Simplest explanation - in GR photon is massless, best measurements confirm its mass is below 10-18 eV.
If the photon is not a strictly massless particle, it would not move at the exact speed of light in vacuum, c.
Iwhere did the notion that it's massless come from if we can only confirm that it is under a specific mass?
When you are checking things experimentally you can only do the experiment with a finite accuracy. That means you can never say "exactly zero" but "zero within the accuracy of the experiment". Best experimental accuracy so far proved mass is below 10-18 eV.
Similarly - when talking about mass, we in fact talk about two different properties of matter, inertial mass and gravitational mass. Seems like they are identical - but experimentally we were so far able to prove it "only" with accuracy around 10-12 (that was result of Braginski & Panow from 1972, could be there are better results available now).
Yes I understand that, but I don't understand what's preventing smaller particles from existing.
Photon has energy. E = mc^2. Therefore photon has mass.
That's just how science works: no measurement can ever be 100% accurate and no theory can ever be 100% proven. So the best we can do is 99.9999999999999% certain.There's key words here though. Very high accuracy, "seems like". Of course with such its fragile size that we can not measure it perfectly, as the probability of that is very low. Though I am confused in the area of, if we are so sure that it is massless, then why is there that area of uncertainty?
That's just how science works: no measurement can ever be 100% accurate and no theory can ever be 100% proven. So the best we can do is 99.9999999999999% certain.
I'm just confused as to why we assume its massless(besides aforementioned speed of light reason)
That formula is not saying the photon has mass. That's a common misuse of the formula.Does that not defy the Mass–energy equivalence formula to say that the photon is massless, when the formula says otherwise? We know the photon has energy.
Of course not! A theory predicts it, all evidence we have to date validates the theory, and no other theory exists that can explain the evidence. That's perfectly scientific.Isn't it unscientific to say the speed of light is the top speed?
Certainly not. There is no theory that predicts a non-zero mass for the photon that doesn't contradict the evidence we already have.Wouldn't it be more accurate to say it's the highest speed we can measure, but there very easily could be higher speeds if lighter particles existed that we don't have the current technology to measure?
Of course. That's not what's being claimed. What you're claiming is no less profound: That a 100 year-old, exquisitely well proven theory is wrong. That would be earthshattering.I'm sure everyone can agree it will always be unscientific to say we've reached the peak of universal discoveries.
Of course. That's not what's being claimed. What you're claiming is no less profound: That a 100 year-old, exquisitely well proven theory is wrong. That would be earthshattering.
We're starting to go in circles here: It is a combination of logic and measurement imperfection. The uncertainty in the measurement exists because it is impossible to have 100% measurement accuracy. At the very least, measurement devices are man-made and therefore have flaws that can never be completely eliminated.Russ I understand what you're saying, but why is there that area of uncertainty.
Of course: Being 99.999999999% sure of one thing means there is a 0.0000000000001% chance that there is something being missed.Yes there are countless test reverifying that the mass of a photon is very small. Just because no theory exist predicting otherwise does not mean that 'otherwise' isn't true.
That's not quite right. First, the prediction is masslessness. I think you meant measurement: A measurement would say something like 0.01 +-.02, which verifies that the mass is somewhere between -.01 and +.03. .03 is an upper bound in the range. So the experiment verifies no mass (because 0 is inside that range) to within a certain accuracy.But we can not confirm masslessness, we can only predict really close to it, which is why it baffles me that we can just say, there is no mass. We can't verify no mass, it's logically impossible, we can only verify extremely small masses.
Isn't mass just energy in a different form? And a photon is just energy? Which would make it impossible for a photon to have mass(per definition that is)?
I think this shouldn't really be discussed here, but well. No theory can be 100% proven. The entire point of measuring the mass of a photon is in my opinnion that it would disprove the theory "directly".
And I think this is the mistake:
"The theory of a "massive photon" would not contradict any theories, other than the notion of it being massless"
The theory is not just one notion. Measuring the mass of a photon would disprove the entire theory of relativity, and probably some other things and concepts too.
I am not an expert on R.T., but am pretty sure it would destroy it, someone might back me on it. But again, it really shouldn't be discussed under this topic.
Also you should understand that no theory can be 100% proven, that's how physics works.