**Ask a monkey a physics question thread**

[MadMojoMonkey]

Ok that's a really good explanation for why information isn't lost as a result of equilibrium, thanks.

I'm still struggling with entropy, and I still feel like nitpicking anything that comes close to "perfect equilibrium". But then again I'd argue there's no such thing as a perfect circle, and feel exactly as pedantic.

Keep digging into the 2nd Law of Thermodynamics. Investigate the Carnot Engine (or Carnot Cycle). This is the theoretically most efficient possible heat engine.

Think about how broad a category of things is encompassed in the term heat engine. This includes refrigerators, ovens, auto and diesel engines, rocket engines, pressure vessels and hydraulic systems, pumps, fans, etc.

There was something I thought of relating to space expansion... if dark energy is what's at play here, and we assume our universe to be expanding at an accelerating rate, then surely this tells us a great deal about dark energy? In particular that it isn't uniform across the universe with a static energy value. It must either be decreasing in value as space expands, or non uniform (or both).

We don't know what it is. We just noticed it. We are scrambling to see if our current theory does or doesn't predict this by jiggering with some presumed "constants" in our equations. We don't know where it's coming from. We don't know if it's in violation of Conservation of Mass-Energy, or a consequence of it.

It does appear to be a property of space which acts over volume. The "new space" is identical to the "old space." I.e. spacetime is spacetime; when it expands, it doesn't become "stretched." It's not a material, no matter how much we love to hear about "the fabric of spacetime" in science fiction.

For it to remain uniform and static in value, energy is being created from nothing, which is a clear violation of our laws of physics.

This is a better statement. However, it is only a clear violation of classical physics. Which we kinda expect. It is not at all clear if it is a violation of QM or GR. We are unclear of the source. It is premature to assume, "There is no source."

If we assume dark energy to be fixed in value and uniform cross the universe, and that energy cannot be created from nothing, then we must assume the universe as a whole is not expanding.

Not this.

Observation: The universe is not only expanding, but accelerating (on the largest measurable scales).

Ong: So it's definitely not expanding, then.

Does that make any sense?

I hope I didn't misinterpret you.

We're still at the point of asking questions.

There is no explanation for dark energy in our current understanding of physics. It is well worth questioning if it is in violation of the Law of Conservation of Mass-Energy. It is not a good time to be drawing conclusions.

I hope I have impressed upon you how weakly the dark energy contributes to the total energy over even the scale of Super Clusters. There is reason to be skeptical about what our theories can say when we extrapolate far from the domain of the measurements which motivate them. Sometimes a theory predicts many things beyond it's initial assumptions. This was true for both QM and GR, but we're pushing the limits of those extrapolations to the point of adding new data which was not predicted.

This is not too different from what was going on during the early 20th century when QM and GR were being discovered. There is something going on which our theories are having trouble dealing with. As our measurement devices become more precise, we find counter-intuitive stuff which has us scratching our heads.

Not completely unlike the Ultraviolet Catastrophe (more boring than it sounds).