What will happen if 2 particles travelling at velocity equivalent to light collide with each other?
541473
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
33169
IF YOU WERE GOING AT THE SPEED OF A BULLET,YOU WOULD BE RIGHT NEXT TO IT AT SPEED O. THE SAME WITH LIGHT, IF YOU WERE GOING THE SPEED OF LIGHT IN YOUR CAR (LET'S SAY )YOU WOULD SEE THE LIGHT ON,BUT TO SEE THE LIGHT OFF YOU MUST BE GOING FASTER THAN THE SPEED OF LIGHT.SO THEN YOU SEE THE LIGHT ON AT THE SAME SPEED THE CAR IS GOING.
667965
No, at the speed of light, the space the arrow would occupy is everything, therefore I'd only be hit by an infinite fraction of the arrow, ergo nothing would be felt, noticed nor seen. Furthermore, the arrow would take an infinite amount of time to get anywhere, although it would, from the arrows point of view, still move at the speed of light.\n\n[edit]: After having read all the other posts, I realize that I need to bring some proof of my statement since everyone are making a clueless guess. Thusly, I present to you a link to wikipedia, which fortunately validates my school/university teachings. If you search for the Lorentz Transformation (the factor of which an object stretches in relation to its velocity), you will find that at low speed this factor is very close to 1 (meaning no noticable change in stretch). Though, at a speed infinitely close to the speed of light, the factor also reaches infinity, meaning the object will have an infinite size (but not infinite mass), which means that the atoms of the arrow will hit everything at once, causing its finite momentum (movement energy) to be exerted upon every single atom in the entire universe. Not only does this mean that an arrow with the velocity of light cannot hit a single target, but it also means that nothing will notice anything other than the arrow suddenly disappearing. Furthermore, special relativity states that nothing can achieve the speed of light within a finite time-frame, making you question very theorical.\n\nI would also like to point out the sheer lunacy of the average 'answerer' here on Answers. If you take my answer as being truthful, which you should given the high support within modern physics (which I am also a student of), you would notice that only a small fraction of the members of Answers aren't guessing cluelessly. This is quite sad, and I advice you to regard every answer with suspicion, and use google/wikipedia for valification.
336972
Wow, great question(s)!  You're brooding over something called the 'twin's paradox', read more about it in the link below.  Basically, what you're fretting over are a couple of the (wierd) implications of special (and general) relativity.  You (and what some others have said) are right, all velocity is relative, which comes from the simple fact that there is no special place that we can call 'still' which we could measure our velocity against.  The single exception to this lies in the speed of light, which is constant for everyone everywhere, no matter what their speed is relative to anything else.  (Note: light isn't special, the only reason it's able to travel at the upper speed limit is because it's particles, photons, have no mass.  Nothing with mass can ever travel AT the speed of light, only near if it is pumped up with huge amounts of energy.)  Think about the wierd implications of this; even if you were able to travel at 99.999999% the speed of light, and your friend would also be able to travel the same speed in the opposite direction, if you shined a light back toward your friend and could measure the photon's speed as they travelled between you the photons would STILL be travelling at the speed of light.  Ok, what does that mean?  The speed of light is just a speed, like any other, but is a constant that can not be exceeded.  Well, like any other speed, c (the usual symbol for the speed of light) is definded as the ratio of the distance travelled (call it 'x') by the time it took to travel it (call it 't'), or c=x/t.  But if 'c' can't change (because it's a constant) what is changing?  There's only two other things in the equation, x (the distance, a measure of space) and t.  Time and space enter into Einstien's equations here, the only way to keep c constant is for x and t to somehow collaborate to change together to make it so.  This is why time (and space) are so 'relavent' to velocity.  And as a matter of fact, time is 'relavent' to gravity as well, as Einstein pointed out so much better than I can.  For Einstein, the breakthrough came when he realized that there is no measurable way to distinguish between gravity and acceleration (a.k.a. the rate of change of velocity with respect to TIME), or more importantly, between the lack of gravity (say a person floating in space) and a particle (or person) in a falling box, they're indistinguishable.  From these two simple ideas (the constancy of c, and the equivalence of gravity and acceleration) Einstein formulated the theory of general relativity, one of the crowning achievements of human thought.  You ask good questions, keep wondering!
38506
yikes, everyone is giving you the wrong formula. it's not e=mc^2. that would be converting energy into mass and back which is done like when subatomic particles crash into each other really fast and such... the mass dialation formula you are looking for is \nm'= m/sqrt(1-v^2/c^2)\nwhere m' is the mass you would be not moving at the high velocities, m is the mass moving at the high velocities, v is the velocity you're traveling at, c is the speed of light, sqrt means we're square rooting everything in those parenthesis, and ^2 means squared. if you were to plug numbers in for velocity, you can see that this effect is absolutely neglagible unless you are moving very very close to the speed of light. and it is impossible to actually move at the speed of light, because then v^2/c^2 would be 1, and 1-1=0 so you would have a 0 in the denominator of that equation, which is impossible.  that equation is actually very interesting in that it is part of the lorentz factor which also effects time and length. in fact, as you increase speeds close to the speed of light, not only does mass increase, but time moves slower for you and length shrinks.  I've had to derive these equations in physics class, it's very interesting to do it yourself and come up with the equation proving that things like velocity, mass, and length are affected by velocity.  but again, you need to be going very very close to the speed of light for the velocity to have any effect on these things.\n\nas far as practicality, instances of the lorentz factor have been proven. there are these particles that have a certain lifespan before they disintigrate.  so now, we know how fast they are going and we know how long before they disintegrate, so theoretically, we should easily be able to figure out how much distance they cover before they disintigrate, right? but somehow, the particles go a lot farther than they should... if we plug their velocity into the lorentz transformation formula however, and put in how far they should travel (but don't), they we come up with how far they actually do travel.  this proves the validity of the lorentz factor.\n\nthere is no practical application of the mass increase since objects of great mass would require way too much energy to accelerate to speeds great enough to see this effect, so therefore it can't really happen.. if ever it did though, the only thing this mass expansion would serve to do would be to limit time travel. i mean, if time is slowing down for us at high speeds, technically we could make it slow down so much so that it would be going slower for you than everyone else and so you could basically travel forward in time. but if your mass was expanding and length shrinking, then either the pressure would kill you, or your blood would get so dense it couldnt carry oxygen to your cells and that would kill you, so there goes the time travel thing.
718668
Neglecting the fact that it would be imposible to accelate a train (non-zero rest mass) to the speed of light,\nif you did, an observer in the train would still see light moving away from them at the speed of light.\nThe speed of light is constant in all frames of reference.
1039444
No, there would be no interference pattern if light were behaving strictly as a particle.  If light acted only as a particle, the pattern seen behind two slits would be the superposition of the patterns seen behind two single slits.  That is, if light acted only as a particle, then you should see the same pattern whether you let light pass through two slits for five minutes, or whether you opened only one slit for five minutes, then closed that slit and opened the other for five minutes.\n\nOpening one slit at a time produces no interference pattern, leaving both slits open produces an interference pattern.  This cannot be explained by assuming a strictly particle interpretation of light.\n\n==============\n\nComment on "Additional Details #1"\n\nParticles of light have never been observed to bounce from one another.  Quantum electrodynamics predicts that they should, but the effect is so slight, and the probability so low, that there has never to my knowledge been a successful measurement of photon-photon scattering in the laboratory.  If the interference patterns in a Young's two-slit apparatus were to be explained by particles of light bouncing off one another, it would imply that light scatters from light very, very easily.  Crossing two flashlight beams would produce a diffuse glow from the area of intersection, and the beams would not continue onward to the places they were pointed.  We don't see that happening.  Another example:  if somebody is driving toward you with their headlights on, you cannot reduce the amount of light hitting your eyes by shining your headlights at them and deflecting their beam.
588349
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.
546523
Well according to Relativity Theory it is known that an Object of Mass (M) travelling at Velocity (V) would have a Change in Mass: ie\n        \n          Mass at Velocity (V)  = ( Rest Mass) / sqrt(1-(V^2/C^2) ) \n\nTherefore if we replace C^2 by V^2 then the Whole Equation becomes Infinite. in other Words You cannot Travel at the Speed of Light, because according to Physics an Object cannot have Infinite Mass.
40471
E=mc^2 \nEnergy = mass * (speed of light)^2, c = the speed of light (approx. 186,000 miles per second).
997396
E=mc^2  Wow!  This mean that you can transform energy into a mass as it goes at the speed of light squared.  In other words, if you were to take two objects and both collide at the speed of light, what will be left is only energy in a form of light, fire, etc.  Cool!  Other forms of energy are as mechanical energy, electrical energy, light energy, thermal energy, chemical energy etc.
214563
The previous answer is wrong. There is absolutely nothing stopping your reference frame travelling near (or even at) the speed of light. Even if you were travelling at 0.999999% the speed of light, you would still observe a light beam travelling past you at c. This speed is a constant because the speed of light does not depend on the velocity of the object emitting the radiation (see Maxwells equations).
312163
the first after collision moves in an opposite direction and the second ball moves towards the direction of collision\nfirst ball moves with a velocity of  16.66cm/s\nsecond ball with 66.66cm/s
1028951
The example of each person going faster than the previous assumes a consistent additive nature of speed which unfortunately falls apart (shown by experimentation) as your speed approaches the speed of light.\n\nSpeed is not absolute in the sense that there isn't a universal stationary reference point.  If there were, then the example will apply.  According to experiments, however, something travelling away from you at light speed will do so regardless of whichever direction you happen to be moving.  This is not something to reason about (nobody arbitrarily made up this rule so that philosophers can find loopholes around); it's just what's been observed so far.\n\nThe Wikipedia article at http://en.wikipedia.org/wiki/Speed_of_light explains it a lot better than I can.  Jump to the section "Constant velocity from all reference frames" for the discussion applicable to this example of yours.\n\nHowever, an article at http://science.howstuffworks.com/news-item6.htm suggests that at least two experiments (pending validation) may have found exceptions?
566668
No object that has mass can be accelerated to move at the speed of light. If you were somehow moving at 0.99c and then shown a flashlight, the velocity of the photons would not be 1.99c, it would just be c. The speed of light is invariant. The true formula at relativistic speeds is the following:\n\nV = (v+u) / (1 + vu/c²)\n\nWhen the velocites are not relativistic (i.e. throwing a ball out of a moving car) this approximates to V = v+u. So if you are moving toward something that is emitting photons at c, and you yourself are somehow also moving at c, the velocity you observe the photons to be moving is still just c. Try it in the formula: V = (c+c) / (1 + cc/c²) = c\n\nIt can be derived from special relativity or the Lorentz transformations.
985678
Incoming momentum = p1 = mv1\nOutgoing momentum = p2  = mv2\nChange in momentum = p2 - p1 = m(v2-v1)\nThis change occurs in time, t.\nRate of change of momentum = m(v2-v1)/t = impressed force, f.\nm=0.149 kg, v1 = 43.4 m/s, v2 = -48.7 m/s, t = 1.1x10^-3 sec\n\nf = m(v2-v1)/t\nYou do the arithmetic.
54308
As you travel faster and faster, time for you slows down, and length contracts. From your point of view, when you measure the speed of light, it will always be the same. An observer standing still with respect to you and the beam of light could measure your speed at 185000 mps and the speed of light as 186000 mps, and say the difference in speed is 1000 mps. But that is relative to them. The speed of light will always be the same for whoever measures it, no matter how fast they are moving.\n\nSee the website below for more about relativity.