Kip Thorne, the Casimir force, and Exotic matter (split from Reality Paradox)

[beecee]

On 9/27/2021 at 10:23 AM, swansont said:

That's a tad strong

That remark was in reference to "Forget about time travel. I wish ordinary travel were restored"...remembering that some of us are still in lockdown.

On 9/27/2021 at 10:23 AM, swansont said:

"Backward time travel is another matter; we do not know whether it is allowed by the laws of physics"

and 

"We physicists have been working hard since the late 1980s to understand whether the laws of physics allow backward time travel. We do not have a definitive answer yet"

(he also equates negative mass, anti-gravitation exotic matter with the Casimir force without anything pointing to where this connection has been definitively made)

Are you referring to this paragraph? "The quantum laws of physics do permit exotic matter to exist, and it has been created in the laboratory in very tiny amounts: in the so-called Casimir vacuum between two electrically conducting plates, and in the so-called squeezed vacuum that is generated by optical physicists using nonlinear crystals."

I admit my understanding of exactly what he is saying, is probably somewhat flawed. Swansont, can you elaborate on what exactly your objection to Thorne's rundown is, as dumbed down as is humanly possible to prevent my eyes from completely glazing over? 

Reading on further, he does go on and say "My personal guess is that these constraints on exotic matter do not prevent wormholes from being held open and thus do not protect chronology, but I could well turn out to be wrong. To learn the truth, we physicists must develop a deeper understanding of quantum theory in warped spacetime than we now have — i.e. a deeper understanding of the combined laws of quantum theory and general relativity, the laws of quantum gravity."

If we scroll down to the comments section, I see some weird take on the essence of time itself and comments that it isn't real. I fail to understand how anyone can arrive at that conclusion.

[swansont]

18 hours ago, beecee said:

Are you referring to this paragraph? "The quantum laws of physics do permit exotic matter to exist, and it has been created in the laboratory in very tiny amounts: in the so-called Casimir vacuum between two electrically conducting plates, and in the so-called squeezed vacuum that is generated by optical physicists using nonlinear crystals."

I admit my understanding of exactly what he is saying, is probably somewhat flawed. Swansont, can you elaborate on what exactly your objection to Thorne's rundown is, as dumbed down as is humanly possible to prevent my eyes from completely glazing over? 

Yes, this is basically the problem, along with his clarification "By the phrase "exotic matter" I mean matter that has negative energy and therefore anti-gravitates, i.e. repels."

First of all, the Casimir force is attractive, not repulsive. The plates get pushed together. It also has nothing to do with gravity - the derivation of the force relies on the electric and magnetic field boundary conditions applied to the conducting plates; it's purely an electromagnetic phenomenon. You eliminate photon standing wave modes (of one polarization) because the field needs to go to zero at the boundary. The QM solution says for the vacuum, each state has an energy of hv, so there are fewer photon modes inside the plates than outside. The energy density imbalance means there is a pressure that pushes them together. In short, if the plates are a micron apart, then no photon states of 2 microns or longer can exist in between the plates (plus more that wouldn't form standing waves) but they do exist outside the plates.

There's no gravity involved, and no matter identified with it, AFAICT.

Maybe his point is that if the Casimir force exists maybe there's something like this for gravity, but still, the Casimir force isn't tied to exotic matter and it's attractive and it relies on there being boundary conditions for E and B fields that AFAIK don't exist for gravity, so it would be a really weak analogue for the kind of exotic matter you need for wormholes to become stable

 

 

[beecee]

4 hours ago, swansont said:

 it's purely an electromagnetic phenomenon.

There's no gravity involved, and no matter identified with it, AFAICT.

Interesting..while I did pride myself on thinking I knew what the Casimir effect was, the above makes heaps of sense. Thanks for the excellent  rundown.

Edited September 28, 2021 by beecee

[StringJunky]

Yeah, added a bit more to my understanding of Casimir force too. Cheers swansont.