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Comment by PaulDavisThe1st | Hacker News Reader

Tweak your intuition: energy IS motion. When things are not moving, there is no energy. When there is energy, things are moving.

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How would you describe a rock sitting on the top of a mountain? It is not moving relative to the matter around it, but it certainly contains quite a bit of energy, in a variety of different forms.

I am trying to recognize that even in that rock, energy is dissipating in multiple ways, and any number of different events can lead to it dissipating in different ways.

I suppose you can say that the individual atoms composing the rock are moving, but are those movements connected to the potential energy it has by virtue of being far from the relative minimum in a gravity well?

That rock could fall down the mountain mostly intact - a highly energetic event, compared to being eroded away chemically by rain over millennia.

potential energy is. IMO, largely a pedagogical tool. it's an explanatory position, rather than a thing.

the rock, does, obviously "contain" energy thanks to e=mc2. but the notion that the rock is energetically in a different state as it sits on top of the mountain that when it sits at the bottom never sat well with me in high school, and it still doesn't, 45 years later.

It takes energy to move a rock to the top of a mountain, and you can get some of that energy back (minus friction etc) if you let it roll down. So it's got something.

I mean any type of energy is just as intangible as potential energy, so I don't see that the energy stored by doing work (i.e. interacting with one four forces) is that different to the idea of energy stored by being in motion. You never measure "energy" directly after all, but it's a useful abstraction - after all, everything in science is an explanatory position.

Yes, everything in an explanatory position. That's precisely the point I was trying to get to.

I just happen to consider the explanation that a rock sitting on top of a mountain having "potential energy" to be relatively content free.

There's always a tension in physics (or has been for a couple of centuries or so) between force-based explanation and energy-based explanation.The force-based explanation (gravity) of why the rock might move downhill makes vastly more sense to me than the notion that it has "potential energy". However, the force-based explanation is not always clearly the right one either.

Also, I wasn't referring to "the idea of energy stored by being in motion". This is precisely the hangup that trips up so many. An object doesn't have energy because it is moving. And it doesn't move because it has energy. The motion and the energy are the same thing, just two different ways of talking about the same thing. The distinction matters because the way we've developed the semantics of "motion" and "energy" in physics means that, for example, "motion" is not something that is transferred between objects, but "energy" is.

A static point mass in a gravitational field is already at its lowest energy state (a literal ground state if you will). It can only really do one thing, which is to stay. The logarithm of the number of states then is zero. So in some sense it cannot encode information at all. In fact I think more generally speaking, things that are at a global minimum of energy level cannot really be used to encode information (unless you have a mechanism to add entropy w/o increasing energy), because they have one state, and the log of the number of states then gives you zero bits. Probably another way to look at the idea that gravitational potential path-independence means memorylessness means devoid of bits of information.

The rock is continuously applying pressure to the mountain. That's why we have round planets and not huge random looking rocks. On an atomic level, the atoms themselves are full of action, though that will take a really long time to see the consequences of that.

ps: I subscribe to the heat death theory.

That rock is moving though, at c through time.

Then energy is relative? An object is 'stationary' in space, a comet comes along and hits it. The comet has energy.

OR the comet is just sitting there, 'stationary', the object hits it. Not the object has energy.

There's no total energy to a system, except calculated from some point of view?

energy is a term we use that describes the probability for some unit of matter to be in a different state at time T' than it was at time T.

if you consider the state to include position - relative to a frame of view - then energy describes (at least in part) the likelihood that the position at time T' is different than at time T

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