If probability wave is true wouldn't there be flickering?

  • #26
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thanks for all the answers (and the little debates in between). I'm still trying to get my head round the movement (and existence) of photons. ie. Why do they move...if nothing propels them...why are they moving? Are they attracted towards something? I can't just accept that they move constantly for no reason. And how are they created? If a photon is created what is it created from?
 
  • #27
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If a photon is created what is it created from?

Interestingly after Feynman got his Phd and was chatting to his father, his father asked the same question. He explained the general principle is photon numbers are not conserved and they don't come from anything. His father couldn't understand that and said - my son - you have surpassed me. Actually of course he hadn't - its just you need to let go of preconceived ideas.

In QM a lot of things are like that - and I know from experience. For a long time when I was studying QM from a number of sources I used to take walks and think about things like Schroedinger's Cat, wave-function collapse, all the borderline philosophical stuff some really get caught up in about QM. Slowly, oh so slowly, I realised the solution was simply letting go of preconceived ideas rooted deep in our intuition. In particular realising observation was the basic primitive of the theory. Once that was done progress in my understanding of such things was swift.

Thanks
Bill
 
  • #28
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so is it right to say that a photon doesn't actually exist and what we are measuring and calling a photon is merely the affect/result of an action. So a dot appearing and being recorded when 'firing a photon' is not where a photon has hit as it doesn't actually exist? The dot is just what happens to that particular material because of the reactions taking place at the source of the photon creation - everything in between is nothing?

EDIT: That was in my head in a much more clear manner...reading it back sounds like gibberish
 
  • #29
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so is it right to say that a photon doesn't actually exist and what we are measuring and calling a photon is merely the affect/result of an action. So a dot appearing and being recorded when 'firing a photon' is not where a photon has hit as it doesn't actually exist? The dot is just what happens to that particular material because of the reactions taking place at the source of the photon creation - everything in between is nothing?

No.

QM is a theory about observations. The dot on the screen is an observation. What's going on when it's not observed the theory is silent about - we have all sorts of interpretations with all sorts of takes - but that's all they are - interpretations. It may exist when not observed - it may not - QM isn't worried one way or the other.

To make the next step in your understanding of QM simply let go of these things that seem to worry you - its a theory about observations - don't read more into it.

Thanks
Bill
 
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  • #30
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but is it not about finding out what is going on in those unknown places?
 
  • #31
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but is it not about finding out what is going on in those unknown places?

That leads down a rabbit hole that no-one has ever escaped. Everyone that has tried has failed. Its a standing joke in physics a professor asked about so so who was an outstanding student with a lot of potential. The reply was he wanted to find out what QM really means. They all knew he was lost.

Sometimes you get these threads where people will quote Feynman or some other famous scientist that says no one understands QM. That's rubbish - plenty do. What's meant is no one understands it on the terms you wrote above. If you try you will get nowhere. Let go and slowly things will be clearer.

Watching Feynman's first lecture in the following may help:
http://www.vega.org.uk/video/subseries/8

Thanks
Bill
 
  • #32
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is that not like saying "just accept that things just are the way they are and don't question it"?
 
  • #33
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is that not like saying "just accept that things just are the way they are and don't question it"?

No - its a bit different.

What its saying is QM is a theory about observations. Attempts to extend it beyond that have succeed - but not in a unique way. Trouble is no-one has ever figured out how to experimentally prove any of them correct. And many many smart, and I mean smart, people have tried. Until someone does then its pretty meaningless to worry about it - so don't.

Another way of looking at it is this. Every theory, every single one, is based on primitives the theory accepts as fundamental. Future progress may explain those primitives in terms of other things - but you will have to accept them as well. Ultimate explanation is impossible. QM has observations as its primitive - if you don't like that and want other primitives exactly what have you gained? Its simply a reflection on how you want the world to behave - trouble is - nature doesn't particularly care about that.

Thanks
Bill
 
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  • #34
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EDIT: That was in my head in a much more clear manner...reading it back sounds like gibberish
That will happen every time you to try to describe photons in natural language :smile:.... Seriously, kidding aside, natural language describes things in classical terms, and photons aren't classical. You can try to think about the position of a photon if you want, and you can try to think about the position changing and call that the photon moving if you want.... but neither concept is present in the math. The closest you can come is to say that there is a certain probability that a photon detector such as the screen will trigger if it is in a given place at a given time.

so is it right to say that a photon doesn't actually exist and what we are measuring and calling a photon is merely the affect/result of an action. So a dot appearing and being recorded when 'firing a photon' is not where a photon has hit as it doesn't actually exist? The dot is just what happens to that particular material because of the reactions taking place at the source of the photon creation - everything in between is nothing?

I would much rather say that the dot appeared and was a recorded because a photon did exist at the exact place and time that the dot appeared - but just there. The dot appeared - that's real. The dot appeared because a small amount of energy was transferred from the electromagnetic radiation impinging on the screen to the photosensitive material on the screen - that's real. We call that quantized amount of energy a photon, so we're justified in saying that the photon really exists when it hits the screen.

Does it really exist before it hits the screen? Our experience with small classical objects like bullets, grains of sand, infinitesimal motes of dust, leads us to say "yes", or even "yes, of course". But that's an assumption not supported by any experimental evidence, and it's an assumption that is almost guaranteed to get us into trouble if applied to photons.
 
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  • #35
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That will happen every time you to try to describe photons in natural language :smile:.... Seriously, kidding aside, natural language describes things in classical terms, and photons aren't classical. You can try to think about the position of a photon if you want, and you can try to think about the position changing and call that the photon moving if you want.... but neither concept is present in the math. The closest you can come is to say that there is a certain probability that a photon detector such as the screen will trigger if it is in a given place at a given time.

That's it. Let go of your classical intuition and your confusion will dissipate.

Thanks
Bill
 
  • #36
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is that not like saying "just accept that things just are the way they are and don't question it"?

No - its a bit different....

I agree with Bhobba's response above. However, I also feel obligated to mention that David Mermin, one of the pioneers in the field, once summarized quantum mechanics by placing his tongue firmly in his cheek and saying "Shut up and calculate".... So deansatch, it's one thing to know how QM works, but another thing altogether to like it :smile:
 
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  • #37
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However, I also feel obligated to mention that David Mermin, one of the pioneers in the field, once summarized quantum mechanics by placing his tongue firmly in his cheek and saying "Shut up and calculate".... So deansatch, it's one thing to know how QM works, but another thing altogether to like it :smile:

People say it was Feynman that said that - but really it was Mermin - although it's the type of thing Feynman would have said.

I don't think anyone likes the situation in QM, they just accept it. Even Einstein, whose real attitude to QM is often misrepresented, agreed it was correct - but incomplete. Its perfectly valid to hold Einstein's view and simply accept it until something better comes along. But until it does don't be consumed by the issue - you will get nowhere.

Thanks
Bill
 
  • #38
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I'm still trying to get my head round the movement (and existence) of photons. ie. Why do they move...if nothing propels them...why are they moving? Are they attracted towards something? I can't just accept that they move constantly for no reason.
You can try to ask this question in relativity subforum. It might be easier to take moving at the speed of light as basic idea and rather ask question why things are staying in place (moving inertially). Possible answer is that you can view massive particles as moving at the speed of light but not getting anywhere (not moving straight in the same direction).
And how are they created? If a photon is created what is it created from?
Photon is viewed as excitation of electromagnetic field so in a sense you can say it's made from electromagnetic field.
 
  • #39
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Maybe if you think of it as a symmetry? It's called lights duality, meaning that it has both wave and particle aspects. If you think of it as a field, then it should be about probabilities to my eyes. And those probabilities are actually probabilities, for me that is. The idea of a 'field' do not tell you that it has to be waves, neither does it tell you that it has to be particles. People likes waves, and it's a concept that seems to work, but I like probabilities myself, and a duality.
 
  • #40
Bill,

Even though I had trouble with QM in college, I enjoyed reading the paper you linked. . Your exposition helped me follow the application of the conceptual framework along with the notation.

Thank you!

Ralph Dratman
 

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