5 ms·

There's an important distinction here which is often misunderstood. The loss of interference is due to the photon (really, light wave) interacting with the dete

There's an important distinction here which is often misunderstood. The loss of interference is due to the photon (really, light wave) interacting with the detector. That results in an entanglement, and it's easy to show (mathematically) that interference is lost. That's not the difficult part. Any physical interaction that causes a correlation between the particle's state and some other state (effectively making that thing a detector) will cause this. This includes air molecules, which is why we have to isolate the systems very well. After interacting with the detector, the particle+detector system is still in a superposition of two states (corresponding to the two slits). When the particle hits the screen, the screen gets in on the entanglement. At all times there are (effectively) two paths, including when your body and brain interact with the experimental setup. So why do you see only one result? One answer (the Many-Worlds Interpretation) is that you don't see one result. One "copy" of you sees this one and "another" sees the other. Another possibility is that there really is some particular event that "collapses" the wave function, but AFAICT people mostly use this interpretation for practical reasons, bypassing the philosophical conundrum. Or, if you insist that you you sees only one result, but you still like MWI, then the question becomes: why did I end up on this branch rather than another one? But any explanation would have to come from outside the system (the multiverse) more or less, so I wouldn't hold my breath waiting for an answer.

david927 9y ago
Fascinating. And the fact that it's entanglement makes it information and thus not subject to space/time constraints.
- monktastic1 9y ago
  Depends on what precisely you mean by that. It can allow you to exhibit correlations that are hard to explain within a classical framework, yes. But that requires very precise control over the system, so has no practical import most of the time. Things are being entangled pretty much nonstop around you all the time. BTW, I added a paragraph to my answer above.
- EGreg 9y ago
  I think that basically the observer is considered "entangled" with a phenomenon after they have interacted with it. That's all. The observer can be anything. You are you, so by the time information comes to you, you've become entangled. I find this interpretation to be mostly wordplay. After all how can something be "real" if you can never observe it or detect it? It's sort of saying the theoretical construct "those other worlds" are real, but in what sense? Bohmian mechanics makes way more sense to me.
  - goatlover 9y ago
    Do we ever observe or detect the larger universe outside our light cone? Yet astronomers say it exists. What about other minds? Do you ever observer/detect someone else's experiences, thoughts, feelings? Or just their behavior from which you infer a mind?
jodrellblank 9y ago
but you still like MWI, then the question becomes: why did I end up on this branch rather than another one? If you like MWI, then the answer is you end up on every branch. It's like another invocation of the hateful anthropic principle - in every branch you are asking about the result you saw in that branch. You are asking why you ended up in this branch because this is the branch in which you exist to ask that specific question. The real question of MWI for me is, where the heck are all these squillions of universe copies every second and where does the energy come from and go to making squillions of universes worth of matter and creating universe sized places to put them and how does you interacting with a photon on Earth cause a copy of the Andromeda galaxy anyway?
- TheOtherHobbes 9y ago
  The other real question with MWI is why you still experience one universe and not a superposition of universes? How exactly, in moment-to-moment physical detail, do these splits happen? And as for branching - how are observers assigned among universes? The MWIers will shrug and tell you observer experiences are distributed at random. Well - fine. So why can’t the collapse experience be inherently random too, without demanding squillions of Occam-busting unobservable universes? It seems like the least plausible interpretation. Not only does it multiply entities for no good reason, and assume they can never be observed, but it doesn’t even solve the original problem. “Yes, but the math...” isn’t a defence because there are plenty of situations in physics where technically correct solutions are discarded as unphysical. Why make an exception here?
  - FeepingCreature 9y ago
    > The other real question with MWI is why you still experience one universe and not a superposition of universes? Because the brain is warm and messy? And Occam does not work that way.
    - coldtea 9y ago
      >And Occam does not work that way. Well, Occam is not a physical law, so that's neither here, nor there.

david927 9y ago

Fascinating. And the fact that it's entanglement makes it information and thus not subject to space/time constraints.

monktastic1 9y ago
Depends on what precisely you mean by that. It can allow you to exhibit correlations that are hard to explain within a classical framework, yes. But that requires very precise control over the system, so has no practical import most of the time. Things are being entangled pretty much nonstop around you all the time. BTW, I added a paragraph to my answer above.
EGreg 9y ago
I think that basically the observer is considered "entangled" with a phenomenon after they have interacted with it. That's all. The observer can be anything. You are you, so by the time information comes to you, you've become entangled. I find this interpretation to be mostly wordplay. After all how can something be "real" if you can never observe it or detect it? It's sort of saying the theoretical construct "those other worlds" are real, but in what sense? Bohmian mechanics makes way more sense to me.
- goatlover 9y ago
  Do we ever observe or detect the larger universe outside our light cone? Yet astronomers say it exists. What about other minds? Do you ever observer/detect someone else's experiences, thoughts, feelings? Or just their behavior from which you infer a mind?

jodrellblank 9y ago

but you still like MWI, then the question becomes: why did I end up on this branch rather than another one? If you like MWI, then the answer is you end up on every branch. It's like another invocation of the hateful anthropic principle - in every branch you are asking about the result you saw in that branch. You are asking why you ended up in this branch because this is the branch in which you exist to ask that specific question. The real question of MWI for me is, where the heck are all these squillions of universe copies every second and where does the energy come from and go to making squillions of universes worth of matter and creating universe sized places to put them and how does you interacting with a photon on Earth cause a copy of the Andromeda galaxy anyway?

TheOtherHobbes 9y ago
The other real question with MWI is why you still experience one universe and not a superposition of universes? How exactly, in moment-to-moment physical detail, do these splits happen? And as for branching - how are observers assigned among universes? The MWIers will shrug and tell you observer experiences are distributed at random. Well - fine. So why can’t the collapse experience be inherently random too, without demanding squillions of Occam-busting unobservable universes? It seems like the least plausible interpretation. Not only does it multiply entities for no good reason, and assume they can never be observed, but it doesn’t even solve the original problem. “Yes, but the math...” isn’t a defence because there are plenty of situations in physics where technically correct solutions are discarded as unphysical. Why make an exception here?
- FeepingCreature 9y ago
  > The other real question with MWI is why you still experience one universe and not a superposition of universes? Because the brain is warm and messy? And Occam does not work that way.
  - coldtea 9y ago
    >And Occam does not work that way. Well, Occam is not a physical law, so that's neither here, nor there.