Guest ElGargamel Posted June 15, 2004 Share Posted June 15, 2004 Hi there, I'm new here so I'll make a quick introduction for the few who care I'm a 19y old biology student from Belgium at university of Leuven. And in a few days I have my physics exam. There is this one thing that keeps bothering me because I dont know the answer. What if you were to travel at the speed of light with a car and you put on your lights. What would happen and can you explain this physical and quantumphysical. If I'd got this question I'd be shitting my pants. But this is what I came up so far. First of all, it's impossible to travel at the speed of light, see Lorentz-Einstein formula's, you could only travel at the fraction of light (a close one). But exept that, if you were going that fast, I dont think you'd see the light, because you are travelling as fast as it, so the light cant be ahead of you and thus not be visible. Another approach would be with the Doppler effect because light is made of electromagnetic waves and the doppler effect is all about waves. But when working with the doppler effect, well the observer or the source , one of the 2 must be at rest. So I dont think you can use the Doppler effect, though I have heard from other students that you can. To bad I cant reach them so I could ask them thanks anyway Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted June 15, 2004 Share Posted June 15, 2004 You would see the light. Relative to you, it would go twice the speed of light. However, to an observer, it would only go the speed of light. As fast as you. This is described in the theory of relativity, but I really can't explain it. I know the theory, not how it works. Link to comment Share on other sites More sharing options...
swansont Posted June 15, 2004 Share Posted June 15, 2004 Relative to you, it would go twice the speed of light. No, it wouldn't. Relative to any inertial observer, it goes as the speed of light. If one is asked the question, you can stop after "it's impossible to travel at the speed of light, see the Lorentz-Einstein formulas." Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted June 15, 2004 Share Posted June 15, 2004 I meant that it would be going the speed of light faster than you, or 2x the speed of light. Sorry. Link to comment Share on other sites More sharing options...
apathy Posted June 15, 2004 Share Posted June 15, 2004 No! don't you get it? I'm not even a physicist but this is so easy to understand. No matter where you are, light is going c. So you may be going 99.999% the speed of light (a stupendous feat) but those phtotons leaving your headlights are going c. That means c with respect to you, someone you just passed, and the folks still sitting at the starting line. All inertial reference frames will see light travelling at c. Never 2c. Link to comment Share on other sites More sharing options...
Skoteinos Posted August 10, 2004 Share Posted August 10, 2004 It has to do with the fact that the speed of c is constant Everywhere, all the laws succumb to it. Think of it like this, your going at a fraction of c, the headlights are going at c to a guy on the road, to you, and to an alien 500 billion lightyears away, for each observer, c is measured constant always, the measurements themselves get warped by the differences in velocities, as your going faster and faster, your length shrinks/flattens, hence if you measured how far a photon traveled in 1 second, you will always come up with 300,000 km (roughly), the faster you go relatively, the more skewed your measuring instruments. at 10% c, your meter ruler will be shorter than a ruler to an outside observer, you'll think everything's dandy, but in the end, all measurements of c always turn out to be perfectly sychronized at the universal speed of light. (P.S.- Light going through any medium [water] 'slows' via refraction, the speed of light never changes) Link to comment Share on other sites More sharing options...
Severian Posted August 12, 2004 Share Posted August 12, 2004 All inertial reference frames will see light travelling at c. Never 2c. They might see light travelling less than c though (if it is ex-vacuo for example). Link to comment Share on other sites More sharing options...
Aeschylus Posted August 12, 2004 Share Posted August 12, 2004 In relativity the question simply does not make sense, there is no way of defining a frame of refernce for an observer travelling at c. In other words all relativity says is that this is impossible and it doesn't say what were to happen if it were possible. Of course particles can travel fastre than light thorough some medium, in this case Cherenkov radiation is produced, which is in some ways analgous to the sonic boom produced when soemthing breaks the sound barrier. Link to comment Share on other sites More sharing options...
5614 Posted August 12, 2004 Share Posted August 12, 2004 whilsts we are all answering the question, if you dont mind, may i ask: is this realsiticaly going to be asked in an exam, as swansont said, the answer is it's impossible to travel at the speed of light, see the Lorentz-Einstein formulas. this is a short, simple answer, is the question going to appear on the exam paper, as the question itself it flawed, in the way that it is impossible. so would it be an exam question? Link to comment Share on other sites More sharing options...
TheProphet Posted August 12, 2004 Share Posted August 12, 2004 whilsts we are all answering the question' date=' if you dont mind, may i ask: is this realsiticaly going to be asked in an exam, as swansont said, the answer is it's impossible to travel at the speed of light, see the Lorentz-Einstein formulas. this is a short, simple answer, is the question going to appear on the exam paper, as the question itself it flawed, in the way that it is impossible. so would it be an exam question?[/quote'] I see no reason why it couldn't be! A such question would see if the students fully understand the implication of the Lorentz-Einstein formulas! Link to comment Share on other sites More sharing options...
5614 Posted August 12, 2004 Share Posted August 12, 2004 yes ok, in which case, presumably would the answer, for all of the marks be something along the lines of: "it's impossible to travel at the speed of light, see the Lorentz-Einstein formulas." or would you then need to say, "however, in theory......... etc etc" remember you dont know the marking sceme, what would you advice a student to write? Link to comment Share on other sites More sharing options...
Aeschylus Posted August 12, 2004 Share Posted August 12, 2004 All that you need to recognize is that gamma is undefined when u = c. Link to comment Share on other sites More sharing options...
TheProphet Posted August 12, 2004 Share Posted August 12, 2004 yes ok' date=' in which case, presumably would the answer, for all of the marks be something along the lines of: "it's impossible to travel at the speed of light, see the Lorentz-Einstein formulas." or would you then need to say, "however, in theory......... etc etc" remember you dont know the marking sceme, what would you advice a student to write?[/quote'] I would say: "it's impossible to travel at the speed of light since according to the Lorentz transformation it would imply needing Infinit mass! And that is not possible." Then write out the formulas to further denote it! The however in theory is not to recomend.. since we don't know what really happens! We can say that time stops at c or that if travveling at absolute c time you'd experience all further time in an instance.. What is right here we will never now. All we know is that light is traveling at c an in turn t=0! But that really says noting about our experince in a such specific moment! Link to comment Share on other sites More sharing options...
Aeschylus Posted August 12, 2004 Share Posted August 12, 2004 I would say: "it's impossible to travel at the speed of light since according to the Lorentz transformation it would imply needing Infinit mass! And that is not possible." Then write out the formulas to further denote it! The however in theory is not to recomend.. since we don't know what really happens! We can say that time stops at c or that if travveling at absolute c time you'd experience all further time in an instance.. What is right here we will never now. All we know is that light is traveling at c an in turn t=0! But that really says noting about our experince in a such specific moment! The problem is the formulas don't work as gamma is undefined, all specila relativity says is that it is impossible for any object with non-zero mass to travel at c, also we can't define a frame of refernce for anything travelling at c such as a photon. Link to comment Share on other sites More sharing options...
TheProphet Posted August 12, 2004 Share Posted August 12, 2004 The problem is the formulas don't work as gamma is undefined, all specila relativity says is that it is impossible for any object with non-zero mass to travel at c, also we can't define a frame of refernce for anything travelling at c such as a photon. But with a formula u can set it upp to se that it is imposible.. it was this Einstein did in the first place i guess! Link to comment Share on other sites More sharing options...
Aeschylus Posted August 12, 2004 Share Posted August 12, 2004 But with a formula u can set it upp to se that it is imposible.. it was this Einstein did in the first place i guess! And all you need to do is to prove that gamma is undefined and hence the Lorentz transformation only gives results that are undefined, which is a fairly trivial exercise. Link to comment Share on other sites More sharing options...
TheProphet Posted August 12, 2004 Share Posted August 12, 2004 And all you need to do is to prove that gamma is undefined and hence the Lorentz transformation only gives results that are undefined, which is a fairly trivial exercise. My bad math skill here again.. i see we are talking of the same thing so... Link to comment Share on other sites More sharing options...
Skoteinos Posted August 12, 2004 Share Posted August 12, 2004 They might see light travelling less than c though (if it is ex-vacuo for example). Thanks for correcting me on that heh, I should have elaborated light in vacuum. Link to comment Share on other sites More sharing options...
noz92 Posted August 16, 2004 Share Posted August 16, 2004 i would think that if you somehow reached c, and then you turned on your head lights, i would think that you would use zeno's paradox for this. if you're traveling at c, and you turned on the head lights, then because the head lights are slightly in front of you, then you would simply be driving the lights foward, and you would stay the same distance away from the light for ever (unless you turn the lights of and turn away). but the above wouldn't matter, because by our modern scientific knowledge, you couldn't reach c (but then again, this may be wrong like many things in science, which is why i think science is so interesting). Link to comment Share on other sites More sharing options...
Wolfman Posted August 16, 2004 Share Posted August 16, 2004 is that like asking when traveling the speed of sound can you yell and hear yourself? Link to comment Share on other sites More sharing options...
TheProphet Posted August 16, 2004 Share Posted August 16, 2004 Well there is just more problems too it than that.. when reached c.. time stops.. so if there it really where possbile i'd have a bet that once there you're stuck! So you woudn't be able to turn any headlights on at all! Nor deaccelarating! Bummer ha? As u see Wolfman from my reply c speed gives a couple of other problems. so it would be an ill comparision! Link to comment Share on other sites More sharing options...
fuhrerkeebs Posted August 16, 2004 Share Posted August 16, 2004 Now, assuming your fairy godmother allows you to move at the speed of light, you wouldn't see anything. You'd be too small Link to comment Share on other sites More sharing options...
TheProphet Posted August 16, 2004 Share Posted August 16, 2004 Now, assuming your fairy godmother allows you to move at the speed of light, you wouldn't see anything. You'd be too small Well not to small really but to thin in the travelin direction! Probaply infinitly thin too! So there is yet another problem. Wounder how it will feel to be smashed into noithingess and back again! Link to comment Share on other sites More sharing options...
fuhrerkeebs Posted August 16, 2004 Share Posted August 16, 2004 When I said small that's what I meant...and you will become infinitely thing...your length would become 0. You wouldn't feel anything if your smashed into nothingness and come back again, because from your point of point everything is just getting longer...that's the principle of relativity. Link to comment Share on other sites More sharing options...
TheProphet Posted August 16, 2004 Share Posted August 16, 2004 When I said small that's what I meant...and you will become infinitely thing...your length would become 0. You wouldn't feel anything if your smashed into nothingness and come back again, because from your point of point everything is just getting longer...that's the principle of relativity. And that's the other nice thing with SR... Since u can't still be and have a length of 0, it's just again another argumetn why c speed is impossible Link to comment Share on other sites More sharing options...
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