<p>If you count time by number of events that have occurred, then lower temperature in general slows down time. However, time in physics is usually taken as a coordinate on the spacetime manifold and is basically a distance: even if absolutely nothing happens in a spacetime region it makes sense to say that time passes.</p>
<p>In a universe where temperature rapidly decreases there might be a finite number of classical events happening. However, quantum mechanical events like tunnelling still do occur even at <span class="math-container">$T=0$</span>. So random fluctuations will occur, and there would be new events. To add to this, accelerating expansion causes the horizon to emit radiation at a very low but nonzero temperature, the de Sitter temperature.</p>

CC BY-SA 4.0
2024-06-05T14:55:09.047Z
Thank you, so the probability that statistically we are more likely Boltzmann brains (by a lot) holds as time passing is not related to the number of events and is still "progressing" even though nothing happens, right?
Radoslaw Garbacz
CC BY-SA 4.0
2021-03-24T18:08:42.333Z
2021-03-24T18:08:42.333Z
Anders Sandberg
<p>A question about the Boltzmann brains assuming heat death of the Universe.</p>
<p>It is said that if so, than it's more likely were are such constructs instead of having reality as we perceive it, however it seems to me that it makes certain (very strict) assumptions about the time, which do not seem proven, e.g. if the time is emergent and related to the entropy change, then the colder the Universe gets the slower passage of time, which would change the probability calculation (e.g. what if time follows on average 1/x), however another variable is that the space itself would get much bigger - would the space itself be enough to still get Boltzmann brain probability higher? How about the accelerated expansion of the Universe due to &quot;dark energy&quot; - would it &quot;dilute&quot; time the same way?</p>

CC BY-SA 4.0
2021-03-24T18:07:55.393Z
Honestly I do not know what question you are trying to ask.  Please note also this is not a discussion-type forum so questions need to have enough focus to generate a well focused answer that can be voted on by the community.
StephenG - Help Ukraine
<time-dilation>
Boltzmann brains - probability
Radoslaw Garbacz
# Boltzmann brains - probability

(Asked by: username_0 on 2021-03-24)

A question about the Boltzmann brains assuming heat death of the Universe.

It is said that if so, than it's more likely were are such constructs instead of having reality as we perceive it, however it seems to me that it makes certain (very strict) assumptions about the time, which do not seem proven, e.g. if the time is emergent and related to the entropy change, then the colder the Universe gets the slower passage of time, which would change the probability calculation (e.g. what if time follows on average 1/x), however another variable is that the space itself would get much bigger - would the space itself be enough to still get Boltzmann brain probability higher? How about the accelerated expansion of the Universe due to "dark energy" - would it "dilute" time the same way?

**Tags:** time-dilation

> **Comments:**
> **username_1**: Honestly I do not know what question you are trying to ask.  Please note also this is not a discussion-type forum so questions need to have enough focus to generate a well focused answer that can be voted on by the community.  

---

## 1 answers

### Answer by username_2 on 2021-03-24. Score: 2 | Accepted answer

If you count time by number of events that have occurred, then lower temperature in general slows down time. However, time in physics is usually taken as a coordinate on the spacetime manifold and is basically a distance: even if absolutely nothing happens in a spacetime region it makes sense to say that time passes.

In a universe where temperature rapidly decreases there might be a finite number of classical events happening. However, quantum mechanical events like tunnelling still do occur even at $T=0$. So random fluctuations will occur, and there would be new events. To add to this, accelerating expansion causes the horizon to emit radiation at a very low but nonzero temperature, the de Sitter temperature.

> **Comments:**
> **username_0**: Thank you, so the probability that statistically we are more likely Boltzmann brains (by a lot) holds as time passing is not related to the number of events and is still "progressing" even though nothing happens, right?  

---

