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Blazing Speed: The Fastest Stuff In The Universe
Unfallversicherung writes "'If you're light, it's fairly easy to travel at your own speed -- that is to say 186,282 miles per second or 299,800 kilometers per second. But if you are matter, then it's another matter altogether.' Astronomers are now measuring matter that moves at 99.9 percent of light-speed. Jupiter-sized blobs of hot gas embedded in streams of material ejected from hyperactive galaxies known as blazars."
How about linking to the original Space.com article?
Blazing Speed: The Fastest Stuff in the Universe.
1) Under the current physics, light-speed travel is impossible. As you approach the speed of light, the energy required to accelerate you further approaches infinity.
2) As you accelerate to 99.9% the speed of light, time slows down very significantly. Theoretically, at the speed of light, the passage of time stops, but since you cannot accelerate to the speed of light, that's a moot point.
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You're joking - but in truth, our Universal constants cannot exactly be called that - they have been changing, albeit very gradually.
So, the speed of light need not necessarily be a constant for all time (and need not have been a constant for all time).
Speed measurements in astronomy are usually made by measuring the doppler shift of of the light emitted. If you find the spectrum of for instance Hydrogen (a very common pattern) but the spectral lines are shifted compared to the spectrum of hydrogen on earth. From this you can measure the relative speed between us and the source. This is accurate , hard to distort and relies on only one measurement.
But what exactly is the speed of light? If I stand here and shine a laser, sure, it has a speed, but think about it: This planet is hurtling through space at breakneck speeds. Now add the speed of light from my laser to the speed the Earth is moving, and voila! You have a speed faster than the speed of light
First rule of relativity club is the speed of light is the same for all observers. Which means your laser will appear to be travelling the same speed for somebody travelling through space at "Breakneck speeds" as it would for somebody just leaning back in a chair sipping a Corona watching you.
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I don't have to think about it, Einstein already did it for me: the speed of light does not "add" to other speeds. Time warps instead. That's (very very basically) what the Theory of Relativity is all about.
TWW
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Not really, see this is exactly what special relativity explained. The speed of light is constant. If you're moving at 50% of the speed of light, and some light wizzes past you, it looks to you as if it were going at 100% of the speed of light (not 50%). And to an outside observer seeing you go past, it also looks like the light is going at 100% of the speed of light (not 150%). What has happened is that because you are going at 50% of the speed of light, time for you has slowed down, so the if the light goes past at what would apparently be 50% of c if time were not slowed, it still looks to you as if it were going at c.
LOL. Talk about misinformation and hype. It's trivial to transmit an interference wave with a phase velocity faster than the speed of light. That doesn't imply that you can send a signal with information content faster than light - the group velocity (the information carrier or signal you actually control) can't go faster than light.
That argumant is SO 1700's. You simply can't add speeds that way, unless the speeds involved are so low that there are only negligable relativistic effects. Read a little Einstein, the speed of light is constant, no matter who measures it or who produces the light.
It's easy to create signals with "phase velocities" faster than the speed of light, for example set up a series of identical oscillators such that the phase of oscillation is perfectly in sync (within a stationary observers frame). Such a system will have an infinite phase velocity, (or within the limits of experimental error it can easily be made greater than c). This phase velocity merely means the phase of the "wave" of the oscillation appears to travel infinitely fast from one oscillator to the next.
But the key point is that no information is transferred faster than the speed of light, and thus everything still adheres to the confines of special relativity. So the parent AC is correct that one can create an effective velocity larger than c, but one cannot do anything useful with it.
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how to add relativistic speeds
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If you're travelling at a very high speed (close to the speed of light) your time would, from an outsider's point of view, be slower (i.e. a second would last longer in your spaceship/whatever than on the outsider's watch,) given that the outsider moves slower than you. This means that if you flew off into space at a very high speed and turned around and flew back to earth after, let's say, 5 minutes (on a watch in your ship,) earth would have aged several thousand years (i.e. you would have travelled forth in time.)
If you wanted to go back in time you would have to move faster than the speed of light, which is impossible unless you use some sort of wormhole (which is completely theoretical.)
The difference is that it has been accelerated to a speed of .999c. It's been a year or so since I did this sort of stuff but the fact that a force has acted on it to accelerate it to that speed (which hasn't acted on us) is the difference. I think.
A good post, though it's a little vague for the most of non-science geeks.
Basically, in the relativistic frame, the Newtonian kinetic energy (0.5*mass*velocity^2) is no longer valid. To make "relativistic" correction, it needs to be scaled by the quantity called "gamma", which has the form:
gamma = 1.0/sqrt(1.0-(v/c)^2)
where c = speed of light and v is the motion of an object (here 0.999c). Now the relativistic kinetic energy is scaled by this gamma factor as:
Kinetic Energy = mass * c^2 * (gamma - 1.0).
In this case, v=0.999c, the gamma factor has the value of 22.4. Then for the mass of a Jupiter size planet, the relativistic kinetic energy is about 2e52 erg, which is about 10 supernovae explosion worth of the energy.
Now if you imagine that v=0.9999 (another "9"), then the gamma factor jumps up to 70.7, instead of 22.4. That's what the parent poster meant to say by the "non-linear" term.
The more you know, the better off you are.
As I recall from a late 1990s lecture by Hawking, some matter can exceed "the speed of light" and in doing so, escape a black hole. At an event horizon exactly, that border at which matter including light either escapes a black hole or not, the position of particles is known with complete precision. As such, Heisenberg's Uncertainty Principle dictates that the speed of the particles cannot be known as precisely. Photons at the event horizon of a black hole are allowed, by a tiny quantity, some Scotty Factor in their speed because their position is certain. In plain words, these are the mathematics of the matter :) Some leptonic matter, in only such a particular position, can be slightly faster than "the speed of light."
As theorized, Hawking's predictions that black holes might leak have, I understand, been observed as radiation from what are as-yet assumed to be black holes. Anyone knowing more than I do about this particular phenomenon is (un?)certainly welcome to add more. The explanation Hawking made was directed at interested and able nonprofessionals; he put forward some mathematics around but not specifically deriving the surprising conclusions. Made sense to me, anyhow. I believe the matter discussed here, blasers measured at .999999... of light's speed, is the fastest measured "directly." But I do not believe this is the fastest known matter, if you allow that "knowing" the speed of the matter Hawking discussed (observed as radiation) was theoretical and later indirectly measured.
BG
Observing particles moving at 99.9% c is not so amazing as it sounds. First of all we routinely accelerate matter to great speeds for use in particle physics experiments (in places such as CERN, SLAC, FermiLab, Brookhaven, etc.).
As an example, the LEP accelerator at CERN which was used in the period 1989-2000, acceleratod electrons to about 99.9999999977% c.
But even outside the laboratories we have previously observed even larger speeds. The UHECR (ultra high energy cosmic rays) whose origin is still a mystery seems to consist of protons moving at speeds of 1-1^(-22) = 0.9999999999999999999999 c.
Furthermore, it might seem like we need absurd accuracies in our measurements to discern the numbers from each other. But we don't really - the speed of the particle is practically the same when 0.99c and 0.99999c are compared, but things like the momentum of the particle will still differ wildly. For the curious, the formula is: momentum = m*v/sqrt(1-(v/c)^2).
I think you missed the Futurama reference in the actual article... "...become your own grandpa..." :)
The speed of light can be given in terms of other fundamental electromagnetic constants (1/sqrt(permeability of vacuum * permittivity of vacuum)), but I suspect that this doesn't really answer your question.
Now, the question does have a less profound answer that is not what you have in mind. A meter is DEFINED as the amount of time that light moves in 1/299792458 seconds, so light moves exactly at 299792458 meters per second. The miles per hour speed is just a conversion factor away.
E = m c^3 Don't drink and derive E = m c^3
Here you make a Newtonian assumption - velocities in relativity cannot be added so simply. As someone posted before, velocities have to be added only with the help of the Gamma factor, which would basically adjust your answer such that it remained under 100%. It's still impossible ;)
As you rightly point out, the speed depends on the frame of reference (i.e. the speed is always relative to the position of the observer).
However, adding the velocities the way you did is only possible with slow-moving objects (slow in comparison with the speed of light, that is). When dealing with fast objects, the Lorentz transformations creep in.
That means, for example, that shooting a cannonball at the speed 0.75 c from a spaceship that is moving at the speed 0.5 c in the same direction, you would get a cannonball travelling at some 0.8 c (my guesstimate, I'm too lazy to calculate it), rather than at 1.25 c. At low speeds, these differences are negligible and Galilean ("normal") transformations apply.
As for your other comment, when you really think about it ;-), speed does exist - not as an absolute number, but as a speed relative to something.
Yes, it is often said "the speed is 65 mph," but this is mostly a shorthand for saying "65 mph relative to the Earth." Two cars travelling against each other, each at a speed of 65 mph relative to the Earth, travel at a speed of 130 mph relative to each other. Both of the speeds do objectively exist, but it takes two to play the game - the object and the reference frame:-).
(Feel free to correct me, IANAP)
In math, something is said to approach infinity when its value increases endlessly, without bound. It may always have a finite value, but that value will increase past any arbitrary limit you care to name, not matter how high.
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Yes, the spectral lines always appear in the same place, relative to other elements, because they are emitted at fixed, known frequencies. By identifying them and seeing how far shifted they are from what they'd be if they were at rest relative to us, you get the doppler shift.
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This is true only if you're only measuring radial velocity. That is, the target's velocity directly toward or away from us. You can also measure the target's proper motion, or motion at right angles to us. This is done by measuring its change in position over a known time. Once you have both, simple vector addition gets the total velocity.
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And read this for a more detailed explanation of the issue.
Actually, light does have mass, depending on how you define mass.
There is inertial mass, defined by Newton's second law (F=ma) as the proportionality constant between force and acceleration of an object) Since light doesn't accelerate, this definition doesn't apply.
What does apply is gravitational mass. We know newtons law of gravity, and we can measure how much light is affected by gravity, as in a black hole. This gives us a mass for light, since objects need mass to be affected by gravity. If use this "mass" for the light in other equations to calculate things like the energy of the light (E=mc^2) or the momentum of the light (p=mv), it all works out.
All material objects in the universe have both inertial mass and gravitational mass that are equal within an accuracy of any experiment ever devised. Light is strange in that it only has gravitational mass.
E = m c^3 Don't drink and derive E = m c^3
It's frequently observed as a ghostly blue light in the deep water holding tanks for freshly-spent fissile material from nuclear reactors. Some of the active particles travel faster than the speed of light in the water, leading to the Cerenkov effect.
For anybody out there wondering why you can't go faster than the speed of light, this equation is the reason. If v is greater than c, then this equation would require the square root of a negative number.
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Well the rest mass of a single star (say the same mass as the sun) is 2x10^33 * (3x10^10)^2 ergs ~ 1.8x10^54 ergs. In this post the energy of these objects is estimated at 2x10^52 ergs, so the rest mass of a single star is 90 times one of these objects, and there are on the order of 10^10 stars per galaxy. So before we even discuss dark matter you'd need a hell of a lot of these objects to have greater energy than just the visible stars in our galaxy.
Doug
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When people say that light is massless, they are referring to its invariant mass (sometimes incorrectly referred to as its "rest mass"); the full relativistic equation is,
E^2 = (mc^2)^2 + (pc)^2
where p is relativistic momentum. For light, m=0, and this reduces to E=pc (the energy of a photon is directly proportional to its momentum).
Likewise, when people say that objects with mass can't travel at the speed of light, they are referring to objects with nonzero invariant mass.
No. That equation has nothing to do with the speed or energy of a photon. It's only used to calculate the energy equivalent of mass, or the mass equivalent of energy. Just because a photon has no mass doesn't mean it can't have energy or velocity.
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You can have tachyons It's a little misleading to say that, I think. Someone please correct me if I'm wrong, but as far as I know, no evidence of tachyons (a certain amount of radiation emitted by a vacuum) have ever been observed, and a large percentage of physicists in this field do not believe they exist.
There is no evidence of tachyons, I agree. But, Special Relativity says that you can have them! This says nothing about whether or not the actually exist.
No, actually, a meter was DEFINED as one 10-millionth of the line between Paris and the Equator. Since 'Paris' isn't too exact a point, the new definition of a meter, the one you've given, is vintage 1988 and meant to be a little more precise. If anything, it should be considered a refinement of the Paris to the equator size.
No, actually, you're an ass. Learn the difference between WAS and IS.
No, because velocities don't add in relativity. For instance, if A and B are moving in opposite directions at 0.5c with respect to observer C, then A is moving at 0.8c with respect to B as measured by observer A (or vice versa).
Okay, basic rocket physics:
:)
dV = Ve * Me / Mr, where dV is the change in velocity of the rocket, Ve is the velocity of the exhaust, and Mr is the mass of the rocket.
Now, basic relativity:
S = sqrt(1 - V^2/C^2) -> A scaling factor
M' = M / S -> Mass increases as V increases.
T' = T / S -> Time slows down as V increases.
L' = L * S -> Lengths decrease as V increases.
Now, if you just consider M, you're right. Me' / Mr' = (Me / S) / (Mr / S) = Me / Mr. Thus, dV remains constant, because the increases cancel out.
However, you have to consider that Ve is measured relative to an observer. Further, you have to remember that lengths and times measured by the observer are not the same as those measured on the rocket. Consider that a rocket is moving at Vr relative to a stationary observer. The observer can measure the velocity of the exhaust, Ve, by measuring how far the exhaust travels in a given unit of time.
Ve = L / T.
However, that "L" and "T" are actually L' and T', because the rocket (and it's exhaust) are moving relative to the observer. So:
Ve = L' / T' = S^2 * L / T.
Since S is always less than one (eg: S at 0.99c is about 1/7), Ve measured by the observer will be less than Ve measured by the rocket by a factor of S^2. That means, as the rocket accelerates closer to the speed of light, Ve measured relative to the observer approaches zero. As a result, the rocket cannot ever accelerate to the speed of light.
My numbers could be completely wrong, but hopefully I remember my rocket physics well enough from class that the results are correct
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Actually, gravity couples to relativistic mass-energy (or just "relativistic mass") density, not rest mass. The reason why you don't collapse into a black hole near c is because momentum density also couples to gravity, and counteracts the increasing attraction due to mass-energy increase.
I think it was in Mehra's The Beat of a Different Drum. IIRC, Feynman's main objection was that the theory would require equal numbers of electrons and positrons in the universe. (Thinking back, I think it was Feynman who shot the idea down, not Wheeler himself.)
The equations of relativity do rule out the possibility of faster then light travel, but not for the above reasons. They do so for the fact that faster then light travel would break causality in the universe.
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excuse my ignorance in physics, but i always wondered: if light has no mass then it has no speed or energy because E=MC^2, right ? if you insert a 0 in M, then 0 times C^2 is 0, thus E = 0
That's a good question, and the answer is very simple. The equation E=MC^2 is a simplification. The actual equation is E^2=M^2*C^4 + P^2*C^2, where P is momentum. For particles at rest, momentum P is zero, so the equation simplifies to E=MC^2. For photons, rest mass M is zero, but they are always in motion, and the equation is E=PC. (Photons do have momentum even though their rest mass is zero.)
No, it can't have any mass or it wouldn't be able to travel at c. It has energy, of course, and that energy can be considered to be equivalent to a certain mass, but that's different.
There are two ways you can think about gravity affecting light. One way is to think of it affecting the mass-equivalence of the photon's energy. The other way is to think of gravity as bending space so that the light travels in the straightest line possible in warped space.
Remember that any effect you can get from gravity you can duplicate with acceleration and the other way around. It's easy to show that if you accelerate at right angles to the path of a light beam the beam will appear to bend, so the same thing must happen when the light passes through a gravity well.
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