# I Distinguishing electrons through spin

1. Nov 16, 2017

### Josh1079

Hi

I'm recently reading something about the moller scattering in QED, and I'm feeling a bit curious about how plane waves change their spin orientations (e.g. up to down)(I mean in the scenario that one is up and one is down). In the text it seems that it's because the electrons are indistinguishable, so it can end up in either final state. Therefore, I'm just wondering whether it is possible to distinguish the electrons through spin orientations. If this is not the case then I actually pretty curious about how the angular momentum is tossed between the two in order to flip the spin.

Thanks!

2. Nov 16, 2017

### Staff: Mentor

That’s not what indistinguishable means. If you would label the electrons with A and B and exchange them (put A in the state of B and vice versa) you wouldn’t see a difference - because the two electrons are exactly the same particles. Of course you can say “I use the spin up electron to do X”, but you can’t say “I use electron A” because that doesn’t mean anything.

3. Nov 18, 2017

### Josh1079

Hi,

Sorry I'm still a bit confused about this. Does this mean that two electrons intially in different states can actually somehow switch states through scattering? Or is this because at the scattering region their wave functions are mixed so it becomes meaningless to say about which is which after leaving the scattering region?

4. Nov 18, 2017

### Orodruin

Staff Emeritus
It is always meaningless to say that "this is electron A and this is electron B". Electrons are identical particles and there is no possible test you can make to check whether an electron is one or the other.

5. Nov 18, 2017

### jerromyjon

Aren't we all... no one really knows. I agree it's not possible now, but I imagine there might be ways in the future...

6. Nov 19, 2017

### Staff: Mentor

We can test if they are exactly identical and indistinguishable. They are.

7. Nov 19, 2017