Feynman Double Slit

CANGAS,

The problem with this is that the most physical way to explain this is with wave functions, but I cannot talk mathematically about wave functions if most of the readers do not know what they are. If I can talk about this as propagators and such, all's the better.

Honestly, to really learn the subject you have to get into the math because it guides you through the physics, and this is true for any physics subject. If the math doesn't support something think may happen, then there is one of two things: the theory is wrong (for established things like QM this is unlikely unless you're trying to break QM) or what you're conjecturing will happen cannot happen. Removing math from physics is like removing books from a literature class. All you're left with are these nebulous concepts without any grounded basis of discussion.
 
Phys:

Did you notice that the thread starter couched the original question, and subsequent comments and questions, in non mathematical, layman language?

I noticed it.

Sayonara. :cool:
 
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^^^^^ Ah, your smugness belies your wisdom.

Well, OP, basically here's all there is to it. Particles behave more like waves than localized objects, and waves can interfere with each other. If you measure which slit the "particle" went through, then the particle will begin totally localize and disperse from that one slit as if it's the only source. If you don't do this, then in passing through each slit the waves will interfere like light does. You can observe this effect experimentally, too.
 
PhysMachine said:
^^^^^ Ah, your smugness belies your wisdom.

Well, OP, basically here's all there is to it. Particles behave more like waves than localized objects, and waves can interfere with each other. If you measure which slit the "particle" went through, then the particle will begin totally localize and disperse from that one slit as if it's the only source. If you don't do this, then in passing through each slit the waves will interfere like light does. You can observe this effect experimentally, too.
Click to expand...

Ok, so can we assume that an electron isn't really a particle but more like any other wave eminating from one point and travelling out in all allowable directions. Is it ok to think of it like that being as we KNOW it travels through both slits?
 
Phys:

Your garbled syntax belies veracity in your attempts to explain Quantum Physics.

It is important to note that since not everyone is a Pulitzer Prize grade writer, anyone can write badly, not just you. My reaction to your garbled syntax is because it leaves me unable to understand what you are trying to communicate. This causes me to conclude that you may be totally incorrect, scientifically.

You seem to have told us both that an electron really does NOT, and also, that an electron really DOES travel through both slits.

If you do know which case is true according to currently accepted QP, why don't you clarify for us now, in clear grammar, if possible?
 
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dav57 said:
Ok, so can we assume that an electron isn't really a particle but more like any other wave eminating from one point and travelling out in all allowable directions. Is it ok to think of it like that being as we KNOW it travels through both slits?
Click to expand...
An electron isn't really like a particle. But it's not really like a wave either.

But why should it be like either, anyway? Why not accept that it's like an electron, which is unlike anything we're familiar with?
 
Pete has hit the nail on the head. The electron is neither a classical wave nor a classical particle. Attempts to put the electron in one classical box or the other led many pioneers of quantum theory to talk at great length about the mysterious wave particle duality. With our rather more complete modern understanding, we now know that the electron is a quantum unity rather than a classical duality.
 
Physics Monkey said:
Pete has hit the nail on the head. The electron is neither a classical wave nor a classical particle. Attempts to put the electron in one classical box or the other led many pioneers of quantum theory to talk at great length about the mysterious wave particle duality. With our rather more complete modern understanding, we now know that the electron is a quantum unity rather than a classical duality.
Click to expand...

Well, not exactly. The particle and wave interpretations are still used in quantum theory. It's just been recognized that they are equivalent to eachother. This is why it's called the "Particle/Wave Duality" rather than the "Particle/Wave Paradox." That is to say, all particles ARE waves, and all waves ARE particles; which one you choose to in terms of is an issue of convenience. The question of wheter an electron (or whatever) "is" a particle or a wave is literally meaningless. There simply is no distinction between the two.
 
I disagree, the electron is not a classcial particle or a classical wave, and it certainly isn't both. The statement that particles are waves and vice versa makes no sense. This is exactly why every student of quantum mechanics is baffled by this statement. It is logically inconsistent with the ideas of classical particles and classical waves that they have in their head. Electrons are quanta, and under certain experimental circumstances they can give results that can, if we didn't know better, be interpreted as classical wave like or classical particle like. But we do know better, and unless you change your definition of wave and particle then the electron isn't a wave or a particle. If you do change your definition then you haven't really done anything except give me another name for quanta, and quanta is shorter than "dual wave-particle object".
 
"In order to interpret these results, one is forced to conclude that an electron interacts with both slits simultaneously." Page 953.

"In this situation, one cannot say that the electron is in state 1 or in state 2. It is only correct to say that that the electron is in both states, since the wave function is a combination of the two states. In effect, we can say only that the electron passes through both slits!" Page 954.

Physics for Scientists and Engineers, with Modern Physics, Second Edition.
Raymond Serway, author.
ISBN 0-03-004854-0.
 
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Physics Monkey said:
I disagree, the electron is not a classcial particle or a classical wave, and it certainly isn't both. The statement that particles are waves and vice versa makes no sense. This is exactly why every student of quantum mechanics is baffled by this statement. It is logically inconsistent with the ideas of classical particles and classical waves that they have in their head. Electrons are quanta, and under certain experimental circumstances they can give results that can, if we didn't know better, be interpreted as classical wave like or classical particle like. But we do know better, and unless you change your definition of wave and particle then the electron isn't a wave or a particle. If you do change your definition then you haven't really done anything except give me another name for quanta, and quanta is shorter than "dual wave-particle object".
Click to expand...

Never heard the term "quanta" used as above. All of the quantum phycisists I know refer to electrons, photons, etc. as "particles." Perhaps you can give me a better idea of what you mean by "classical wave" and "classical particle"? And most students of quantum that I've met are already familiar with wave/particle duality from the classical setting of geometric optics. It's basic high school physics that all "waves" act like "particles" when the features they interact with are very large compared to the wavelength. That right there is the wave/particle duality in a nutshell. It's not until quantum that you see what you thought were particles (electrons) acting like waves, but it doesn't require any real adjustment. You just recognize that what you thought were particles are actually waves with very high frequencies.

I recall being kind of disappointed when I realized that was all there is to it.
 
Peggy Lee sang that in a song, "Is that all there is?".

Quantum Physics is both, simultaneously, much more simple than we might think, and, much more complicated than we might want.

Huh? Wha'd I say?
 
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Physics Monkey,

Can you please explain to me what the mysteries are that surround the Feynman Double Slit Experiment? Are there any?
 
CANGAS,

I'm sorry, I thought my post was simple coherent English using terms everyone who has studied quantum mechanics would know. In particular, the word "quanta" was first introduced by Planck way back when. In the future, it may help to read some background material on the discussion, this will help you understand what were talking about.
 
quadraphonics,

Thank you for your reply. It is true that most physicists just call the electron a "particle" but the important thing to remember is that they don't mean a classical particle. When a student from classical mechanics hears the word "particle" they think of little rigid balls bouncing around, but this isn't what the electron is. The modern use of the word "particle" by physicists is simply another way of saying "quanta", I used the more precise but less common term here for explanatory purposes.

Regarding your other points, I have to disagree. Classical particles are discrete point like objects. Classical waves are extended continuous things. There is a qualitative difference in the number of degrees of freedom in both cases. When one tries to put the two together in a purely classical fashion, well known difficulties arise. One can say that classical waves can be localized and can move like classical particles, but only to a certain limited extent. Classical particles also don't behave like classical waves except in certain limits. Now, suppose I prepare an electron in a plane wave state in a box of some volume. When you measure the position of that electron, you always find it sits at just one place (within the limits of your apparatus), classical waves just can't do that. On the other hand, it is well known that electrons can diffract, classical particles can't do that. Rather than saying the electron is somehow two contradictory things, call it something new.
 
I think PM pretty much summed up anything useful I might have had to say.

The key feature is that an electron is something completely separate from the "classical experience" I guess you could call it. It's this thing that does something and is completely indeterminant until we measure it, and then we can know exactly where the particle is (remember "exactly" with the caveat of experimental error and such). It's not some wave with amplitude, nor is it some deterministic particle. It's neither at all.
 
Both PMs are of course right, but some may at least be amused by the old alternative theory (not original with me) but :cool: :

On Monday, Wen. & Fri - Electron is particle
On Thue, Thru & Sat - Electron is a wave.
On Sundays, God told physicists to rest, not do experiments.
 
PhysicsMonkee:

Having read more than "a" book about Quantum Physics, I do know what you are talking about, and I know what the genuine experts are talking about.

And I know when you are saying the same things as the real experts, and I know when you are not.

Are you happy with your batting average?

PS Didn't somebody ask you a question about Quantum Physics mysteries?
 
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A serious student of Quantum Physics who wishes to start their study with a strong dose of scairy math might beg, borrow or buy :eek: :

The Physical Principles Of The Quantum Theory
by Werner Heisenberg
published by Dover
Library Of Congress Catalog Card Number 486-60113-7


A serious student of Quantum Physics who wishes to study up to date concepts, with no math, written by a genuine expert, might beg, borrow or buy :eek:

The Fabric Of Reality
by David Deutsch
published by Allen Lane The Penguin Press
ISBN 0-7139-9061-9
 
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