tag:blogger.com,1999:blog-22973357.post5017588250706318624..comments2021-03-01T02:02:38.504-05:00Comments on Sabine Hossenfelder: Backreaction: Dear Dr B: If photons have a mass, would this mean special relativity is no longer valid?Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger33125tag:blogger.com,1999:blog-22973357.post-52461081078731192672016-05-21T12:47:12.002-04:002016-05-21T12:47:12.002-04:00For purposes of deriving the Lorentz transformatio...For purposes of deriving the Lorentz transformations, I don’t think we should be too critical of the assumption that light has no rest mass. As you said, there are good reasons (gauge invariance) for thinking that electromagnetic radiation is massless energy. The fact that people sometimes investigate the possibility of a tiny non-zero rest mass for light (which would be very unsettling for ourAmoshttps://www.blogger.com/profile/00595591283398023248noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-32873292521637803282016-05-20T01:16:40.578-04:002016-05-20T01:16:40.578-04:00Henning,
Oh, yes, the geometric algebra. I only l...Henning,<br /><br />Oh, yes, the geometric algebra. I only learned of this quite recently, but my reaction was also "why didn't I know of this earlier." As a student I spent quite some time with Clifford algebras, and this would have been dramatically helpful. Now I kind of feel to old to spend much time on it (time I don't have, and also, I don't really need it). In any Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-8295245920033342442016-05-19T18:08:30.495-04:002016-05-19T18:08:30.495-04:00Can very much relate to the spaceship and synchron...Can very much relate to the spaceship and synchronized clocks confusion. Fortunately, at the same time when this confused me in physics class we also learned about linear algebra and I realized that applying this to a Minkowski diagram was all it took.<br /><br />Much later I had a similar why-the-hell-did-they-not-teach-me-this-earlier moment when I came across Hestenes Geometric Algebra. <br /Anonymoushttps://www.blogger.com/profile/14479459346584756683noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-26241576453821077572016-05-19T03:03:46.483-04:002016-05-19T03:03:46.483-04:00raattgift,
It wasn't before I encountered the...raattgift,<br /><br />It wasn't before I encountered the idea of curved spacetime, but before I knew how to mathematically deal with it. I don't recall having difficulties giving up on global symmetries if that is what you mean. I learned GR from Weinberg's textbook, and while in hindsight I don't like the emphasis he puts on the geodesic equation (which I believe is another one Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-21841363957551915512016-05-19T02:23:10.374-04:002016-05-19T02:23:10.374-04:00"Why didn't you tell me this earlier?&quo..."Why didn't you tell me this earlier?" is a really good question. I'm glad you keep writing about the Poincaré group and c as its free parameter; I think it's useful.<br /><br />I have a question, though. Was this before you first encountered general curved spacetime? If so, what "clicked" for you when dealing with curved spacetime on which the Poincaré groupAnonymoushttps://www.blogger.com/profile/16524954894982364194noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-6976962843475285742016-05-17T06:43:31.802-04:002016-05-17T06:43:31.802-04:00kashyap,
Yes, as I said above, the difference dep...kashyap,<br /><br />Yes, as I said above, the difference depends on the mass of the photon, which has to be tiny. Actually the MM-type measurements do not give the strongest constraints on the photon mass. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-87825265441324444342016-05-17T06:42:19.740-04:002016-05-17T06:42:19.740-04:00Henning,
I don't know, but I also find it ann...Henning,<br /><br />I don't know, but I also find it annoying. When I was a teenager, I had great trouble following all these funky arguments with satellites and rocket ships and laser clocks and whatnot because one gets hung up on all kinds of irrelevant questions (what's the clock made of, can you actually see this, was the rocket ship always moving at this velocity, and so on). I was Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-4299141115486908102016-05-17T06:37:51.412-04:002016-05-17T06:37:51.412-04:00George,
I didn't mean to say that Einstein kn...George,<br /><br />I didn't mean to say that Einstein knew this was what he wanted...Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51050406084710366842016-05-16T15:35:26.737-04:002016-05-16T15:35:26.737-04:00SH: "Einstein wanted the laws of physics to b...SH: "Einstein wanted the laws of physics to be the same for all inertial observers in Minkowski-space"<br /><br />I thought Minkowski suggested the geometric form some years after Einstein's publication and Einstein at first dismissed the idea. That seems to be the sequence given here:<br /><br />https://en.wikipedia.org/wiki/Hermann_Minkowski#Work_on_relativityFleetFoothttps://www.blogger.com/profile/15770404644841730794noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75101186780304727172016-05-16T11:03:23.646-04:002016-05-16T11:03:23.646-04:00Always thought it was idiotic that Special Relativ...Always thought it was idiotic that Special Relativity is still mostly taught in the same convoluted way that Einstein originally established the theory. (Very doubtful that Einstein would still teach it that way if he was still around).<br /><br />As you pointed out, it just comes down to understanding what group is appropriate for spacetime. Other than that SR can be derived from the same Anonymoushttps://www.blogger.com/profile/14479459346584756683noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-13174637123742815982016-05-16T10:59:37.482-04:002016-05-16T10:59:37.482-04:00Hi Bee,
Ok.I understand that SR needs only some v(...Hi Bee,<br />Ok.I understand that SR needs only some v(max). But if c is not v(max) then Michelson Morley and other more refined experiments which prove frame independence of velocity of light will be in trouble. Probably this fact restricts deviation of c from v(max) to be very small. Do you agree? I suppose gauge invariance etc can be fixed!kashyap vasavadahttps://www.blogger.com/profile/10732897306667764590noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54817153586988866272016-05-16T01:05:20.890-04:002016-05-16T01:05:20.890-04:00John,
I don't know what your referral to neut...John,<br /><br />I don't know what your referral to neutrinos means. Neutrinos don't change their polarization, to begin with they're not bosons. Neutrino oscillation is a mixture between different particles, you need at least two particles for that.<br /><br />As to the additional degree of freedom, you have to somehow get rid of this if you want your theory to be viable, at least Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-16294283328915843982016-05-15T23:56:58.938-04:002016-05-15T23:56:58.938-04:00So a non-zero photon mass would permit a photon st...So a non-zero photon mass would permit a photon state with zero momentum projection along its direction of travel. Would it also lead to a precession/ transition in polarization, similar to neutrino oscillations? If so, aren't there some atomic or nuclear transitions that might yield a fotrumfor placing a lower bound on the photon mass? <br /><br />Populate a spin 1, parity minus state with mAnonymoushttps://www.blogger.com/profile/13066792698431648355noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-14557157488435063952016-05-15T16:37:57.254-04:002016-05-15T16:37:57.254-04:00@Brian Clegg Massless boson photons detect no vac...@Brian Clegg Massless boson photons detect no vacuum refraction, dispersion, dissipation, dichroism, or gyrotropy. Pulsar, gamma-ray burst, supernova, and quasar outputs across the spectrum arrive simultaneously and in register.<br /> <br />Fermionic matter (quarks, hadrons) exhibits baryogenesis, parity violations, symmetry breakings, chiral anomalies, and Chern-Simons repair of Uncle Alhttps://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-36123656445446530142016-05-15T11:49:33.520-04:002016-05-15T11:49:33.520-04:00Brian,
Yes.Brian,<br /><br />Yes.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74206384176531116382016-05-15T11:48:18.083-04:002016-05-15T11:48:18.083-04:00Amitabha,
I don't disagree.Amitabha,<br /><br />I don't disagree. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-66155159727555685412016-05-15T11:47:51.938-04:002016-05-15T11:47:51.938-04:00gda,
Yes, is what I'm saying.gda,<br /><br />Yes, is what I'm saying.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3998117019585252292016-05-15T11:10:43.777-04:002016-05-15T11:10:43.777-04:00Sabine, nice answer to the question. I think one s...Sabine, nice answer to the question. I think one should clarify that the most important principle of spetial relativity, is the principle of relativity itself, when Maxwell theory is taking into the game (back then it was only applied the galilean transformations to classical mechanics). The second postulate of the constancy of ligth seems that only fixes the constant paramerter of the boosts to Anonymoushttps://www.blogger.com/profile/07757540680872655803noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-56091999076623939282016-05-15T10:39:34.645-04:002016-05-15T10:39:34.645-04:00"Poincaré-group" Poincaré group gauge t..."<i>Poincaré-group</i>" Poincaré group gauge theory maps Einstein-Cartan gravitation. Absent spacetime torsion, pseudo-Riemannian spacetime V4 is general relativity. Absent spacetime curvature, Weitzenböck spacetime A4 has a teleparallel gravitational energy-momentum pseudotensor anti-symmetric to parity transformation. Absent both, Minkowski spacetime M4 is special relativity.<br /Uncle Alhttps://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-78768094485606938462016-05-15T08:43:05.219-04:002016-05-15T08:43:05.219-04:00Right, my misunderstanding was that the factor of ...Right, my misunderstanding was that the factor of 2 came from the photon's masslessness per se, when I guess in fact it shows up for any ultra-relativistic particle (otherwise the whole idea of a massive photon would have been put to bed observationally 100 year ago).Jasonhttps://www.blogger.com/profile/15293237536594816538noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-34905587653556107632016-05-15T08:31:47.808-04:002016-05-15T08:31:47.808-04:00Sabine,
The question was about photon mass (yes,...Sabine, <br /><br />The question was about photon mass (yes, I should have said 'gauge invariant mass' rather than 'gauge invariant mass term'). And a pole in the propagator, or a massive wave equation, are the signatures of a massive particle. So what I described produces a massive photon without breaking gauge invariance.<br /><br />The Higgs mechanism in the Standard Model Amitabhahttps://www.blogger.com/profile/17140154364941569189noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74521154590931623652016-05-15T08:07:08.984-04:002016-05-15T08:07:08.984-04:00Sorry to keep asking questions, but it's inter...Sorry to keep asking questions, but it's interesting! I hadn't really thought about energy. So if a photon has mass and we know how energy varies with frequency, does that mean velocity should also vary with frequency?Brian Clegghttps://www.blogger.com/profile/12723555872580740773noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23393837258844390222016-05-15T08:01:37.529-04:002016-05-15T08:01:37.529-04:00Amitabha,
You could do this, but I wouldn't c...Amitabha,<br /><br />You could do this, but I wouldn't call that a mass term. (It's not quadratic in A.) The Higgs mechanism leaves the photon massless. If you are speaking of some other symmetry breaking mechanicsm, well, that would have to break the gauge symmetry, which is what I'm saying.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23182365920607896612016-05-15T07:32:45.844-04:002016-05-15T07:32:45.844-04:00There are at least two ways in which the photon ca...There are at least two ways in which the photon can have a gauge invariant mass. One is to couple the photon to an antisymmteric tensor 'gauge field' B using a B\wedge F term. This is a two-point derivative coupling, whose coefficient provides a pole in the photon propagator. Classically, one gets massive wave equations for the field strength F. The B field carries one degree of freedom, Amitabhahttps://www.blogger.com/profile/17140154364941569189noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-16321368337781343912016-05-15T07:16:08.241-04:002016-05-15T07:16:08.241-04:00Jason,
I can't recall the calculation off my ...Jason,<br /><br />I can't recall the calculation off my head, but I don't think it's a continuous limit. The extra factor I think comes in roughly because in GR for light you have to take into account both the space and the time curvature. No matter how much you approximate this in Newtonian gravity, you'll never get the extra part. What you can do is the the opposite limit: take Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.com