# Are all electrons perfectly identical?

1. Dec 9, 2015

### Xalkias

Are all electrons perfectly identical? How can we be sure that all electons have the exact same mass electric charge etc. considering that we leave in a world that perfect doesnt exist ... I mean how do we know that electon's A mass cant defer at some point in infinity than electon's B mass thus having different mass that we simply arent able to measure?

2. Dec 9, 2015

### rootone

An electron is a fundamental particle which has certain observed properties.
Anything which had other observed properties would not be an electron.

3. Dec 9, 2015

### Buzz Bloom

Hi @rootone:

Perhaps you ought to add a short discussion about spin, since electrons are distinguishable into two sub-categories based on spin. This concept may be a bit advanced, but I think a brief explanation would be helpful to Xalkias.

Regards,
Buzz

4. Dec 9, 2015

### rootone

True, I was aware of the spin property, but didn't think of it at the time.
Yes the spin property can be one way or the other.
I really can't be on here longer for tonight or will have GF trouble, but hopefully somebody else might be able to elaborate.

5. Dec 9, 2015

### mathexam

Yeah, electrons are standard. They all have the same charge, which is fundamental to the electron. Even though their mass is probably not the same for all of them, it probably varies by an amount that is negligible and not worth discussion. So for all basic purposes, we shouldn't have to worry about electrons differing much.

6. Dec 9, 2015

### mathman

Spin is a quantum number associated with an electron in an atom. Free electrons don't distinguish spin up from spin down.

7. Dec 9, 2015

### Staff: Mentor

All electrons have the same magnitude of intrinsic angular momentum ("spin"), namely $(\sqrt{3}/2) \hbar$. What differs between electrons is the orientation of intrinsic angular momentum, or more precisely the probabilities of its orientation relative to a specified axis. These probabilities can change for a particular electron depending on circumstances, so they shouldn't be considered as fundamental properties.

8. Dec 9, 2015

### davenn

I suspect you don't understand the spin property of an electron

from Wiki
The electron has an intrinsic angular momentum or spin of 1/2.[69] This property is usually stated by referring to the electron as a spin-1/2 particle.[68] For such particles the spin magnitude is √3/2 ħ.[note 3] while the result of the measurement of a projection of the spin on any axis can only be ±ħ/2. In addition to spin, the electron has an intrinsic magnetic moment along its spin axis.[69] It is approximately equal to one Bohr magneton,[73][note 4] which is a physical constant equal to 6976927400914999999♠9.27400915(23)×10−24 joules per tesla.[69] The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as helicity.[74]

jtbell beat me to it

Dave

Last edited: Dec 9, 2015
9. Dec 9, 2015

### Helios

There's also the muon and tau, which are not exactly electrons, but are like more massive versions of electrons.

10. Dec 9, 2015

### Buzz Bloom

Hi mathman:

An apparatus can be set up that will measure the spin of a free electron with respect to a reference vector. The measurement will turn out to be either parallel to the vector, or in the opposite direction. This will be true no matter what direction the reference vector points. Calling one direction "up" and the other "down" is arbitrary, since the reference vector could just as well been pointing in the opposite direction.

Regards,
Buzz

11. Dec 9, 2015

### Buzz Bloom

Hi davenn:

You may certainly be right about this. That is why I used the word "perhaps". I am curious why you decided that the OP's purpose in asking the Q implies that he would have no interest in spin as a distinguishing property of different electrons.

Regards,
Buzz

12. Dec 9, 2015

### DrStupid

<irony>That's why the Stern–Gerlach experiment doesn't work.</irony>

13. Dec 9, 2015

### davenn

and if YOU want to include spin as well, then it also doesn't change as has been said, its an intrinsic property of an electron

Dave

14. Dec 9, 2015

### dipole

The evidence is, like in all science, statistical. All known behaviours of electrons that have been observed are consistent with what is known as the Fermi-Dirac distribution - which describes the probability of finding an electron (any electron) in a given state $\vec{\mu}$ , given some Hamiltonian $H(\vec{\mu})$ at a specitic termperature $T$.

One of the fundamental assumptions of the Fermi-Dirac distribution is the indistinguishably of the particles. They are perfectly the same in every respect and you can't even in principle identify one from the other. All you can say is how many electrons are in a specific state, (which must be either 0 or 1), but nothing about which electron is in that state.

15. Dec 9, 2015

### Buzz Bloom

Hi jtbell and davenn:

I am sure that both of you have a great deal more understanding of QM than I do. I have a feeling that our disagreement is one of interpretation of "orientation" and "spin property" rather one of facts, but I may be mistaken about this as well.

Are you both telling me
(1) that when a measurement is made of the orientation of the spin of an electron, there are more than two possible values the measurement can be,​
or
(2) that the two possible measurement values are not a distinguishing characteristic of electrons,​
or
(3) Neither?
If (1), then I would much appreciate a reference that will explain this, since as far back as I can remember trying to learn about QM, this was always a certainty.
If (2), then it is possible I am misinterpreting the concept of spin as a "degree of freedom" regarding the number of possible distinct particle types/species that are in equilibrium with each other as a function of temperature. The following is from

If you look at Leptons, there are 12 of the charged variety, of which four are of the electron-positron variety: two electrons and two positrons, each of which have two varieties of spin. This is an example of why spin seemed to be a much of a distinguishing characteristic as charge.
If (3), then please post an explanation.

Regards,
Buzz

16. Dec 9, 2015

### Buzz Bloom

Hi dipole:

I agree that this is the values of a property of electrons before a property is measured is undefined. Only a distribution of probabilities of what a measurement might be for each (assuming discrete values) possible values is knowable. However, a measurement can determine an actual value for a particular particle, but then that particular particle is no longer in equilibrium with the other particles as established for the Fermi-Dirac distribution.

Regards,
Buzz

17. Dec 12, 2015

### lychette

the great Richard Feynman believed that there was only 1 electron to expain everything :)

Last edited by a moderator: Dec 12, 2015
18. Dec 12, 2015

### rootone

I'm not sure if that story is a myth although I heard it before.
If he did say that, I doubt that he put it as strongly as a belief, more likely meaning that such as solution is allowable mathematically, not that it is probable.

Last edited: Dec 12, 2015
19. Dec 12, 2015

### lychette

rootone. I agree, if there is any difference it does not show :) only 1 electron 'could' explain all. I love the ideas and the thought processes

Last edited by a moderator: Dec 12, 2015
20. Dec 12, 2015