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Originally Posted by Ravana
What JD said.
Where does the "mass" come from, emp? What experimental data is there to prove that this happens at all? (Honest question; it's not a field I keep up on too closely. There may be some--aside from particle accelerator experiments, which I'll get to presently. But clocks running at different times only demonstrates one part of the theory--and that's assuming even that data is correct.)
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A single electron is accelerated using magnetic fields (I'm simplifying). It is not much different than the CRT tube, only you keep on accelerating...for miles! The electron can be bent into a ring using megnetism, just as the CRT uses magnets to scan the target accross the screen.
Now, by bending it into a circle, it can come back through the kicker again and again and again, and you can keep pumping more and more energy into it.
It is apparent when getting it to work right that each kick adds less and less to the speed. It's getting harder to push! That is, "heavier". Now there might be more than one possible hypothesis for this effect, given the mechanism's specific workings.
But, here is the clincher: The magnets used to bend the electron's path also have a harder time pulling on it. You have to tune the strength of the field as if the particle being aimed is heavier.
That is just one example, one that was run into as a real engineering problem early on. The tech's quickly learned to trust what the theory geeks were telling them! It just doesn't work if you don't plan for this effect.
Special Relativity has been tested so many times in so many ways, it is found to be one of the most successful theories ever.
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Originally Posted by Ravana
I reiterate: how do we *know* matter cannot travel faster than light? Einstein wasn't god; he wasn't working under divine revelation. At the very least, let somebody set up the experiment I described and see what *does* happen.
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See above. All objects accellerated to near the speed of light behave exactly as predicted. Unless you are trying to say that a large object behaves differently than a small one, even when the large one is made up of many instances of the small one and nothing else; stop wondering. It has been done, many times. The results back up the math, perfectly.
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Originally Posted by Ravana
check out recent experiments that seem ... to show that lasers can be accelerated beyond the "speed of light,"
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You'll have to post a more specific citation. In the mean time, I offer the usual reasons for such stories: (1) the guy is a quack; (2) the news report messed it up rather badly.
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Originally Posted by Ravana
How do they measure this? You can't take it out and put it on a scale.
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See the ring example above. That's two ways to notice the effect without stopping the thing to weigh it.
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Originally Posted by Ravana
Do they measure based on the energy released when the thing hits a target?
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Ah, an excellent suggetion. Let's look into that.
How hard the thing hit the target is a function of the kenetic energy, which is mass times velocity squared. But... I know how much energy I pushed it with, so stopping it will release the same amount. It doesn't tell you how much of that energy was in the form of the velocity and how much was in the form of its mass. If you also noted the velocity, perhaps from the time it takes it to go around the ring (something you need to know to sync the kicks), you can indeed figure out that the velocity is lower than expected given that much of a push, while the total energy is the same so it didn't leak out anywhere.
In and of itself, I'd call that a strong clue but not enough to consider it prooved. Combine that with the sideways magnet data, and you have something worth publishing: the experiment is consistent with the mass increasing.
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Originally Posted by Ravana
Pardon my naivete, but I would expect a proton moving at near lightspeed to have a bit more energy than one at rest. The question is how great the difference is: does it have more energy than it ought to have based on the speed it was traveling?
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You ask if the difference is significant enough to measure. Well, when it gets close to the speed of light, very much so. The velocity difference between 0.9c and 0.999c is very small; about 1%. But the mass goes up by
(excersize for the reader: crank though the function for "gamma" and post what you get). Enough to notice? Repeat with 0.999999c.
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Originally Posted by Ravana
Where does this extra "mass" come from? If it is really "mass," would it be retained if the particle was decelerated to a rest state? If not, where does it go?
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OK, there is no extra mass.
That is an explaination which makes it easy to calculate the behavior of the ring discussed above, but is confusing and misleading and falls short of acting like mass ought to. So, physicists don't call it that anymore. Mass is rest mass.
Instead, the formula for accelleration needs to be updated. F=ma is missing a term which is near zero for our normal experience so it was never noticed before the electronic age.
Refine the conclusions from the ring experiment, or at least the way of understanding it. Instead of saying "First, adjust the value of m by a factor r, then use F=ma as we've been doing for hundreds of years", say "F=r ma" where r is exactly the same thing.
Small difference, you say; but it clears things up because velocity (and hense r) is a vector quantity; it must be figured relative to the direction of the applied F. And you don't have to ask where the mass "comes from". Asking why F=r m a is no worse than asking why F=ma, and does not introduce a new mystery.
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Originally Posted by Ravana
I would still like to see an explanation of the basic question underlying my suggestion, though: what is so special about the speed of light that it is a "privileged" speed? It would be less of a question if the theory stated simply that it represented an absolute speed for anything existing in the universe--although it would still be question-begging without an explanation as to why this should be. However, as you pointed out, the theory also states that "objects traveling faster than the speed of light can not travel slower." This implies the recognition that, at least theoretically, such "objects" (which, presumably, cannot be made up of "matter" as we understand it) could exist (okay, everybody: don't start talking tachyons at me unless you're ready to back it up with evidence...). What, then, makes 186Kmps so special that only one type of thing in the entire universe can travel at this exact speed, and everything else has to be going either faster or slower than that, but nothing can possibly do both?
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A full treatment explaining what is special about the speed of light needs a book to explain. I suggest you find one and buy it. Then ask more questions!
Given that things are indeed as Special Relativity would comput it, substitute the function for r (which involves the velocity v) into F=r m a and solve for F with v something greater than c. Try it.
Now the function works for 0.9 c, 0.999999c, and everything else. There are no signs that it fails for something even closer to c, but I admit extrapolation is where theories fail.
I said "get a book" but I'm answering this section too just to address the "greater than c can't slow down" thing. That is confusing you, and you should not worry about it. If you get into the math above, you'll see that nothing can go faster than c. But... play some games with the math. Mass is a "real" number. What if you work the function with m as an "imaginary" number? What would be the behavior of such things, if they existed? A game, and an example of thinking outside of the box, as is good during a creative process. But such tacyons as they are called are not matter as we know it.
Good luck in your studies!
--John