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Post by abacus9900 on Sept 6, 2010 16:03:59 GMT 1
How can an electron be in two places at once?
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Post by speakertoanimals on Sept 6, 2010 16:24:55 GMT 1
There isn't really a how about it. If you are stuck with the classical way of looking at things (electron is like a little billiard ball, and moves about), then of course it doesn't seem to make sense.
Which is what quantum theory is really saying, that our classical view of what describes what an electron is doing at any one time (it is here, and moving in this direction) is just wrong. Turns out that in quantum terms, a complete description of the state of the system is different. We no longer have the electron as a little ball, but instead an electron is actually a wave (something like light waves), where the 'height' of the wave tells us the probability of finding the electron there is we measure it, and look to see where it is.
That's just the way quantum theory says the world is, there is no HOW as to how you fit the classical picture of an electron in with this wave picture -- you can't.
So, in short, classical physics says:
A thing like an electron is in a definite place at a definite time, moving with a definite speed.
whereas quantum physics just says that is plain wrong, and an electron can be in many places at once.
And experiment agrees with the latter statement. Don't blame the universe, that just is the way it is!
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Post by abacus9900 on Sept 6, 2010 16:40:56 GMT 1
whereas quantum physics just says that is plain wrong, and an electron can be in many places at once. And experiment agrees with the latter statement. Don't blame the universe, that just is the way it is! If that is true why do I not see many copies of myself all over the place?
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Post by speakertoanimals on Sept 6, 2010 17:37:59 GMT 1
Because there is an inherent scale to quantum effects, determined by Plancks constant.
Which is why classical objects (like you, and coffee cups) are seen to not jig about all over the place, whereas on the scale of electrons or atoms, we can't really ignore this being in many places at once stuff.
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Post by abacus9900 on Sept 6, 2010 17:45:43 GMT 1
Because there is an inherent scale to quantum effects, determined by Plancks constant. Which is why classical objects (like you, and coffee cups) are seen to not jig about all over the place, whereas on the scale of electrons or atoms, we can't really ignore this being in many places at once stuff. Right, so whereas individual electrons or whatever can exist in different places at once, when part of a big object like me they can't. Right?
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Post by speakertoanimals on Sept 6, 2010 17:54:52 GMT 1
Wrong. An individual electron in you can be described by a wave (spread out nature of a wave captures the can be in many places idea).
How spread out? Over the atom or molecules (which is the chemical bond, in basic terms).
For all of you to be in two places at one, not only would the scale of the wave for every electron and every atom in you have to be bigger than usual, but they'd have to be all in phase in effect, so that every bit of you decided to be one inch to the right.
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Post by abacus9900 on Sept 6, 2010 18:31:35 GMT 1
Wrong. An individual electron in you can be described by a wave (spread out nature of a wave captures the can be in many places idea). How spread out? Over the atom or molecules (which is the chemical bond, in basic terms). For all of you to be in two places at one, not only would the scale of the wave for every electron and every atom in you have to be bigger than usual, but they'd have to be all in phase in effect, so that every bit of you decided to be one inch to the right. Thought that's what I said.
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Post by Progenitor A on Sept 6, 2010 18:44:27 GMT 1
I do not think that there are any experiments that have observed an electron in 2 places at once. If not then the many-places-at-once phenomenon is an hypothesis that has yet to be proved. The Uncertainty Principle tells us that we cannot know the position AND momentum of an electron. We can know the POSITION (and there are millions of records of th epositions of electrons), but I do not know of any cases where an electron has been observed in more than one position at the same time. The Quantum theory tells us that electrons can suddenly vanish and appear elsewher, surmounting massive enrgy gradients that should be impossible. That is how transistors work, possibly the single most useful phenomenon of the quantum theory
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Post by abacus9900 on Sept 6, 2010 18:57:16 GMT 1
I do not think that there are any experiments that have observed an electron in 2 places at once. I saw a TV programme the other day that dealt with other dimensions and one of the speakers had a laser (I think) and shone it through some kind of lens and the laser seemed to shine on several different spots at once. Is this not the same thing?
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Post by Progenitor A on Sept 6, 2010 20:01:23 GMT 1
I do not think that there are any experiments that have observed an electron in 2 places at once. I saw a TV programme the other day that dealt with other dimensions and one of the speakers had a laser (I think) and shone it through some kind of lens and the laser seemed to shine on several different spots at once. Is this not the same thing? I do not know the experiment and cannot therefor comment It would however, be remarkable if it DID show an electron in 2 places at once.
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Post by abacus9900 on Sept 6, 2010 20:19:41 GMT 1
Perhaps, but I think the point that was being made is that photons can be at a number of places at once (unless I got it completely wrong).
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Post by Progenitor A on Sept 6, 2010 20:25:37 GMT 1
Perhaps, but I think the point that was being made is that photons can be at a number of places at once (unless I got it completely wrong). Strange thing QM Odd things such as instantaneous-action-at-a-distance, whereby paired-spin particles separated by a great (relative) distance will instantaneously change orientation if the spin axis of one particle is changed. As they say about QM, if you think that you understand it, you have got it all wrong
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Post by abacus9900 on Sept 6, 2010 21:26:35 GMT 1
Odd things such as instantaneous-action-at-a-distance, whereby paired-spin particles separated by a great (relative) distance will instantaneously change orientation if the spin axis of one particle is changed. As they say about QM, if you think that you understand it, you have got it all wrong Exactly, naymissus, and I think it kind of tells us that the traditional ideas about out universe are not correct. Some of the brightest minds in this field consider that our everyday reality is but one in an innumerable 'sea' of realities that we are not directly aware of. There could be other dimensions that you are not aware of right in your front room.
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Post by speakertoanimals on Sept 7, 2010 13:18:33 GMT 1
Except yopu can't -- observing position collapses the wavefunction, you either measure it as there, or not there.
but other experiments confirm that things are not that simple. Take a double slit, pass particle (electron, photon, molecule) through the system, and watch pattern of arrivals build up on a screen.
Only way to explain pattern is that particle somehow passes through BOTH slits. Try to decide which one (detector at a slit) and pattern disappears.
So, the single particle that appears at the screen in a definite location somehow went through both slits earlier on.
There are many complicated versions of such experiments, and all so far agree with what quantum theory predicts, no matter how seemingly illogical the effects.
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Post by speakertoanimals on Sept 7, 2010 13:24:21 GMT 1
Sorry this is exactly totally wrong!
If we could do that (I change spin here, spin changes four light years away) I would have an instantaneous message transmission system, so beloved of science fiction writers.
Whjat actually happens is that before you measure, the spin of a single particle is undetermined -- not just we haven't measured it so don't know what it is, but that the statement that it has a single value is not true. It has all possible values at once.
When we measure, we now find it has one particular value, the one we measured. And hence so does its connected twin, even though before we measured, they both had all possible values, just linked, so that values always cancelled.
Think of it like spining a coin -- before I catch it, it could be either heads or tails, 50% chance of each. Once I have caught it, then if heads, I know the other side must be tails. Same with photons, except the other side is the other photon, which might be a very long way away.
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