Photons cannot accelerate
this post was submitted on 19 Nov 2023
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Acceleration and Velocity are vectors. Changes in a velocity vector are an acceleration. Therefore when photons change direction technically it’s a form of acceleration.
I thought photons are always moving in straight lines from their perspective, and it's space that's bent. Unless it's through a medium, then they just get absorbed and re-emitted, sort of.
Space bending is a general relativity thing, which isn’t really related much to how mirrors work.
Regarding the medium bit, photons being absorbed and remitted can’t explain how light moves slower in glass. This is just an extremely popular myth. Photons are only absorbed by atoms at very specific frequencies. Also, the entire reason glass is transparent to begin with is that it’s not absorbing the photons (requires too much energy to bump the electron’s energy level so the photon isn’t absorbed and it keeps on trucking). Also photon absorption and remission is stochastic so there’s no way to control the direction it happens in or how quickly it happens. Random directions of remitted light would make glass translucent, not transparent. So for a few reasons, that’s not how it works.
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They do at 0m/s^2.
Not with that attitude.
What about diffraction?
Since photons are indistinguishable, it's hard to say too much concretely, but it some sense a diffracted photon is different photon. In order for a photon to interact with say, a diffraction grating, the interaction is done with "virtual photons".
So for a photon to change course, aka accelerate, it does it by absorbing a virtual photon and emitting another. Whether that is the "same photon" after the interaction is kinda more philosophy than physics, at least to me.
Feynman diagrams are surprisingly accessible for how much information they contain. It's one way to think about photon (and other particle) reactions.
There is no tree level photon-photon interaction. Photons scatter off electrons (or any other charged particle), not off neutral photons.
Are you claiming this is done without a force carrier? If you are working outside the standard model, I guess that's fine, but I don't want to spend time arguing with you.
The electromagnetic field does have a force carrier. It is the photon.
The photon mediates the force between electrically charged particles. It cannot mediate any reaction between two neutral photons.
Ah, I see. Sorry for the snark. I was thinking more in line with the Compton effect, and thought you were talking about something like that too. (Even though it's clear that you were explicitly not. I thought you were denying photon-virtual photon interaction because I was talking about it in a funny way.)
I would still say it's still philosophical whether photons experience acceleration, but I concede that photon-photon interaction is not done by virtual photon exchange.
I am indeed denying the existence of photons interacting with virtual photons. I am also saying there is no tree level photon-photon interaction of on shell photons. Neither Compton scattering nor Bhabha nor pair production nor pair annihilation involves a photon-photon interaction. There is no photon-photon vertex in QED. There is no tree level Feynman diagram that you can look at and say “this is, at least philosophically, a photon changing its momentum”.
There is a 1 loop diagram that represents photon-photon scattering. But even that doesn’t have any photon-photon vertices, instead it is mediated by electron-positron pair.
Non-abelian gauge bosons (gluons) couple to themselves. So does gravity (gravitons). Abelian ones (photons) do not.
Photons don’t accelerate. They are emitted or absorbed. That’s their only interaction.
Someone asked if diffracted light accelerated. I said no. A diffracted photon is a different photon.
I gave some lip service to the Feynman "there is but one electron" idea, and you seemed to take that personally.
If someone asks you if diffracted light accelerates, answer them how you want. I just thought it'd be cool to show them Feyman diagrams.
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Does a photon actually accelerate? Sure seems like it always goes at light speed through whatever medium from its creation.
well, if it get reflected and change direction it going to be at light speed, so it can be interpreted (probably incorrectly lol) that it "accelerated instantly to the other direction after the reflection"?
This is an interesting question. Instant acceleration is mathematically implausible, but I don't know if there's a better physical interpretation for what happens to a bouncing photon. I'm guessing this is one of those "less particle, more wave" situations where the instantaneous velocity of the photon is undefined.
According to some random internet sources, reflection is the not-quite-instantaneous process of the photon being absorbed and then emitted by the electrons in the mirror.
As a rule, it’s probably best to avoid “random” internet sources on matters of how light works because there’s so much confidently parroted misinformation out there. For example, this is completely wrong: https://youtu.be/FAivtXJOsiI See here for correct answers to that issue: https://youtu.be/CiHN0ZWE5bk
For how mirrors work see this: https://www.scientificamerican.com/article/what-is-the-physical-proc/ https://youtu.be/rYLzxcU6ROM
This is acceleration with no mass and no resistance to medium.
Photons are born and die at c. They experience no time and have no frame of reference.
The loneliest of experience.
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PHOTONS HAVE MASS
ANYONE WHO DOES NOT BELIEVE THEY HAVE MASS IS A COWARD
Photons can have little a mass, as a treat.
But every time i put it on a scale, it just flys away. GIVE ME PROOF. I have a kitchen scale to offer.
MEASURE FASTER
IT MOVES REAL QUICK
Who is the dude on the right?
A scientist at CERN.
Ah, I get the joke now. Classic
Because you're so light
Without mass how could you do anything else?
Wave!
I see you there
Without mass you have to occupy parts of time and possibly gravity.
39 years old... Can confirm that time is perceptibly accelerating
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