you determine growth of the scale factor ?

Periodically launch probes into deep space and carefully watch their red shift? Long term experiment, but what else are you going to do for a googol-year?

20 hours ago, sethoflagos said:

Not sure that 'equilibrium' has any meaning at such infinitessimally low densitities. No collisions: no equilibrium.

Not even clear on how photons can in any sense be real if they never interact. "Particle" seems like a term of convenience for some transfer of energy/momentum, not some timeless thing flying through eternity without a transaction. (I'm also suspicious of oscillating leptons in isolation, but that's because I stupidly (densely?) don't grasp the whole particle-as-ontic thing) "Here there be dragons."

2 hours ago, TheVat said:

"Particle" seems like a term of convenience for some transfer of energy/momentum, not some timeless thing flying through eternity without a transaction

Photons of the CMB have red-shifted from 3500^o to 2.7^o in 1.4x10¹⁰ years.
Once all the stars burn out ( say 10²⁰ years ), how long do you think it will take for any of their emitted photons to red-shift to an energy where they can no longer excite fundamental particles? Another 10¹⁰ years ?
What will they be then ?

At that time, the only source of useable energy might come from proton decay ( assuming it actually happens ).

4 hours ago, TheVat said:

Not even clear on how photons can in any sense be real if they never interact.

The thermodynamics of a 'photon gas' is well established and quite real. Very similar to the thermodynamics of a molecular gas, but slightly different equations: (there is no conservation of photons etc.)

On second thoughts, that's not what you're saying is it. You're referring to that unheard falling tree in a forest malarkey. Never really gone in for that viewpoint. Bit too solipsistic for my taste.

7 hours ago, TheVat said:

Not even clear on how photons can in any sense be real if they never interact.

My understanding is that anything that can be measured is considered real.

10 hours ago, MigL said:

Photons of the CMB have red-shifted from 3500^o to 2.7^o in 1.4x10¹⁰ years.
Once all the stars burn out ( say 10²⁰ years ), how long do you think it will take for any of their emitted photons to red-shift to an energy where they can no longer excite fundamental particles? Another 10¹⁰ years ?
What will they be then ?

At that time, the only source of useable energy might come from proton decay ( assuming it actually happens ).

In 10^10 years there will still be radioactive nuclei around. e.g. Rb-87’s half life is ~50 billion years. The list of isotopes with billion-year or longer half lives has quite a few members

https://en.wikipedia.org/wiki/List_of_radioactive_nuclides_by_half-life

Sure, but the time span I mentioned is 10⁴⁰ years.
How much Rubidium 87 will be left after Ten Thousand Billion Billion Billion Billion years ?

12 hours ago, MigL said:

What will they be then ?

Yes, good question. Part of my struggle with "particle."

10 hours ago, sethoflagos said:

On second thoughts, that's not what you're saying is it. You're referring to that unheard falling tree in a forest malarkey. Never really gone in for that viewpoint. Bit too solipsistic for my taste.

No solipsism here, I just don't understand what particles are, betwixt emitter and absorber, so I'll have to just SUAC. 😬

6 hours ago, StringJunky said:

My understanding is that anything that can be measured is considered real.

Yes. A dying universe of unmeasured photons. They could, in principle, be measured. But only in a lower entropy universe. At least where a Rubidium 87 nucleus can absorb one?

3 hours ago, MigL said:

Sure, but the time span I mentioned is 10⁴⁰ years.
How much Rubidium 87 will be left after Ten Thousand Billion Billion Billion Billion years ?

I missed the 10^20, but you’ve got Te-128 at 2.25 x 10^24

You didn’t mention 10^40, to my thinking. “Another 10^10 years” suggests addition, not multiplication.

On 6/12/2026 at 10:31 PM, swansont said:

In 10^10 years there will still be radioactive nuclei around. e.g. Rb-87’s half life is ~50 billion years. The list of isotopes with billion-year or longer half lives has quite a few members

https://en.wikipedia.org/wiki/List_of_radioactive_nuclides_by_half-life

My understanding of entropy is that it is a measure of increasing randomness

I also see entropy as a kind of unfolding

53 minutes ago, julius2 said:

My understanding of entropy is that it is a measure of increasing randomness

I also see entropy as a kind of unfolding

I suppose I'm fighting a loosing battle against the general misunderstanding of Entropy partly due to snappy soundbites like this.

No offence meant Julius, but at the very least the soundbite should read entropy is a measure of 'randomness' not 'increasing randomness'.

But then that leaves you seeking a definition of randomness, which simply replaces a short difficult word with a longer difficult one.

Neither have mean much meaning without reference to the system to which they refer.

The Wiki article is quite good, if you understand the Mathematics, but note carefully the caveats.

https://en.wikipedia.org/wiki/Boltzmann%27s_entropy_formula

This reflects the original statistical entropy function introduced by Ludwig Boltzmann in 1872. For the special case of an ideal gas it exactly corresponds to the proper thermodynamic entropy.

For anything but the most dilute of real gases, S B leads to increasingly wrong predictions of entropies and physical behaviours, by ignoring the interactions and correlations between different molecules. Instead one must consider the ensemble of states of the system as a whole, called by Boltzmann a holode, rather than single particle states.^[10] Gibbs considered several such kinds of ensembles; relevant here is the canonical one.^[9]

There is more than one way to interpret entropy.

Further there are systems for which entropy does not increase.

The correct interpretation is that entropy can never decrease, it either always increases or remains the same.

Furthermore the equations give no measure as to how long it may take for the change to occur.

You require additional theory (equations) to attempt an answer to that.

Edited yesterday at 08:51 AM1 day by studiot

On 6/11/2026 at 4:19 AM, swansont said:

I can see how you couldn’t measure time in that case, but is time dependent on that? Does time pass if there’s nothing around to experience it?

If there is "nothing", then there is "nothing".

That is, it is possible that "time" itself was never known, and never existed.

It is like tomorrow earth = 57. Just a number in space. Everything vanished.

But what is the chance anything on the planet would guess that this would happen......

Bizarre states....

7 hours ago, julius2 said:

My understanding of entropy is that it is a measure of increasing randomness

I also see entropy as a kind of unfolding

As studiot notes, it’s not really this. Entropy tells you about how useful your energy is, i.e. what can be done with it.

1 hour ago, julius2 said:

If there is "nothing", then there is "nothing".

That is, it is possible that "time" itself was never known, and never existed.

It is like tomorrow earth = 57. Just a number in space. Everything vanished.

But what is the chance anything on the planet would guess that this would happen......

Bizarre states....

Time isn’t a physical substance, so I don’t see how something vs nothing applies to it. And we are aware of time right now, no how could it have never existed in the future?

2 hours ago, swansont said:

As studiot notes, it’s not really this. Entropy tells you about how useful your energy is, i.e. what can be done with it.

Time isn’t a physical substance, so I don’t see how something vs nothing applies to it. And we are aware of time right now, no how could it have never existed in the future?

We are aware of time right now.....

Like I said...."bizarre states"

E.g. all registered entities on the planet will have forgotten that time was existing

2 hours ago, swansont said:

As studiot notes, it’s not really this. Entropy tells you about how useful your energy is, i.e. what can be done with it.

Time isn’t a physical substance, so I don’t see how something vs nothing applies to it. And we are aware of time right now, no how could it have never existed in the future?

Ok, entropy is probably about the degree of randomness. Ie. It doesn't necessarily have to increase.

In terms of unfolding this probably relates to spacetime and the big bang again.

One error I realised recently is the layman view - there is space and our planets and stars developed within it.

Instead everything started at the singularity and is moving outwards. And I guess it would be doing this today.

Allowing the general relativity to be valid.