The electron

mickeydevine

Hypothetical Question, Think Hydrogen atom.

An eletron cannot be observed constantly. If we can only guess where one could possibly appear in the orbit of an atom then can we prove that the one we 'saw' an hour ago is the same one we 'see' now. I mean because the electron disappears could the one we then detect be a totally different one. Amazingly, i'm suggesting electrons are interchangable. Just a thought.

c-note

interesting
Richard feynman posited that there was only one electron in the universe.
I dont think he was serious, but he may have been trying to make the same point that you are making. That one electron (or proton or any other sub atomic particle) is indistinguisable from from another.
it can be very thought provoking and confusing stuff this!

Vordaci

c-note wrote: »

Richard feynman posited that there was only one electron in the universe.
I dont think he was serious,

From my limited knowledge, and please correct me if I'm in any way off the mark here, but Feynman was quite serious in his meaning. Though when you mention the "one electron", what Feynman was talking about was the electron field in Quantum electrodynamics (QED), which permeates throughout the universe. From the excitations of this single field all the electrons in the universe are formed. An analogy could be that of the better known electromagnetic field. The excitation of which are photons.
So in this respect all electrons are one in the same.

mickeydevine wrote: »

An eletron cannot be observed constantly. If we can only guess where one could possibly appear in the orbit of an atom then can we prove that the one we 'saw' an hour ago is the same one we 'see' now. I mean because the electron disappears could the one we then detect be a totally different one. Amazingly, i'm suggesting electrons are interchangable.

I would agree with you, in so far as, all electrons are identical in the particle physics sense. So all the defining properties of an electron, i.e. mass, charge, spin are the same for each. So if you have some atomic system, as you pick a Hydrogen atom, if one were to 'pluck' out its electron and replace it with any other we should not be able to tell the difference.

I hope this has helped. And I hope more so that it is accurate!

Professor_Fink

mickeydevine wrote: »

I mean because the electron disappears could the one we then detect be a totally different one. Amazingly, i'm suggesting electrons are interchangable. Just a thought.

Well, you'd be right. Electrons are indistinguishable. In fact this is true of all fundamental particles (and so all identical structures). This is an extremely important fact, since an overlap in electron wavefunctions means they can swap (picking up a negative phase) without us telling where this has occured or not. This is what leads to the exchange interaction which is important in many condensed matter effects, especially magnetism and electrical conductivity.

Quantum field theory also allows particles to decay into other particles which may then recombine. So the electron may disappear and later be replaced by a 'new' electron, although this happens on an incredibly short timescale.

Svenolsen

The electron is Irish...in a way!

It was given its name by George Johnstone Stoney in 1891 at University College Galway:

http://en.wikipedia.org/wiki/George_Johnstone_Stoney

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mickeydevine

So just to clarify. If every electron in the universe was blue and we managed to isolate the electron in a hydrogen atom and paint it red, what colour would it be the next time we looked at this specific hydrogen atom? Or is this too simplistic.

Svenolsen

mickeydevine wrote: »

So just to clarify. If every electron in the universe was blue and we managed to isolate the electron in a hydrogen atom and paint it red, what colour would it be the next time we looked at this specific hydrogen atom? Or is this too simplistic.

Red.

The electrons and photons and neutrinos etc. being emitted by our Sun are not the same ones that are being emitted by Alpha Centauri.

There are untold gazillions of them.

Not just one.

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c-note

i dont know if it would be red or blue
but i do know that you cant paint an electron.
because if you did it would no longer be an electron.
i know you may not mean paint in the conventional way,
but as far as i know its impossible to tag an electron.

i'm just starting to read about symmetry,
one thing it says is that symmetry exists between particles
if replacing one with the other does not change the outcome of
an event. i guessing you could say that all electrons are symmetric?
they are fundamentally indistinguisable from eachother.

i dont know enough about it to give a good answer, its a good question but i'm not sure you'll get a definate answer!

Svenolsen

c-note wrote: »

i guessing you could say that all electrons are symmetric?
they are fundamentally indistinguisable from eachother.
!

If I am hit by a falling brick and then hit again by a second,identical,falling brick it is no consolation to know that both bricks are identical and indistinguishable.

They are indistinguishable....but they are not the same brick.

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mickeydevine

Thanks guys, my thinking is a little clearer now. I was just contemplating if electrons 'phase' i.e disappear then the electron present is the hydrogen atom disappears replaced by an electron from a totally separate atom, not connected but maybe billions of lightyears apart but happening on such a short time scale that it doesn't affect the properties/stability of the atom. Thanks for your input C-Note but I dont think you can 'paint' an electron, purely hypothetical.:)

Professor_Fink

mickeydevine wrote: »

So just to clarify. If every electron in the universe was blue and we managed to isolate the electron in a hydrogen atom and paint it red, what colour would it be the next time we looked at this specific hydrogen atom? Or is this too simplistic.

I'm afraid Svenolsen is slightly off. You can't paint an electron red. You can't in any way alter it's properties. This is extremely important for it to be formally indistinguishable. You cannot distinguish it in any way from any other electron. If you could, it wouldn't be an electron.

Professor_Fink

mickeydevine wrote: »

I was just contemplating if electrons 'phase' i.e disappear then the electron present is the hydrogen atom disappears replaced by an electron from a totally separate atom, not connected but maybe billions of lightyears apart but happening on such a short time scale that it doesn't affect the properties/stability of the atom.

Well, you can calculate the probability of this happening. Actually it is exactly what gives rise to the exchange interaction. Because electrons are Fermions, if you swap them, you pick up a negative phase. So, if you have two electrons in the same state (i.e. an symmetric state), and they are coupled by an exchange interaction, then they will pick up a different phase to the case where they are in an anti-symmetric state. The strength of this exchange interaction is proportional to the overlap in the wavefunctions for the electrons, which necessarily fall off exponentially with distance. As a result, only electrons which are close to one another can swap in the manner you describe. If the wave functions do not overlap, then there is no chance for them to swap, since they are distinguishable because they are in different states (specifically orthogonal spatial modes). Any overlap leads to a non-zero exchange interaction.

Svenolsen

Professor_Fink wrote: »

I'm afraid Svenolsen is slightly off. You can't paint an electron red. You can't in any way alter it's properties. This is extremely important for it to be formally indistinguishable. You cannot distinguish it in any way from any other electron. .

We are "conceptualising" of course.

No Du Luxe Weathershield Paint need be used.:

The one coming from the left is "RED".

The one coming from the right is "BLUE" .

The fast one is PINK .

The slow one is YELLOW .

The decelerating one is BROWN.

The accelerating one is GREEN.

The one whose "properties I have altered" by stopping it in it's tracks is ORANGE .

I can distinguish between electrons Professor Fink !!!!
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The point is that any individual electron is competely and utterly indistinguishable from any other electron. If you find a way to make one distingiushable, then it's no longer an electron: you've just created a new fundamental particle.

Svenolsen

-JammyDodger- wrote: »

The point is that any individual electron is competely and utterly indistinguishable from any other electron. If you find a way to make one distingiushable, then it's no longer an electron: you've just created a new fundamental particle.

So when you distinguish between an electron travelling at 1 meter per hour from your left from the electron travelling at at 9/10 light speed (which has has more mass than the slow one incidentally) but from your right you are creating a new fundamental particle.

Really !

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napapa

-JammyDodger- wrote: »

The point is that any individual electron is competely and utterly indistinguishable from any other electron. .

I agree completely but what about lone pairs of electrons, in organic chemistry we have the anomeric effect, link below, it describes how electrons on heteroatoms can alter the structure of a molecule compared to electrons on carbon.

http://www.scripps.edu/chem/baran/images/grpmtgpdf/Krawczuk_Nov_05.pdf

Could be off the topic but enjoying discussion...

Podge_irl

Svenolsen wrote: »

So when you distinguish between an electron travelling at 1 meter per hour from your left from the electron travelling at at 9/10 light speed (which has has more mass than the slow one incidentally) but from your right you are creating a new fundamental particle

In whose frame of reference are you measuring?

How do you know the one that was moving from the right and the one that was moving from the left haven't just swapped positions and velocities?

Velocities and accelerations aren't fundamental properties of an electron.

c-note

steady on lads, this is deteriorating into semantics and is in dager of getting silly.:eek:

no sven, no new particles are created as in your last post.
yes, i take your point of electrons coming from the left/right,etc being distinguisable, but the fact is, it is only the EVENT of the electron coming from left/right, fast/slow etc that is distinguisable, the electrons themselves are not.

i think its also important to remember that there is no preferred reference frame, so that if an electron is travelling at 9/10 of c, you could just ride along beside it and thus it is at rest. and all other things previously at rest are now at .9c.

Svenolsen

It does sound a bit semantic all right.

However a relativistic more massive electron is not, in my humble opinion, "indistinguishable" from an electron at rest.

Also "Cooper Pairs" of electrons,which cause Superconductivity, seem to have different properties "collectively" than electrons acting "alone".

Why the need for this "indistinguishability" anyway?

Of course they are all the same when they are all doing the exact same thing at any one time.

Not many of them are doing that though.
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Podge_irl

Svenolsen wrote: »

However a relativistic more massive electron is not, in my humble opinion, "indistinguishable" from an electron at rest.

Suppose you are in a frame of reference where each electron is travelling at the same speed. How then do you tell them apart?

Svenolsen

Svenolsen wrote: »

However a relativistic more massive electron is not, in my humble opinion, "indistinguishable" from an electron at rest.

But it all depends on what frame of reference you take to measure the mass of the electron. If you're comparing two electrons, one moving at .9c relative to you, and another stationary to you; then, yes, relative to you one will be more massive. But, that's only in your reference frame, another equally valid frame would be one moving at .9c, moving along beside the electron. Now, you'll measure the mass of the electron to be its rest mass; and the one that was stationary is now doing .9c. Electrons are indistinguishable because there is no absolute reference frame.

Svenolsen

I think we are tripping up on the definition of word "indistinguishable".

One other point.

A single electron is a Fermion.

A Cooper Pair of electrons is a Boson.

Different things or not !

Quote:

"Since electrons have spin-1/2 (so they are fermions), a Cooper pair is a boson, to which the Pauli exclusion principle doesn't apply, so they are allowed to be in the same state. The tendency for all the Cooper pairs in a body to 'condense' into the same ground quantum state is responsible for the peculiar properties of superconductivity."

Electrons are multi-talented little devils all right.

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Here's an analogy that might help make it a bit clearer.

If you had two identical objects (I know they're not identical in the same way electrons are, but, that's not the point), just say, soccer balls. Now, just say you weighed one on earth, and you found its weight to be .6kg; you then weighed the other on the moon, and you found its weight to be .1kg. Would you say that the balls are any different? No. They're the same, but, relative to the reference frame you're using, they're different. Weight isn't an intrinsic property of the balls.

It's similar to electrons moving at relativistic speeds. They're still the same, as velocity/acceleration aren't intrinsic properties of the electrons, in the same way that weight isn't an intrinsic property of the soccer balls. It's just because there's no absolute reference frame which to measure their masses, that's why you measure their masses to be different.

Professor_Fink

Svenolsen wrote: »

I can distinguish between electrons Professor Fink !!!!

No, you can't. In many of the cases you mention there is likely to be a non-zero overlap in wave functions, which means that after some finite time, the "stopped" electron becomes a superposition of many colours.

Professor_Fink

Svenolsen wrote: »

So when you distinguish between an electron travelling at 1 meter per hour from your left from the electron travelling at at 9/10 light speed (which has has more mass than the slow one incidentally) but from your right you are creating a new fundamental particle.

Really !

You can't perfectly distinguish between them. You have labeled each electron by it's state. Since there is non-zero overlap in the wavefunctions, there is some probability of the electrons swapping state.

Professor_Fink

Svenolsen wrote: »

A single electron is a Fermion.

A Cooper Pair of electrons is a Boson.

Different things or not !

What has this got to do with anything? Fermions pick up a negative phase when exchanged. Swapping pairs of electrons means your doubling up the phase, and so since (-1)^2 = 1, you get a poitive phase (and hence bosonic statistics). What's so surprising about that?

Svenolsen

I think my problem is in defining "individuality" .

If the quarks which make up the hadrons which make up two footballs (for instance)can equally be said to be indistinguishable like electrons surely the two footballs are indistinguishable deep down and nothing at all can truly be said to be distinguishable ?

We end up with only one electron and one quark (of each type) in the whole universe!

Yet all the subatomic particles conspire together to make two footballs which are very much distinguishable and individual at the macro level.

The individualistic "macro" world which we can see seems to obey different "rules" to the Quantum world.

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No.

See, you're getting confused. An individual electron and individual quark can be completely common, in no way unique; but, when they combine, they can make different things. No two items (on a relatively marco scale) are identical, there's bound to be at least one more atom or molecule in one than there is in the other. So this way, electrons and quarks can be in no way unique, but the things that they combine to make up can be completely unique.

Professor_Fink

Svenolsen wrote: »

If the quarks which make up the hadrons which make up two footballs (for instance)can equally be said to be indistinguishable like electrons surely the two footballs are indistinguishable deep down and nothing at all can truly be said to be distinguishable ?

As JammyDodger says, differences in the number and types of particles in the balls result in them being in orthogonal states. If they had identical composition, then indeed they would be indistinguishable. However on the macroscopic level the seperation between the particles is large enough to reduce the overlap in wavefunctions to a virtually zero.

Svenolsen wrote: »

We end up with only one electron and one quark (of each type) in the whole universe!

Wait, what? Why do you think that indistinguishability means there is only one of each particle? There is a well defined number operator that allows you to count the particles.

rgunning

mickeydevine wrote: »

So just to clarify. If every electron in the universe was blue and we managed to isolate the electron in a hydrogen atom and paint it red, what colour would it be the next time we looked at this specific hydrogen atom? Or is this too simplistic.

It would be red, I reckon. Because by changing the colour of a fundmental particle, you are acutally redefining the colour I would have thought. Paint one of them red, and blue becomes red.

Professor_Fink

rgunning wrote: »

It would be red, I reckon. Because by changing the colour of a fundmental particle, you are acutally redefining the colour I would have thought. Paint one of them red, and blue becomes red.

Small things don't have colours. Colour is a statement about the frequency of light emitted/reflected by an object. For a fundamental particle, there is no internal structure to absorb or emit the light, and so it has no colour.

mickeydevine

So say you have a solid object i.e some gold. Are the electrons swapping or are they stable/fixed to each gold atom.

mickeydevine

mickeydevine wrote: »

So say you have a solid object i.e some gold. Are the electrons swapping or are they stable/fixed to each gold atom.

Some are stable (i.e. attached to atoms) and some are "free". The free ones are actually bound to the metal lattice - that is, the structure of the atoms in the metal. The electrons move around randomly due to thermal energy, but, the net total current (i.e. movement of electrons) is still zero. When you run a current through a piece of metal the electrons move due to the presence of an electric field. So basically, no, they're not exactly fixed to each individual gold atom.

mickeydevine

-JammyDodger- wrote: »

Some are stable (i.e. attached to atoms) and some are "free". The free ones are actually bound to the metal lattice - that is, the structure of the atoms in the metal. The electrons move around randomly due to thermal energy, but, the net total current (i.e. movement of electrons) is still zero. When you run a current through a piece of metal the electrons move due to the presence of an electric field. So basically, no, they're not exactly fixed to each individual gold atom.

So some are free. If they're not bound then there must be some atoms which have -1 electron, does this not change the type of element it is i.e in this case platinum.

mickeydevine

mickeydevine wrote: »

So some are free. If they're not bound then there must be some atoms which have -1 electron, does this not change the type of element it is i.e in this case platinum.

No, because it's the number of protons in the nucleus that determine what element it is; the number of electrons in a single atom determine how ionized it is. So, if an individual atom has one less electron than the number of protons, it will be a +1 charge ion; likewise if it has one more electron than the number of protons, it will have -1 charge. Essentially, the net total of all of these ions (the +1 +2, -1 -2 etc. individual atoms) balance out, so the over all charge of the piece of metal is zero.

mickeydevine

Gotcha. Proton + charge, electron - charge, neutron 0 charge. Protons and electrons equal in an atom to cancel charge therefore metal has 0 charge. Thanks. So what about electrons from different atoms i.e say you melted gold and silver together, would the electrons swap between gold and silver atoms. Does everthing found naturally have 0 charge, do they always have to balance.

Professor_Fink

mickeydevine wrote: »

So what about electrons from different atoms i.e say you melted gold and silver together, would the electrons swap between gold and silver atoms.

Yes. They can swap whenever the electron wavefunctions overlap, which is quite often the case.

mickeydevine wrote: »

Does everthing found naturally have 0 charge, do they always have to balance.

Not exactly. Atoms do, since if they have excess charge, they quickly interact with other particles until the charge has been canceled. High energy events (such as lightning) can seperate electrons from atoms creating charged ions and free electrons, although these recombine relatively quickly.

mickeydevine

Professor_Fink wrote: »

Not exactly. Atoms do, since if they have excess charge, they quickly interact with other particles until the charge has been canceled. High energy events (such as lightning) can seperate electrons from atoms creating charged ions and free electrons, although these recombine relatively quickly.

So would your example of lightning, the charged ions react with nitrogen in the atmosphere. I read lightning is a good source of fertiliser. Do all chemical reactions result from charge differences.

mickeydevine

mickeydevine wrote: »

So would your example of lightning, the charged ions react with nitrogen in the atmosphere. I read lightning is a good source of fertiliser. Do all chemical reactions result from charge differences.

Almost every atom wants 8 electrons in its "outer shell". When they have 8, they're stable etc. etc., so two or more atoms will react if they can combine in some way to have a total of 8 electrons in their outer shells. For example, an oxygen atom has 6 electrons in its outer shell, and a hydrogen atom has only 1. Now, if one oxygen atom combines with two hydrogen atoms, each will have a shared total of 8 electrons in their outer shells - thus, they'll be stable. That's basically the concept under atomic bonding, thus, chemical reactions. Albeit a very simplified version of what actually happens - it justs works to think about bonding in this way.

mickeydevine

-JammyDodger- wrote: »

Almost every atom wants 8 electrons in its "outer shell". When they have 8, they're stable etc. etc., so two or more atoms will react if they can combine in some way to have a total of 8 electrons in their outer shells. For example, an oxygen atom has 6 electrons in its outer shell, and a hydrogen atom has only 1. Now, if one oxygen atom combines with two hydrogen atoms, each will have a shared total of 8 electrons in their outer shells - thus, they'll be stable. That's basically the concept under atomic bonding, thus, chemical reactions. Albeit a very simplified version of what actually happens - it justs works to think about bonding in this way.

A hydrogen atom must be very unstable then. 2 electron in the first shell isn't it. That's why we get H2. Full shell = stability. Neon = more stabile. Radon = most. Alkali metals most unstable. (Just looked up periodic table, does it show?) So pretty much everything is based on electron interaction then.? Its so small yet so important.

Just a thought. Would it be reasonable to say then that an electron that has been part of me at one time has been to every corner of the planet?

mickeydevine

mickeydevine wrote: »

A hydrogen atom must be very unstable then. 2 electron in the first shell isn't it. That's why we get H2. Full shell = stability

It isn't as simple as I'm describing though. The first shell has a maximum 2 electrons - this is called the 1s shell. Then, the next shell has a maximum of 8, and after that it gets a little more complicated. Hydrogen only has one electron, so it has a half full 1s shell, so two hyrodgen atoms can bond together, giving each a shared total of 2 electrons - this will fill the maximum of two electrons allowed in the 1s shell - which "satisfies" both atoms.

The actual theory behind all of this is vastly more complicated than what I've just said. But, thinking of bonding in terms of atomic shells makes it easier to visualise how bonding occurs (even if it's basically incorrect).

Neon = more stabile. Radon = most. Alkali metals most unstable. (Just looked up periodic table, does it show?) So pretty much everything is based on electron interaction then.? Its so small yet so important.

Yes, the most stable atoms are the ones with a full outer shell.

That's true, every single interaction thats noticable by us (excluding gravity) is based on the electromagnetic force. Every atom is pulled together with this force, and groups of atoms are pulled together with this force. So, if you can understand quantum electrodynamics (the field of quantum physics which deals with this), then you should, in theory, be able to understand every interaction that's noticable on a relatively large scale. (This is, of course, excluding gravity. And the other two forces: the strong nuclear and the weak nuclear, don't affect the world around us on a marco scale).

Just a thought. Would it be reasonable to say then that an electron that has been part of me at one time has been to every corner of the planet?

It could be, I'm sure that they've travelled very far. I don't know about the whole planet, but, it's an interesting thought.