# I Why not hidden variables?

1. Apr 9, 2017

### Flatland

Would hidden variables still be consistent with QM if we abandon the concept of locality? For example, entangle particles could be connected via Einstein-Rosen bridges and any measurement would cause this bridge to collapse.

2. Apr 9, 2017

### Staff: Mentor

Yes. Bell's theorem shows that no local realistic hidden variable theory can agree with QM; clearly that still leaves room for non-local hidden variable theories.
Yes, although Bohmian mechanics would be a more plausible example.

3. Apr 10, 2017

### Demystifier

In string theory there is a very popular conjecture that ER=EPR, i.e. that entanglement and Einstein-Rosen bridges are equivalent.

4. Apr 10, 2017

### Denis

There is even no need to abandon locality. It is sufficient to abandon Einstein-locality, which is something different. Say, a universe where everything is local, but the maximal speed of information transfer would b $10^{100} c$ or so, would still be viable, compatible with all empirical evidence. It would be, yet, incompatible with quantum theory as it is now. But so what? This would be still a local world.

5. Apr 10, 2017

### Denis

Yes, but this is what I consider the most obvious example of mainstream science going completely insane.

6. Apr 10, 2017

### Demystifier

I pretty much agree with you. Indeed, I have criticized ER=EPR quite early, before it became mainstream:
https://arxiv.org/abs/1307.1604

7. Apr 10, 2017

### stevendaryl

Staff Emeritus
Well, there are two halves to the ER = EPR conjecture. One half seems pretty uncontroversial to me (but I'm not sure about the technical details, so perhaps someone who understands the details would disagree about it being uncontroversial).

The uncontroversial half is that "wormholes imply entanglement": If there is a wormhole connecting distant regions of spacetime, then there will be entanglement between particles on the two ends. It's easy enough to see that there is a possibility of such entanglement: If you create an entangled pair near one end of the wormhole, and one particle travels through the wormhole to the other side, then the two ends will be entangled. So the two ends are possibly entangled. To argue that they are necessarily entangled involves QFT. There's a handwavy argument in terms of virtual particles, but I don't know whether it can be made rigorous.

The second half is that "entanglement implies wormholes". For the two to be equal, this one has to be true, as well. That's what I don't understand. It seems to me that you can have entanglement without any gravitational effects.

8. Apr 10, 2017

### Staff: Mentor

I hope "Einstein-Rosen bridges" is not meant to specifically refer to that solution (the maximally extended Schwarzschild vacuum), since the wormhole in this solution is not traversable.

9. Apr 10, 2017

### stevendaryl

Staff Emeritus
I'm in the middle of watching Susskind's talk about the subject, and I'm not sure yet what kind of wormhole he is talking about:

10. Apr 10, 2017

### stevendaryl

Staff Emeritus
At 56:15, he starts talking about wormholes connecting distant regions, and he explicitly says that they are not transversible. The wormhole is not transversible, but it is possible for an observer (Alice) on one end to communicate with an observer (Bob) on the other end. How? If they both jump into the wormhole, they can meet inside (just before they are crushed by the singularity). I don't understand the argument for why this kind of connectivity implies entanglement.

11. Apr 10, 2017

### Staff: Mentor

I have found some of Susskind's writings in this area to be confusing as well. This might be a case where we really need to see the actual peer-reviewed papers to figure out what actual physics he is describing.