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Author Topic: Can an electron be in two places at the same time?  (Read 34160 times)

Offline PmbPhy

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I've seen the question
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Can an electron be in two places at the same time?
poised a great number of times and in almost all cases the responder says "yes" where in fact the answer is "no." I'm looking for the source of such assertions because I want to write a paper on the subject. Can someone find the source of this question and the answer as well? Thanks.


 

Offline evan_au

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Re: Can an electron be in two places at the same time?
« Reply #1 on: 12/09/2014 23:41:00 »
An extreme case of this is Richard Feynman's conjecture that there is only one electron in the universe - we just see it in many places at once.
See: http://en.wikipedia.org/wiki/One-electron_universe

However, the question seems to be more aimed at the double-slit experiment conducted with electrons, where the interference fringes suggest that a single electron has passed through both slits at the same time before hitting a target.

This is just like laser light, which can pass through two slits at once, causing an interference pattern - even if the light intensity is so attenuated that only one photon is in transit at once.
 

Offline chiralSPO

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Re: Can an electron be in two places at the same time?
« Reply #2 on: 13/09/2014 00:02:15 »
I believe that the misconception has to do with the fact that an electron is usually not localized. There can be two (or infinitely many) positions in which something has an equal probability of interacting with the electron...
 

Offline lightarrow

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Re: Can an electron be in two places at the same time?
« Reply #3 on: 13/09/2014 11:10:02 »
It depens on how you define "an electron"   :)
Defined as the wavefunction which represents it, the answer is yes; defined as the properties of its detection the answer is no.
Defined as "an irreeducible representation of an Hilbert space on the Poincarč Group with charge -e, mass 9.11*10-31 kg and spin ħ/2" I would have some difficulty to answer.

--
lightarrow
 

Offline JohnDuffield

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Re: Can an electron be in two places at the same time?
« Reply #4 on: 13/09/2014 16:22:58 »
Can someone find the source of this question and the answer as well? Thanks.
I can't find the source, but the answer is yes. The electron has a wave nature. A wave is not some point-particle thing. It's quantum field theory, and the electron's field is what it is. It's always in more than one place at once.   
 

Offline PmbPhy

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Re: Can an electron be in two places at the same time?
« Reply #5 on: 13/09/2014 20:30:27 »
Can someone find the source of this question and the answer as well? Thanks.
I can't find the source, but the answer is yes. The electron has a wave nature. A wave is not some point-particle thing. It's quantum field theory, and the electron's field is what it is. It's always in more than one place at once.

As is the case too many times John, you're wrong. It most certainly is not the case. As I said in the OP in fact the answer is "no." so if you have another opinion I have no interest in hearing it.

I wrote about this to a physicist I know. He got his PhD at Princeton and worked as a physics professor at Harvard.
Quote
The statement is nonsense.  It arises from the mistaken idea that an electron is a little spinning object (made out of ...?).  An electron is much more subtle than that.

A similar confusion exists with respect to the photon.  While teaching the course from which my book Newton to Einstein emerged, I coined the sentence, "Light travels as a wave but departs and arrives as a particle."  No classical concept--electromagnetic wave or tiny solid particle--corresponds to the truly novel nature of light.

Similarly, no classical concept can capture all the attributes of what we call "an electron."

My friend at Boston University, whose also a world renown physicist, also confirmed this for me too (since I always knew it but enjoy having things confirmed before I talking about them in forums).
 

Offline jeffreyH

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Re: Can an electron be in two places at the same time?
« Reply #6 on: 13/09/2014 22:35:14 »
I agree with you Pete but out of interest how does this relate to the double slit experiment. Is it a wave disturbance in the electromagnetic field that causes interference? Like an echo?
 

Offline PmbPhy

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Re: Can an electron be in two places at the same time?
« Reply #7 on: 14/09/2014 07:26:35 »
Quote from: jeffreyH
I agree with you Pete but out of interest how does this relate to the double slit experiment. Is it a wave disturbance in the electromagnetic field that causes interference? Like an echo?
Thanks buddy! :) The particles have a specific energy and that energy is used to determined the de Broglie wavelength. Then we have particles moving along different trajectories and as such they have a different phase when they get to the screen. That difference in phase causes an interference pattern to form.
 

Offline JohnDuffield

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Re: Can an electron be in two places at the same time?
« Reply #8 on: 14/09/2014 10:54:44 »
As is the case too many times John, you're wrong. It most certainly is not the case. As I said in the OP in fact the answer is "no." so if you have another opinion I have no interest in hearing it.
I'm not wrong about this. Your friend must have misunderstood what you were asking. The electron is not some little point-particle thing. We make electrons (and positrons) out of light waves in pair production. We can diffract electrons. In atomic orbitals electrons "exist as standing waves". The electron has a magnetic dipole moment, and the Einstein-de Haas effect demonstrates that "spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics." And when we annihilate the electron with a positron, we typically get two light waves. The evidence is rock-solid, the wave nature of matter is not in doubt. And waves are not point-particles. Again, the electron is not some point particle thing that has a field, its field is what it is. And that field is always in two places at the same time.

I rather fear your friend gave you the brush-off with this. You should contact him referring to the above evidence, and perhaps he'll give you a considered response.

The particles have a specific energy and that energy is used to determined the de Broglie wavelength. Then we have particles moving along different trajectories and as such they have a different phase when they get to the screen...
They have a wavelength and a phase because they are waves.
« Last Edit: 14/09/2014 10:59:03 by JohnDuffield »
 

Offline PmbPhy

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Re: Can an electron be in two places at the same time?
« Reply #9 on: 14/09/2014 11:50:48 »
I agree with you Pete but out of interest how does this relate to the double slit experiment. Is it a wave disturbance in the electromagnetic field that causes interference? Like an echo?
I see from John's misunderstanding how you might have also misunderstood something too.

I think you confused a moving electron's electric and magnetic field as being an electromagnetic field that causes interference. That's not the case at all.

What electromagnetic field are you talking about? Is it the EM field of electron? No. It's the wavelength and phase of the wave function of the electrons.

As I said earlier. The frequency is due to the wave function. The electric and magnetic field of a moving electron doesn't have a frequency to it. However the location of the slits are related to the phase of particles as I recall.
 

Offline JohnDuffield

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Re: Can an electron be in two places at the same time?
« Reply #10 on: 14/09/2014 13:19:43 »
Pmb: have a read of Ehrenberg and Siday's 1949 paper The Refractive Index in Electron Optics and the Principles of Dynamics . This is the paper that predicted the Aharonov-Bohm effect, see figure 2 on page 19 which depicts the phase being "advanced" by the solenoid. It's a paper that talks of optics and potential and waves, not point particles. In QED the electron is described as an excitation of the electron field. QFT stands for quantum field theory. Not quantum point-particle theory. Also have a look at weak measurement work by Aephraim Steinberg et el and by Jeff Lundeen et al
 

Offline yor_on

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Re: Can an electron be in two places at the same time?
« Reply #11 on: 16/09/2014 14:33:25 »
Pete, I don't agree there. The electron is normally defined as some sort of probability cloud. Doing so you can define it to anywhere inside that 'cloud', before a measurement. After a measurement it is different though, as seen by the photographs made by Lund university of a 'electron orbiting' :)

"To demonstrate the quality and value of the triplets, researchers tested local realism—finding evidence that, as quantum theory predicts, entangled particles do not have specific values before being measured.* Researchers also measured one of each of a succession of triplets to show they could herald or announce the presence of the remaining entangled pairs. An on-demand system like this would be useful in quantum repeaters, which could extend the range of quantum communications systems, or sharing of secret data encryption keys." http://phys.org/news/2014-09-charm-nist-detectors-reveal-entangled.html#ajTabs

It's just a example of the principle I think is there.
==

Also I had some papers defining the possibility of finding electrons existing in different places 'simultaneously', and experimentally so, but it's been some time since? I know I linked them here though, but maybe a year or two ago?
« Last Edit: 16/09/2014 14:53:54 by yor_on »
 

Offline yor_on

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Re: Can an electron be in two places at the same time?
« Reply #12 on: 16/09/2014 14:59:20 »
Logically it shouldn't be possible to a 'real time' measurement of a 'same electron' though, in two 'places' so if that is what you mean I will agree. But the probabilities, and possibilities, of a electron affecting outcomes even without that observer measuring seems very high, I would call it a certainty that it could, assuming it to exist. And as it is that cloud?
=

You can do the interference pattern using just one 'photon' at a time, and the only way that singular 'photon' can create that 'wave pattern', as I know? is for it to be assumed to somehow interfere with itself, passing both slits simultaneously. Alternatively define it as a product of a field, observed. There is no real problem to this if we define under a arrow though. Under a arrow you should only find one outcome at a time, measuring. At least I think it should be that way, although it might also depend on how you define that outcome, aka setting your 'system'.
« Last Edit: 16/09/2014 15:30:24 by yor_on »
 

Offline Bill S

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Re: Can an electron be in two places at the same time?
« Reply #13 on: 16/09/2014 19:29:31 »
Quote
It depends on how you define "an electron"

It also depends on how you define “place”.  In general it must be defined as a position in space.  Space must be restricted to the three dimensions that we experience.  Any additional dimensions that may be suggested are mathematical concepts which may, or may not, bear any relation to reality. 

The question that must arise is: “Can we restrict a quantum object (quon) to the dimensions of the observable – macro – Universe?”

Quantum mechanics works, but no one really knows why.  There is something about QM that eludes the best efforts our scientists and mathematicians.

Infinity has similar features.  Mathematicians have shown that infinity can be a valuable concept, but there is always something about it that cannot be tamed.

Perhaps looking for a link here is fanciful.  Perhaps it should be left to philosophers, but, on the other hand, if it could lead to a clearer understanding of reality; if it could throw some light on some of the apparent paradoxes of the Universe, surely it is worth considering.
 

Offline JohnDuffield

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Re: Can an electron be in two places at the same time?
« Reply #14 on: 16/09/2014 19:52:03 »
Yor_on, Bill: IMHO if you read up about weak measurement, you come to appreciate that the Copenhagen Interpretation is old hat, and the photon really is a wave. Have a look at an ocean wave:



Look under the surface. That wave isn't some localized point-particle thing. It's always in two places at the same time. So is the photon. It's a wave in space, where there is no ocean surface, and it genuinely goes through both slits. But when you detect it at one slit, something like an optical Fourier transform occurs and the photon is transformed into a dot. This goes through one slit only. Then when you detect it at the screen, something like an optical Fourier transform occurs and the photon is transformed into a dot. Simple mundane stuff, no magic, and no multiverses.
 

Offline David Cooper

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Re: Can an electron be in two places at the same time?
« Reply #15 on: 16/09/2014 21:25:15 »
For something to be in one place, the whole of it must be in that place. If some of it is not in that place, that part is in a different place. To say that anything is in two places at the same time is wrong unless the whole of it is in both places at the same time. If a green apple is in two places at the same time, it could be sitting on one side of a set of scales while also being in a fruit bowl on a table some distance away. It would be able to balance a red apple on the other side of the scales, an apple of the same mass but which is only located in one place. That doesn't happen though, because when we're dealing with the quantum world we would have to say that the green apple is both sitting on one side of the scales while balancing the red apple AND it's sitting in the fruit bowl while not balancing the red apple, though that then spoils things because it means the red apple has to be sitting on balanced scales and sitting lower down on unbalanced scales at the same time as well.

So, it's complicated stuff, and it's easy for people to disagree while actually believing the same thing and talking at cross purposes. Tighten up your use of language and you might resolve the issue.
 

Offline jeffreyH

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Re: Can an electron be in two places at the same time?
« Reply #16 on: 16/09/2014 21:27:02 »
Yor_on, Bill: IMHO if you read up about weak measurement, you come to appreciate that the Copenhagen Interpretation is old hat, and the photon really is a wave. Have a look at an ocean wave:



Look under the surface. That wave isn't some localized point-particle thing. It's always in two places at the same time. So is the photon. It's a wave in space, where there is no ocean surface, and it genuinely goes through both slits. But when you detect it at one slit, something like an optical Fourier transform occurs and the photon is transformed into a dot. This goes through one slit only. Then when you detect it at the screen, something like an optical Fourier transform occurs and the photon is transformed into a dot. Simple mundane stuff, no magic, and no multiverses.

I can very much appreciate that point of view.
 

Offline Bill S

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Re: Can an electron be in two places at the same time?
« Reply #17 on: 16/09/2014 21:44:06 »
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So, it's complicated stuff, and it's easy for people to disagree while actually believing the same thing and talking at cross purposes.

Absolutely!  I think that's very common.
 

Offline Bill S

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Re: Can an electron be in two places at the same time?
« Reply #18 on: 16/09/2014 21:52:31 »
Arguing that a wave is not in more than one place at a time unless the whole wave is in two places at once seems very reasonable.  I would certainly agree with that if the wave is finite; but what if the wave is infinite?  Does that make any difference?
 

Offline jeffreyH

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Re: Can an electron be in two places at the same time?
« Reply #19 on: 16/09/2014 21:59:57 »
I think the magnetic flux through a surface external to the source of the field is an important consideration.

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

Offline alancalverd

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Re: Can an electron be in two places at the same time?
« Reply #20 on: 16/09/2014 22:50:07 »
Go back to the double slit experiment. When we detect a single photon or electron, we find a single-point interaction with the detector. But if we look at the spatial distribution of many such single events, it looks as though each photon or electron has interfered with itself.

It's nonsense to say that a photon or even an electron is a particle or a wave. It is an entity whose behaviour can be modelled by wave and particle equations. Models are not reality, only a convenient approximation to it. 
 

Offline jeffreyH

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Re: Can an electron be in two places at the same time?
« Reply #21 on: 16/09/2014 23:17:02 »
When considering the path of the magnetic field around a superconductor we see a disturbance of the normal behavior. A field is not a particle but we can split it in two. What happens if we fire a photon or an electron at a superconductor? We think we already know the answer but has anyone actually tried this? Also what happens to an electric field in the vicinity or a superconductor?
 

Offline Bill S

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Re: Can an electron be in two places at the same time?
« Reply #22 on: 16/09/2014 23:18:18 »
I need some help here, please.  I don't see the connection between the Meissner effect and the possibility of a quon being in more than one place at a time.
 

Offline jeffreyH

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Re: Can an electron be in two places at the same time?
« Reply #23 on: 16/09/2014 23:44:53 »
The electric field arises from particle charge. If this can be split by a superconductor then if an individual particle is very close to a superconductor what happens to its field lines? If the field from an individual particle can be split in two what does that say about the properties of particles?
 

Offline yor_on

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Re: Can an electron be in two places at the same time?
« Reply #24 on: 17/09/2014 02:22:02 »
Tried to search for it Pete, but there's too many posts nowadays :)
Found this though: http://www.mpg.de/511738/pressRelease20051011

It's not the exact same as I was thinking of though, but it is interesting.
 

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Re: Can an electron be in two places at the same time?
« Reply #24 on: 17/09/2014 02:22:02 »

 

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