Until someone does the inevitable and proves that objects can, in fact, travel faster than the speed of light I'll accept, for this question, that nothing can travel faster than light.\nTake 2 spaceships, A and B, both traveling at 0.95 speed of light directly towards each other, how fast does A appear to travel relative to B's perspective and vice versa?
137869
In the relativistic limit (i.e. speeds near the speed of light [here denoted "c"]) velocities are not additive in the normal sense.  In particular one must use the relativistic velocity addition rule given by:\n\nv_1 + v_2 / { 1 + (v_1 * v_2 / c^2 ) }\n\nWhere v_1 and v_2 are the speeds of the moving observers.  Notice that when v_1 and v_2 are both siginificantly less than c this reduces to \n\nv_1 + v2, which is what you expect from the everyday world.\n\nIf you plug in .95 c for v_1 and v_2 you obtain that the apparent velocity of the observers to each other is given by:\n\n.998685939553 c or 99.865% of the speed of light.\n\nWhich is how fast they will appear to approach each other from each other's perspective.
592613
There may be objects (tachyons) that move faster than light, up to perhaps infinite speeds.\nHowever, nothing already slower than light can accelerate to or beyond the speed of light.
328776
The speed of light is the upper limit of speed in our space-time universe. Nothing here can be faster. And no car or any other macroscopic object can be equal to the speed of light. But the question is a thought experiment, hence, a good one indeed. Questions like this were raised by Einstein and Relativity became part of modern physical theory.\n\nSince the speed of light is an upper limit, the light from the headlamp of the relativistic car cannot be faster than the car. You won't see them in front.
109523
You can't reach the speed of light in any conventional way, but you can get as close as you want, provided you can keep applying acceleration.  \n\nThe best way to do a thought experiment of time dilation for special relativity (special relativity being the case in which you consider high velocities, general relativity just applies this same model to all spacetime trajectories with the observation that gravity is indistinguishable form a physical acceleration) is to consider the case of a "light clock".  \n\nFor a light clock, you have a laser pulse generator, a mirror at some distance, and a pulse counter next to the laser.  Everytime a pulse is recieved at the counter, another pulse is sent from the laser, and so you have a clock that "ticks" at a rate determined by twice the distance from the laser to the mirror.  So, what happens when you move this clock?  If the clock is arranged such that the pulse bounces back and forth perpendicular to the direction of travel, it's easier to get the basic idea.  \n\nThe speed of light is always constant, but as the clock moves at higher and higher speeds, from the perspective of a stationary observer the total distance traveled by the light increases, since now it's going diagonal.   But, to a person traveling along with the clock, it doesn't appear to travel any greater distance.  \n\nIt's something like a person standing in a train car or bus tossing a ball up and down.  While the ball is up in the air, it travels horizontally by the distance the bus has moved while it's been up in the air, so the total distance traveled by the ball is much longer if the bus is moving rapidly instead of stationary.  For normal speeds, the Gallilean transforms are sufficiently accurate, so a stationary observer and the person tossing the ball can agree how fast it's moving in each axis, and how far it moves, just by adding the horizontal velocity of the bus to the vertical velocity the ball is tossed with, and come up with the same wider parabola for higher speeds and narrow parabola for low speeds, or stationary cases.  \n\nBut, light has an interesting property...  it must remain at the same velocity for all observers no matter what their speed relative to the light.  So, in the case of a ball, we can simply say that it's moving faster than it looks to the person on the bus with it, because there's the added background horizontal velocity.  If you add the vertical and horizontal velocity vectors, the sum is longer than just the vertical velocity.  \n\nBut, in truth, how can you know if you're moving at a constant velocity?  There are no pseudoforces of acceleration if you're moving at a constant velocity, but if light behaved oddly by traveling faster in one direction that the other, you would be able to tell if there was a fixed frame of reference outside of your motion, and this would allow you to determine a fixed location relative to the universe as a whole, and even determine where the center of the universe is.  But it doesn't have a center, or all points are equally the center, depending on how you want to look at it, so there can't be any way to tell if you're moving at a constant velocity, and so light must travel at the same speed in any direction when viewed by any set of observers, no matter what their relative velocities are.    Not surprisingly, we find this also comes out from Maxwell's equations describing the propagation of light, the velocity winds up being proportional to one over the square root of the product of the electrostatic permittivity and the magnetic permeability of empty space, a number which is absolute and gives no preference for directions or relative motions.  This isn't surprising since, like I said, it's a necessary condition for a centerless universe.    \n\nSo, the speed of light must remain absolute, but something has to give.  Since the light clock is ticking slower becaus
600443
The most recent research that I've seen was shown on the TV program "Horizon" here a few years ago.  The research suggested that under certain conditions (somehow linked with Einstein's cosmological constant) the speed of light could possibly change.\n\nHowever, for the time being at least we can easily assume that the speed of light is a constant.  The last I heard was that the research they were doing on the speed of light has was inconclusive, so it may take a while longer before we really know if it can change or not.
242387
*\nThe time-honored phrase "faster than the speed of light" might have to be reworked, thanks to the work of a Danish physicist.\n\nBy shooting a laser beam of light through a super-cooled glob of a kind of optical molasses, Lene Vestergaard Hau and her team at the Rowland Institute for Science in Cambridge, Massachusetts, were able to slow the speed of light down to just 38 miles per hour -- not even fast enough for the slow lane of a freeway.\n\nBy contrast, the normal speed of light in a vacuum is about 186,000 miles per second -- 20 million times as fast.\n\n"I would probably not call it God-like, but I would probably say ... we are tampering with nature in a very peculiar, very bizarre way," Hau says.\nlight maze\nHau points to an intricate maze of mirrors, part of the slowing process  \n\nThe research, conducted at the Rowland Institute and Harvard University, was reported in Thursday's issue of the journal Nature.\n\nThe substance that slows the light, called Bose-Einstein condensate, is a microscopic glob of atoms slowed to almost absolute zero -- 459.67 degrees below zero Fahrenheit, the lowest temperature theoretically possible.\n\nResearchers believe that it may be possible to slow the speed of light even further, by a factor of 1,000.\n\n"A human could move faster than that" says Stanford University's Steve Harris, who participated in the project. "But a human couldn't move through a Bose-Einstein condensate, I'll tell you that."\n\nResearchers believe learning how to slow light could eventually have a number of practical applications -- improving computers and communications devices, making television displays and laser light shows more vivid and creating better night-vision goggles.
466341
nothing can go faster than the speed of light (in theory) so the answer is 3*10^8
316220
An outside observer would say that the distance between you and the object is increasing at a rate equal to the speed of light, but if the object shone a light at you, that light would still reach you, in the observer's frame.  In the observer's frame, no object is moving faster than light, and there is nothing wrong with the relative separation of objects increasing faster than the speed of light in a frame of reference where both objects are moving.\n\nIn your own frame, you and the object would be moving apart at a relative speed of 0.8c.  Speeds do not add linearly when they are very large.
252553
Only massless particles can travel at the speed of light. Photons obviously can, since they constitute light. They can't collide, they simply pass each other. Look into a mirror...what happens? Nothing. Light goes towards the mirror, is reflected, hits the light coming towards the mirror but doesn't interact with it.\n\nVelocities don't add together in the normal sense (V = v + u) but instead they obey the relativistic formula at high velocities:\nV = (v+u) / (1+uv/c²)\nThis formula also works for lower velocities (like cars colliding) but try putting in the numbers...you'll realize it approximates extremely accurately to V = v + u
499020
No.  Nothing goes faster than the speed of light.
109682
The two key elements in this question are that the speed of the spacecraft is constant, and that you are at rest relative to the spacecraft.  In this situation, you will observe the beam of light moving forward and hitting the object just the same as if you were sitting in your living room.  This is in accordance with Einstein's Special Theory of Relativity.\n\nHowever, if the spacecraft were accelerating instead of moving at a constant speed, the same might not be true. As long as the spacecraft continues to accelerate, even at speeds below the speed of light, it is possible to set up a scenario in which the spaceship stays ahead of the beam of light forever!  This is in accordance with Einstein's General Theory of Relativity, which considers the effects of acceleration and gravity on light.
556925
The only thing that can travel at the speed of light is light. So basically yes.
614788
According to some scientists, if you can get faster than the speed of light, you can cross time barriers by bending and manipulating the space-time continuum.  Also, some quantum physicists believe that the universe and all of existence is made up of separate, infinite numbers of dimensions, so time travel without going faster than the speed of light would essentially be traveling to a different dimension in a different time that is not too different from the history of our world.  That's pretty far-fetched, though.  However, I still believe in the possibility.  Nothing's impossible (almost).
437498
It is exactly that question that inspired Einstein to formulate his theory that nothing can ever travel faster than light. I am not saying the Einstein had a goal to make a theory saying nothing can travel faster than light. I am saying that the question made him think about how to explain what would happen in such a case and then the math lead him to a theory of motion in general which says nothing can travel faster than light.
249138
I think what you're looking for is\n\nt' = t * sqrt (1 - (v/c)^2)  where c is speed of light, v is the velocity of the observer, t is time external to the observer and t' is the observer's experienced time.\n\nThe problem with this equation is that when v>c, t' goes negative.  This is thought to believe that one can go backwards in time if the speed of light is exceeded.  However, there can also be the interpretation that the speed of light is an asymptotic limit.  In this case, backward time travel is not possible as one could not exceed the speed of light.\n\nIn terms of traveling to the future to go to the past, I'm not sure what exactly you mean.  An early theory posited a cyclic universe so that by traveling far enough in time, you would indeed end up in the past but it would be the past of the universe after the next cycle.
564878
It doesn't matter if the person inside the ship isn't aware of his speed, he cannot double his speed if he started out going 99.9 times the speed of light.  Period.\n\nSo, your question doesn't have any relevance.  \n\nAlso, it is the observer from the outside that sees the slowing of time for the people in the ship.  The people in the ship aren't aware of any slowing of time, because everything including their motion inside the ship, and brain functions slow down as well.  They have no idea that their time is slowed.\n\nBut, you are correct: neither ship can go faster than the speed of light, and each ship will not see the other ship going faster than light either.  It can't even look like something is going faster, even if its speedometer shows a speed slower than light.
109850
No, the universe is not a single object.  The universe is the whole of all matter.  Within that no object can travel faster thanthe speed of light.