Particle duality

[Advaithi]

Physicst say according to the rules of quantum physics, sub atomic particles have duality as "particle and waves" . I dont understand this. We all know the sub atomic particles are the basic matter of an atom and all the solid materials including you and me are made up of atoms. Then what is reality? What we are seeing in every day life is just a pattern of waves? is there nothing solid?

[swansont]

The basic behavior of anything on the scale of h/p (planck's constant divided by momentum) is wave-like. Some properties are quantized, though, so they act like particles at times. As far as atoms go, they are mostly empty space, even of you look at the constituents as particles. Solids seem that way because of electromagnetic interactions that get very strong at short range.

[Sharapovaphan]

Physicst say according to the rules of quantum physics, sub atomic particles have duality as "particle and waves" . I dont understand this. We all know the sub atomic particles are the basic matter of an atom and all the solid materials including you and me are made up of atoms. Then what is reality? What we are seeing in every day life is just a pattern of waves? is there nothing solid?

 

http://superstringtheory.com/basics/basic2.html

[IM Egdall]

When you feel the "solid" tabletop with your hand, you are really sensing the electromagnetic forces which hold the molecules at the surface of the table together. Your hand's molecules are also being held together by electromagnetic forces. And the so-called "particles' which make up atoms and molecules are really matter fields spread out like waves. They don't act as individual particles until they are detected. So "solid" is an illusion, albeit a very convincing one.

[steevey]

Physicst say according to the rules of quantum physics, sub atomic particles have duality as "particle and waves" . I dont understand this. We all know the sub atomic particles are the basic matter of an atom and all the solid materials including you and me are made up of atoms. Then what is reality? What we are seeing in every day life is just a pattern of waves? is there nothing solid?

 

 

Basically, all elementary particles have properties of their existence oscillating like a wave. The the elementary particles themselves are particles, but their trajectory and locations and any given point in time occur in wave patterns which is why you need wave mechanics to describe them. The particles, as far as our understanding goes, are not waves themselves. However, the regions these particles oscillate their existence is very very small and most of the time occurs very repetitively in specific areas, thus giving the illusion of solid objects. As a part of having wave-like properties, you cannot determine with 100% certainty where a particle will appear at any time but can figure out the most likely place for it to appear in a given system, implying that waves spread out over areas with no specific location which have crests and troffs, or most likely and least likely places to exist exactly matching the patterns found in sine waves. Even when particles are observed at a localized state, the next location cannot be determined, since even at that point, they still have some of those wave like properties.

Edited April 14, 2011 by steevey

[swansont]

The the elementary particles themselves are particles, but their trajectory and locations and any given point in time occur in wave patterns which is why you need wave mechanics to describe them.

 

No. This misses the point of QM. They are not particles with some wave properties. They don't have trajectories and they don't have locations when they aren't being observed. They are waves.

[steevey]

No. This misses the point of QM. They are not particles with some wave properties. They don't have trajectories and they don't have locations when they aren't being observed. They are waves.

 

 

We can't determine that they themselves are waves if I can remember, only their locations on an atomic level can be described using wave mechanics and maybe a few other properties and thats it. Something about a particle would be wave-ing which is what the math is describing.

This would perfectly explain why particles can seem classical and quantum at the same time. Like spin, its properties are "like" a classical piece of matter, but with something in matter oscillating as a wave, spin also seems to act like a wave.

 

And if particles are only waves, why is it that they only have particle properties when we look around? Being localized is roughly the same as a particle existing since its a specific region, so being a particle isn't a property of matter acting like a wave, its a property of matter not acting like a wave, or being determined.

 

 

Edited April 14, 2011 by steevey

[swansont]

We can't determine that they themselves are waves if I can remember, only their locations on an atomic level can be described using wave mechanics and maybe a few other properties and thats it. Something about a particle would be wave-ing which is what the math is describing.

This would perfectly explain why particles can seem classical and quantum at the same time. Like spin, its properties are "like" a classical piece of matter, but with something in matter oscillating as a wave, spin also seems to act like a wave.

 

And if particles are only waves, why is it that they only have particle properties when we look around? Being localized is roughly the same as a particle existing since its a specific region, so being a particle isn't a property of matter acting like a wave, its a property of matter not acting like a wave, or being determined.

 

But what you are ignoring here is that they act like waves when we aren't looking — we see interference effects, for example — and experiments have shown that there aren't local hidden variables, i.e. it is not the case that they have the particle properties and we just can't see them.

 

The QM picture is larger than what you've seen.

[Advaithi]

I am not a physcist, not even a student. But My average man's mind cannot understand how a particle can act like a wave when we are'nt looking? though I am an atheist, I agree with einsteins words " God does not play dice".

 

 

[swansont]

I am not a physcist, not even a student. But My average man's mind cannot understand how a particle can act like a wave when we are'nt looking? though I am an atheist, I agree with einsteins words " God does not play dice".

 

Einstein was wrong.

 

It's all waves, but you don't notice the wave behavior for particles with large momenta.

[farmboy]

I am not a physcist, not even a student. But My average man's mind cannot understand how a particle can act like a wave when we are'nt looking? though I am an atheist, I agree with einsteins words " God does not play dice".

 

When Einstein said that I don't think the idea was to disagree with wave particle-duality as such. QM shows that sometimes in quantum systems you can essentially set up an experiment with the same conditions, and not get the same result each time. Thats not a great description lol, but I think an example they often use is that if you send a stream of photons through a piece of glass, some will be reflected some will be transmitted but we can't predict which will go through and which won't, we can only say how many will go through on average. Now this didn't sit well with einstein because he couldn't accept that the same experimental conditions could produce different results, even though all the evidence suggests that this is the case. He believed that there must be some unseen factor that was influencing the results. Not really how science should be performed in my opinion. We shouldn't let our personal beliefs about what we think should happen override what the evidence tells us happens.

 

And yeah, I think that with the quantum mechanical world you really have to stop trying to think about it in ways that directly correlate to phenomena in the macroscopic world. Electrons aren't little balls of negative charge circling a nucleus in a way that can be described using classical mechanics. My understanding of it (which I admit is probably inferior to that of many of the physicists on this board) is that an electron in its natural state is more like an area of negativity which can be described using a wave equation. The exact nature of the electron is dependant on its environment, but it is only when we attempt to probe it that we change its nature giving it the characteristics of a particle.

 

If that is inaccurate in anyway I'd be happy for someone to point it out, as this is undenibaly a difficult concept to grasp, and one which I could really do with understanding a little better myself.

[steevey]

But what you are ignoring here is that they act like waves when we aren't looking — we see interference effects, for example — and experiments have shown that there aren't local hidden variables, i.e. it is not the case that they have the particle properties and we just can't see them.

 

The QM picture is larger than what you've seen.

 

I can see QM just fine now, and I use to think that matter was a wave itself, but now it makes even more sense that its just the existence of that matter that is waving and not that matter is necessarily a wave itself. Strictly speaking, matter isn't anything we think of at a classical level at all, whether thats waves of marbles, its its own thing which exhibits both properties of being in a determined location and being an in undetermined location, one can be described as having oscillating characteristics and one can be described of as not oscillating or static properties.

Edited April 15, 2011 by steevey

[elas]

No. This misses the point of QM. They are not particles with some wave properties. They don't have trajectories and they don't have locations when they aren't being observed. They are waves.

 

Given the number of electromagnetic waves is vast whereas the number of elementary particles is around 110 (depending on who you read), are you saying that only a minute number of electromagnetic waves can be observed as particles?

Edited April 19, 2011 by elas

[swansont]

Given the number of electromagnetic waves is vast whereas the number of elementary particles is around 110 (depending on who you read), are you saying that only a minute number of electromagnetic waves can be observed as particles?

 

As best as I can interpret, that's not even close to what I said.

[Klaynos]

There is a finite number of particles that we know about....

 

These particles are NOT particles in a classical sense...

 

They are also not really waves...

 

They are something else, something that we have no everyday experience of.

 

I cannot give you a nice analogy of what they are because we don't experience them, before very recently humans have never had a need to understand them, so we've not evolved the required mechanics to do so.

 

So, I could give you a mathematical description which would for the most part be very very wavelike, but then sometimes it'd be very very particle like. There would be no traditional trajectories.

 

As for how many there are, well there is an acceptable list here:

 

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

 

Now notice that for electromagnetism, there is the photon, that's one fundemental particle. Not a vast number...

[lemur]

The basic behavior of anything on the scale of h/p (planck's constant divided by momentum) is wave-like. Some properties are quantized, though, so they act like particles at times. As far as atoms go, they are mostly empty space, even of you look at the constituents as particles. Solids seem that way because of electromagnetic interactions that get very strong at short range.

Saying that atoms are mostly space implies that point-particles have some definable volume. I don't think that's the case. So why do people say that atoms are "mostly empty space" instead of saying that they're completely empty space whose operative volume is a result of their forces and energies? Do point-particles have volume independently of the configurations they form? Is it possible to predict a minimum volume for any type of particle, such as a collection of electrons, protons, or neutrons?

[swansont]

Nuclei have fairly well-defined sizes, many orders of magnitude smaller than atomic sizes.

[elas]

Saying that atoms are mostly space implies that point-particles have some definable volume. I don't think that's the case. So why do people say that atoms are "mostly empty space" instead of saying that they're completely empty space whose operative volume is a result of their forces and energies? Do point-particles have volume independently of the configurations they form? Is it possible to predict a minimum volume for any type of particle, such as a collection of electrons, protons, or neutrons?

 

This might be of some help:

 

http://web.mit.edu/newsoffice/2010/casimir-0511.html

 

Quantum mechanics has bequeathed a very weird picture of the universe to modern physicists. One of its features is a cadre of new subatomic particles that are constantly flashing in and out of existence in an almost undetectably short span of time. (The Higgs boson, a theoretically predicted particle that the Large Hadron Collider in Switzerland is trying to detect for the first time, is expected to appear for only a few sextillionths of a second.) There are so many of these transient particles in space — even in a vacuum — moving in so many different directions that the forces they exert generally balance each other out. For most purposes, the particles can be ignored. But when objects get very close together, there’s little room for particles to flash into existence between them. Consequently, there are fewer transient particles in between the objects to offset the forces exerted by the transient particles around them, and the difference in pressure ends up pushing the objects toward each other.

 

In my view this implies that there is no empty space just a load of transient particles. The 'objects' presumnably are stable particles and if they can get 'close together' then they must have volume; the term 'point-like' is simply an admission that the volume cannot be measured neither is it predictable by QT.

Edited April 19, 2011 by elas

[swansont]

This might be of some help:

 

No, not really. It has nothing to do with the question.

[lemur]

edit: I'm moving this post to start a new thread on volume and empty space in an atom.

Edited April 19, 2011 by lemur

[DrRocket]

I am not a physcist, not even a student. But My average man's mind cannot understand how a particle can act like a wave when we are'nt looking? though I am an atheist, I agree with einsteins words " God does not play dice".

 

 

 

Here's Feynman on "wave-particle duality.

 

 

 

From the book QED based on the Robb Lectures by Feynman: "Quantum electrodynamics "resolves" this wave-particle duality by saying that light is made up of particles (as Newton originally thought), but the price of this great advancement of science is a retreat by physics to the position of being able to calculate only the probabilities that a photon will hit a detector, without offering a good model of how it actually happens."

[lemur]

Here's Feynman on "wave-particle duality.

 

 

 

From the book QED based on the Robb Lectures by Feynman: "Quantum electrodynamics "resolves" this wave-particle duality by saying that light is made up of particles (as Newton originally thought), but the price of this great advancement of science is a retreat by physics to the position of being able to calculate only the probabilities that a photon will hit a detector, without offering a good model of how it actually happens."

What's the probability that Feynman was wrong and what's the confidence level of certainty for the answer?

[DrRocket]

What's the probability that Feynman was wrong and what's the confidence level of certainty for the answer?

 

Feynman probably understood quantum yheory as well as anyone who has ever lived.

 

There are different, valid, ways to view QM. The post above gives you his perspective. To say that Feynman is "wrong" would be pretty sporting.

Edited April 19, 2011 by DrRocket

[IM Egdall]

What's the probability that Feynman was wrong and what's the confidence level of certainty for the answer?

 

Feynman's Quantum Electrodynamics (QED) has made predictions on the behavior of subatomic particles which have been verified by numerous experiments to extraordinary accuracy. Based on all this empirical evidence, QED is a triumph, a superb theory.

 

What can be confusing is that there are different approaches to quantum theory, and they give different interpretations as to what is happening. For example QED represents electrons as particles. But these particles have a "phase" and the probability of a single electron arriving at a detector is calculated by considering the sum of all possible paths of that electron (and the phase for each path). Weird, huh!

 

And in Quantum Field Theory (QFT) an electron is considered a probability wave as it travels from place to place - the so-called wave function. This wave funcvtion then collapses once the electron is detected. So the electron travels like a wave and is detected like a particle. But exactly where the electron is detected cannot be predicted; only the probability of finding the electron at a given location.

 

Both models, QED and QFT, are extraordinarily accurate, and give identical predictions. Both apply to all subatomic particles, atoms, and molecules (and the objects they make up.) They both tell us that a single electron or any other particle travels through both slits in the double-slit experiment and interferes with itself. And this is just what physicists see when they do the actual experiment.

[timo]

I ME: QED is a QFT. So QED and QFT are not different as in "car and bike" but as in "car and vehicle".