I read Einstein’s Cosmos by Michio Kaku and in it we find that time slows down as we approach the speed of light.  A clock will run slower.  From other sources, we find that the molecules (or something) slow down when we near absolute zero.\n\nWould someone with an extensive scientific background tell us what would happen to a person on a comet traveling at the speed of light at absolute zero?   Would everything stop, i.e. time, life, etc.  And what would happen to the corpse if you would die?  Would it decompose, assuming that there is an Earth-like atmosphere on the comet for oxygen since you need oxygen for decomposition?  We would also have to assume that the comet is quite large to sustain gravity.\n\nWhat laws of physics would theoretically change in the above conditions (e.g. gravity, etc)?
212226
This is an impossibilty.  The more you accelerate, the more mass you attain.  The more mass you attain, the more energy needed to accelerate you until the required energy becomes infinite (before you reach light speed).  However, if you are a massless person, travel at light speed would be possible but the laws of physics remain stable as massless particles have little power of interaction with the universe around them.  If you were massless, and could withstand the cold, the laws of relativity state that time would pass normally for you but you would observe the universe evolving around you at an incredible rate of speed.  At absolute zero, most of the molecules in your body will have undergone a phase transition, eg all gases (oxygen, carbon dioxide etc) will have turned into a liquid and all water would have crystallized long ago.  I would suggest wearing a set of thermal long johns before attempting this venture!
474799
You wanted a serious answer so here goes.\n\nWhat you ask is impossible to put into practise. It is impossible under Einsteins theory for anyone to travel at the speed of light.\n\nSimply put I will try to explain why,, as you approach the speed of light matter expands or rather the mass does. According to the research , the speed of light would produce infinite mass so it is impossible to travel at that speed.\n\nThat's were the theory of worm holes came about, by creating a rip through space you can jump if you like from one point to another, crossing several light years of travel in an instant. But as you have made use of a warp in space itself you don't actually go the speed of light.\n\nSo basically, you cannot answer your question,, I can see were you get this idea from though as it is true that the faster an objects velocity is, the slower time passes for that object.\n\nThis was proven some 50 years ago by use of atomic clocks on a plane, one flew round the world while the other remained in London. When they were brought together it was noted that time passed slower for the moving clock.\n\nHope this helps.
136074
OK, to answer this question, we first have to make a few important assumptions, otherwise the question is meaningless.\nFirst, we have to assume that you can accelerate your car to the speed of light....this is not actually possible since it would have an infinfity mass and thius take an infinite amount of energy to achiece.  Secondly, wehave to assume that at the speed of light, your head lights will opperate noramlly (i.e. you turn them on and light shines out) due to [for reasons beyond the scope of this answer] the way head lights actually work.\n\nI would also like to preface my answer with say that traveling AT the speed of light is much different than traveling just UNDER the speed of light.\n\nOne VERY important thing to remember is that in ALL frames of reference, the speed of light is constant.\nNo matter who is watching the light travel and measuring its speed, it will always come out to be the exact some value, 299,792,458 m/s exactly.\n\nWhen you, inside your car traveling at the speed of light (with respect to some "stationary" observer), swtich on your head lights and look out the wind shield, you WILL see light traveling away from you at the speed of light.\n\nIf this "stationary" observer (by which I mean a someone who you are traveling past at the speed of light) watches all this happen, both you and the light are still traveling at the same speed in his reference frame....the speed of light.\n\nSo the answer depends on who's frame of reference your talking about.  From your point of view, yes, you would see the light traveling away from you at the speed of light as if nothing was out of the ordinary.\nFrom the "Stationary" person's reference frame, you and the light would be keeping up with eachother, neither moving infront or falling behind the other one...tied.
278823
The speed of light is invariant---no matter how fast or slow its source is moving, the speed of light remains unchanged (...please don't ask 'why?' because nobody has the vaguest idea) If you're in spaceship going at 99% the speed of light and shine a light outward in any direction, that light will move away from you at the speed of light, no faster, no slower.\n\nWith regards to the answer given that mentions the Doppler effect. The FREQUENCY (wavelength) of light is affected by the speed of the light source (Doppler effect), but frequency has nothing to do with the actual velocity of the light itself.
505112
The theory is that gravity, or magnetism, moves at a certain speed.  The last I heard, that speed is still unknown but under study.  Thus, if the sun disappeared the earth would remain in orbit at the "speed of gravity"  and it would remain daylight at the "speed of Light."   Which speed is greater is yet to be determined.  However, my guess is that the speed of light is faster than the speed of magnetism.
650962
Special Relativity saids that if a body (not massless) were to reach the speed of light, it would require that all its kinetic energy (energy used for its motion) to become converted into mass. The reason that the mass of the body would become infinite is because it would require infinite amount of kinetic energy to propel a non-massless body to the speed of light, i.e. a physically impossible feat.\n\nThis means that you can only approach the speed of light, but never reach it. As you get closer to the speed, you'll find that you need to put ever more energy to get just a minuscule more increase in speed. So where are the all energy going? The energy is increasing the mass of the moving body. Of course, the more massive the body is, the more energy is required to move it.
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.
206382
Remember Einstein, It is all relative to the observer. You and the mirror would be traveling at the same speed so your observational world would be the same. Now if somebody was traveling with you slightly less than the speed of light, they would see a empty mirror. It is a paradoxical question just as if you where to travel the universe for 5 yrs at the speed of light, then return to earth, you would have only aged the 5 years, but all of your friends would have long ago died of old age waiting your return.Interesting, No? Good luck and happy perplexing.
548613
On the contrary, a light beam would merely percieve that it travelled instantly inbetween origin and destination. Space would be warped to Zero distance in the direction of travel, not Zero space. I know it seems like a sleight-of-hand trick with the mathematics, but the distinction is important.
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.
324937
The universe, from your reference frame, would be length contracted into a single plane perpendicular to your direction of motion, thus enabling you to cross it by traveling no distance. Time for you would be stopped completely, thus you would travel this no distance in no time, at a speed of precisely c in your reference frame (light does that in every reference frame), despite the fact that by definition you are stopped in your own reference frame. Every other light ray would also travel at c in your reference frame and so would pass you in a finite period of time, except time would never move forward and so it wouldn't actually go anywhere. If you looked outside at the infinitesimally thin slice of universe, you would find that the area no distance ahead of your light ray is in the future of the origin (as viewed from any valid reference frame) and the area no distance behind it would be in the past. The beam you are riding on would have no frequency and would appear as a constant electric or magnetic field. Since the beam you are riding on is still traveling at c, it would therefore have infinite wavelength and so the field in question would permeate out to infinite distance in front of and behind you - not that it matters because there is no universe in either place. Speaking of the universe, every particle in it would appear to you to be infinitely massive and the universe would thus collapse on itself infinitely fast, if only there were time for it to do so.\n\nBy the way, there is a reason the speed of light is not considered a valid reference frame in special relativity. This is it.
308761
As weird as it sounds, the theory of relativity says that if you are in a car traveling at 200,000,000 m/s with the headlights on, then the light from those headlights will pass a person standing still at 299,792,458 m/s and not 499,792,458 m/s. And if that stationary person shines a light at your car, you will see his light approaching you at 299,792,458 m/s and not 499,792,458 m/s.\n\nThe theory is so weird that numerous scientists have done numerous experiments to test it. The most famous of these experiments is the Michelson-Morley Experiment. All experiments have confirmed that this strange prediction of relativity is true.\n\nBelieve it or not!
312536
*sighs* Why can't people do any research on their own? Anyway... you are traveling through time right now, how else did you push those keys in sequence to form your question?\n\nI think that what you are attempting to refer to (lol I'm never gonna get a best answer replying like this) Is that as you travel faster and faster, closer and closer to the speed of light, time flow for you slows down, and the misconception of the public that if you go faster than light you will reverse time. WRONG!\n\nThat's not specifically what you asked though, so I will focus on teh misconceptions regarding the speed of light. First of all, accelerating mass to the speed of light is impossible as it would require an infinite amount of energy, so your question is meaningless. Second, since your question is meaningless tehre is nothing more to say except maybe a supporting and enlightening example. Third, I do not feel creative tonight so that example is gonna have to pass tis time, unless you email me and I will explain it better.\n\ndavid_lapierre@sbcglobal.net\n\nUnless this is just a school project, which I doubt since they are going donw the drain is sciences these days... you might wanna ask me a question, I can be very helpful when I know my time is not going to be wasted on a person who won't bother to take a few minutes to learn something... :-)
92939
Some people would argue the logic of a space craft having headlights at all, others might find fault in the fact that, physically, nothing with mass can ever travel at the speed of light.  But lets put that aside.\n\nThe speed of light is constant in any frame of reference, no matter who is "watching" it, it always travels with respect to them at the speed of light (c).\n\nIf you are in a space ship already traveling at the speed of light [with respect to some outside observer], when you turn on the headlights, the light will move away from you at the speed of light.\nIf some outside observer (who you are flying past at the speed of light) watches all this, they would, too, see the light travel at c with respect to them.  But since you and the light are traveling both at the speed of light with respect to the observer, you and the light would be keeping up with eachother.
475387
You would be affected by relativity\n\nThe principle of relativity, which states that there is no stationary reference frame, dates back to Galileo, and was incorporated into Newtonian Physics. However, in the late 19th century, the existence of electromagnetic waves led some physicists to suggest that the universe was filled with a substance known as "aether", which would act as the medium through which the vibrations traveled. The aether was thought to constitute an absolute reference frame against which speeds could be measured. In other words, the aether was the only fixed or motionless thing in the universe. Aether supposedly had some wonderful properties: it was sufficiently elastic that it could support electromagnetic waves, and those waves could interact with matter, yet it offered no resistance to bodies passing through it. The results of various experiments, including the Michelson-Morley experiment, indicated that the Earth was always 'stationary' relative to the aether — something that was difficult to explain, since the Earth is in orbit around the Sun. Einstein's elegant solution was to discard the notion of an aether and an absolute state of rest. Special relativity is formulated so as to not assume that any particular frame of reference is special; rather, in relativity, a system appears to observe the same laws of physics independent of an observer's velocity with respect to it. In particular, the speed of light in a vacuum is always measured to be c, even when measured by multiple systems that are moving at different (but constant) velocities.\n\n\nEinstein has said that all of the consequences of special relativity can be found from examination of the Lorentz transformations.\n\nThese transformations, and hence special relativity, lead to different physical predictions than Newtonian mechanics when relative velocities become comparable to the speed of light. The speed of light is so much larger than anything humans encounter that some of the effects predicted by relativity are initially counter-intuitive:\n\nTime dilation — the time lapse between two events is not invariant from one observer to another, but is dependent on the relative speeds of the observers' reference frames (e.g., the twin paradox which concerns a twin who flies off in a spaceship travelling near the speed of light and returns to discover that his twin has aged much more). \nRelativity of simultaneity — two events happening in two different locations that occur simultaneously to one observer, may occur at different times to another observer (lack of absolute simultaneity). \nLorentz contraction — the dimensions (e.g., length) of an object as measured by one observer may be smaller than the results of measurements of the same object made by another observer (e.g., the ladder paradox involves a long ladder travelling near the speed of light and being contained within a smaller garage). \nComposition of velocities — velocities (and speeds) do not simply 'add', for example if a rocket is moving at ⅔ the speed of light relative to an observer, and the rocket fires a missile at ⅔ of the speed of light relative to the rocket, the missile does not exceed the speed of light relative to the observer. (In this example, the observer would see the missile travel with a speed of 12/13 the speed of light.) \nInertia and momentum — as an object's velocity gets close to the speed of light, it becomes more and more difficult to accelerate it. \nEquivalence of mass and energy, E=mc2 — mass and energy can be converted to one another, and play equivalent roles (e.g., the gravitational force on a falling apple is partly due to the kinetic energies of the subatomic particles it is made of).
167221
As the others have said, all light travels at exactly the same speed.  This is even true if the observer and/or the  light source are moving very very fast.  Once this was proved by experiment, everyone was very upset until Einstein figured it out and showed that time and space can distort. If you want a real bad headache, you can read all about this.  If it doesn't give you a headache, become a physicist!
587704
I saw a lot of good answers out there that hit the answer pretty much on the head.  I only wanted to point out one minor mistake in what you wrote (which you probably won't run into in most freshman courses in relativity).  That the astronauts would actually be older than those who stayed on Earth.  The special relativity people were explaining was correct.  If you move => time slows down.  The thing is that gravity has a greater effect in slowing down clocks and the gravitational field you experience in orbit is weaker than on the surface of the Earth (obviously it won't matter though if you are flying around space at speeds near the speed of light, then the special relativity part becomes dominant over the general relativity i.e. gravity).