And has that ever actually happened? Can you cite experimental results?
No one said that light “doesn’t have mass.” Light has energy; energy and mass are equivalent. E, mc squared, you know.
Photons don’t have “rest mass,” but that’s okay, as they never exist at rest.
You’re rebutting things that relativity doesn’t say.
Yes it has, and no I can not.
It is hardly spelled out since it contradicts SR. (or at least limits the constancy of the speed of light to specialist cases)
But here I will quote naita:
“The closed circuit light speed in a rotating reference frame exceeds c. This is quite obvious and has to be so for it to stay at c in all inertial frames.”
And he is correct, it is obvious and must be so.
It is known that the Sagnac effect shows 2 different speeds for light CW and CCW in a rotating Sagnac loop.
It is known that if it was not rotating, both paths would be essentially equal and measure C.
So now one is early and one is late, the early one is exceeding C, it completes the race sooner than it otherwise would have since as far as the light is concerned the finishing line has moved.
So it is not disputed by SR, but it is probably not spelled out either since talking about light exceeding C is about as polite to SR as talking about an syphilis at the dinner table.
If you look hard however you may find places where it has been said other than naita’s admission.
Oh, and Ronald Raygon’s admission too.
The fact that the Sagnac loop works the way it does means that the speed of light is being exceeded, and being found to every time it is used.
This is not controversial, just not often talked about.
Actually, photons do stop.
Sorry, but they do, it was achieved in an exotic atmosphere in a lab, the same line of research that has slowed it to a crawl actually managed to stop it entirely for a short period of time.
I am sure you will say that this is irrelevant, so save your breath, er fingers.
Translated into English - “No”
It is well known that photons can move slower than c in a medium. The index of refraction of a medium is the ratio of that speed to c.
You are being dishonest, and, at this point, I can only presume you re being deliberately dishonest. I gave you every possible credit for being naive, but you have gone well beyond that now.
Actually translated into English, Yes!
But to arrive at that conclusion you have to take the length of the path and the velocity and calculate.
But why do you think there is wide admission that within the non-inertial rotating frame the speed of light over the entire loop exceeds C?
Because it is obvious, certain, clear, necessary and true.
You seem to be unaware that light has not only been slowed, but also stopped entirely.
I was unable to find the reference I was looking for, but these will do:
http://www.extremetech.com/extreme/162289-light-stopped-completely-for-a-minute-inside-a-crystal-the-basis-of-quantum-memory
http://cerncourier.com/cws/article/cern/28403
http://www.geek.com/news/physicists-succeed-in-stopping-light-completely-551694/
Actually, you’re quite right. I am unaware of this.
If one of the scientifically literate persons reading this thread would care to step in and enlighten me, I would happily learn from them.
You have only served to teach dishonesty, and that’s a lesson I don’t really need to learn. At best, I’d prefer to learn it from someone competent at it.
I’ll wait for the experts - but I think he is giving that more spin than it deserves - a quick review of the first article refers to it as ‘effectively stopped’ because of it being trapped in a crystal, etc - I don’t believe this quite qualifies as stopping it in the ‘traditional’ sense - nor does it have anything to do with what ‘c’ is or if anything can move beyond it.
Its absolutely exciting stuff -
When you get into exotic materials, you have to define “stop”.
In this case, the light doesn’t stop like a car would stop.
By my reading (amateur, of course), the photons get trapped by in a material to which they are opaque. The photon energy goes to atomic spin. This energy is then emitted as photons (more or less the “same” photons in a sense) when the material is “switched” to transparent.
Is this “stopping” the photons? Sure, in a manner of speaking, but, as I noted, it’s not “stopping” in the same sense as stopping a car or even a baryon.
Really good stuff but little to do with relativity or disproving it, unless you’re some kind of arrogant asshole.
Of course, SR isn’t really even about photons, anyway. SR exists to explain that the maximum observed velocity of particles (in which I’m including bosons - like photons) is c. We’ve only observed bosons hitting this velocity in vacuum, though we’ve observed very low mass particles get close (neutrinos and such). So it’s not necessarily that light is intrinsically special in this regard but it’s the first thing we’ve observed that hits the universal speed limit.
simster and Great Antibob: Thank you most very kindly. I hate to be unchivalrous, but if our learned correspondent were to tell me that water was a molecule, I’d start studying the periodic table of the elements.
The real science here is, definitely, exciting. I’m also behind the curve: have neutrinos been shown to have non-zero rest mass? This is the stuff that we all love to read about!
(And it’s so cool that Peter Higgs lived to see the discovery of his eponymous particle. Too often, physical discoveries come too late to be enjoyed by those who first came up with the mathematical predictions.)
Yes, we know they do now. Wiki has a summary.
We’re still putting upper bounds on the possible mass, and there’s some really kickass work on it. That said, the mass is incredibly low. The observed velocity for neutrinos is c for all practical purposes.
The experiments (which have been mentioned a few times in a this thread) showing a velocity greater than c measured neutrino velocities.
The slowing or stopping of light is neither here nor there when discussing the behavior of a freely propagating photon. In these experiments, the photon(s) are strongly coupled to some medium (e.g., a cold gas of sodium atoms), and they are no longer describable as independent particles. It is analogous (if not actually equivalent) to light slowing down in window glass. It doesn’t imply anything about free, massless photons not always propagating at c or anything. It just shows that photons traveling through a medium will have interactions with that medium.
(Aside for Trinopus: in modern jargon, one would say that a photon has no mass, full stop. One can define a “relativistic mass” as you have used upthread, and historically people have done so because it helps preserve some of the Newtonian equations, but on the whole it makes everything more cumbersome. The math is much more elegant if one discards the Newtonian formulas. In this modern approach (for a generous definition of “modern”), relativistic mass doesn’t appear. The only mass is rest mass. In some contexts it is called “invariant mass”, usually when looking at the mass of a system of particles. This mass, I should point out, is not the sum of the rest masses of the individual particles.)
Yes, but the values of the masses are unknown. They are known to have mass because they have been observed to undergo a process called “flavor oscillation”, where one type (or “flavor”) of neutrino changes into another type as it travels. This process is described by the Standard Model, but it can only happen if neutrinos have mass, and only if the masses are not all equal. Flavor oscillations depend only on the differences in the squares of the masses, so one cannot determine the actual values of the masses through this process. Cosmological observations suggest that the sum of the neutrino masses is something less than 0.5 eV (for comparison, a proton is about 2,000,000,000,000 times heavier). Terrestrial measurements are more direct, but they are difficult. The KATRIN experiment is the only current player and will begin operations in the next year or two.
I haven’t scanned for the mention of these, but for completeness: there are no extant results demonstrating faster-than-c velocities for neutrinos. There was a result from the OPERA collaboration[sup]1[/sup] for a while, but it has since been retracted and updated with a result consistent with c.
[sup]1[/sup]or, the subset of the collaboration that agreed to sign the original article
I’m definitely showing my age! I took college physics in (um) 1977 or so, and the textbooks still talked about rest mass and relativistic mass. Also momentum.
I remember another thread here on SDMB where it was said that no one uses “mass expansion” – objects get more massive as they go very fast – because the equations get messy and it’s easier just to talk about energy.
This is all definitely past my pay grade… (But, at least, I’m not saying, “Oh, wait, I know better, look at this thought-experiment where you take a proton going .99c and reflect it from a magnetic field so that the rotating mirror turns to chocolate…”)
(Bitter? Me? Bitter? Well, fuck: we tried being chivalrous.)
Oops. That’s what I get for posting drunk without looking my posts over.
Yes, the initial OPERA results were retracted, and this experiment and corresponding investigation has been mentioned a couple times in the thread.
I only meant to mention it in passing to note that neutrino mass must be very low to see a velocity near c.
Super cool, and thank you! I remember reading about such oscillation in Scientific American, some while ago, as a possible explanation for the observation of too few neutrinos coming from the Sun. If our detectors were only set up to detect on variety, and the neutrinos shifted in and out among varieties, then, naturally, we’d detect too few of them.
(Some very few people, at the time, suggested the core of the Sun had stopped undergoing fusion. Nice to know, at least, that they were wrong!)
And, see? Science can be explained in “ordinary language.” We can communicate the upshot of the discoveries without mathematics. We just can’t participate in real discoveries – and most certainly in revolutionary ones – without the math.
(I’m still trying to set up a particular integral to explore an argument regarding “Ringworld” gravitation. It’s making me go way back to my old geometry texts!)
I feel like this has to be expanded on. It was retracted due to errors in the instrumentation - not an elaborate conspiracy to keep c right where “the man” wants it. But then again, how would we know the difference?
A little CTRL-F brings me to the neutrino velocity mention…
mythoughts, I was not reading the thread during this portion, but… what are you implying here? What group do you envision is pressing their thumb down on the scientist minions below them? And with what motives are they doing so?