# Entanglement and String Theory

1. Oct 2, 2009

### Qubix

I'm a physics undergraduate (2nd year), and I'm just learning the basics of Quantum Mechanics. As you would expect, I've been fascinated by the elegance and.....paradoxes involved. My question here is about the phenomenon of entanglement. I know the mathematics of it, but when I asked my professor: what does entanglement actually mean?, he said that no one knows physically, all we can say is that QM is a non-local theory.
The question I pose here is this: Quantum mechanics cannot tell us anymore about this phenomenon, what does String Theory (or any other scientific hypothesis) have to say about it? Does string theory offer some inside into this strange phenomenon?

2. Oct 2, 2009

### sokrates

String theory is not at the stage to produce insightful reasons for concepts such as entanglement and such, if there's any deeper understandable reasoning behind such phenomena, at all...

If there was a good intuitive reason, it would be in textbooks already. So you just have to live with the subtleties (I wouldn't use the word "paradox") QM poses...like everyone else.

3. Oct 3, 2009

### javierR

Entanglement is a fundamental part of quantum mechanics, and string theory is a quantum theory.

4. Oct 3, 2009

### Naty1

Here's most of a post I made in the last few days on another thread.....you might find the view interesting and ask your professor...likely he won't like it based on your post because it disagrees.....

The following quote is from Roger Penrose celebrating Stephen Hawkings 60th birthday in 1993 at Cambridge England.....this description offered me a new insight into quantum/classical relationships:

5. Oct 3, 2009

### Qubix

Thank you for your answer Naty1. Keeping in mind the fact that we don't actually know what the quantum level or classical level mean (although some authors of textbooks say that we should compare the size of the object to it's de Broglie wavelength, and if the object is larger than the wavelength, we're talking classical). This explanation does not give us a clear definition of the two terms, since they have discovered quantum behavior in fullerene (hope I spelled it correctly) molecules, which are quite large objects, compared to photons or electrons.
Another thing I would add is what John Bell said in his (rather violent and ironic) article in Nature, entitled "Against Measurement" : what gives us the right to say one system acts upon another, isn't wave function collapse going on all the time, more or less ?

6. Oct 4, 2009

### sokrates

Considering the well-known facts that Quantum Theory has been the most successful theory in physics, and there's not even a single glimpse of experimental evidence suggesting Quantum Theory is an "approximate" theory , I think that even merely suggesting that the theory is approximate is not scientific at all - to say the least, no matter who states it.

You can disagree on interpretations or you can disagree on unexplained experiments, - but you cannot disagree with a fundamental phenomenon like Entanglement, which is both theoretically and experimentally very sound - just because Roger Penrose "thinks so"..

It's quite misleading to even bring that up here. Because it's not science. It's just somebody's opinion, and I am sure everybody has their own.

Last edited: Oct 4, 2009
7. Oct 4, 2009

### Qubix

Well, he was probably referring to the fact that QM is not a deterministic theory, and people still hope, after almost a hundred years, that the "romantic years" of determinism will, somehow, return. I agree with the fact that it's only an opinion.

So from what I understand, from your answers, String Theory has it's basis on Quantum Mechanics and it cannot give us anymore detail into the quantum world, other than what Quantum Mechanics has already given us?

8. Oct 4, 2009

### atyy

In classical general relativity, there was Bekenstein's suggestion that the area of a black hole is proportional to its entropy.

In semi-classical general relativity, a formula for the black hole entropy was computed by Hawking.

In string theory, there is a formulation of gravity (in some universes) as a quantum field theory on the boundary of the space. It appears that some of the black hole entropy may be "entanglement entropy". http://arxiv.org/abs/0905.0932