[snowwrestler]

I believe the Casimir Effect is usually taken as proof that virtual particles physically exist.

[cygx]

No, it's generally taken as a proof of vacuum energy. However, it's arguably just the van der Waals force in disguise.

[snowwrestler]

We don't disagree. The theory is that vacuum energy creates virtual particles, which are what interact with the plates in the Casimir experiment.