Timeline for Why can't photons have a mass?
Current License: CC BY-SA 2.5
17 events
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| Feb 18, 2017 at 6:12 | comment | added | Luboš Motl | OK, I actually agree. I would still bet anything that the photon is exactly massless - and there are also reasons that will be understood beyond the QFT framework why it has to be so. I think it's not an accident that the light but massive gauge bosons we know get their mass from the Higgs mechanism, not via Stueckelberg, and in quantum gravity, the Stueckelberg masses have to be high enough - comparable to the fundamental scale - for consistency, for some reasons similar to the weak gravity conjecture if not exactly that one. | |
| Feb 17, 2017 at 12:37 | comment | added | AccidentalFourierTransform | @LubošMotl This answer is wrong. If you add the mass term $\frac12 m^2 A^2$ to the QED Lagrangian, you break gauge invariance but there are no negative norm quanta. The theory (Proca Lagrangian) is well defined, unitary and finite (there are problems with naïve power-counting renormalisation, but as long as the current is conserved, all measurable quantities are finite). The most correct and general treatment of massive photons is through the Stückelberg mechanism (which becomes the Proca theory in the unitary gauge). The S. theory is perfectly well defined, unitary, covariant and finite. | |
| Mar 14, 2016 at 15:16 | comment | added | Curious Layman | @MurodAbdukhakimov: that nothing with mass can travel at the speed of light is an axiom of physics. Einstein's equations show that in order for mass to travel at the speed of light would take an infinite amount of energy. Also, results show that neutrinos ALWAYS travel sub-C. So, you asked Crazy Peanut how he knew that neutrinos did not travel at the speed of light. I am going to reverse that on you. How do you know that neutrinos travel at the speed of light? Your profile lists theoretical particle physics as your specialty, so you must have some basis for your stance. | |
| Feb 1, 2016 at 12:19 | comment | added | HolgerFiedler | And the EM radiation is not a force. But of course it's range is infinite because photons are indivisible particles, travelling until they hit something. | |
| Feb 1, 2016 at 12:17 | comment | added | HolgerFiedler | The related elaboration shows how with a postulate about finite electrostatic fields the exchange between positive and negative charges happens without virtual photons. | |
| Feb 1, 2016 at 12:11 | comment | added | HolgerFiedler | Luboš That the electrostatic force is a infinite force seems to be a postulate. Please pay attention to my answer here. | |
| Aug 18, 2015 at 4:39 | comment | added | Luboš Motl | Hi @XiaoyiJing - most things are related in some way. The mass gap of Yang-Mills fields is just a different statement of the fact that there exist no massless - or arbitrarily light - allowed (color-neutral) bound states in QCD and similar theories. For QCD, the conclusion is the opposite one - a massless particle does not exist. | |
| Aug 17, 2015 at 20:27 | comment | added | Xiaoyi Jing | Hi Professor Motl. Is that also related with the mass gap of Yang-Mills fields? | |
| Mar 13, 2015 at 20:26 | comment | added | Isomorphic | Can the answer be because it is impossible to accelerate them ? | |
| Apr 14, 2014 at 7:45 | review | Suggested edits | |||
| Apr 14, 2014 at 8:38 | |||||
| Feb 18, 2014 at 13:36 | comment | added | Luboš Motl | Because the strong force is confining, so only color-neutral ("uncharged") particles are allowed to exist in isolation. Correspondingly, the force among such neutral particles decreases quickly with the distance. In fact, the decreases is faster than the power law because the gluons self-interact so they are confined, too. The mass of colored objects is a subtle thing - it depends on the RG scale and the masslessness is only relevant at very short distances, much shorter than the proton radius (QCD scale) where the confinement starts to matter. | |
| Feb 18, 2014 at 12:41 | comment | added | Hakim | Why the strong force has a short-range but gluons are massless? | |
| May 27, 2013 at 7:18 | comment | added | Waffle's Crazy Peanut | @MurodAbdukhakimov: Well, I believe in observations ;-) | |
| May 27, 2013 at 6:58 | comment | added | Murod Abdukhakimov | @ϚѓăʑɏβµԂԃϔ: How do you know that? | |
| May 26, 2013 at 16:29 | comment | added | Waffle's Crazy Peanut | @MurodAbdukhakimov: That's not quite correct. Neutrinos always travel at some significant fraction of $c$ ;-) | |
| May 26, 2013 at 10:01 | comment | added | Murod Abdukhakimov | Neutrinos also travel at the speed of light but have non-zero masses. | |
| Feb 6, 2011 at 19:05 | history | answered | Luboš Motl | CC BY-SA 2.5 |