"Light Barrier" question....

worthj1970 · Sep 13, 2004

We talk about breaking the sound barrier; is there such a thing as a 'light' barrier (or some such)? Also, when we break the sound barrier there's a sonic boom; theoretically what happens when we go past the speed of light?

nacnud · Sep 13, 2004

If you break the local speed of light you create something called Cherenkov radiation . This is the light equivalent of a sonic boom. This is not the same as breaking the speed of light in a vacuum which is impossible, this only happens when you break the local speed of light, i.e. in water or glass where the speed is lowered.

newtonian · Sep 13, 2004

worthj1970 - excellent question. You might look up light cone (s). One thing that happens is that you leave the light cone of the reference point you are expanding away from FTL (= faster than light). Some theoretical astronomers postulate versions of inflation theory which indicates our universe expanded faster than light at some past period. This is why they believe a large portion of our universe is beyond our light cone, aka our visibility horizon. Now, what would happen if a quasar accelerated in expansion rate to FTL while we were observing it - is that your question? Or, were you referring to an object that decelerated to slower than light and entered our visibility horizon from beyond that 'barrier?' In the latter case, I do not know if there would be some sort of light boom analagous (comparable) to a sonic boom.

Saiph · Sep 13, 2004

Right, the key difference between the sound barrier and the light barrier is a matter of practicality, vs physicality. The sound barrier was a practical problem. People weren't sure how to design a craft able to withstand the stresses involved, and still fly in a controlable fashion. Or not disintegrate. The light barrier (speed of light in a vacuum is a theoretical problem. You cannot, even theoretically, surpass that barrier. Now, if something started out going faster than C (it's allowed, you just can't transition from slower than, to equal to or greater than) they'd go slower with more energy (odd, I know) and go back in time. I.e. opposite of what you'd normally experience. Oops, late for Optics. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Sep 13, 2004

Saiph - You think tachyons would go back in time? Yes, I know: tachyons are another matter. (pun intended) You think that FTL expansion of our universe at inflation went back in time? I see your problem - you are presenting a conceptual interpretation based on our reference point. Yes, this portion of our universe is beyond 14 billion light years away- we must OBSERVE back in time to before the date of the origin of our universe to SEE this portion of our universe. However, that is because you are using our light cone. The portions of universe beyond our visibility horizone have their own light cone and different reference points. From their reference point nothing they observe has gone faster than light!

Maddad · Sep 13, 2004

worthj1970 The others have covered the idea that the sound barrier is hard to do while the light barrier is impossible to do. I add that the speed of sound near the earth's surface is about 1,200 kilometers per hour. The speed of light though is 1,000,000,000 kilometers per hour, about 900,000 times faster.

worthj1970 · Sep 13, 2004

What is C? <img src="/images/icons/smile.gif" />

worthj1970 · Sep 13, 2004

I was sort of interested in experiencing it from both first and third person perspectives. As for the theoretical arguments, I must admit they don't really interest me all that much; it wasn't that long ago that we assumed the earth to be the center of the universe, after all, so theories can change as knowledge is gained. John W.

mooware · Sep 14, 2004

C=Speed of Light

larper · Sep 14, 2004

I think he is being pedantic. c is the speed of light. C is what, the abbreviation for Coulomb, maybe? <div class="Discussion_UserSignature"> Vote Libertarian </div>

worthj1970 · Sep 15, 2004

Thanks. I've heard that used here but could only assume its meaning. John W.

yruc · Sep 15, 2004

I hope that mankind will rise to the "challenge" of the light barrier. Just as before when it was impossible, that the world was round, impossible that man could fly, impossible that man could break the sound barrier, impossible that man could enter space, impossible that man could land on the moon.. etc. I doubt it will be in my lifetime, but its the nature of man to do the impossible.

Saiph · Sep 16, 2004

actually, except for the round one (which you, know, it actually is, and was figured out over 2,000 years ago by the greeks), those are all "practical" impossibilites. Or were, rather. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

nacnud · Sep 16, 2004

It's been known for a long time that the earth was round; you can blame the Victorians for the flat earth myth. As for your other impossible things many had been observed to happen before man was able to achieve those feats, ie birds flew, meteors travelled through space (just energetic rocks <img src="/images/icons/smile.gif" />), etc. However nothing has ever been observed to travel faster than light in a vacuum. I think that FTL is an impossible that is here to stay.

mooware · Sep 16, 2004

"Just as before when it was impossible, that the world was round, impossible that man could fly, impossible that man could break the sound barrier" There is an analogy for this argument. For the life of me I can't seem to remember it. It's something like. because a=b does not mean that b=a or some such thing like that. But to put it a different way, because some things that were once said to be impossible were found possible, does not mean that all impossible things will be possible. Perhaps we may find a way to circumvent FTL without actually breaking it.

siarad · Sep 16, 2004

The speed of light is constant so how could we know we were going faster than it as our speed is always -C w.r.t. light

worthj1970 · Sep 16, 2004

"However nothing has ever been observed to travel faster than light in a vacuum." But at least one thing has been observed to go the speed of light. Light. So it's possible for that speed to be reached, right? John W.

worthj1970 · Sep 16, 2004

I'd say 'practical' is relative, though. A short time (few hundred years or so) ago travel to space was impossible for all intents and purposes. Even the greatest scientists in the world didn't know how things moved through space, didn't know that things even moved through space in the way we do today. Now we know that things can fly in space because science eventually opened up some doors into what is possible. To say that it is impossible -- regardless of scientific proof -- to travel at the speed of light is perhaps accepted, but it hasn't been proven because to the best of my knowledge we have yet to try. John W.

kelle · Sep 16, 2004

But at least one thing has been observed to go the speed of light. Light. So it's possible for that speed to be reached, right? It is possible to HAVE the speed of light, but not theoretically possible to REACH it.

Saiph · Sep 16, 2004

actually, we try to get there all the time. Fermi-lab (a giant particle accelerator) routinely get's particles up to .999C (several times a day). And they notice the trends we talk about. And yes, light goes C. But it didn't "reach" C. It just goes C. It starts at that speed. IT doesn't go from slower, to C. And, being massless, the rules affect it differently (same rules, different results). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

worthj1970 · Sep 17, 2004

"Not any mass can reach the speed of light, except photons, and they are not mass." I know it's probably a complex explanation, but why can things that have mass not go the speed of light? I guess I also realize I don't actually know what light is, which is probably another thread altogether. Along these lines, if a black hole is so powerful that even light cannot escape, how fast would an object with mass be moving as it fell into a black hole? But maybe that's not a logical question. Thanks! John W.

Saiph · Sep 17, 2004

I don't have time just now for the thurough answer you're post deserves, but here's the outline: 1) Reletivistic kinetic energy. The faster you go, the more energy you have. However, it isn't 1:1 ratio (double speed, double energy). We've found (well, predicted, then found) a scaling factor, that acts on the "mass" of an object, which turns the ratio into a 1:1^x or somesuch (it becomes exponential). As such, light, with no mass, isn't affected, while everything else is. 2) Light is a set of electric and magnetic fields oscillating and tuging on eachother. Specifically, its a disturbance in teh electromagnetic fields. 3) If if fell in from infinity, it should reach C upon entering. Of course...nothing can get that far. So it just gets close (.999C for example). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Sep 18, 2004

Worth - I hope you have a sense of humor: First, the lighter the matter, the easier it can be accelerated. If the mass truly becomes light, it will reach c or the speed of light. And mass can actually have an increase of distance from a certain reference point which is more than 186,000 miles per second provided it is the space between the mass and the reference point which is increasing, but not the distance in the sense of motion. I.e. the distance can increase FTL provided the FTL portion is provided by the expansion of space and not by the motion of the reference points. To simplify, a reference point may go FTL provided the distance increases FTL but the reference points actual motion is less than FTL. The key is to make light of the matter! If you can make light of inflation!

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