Photon dimensions

  • #26
Hootenanny
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is mass a form of energy or not?
I apologise, as I always seem to be quoting other people in reply to your threads, but most of your questions have been answered pretty comprehensibly, in your own threads. I draw your attention to the thread you created entitled https://www.physicsforums.com/showpost.php?p=1203679&postcount=7". And in particular, the following posts;

https://www.physicsforums.com/showpost.php?p=1203679&postcount=7"
https://www.physicsforums.com/showpost.php?p=1204278&postcount=36"
https://www.physicsforums.com/showpost.php?p=1204345&postcount=40"

All indecently by Zz. If there is anything that you don't understand, please feel free to ask specific questions. But just repeating or restating your original question, over and over, either in the same thread or different ones such as this isn't going to get you anywhere. You won't gain any understanding and the people replying to your threads are just going to become more frustrated. I urge you (as cristo did in the above thread) to read the thread carefully and pay particular attention to the posts I outlined above.
Essential caveat: as you probably know, quantum theory has proven hard to reconcile with the curved spacetime models used in general relativity, so it is currently difficult to say very much with certainty about how photons and other particles might be treated in the yet unknown quantum theory of gravity.
The important point to note from Chris' excellent post above; is that you are attempting to reconcile two theories, QFT and GR, which as yet have been found to be incompatible. The photon has no place (as yet) in GR and curved space time.
 
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  • #27
ZapperZ
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All indecently by Zz.
All indecently by me? Hoot, how could you? I assure you that while I was typing that without wearing any pants, I was wearing a bright smile!

:rofl:

Zz.
 
  • #28
I dont get how mass is Converted to energy!Thats it.And thanks for being patient
 
  • #29
T
is mass a form of energy or not?
I just asked this again as i read this on page 941 in the physics text by Resnick,Halliday and Walker(Fundamentals of Physics:Extended 6th edition)

In the last paragraph it is clearly mentioned:
mass can be considered to be another form of energy
 
  • #30
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To add to Chris' very nice explanation, I might suggest that going back to the photoelectric effect could help in understanding the photon. This is the experiment that led to the photon concept. If the incident light has a frequency below the threshold for atiomic emission, then no amount of increased intensity will eject an electron. But when the frequency of the light is raised above the threshold, electrons flow. The electrons are absorbing the radiant energy in discrete amounts equal to the the threshold energy (plus kinetic energy). Each amount is equal to h*freq, leading to the idea that the light consists of a bunch of photons and each photon has this energy. The quantized nature of light comes from how it interacts with matter. There is no requirement that the photon in the radiant beam has a size or a location. The only location is where the absorption occurs.
 
  • #31
Hootenanny
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All indecently by me? Hoot, how could you? I assure you that while I was typing that without wearing any pants, I was wearing a bright smile!

:rofl:

Zz.
One of my more amusing typos! :rofl: Damn this Google toolbar :rolleyes:
 
  • #32
pervect
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Your question is still unclear. Imagine that you had an unlimited budget, a very large laboratory, and a trained staff. What sort of experiments would you do to determine whether or not a photon "occupied space"?

The question is so vague and general in its current form that it's not really clear what you are interested in. I wouldn't know what sort of experiments you'd perform, nor what answers would convince you that the answer was that the photon did occupy space, or what answers would convince you otherwise.

Without this understanding of how you would reduce the question to experiment, I can't answer the question. Any answer would be highly misleading, esp. if you are using it to attempt to derive other results.

Science is supposed to be about questions that are ultimately testable. If you can't come up with a scenario that explicitly answers your questions through experiment, you are not doing science, but philosophy.

I suspect very much that the questions you have may be more related to quantum mechanics than relativity. But it's possible (because of the vagueness of the question) that I'm wrong. So I'll try and outline the relevant aspects relating to GR

1) GR is a classical theory, while photons are a quantum concept. We can certainly talk about whether or not light interacts via gravity though. The answer is basically yes. Light has energy and momentum. The "stress-energy" tensor that is the source of gravity in General relativity arises from energy and momentum, and how it is transported. Thus light contributes to gravity via its contributions to the stress-energy tensor.

That is about as much of an answer as you are going to get out of GR.

For a taste of the quantum questions (which should go in another forum, either philosophy or quantum mechanics) - suppose we have a light source that shines through two slits. We can experimentally see that it generates an interference pattern. We say that the light is due to waves, which interfere with each other. Suppose we make the light beam so weak that only one photon is ever in the apparatus at any given time. Does the light beam still generate an interference pattern.

The answer to this question is yes, and one philosophical interpretation of this result is that photons, regarded as particles, take multiple paths, and interfere with themselves.

Some people don't like this philosophical interpretation, which is in general fine, there are many. This particular philosophical interpretation is due to Feynman. People with different philosophies of QM often have a hard time communicating with each other, though if they both know what they are doing, they can both come up with the same answers to a well-posed experimental problem.
 
  • #33
I was just wondering......

Is it possible to a see a photon in an absolutely dark room with a very high speed camera?
 
  • #34
ZapperZ
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Why are you hijacking your own thread?

Obviously, since you don't have any follow-ups to this, your question has been answered and this issue is settled. So this thread is closed.

Zz.
 

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