Ignoring the laws of physics for one minute...

[Dougie69]

A question that's confused me for years... if we ignored the laws of physics for one minute and imagined flying in an aeroplane at the speed of light, we then look in our rear view mirror at the plane behind us (which is also flying at the speed of light) what would you see if he switched on his headlights ?

Would we see the plane, would we see the light, would we see anything ?  I asked my physics teacher this question years ago when I was at school and he told me not be subordinate and "shut up" !

[Loosehead]

OK as you wish, if at the speed of light objects behaved exactly as they do at lower speeds then you would not see the plane behind or it's "lights" as they are travelling at 0 relative to the plane in front so nothing from that plane could reach.

However as speed goes up the passage if time get's slower. The relativity equations tell as that as speed tends toward light speed time slows and if you could reach light speed time would stop.

I think the reason the teacher avoided the question was the difficulty in explaining the constancy of light speed relative to the observer and by association the slowing of time made it out of scope of the lesson.

[bernardo]

If you "ignore the laws of physics", then you are allowed to change the answer to whatever you want it to be.  But if you don't, and if your plane is travelling at just below the speed of light, then the light would be coming at you at the spped of light anyway.  It would be iumpossible for your plane to get to the speed of light in the first place.

[mibn2cweus]

This is undefined.  Your moving at the speed of light relative to what?  A aeroplane following you at the same speed as you would look as normal as if you were both standing still.

[jake-the-peg]

The equations of relativity do not definately prohibit travelling faster than the speed of light (c). They do stop you travelling at c.

At faster velocities you get a negative square root in the equations.  Now that might tell you that it's impossible or it might tell you that something special happens when you pass that speed.

If it were possible you couldn't make any real prediction on how anything would work as we have no experience of anything faster than c - Nobody ever found a tachyon.

Three are also some fairly good reasons for believing it's not possible.

[jimmer]

i'm not sure about that Jake. the laws of physics make it impossible for anything with mass to travel at the speed of light. Bernardo is right. If you ignore the laws of physics you can just make anything up.

Dougie, I think, but i'm quite likely wrong, that if you did manage to find yourself travelling at 300 000 kps and the plane behind was doing the same speed it would just look normal. the speed of light would still travel at c relative to you.

 

jim

[Space]

if you "ignore the laws of physics", then you can make up your own answer, use your imagination.
If you want a correct answer, then you can't ignore the laws of physics.
If you traveled at the speed of light, time would stop for you, just like loosehead said. So you wouldn't actually "see" anything, because your body would be sort of "paused"

[CT]

If we change the experiment slightly then we can explain this a little differntly. If we use the speed of sound (in air) instead of light we can make this a little more real world. If the two planes were both travelling at the speed of sound. Then the one behind 'tooted it's horn' or something, the sound from the second plane would never reach the first plane.The sound wave would travel at exactly the same speed as both planes, thus the first one would never hear the signal.
This doesn't work for light because no object can travel at the speed of light.

[jake-the-peg]

You're missing the subtlty here Jimmer.

Because something cannot travel at the speed of light does not mean that nothing can exceed the speed of light.

Imagine for a moment a tiny subatomic particle. You accelerate it closer and closer to c. It's mass increases and so it meeds more and more energy to get faster.

Eventually it gets so close to c that an additional quantum of energy will push it over the edge. The quantisation of the energy implies a quantization of the velocity and hence the particle breaks c without ever travelling at the speed of light.

Now the sort of energies we're talking about here meamn that if it were possible it could only have happened as a consequence of the big bang. As nobody ever found tachyons (yes they got a name) the chances are it's not possible.

There are also some other reasons to think that it's not possible to do with causality but lets put it this way I'd probably be quicker to believe that somebody found a tachyon than cold fusion

[Baronvhb]

I think it highly irresponsible to ignore the laws of physics, even for just one minute! We would all be floating around on the ceiling...objects wouldn't stop moving...we would be in complete darkness...energy would no longer equal mass. I think the AB health and safety execs will be watching you!!!