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Can an electron be in two places at the same time?
Can someone find the source of this question and the answer as well? Thanks.
Quote from: PmbPhy on 12/09/2014 18:29:08Can 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.
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."
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?
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.
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...
It depends on how you define "an electron"
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.
So, it's complicated stuff, and it's easy for people to disagree while actually believing the same thing and talking at cross purposes.
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...
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.
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.
QuoteIt depends on how you define "an electron"
..we're dealing with quantum field theory.
The purpose of this thread is quantum mechanics, not quantum field theory. The subject of this thread is about location of particles in space and not fields. If you wish to talk about QFT then please start your own thread. Please don't usurp mine.
Each fundamental component of the apple then is spread over a wide area, but there are two tightly defined locations where it is more probably going to interact with other things if it is forced to narrow down its range at any time.
A photon is not a point particle.
electrons "exist as standing waves".
"spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics."
The evidence is rock-solid, the wave nature of matter is not in doubt, in QED the electron is said to be an excitation of the electron field. It isn't some point particle thing that has a field, its field is what it is.
What is there in an apple that isn't just like an electron or photon?
The whole thing can be turned into photons.
Every part of the the apple is spread across multiple locations (possibly ranging across the entire universe),
but they're all tied together in such a way that they hold together collectively as an apple, and in an extreme case it could be possible for the probabilities relating to each component of the apple to be in agreement with each other that the whole apple is essentially occupying just two apple-sized locations with high probability while occupying all other possible locations with extremely low probability. Each fundamental component of the apple then is spread over a wide area, but there are two tightly defined locations where it is more probably going to interact with other things if it is forced to narrow down its range at any time.
Oh yes it is. You can capture a single photon on a phtographic plate and it's all there in one place.
no, their distribution can be modelled as standing waves.
No, spin can be adequately modelled as angular momentum but unlike classical angular momentum it is quantised.
No, the behaviour of matter on an atomic scale can be modelled as waves.
Waves and particles are convenient descriptors of things we observe, but the description is not the object and since neither completely describes the behaviour of electrons or photons, neither can be said to be "true" - whatever that means.
I can describe the motion of a car with a Euclidean vector, but it doesn't mean a car is a vector.
Quote from: lightarrow on 13/09/2014 11:10:02It 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.
IMHO you should forget about probabilities.
But I can make an electron (and a positron) out of electromagnetic waves. Then I can diffract them. Then I can annihilate them, and I've got electromagnetic waves again. That's nothing like describing the motion of a car with a vector.
So you are now asserting that electromagnetic waves have mass?
Why would I want to forget about probabilities?
The probabilities are determined by the distribution of the item that is spread out across a space, dictating how likely it is that that item will appear as a point particle at any position within that space if it is forced to choose a location to do so. Until it is forced to choose, it is able to maintain multiple possibilities as to where that point will be based on its distribution. Things are spread out while they keep the possibilities open, but there are times when they are forced to narrow down that range (though not necessarily to a single possibility).
The result is that when a photon or electron is forced to interact with something in a way that requires it to have a tightly constrained location, it will then appear to exist at that single location.
We can work out where it is most likely to do so based on probabilities...
Now, you seem to have decided that when an electron and proton get together (let's go the whole hog and combine them to make a neutron), the fields cancel out and result in something that is no longer spread out in the way that an electron is, but can that really be so?
An experiment has been done in which an object made up of many atoms was oscillating in two opposite directions at the same time, and by that I mean that it was moving from right to left to right to left while also moving from left to right to left to right at the same time.
I forget the details as to how the scientists proved that it was doing this, but it was held up as a demonstration of quantum effects with objects on the macro scale. That means we have large physical compound objects (not unlike an apple) behaving as if they are spread out and wavy. If you interact with the thing, you then force it to reduce the range of what it is doing and to pick only one of the two options, but up to that point it was doing both, and at many points along the way the end of this oscillating thing was "in two different places at the same time", in much the same way as Schrödinger's cat is both alive and dead at the same time (one walking around while the other is lying still), and in much the same way as my apple was in two places at the same time.
Everything I've just said may be hogwash, of course, because I'm not an expert in this at all. I merely listen to what more knowledgeable people say, probably misunderstand a great deal of it, try to build a model of what I think they mean in my head, and then I come to places like this to see if people who know more than I do can spot the points where I've gone wrong, and then I hopefully improve my understanding as a result. So, I'm always delighted to be shown to be wrong.
From John Duffield."Schrödinger devised his cat to demonstrate the stupidity of the Copenhagen interpretation. But it got hijacked by people who promote quantum mysticism."It's about time people realized this!!
Schrodinger regarded this as patent nonsense, and I think that most physicists would agree with him. There is something absurd about the very idea of a macroscopic object being in a linear combination of two palpably different states. An electron can be in be in a linear combination of spin up and spin down, but a cat simply cannot be in a linear combination of alive and dead.
If the electron can be in two places at once then the two places can be anywhere including right next to each other. If they are right next to each other the Pauli Exclusion principle makes them into entirely different electrons. They are then not identical. If every electron in the universe can be considered to be in two places at once then all pairings become unique. So what is to stop these two unique objects from also being in two places at once. On and on ad infinitum.
…, if one assumes that any energy E possesses the inertia E/c2, then the contradiction with the principle of mechanics disappears. For according to the this assumption the carrier body of mass E/c2, while it transports the amount of energy E from B to A; and since the center of gravity of the entire system must be at rest during this process according to the center-of-mass theorem the cylinder K undergoes during it a total shift S’ to the right.. If we assign the electromagnetic field too a mass density [tex](\rho_e)[/tex]Consider also what Einstein said in is 1916 paper on GR tooQuoteWe make the distinction hereafter between "gravitational field" and "matter" in this way, that we denote everything but the gravitational field as "matter." Our use of the word therefore includes not only matter in the ordinary sense, but the electromagnetic field as well....The special theory of relativity has led to the conclusion that inert mass is nothing more or less than energy, which finds its complete mathematical expression in a symmetrical tensor of second rank, the energy tensor.
We make the distinction hereafter between "gravitational field" and "matter" in this way, that we denote everything but the gravitational field as "matter." Our use of the word therefore includes not only matter in the ordinary sense, but the electromagnetic field as well....The special theory of relativity has led to the conclusion that inert mass is nothing more or less than energy, which finds its complete mathematical expression in a symmetrical tensor of second rank, the energy tensor.
The item is wavefunction, it's distributed in space, and it's real, not some abstract probabilistic thing.