In relativity theory, is it possible to ever stand still (i.e., velocity = 0)?  And also...?
411874
relative means what you compare it to, so anything can be still. even me, although im moving on the earth at a very high speed. if i compare myself to my computer, i am standing still. \n\nspeed of light relative to whatever isnt moving, otherwise it wouldnt be the speed of light. actually this is getting advanced, i think the speed of light is a tricky subject because it does not obey traditional newtonian physics
137676
There are plenty of good websites that answer this question, for any knowledge level. The concept is complex enough that you won’t get a meaningful answer here.\n\nIn horribly oversimplified terms Relativity simply states two things.\n\nOne that there is no universal ‘at rest point’, it all depends on how you choose to define it. You sit in a car doing 100mph and I stand beside the road. Normally we assume that you are in motion and I am at rest. Relativity states that we can just as accurately say that you and the car are at rest and I am moving at 100mph. Alternatively, we normally believe that the Earth orbits the sun and the Moon orbits the Earth. Relativity states that it is just as accurate to say that the Earth orbits the moon and the sun orbits the Earth, or we could say that we all orbit some imaginary point in between all three. It is all a matter of choice what we define as being the fixed point.\n\nThe second is that the speed of light is constant regardless of whether you are at rest or moving, and regardless of how fast you move. If you are sitting in a car doing 9/10 of lightspeed and are going past me standing still beside the road and we both look at exactly the same light beam shining down the road we will both see that light beam travelling away from us at exactly the speed of light relative to both of us. You don’t see it slowed down just because you are travelling almost as fast as it is. It will move away form me just as fast as it moves away form you.\n\nThose are the basics, and they aren’t all that hard to understand, even if they don’t seem to make much sense. What Einstein did was sit down and think really hard about the logical consequences of those two points.\n\n\n>>>>>>also is it true gravity on sun is greater than earth?\n\nYes.\n\n>>>>>if it is so ,sun would have had sucken all planets\n>>>> in it!!\n\n\nNo. Just as the Earth doesn't suck the moon in despite having much higher gravity.\n\nThe planets orbitthe Sun. In simple terms that means they are constantly falling around the sun in a ciruclar pattern.\n\nThe best way I have heard this described for the layman  is to imagine yourself throwing a heavy weight like a shotput. You could only throw it a few metres. Now imagine standingon the roof of a house and throwing that same shotput. This time it will go much further before it hits the gorund. Now go to the top of a rally high cliff and throw it. This time the shotput will travel for 20 or 30 metres before it hits the ground.\n\nThe higher you go the further somehting thrown will travel before it hits the ground. And if you go high enough the object will travel right around the world and back to where it starts before it hits the ground. It will continue falling forever. \n\nThe planets are doing exactly that WRT the sun. We are constantly flaling aorund the sun, but we can't be sucked in because we are falling from such a great height.
271178
yeap. We came out with all this ¨fictional¨forces so we can be able to use Newton's law in non-inertial frames of reference ( most of the references we have ) , so when one frame of reference is accelerating ( like in a circular movement cause velocity is changing direction ) F=ma won't work unless you add this ¨force¨ , wich is not real ( cause there is no a physical thing applying the force like gravity ), so we came up with: ¨centrifugal force¨, ¨coriolis force¨ and many others that I've forgotten :P .\nthat's why we have relativity, wich newton's laws for explaining gravity..we don't use it frecuently cause we don't need to ( normal people doesn't use big numbers ), but it gives a better explanation of things.
1017091
Actually, the inverse argument of your proposition was used in an extra credit question on an examination I took for a mechanical engineering course in college:\n\n"Using the special theory of relativity, show that no material can have an infinite rigidity"\n\nAnswer: If a material of infinite rigidity existed, you could send signals along it at greater than the speed of light, a prohibition of the special theory of relativity..........\n\nThe most rigid stuff we know about has a wave propagation speed of only a few thousand meters/sec, a long way from 300 million m/s value of c.
308200
Neither Observer EXPERIENCES a change. The ONLY way any comparison can be made between the two unmentioned but essential clocks is to bring them together in the same rest frame again: then whichever clock ticktocked the least would be shown to be the one which accelerated and slowed down in their relative travel.
492519
There is nothing like antidirection. \nWell, if it becomes possible (assuming) to move at the speed of light, the time dilation formula of the special theory of relativity says that the time would not elapse. That means your aging will stop!\nIf it becomes possible (assuming) to move with speeds higher than that of light, many things could happen. According to the time dilation formula, the time would become an imaginary quantity. One of the interpretation of this imaginary time goes like this: the time will start moving backward. Possibly, that is the situation when you can expect moving back to past. But, further mathematics shows that you are not necessarily going to reach to your own past. Rather, you could land onto some other, strange, alien universe!\nAt this point we have not talked about the change in your mass or length if you are moving with such a high speed. But, for sure you are not going to be the same!
711259
I have always been a fan of this discussion. I propose that ANYTHING can travel faster than the speed of light (SOL). I also believe that was the driving force behind Einstein's assumptions. When we start talking about time slowing down as we approach SOL, we are talking about time RELATIVE to something else...If two people are together on a SOL spacecraft, then the time they experience is the same as if they were standing still. \n\nBefore I ramble on too much, What stops light from going any faster? If we had a theoretical spacecraft that could travel at 1/2 SOL, and we shot a laser off the front of it, how fast would the light be travelling? To the observers on the SOL-craft, the light would be travelling at absolute SOL, but to someone standing next to the craft when the laser was activated, would the light NOT be travelling at 1.5 SOL?
3887
It is impossible to actually go at the speed of light because in the formula for time dialation (That's right Velocity distorts time. The faster you go, the slower time goes for you. This effect is negligable unless you are going very close to the speed of light.) if v(velocity) were equal to c(the speed of light) you would have a zero in the denomonator.\nthe formula is:\nt'=t/sqrt(1-v^2/c^2)\n\nwhere t' is the time that has passed from a stationary observer, t is the time that has passed for you, sqrt means square root and ^2 means squared. As you can notice, when v is small, since c^2 is so huge, you get a miniscule decimal, and 1 minus that number is basically as small as 1.0000000000001 or something, and so time is not really affected. As v gets larger(it can never be the speed of light, then the denomonator would be zero) that fraction becomes closer to 1, so when you subtract it from one, the denomonator gets smaller and smaller, meaning t gets smaller(in order for t' to remain constant) this means that time actuall slows down for the object moving at such velocities. This formula is correct, it is part of Einstein's theory of relativity, and I have had to derive it myself from ordinary mechanics formulas. \n\nAlong with time, length contracts and mass expands by the same factor.  If you were to go close to the speed of light, your mass would increase and length would decrease. This means that the density of your body would increase more and more as you went faster and faster, and your blood eventually wouldn't be able to flow anymore and your cells would die of oxygen starvation.  Not that it really matters, because to even begin witnessing this effect, you would have to be going at least 90 or 95% or so the speed of light.  \n\nNow to answer your question in that is it actually physically possible to get close... considering they have particle accelerators stories high and miles long requiring tremendous amounts of energy in order to even get tiny protons and neutrons to move at such speeds, it doesn't seem like they're anywhere near accelerating something big anytime soon.  F=ma, meaning in order to get something that weighs one gram, like a paperclip to accelerate to the same degree as they do the protons, you would need about 2x10^24 times the force.  That notation just means a 2 with 24 zeros after it.  The reason for this is that that is how much more mass a paperclip has then a proton.  An actual human isn't going to get anywhere close for a very long time.
341703
Yes, and no- The theory of relativity states that light moves at the same speed regardless of the viewer-it is "special relativity".  If you are riding a beam of light, and switch on a flashlight, that light will speed away from you at the speed of light.  However, to a person standing still behind you, both you and the beam of light you just sent out, are traveling at the same speed.  So, light is always in motion, but it is not relative to the source.  Light, no matter how fast you are moving or in what direction, always travels relative to you (and everything else) at the same speed.  All that will happen is a change in the frequency of the light.
25302
There isn't an easy explanation, though it isn't that hard either.  \n\nThe whole idea of special relativity is that all motion is relative to the speed of light and that nothing with mass can travel that speed.  So, in answer to your first two questions, the speed of the light in both directions is still the same as it would be if you were standining still.  \n\nWhat Einstein proved was that there are no fixed points in space, but that space and time are constantly streching and contracting to accomodate the fixed speed of light.  The important thing to understand is that distances of space and lengths of time are different depending upon your relative motion.  I hope that begins to answer your question.
872305
No.  The theory of relativity states that an object moving at a high enough velocity will appear to shrink along the direction of motion and increase mass from the point of view of a non moving observer, so much so that, if a physical object would be to travel at the speed of light, its dimension will be zero and its mass infinite.
855043
It's all theory, we don't know if (something) can exceed the speed of light. I would argue that time would be void at that moment, but again it's my theory. Interesting thought though.
676832
YES\n===\nEverything is relative so in relation to some other object in space, yes it would be completely stopped as the train slowed down from the impact.\n\nNO\n==\nEverything in the universe is in constant motion.
931618
Simultaneity in Special Relativity is based on 2 assumptions:\n\n- the laws of physics apply equally to all inertial reference frames\n- the speed of light in empty space is constant and independent of the relative motion of its source\n\nThis implies that there is no absolute simultaneity, meaning that two events that happens at the same time in one inertial frame may not happen at the same time in another inertial frame.\n\nSo Einstein is NOT defining Simultaneity based on the invariance of the speed of light in all inertial frames, but instead the failure of absolute Simultaneity is a consequence of the invariance of the speed of light in all inertial frames.\n\nSo why does the invariance of the speed of light in all inertial frames imply the lack of Simultaneity? The argument for this is exactly the same as why there can be no absolute reference frame if we assume that the speed of light is constant in all reference frames.\n\nThe only way for the speed of light to be constant in all reference frames is for distance and time to be relative and be a function of speed of the reference frame, i.e. speed = distance/time implies that distance must contract and time must dilate if the reference frame is moving with a certain speed.\n\nSo if distance and time is different in one reference frame than another, then there is no way that two observers, each in separate reference frames, can agreed on when some event has happened. Thus simultaneity is violated.
3115
This is considered to be impossible.  As you APPROACH the speed of light, your energy and/or mass change.  If  you HIT the speed of light, your energy and mass approach zero and infinity.  So there would be nothing left of you to actually EXCEED the speed of light.\n\nBut I encourage you to try.  Write us and tell us how it goes!
1008364
You have the old Newtonian physics, which is called classical physics.  It is built on the premise that space and time are absolute fixed entities, and cannot change.  This is the physics that you learn in High School, and is true and works for our everyday life.\n\nHowever, when one begins to approach the speed of light, and apply the classical physics to that situation, we see violations of physical law: such as an object can go faster than the speed of light.  For example, let's say a car is traveling at half the speed of light, and you shoot a bullet that is traveling at .6 times the speed of light (all hypothetical of course).  An observer would see the bullet traveling at 1.1 times the speed of light, which is obtained by adding the speed of the car and the bullet together.  That is the classical method of finding the bullet's speed.\n\nEinstein correctly surmised that nothing can travel faster than the speed of light, or even be seen traveling faster than light, such as our bullet.  Therefore, he considered how classical physics would look if space and time were not fixed entities.  In doing so, he developed a more comprehensive physics, called relativistic physics, which fixes our bullet problem.  \n\nThe cool thing is, the relativistic equations are almost exactly the same as the classical equations, with one exception: the have what I call a relativistic adjustment.\n\nFor example, to find the bullet's speed as seen by an observer, requires the following equation:\n\nV = Vc + Vb\n\nWhich in our problem would be:\n\nV = .5c + .6c = 1.1c\n\nThe relativistic equation is almost the same:\n\nV = (Vc + Vb)/(1+Vc*Vb/c^2)\n\nThe numerator is the same as the classical equation.  The denominator is the relativistic adjustment.  So, the equation becomes with our example:\n\nV = (.5c + .6c)/(1 + .5c*.6c/c^2) = .846c\n\nThe bullet would be seen traveling at almost 85% the speed of light.  \n\nThe cool thing here is that when you use speeds that are very small, like everyday speeds, the relativistic adjustment bascially equals one, so it reduces to the classical equation.
733773
Zero.  If the velocity is constant, acceleration is 0.