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177 Comments
- dirtyfratboy, on 10/12/2007, -0/+7@bigd063
Please at least read the caption:
Cerenkov Radiation is when high velocity particles travel faster than the speed of light in a medium.
Light is impossible to surpass in a vacuum, however while traveling in a medium, its speed is decreased, which allows for Cerenkov radiation to exist.
It's pretty fascinating stuff:
http://www.news.harvard.edu/gazette/1999/02.18/light.html - teece, on 10/12/2007, -0/+5berean: when you have absolutely NO IDEA about the special and general theories of relativity, it's best not to mouth off about them.
Trust me, you have no idea, And your trivial "refutations" are the kind of thing you'd figure out if you spent even the slightest bit of time studying what Einstein postulated (and has since been experimentally proven) in 1905 and 1914. (Do you really think physicists that spend their entire lives studying this stuff, and are among the brightest folks in the world, have not thought about your trivial statements? They have).
You're comically wrong. Spend some time at the library, if you can handle a little algebra and some reading of physics. The crux of the matter is that your intuition about what time, length, mass, energy, and velocity are is crap. The real universe behaves differently than you imagine. c is an absolute speed limit.
As for these, my old quantum prof. called 'em light booms. I always thought that was a cool term (analogous to sonic booms). - mwarfield, on 10/12/2007, -0/+4I have to agree with others comments that the lack of knowledge of physics here is pretty spectacular. I only majored in it in college. I didn't get a doctorate. But I did study some of this even way back then, 35 years ago.
1) Einstein, contrary to popular myth, was not always right. He hated quantum mechanics, arguing that God wouldn't "dice with the universe". Well, he lost on that one. He also couldn't deal with "entanglement" (more on that below), one of the consequences of quantum theory. He also had some problems with his "cosmological constant" (calling it his own worst mistake) but that wanders off into some really esoteric modern cosmology (dark energy and such). He was a genius... But he had his limits.
2) He didn't prove that nothing could go faster than light. Only that something with a "non-zero rest mass" could travel AT the speed of light (infinite energy, time and dimensional singularities, and a couple of other gotchas). OTOH... Things which have NO rest mass (photons), can only travel at the speed of light in a vacuum (or less in a medium). This was a central issue over whether neutrinos have rest mass or not...
3) Nothing prevents you from traveling FASTER than light other than the discontinuity AT the speed of light (how do you go faster if you can't get as fast as). BTW... A Cherenkov particle is a particle traveling faster than light "in a medium" but slower than C. A (hypothetical) particle traveling faster than C is referred to as a tachyon. Just like the "magnetic monopole", there are lots of theories about what the characteristics of one might be if one exists but one has never been detected.
4) If you travel FASTER than light you do NOT go back in time. Where you go, I'm not sure. The value that comes out of the Einstein Lorenz (sp?) transforms is NOT negative. The transform has a denominator incorporating of the square root of C minus your velocity (making the transform infinite at C). It has a coefficient of "i" (the imaginary number - the square root of -1) for v > C. So you just multiplied your translation along the time dimension by the square root of a negative one. Where does that leave you?
You want something spooky that's faster than C then look up entanglement. Einstein hated it but it's now been repeated demonstrated over some very significant distances. Polarization is not a conserved quantity in quantum mechanics. Create two entangled photons (which then separate at the speed of light in opposite directions) and later alter the polarization of one. The other changes polarization to match. Instantaneously, regardless of the distance. There are a couple of real esoteric reasons why this does not violate causality or the limits on transferring information faster than light (think reference beams and energy) but it has been verified even to the extent of transmitting "quad bits" of information over a distance. Last I heard, it had been confirmed over miles of distance, not just at the atomic level. Several good books on that subject out there. Much more interesting than Cherenkov radiation, which is pretty mundane and been know about since before I was studying physics in college back in the 70s. It's really a stock tool for measuring the speed of high speed particles. You fire them through quartz and measure the angle of the Cherenkov radiation and that tells you their velocity. Yawn... - Vladek, on 10/12/2007, -0/+4The keyword is the MEDIUM!!!!
This digg headline is sensationalistic, and false. The proper headline should be
"What happens when something travels FASTER than the speed of light in a MEDIUM?"
The speed of light in vacuum is c. Nothing can travel faster than c.
However, when you put light in a medium (such as water), it's "effective" speed is less than c
(it's actually traveling at c, but it "bounces" around the atoms in the water, so when you measured it in the laboratory it appears to be less than c). Let's call this speed d.
This radiation that the article refers to is simply traveling FASTER than d, but is still SLOWER than c!
Take home message: Nothing can travel faster than the speed of light in vacuum. Nothing.
No digg. - ViperDaimao, on 10/12/2007, -0/+2why? They are interesting reads, and undoubtedly tech related.
- krazikamikaze, on 10/12/2007, -0/+2About the lever thing, and to clarify what dongiaconia said about it. If something with nonzero mass is going the speed of light it has infinite energy. To give something infinite energy requires infinite work. Work is (simplistically) force times distance.
The key point is a lever does not reduce the amount of work you need to do, it just allows you to vary the force or distance required to do the work. A long lever arm means big distance but small force, and vice versa with a short lever, but you still have to do the same amount of work no matter what. Since you need to do infinite work and you can't apply an infinite force, you need an infinitely long lever arm, which is obviously impossible. - SlowOnTheUptake, on 10/12/2007, -0/+2This is a well established phenomenon and has been well know for decades. No know laws of physics are violated here. The particles are moving faster than light would move in that medium. That speed is related to the refractive index of that medium. What's forbidden is for something to travel faster than light in a vacuum.
- 4vector, on 10/12/2007, -0/+1the lack of physics knowledge on this site is absolutely amazing!!
- dongiaconia, on 10/12/2007, -0/+1Direct quote from "Understanding the Theory of Relativity"
[quote]
By the turn of the century experiments showed that light did not behave the way our common sense says it should. No matter what speed or direction an object moved, a beam of light from that object was always the same--186,000 miles per second. Whether a beam of light was traveling in the direction of Earth's motion, at right angles to its motion, or in the opposite direction of its motion, the speed of the light beam was precisely the same.
[endquote]
So no more lever questions. :) - dongiaconia, on 10/12/2007, -0/+1I guess we have to wait until apple releases iLight, which will do everything Light does except be easier to use and travel at 187,000 miles per second....
- pmarks, on 10/12/2007, -0/+1@berean
You could only do the lever thing if you had a lever built from an infinitely rigid material, and an infinitely rigid material would require the nuclear force between the atoms to travel faster than light, and that doesn't happen. - bigd063, on 10/12/2007, -1/+2Ok my bad
- Vladek, on 10/12/2007, -0/+1@berean and other about the "lever"
Instead of a solid level, just think of a laser spotlight going round and round. Yes "it" will travel faster than light given big enough radius, but "it" doesn't carry any information and can't be used to transmitt anything useful at speed greater than c. This is consistent with all laws of physics.
Another artifact that seems to travel faster than light is group velocity of interfering waves. Again, this can't be used to transfer any information. The phase velocity is of course aways less than c. - OBKenobi, on 10/12/2007, -0/+1[quote]Radar signals travel at light speed. [/quote]
Sigh...
http://electronics.howstuffworks.com/radar.htm - inactive, on 10/12/2007, -0/+1It is possible to traverse a distance faster than it would take light to linearly transverse with no ill affects... This is old school.
Please stop spreading the nothing can travel faster than light mumbo jumbo... it's all lies. - Vladek, on 10/12/2007, -0/+1"If you travel at the speed of light, I doubt you'd be able to throw your hand out in front of you. In fact, I'd think you'd be very much dead, if you were even still recognizable as a human being at that velocity."
This is because of the air resistance and perhaps the acceleration, and not due to any particular speed.
First of all, you can't travel at light speed because you have mass. Even if you could, you wouldn't even be able to tell the difference in vacuum without referring to something else. It's all relative. - dongiaconia, on 10/12/2007, -0/+1@funkymonkey: 'C' isn't the thing that is supposed to be infinity, its the force applied that is infinity.
- inactive, on 10/12/2007, -0/+1Besides, anyone that claims definitively that you can't go faster than light is obviously missing the fact that we really don't understand light to begin with. Theories based on theories based on theories.
- outcast81, on 10/12/2007, -0/+1"Oh really? Explain to me how accelerating one end of a lever to the speed of light WOULDN'T accelerate the other end past the speed of light?"
You wouldn't be able to accelerate the lever to the speed of light (c). Lets say you have an infinitely rigid lever. Lets also, for example, say that the speed of your side of the lever is half the speed of the other end. If you accelerate your side to 0.3c the other side is going at 0.6c, so far so good. However, when you reach 0.499c on your side, the other side is traveling at 0.998c. Since the whole lever is one piece, its mass will have increased tremendously, and will continue doing so as the speed of your side is approaching 0.5c (i.e. the other side approaching c). You will never be able to pass, or reach, half the speed of light on your side because doing so will make the other side pass, or reach, the speed of light simply because the mass of the entire lever will increase infinitely.
On the other hand, I don't know if the speed of light limit applies to angular velocities so maybe this discussion is pointless... - thatsiebguy, on 10/12/2007, -0/+1Per Star Trek, if you go faster than Warp 10, you would occupy every point in the universe at once, then you would start to de-evolve into a pile of goo.. :D
- Vladek, on 10/12/2007, -0/+1@macslut
Gravity is not an instantaneous force. It travels at c. Google for LIGO for an experiment attempting to directly detect gravitational waves. - mr_mechanics, on 10/12/2007, -0/+1Everyone here (almost everyone at least) is applying newtonian ideas to relativity. This is not correct. Newtonian mechanics breaks down at high, or relativistic, velocities, hence the need for relativistic mechanics. Why do people who have no training in physics insist on posting thier ideas? Your making yourself look ridiculous.
- aMMgYrP, on 10/12/2007, -0/+0@vladek
actually, Rejecting physics != rejecting our physical universe
Rejecting the model of Physics and the training in Physics is far different than rejecting our physical universe. I think that the current model of physics is fundamentally wrong is all. is that so bad?
Physicists are so close minded that I betcha that if I locked you in a 10x10 room, and convinced you with formulae and empirical evidence that the room was the total universe, You'd happily believe it and never try to break its boundaries. Then I (and by extension the rest of humanity) could live in the rest of the universe without your impedance. - Vladek, on 10/12/2007, -0/+0@aMMgYrP
There are only 20 or so free parameters in the standard model. Physicists don't have The-Ultimate-Model-of-Everything-Without-Arbitrary-Parameters yet, and they admit it, but they're working on it. What else do you think physicists do all day besides teaching?
If you rejected Physics because it's incomplete, well, good luck with CS and their NP-"complete" problems, lol! No subject of study is complete, otherwise people would stop researching them, duh.
Rejecting physics == rejecting our physical universe - Vladek, on 10/12/2007, -0/+0How one can judge something that one doesn't even understand is beyond me...
- topper24hours, on 10/12/2007, -0/+0@berean
You should have taken a physics class in high school or maybe try reading a SINGLE scientific joural mag or something. I've never heard somebody w/ less knowledge of a topic spout off more. Your post about throwing your hand in front of you when you are almost at light speed and thus your hand breaking the speed of light made me cringe w/ embarassment for you. So, out of curiousity: do you believe that if I'm on an airplane traveling 9mph under the sound barrier and I start running torwards the cabin at 10mph that a sonic boom wil occur because the sound barrier was broken? Please do us all a favor and THINK before you post! - aMMgYrP, on 10/12/2007, -0/+0lets try this again, because I manages to confuse myself and everyone else, Sonar! what happens to a supersonic jet from the perspective of a SONAR array. Apologies, I just woke up from a very delicious nap.
- mr_mechanics, on 10/12/2007, -0/+0as said by mwarfield, theories of light and matter encounter mathematical singularities at the speed of light. dirac actually did some work on quantum field theory assuming a velocity greater than c (along time ago i might add). addressing time travel, all kinds of things happen in the mathematics when you assume a velocity greater than c. it was best said by feynman, that there is no single equation or explananation as to the direction of time.
- Vladek, on 10/12/2007, -0/+0@mwarfield
Entanglement, much like the light boom, cannot transmit information. Again, Einstein's postulate of
the limiting speed of light holds. As Brian Greene puts it, "it survives by the skin of its teeth" given entanglement. - apache2, on 10/12/2007, -0/+0""Non-material substance has been proven to be able to go faster than light. Take for an example, you have a very LARGE disk spinning at incredible RPMs.... once you have that imagined, place a laser pointer on the outside rim of the disk, pointing out. Now aim that laser beam at a wall, 50 miles away. Bingo, it can easily travel faster than light."
Woah woah woah! Hold on now... you're *actually* trying to pass this one off as fact?
http://van.hep.uiuc.edu/van/qa/section/New_and_Exciting_Physics/Relativity/20010513103853.htm"
That article has no relevance, I said "non-material substance" - zenghost, on 10/12/2007, -0/+0heres something to think about: what if i had a car that traveled as fast or faster than the speed of light? what would happen when i turn on the headlights? Would the light be turned of when its on when i meet the speed of light? Would the light be behind me when i surpass it? i wish the mythbusters were capable of doing this little experiment... =P
- Vladek, on 10/12/2007, -0/+0mr_mechanics, I know. I brought it up first. I've been in enough of such discussions to know where their anti-science _feelings_ come from. It's not based on logic, it's emotion. There is no arguing with such people.
Much the same with the Intelligence Design camp. They make absolutely no mention of god. Their basic strategy is to nitpick flaws in scientific theories. In this case, it's the "arbitrary constraints" (sic). - mr_mechanics, on 10/12/2007, -0/+0aMMgYrP,
what observations have you made that make you believe that physics is fundamentally flawed? just curious, since all physics researchers simply mean to explain what is observed. - mr_mechanics, on 10/12/2007, -0/+0krazikamikaze,
you are making a common mistake. mathematics is only a tool. it is simply a convienient tool for describing physical phenomonon. as an EE major you should be familiar with the subject of control systems so I will use this as an example. in a control system you always want to be on the left side of the imaginary plane so that you have a exponentially decreasing value for your I/O relation of your transfer function. that fact that you are in the imaginary plane has no consequence on the physical system since the mathematics is just a tool. - krazikamikaze, on 10/12/2007, -0/+0I'm not a physics student, so maybe someone can help me out with this.
I'm always skeptical whenever imaginary numbers arise in physics. Ok so gamma is only infinity when v=c, and becomes imaginary when v>c. So you say it's possible for v to be larger than c. That makes no sense to me.
Don't get me wrong, I'm familiar with the power of imaginary numbers. As an EE student I use them all the time. However they just simplify the process of getting from point A to point B. If you're working in the real world you better start and end with real numbers, or it just doesn't make any sense.
So my question is this: have imaginary quantities been observed in the real world, or are they just math tricks? - aMMgYrP, on 10/12/2007, -0/+0Hi everyone, I used to be a Physics major before switching to Computer Science and English. I changed because, well, it seemed to me that a lot of physics was 'limits' and 'constants' arbitrarily placed here and there for no apparent reason. It's not that I have no training in Physics, it's more that I have rejected it.
- mr_mechanics, on 10/12/2007, -0/+0 aMMgYrP,
i really doubt that at a sophomore level you could really study string theory. at the sophomore level you shouldn't have even finished you compulsory physics classes, much less any upper division level classes that would help you start to understand string theory. you have to be very trained in physics and mathematics to study string theory, which is still in its very fundamental stages. - dongiaconia, on 10/12/2007, -0/+0Newtonian mechanics also breaks down in silly putty. (also known as a Non-Newtonian Fluid)
- aMMgYrP, on 10/12/2007, -0/+0@Mr. Mechanics
Nah I did my compulsories the summer of my freshman year, A lot of my HS level credits were AP and as I said I attended a specialized Science and Math School (with a Robotics Club) So I was (just) a bit ahead of the curve, I saw a special on Nova (PBS Rules) about String theory, and went out and got to reading. Maybe you are right, maybe i did not and do not have enough of a background to really understand either way, I will concede that. But at some point, Nick Copernick had to think something was not quite right and pursue it. - mr_mechanics, on 10/12/2007, -0/+0dongiaconia,
a non-newtonian fluid is simply a fluid which the shear stress is equal to a constant times the velocity to some power, whereas in a newtonian fluid the shear stress is equal to a constant times the velocity to a power of unity, or just the velocity. tau=mu*du/dy^n. This is just a power-law relation and is very common. This leads to what is called shear hardening (why it is hard to get ketchup out of a bottle at first). This also has nothing to do with relativity or newtonian mechanics (fluid mechanics). - Vladek, on 10/12/2007, -0/+0@dongiaconia
Radar signals travel at light speed. There is no way a "closer instance of the jet gets to the radar receiver before the further ones bounce back". The jet is not anywhere close to light speed. - aMMgYrP, on 10/12/2007, -0/+0@ vladek
I'm not "subtly insinuating" anything. I'm simply disagreeing. I'm also not stupid enough to believe that God and Science are existentially mutually exclusive. Why could they both not exist simultaneously? I dunno? Who's to say that some super dimensional entity did not create the universe, and our model of physics is the reverse engineering of said universe's systems? Seems to me that they fulfill different yet adjacent niches within our psyche. and as Mr Mechanics said, I didn't say anything about God, and let me go on the record and state that I did not even mean to insinuate anything about God. - mr_mechanics, on 10/12/2007, -0/+0aMMgYrP,
to clarify, what i mean is that you, at the sophmore level, would not have practiced enough physics to understand such a new and current theory. at this level string theory is little more than complicated mathematics that predict things that have already been predicted. it has yet to come up with something unique. what is remarkable about it is mathematically sound. despite ranging from 10-26 dimensions, it correctly predicts behavior. higher dimensions are a result of the quantum geometry. to begin to understand it you need extensive knowledge of supersymmetry and quantum field thoery. the graviton is perhaps the most interesting aspect of string theory, and if ever verified will fundamentally change physics and solve one of the biggest problems in physics. how can you decide to refute physics based on a new, incomplete, and possibly false theory. recently, physicists were able to use lattice quantum chromodynamics to compute the proper mass of sub-atomic particles. how is this wrong? - mr_mechanics, on 10/12/2007, -0/+0aMMgYrP,
i agree with you that rejecting physics does not mean rejecting our physical universe. however, your claim that physicists are close minded in mundane and ignorant. is physicists were closed minded there would be no need for modification of theories. nothing after newtonian physics would have been developed since it would simply have been accepted as true. it is typical of people who don't bother to really learn physics to attack it. physics is not a hard subject and anyone can learn it if they tried. - aMMgYrP, on 10/12/2007, -0/+0@ Mr Mechanics
It seemed to make sense to me, but that's neither here nor there. All I can do is pursue my theory until either it fails or succeeds. Either way I will be satisfied. There is a very great chance that I am wrong, but I could also be right. And to be sure at sophomore level i should not have had the knowledge to understand ST or super symmetry. and truth be told that I did not all i had was a desire to know more. But the human mind is a learning machine. Nothing either existed nor exists to stop me from pursuing that knowledge. Heck, If I'm wrong I'll buy you a Keg in 5 years :) - krazikamikaze, on 10/12/2007, -0/+0@chazzzzy,
Light has zero mass. Each photon has energy hbar (a constant) times omega (angular frequency) and momentum E/c
@tr176,
Good enough for me! Though that wikipedia article then goes on to talk about how tachyons are valid states for strings in string theory. Having no knowledge of string theory, I'm just going to assume it's like solutions to Schrodinger's equation: they may be imaginary, but don't try to interpret it. Just take the magnitude and be happy. - Tr176, on 10/12/2007, -0/+0um... it doesn't
- aMMgYrP, on 10/12/2007, -0/+0@Mr Mechanics
I did bother to really learn physics, it simply did not hold my interest. And as I said I believed it was fundamentally flawed. So I figured I get a degree in the two other things I really loved in high school, those being CS and English (I went to a Sci-Math HS). - krazikamikaze, on 10/12/2007, -0/+0@mr mechanics,
That's kind of what I was trying to say in my first post, I see imaginary numbers as a tool. They are a means to an end, but I always see people saying things like "it actually is possible, it just has imaginary veolcity" or something like that, which seems absurd to me.
Here's a good example from the wikipedia article on tachyons:
"If m is imaginary, on the other hand, the denominator of the fraction must also be imaginary to keep the energy a real number (since a pure imaginary divided by another pure imaginary is real). The denominator will be imaginary if the quantity inside the square root is negative (recall the problem imaginary numbers were invented to solve), which only happens if v is larger than c. Therefore, just as tardyons are forbidden to break the light-speed barrier, so too are tachyons forbidden from slowing down to below light speed."
I'd immediately say that tachyons don't exist because nothing can have imaginary mass, yet people continue to search. Am I being too closed minded? Maybe mass is just a means to an end and all that matters is that it has real valued energy, in much the same way that a cosine is made up of 2 complex conjugate exponentials. - dongiaconia, on 10/12/2007, -0/+0(sheepish: yea, I realized I was thinking SONAR instead of Radar after I posted that)
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