Quantum particles

[Upisoft]

We had a little discussion with Chalnoth in an inappropriate forum. So I'm moving my answer here.

They are quantum mechanical particles. This is what quantum mechanical particles are: particles with wave-like properties.

I agree, Chalnoth, but what I origianlly said was that they do not react as a wave and as particles in the same time. Each separate interaction is either wave like or particle like.

The particle property stems from the simple fact of quantization, where everything has to come in discrete levels. The wave property stems from the particles following a particular field equation.

In both statements you're trying to put the cart before the hourse. Particle property is fact. It is observable. The same is with the quantization. It also is observable. What stems from what is not observable. Also, wave properties are observable, but the field equation is not. The scientists did very good job to find equation that describes the observed wave properties.
Did you see the pattern? I use the word "observed" a lot. That's because what we know about them was result of observation. And we can observe them only when they interact. You seem to say that you know what is their behaviour between the interactions. And that we don't know.

So, for example, if you shoot single photons through a dual-slit apparatus, they still interfere. They are clearly single photons, because they show up as individual dots on the receiver apparatus. But they hit the receiver apparatus with a probability consistent with wave interference.

That is because there are al leat 2 interaction of that photon. First is the interaction with the dual slit. It is wave like. The second is the interaction with the "screen", which is particle like. They do not happen in the same time.

It is somewhat misleading, though, to state that they are much like the classical definition of either a particle or a wave. They are quantum mechanical particles that have properties of both, but are also distinct from both.

Yes, they're different. And do have both properties, but do not express them in the same time.

 

[michabo]

Not sure what your claim is, here. Can you give us some context?


The simple answer is that both of you are wrong

Photons and electrons are neither particles nor waves, they don't behave like anything that we have experience with in the macro world. We may use the terms "particle" and "wave" as metaphors to help our intuition when we begin learning about them, but we must bear in mind that these metaphors are inherently flawed.

 

[arunma]

Photons and electrons are neither particles nor waves, they don't behave like anything that we have experience with in the macro world. We may use the terms "particle" and "wave" as metaphors to help our intuition when we begin learning about them, but we must bear in mind that these metaphors are inherently flawed.

Actually I would say that they are "both" rather than "neither." Photons and electrons both exhibit genuinely wavelike and particlelike behaviors. Why are these terms less than ideal?

 

[michabo]

Actually I would say that they are "both" rather than "neither." Photons and electrons both exhibit genuinely wavelike and particlelike behaviors. Why are these terms less than ideal?

Quite simply, they aren't a particle since they have wave-like characteristics, and they aren't a wave because they have particle-like characteristics.

These two are mutually exclusive, hence "neither" not "both".


It also gets to their true nature, which is that they are something wholly unfamiliar to us. And do I need to tell you that there are many traits which are neither wave nor particle, such as entanglement, tunnelling or uncertainty in general? How can you understand the behaviour of light passing through polarized lenses if we think of light as either a particle or wave?

 

[HypnoToad]

Actually I would say that they are "both" rather than "neither."

hese two are mutually exclusive, hence "neither" not "both".

"You got your peanut butter in my chocolate!"
"No, you got your chocolate in my peanut butter!"

 

[[serious]]

Quite simply, they aren't a particle since they have wave-like characteristics, and they aren't a wave because they have particle-like characteristics.

These two are mutually exclusive, hence "neither" not "both".


It also gets to their true nature, which is that they are something wholly unfamiliar to us. And do I need to tell you that there are many traits which are neither wave nor particle, such as entanglement, tunnelling or uncertainty in general? How can you understand the behaviour of light passing through polarized lenses if we think of light as either a particle or wave?

Actually, wave properties can be detected in conventional particles too. All objects are assumed to have wave properties as well, but due to the increasing role of the particle properties, larger object's wave properties can't be directly observed.

 

[michabo]

"You got your peanut butter in my chocolate!"
"No, you got your chocolate in my peanut butter!"
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Your peanut butter tunnelled out of the jar and because I knew where my chocolate bar was, now I can't tell in which direction it is moving or how fast!

Tell me: is an electron acting like a wave or a particle when it tunnels? Is the uncertainty principle a feature of waves or particles?

It's easy to crack jokes, but not so easy to understand the issues.

 

[Upisoft]

Not sure what your claim is, here. Can you give us some context?

Follow the link back to the original thread. Probably he misunderstood me or I misunderstood him.

The simple answer is that both of you are wrong

That's quite probable.

Photons and electrons are neither particles nor waves, they don't behave like anything that we have experience with in the macro world. We may use the terms "particle" and "wave" as metaphors to help our intuition when we begin learning about them, but we must bear in mind that these metaphors are inherently flawed.

Neither he nor I say that. He say that they have both properties. I say that we can't say that. We can say that they can act wave like and particle like. I also say they do not express their duality in a single interaction. Latter means they don't have both properties. At least not in a single interaction. And since we can only observe them via their interactions, it is impossible to say what are photons while they are not interacting.

 

[Upisoft]

Tell me: is an electron acting like a wave or a particle when it tunnels? Is the uncertainty principle a feature of waves or particles?

I would say that this is third type of interactions they have and most probably we will find more in the future. Anyway, that does not mean they express two or more ways of interaction in a single event.

 

[michabo]

I would say that this is third type of interactions they have and most probably we will find more in the future. Anyway, that does not mean they express two or more ways of interaction in a single event.

In some circumstances, they have some properties of particles or waves.

I'm not sure what you mean in the last sentence. They aren't flipping between waves and particles. Instead, they are always behaving as something that is neither a wave nor a particle, but at times they appear to behave sufficiently like a wave or a particle for us to simplify things. In many cases, it simply does not make sense to treat them as either a wave or a particle, and we must treat them as what they are: something else entirely.

Take the double-slit experiment with electrons. Are they behaving as particles or waves? When you answer, what aspect of the experiment are you talking about? If we add in a detector on either side of the slits, then are they acting as a wave or as a particle?

If you wish to understand the experiment properly, you cannot treat the particles as merely a wave or a particle. And the double-slit is probably the biggest "I'm a wave" gimme that I can think of. Everything else is far more complex.

 

[Upisoft]

Take the double-slit experiment with electrons. Are they behaving as particles or waves?

There are at least two interaction. First interaction is between the electron and the doulbe-slit. It is wave like. When you combine enough attemts you will get interference fringe.The second interaction is between the electron and the screen. It is particle like, you get a dot where the electron hits.

If we add in a detector on either side of the slits, then are they acting as a wave or as a particle?

3 interactions here.
1. wave like (like in fist experiment)
2. erasure event. (detector erases the information about the interference.)
3. praticle like (like in first experiment)

If you wish to understand the experiment properly, you cannot treat the particles as merely a wave or a particle. And the double-slit is probably the biggest "I'm a wave" gimme that I can think of. Everything else is far more complex.

Well, of course, as you said there are such things like entanglement, tunneling and may I add superposition. I did not attempt to describe them simply as wave/particle. I just wanted to say that you can't make them to act both as wave and particle. In other words, you can't get interference and which slit information.

 

[michabo]

There are at least two interaction. First interaction is between the electron and the doulbe-slit. It is wave like. When you combine enough attemts you will get interference fringe.The second interaction is between the electron and the screen. It is particle like, you get a dot where the electron hits.


3 interactions here.
1. wave like (like in fist experiment)
2. erasure event. (detector erases the information about the interference.)
3. praticle like (like in first experiment)

Do you see what you're doing here?

In the first case, you say that the electron acts like a wave when it passes through both slits, but in your second explanation, when you toss in your magical time-altering "erasure event", you acknowledge that no, the electron isn't acting like a wave at all when it passes through the double slits.

You may simplify the situation and imagine that electrons act like waves, but you are wrong. The experiment proves that you are, and your own words show you know this. The electron doesn't act like a wave when it passes through the double slits. It acts like an electron, which is neither a particle nor a wave but something else that doesn't resemble anything in the macro world.

I notice too that you say it acts like a particle when it his the detector. You say that because it comes in discrete quanta, but you should know that the interaction with the screen is actually something quite strange that shatters any notion that it is a particle or a wave. Before it registers a hit on the phosphorous screen, the electron can only be said to be in almost a cloud of probabilities. The position cannot be known with any certainty. The probability moves almost like a wavefront (again with the poor metaphors) and the electron only achieves a definite position when it interacts with the phosphorous.

So you say that it acts as a particle when it strikes the phosphorous, but again, you are wrong. It has particle-like properties such as a mass and position for a brief moment, but this just illustrates how very unlike a particle it really is.

I just wanted to say that you can't make them to act both as wave and particle. In other words, you can't get interference and which slit information.

Which slit information, no.

But with a detector behind the slit, you have to resort to these magical sentient electron contortions to make your argument. If anything, once you have to say that electrons can analyze the experimental setup and travel back in time to repeat the experiment using a different "mode" of existence, I think that it's fair to say that your argument needs work

 

[Loudmouth]

Tell me: is an electron acting like a wave or a particle when it tunnels? Is the uncertainty principle a feature of waves or particles?

Uncertainty is a feature of the wave function. The wave function is actually a probability function. There is a finite probability that an electron will be in an area described by a wave function. When the electron is observed, forcing it to be a particle, that probability function collapses to one possibility out of many.

The best experiment I know of to illustrate this counterintuitive characteristic is the polaroid lens experiment. Polarized lensis have slits like a picket fence. Only photons that have wave functions parallel with the slats can make it inbetween the slits. If a photon's wave is perpendicular to the slits then it is absorbed by the lens. Light at 45 degrees to the slits also squeezes through. This is how polaroid lenses cut down on glare, they eliminate the light that is not parallel to the line of sight.

Get three of these lenses (they also come in sheets). Now, if you line up the slits from two lenses so that they are perpendicular then no light goes through. However if you line them up so they are at 45 degree angles to each other then half of the light gets through. Here comes the fun. Line up two sheets again so that the slits are perpendicuar. No light gets through. Now, insert the third sheet in between the other two so that it is at a 45 degree angle to both. What happens now? 25% of the light gets through!! Why is that? Well, the light had a 50% chance of getting through the first two and a 50% chance of getting through the second two. 0.5 * 0.5 = 0.25.

If photons actually were a particle travelling as a wave this experiment wouldn't have these results. No matter how many lenses you went through if there are two lenses anywhere in the series that are perpendicular then you get absorbed. However, if the wave is actually a probability then each event is separate and you can get through even if two of the lenses in the series are perpendicular.

The same experiment is also described here if my description is hard to follow.

It's easy to crack jokes, but not so easy to understand the issues.

It's easy to say that they have to be a wave AND a particle at the same time, but the experiments say otherwise.

 

[Chalnoth]

If photons actually were a particle travelling as a wave this experiment wouldn't have these results.

This isn't actually true. The behavior of polarizing filters can be described just fine using classical electricity and magnetism, without resorting to quantum mechanics.

Basically, when the light travels through the filter, only the component of the electric field of the light wave that is parallel to the polarization axis makes it through. This picks up a dot product of the electric field direction with the polarization axis. Since the intensity of the light scales as the electric field squared, you end up with a cos(theta)^2 term when linearly-polarized light passes through one filter.

This turns out to produce identical behavior to the quantized explanation of what is occurring.

It's easy to say that they have to be a wave AND a particle at the same time, but the experiments say otherwise.

Well, more specifically they are just quantum mechanical particles. And quantum mechanical particles act neither like a classical idea of a particle, or a classical idea of a wave, but instead share properties of both. There is no separation between particle and wave in quantum mechanics.

 

[Loudmouth]

This isn't actually true. The behavior of polarizing filters can be described just fine using classical electricity and magnetism, without resorting to quantum mechanics.

Basically, when the light travels through the filter, only the component of the electric field of the light wave that is parallel to the polarization axis makes it through. This picks up a dot product of the electric field direction with the polarization axis. Since the intensity of the light scales as the electric field squared, you end up with a cos(theta)^2 term when linearly-polarized light passes through one filter.

How does this explain why no light gets through if the middle lens is removed?

Well, more specifically they are just quantum mechanical particles. And quantum mechanical particles act neither like a classical idea of a particle, or a classical idea of a wave, but instead share properties of both. There is no separation between particle and wave in quantum mechanics.

Right, but the major point is that quantum particles never act as both a wave and a particle at the same time. It is either one or the other.

 

[Chalnoth]

How does this explain why no light gets through if the middle lens is removed?

The electric field is perpendicular with respect to the axis of the second polarizing filter, admitting no light. With the filter in the middle, the electric field hits both the second and third filters at 45%, rotating each time due to electric field on exiting the filter being parallel to the polarization axis.

Right, but the major point is that quantum particles never act as both a wave and a particle at the same time. It is either one or the other.

Well, no. If you're talking about classical waves and classical particles, it's neither. Quantum mechanics has one description for these things, and that description does not make sense as being 'sometimes wave and sometimes particle'. An example where a quantum mechanical particle acts with properties similar to both is when photons travel through a dual-slit one at a time, as they hit the screen with a probability distribution given by an interference pattern (wave-like property), but hit the screen at points (particle-like property). One cannot separate the two.

 

[michabo]

The electric field is perpendicular with respect to the axis of the second polarizing filter, admitting no light. With the filter in the middle, the electric field hits both the second and third filters at 45%, rotating each time due to electric field on exiting the filter being parallel to the polarization axis.

That's very cool. I can recall having it explained to me this way before and even working through the equations, but it was almost half my lifetime ago and I've blanked on the details. Thanks for explaining it to us.

 

[Chalnoth]

That's very cool. I can recall having it explained to me this way before and even working through the equations, but it was almost half my lifetime ago and I've blanked on the details. Thanks for explaining it to us.

Any time. I love this stuff

 

[Upisoft]

Do you see what you're doing here?

In the first case, you say that the electron acts like a wave when it passes through both slits, but in your second explanation, when you toss in your magical time-altering "erasure event", you acknowledge that no, the electron isn't acting like a wave at all when it passes through the double slits.

Didn't said that. The electron is still acting like a wave until it interacts with the detector where that information is being erased from its state. No magic here.

You may simplify the situation and imagine that electrons act like waves, but you are wrong.

We're all wrong. The electrons are what they are.

The experiment proves that you are, and your own words show you know this. The electron doesn't act like a wave when it passes through the double slits. It acts like an electron, which is neither a particle nor a wave but something else that doesn't resemble anything in the macro world.

Of course it is something more complex than wave or particle. That was not my point. My point was that in single interaction it will express either particle like or wave like behaviour, but not both in the same time. In other words you can't make a single electron to hit more than one place. Nor you can get interference if you know which slit it passed through.

I notice too that you say it acts like a particle when it his the detector. You say that because it comes in discrete quanta, but you should know that the interaction with the screen is actually something quite strange that shatters any notion that it is a particle or a wave. Before it registers a hit on the phosphorous screen, the electron can only be said to be in almost a cloud of probabilities.

Do you have an experiment that shows the electrons have been observed in this state?

The position cannot be known with any certainty.

It is the dot on the screen.

The probability moves almost like a wavefront (again with the poor metaphors) and the electron only achieves a definite position when it interacts with the phosphorous.

Exactly what I was saying. in the moment of interaction, i.e. what can be observed, it acts like particle with definite position.
When you show me an electron hitting several places on the screen, then I'll change my mind.

So you say that it acts as a particle when it strikes the phosphorous, but again, you are wrong. It has particle-like properties such as a mass and position for a brief moment, but this just illustrates how very unlike a particle it really is.

And that brief moment was the only moment when you can observe it. Other moments are some fancy mathematics that do pretty good job to predict their behavior, but in fact it have not been observed.

 

[Upisoft]

The electric field is perpendicular with respect to the axis of the second polarizing filter, admitting no light. With the filter in the middle, the electric field hits both the second and third filters at 45%, rotating each time due to electric field on exiting the filter being parallel to the polarization axis.

Don't you see. You explain that using only electromagnetic field, which has wave-like properties. Where was your "but it was particle in the same time" part?