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Francis Ward
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Pretty self explanatory really. If a photon has a mass (1.67 * 10^-27 kg), and it travels at the speed of light, why does it's mass not increase to infinity?
It doesn't.Francis Ward said:If a photon has a mass (1.67 * 10^-27 kg)
Also, mass is an invariant quantity. Relativistic mass is an obsolete concept that is no longer in active use among physicists.Francis Ward said:why does it's mass not increase to infinity?
Where did you see that ##1.67\times{10}^{-27}## kg?Francis Ward said:Pretty self explanatory really. If a photon has a mass (1.67 * 10^-27 kg), and it travels at the speed of light, why does it's mass not increase to infinity?
Francis Ward said:If a photon has a mass (1.67 * 10^-27 kg)
Nugatory said:Where did you see that ##1.67\times{10}^{-27} kg##?
Nugatory said:Most likely you were reading something that was reporting an upper bound on the photon mass
Ah - right. I must confess that I didn't even check, just fixated on the "travels at the speed of light" bit.PeterDonis said:I wouldn't think so, since the upper bound on the photon mass is much smaller; about ##10^{-54}## kg last I checked.
If you could provide a link to whatever you've read that says that? Either it's wrong or you've misunderstood it, but we can't tell which if we haven't seen it.Francis Ward said:Reading further, documents say that photons (not protons) have a mass varying from massless to the figure I said.
Einstein's equation is ##E^2=(mc^2)^2+(pc)^2##, which allows for particles with energy by no mass.If Einsteins equation is to hold true (IF) then photons must have mass, or must be energyless.
Francis Ward said:Pretty self explanatory really. If a photon has a mass (1.67 * 10^-27 kg), and it travels at the speed of light, why does it's mass not increase to infinity?
girts said:I kind of get the feeling that we only say that the photon has no mass because it works nicely with the Einstein equation which itself works nicely with everything else, is that correct?
girts said:do we have definitive physical experimental evidence of the photon having exactly no mass at all or did we concluded that part based from math?
girts said:but reading this discussions I kind of get the feeling that we only say that the photon has no mass because it works nicely with the Einstein equation which itself works nicely with everything else, is that correct?
Dr Whom said:At the speed of light they experience zero time from their point of origin to the time they are absorbed
Dr Whom said:In this way they preserve precisely the information encoded within them at the moment of their creation.
No. You can never measure anything exactly. Measurements are always subject to measurement errors leading to uncertainties.nitsuj said:Can we not measure the exact energy of a photon?
Bearing in mind that my knowledge of quantum field theory is somewhat limited, the following is my understanding. Photons are excitations of the (quantised) electromagnetic field. That means that if they have mass it's because the electromagnetic field has a non-zero mass density associated with it. And that would make a difference to the behaviour of all electromagnetic phenomena, not just the speed of light.girts said:Ibix mentioned here and I also see it written in the wiki article that if photon had a mass with value above that lowest current detectable threshold then there would exist an E field inside a hollow but closed conductor like in a metal sphere, now can someone explain why would that be and by what mechanism?
nitsuj said:Can we not measure the exact energy of a photon?
Photons are very interesting and show wave properties. Have a look at this tutorial articlegirts said:well I assume @Ibix that no one has ever seen a photon and unlike a proton or an electron it even can't be seen as it's just a name given to what we observe as being discrete events of energy striking say a metal plate and knocking out electrons with corresponding energy levels so we kind of decided that there must be something particle like hitting on the other side.
I guess its kind of mind boggling and interesting that we can detect these quanta of the EM field yet their so mysterious, it kind of seems like we know certain properties of a person and their character without ever knowing or even being able to see the person.@nitsuj, I think we can measure the energy from even a single photon IIRC, but what has that to do with it's mass (even if there is some) ?
Of course, what you mean by seeing a proton is that your eyes absorb these "discrete events of energy" as they arrive in a way you interpret as consistent with them having been deflected by some particle. All observation has an element of interpretation to it, and protons and electrons are no more real than photons.girts said:no one has ever seen a photon and unlike a proton or an electron it even can't be seen as it's just a name given to what we observe as being discrete events of energy striking say a metal plate and knocking out electrons with corresponding energy levels so we kind of decided that there must be something particle like hitting on the other side.
In what way do you believe photons change during their travel? If they did then the information they contain would be compromised making all observational data unreliable. .PeterDonis said:This is not correct. The correct statement is that the concept of "experienced time" does not apply to photons. It only applies to objects that move on timelike worldlines.
By moving only on spacelike worldlines at the speed of light no time passes. Basic SR.Your implied logic here is also not correct. The fact that a photon's worldline is null (has zero "length" according to the metric of spacetime) does not mean the photon cannot change during its travel.
Dr Whom said:In what way do you believe photons change during their travel?
Photons do not exist in elementary SR. You need QFT for that. Furthermore it is generally not relevant to talk about what is “experienced by” a classical massless particle, since it has no rest frame.Dr Whom said:So besides their position they do not change or undergo any entropic increase or equivalently experience time. Which is precisely what I stated in the first place. Elementary SR.
Dr Whom said:In what way do you believe photons change during their travel?
Please quote correctly. This was something you wrote, not something Peter wrote. It's also incorrect - light travels on null worldlines, not spacelike ones, and proper time is not defined along them. Coordinate time is, though. So a correct statement would be that proper time is not a concept that applies to light.Dr Whom said:By moving only on spacelike worldlines at the speed of light no time passes. Basic SR.
Redshift is the obvious one.Dr Whom said:In what way do you believe photons change during their travel?
It seems like you are saying that only things traveling on null worldlines can carry information. If you are claiming that, could you explain how a CRT monitor works? If you are not claiming that, could you say what you do mean?Dr Whom said:If they did then the information they contain would be compromised making all observational data unreliable. .
girts said:@nitsuj, I think we can measure the energy from even a single photon IIRC, but what has that to do with it's mass (even if there is some) ?
What about, are the errors and uncertainties known; their causes? I'd consider the uncertainty principle to be a known unknown and kind of irrelevant with respect to experimental errors. Surely for the equipment and other parts of the experiment the source of the errors are known, mitigated and corrected for as reasonable.Orodruin said:No. You can never measure anything exactly. Measurements are always subject to measurement errors leading to uncertainties.