Negative Energy

Question

I am uneducated on physics so please excuse my ignorance. I've been looking into negative energy which hasn't made much sense to me thus far. Through what I've read I think negative energy is simply the potential energy.

From my understanding, the logic is that if we add energy to an object and then consider it to have zero energy, there must've been negative energy before (via. Conservation of Energy). I take issue with this since can't zero energy be defined at any point? The argument for defining the system (at 0 energy) is mentioned frequently but I don't understand why there is necessarily negative and positive energy as opposed to an energy difference.

Even with the Casimir effect- in which all energy is attempted to be removed from the system, the plates move together. Is this not just from the law of gravitation, that masses attract each other?

To me, the explanation is very similar to Newton's Third Law, but that law does not state that the objects were at rest, to begin with only that the net force is 0 before, similarly that the energy before is zero.

I see this as similar to pressure distribution. You cannot have negative pressure since pressure is defined as a function of mass/volume (mass cannot be negative). I would consider the same principle to apply to this except with energy and particles but please inform me if I am mistaken.

This is how physics is done anyways, we already treat energy differences as the physically meaningful quantity since potential can be redefined up to an arbitrary constant. — Triatticus, Nov 01 '23 at 22:29
so negative energy doesn't necessarily exist? just less than we had? — cav3, Nov 01 '23 at 22:32
The value of a potential energy (like gravitational potential energy) can be negative. There is nothing wrong with potential energy being negative. The value of kinetic energy can not be negative (the lowest it can be is zero). The value of total energy (kinetic energy plus potential energy) can be negative. Again, there is nothing wrong with this, since it is generally only energy differences that are physically meaningful. — hft, Nov 01 '23 at 22:42
Does this answer your question? How energy can be negative without any applied potential? — hft, Nov 01 '23 at 22:44
This may help - How is energy "stored in an electric field"?. And this - Understanding Electric and Gravitational Potentials — mmesser314, Nov 02 '23 at 03:19

score 3 · Answer 1 · answered Nov 01 '23 at 22:33

You have some correct ideas and some muddles. The question is not very clearly stated. Perhaps it would be more useful to ask something more precise.

Energy comes in various forms. Kinetic energy is always positive. The energy associated with binding forces is the energy which would have to be supplied in order to pull something apart. Let's call this quantity $B$. It is positive. If we wish to say that when the pieces are far apart and not moving they have no energy, then when they are close together we will have to say they have energy equal to $-B$. This makes sense because then we have to supply $B$ to pull them apart, and then their energy will be $-B + B = 0$ which is what was agreed. However you are correct, the choice to say the energy is zero when far apart was a human choice. We could say the energy is zero when they are close together and then the energy when far apart will be $B$. It doesn't really matter which policy we adopt as long as we are consistent. The behaviour in the end is all about energy differences.

Coming now to pressure, it is defined as the outward force on the boundary of a system. But you can have things like a stretched spring. These produce a pulling-in force that is ordinarily called tension. But tension is just another word for negative pressure. So in this sense, pressure can be negative. This is less familiar than positive pressure because the pressure in a gas is always positive. But for a solid material the pressure can be either positive or negative.

Finally a brief word on Casimir effect. This is a form of tension associated with the electromagnetic field when it is in its least excited state, called ground state. The Casimir force between conducting plates can equally be regarded as a force owing to correlated motions and consequent attractions between electric dipoles in the conducting plates. If we wish to pull the plates apart we shall have to provide some energy. Where does this energy go? It goes into the electromagnetic field in its ground state. That is the state we ordinarily associate with zero energy. However the physical issue is not whether we define the zero that way; the physical issue is whether or not the plates attract and they certainly do.

Another consideration is the gravitational effects. Now things get further complicated because pressure and energy both give rise to gravitation (in the full treatment by general relativity).

Negative Energy

1 Answers1