Each set of four letters designates a rectangle according to the geometric notation that was second nature to Newton and his contemporaries. Of course, his diagram is not in color!
Posted on 03/26/2006 8:51:36 AM PST by PatrickHenry
Can anything travel faster than the speed of light? "No," is what Albert Einstein would likely say if he was alive today -- and he would be the man to ask, because scientists have been taking his word for it ever since the early 20th century.
According to Einstein's theory of special relativity, published in 1905, nothing can exceed the speed of light. That speed, explained Einstein, is a fundamental constant of nature: It appears the same to all observers anywhere in space.
The same theory says that objects gain mass as they speed up, and that speeding up requires energy. The more mass, the more energy is required. By the time an object reached the speed of light, Einstein calculated, its mass would be infinite, and so would the amount of energy required to increase its speed. To go beyond the infinite is impossible.
One hundred years of testing have only reinforced what Einstein wrote, said Donald Schneider, professor of astronomy and astrophysics at Penn State. "There is no experiment that has contradicted special relativity. We have accelerated sub-atomic particles to well over 99 per cent of the speed of light, but not equal to or exceeding the speed of light.
"Theoretically, strange things happen when you exceed the speed of light," Schneider added. Time travel, for one thing, and a breakdown in cause and effect. Schneider uses an example of hitting a target with a gun that shoots bullets faster than the speed of light. "Some observers would see the bullet hit the target before they saw the shooter fire the gun," he said. "Since one of the guiding principles of relativity is that all physical laws are the same to all observers, this violation of causality would be a big problem."
Another oddity: tachyons. In 1967, Gerald Feinberg, a physicist at Columbia University, proposed the existence of these faster-than-light particles. In their mirror world above the light-speed barrier, tachyons would require infinite energy to slow down to the speed of light.
Other concepts that have popped up include "wormholes" -- shortcuts through space-time that would permit point-to-point travel faster than light -- and "warp drives," a kind of bubble created in space in which relativity wouldn't apply.
Although they have become staples of science fiction, tachyons, worm holes and warp drives remain speculation, and many physicists dismiss their significance. There is, however, at least one real-world example of superluminal (i.e., faster-than-light) travel. It occurs when light passes through water.
In this dense medium, Schneider explained, light is slowed to three-fourths of its speed in a vacuum. In a nuclear reactor, charged particles flying off the radioactive rods through the water they are submerged in exceed this reduced speed.
Because these particles contain an electric charge, they emit energy, called Cherenkov radiation. Any particles they bump into become radioactive, giving the water a characteristic blue glow.
"It's not at all exotic," Schneider said. "Every time you look at the water in a nuclear reactor, the bluish glow you see is radiation produced by charged particles moving faster than the speed of light in the water."
Still, slowing light down in order to beat it is cheating, Schneider conceded. And although he's not closing his mind to the possibility that relativity will one day be amended, for now, he said, Einstein's theory is the final word.
Source: Penn State, by Joe Anuta
Yes, and Chuck Schumer and Arianna Huffington when they spy TV cameras.
Yes, my wife knows I'm looking at another female before I do.
L
So, if we were to measure the speed of the train plus the speed of the light, from a fixed reference on the train track, the total speed would equal... Not terribly intuitive is it?
I can't handle this one. Perhaps one of the others can. I don't have a separate list of physicists, but those I'm pinging will know who I've missed.
Thanks PH. I would really appreciate some expert comment on this. I know QM is contradictory but I can't wrap my mind around this one.
Each set of four letters designates a rectangle according to the geometric notation that was second nature to Newton and his contemporaries. Of course, his diagram is not in color!
What you probably mean is the apparent contradiction between Special Relativity and Einstein-Podolsky-Rosen correlations. The fact of the matter is that there is no contradiction. EPR phenomena are correlations, not causal relationships. To borrow a clause from statistics, "correlation is not causality".
Quantum mechanics predicts EPR correlations. It predicts them without postulating any hidden variables, and without postulating any sort of signal between one measurement and another. Such a signal might violate SR--QM is agnostic about the structure of spacetime--but the fact that QM demands such correlations whether such a superluminal signal exists or not should tell you that it's a philosophically unnecessary concept.
[Geek alert: it is possible to construct interpretations of QM where a superluminal signal exists (e.g. the Bohm interpretation), but it's a very peculiar kind of signal, and it cannot be used to send information.]
EPR correlations cannot be used to transmit information faster than light. In the case of the Aspect experiment, the correlation between the two polarization states cannot be seen until the two answers are brought together (a process that is slower than light), and compared.
What the correlation represents is the limits of information. The reason why the two measurements get the correlated answers is because they're extracting the same piece of information...and this despite the fact that the information wasn't in a definite state until it was measured. (If it were in a definite state, it would have to obey Bell's Inequality; this is what sank Einstein's interpretation well after his death.)
"A-ha!" you say. "A-ha! I have you. You said 'until'! What does 'until' mean, when the events have a space-like separation, and the second event isn't causally allowed to know the outcome of the first event? How can it know when to collapse, without a superluminal signal?" Good question, well put. It's tempting to say that since measurement A happened first, it therefore caused the outcome of measurement B to turn out as it did, and because they have a space-like separation, there must have been a superluminal signal. I can turn this around, however: because the events have a space-like separation, it's always possible to choose an inertial frame where measurement B occurs before measurement A. A similarly prejudiced observer would postulate a superluminal signal going from B to A. The information can't flow in both directions, so it's hard to call it a signal, exactly.
So there you have it. The correlation is required to exist. You can postulate a signal to do it, if it makes it fit more comfortably in your imagination, but the signal needs to work equally well backwards, too, which is an uncomfortably weird property to imagine, and mathematically you don't actually need it, anyway.
There are other interpretations, besides. I'm leaning towards the "consistent histories" interpretation, myself. (The measurements occur more or less independently in different, parallel realities, but the realities in which the measurements don't properly correlate get cancelled out, and so are never seen. It makes things like the Elitzur-Vaidman bomb testing problem easier to understand.)
Einstein formulated a law for normal space.
He is correct: time and time again it was proven that in normal space nothing cantravel faster then light.
However, in a different place, that may not be the case.
It's like a scientist in the dessert concluding there aren't any lakes around here. Finding an ocean on the other side of the planet does not make him incorrect.
Remember, for an outside observer who measured your train's speed to be 99.9999% the speed of light, your clock would run extremely slowly. That's one of the main features of relativity. So while you would swear that you were advancing toward the front of the train at 3mph (4.4 ft/sec), the outside observer wouldn't see you doing that at all. Instead, he would see you advancing toward the front of the train at 3 in/sec, say. That's because your seconds are not the same as his seconds. Any attempt by you to go faster (by running, jumping on a bicycle, etc.) would only result in the outside observer noting that your clock was running even slower than before, such that you could never exceed the speed of light no matter how fast you advanced toward the front of the train.
Yeah, seemingly "GOSSIP"!
Absolutely.
Anything that God wants to travel faster than the speed of light!
'Light' is made of a variety of frequencies that depict color, from Infared(unseen) to X-ray(also useen)and all the colors in between. now, if it is possible to 'slow down' light and have that energy captured as a fuel for use in an engine, it should be possible to move the mass at the speed the frequency that you are using for the fuel. Theoretically, couldn't you move beyond the speed of light by combining two of these energy releasing frequencies at the same time?
I don't think I fully understand you. Anyway, there's not all that much "fuel for use in an engine" to worry about. For an idea of what light might be useful for, see: Solar sails.
Well written. :-)
I was referring to this explanation of how light moves in a dense medium. If there is energy being released in any kind of form, it is possible to use as fuel or an energy supply to convert to fuel. The Solar Sail is an idea, but what if you could use this extra 'energy' to help push the craft?
You won't get more energy out of the system than you put into it. If you were putting in energy for some other purpose, then it might make sense to capture some of the wasted radiation -- if it were efficient to do so. But the whole system wouldn't be a net source of fuel.
To me it seems to be a possible or impossible but unprovable in either situation.
At this point I guess travel to distant stars will come in the form of another method.
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