There is something about the articles that Ethan Siegel writes for Forbes that don’t grab me. It might be that I’m not in the target demographic — he often writes about stuff I explored long ago. I keep an eye on him, though, because sometimes he comes up with a taste treat for me.
Such as his article today, No, Thermodynamics Does Not Explain Our Perceived Arrow Of Time. I jumped on it because the title declares something I think many have backwards: the idea that time arises from entropy or change. Quite to the contrary, I think entropy and change are consequences of time (plus physics).
Siegel makes an interesting argument I hadn’t considered before.
His argument isn’t quite as bullet-proof as he seems to think it is, but it’s pretty good, and I think it gives serious weight to the idea that time is fundamental.
Which is something I believe to be true.
Immanuel Kant thought time was a fundamental intuition underlying our perceptions, and it’s certainly true that we can’t think without implying time. The notions of now, before, and after, wind through our most basic thinking.
I think this speaks to the fundamental nature of time. It’s a fundamental intuition because it’s a fundamental property of reality.
If entropy makes the temperature of a room even out, then a Thermodynamic Demon can use its powers to confine warmer air to one side of the room and cooler air to the other. But it’s been shown that the Demon expends energy doing this, so the total entropy of the system increases (as required by the Second Law of Thermodynamics).
Siegel points out that, if you live in the room, and don’t know about the Demon, from your point of view, entropy decreases.
But time still passes for you!
Therefore, the argument goes, entropy clearly does not produce time.
The counter-argument might be that, because the total entropy of the system increases, time emerges (from that entropy) and applies to the whole system, including the inner low-entropy one.
With regard to the universe, since its total entropy is increasing, time in the universe emerges from that and applies to all sub-systems.
The weakness in the counter-argument might be that, if time really does emerge from entropy, shouldn’t there be some difference in how time works in the low-entropy environment?
Why does the total system govern all time within the system? This seems to imply the overall system “drags” any subsystems along with it and that only the total entropy matters.
Any of this could be true, but it seems simpler to take time as axiomatic and fundamental.
Siegel also mentions classic examples of entropy in action, the scrambled egg, the coffee and cream, the hot drink and ice cube, and points out that, even if you apply the right forces to reverse these, time still runs forward for you.
You can’t make time go backwards by reversing entropy.
Whether it’s the beginning of the universe, when entropy was astonishingly low, or the distant future, when entropy is high, time still ticks by for every observer at the same rate: one second per second.
For me, that’s always been a key argument. Time may be relative between observers (and so what), but time is always the same for any observer.
It ticks past at one second per second. Always. For everyone.
To me, that’s pretty fundamental.
Of course, one can still insist that entropy overall increases and therefore time emerges from that.
Time is one of those great mysteries — one of those things we all experience but which we don’t really understand what the heck it is.
But I think Kant was right, and I think Siegel has a point.
How about you?
Stay thermodynamic, my friends!