I Is it a fact that vacuum energy exists?

[otennert]

Say Casimir effect comes from energy differences of "vacuum energy", anyway Casimir effect has something to do with vacuum energy, doesn't it ?

No, because as I said the Casimir effect relates to "energy differences", not to "vacuum energy differences". There is an effective potential energy as a function of the distance $d$ between the plates, leading to an effective force, that's the main point. But taking the Casimir effect as "proof" for the existence of a vacuum energy (as e.g. hinted at in Weinberg's paper just cited) is plainly wrong.

In my opinion the only thing that is safe to say is that the relation between the cosmological constant and potential quantum effects is unclear.

 

[Suekdccia]

In my opinion the only thing that is safe to say is that the relation between the cosmological constant and potential quantum effects is unclear.

Does that mean that it is unclear to say that the cosmological constant is the same as vacuum energy?

 

[otennert]

Does that mean that it is unclear to say that the cosmological constant is the same as vacuum energy?

Well, this is why it is called the "cosmological constant problem", isn't it? Again, I am referring to the Weinberg review from 1989. There are also tons of more recent literature on this.

Actually I think the Wikipedia entry is also a good entry point into this matter: https://en.wikipedia.org/wiki/Cosmological_constant_problem

 

[anuttarasammyak]

No, because as I said the Casimir effect relates to "energy differences", not to "vacuum energy differences". There is an effective potential energy as a function of the distance $d$ between the plates, leading to an effective force, that's the main point. But taking the Casimir effect as "proof" for the existence of a vacuum energy (as e.g. hinted at in Weinberg's paper just cited) is plainly wrong.

In my opinion the only thing that is safe to say is that the relation between the cosmological constant and potential quantum effects is unclear.

Thanks. I found a web article to explain it with a key word of "field radiation pressure".
"At a cavity-resonance frequency the radiation pressure inside the cavity is stronger than outside and the mirrors are therefore pushed apart. Out of resonance, in contrast, the radiation pressure inside the cavity is smaller than outside and the mirrors are drawn towards each other." https://physicsworld.com/a/the-casimir-effect-a-force-from-nothing/