Entanglement and string theory

Factual Questions
1

I watched the PBS Nova episodes on string theory with Brian Greene the other day. In it, he mentioned one of the theories - that most of the strings (sans gravitons) may be more like horse shoes in shape with the ends rooted in our own dimensions, but the arc free to move about in the other 7 dimensions.

He never mentioned entanglement, but wouldn’t this be a possible answer for it?

We see one particle when the string ends are so close together, but we see two when they are separated in our own dimensions (yet still connected at a close distance in the other dimensions)? Wouldn’t that explain how measuring one particle affects the other instantly seemingly across a vast distance?

2

I once asked Brian Greene a very similar, perhaps identical, question. This was shortly after the publication of the “Elegant Universe,” when he was much less famous. Still, I had to wait in a line of attractive young ladies who wanted autographs of his book, the first and only time I have observed physics groupies. He completely dismissed my question and I had the feeling he thought I was some kind of crack pot. Perhaps true.

3

I am not a physicist, but there may be some validity in what you say. I think I have heard it conjectured that these extra dimensions can account for the “instantaneous collapse of the wave function” in quantum mechanics, in some sense.
Note that in the theory of relativity, the time (4th) dimension is multiplied by i, and then squared, in distance calculations, so two events can be closer to each other in that metric than they are in 3-dimensional space.

4

A better question would have been “Doctor Greene—you’ve dedicated your life’s work to educating the general populace about complex scientific ideas. Have you ever considered trying to do something useful, perhaps reading to the elderly? But not your books—something they might enjoy.”

5

Well that leaves me in the same boat then! I think the biggest problem with these shows and books is that they take an incredibly complex idea and break it down for someone who, while still intelligent, is not a physicist. Once the idea is broken down, the words become more ambiguous and easier to misinterpret. It seemed like such a simple, obvious, and elegant solution to it when I watched it, but I’d expect the same reaction from him should I ever have that opportunity.

6

Well, you can think about Heisenberg’s Uncertainty Principle much like the special order menu that you find in certain Chinese restaurants where you have dishes in column A and other dishes in column B, and if you order the first dish in column A, you can’t order the corresponding dish in column B…

7

I don’t know a great deal about string theory, but my impression is that string theory treats entanglement of particles in the same way that quantum mechanics treats entanglement.

I think as well, whilst entanglement may seem ‘weird’ to us, it does not need an ‘explanation’ as it’s explained perfectly well by basic quantum mechanics

8

If you have some background in quantum mechanics and you want to try to get an idea about string theory and maybe the answer to your question, try the first of Susskind’s youtube video lectures on string theory (he is a leading expert, one of the founders of string theory, and a fantastic lecturer). They are meant for a technical audience (advantage: no bullshit), but the first few lectures are not too technical, and don’t get bogged down in math. I think they are very good.

ETA: link

9

Exactly. String theory is essentially an ordinary quantum theory of 1-dimensional objects instead of 0-dimensional ones; entanglement works the same way in both cases.

As for an explanation of entanglement, I think it’s best to think of quantum theory as a generalized probability theory, where it isn’t extraordinary at all that the acquisition of knowledge about one object changes the knowledge about another, even arbitrarily distant, object, and hence, the way you describe it (i.e. the probability distribution). The difference is that in quantum theory, there’s nothing ‘behind’ the probability distribution, but rather, it’s all you get. So, for a classical example, say you have two boxes, and you know that in one, there is a red ball, and in the other, there’s a green one. One box, you keep; the other, you send to Mars. You describe your box as a probability distribution. Since you have no information helping you to decide whether the ball inside is red or green, that probability distribution is going to assign a probability of 50% to either possibility.

Now, you look inside, and acquire information. Say, you find a red ball. Your probability distribution will ‘collapse’, as one option becomes excluded, and now assign a probability of 100% to the option ‘red ball’. At the same instant, your description of the box on Mars will change accordingly – from first attributing a probability of 50% to either option as well, you now will move to attributing a probability of 100% to the possibility of it containing a green ball. This is the ‘collapse’ as it happens in ordinary probability theory, and it’s nothing mysterious at all.

However, quantum mechanics isn’t ordinary probability theory, but rather, a generalization thereof – or I should be more cautious and say, mathematically identical to a generalization thereof; what, exactly, quantum mechanics is in an ontological sense is still open to debate (but then again, the same can be said of probability theory). So the story is not quite the same, mostly because you can’t a priori assign either the red or the green ball to either box, just waiting to be discovered. But essentially, within its framework, the phenomenon of entanglement is not any more puzzling in principle, but straightforward.

10

I just came in here to say that I watched the same episode of NOVA and wondered the exact same thing as the OP. I also have an additional question. There was a part about M-theory and “branes” colliding causing things like the “Big Bang.” (or at least I think that’s what they were getting at). Anyway… my question is what causes these branes to move? Where does the energy come from? And why do strings vibrate? Where does that energy come from?