# Dark energy = Vacuum energy?

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1. May 26, 2012

### Don'tKnowMuch

Dark energy = Vacuum energy????

I am working on giving a presentation on dark energy and its possible relation to vacuum energy (i.e. one and the same). I have complied information from a couple of books, as well as websites (Scientific American, NASA, Astrophysical Journal). As i understand, dark energy is this force which opposes gravity, causing the Universe to expand at an accelerated rate. I guess my blunder lies in attempting to connect the implications of dark energy to vacuum-energy (zero-point energy). What i gather, vacuum energy can be observed via the Casimir effect. I also understand that this vacuum energy describes "empty space" to have a ground state. How are these two creatures (i.e. dark energy and vacuum energy) related? Any insight is appreciated, and a preemptive thank you to whomever can shed any light on this matter.

2. May 26, 2012

### Mark M

Re: Dark energy = Vacuum energy????

It was hoped that calculating vacuum energy in quantum mechanics would give the exact value of dark energy, and that they were the same thing. The cosmological constant (dark energy) has a value of 10-9 joules per cubic meter of free space. However, quantum electrodynamics, because of Planck's constant, requires it to be valued at least a whopping 10113 joules per cubic meter! This is an enormous disagreement, and no one has been able to see why the calculations vary so dramatically.

It does, however, seem that vacuum energy in quantum mechanics should play a role in our understanding of the cosmological constant. In general relativity, the gravitational force is proportional to $\rho$-3p, where $\rho$ is energy density, and p is pressure. Since $\rho$ must be equal to p for vacuum energy (since density would remain constant), this leads to a negative gravitational field - what is needed to drive acceleration as dark energy does.

3. May 26, 2012