[hashmp]

Maybe someone can chip in here but I was under the impression virtual particles didn't actually exist, they were just used to simplify our understanding of particle interactions.

The uncertainty principle hasn’t gotten in the way of learning the rules of quantum mechanics, understanding the behavior of atoms, or discovering that so-called virtual particles, which we can never see directly, nevertheless exist.

After recently getting to grips with QFT it seems there aren't actually any particles, just fields which are excited at certain locations giving the impression of particles.

[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.

[criddell]

If you keep reducing, I think you end up a Tegmark's mathematical universe.

[dTal]

I got to that point, then I read a LessWrong thing about subjective probability and none of it makes sense again. The basic problem is - what does "subjective probability" i.e. your personal anticipation of events, even mean in a world where every instance of you (experiencing all possible versions of events) is equally 'real'?

http://lesswrong.com/lw/pt/where_experience_confuses_physici...

[criddell]

The multiverse part of the mathematical universe doesn't click with me, but the idea that the universe is mathematics, does.

[dTal]

You can't really have one without the other because mathematics describes lots of universes, not just ours. If you embrace mathematical universe you discard the notion of any particular concrete "reality" - our universe is not the single privileged "real one" just because we happen to be in it. In fact that's pretty much all there is to the idea.

Now throw in the fact that actual physics' best current guess is our universe is in actual fact constantly 'splitting' (although the term is misleading because the process is continuous, not discrete - the universe is constantly diverging from itself, everywhere) - there "really" is a multiverse. This lends a sort of philosophical weight to mathematical universe by rejecting a single, privileged version of events - but it also presents you with some weird dilemmas with subjectivity. To wit - if a quantum, universe-splitting choice is made, and given that both versions of events will be witnessed by some version of you - how does that give rise to the phenomenon of subjective probability i.e. your personal anticipation of witnessing a particular version of events? It seems there is at least some sense in which one universe is more "real" than another - you're more likely to end up there!