Does electron has definite path?

[bhobba]

So if you guys are disagreeing about more than the appropriateness of carllooper's use of the word "observe", I don't see it. And if I'm mistaken and there is a deeper disagreement, I still don't see much connection to the topic of this thread. Am I missing something here?

There is no disagreement.

Its just he is using words in ways I am not used to (dare I say it 'philosophically') and I am having difficulty following the point that is being made.

I have had a look at the latest post, and again I don't disagree with it, but can't quite put my finger on the key physical ideas being elucidated.

Added Later:
One point I will make, and I also made it in another thread with the same person, is we really do need to be careful when applying everyday language to QM. Its best IMHO, when being careful, to use terms with a definite meaning in the formalism rather than its everyday use - eg when being careful I use observation and decoherence synonymously.

Thanks
Bill

 

[Godparicle]

Can you describe, in detail, the apparatus that can be used to illuminate a single electron and track its motion?

Photons can pass through each other. In a given volume, we can have photons such that there is no space without photon (with the electron which has to be observed). Photons get scattered or reflected from the electron, in either case we can expect absorption and re-emission of photon (and thus use this to see the electron with appropriate technology).

Source (covers reflection and scattering, unfortunately there are no replies) : https://www.physicsforums.com/threa...flection-and-scattering-of-photon-qft.574747/

Source (covers only an idea of quantum picture of reflection) : http://arxiv.org/pdf/1207.0998.pdf

(I couldn't find better source on this, any related source or suggestion of reading w.r.t this, particularly on the difference between quantum picture of reflection and scattering, will be of interest to me)

Absorption and re-emission involves time delay (around 10^-23 to 10^-20 s).

Source: http://arxiv.org/ftp/arxiv/papers/1207/1207.0278.pdf

This time delay won't affect if the photons are incident continually.

QED says you can't do that (eg it may absorb the photon or scatter it), but if you have figured out how to overturn the most exactly verified physical theory of all time I am all ears.

Sorry, can you elaborate on how the QED resists me to do this experiment?

 

[carllooper]

I have had a look at the latest post, and again I don't disagree with it, but can't quite put my finger on the key physical ideas being elucidated.

The physical idea being expressed is that which can be found in an interference pattern (or more generally an image or signal). The image or signal can be understood as an effect of the individual particle detections.

But equally each of the individual particle detections can be understood as an effect of the signal. The signal (or image) is that which is visible in the pattern of detections, ie. in the relative densities of the detections across space.

And this signal is physical in the sense that one can physically alter it (ie. alter the relative density or distribution of particle detections) to obtain a physical effect. For example, an image of a sun can be manipulated by a lens to burn a hole in a piece of paper. The resulting fire is not a function of anyone particular particle detection, but the distribution or density of such detections across space.

This distribution is physical in that sense. It is "observable" in that sense. We can say the paper observes the distribution of particle detections as much as it does each individual detection considered on their own.

Carl

 

[bhobba]

Photons can pass through each other.

That's news to me:
http://en.wikipedia.org/wiki/Two-photon_physics

Its a low probability process at normal energies - but at the energies necessary to observe the position of an electron to a high degree of accuracy - that's another matter.

Precisely where are you getting this stuff from?

Its obviously not from an actual physics text.

May I suggest you make a sojourn and study such a text before arguing it.

Sorry, can you elaborate on how the QED resists me to do this experiment?

What experiment? You haven't detailed any experimental set-up. Once you do then we can discuss it. And if you can't do it then you may have to consider the possibility it doesn't actually have an observable path - which of course is the truth - but for some reason you want to doubt it.

BTW it was this precise requirement of exactitude in experimental set-ups that was one of the central themes of the great Einstein-Bohr debates, and why Einstein had to admit 'defeat' - although defeat is not the word I would use - it sharpened his real objection to QM which the EPR thought experiment elucidated, and was seminal to Bells great discovery of his famous theorem - but that is getting off topic.

However its a good example of the kind of experimental set-up I am asking you to detail:
http://en.wikipedia.org/wiki/EPR_paradox#Simple_version

Thanks
Bill

 

[Godparicle]

Precisely where are you getting this stuff from?

The following passage has been extracted from "Feynman's lectures on Physics-Vol I":

"...We have heard that idea so long that we accept it, and it is almost impossible for us to realize that very intelligent men have proposed contrary theories--that something comes out of the eye and feels for the object, for example. Some other important observations are that, as light goes from one place to another, it goes in straight lines, if there is nothing in the way, and that the rays do not seem to interfere with one another. That is, light is crisscrossing in all directions in the room, but the light that is passing cross our line of vision does not affect the light that comes to us from the object. This was once a most powerful argument aganist the corpuscular theory; it was used by Huygens. If light were like a lot of arrows shooting along, how could other arrows go through them so easily? Such philosophical arguments are not of much weight. One could always say that light is made up of arrows which go through each other!.."

 

[bhobba]

One could always say that light is made up of arrows which go through each other!.."

Well leaving aside the meaning of the little arrows in that layman popularisation - why do you think the arrows going through each other is the same as the particles going through each other?

The theory he helped father says photons don't necessarily go though each other - as the Wikipedia article I linked to details.

How can such a dichotomy occur?

Maybe its like the following from the FAQ:
https://www.physicsforums.com/threads/is-light-a-wave-or-a-particle.511178/
'So there is no duality – at least not within quantum mechanics. We still use the “duality” description of light when we try to describe light to laymen because wave and particle are behavior most people are familiar with. However, it doesn’t mean that in physics, or in the working of physicists, such a duality has any significance.'

QM is a theory about observations that appear here in the classical common-sense world. What its doing when not observed is anyone's guess. For some reason you want to doubt it. To argue it you are going to have to go beyond layman presentations.

The first step will be in detailing the exact experimental set-up to observe the path of a single electron. Oh - and you are also going to have to demonstrate the act of observation doesn't affect that path - in violation of the uncertainly principle. Good luck - Einstein tried and failed to get around it - but you are welcome to give it a shot.

Thanks
Bill

 

[Godparicle]

@bhobba: New thread has been started. Visit: https://www.physicsforums.com/threads/do-photons-pass-through-each-other.780524/

 

[Nugatory]

Photons can pass through each other. In a given volume, we can have photons such that there is no space without photon (with the electron which has to be observed).

That logic would work if these quantum particles had definite positions and occupied definite volumes of space - but they don't. If they did, we wouldn't have any difficulty assigning them definite paths, and this thread never would have started.

This thread is done.