Comment by dleary
It sounds like you have basically given a formulation of Maxwell’s Demon https://en.wikipedia.org/wiki/Maxwell%27s_demon
“All you have to do is harvest the hottest/fastest molecules” pretty much describes exactly what Maxwell’s Daemon is.
Now, you can see from the Wikipedia page that there is at least some debate about the topic. But, I think that generally, most physicists think that Maxwell’s Demon would violate the 2nd law, and that the 2nd law is a real limitation.
It certainly sounds like this device would violate the “metaphysics” definition of the 2nd law, “entropy always increases”. Because it sounds like it’s harvesting energy from heat for “free” (not actually energy from nothing, not violating conservation, but free in that you are not paying for the loss of entropy by increasing entropy somewhere else, which is typically “required”).
I am not a physicist, and in my layman’s understanding, I have always felt that the 2nd law seemed fishy. A lot of other people do, too. It’s called “a scientific law”, but it feels more like a philosophical “principle”. It feels different than, for example, “the law of gravity”.
But, this invention, if it is not a hoax or error, sounds world changing. 94 nW/cm2 means a milliwat for 2 square inches. That’s already usable amounts of power for tiny devices. Can you roll up a couple square meters of this stuff into something like a capacitor and get a usable “free” AA battery?
Is heat about to be free energy? No more problems with global warming? Are our refrigerators and air conditioners soon going to be a source of energy rather than a sink?
If this claim is true, then this is world changing technology available to anyone with pretty basic thin film technology…. And there are YouTubers who will be replicating this soon. Let alone real fabrication labs.
You can see why it’s reasonable to be skeptical…
The laws of thermodynamics are empirical: all of our physics experiments and observations thus far support and agree with them. We have no external confirmation, e.g. "god's source code for the universe" or some such that proves them to be absolute laws, but given that they hold up consistently across a huge number of observations, in a huge number of domains- we are nearly certain that they are absolute. Gravity itself (e.g. general relativity) is also on the same footing- like thermodynamics it has proven itself to reliably predict observations across a huge number of different new experiments.
This reasoning isn't convincing enough for some (non-physicist) people- there are whole forums of people working on perpetual motion machine designs, etc. that think thermodynamics is nonsense. However, thus far none of their machines have ever worked.
Although I am not a working physicist, I was trained as a physicist (a long time ago!), and assign a prior of essentially 100% to the laws of thermodynamics, from a huge amount of evidence. E.g. I am certain that either I am misunderstanding this paper, or it is simply wrong. I'm hoping someone whose physics isn't as rusty as mine will step in and explain what I am missing here.