Does gravity slap us into reality?

[seer]

Pick any part of you the photon hits. It's not really important in terms of creating the decoherence, as soon as that has happened, it doesn't matter if your eyes are closed or not.

But the photo isn't hitting me, it is being shot through the slits and hitting the screen behind it.

[Leonhard]

I found the technical article, but it'll need some diving into to see exactly how he plans to solve this, and whether its done as cleanly as he said he did it: http://arxiv.org/pdf/1405.7577v2.pdf

That might be over the weekend though, as I'm busy reading other things this week (can't read everything). Gotta finish Scholastic Metaphysics by Ed Feser.

[Leonhard]

But the photo isn't hitting me, it is being shot through the slits and hitting the screen behind it.

Oh wait you were talking about the double-slit experiment. Sorry Seer, I told you I only wanted to discuss the case with pencils. Otherwise we'll have to move this to physicsforums.com where they have latex equation support, because I hate writing ascii equations, and everyone hates reading them.

[Leonhard]

Generally though with regards to stuff like b-theory, Everett's QM and String Theory, I'm definitely in the camp opposite of Sean Carroll; that its beautiful does not mean that its true, and beauty is not even a good guide to whether its true.

[Boxing Pythagoras]

...because I hate writing ascii equations, and everyone hates reading them.

I really, really wish that every forum had LaTeX support. It's just a super-useful bit of functionality which doesn't require a whole lot, in terms of implementation.

Generally though with regards to stuff like b-theory, Everett's QM and String Theory, I'm definitely in the camp opposite of Sean Carroll; that its beautiful does not mean that its true, and beauty is not even a good guide to whether its true.

I can agree to that, despite the fact that I am a supporter of the B-Theory.

[JimL]

Is it okay if I use a simpler example other than a particle? Because otherwise its going to get hairy, and I'm not good enough to explain it then without resorting to math.

Boxing Pythagoras is free to correct me as its been years since I've done the philosophy of Many-World interpretations.

Lets assume we have a universe where quantum mechanics really works according to the Many-World interpretation.

Take the act of balancing a pencil on its end and releasing it. This is a fairly mundane observation. It falls down in some (ideally) random direction. In the Many-World interpretation the pencil falls down according to all the pathways that it can fall down in with some complex amplitude for each. The big question then (just like the wave vs particle), is why don't we see the pencil fall down in a great rain of them, why do we only see one of the pencils?

Lets say that we set it up so that the pencil isn't observed yet just as its about to fall down. Then the total universe wavefunction would be the product of the state of the universe sans pen, and the state of the pen at t=0. As time passes and the universe evolves, the wavefunction of the pencils starts to develop, 'splitting' up into all the trajectories the pencil can go in.

Now we measure the pencil as it falls. Lets say a photon is emmitted by an observer in the universe, and hits the pencil. This introduces a coupling, and now the universe wavefunction, and the pencil wavefunction are no longer a neat product. There is an entropy increase. And this entropy increase pretty much randomly couples states of the universe wavefunction, with states of the pencil wave function... so one slice of the universe wavefunction, sees only one pencil trajectory. This is decoherence. Its basically also something to be avoided when you want quantum computers to keep running.

If you could observe a pencil falling, without in fact increasing the entropy, you'd see the pencil falling in all directions at once (at least if the Many-World interpretation is true), unfortunately this is impossible.

But here we have an account of measurement, something that causes a decoherence, when coupling an observer to a system in a particular state.

The problem I have with the Many-World interpretation is not how it deals with measurement, its more how it defines probability.

Correct me if I am wrong Leonard, but I don't see how interaction between particles should have anything to do with the evolution of the particular realities as they are defined by the wave function. All of the particles, making up all of the universe evolve according to the wave function, not according to interactions between particles. In other words all particles including those being observed and those making up detection devices, as well as those making up observers are all determined as defined by the wave function. So how could the interaction between particles making up the observer or the detection devises be the determining factor of the position of the particles making up the thing observed?