A few years ago scientists found that neutrinos were going faster than the speed of light. Then they found some problem with the calculations. I read an article that was made this year about faster than light neutrinos. I'm not sure if the journalist is ignorant or if they found that the neutrinos really were going faster.
9327
I was quite surprised to read this all over the news today:     Elusive, nearly massive subatomic particles called neutrinos appear to travel just faster than light, a team of physicists in Europe reports. If so, the observation would wreck Einstein's theory of special relativity, which demands that nothing can travel faster than light.   &mdash;  Apparently a CERN/Gran Sasso team measured a faster-than-light speed for neutrinos.   Is this even remotely possible? If so, would it be a real violation of Lorentz invariance or an "" effect?   The ; a webcast is/was planned .  News conference video
42198
Is it possible to have an alternative theory which is consistent with experiments supporting GR, but which doesn't mandate a speed limit on causality?  In other words, I understand there is experimental evidence for gravitational/relativistic time dilation, spacetime curvature, etc. but is there any inherent reason why these effects cannot be explained without the max speed requirement?  QM clearly shows that "communication" can happen instantaneously but, supposedly, causality cannot break the speed limit.  I also know the speed of light is derived from other principles, but is there anything that says that speed has to be a max limit of any kind?  I want to emphasize that the QM "communication" doesn't imply causation or information exchange, merely the establishment of the entangled attribute.  Bell's inequality tells us that the attributes were not predetermined and were only established upon measuring one of the particles.
47548
Does entanglement not immediately contradict the theory of special relativity? Why are people still so convinced nothing can travel faster than light when we are perfectly aware of something that does?
91131
I have heard from many people that the Flash is faster than Superman. But how do we know this?  Have we ever seen them head-to-head?
13475
I was thinking that maybe photons loss energy naturally when they travel great distances.  Or maybe the mass of all matter is increasing over time and therefore photons emitted in the past are necessarily less energetic.  Or is the expansion of space backed up by so much other evidences that trying to find another explanation is completely foolish?
3678
Let's say I fire a bus through space at (almost) the speed of light in vacuum. If I'm inside the bus (sitting on the back seat) and I run up the aisle of the bus toward the front, does that mean I'm traveling faster than the speed of light? (Relative to Earth that I just took off from.)
23658
Is this true or false: If A and B have clocks and are traveling at relative velocity to each other, then to B it APPEARS that A's clock moving slower, but A sees his own clock moving at normal speed.  Similarly, to A it APPEARS that B's clock is moving slower, but B sees his own clock moving at normal speed.  If the above is true, then both A seeing his own clock moving at normal speed and B seeing his own clock moving at normal speed means that in reality both clocks are moving at normal speed, and neither has slowed down, whereas the other person's clock APPEARING to move slowly is merely an illusion.   Now is this true or false: If A and B have clocks and are traveling at relative velocity to each other, then A sees his own clock move slowly (compared to the speed of the clock when A was at rest with respect to B) and B sees his own clock move slowly, so that in reality both clocks are moving slowly, but they still remain synchronized (since both are slow by the same amount)  If the above statement is not true, then why do muons decay slowly when moving fast? [it could only be possible if the muon saw its own clock as moving slowly. If we saw the muon's clock moving slowly, but the muon saw its own clock moving at the normal rate, then the muon would decay at the normal rate, and not slowly]  Can anyone please explain where I went wrong?
93624
How do you prove that the time for two objects traveling towards each other at relativistic velocities is still d/(v1+v2).  Answer seems to have something to do with velocity addition but I'm stumped...
42012
What is the experimental evidence that suggests the existence of quarks? How were they discovered? I'm going to assume a particle collider is involved, as it tends to be the case with most subatomic discoveries these days.  How are we able to study something so small with any type of instrument? It seems like at some point, we wouldn't be able to build an instrument on the scale required to detect something so small.  (Would be nice if this could be explained in such a way that a College Physics 1 / 2 could understand it.)
37590
Greatings!  I'm trying to understand special relativity and have one question bugging me.  In almost every book or video about the subject there is a thought experiment with moving light clock. I hope I need not elaborate on the sutup and the outcome of the experiment.  So the question is this: When a light source on the MOVING light clock emits a photon of light the path of the photon is triangular.   How this can be?   I thought since light speed is constant in every reference frame the movment of the "emmiter" can't affect the movment of the light so light should shoot right up (from the point of stationary observer) and thus move backward and up from the point of moving observer.  So you see my logic is: light speed is invariant => you can't make it move UP &amp; FORWARD only UP. i.e. you can't change it's direction once it's emited in UP direction. Why the hell light moves sideways then?  And I'm puzzeled. There is flaw in the logic but I don't see it.  Thanks for help.
76733
I've always heard people saying, "Faster than light information transfer can't happen because it would violate causality!  Effects can precede their causes!"  However, I'm trying to think of a situation where this would happen.  I'm sure it has something to do with relativity or something like that.  I sort of understand that people going faster perceive time slower.  Can someone help illuminate this for me by showing a scenario where causality is clearly violated due to FTL information transfer?
50359
This is probably an obvious question, but I don't see it answered anywhere.  Imagine we have an object in the Universe that is traveling, relative to the Milkyway at about .99999999999999999999999999c and I realize that's not possible, but imagine.  Speed is relative, so to the object, the Milkyway is flying past it and to us, the object is flying past us.  That's all good and relative.  But the photons that our superfast object encounters are gonzo blue-shifted, and relativity says that's OK too.   But lets say the object is traveling so fast, the photons it encounters are energetic enough to spontaneously undergo pair production.  That seems difficult to explain.  A relatively low energy visible light photon to our perception won't split into an Electron and a Positron, but a very energetic photon can, but it's the same photon just observed by 2 different reference frames?    I understand that observers won't agree on when things happen or on energy but the two observers should agree on events that take place and pair production for one but not the other seems impossible.     Is there a simple layman's way that this can be explained?
1588
I'm interested if any of the following explanations have enough predictive capability to explain the observations we see today. The claim is that the Universe is not expanding, and that red-shift of light is caused by:    Though a couple of these are simply ridiculous, I'm still interested. Keep in mind that I am not a creationist, but am looking for reasons to see if any of these are valid or invalid.
55655
This question has been touched tangentially by  and  but I do not think they reach the core of my question.  When I read that many other theories, e.g. the Standard Model, have been constructed to be Lorentz invariant it appears that electromagnetism has some of preponderant role in the universe compared to other theories. I suspect that the answer is that this is not the case, and that the space-time Speed of Light (with upper-case) is really more of a universal constant that is not necessarily related to the speed of the electromagnetic waves or of photons.  There are many other related questions:    would it really be devastating for relativity that we find out in the future that photons have a tiny mass and move slower than ... uhh... the speed of light? which "c" is applicable in different situations? I mean, possibly the space-time constant should be used in $E=mc^2\gamma$, it would be the  velocity of gravitational waves, etc..., but in other situations such as the Bohr radius or Compton wavelength I am not sure.   Well, any answer will be appreciated. Please tell me if you know any reference to bibliography that address this issue.
104305
I understand that information cannot be transmitted at a velocity greater than speed of light. I think of this in terms of the radio broadcast: the station sends out carrier frequencies $\omega_c$ but the actual content is carried in the modulated wave, the sidebands $\omega_c\pm\omega_m$. The modulation envelop has its group velocity and this is the speed at which information is being transmitted. We also know, for example, that x-rays in glass have a phase velocity which is greater than the speed of light in vacuum.   My question is, what exactly is it that is travelling faster than the speed of light?    EDIT: I know it couldn't be anything physical as its superluminal. My problem is, what is it that has absolutely no information content yet we associate a velocity with it.
99097
It's well known that, in relativity, if you can go faster than light, you can go backwards in time and create a paradox. Also, attempts to create &quot;warp-drive&quot; space-times in which something moves faster than light (the best known is the Alcubierre drive) usually require lots of &quot;negative energy&quot;, something which in reality may only be available under rather special quantum-mechanical conditions (e.g. Casimir effect). So one might suppose that the universe obeys an &quot;energy condition&quot; which provides a physical (and not just logical) barrier to paradox. But lately there's a news story about an American physicist (Erik Lentz) who claims to have constructed a superluminal soliton using only positive-energy sources.  was released last year and has now been published. I have yet to find a technical analysis of the paper. The closest thing so far is  by relativist Ken Olum, who proved one version of , and who thinks his theorem must apply to Lentz's soliton too. , Lentz also mentions  that talks about slower-than-light positive-energy warp-drives, and faster-than-light warp-drives that violate energy conditions, but says they didn't analyze his own construction (which, to repeat, is meant to be a faster-than-light warp-drive that doesn't violate energy conditions). So what's the story? What exactly is Lentz's new idea? Is there a reason why a sufficiently advanced civilization can't build a Lentz drive and change the past? (Thanks to T.L. for bringing these works to my attention.)
51675
The measurement of the flux of muons at the Earth's surface shows that many more muons are detected than would be expected, based on their mean half-lifetime of 2,2 microseconds. This is a good proof for the time dilatation as predicted by the special relativity theory.  QUESTION: does there exist a similar proof for the Lorentz contraction?