Dancing David
Penultimate Amazing
You don't like the answers if you find them.
A photon has no rest mass, a photon at rest doesn't exist.
Contradiction over.
Incredibly huge inconsistency of modern physics
- Thread starter wogoga
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You don't like the answers if you find them.
A photon has no rest mass, a photon at rest doesn't exist.
Contradiction over.
Dancing David
Penultimate Amazing
Yup, no arguments have you, just appeals to emotion. Way to not convince anyone.
Ziggurat
Penultimate Amazing
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I have some deep thoughts that I think this thread might be the appropriate place for, given the level of discussion:
Why is "god" just "dog" spelled backwards?
If we had six fingers on each hand, would we use a base-12 number system?
Can a vampire get AIDS?
Could a lightsaber cut through Excalibur?
Do whales have swear words?
What do cats think will happen if they catch the laser dot?
What if swans really are just ugly ducks?
Why is "god" just "dog" spelled backwards?
If we had six fingers on each hand, would we use a base-12 number system?
Can a vampire get AIDS?
Could a lightsaber cut through Excalibur?
Do whales have swear words?
What do cats think will happen if they catch the laser dot?
What if swans really are just ugly ducks?
Hellbound
Merchant of Doom
Aepervius
Non credunt, semper verificare
People usually do not realize that the relativisitic energy equation they know is incomplete (an they do not do research or even simple google). They see E=mC^2 and forget that it is actually only true for a particle without momentum, at rest.
The true Equation is Er^2=(m0c^2)^2+(pc)^2
So if pc=0 , particle at rest, then you have the well known equivalence matter energy equation
if m=0 you have a particle like the photon where all the energy is in the momentum. And as you said , a photon is never at rest.
I think the confusion with some posters is with the thermodynamics. The formula for mass-energy equivalence isn't just for fundamental particles. It also applies to composite systems consisting of many particles. The composite system can very well have a rest mass even if individual particles in the system have zero rest mass. I this case, one can claim that the internal energy of the system has a unique rest mass.
Suppose one takes 1 ml cube of liquid water at 0 C at 1 atm. The cube of water will be 1 g in mass when the center of mass is at rest. All the molecules in that cube of water are moving very rapidly. However, the rest mass of that cube of water is still 1 g. The equivalent rest energy of that cube of liquid water is given by:
E=mc2where m is the 1 g, c is the speed of light in cm/s and E is in units of ergs.
Suppose one heats that cube of liquid water to 90 C at 1 atm. One has added 90 calories of internal energy to the original cube. If the mass of this cube is measured in an inertial frame where the center of mass is at rest, then the measured mass is a rest mass. So the rest mass of the cube is now 1 g plus the mass equivalent of the 90 calories. I won't do the calculation. I just point out that there calculated mass of the heated cube is still a rest mass for the cube.
Note that very few, or none, of the water molecules in the cube are ever at rest. So if one measured the mass of a rapidly moving molecule in the cube of water, it won't be the rest mass of the molecule. However, if the center of mass of the composite system (the cube) is at rest, one is justified in calling it a rest mass.
Now suppose instead of molecules one had only photons. The cube is hollow, with the sides made out of perfect mirrors held together by some new type of astronomical force. A large amount of optical energy is pumped into the cube. So in the inertial frame of the center of mass of this system, the energy consists of the kinetic energy of all the photons plus the potential energy of the strain fields in the mirrors that hold the cube together plus what mass is in the initial matter of the mirrors.
Assume most of the energy in this system is in the photons. The photons just bounce back and forth. A detailed analysis has to include the strain fields, but lets ignore those for now.
Let us do measurements in the inertial frame of the center of mass of the cube. Most of the photon energy becomes part of the rest energy of the mirrored cube. However, none of the photons are at rest. Nor can you find any inertial frame where any of the photons are at rest. However, the composite system of mirrors and photons has a center of mass. There is an inertial frame where this center of mass is at rest.
So the meaning of 'rest mass' for the mirrored cube is very clear even though the phrase 'rest mass' means nothing for the photons.
The lesson here is that the internal energy of a system has a rest mass associated with it. The 'rest' in 'rest mass' is associated with the center of mass of the system. The motion of the individual components doesn't really compromise their contribution to the 'rest mass'.
If you look close, most of the weirdness comes from the classical thermodynamics. Relativity just adds a small amount of weirdness to the thermodynamics.
In any case, the OP is wrong. There is no internal contradiction in relativity. I conjecture that relativity may eventually be found to be 'slightly wrong', the way Newton's Laws are 'slightly wrong'. However, Newton's Laws don't have a internal contradiction and neither does relativity.
theprestige
Penultimate Amazing
Because, yes, yes, maybe, yes but they're really long and beautiful and anyway drowned out by the noise of human activity, there's an xkcd for everything apparently, and so what.
HighRiser
Graduate Poster
Does anyone know where Farsight is? I wish he'd come through this thread with his amazing relativity + and explain the true nature of the universe to us. Again.
grmcdorman
Graduate Poster
- Joined
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Thus also you have been led by logical necessity to the conclusion that we do not absorb photons in our eyes!
The refractive index of our vitreous humor n = 1.336. Propagation speed c/n is therefore around 224,400 km/s. If such a vitreous humor moves to the left at 224,400 km/s, and a photon in it moves to the right, then according to SR, the photon is at rest. See: Fizeau_experiment#Derivation_in_special_relativity. With a diamond (n = 2.42) a speed of roughly 40% of c would be enough to produce a photon at rest.
Also the question concerning the concrete physical effect of the invariant mass of a photon in the vitreous humor of the eye is still open. This invariant mass turns out to be 66.3% of Einstein's relativistic mass (see #100).
Wishful thinking!
Cheers, Wolfgang
Controversy over Invariant Mass
Nonpareil
The Terrible Trivium
Y'know, this line strikes me as important. I am by no means a theoretical physicist, but .4c seems like it doesn't quite fulfill the v/c << 1 condition.
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Hellbound
Merchant of Doom
Yeah, but it's wogoga. Sort of an alternative quantum physics.
If you think you understand wogoga, you don't understand wogoga.
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Nonpareil
The Terrible Trivium
Silence! No one saw that.
i totally did not hit 'submit' instead of 'preview'
this is not a thing that i have ever done
Hellbound
Merchant of Doom
Saw what? Didn't see a thing...
Belz...
Fiend God
Well, no, so there.
Belz...
Fiend God
Photons _always_ travel at c. The fact that they are absorbed (destroyed) and emitted (created) along the way, slowing the process down, doesn't mean they travel at another speed when they actually exist.
Ziggurat
Penultimate Amazing
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No. According to QED, a photon traveling through a material with n>1 will take a curved path on the microscopic level. In a reference frame where the macroscopic velocity of light has been reduced to zero, what this essentially means is that the light is moving in a circle, but it's still moving, and still moving at c.
You have not discovered an invariant mass for individual photons. Rather, you have stumbled upon the existence of invariant mass for a system, as described by Darwin123 in post #126 above. The moving diamond acts like Darwin's hypothetical mirrored box. You cannot logically describe a property of the system as belonging to the photon alone.
Indeed, it is wishful thinking on your part.
Dancing David
Penultimate Amazing
And how exactly is it at rest, you seem to be mixing up frames and pretending a universal frame in which it is at rest.
So, where is it at rest?
Ziggurat
Penultimate Amazing
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No, he's not mixing up reference frames, the issue is more subtle than that.
Take a reference frame (call it frame A) where a hunk of diamond is motionless. Send a photon through the diamond from left to right. As it passes through the diamond, its average velocity will be 0.4 c to the right.
Now switch to a reference frame (frame B) where the diamond is moving to the left at 0.4 c. The average velocity of that photon, while it's inside the diamond, will be 0 in reference frame B.
The trick is that "average" is not the same as "instantaneous".
catsmate
No longer the 1
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You might find him on one of the other science fora around the 'net but he's been banned from most of them.