Why the photon is disturbed by a hole?

[meBigGuy]

"

But once the endpoint is known, then we can choose a "valid" (still imagined) path form the all (a final result, the "winner"), and sometimes it is not possible to choose a straight one -- only a curved one. This, the final, curved/kinked path is what I'm talking about."

That is where you are missing the point. There is no single "final" path. There is only the sum of all the paths which sum to a probability amplitude for a given target location. If you only considered a "final" path you would see no amplitude variation. Think about it this way: In order to get cancellation, it MUST take at least two paths AT THE SAME TIME to the target point. Sometimes the two paths add, sometimes subtract to any given target. In reality there are infinite paths to every target, none of which is "the" path.

You can make up a curved path to the target if you like, but it will tell you nothing about the probability (brightness of the interference bands). Your made up path tells you nothing about the hole. The only way is to sum infinite paths through the hole to the target point (a path integral) to get a probability amplitude for the target point.

 

[Drakkith]

Personally I prefer to imagine that photons, and indeed all particles, do not exist as point particles until they interact with something. Easier than imagining a particle taking multiple paths at once and all that. But I'm not sure how "accurate" that is with regards to current quantum theory.

 

[zrek]

"
That is where you are missing the point. There is no single "final" path. There is only the sum of all the paths which sum to a probability amplitude for a given target location.

Yes you are right (thank you for spotting out), this is what was not clear and I forgot to explain. Now it is easier to realize and explain what is my problem.
I wanted to explain but somehow I missed to tell that (as I think) it doesn't matter if the path integral gives a final "single" path or not. Three things matter:

1. We are talking about paths (lots of).
2: We calculate them one by one, and during this process we count with obstacles. We must provide the concrete effect that why an obstacle blocks a path. Mathematically this is not necessary, but phisically this is important. I assumed that maybe this is the same effect as if we assume that if the single path was connected to a real photon, then it would lead the photon to be absorbed by the obstacle.
3: We know that the photon finally absorbed by the final obstacle, the detector screen. So if we are using lots of "single paths" during our calculations (point 2), and we are counting with them as assuming that what would be if that was the "final path" and the real photon, then it is logical to thinking on that the real final absorbtion point with the really real photon is also connected to a single path. (The final obstacle, the screen have no privilegued state, we are counting with it the same way.) (The conclusion is that you are right, we need at least two paths for the calculation, but as we are counting with the paths one by one the same way as "if it would be a real path", the final path is also a single one, and the interference which chooses it is only a side effect, an indirect effect.)

I know that my english is very bad, please forgive me and try to understand. Please let me know if it is confusing and I'll try to explain it on other way.

Also it is not necessary to agree with me in the point 3. But I think that you should consider agreeing that the point 2 must be clearly described, and we must choose a physical effect even if the paths we are calculating with are only imaginary constructions.

 

[zrek]

Personally I prefer to imagine that photons, and indeed all particles, do not exist as point particles until they interact with something. Easier than imagining a particle taking multiple paths at once and all that. But I'm not sure how "accurate" that is with regards to current quantum theory.

This is a good viewpoint, but you still need a modell that describes why the photon interacts finally with a specific point and counts with the obstacles. This modell can be wave based or path based or anything else, but it must involve real properties, real effects of the obstacles, even if the waves or paths are only imaginary.

 

[meBigGuy]

There is no final path. Period. End of story. There is no model of why it ended up at a point. Only a probability for each point that can easily be calculated. There is no way to determine where it will go or, afterwards, how or why it got there. The waves or infinite paths are not imaginary. The effects you are trying to create are what are imaginary. They do not exist. You want a cause for the photon to arrive at a specific point, and it does not exist. You want to rationalize how it might have gotten there, but there is no rationale.

I've pretty much said it in every way I know how. You obviously don't understand, and want to assign a cause where none exists.

 

[zrek]

I've pretty much said it in every way I know how. You obviously don't understand, and want to assign a cause where none exists.

OK I accept that I don't understand, and what do you think about the point 2? It is not about the "one final path", but the way to tell why the paths are blocked by an obstacle.

 

[sophiecentaur]

We are on the 37th post now and you still don't want to let go of the idea of 'paths' being relevant, in a 'physical' way. Imagine you had a cloud (in the sky) and it was moving across the sky, changing shape all the time (as they do). Also, accept that you can only see it in 2d. How would you describe its path in terms of a single raindrop that lands on your head? You cannot know which bit of the cloud produced the raindrop and you cannot specify the 'path' of the drop or the cloud other than, perhaps, from left to right. Because you cannot identify the 3D shape at any time, you can't know where the CM of the cloud is and, because it is in a turbulent atmosphere, you can't apply Newton's Laws to what you see. Then try to define the path to include the evaporation from the sea that formed the cloud in the first place. The precise path would be a meaningless thing to discuss - and so it is with a photon. You are hanging onto too many classical notions and insisting on applying them in a situation where they just aren't relevant.
You keep reacting to the views of all who have answered you by 'Yes, i get that but I want the story told my way'. It is you who need to change your ideas and you cannot expect Physics to change to fit in with your personal view. (that is rule number one in Science). Just consider the fact that your idea may not actually work.

 

[zrek]

We are on the 37th post now and you still don't want to let go of the idea of 'paths' being relevant, in a 'physical' way.

Please read back if you don't believe me, but I never said that I want to give any physical meaning to paths. I always said that it is imaginary and have no effect on the material. I also said that this is only a model from the several possible ones (which are maybe all good ones, and results the same mathematical result: only the probability of the place and not the place itself can be calculated)

Don't think of this. Please don't try to describe this again, since I accepted this long years ago (10?), this is not a problem at all.

Let's take this as a pure mathematical model. Imagine a sketch, a piece of paper, a drawn 1 slit experiment and let's try to calculate the probability distribution on the drawn "screen" which is a line.
The "light" source is a selected point, no more. The wall that blocks the imagined "light" is a drawn, long rectangle. There are two of them, there is a "hole" between them. I think that we need no more thing. We can define the sizes, distances about everything on this paper.
Now everything is given to calculate the probability distribution.
We can choose the wave model, or the path integral, no matter, the final result will be the same.
If we choose the path integral, then we will draw lots of lines, some of them will be blocked by the "wall" "rectangles".

As you can see that there is nothing real in this experiment. Now this have no real meaning at all.
This is a thought experiment, a mathematics task. Mathematical tought experiment. (I have no doubt that this modells well the real behavior of light.)

How can we turn this to physical tought experiment? We have to give some imagined real meaning into it.
To give meaning for this, we need to replace few things to imagined real objects. These objects have to behave in our imagination as we know about the really real ones. For example we put a laser apparatus to the startpoint. Now we have to choose some matherial for the screen and the wall. Now some restrictions arise. For example we can't choose such material that completely transparent. (But why? How we define the opaque material?) Also it is not enough to give the size of the material. A drawn square in a paper as wall - this is OK for a mathematics task. But now we know that our material consists of atoms. We need to define why it is an obstacle in our case.
Still we can leave our "paths" as it was in our paper, since we know that they have no effect on the material. But, the material have an effect in our imagined paths. The material have real properties, for example it is opaque. It consists of atoms. We have to define which property of the atoms counts to make it behave in our physical tought experiment the same as the drawn rectangle behaved in our mathematical tought experiment.

I hope that you can understand that this point of view doesn't mean to destruct the mathematical experiment and its results. Also I have no doubt that the physical tought experiment will have the same results: only probabilities. I need to know only what effect of an atom (or more complex material structure) counts in case of the imagined paths, and if I know I can imagine an obstacle, a non-transparent wall made of this material for a physical tought experiment.

The same question arise if we choose the wave model: we have to define what real property we count with in case of "blocking the imagined wave".

This is independent to the fact that maybe there are no paths or waves at all.
I hope now that you know what I mean on this. If not, then let's close this meaningless topic.

 

[sophiecentaur]

You can 'block' a 'beam' of EM energy by absorbing it, absorbing it or refracting it away. There is a load of information about the details of all these three effects at many different levels. Are you expecting something 'new' from this discussion? Just read around, choosing sources that appeal to you and are at the appropriate level. Just try to avoid imposing the 'path' thing except in the context of any Maths you might use in your analysis. It has no deeper significance and, in any case, nothing is 'really real'; all Science is a model.

 

[zrek]

nothing is 'really real'; all Science is a model.

A scientific model have to fit to the experimented, measured results. That is real.

You can 'block' a 'beam' of EM energy by absorbing it, absorbing it or refracting it away.

Since you stepped back to this, I assume that you still not understand my view or simply don't want to thinking on it. I accept this, no problem, still I thank you for your help. Have a nice day! :-)

 

[sophiecentaur]

A scientific model have to fit to the experimented, measured results. That is real.


Since you stepped back to this, I assume that you still not understand my view or simply don't want to thinking on it. I accept this, no problem, still I thank you for your help. Have a nice day! :-)

Absolutely. And there is no experiment that will reveal what you are looking for. That is my whole point. An experiment can just confirm of contradict the results that are predicted by a hypothesis. Any experiment you propose (and you have not yet proposed one) will not identify any particular photon as coming by any particular path. You keep telling me that you know that so what would your experiment consist of? i.e what actual model are you hoping to demonstrate? You seem to be a bit vague on that point.

There is plenty of information about the interaction of photons with matter, on the QM level and the interaction of waves with material obstacles. Which did you want? I really can't be sure, from what you write.

 

[meBigGuy]

I've already described this, but I'll say it again with more and slightly different words. (I recommend you reread what I have posted already)

Assume the blocking material is an infinitely thin perfect absorber with a perfect hole and a perfect boundary, and assume the particle has 0 dimensions. It can either pass or not pass based on the path. There are no boundary conditions. The barrier cannot interact with the particle except to let it pass, or not pass, based on the particles infinite possible trajectories. To the extent that the conditions of this ideal barrier and particle are met, the patterns will match simple predictions. To the extent that there are any boundary effects, or other particle interactions with the barrier, the pattern will be distorted. Anything varying from ideal will cause anomolies. The basic math assumes ideal conditions. You can adapt the math to account for a realistic barrier (and I'm sure there are ample papers doing so) and the result will be a non-ideal interference/diffraction pattern.

Edited slightly for grammar

 

[sophiecentaur]

I've already described this, but I'll say it again with more and slightly different words. (I recommend you reread what I have posted already)

Assume the blocking material is an infinitely thin perfect absorber with a perfect hole and a perfect boundary, and assume the particle has 0 dimensions. It can either pass or not pass based on the path. There are no boundary conditions. The barrier cannot interact with the particle except to let it pass, or not pass, based on its infinite possible trajectories. To the extent that the conditions of this ideal barrier and particle are met, the patterns will patch simple predictions. To the extent that there are any boundary effects or other particle interactions with the barrier, the pattern will be distorted. Anything varying from ideal will cause anomolies. The basic math assumes ideal conditions. You can adapt the math to account for a realistic barrier (and I'm sure there are ample papers doing so) and the result will be a non-ideal interference/diffraction pattern.

Yes, absolutely. There is little to be gained, in the way of understanding how EM 'waves' behave in the presence of obstacles (I'm trying to be as general as possible here) by going outside the ideal case. The basic diffraction calculations pretty much say it all.
There are some practical occasions where the situation is not ideal, such as in radio wave propagation, where the ground, atmosphere or ionosphere do not behave as simple components and a further layer of analysis is required but that is definitely 'third year work', as we say.

 

[Claude Bile]

Forgive me, I did not read through the thread in its entirety...this is a direct response to the OP.

Firstly, forget QM - you don't need it. This is a classical EM problem if there ever was one...

The reason diffraction occurs - Waves get partially blocked (truncated) by an aperture which generates NEW plane wave components (in the same way, truncating a pulse in time generate new frequencies), causing the wavefront to spread.

The material properties of the obstacle are important as well; e.g. a dielectric will diffract light differently to a conductor due to how the electrons in the contrasting materials respond to the incident field.

Claude.