Thread: Physics!

So, I'm currently in my 3rd year of college going for an eventual Ph.D. most likely focused in theoretical astro-particle physics. I've noticed there are at least a few people on here that are interested or are also studying physics. Figured it would be interesting to discuss current things going on in physics, or older things, or even theories or ideas you've come up by yourselves. I know I have a few. So, any takers?

OK -- here's a question I've been pondering.

When a particle pair with spin is created in a weak force interaction -- say a spin up electron and a spin down electron -- then they are entangled.

Here's the question: When one of these two electrons is annihilated in a positron+electron collision, does the paired electron also get destroyed to conserve spin? And if so, does the the other positron get destroyed? Does it have to be the entangled pair? Can it by any other opposite-spin particle that gets destroyed?

Is it only possible for an up electron to combine with a down positron?

Originally Posted by TorrentMage

OK -- here's a question I've been pondering.

When a particle pair with spin is created in a weak force interaction -- say a spin up electron and a spin down electron -- then they are entangled.

Here's the question: When one of these two electrons is annihilated in a positron+electron collision, does the paired electron also get destroyed to conserve spin? And if so, does the the other positron get destroyed? Does it have to be the entangled pair? Can it by any other opposite-spin particle that gets destroyed?

Is it only possible for an up electron to combine with a down positron?

So, this is quantum physics and especially in this case of entanglement it's your interpretation that matters. In the end the actual observable physics is the same. What happens during the entanglement is up to you. Copenhagen would say that when the positron/electron annihilated the photons that were produced would have a specific spin which would collapse the wave function of the electron. Thus, giving it a specific spin. Then the entangled one would be left with the opposite spin. Many-worlds would say effectively the same thing, just with more mumbo-jumbo. Consistent Histories (which is my favorite, besides that quantum is just wrong) would say that each electron had a specific spin, we just weren't sure of it. And then the resulting events occur according to that. Does that answer your question?

never been that interested in physics, but i am pretty damn excited to see what results the LHC produces

I think i'm going back to college to study Theoretical Physics. And that just because of Quantum mechanics. We are at the breaking point of a big new paradigm shift and i wanna be a part of that revolution.
And have we come any closer to the answer of what defines the observer?

No... not really, DaegonPhyn.

First, I should say I'm an engineering physicist. I never studied nuclear physics, so thus my question...

Actually my question doesn't have anything to do with what happen to the particle pair during collapse, it has to do with conservation of universal spin during a weak force annihilation event.

As I understand it, when a particle pair is created, if a spin up particle is created a spin down particle must be created at the same time.

So I was wondering, if that's so, then what happens when a spin up electron interacts with a spin up positron.

I have these possibilities in mind:

1) This is not possible because spin up e+ interacting with spin up e- would leave a net spin imbalance of 2 spin down and only a spin down e+ can interact with a spin up e-.

2) The up e+ and up e- annihilate each other, but the paired down e+ and down e- simultaneously vanish to conserve spin

3) The up e+ and up e- annihilate each other, but two other random down particles of vanish to conserve spin

4) Annihilation events do not conserve spin

5) There is some other fact I am missing and something else happens.

Originally Posted by TorrentMage

No... not really, DaegonPhyn.

First, I should say I'm an engineering physicist. I never studied nuclear physics, so thus my question...

Actually my question doesn't have anything to do with what happen to the particle pair during collapse, it has to do with conservation of universal spin during a weak force annihilation event.

As I understand it, when a particle pair is created, if a spin up particle is created a spin down particle must be created at the same time.

So I was wondering, if that's so, then what happens when a spin up electron interacts with a spin up positron.

I have these possibilities in mind:

1) This is not possible because spin up e+ interacting with spin up e- would leave a net spin imbalance of 2 spin down and only a spin down e+ can interact with a spin up e-.

2) The up e+ and up e- annihilate each other, but the paired down e+ and down e- simultaneously vanish to conserve spin

3) The up e+ and up e- annihilate each other, but two other random down particles of vanish to conserve spin

4) Annihilation events do not conserve spin

5) There is some other fact I am missing and something else happens.

So, I think you're missing that annihilation does conserve spin. The photons that are produced in the reaction conserve the spin. up e+ + up e- gets three photons(2 up, 1 down). down e+ + up e- gets two photons(1 down, 1 up). So 1-4 are all wrong. Does that answer your question?

Yes, it does! Ah, you have set my mind to rest. One of these days I will check out a particle physics text and read up on the subject.

Have you already studied quantum chromodynamics? I only got as far as quantum mechanics, and then branched off into solid state theory for a semester before leaving "pure physics" for other pastures.

That's good.

....I wish. I'm actually still a Junior. Was taking a class on Nuclear and Particle Physics, but had to drop it because the teacher was terrible and expected us to know more advanced quantum physics than I know right now. But I've read up on the concepts of quantum and particle physics. I plan on going into Astro-Particle physics, so I'll probably eventually do quantum chromodynamics and such.