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Author Topic: Must photons exceed the speed of light when interacting with other particles?  (Read 1963 times)

Offline mxplxxx

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It seems to me that given that a photon travels at the speed of light, that it needs to travel at greater than sol when interacting with another particle. The reaction is instantaneous (quantum leap) yet it takes time to impart energy (e=hf). So it would appear that the photon is travelling backwards in time, i.e. it is from the future. This makes sense given we appear to have a choice of what interactions we allow. So maybe the photon starts out as a tachyon and drops into the present at sol. Makes sense when we consider that nowhere do we see a photon being accelerated to sol.
« Last Edit: 02/02/2014 22:33:49 by chris »


 

Online evan_au

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Real photons travel at the speed we call "c"≈299,792,458 m/s in a vacuum, and can last indefinitely without decay (traveling millions of light-years, in astronomy).
Virtual photons are used to explain some atomic reactions, where no real photon is a product of the reaction. They only exist for a very short period of time and travel a very short distance; these are temporary deviations from the familiar macroscopic physics permitted by Heisenberg's uncertainty principle.

It is possible for a real photon, travelling at c, to interact with a real electron in an atom. Because the photon could be considered as propagating as a wave, its precise position is unknown; the wave function represents the probability of finding the photon at a particular position.
One of those positions could be at the position of the electron which absorbs the photon (bearing in mind that the position of the electron in an atom is not known precisely, either).

So I suggest that a photon does not need to exceed c (or travel backwards in time) in order to interact with another particle.
« Last Edit: 04/02/2014 08:50:59 by evan_au »
 

Offline lightarrow

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It seems to me that given that a photon travels at the speed of light, that it needs to travel at greater than sol when interacting with another particle. The reaction is instantaneous (quantum leap) yet it takes time to impart energy (e=hf).
What do you mean with "The reaction is instantaneous (quantum leap)"? And, if it is instantaneous, how can it take time to impart energy?

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lightarrow
 

Offline yor_on

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When a photon or a wave interacts with matter it slows down, as in glass. So if we look at it as absorbing original photons to then releasing new photons, that in its turn interact with the next atom, etc, etc, it has to take a time for this process. So it can't be instantaneous, as we then still would find a same speed as in a vacuum.
 

Offline yor_on

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What you are thinking of is probably HUP (Heisenberg's Uncertainty Principle), as applied to the concept of 'virtual photons' that can exceed any limitations due to their virtual nature. And that is a concept I think you can exchange for statistics probabilities and indeterminacy. Doing so we don't need to discuss the 'time' something takes, 'created' from indeterminacy, just as we don't need to 'explain' why a photon doesn't need a acceleration. It's the universe at small scale.
 

Offline mxplxxx

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It seems to me that given that a photon travels at the speed of light, that it needs to travel at greater than sol when interacting with another particle. The reaction is instantaneous (quantum leap) yet it takes time to impart energy (e=hf).
What do you mean with "The reaction is instantaneous (quantum leap)"? And, if it is instantaneous, how can it take time to impart energy?

--
lightarrow

Not well thought through by me, although electrons appear to instantly change orbits. Big question is, can the past create the present or is the present created from future possibilities? If the latter, then tachyons may do the work. Pretty speculative on my part I know but food for thought maybe?
 

Offline JP

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Not well thought through by me, although electrons appear to instantly change orbits.

They don't.  The probability for the electron appearing in one orbit and vanishing from the other grows from zero upwards in line with causality.  The electron's wavefunction, which is the thing that has to follow causality, does not change faster than the speed of light.
 

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