particle location

[simong]

.1 as I understand, one particle can be in two places at the same time. for instance tha particle that is building the table can be in the table and in the same time sumewere els. my question is are we talking about two particles or about one. if we are talking about one particle, what makes the table exist at the time the particle is sumewere els?

 

 

. 2what makes the string vibrate according to the string theory?

 

)I'm apologizing for my poor English(

 

simon

[DParlevliet]

1 Not at the same time. It can be for a very short time somewhere else and then is back again. The change is mostly very, very small (longer then the life time of the Universe)

2 Nobody knows

[Delbert]

.1 as I understand, one particle can be in two places at the same time. for instance tha particle that is building the table can be in the table and in the same time sumewere els.

Well, I think you'll find it's not limited to two particles. It can be everywhere at once. Which presumably means an infinite number!

 

It seems to me we get bogged down on this particle business. You know, like little billiard balls. I believe the undoubted fact is they are not little billiard balls, or anything remotely resembling one. Atomic or subatomic particles I think don't operate anything like things we love and know about. They operate in mysterious ways completely unlike everyday objects. More like events occasioned within or by some sort of wave field - so perhaps they don't even exist as such! And as far as I'm aware, a wave is something that spreads out everywhere.

 

Anyway, I understand the billiard ball model was Rutherford's. Prior to that I think there was the plum pudding model. So it's just a convenient model for our imagination to play with.

[Enthalpy]

1 Not at the same time. It can be for a very short time somewhere else and then is back again.

This interpretation is proven false and abandoned for many decades.

[...] if we are talking about one particle, what makes the table exist at the time the particle is sumewere else?

Under normal conditions, particles are much more localized than that. An atom belonging to the table won't be anywhere else.

(if you mean: due to quantum mechanics. Dust or rotting or earthquake is a different question).

 

The typical delocalization of an electron is the size of an atom or a molecule. Heavier particles like atom nuclei are more localized than electrons.

 

In some experiments (or natural processes, especially with photons) the particle can be delocalized more broadly, but then it doesn't pertain to the small object any more.

 

More generally, quantum mechanics gives classical results at big scales - except for artificial conditions. Then you have waves like light, which can be macroscopically delocalized, but about which nobody complaints because they were called historically waves instead of matter. You can imagine quantum mechanics as a unification: matter propagates like other waves do, waves are absorbed like other particles are. QM makes still distinctions, but between fermions and bosons, which is not completely the old distinction between matter and fields.

[MigL]

Keep in mind that a wave function does NOT describe a particle or a wave.

It describes a probability distribution.

[Enthalpy]

Keep in mind that a wave function does NOT describe a particle or a wave.

It describes a probability distribution.

Doesn't it?

 

What else would you desire beyond the wavefunction to describe what you call a "particle or wave"?

[DParlevliet]

What else would you desire beyond the wavefunction to describe what you call a "particle or

 

With a photon it does not describe the absorption by a detector: why, where, when.

[Delbert]

 

...why, where, when.

The why where and when, I understand, is not something that can be observed or even ascribed as a property of subatomic particles.

[DParlevliet]

The why where and when, I understand, is not something that can be observed or even ascribed as a property of subatomic particles.

 

Why: the particle release an electron from an atom (during detection)

Where: at the place where it is detected. Normally in a more or less straight line between emitor and detector.

When: after c * l after being emitted. For instance 3,3 ns after 1 m

[MigL]

Come on Enthalpy, you know exactly what I'm talking about.

The wave function gives us all the information about a quantum particle, but this information is probabilistic in nature.

It may tell us that an electron has a high probability of being found here, but also a diminished probability of being found at a different location.

This is sometimes used to explain tunnelling.

[Delbert]

 

Why: the particle release an electron from an atom (during detection)

Where: at the place where it is detected. Normally in a more or less straight line between emitor and detector.

When: after c * l after being emitted. For instance 3,3 ns after 1 m

No, I think you're missing the point.

The why: you don't or won't know why it's released from any particular atom, as distinct from any other atom.

The where: as above, you won't know from where.

The when: again as above, you won't know what time.

 

And to say: there it has landed at a particular point on a sensor plate (or whatever), is irrelevant. For the simple reason you had no idea where it was going to land. The probability was it could've landed anywhere, and that is no knowledge at all of the where. Indeed, I believe there is a very tiny remote probability that it could even land behind the source!

 

And then there's the two slit experiment, which I think can apply to electrons as well as photons - or possibly any subatomic particle. And what's more, I understand one could even have far more slits, and the particle would appear to travel through all of them! The simple fact is we've no idea where the damn thing is.

 

And as for this other business about something on one side of the universe resulting in a spontaneous event the other side... I understand there's a name for it, but I can't recall.

[Enthalpy]

The wave function gives us all the information about a quantum particle, but this information is probabilistic in nature.

And this is perfect, because the very nature of particles is to be probabilistic. This is the only surviving interpretation of QM presently, the others having been dismissed experimentally.

 

Even better: what we call particle is a word put on the random behaviour of waves. It is because waves have the ability to concentrate at a narrower location (a detector pixel, say) despite being broad, or over a limited duration despite lasting long, or in one polarization despite having a random one, and more examples of choice, that we say "waves are also particles".

 

Waves keeping spread while interacting would be classical. This doesn't suffice to model our world (historically: the photoelectric effect). We need the ability of wavefunctions to collapse.

 

So complaining about particles being probabilistic is a blind alley. Particles are the random behaviour of waves, plus a way to account some conserved quantities.

[MigL]

You still haven't grasped that there is a vast difference between classical particles and Quantum Particles. Look up the definition.

[Enthalpy]

OK, go on without me. Good luck to understand QM through philosophical considerations and newspaper-class knowledge, if you hope such discussions will help you.

[DParlevliet]

No, I think you're missing the point.

The why: you don't or won't know why it's released from any particular atom, as distinct from any other atom.

The where: as above, you won't know from where.

The when: again as above, you won't know what time.

 

You do know when you use particle properties. See the measurement from another topic:

 

Suppose the right path is 1 m, the left path 10 m, then will only (mostly) find photons detected 3.3 ns or 33 ns from the input detector. After detection you can calculate how the photon travelled, also intermediate positions. That can only de done with particle properties. The fact that you cannot see the photon travelling is not relevant, the wave you cannot see either.

[MigL]

Thankyou for granting your permission Enthalpy.

My understanding of QM is based on study, not philosophical considerations or newspaper articles.

My understanding is that you would rather preach than discuss.

[Delbert]

After detection you can calculate how the photon travelled, also intermediate positions. That can only de done with particle properties. The fact that you cannot see the photon travelling is not relevant, the wave you cannot see either.

I think you will find that that is called classical mechanics.

 

" you can calculate how the photon travelled" and "also intermediate positions", how does one calculate how it travelled and identify intermediate positions in the case of the two slit experiment?

 

It seems to me you're getting confused between what happens in the case of individual photons compared to a beam of photons. A beam is the collective probability of umpteen photons (something like that), whereas firing a single photon is completely different - you can't predict.

 

Perhaps a comparison might be tossing a coin. Toss a coin several thousand times and one can say with a betting certainty that half will be heads and the other half will be tails. Whereas toss a coin just once and you can't predict.

Edited December 9, 2013 by Delbert

[DParlevliet]

I think you will find that that is called classical mechanics.

 

Of course. QM tells that photons has properties of classical wave and classical particles and because it is not know how they are exactly related, they have to be described as they are measured, so classical.

 

" you can calculate how the photon travelled" and "also intermediate positions", how does one calculate how it travelled and identify intermediate positions in the case of the two slit experiment?

 

As above, by measuring the travel time. Even if you don't do that, then you know the two possible tracks.

When you measure one photon, you also don't know through which slit the wave went.

 

I only argue about single photons and what I wrote above you know after measuring one photon.

[Delbert]

 

Of course. QM tells that photons has properties of classical wave and classical particles and because it is not know how they are exactly related, they have to be described as they are measured, so classical.

"it is not know[n] how they are exactly related" and then "described as they are measured". I'm sorry, but that sounds like a glaring contradiction.

 

As above, by measuring the travel time. Even if you don't do that, then you know the two possible tracks.

Two possible tracks! So how does one reconcile: "After detection you can calculate how the photon travelled". With the 'the' presumably being the definite article. I'm sorry, but it seems to me you're trying to square the circle.

 

When you measure one photon, you also don't know through which slit the wave went.

I'm sorry, but you can't claim to know the dynamics of this photon as you've previously outlined if you don't even know what path it has taken. I rest my case.

 

The plain fact of this wave/particle duality that we humans wrestle with is that it's neither nor both. It seems all we can say is that an event occurred at the source followed by an event at the destination a moment later. What happened in between cannot be assumed to be a little billiard ball called can photon travelling from the source to the destination. From what I understand, if we do try to observe the path of this billiard ball (say in the two slit experiment) during transit, it gives us a two fingers salute! Apparently its path or journey become two paths or journeys - or more if more slits! Or as I put it in sentence two of this paragraph, two events now become four events. What happens between either one of these two sets of events is not a particle in transit. And I further understand, no experiment has managed to identify a photon actually in motion. If we try so to do, we simply destroy the situation - i.e. the two slit experiment.

 

I further understand that some say we'll always slightly upset things by taking measurements and that may account for resultant different situations. But unfortunately, that does not account for the two slit experiment, whereby firing photons one at a time resulting in an interference pattern, concluding that it goes through two slits at the same time. And not forgetting that by closing one slit you get photons landing where there were no photons with two slits! Trying to measure photon paths is pointless in such a bizarre scenario - claiming measurement disturbance is irrelevant.

 

Indeed, what conclusion would we come to if we could measure such without causing disturbance, and identify a particular slit? We'd doubtless have an even more difficult job explaining the experiment and the diffraction pattern.

[DParlevliet]

 

In above double slit both paths are different. So when measuring the time between input detector and main detector you know through which slit the particle went, isn't it?

[MigL]

The modern definition of a quantum particle is given by Quantum Field Theory.

It is not a classical particle or a wave, or even a combination of the two.

It is an excitation of a quantized gauge field.

 

In QCD the 'colour' field ( not sure of this terminology ) is quantized, giving rise to quarks as excitations.

It would be interesting to see how confinement, such that quarks are not separable, but must be bound to two others ( in a proton or neutron ), would be handled by particles or waves ????

[Delbert]

 

In above double slit both paths are different. So when measuring the time between input detector and main detector you know through which slit the particle went, isn't it?

I don't agree with that hypothesis for the reasons I've already outlined.

 

But just for arguments sake we'll assume your proposed measurements would indicate a preference or actually identify which slit. So, number one: how does lots of those (photons we'll call them) eventually produce an interference pattern? And number two: upon closing one slit we then get detection in areas that didn't detect photons when both slits were open (the dark areas of the interference pattern)?

 

I'm sorry, but you seem to be applying classical mechanics to something that doesn't obey classical mechanics.

The modern definition of a quantum particle is given by Quantum Field Theory.

It is not a classical particle or a wave, or even a combination of the two.

It is an excitation of a quantized gauge field.

Thanks for the info. Although my knowledge of gauge field is somewhat vacant.

[MigL]

Two kinds of symmetries, global and gauge.

Global symmetries, by Noether's theorem, conserve currents and give rise to our conservation laws.

They invoke symmetry betwen two different states.

Gauge symmetries, on the other hand, are symmetries between the same state, but measured a different way

A gauge field, like the electromagnetic, is any field where this kind of symmetry applies.

 

I hope that's a little clearer than mud ( really hard to put into words ).

[DParlevliet]

I don't agree with that hypothesis for the reasons I've already outlined.

 

But just for arguments sake we'll assume your proposed measurements would indicate a preference or actually identify which slit. So, number one: how does lots of those (photons we'll call them) eventually produce an interference pattern? And number two: upon closing one slit we then get detection in areas that didn't detect photons when both slits were open (the dark areas of the interference pattern)?

 

What do you not agree: that you can measure the travel time or that the photon travels with a known speed (of light)?

 

Accordng the double slit description there is no difference between single photon or more.

 

Interference is a wave property. We are talking here about the particle properties.

 

Of course particle and wave are classic, you can only measure classis. But they are just properties.

 

p.s.: I changed the measurement a bit to make it more clear.

[Delbert]

What do you not agree: that you can measure the travel time or that the photon travels with a known speed (of light)?

So, according to your hypothesis one knows from what atom and when a photon is emitted, and time it. Because if you don't your idea is a simply a nonstarter rendering your timing method totally impossible. I'm sorry, but I'd place my salary on you not only having no idea whatsoever about when a particular photon sets off, but more importantly not ever being able to know because when an electron moves from one energy level to another (lower) one to emit a photon, it is down to QM uncertainty rather than classical mechanics.

 

 

Accordng the double slit description there is no difference between single photon or more.

Exactly, so where is the mechanism for producing the interference pattern in your diagram?

 

Interference is a wave property. We are talking here about the particle properties.

Those particles you say we've been taking about here (I'm not) build up and produce an interference pattern. You haven't described or included any mechanism in you diagram to account for such a pattern.

 

Again, I repeat the question in my reply #22. Describe to me how your billiard ball idea and diagram describes an interference pattern after umpteen photons have been fired. And furthermore, how the dark areas of said pattern where photons haven't hit, are then hit when one slit is covered up.