[Physics] Is empty space made of energy

energyvacuum

GR says that matter bends space around it, QM says even empty space must contain something. Is empty space a form of energy?

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I think there are two different questions here.

The first question is "what is spacetime?". This is well covered by the answers to the question Is space-time a special form of energy? and there's no need to go into this again. Suffice to say that spacetime is a mathematical object not a physical obect so isn't made of anything.

The other question is what effect vacuum energy has on spacetime, and this is an area we really don't understand yet.

Vacuum energy should behave like a cosmological constant or dark energy. It behaves as if it has a negative pressure and it should be causing the expansion of the universe to accelerate. You may have heard that dark energy is indeed making the expansion accelerate, but the trouble is that a naive calculation suggests vacuum energy should make the expansion accelerate much, much faster that we observe. So fast in fact that stars wouldn't have had time to form before the expansion diluted all the matter to effectively zero.

And that is a problem because vacuum energy is certainly real, as the Casimir effect shows, but it doesn't appear to affect spacetime in the way we expect. The explanation for this is currently unknown.

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Quantum Field Theory – Nothing vs. Empty Space: A Comprehensive Comparison

is empty space really nothing?

The physicist's 'nothing' is an example of something to the philosopher for which 'nothing' is well, let this philosopher explain in a review of "A Universe from Nothing" by Lawrence Krauss:

empty space governed by quantum mechanics (or any other laws of physics, or even just the laws of physics by themselves) is not nothing, and not even an “example” of nothing (whatever an “example of nothing” means), but something. And it remains something rather than nothing even if it is a “good first approximation” to nothing (which is what Krauss presumably meant by “good first example”). When people ask how something could arise from nothing, they don’t mean “How could something arise from almost nothing?” They mean “How could something arise from nothing?” That is to say, from the absence of anything whatsoever -- including the absence of space (empty or otherwise), laws of physics, or anything else.

[Physics] Vacuum is not really empty

In quantum field theory, the vacuum is the state containing exactly zero particles anywhere in space and at all times. Since it is an eigenstate of the number operator, there is no uncertainty at all about this.

On the other hand, empty space between matter (i.e., what is informally called a vacuum) is never completely empty; it is still filled with the quantum fields emanating from the matter. Just like the space between the sun and the planets is not empty but filled with the gravitational field.

If this field is strong enough one can extract energy from it. For example, a ball falling in a conventional vacuum gains kinetic energy from the gravitational field.

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Related Solutions

Quantum Field Theory – Nothing vs. Empty Space: A Comprehensive Comparison

[Physics] Vacuum is not really empty

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