speed of light and a laser pointing beam?

Question

If you shine a laser pointer beam at a star, and suddenly swing the beam to point at another star, say a thousand light years from the first star, you could say the end of the beam travelled faster than the speed of light. However, I realise the beam's pinpoint itself is not an object, so there's no one thing travelling in this scenario, but what if it wasn't a laser beam but instead it was an incredibly long and strong metal rod extending out into space, and you swung it across (as if you were swiping a sword), wouldn't the end of the rod travel faster than the speed of light? How would the time dilation effect work here?

I know nothing can travel faster than the speed of light. It's a thought experiment. I want to know what would happen.

Answer 1

dd is correct.



I like to use the garden hose analogy. The stream of water from the hose is the beam of light, made up of a zillion water molecules all rushing to the Pansy star. Now you swing that hose over to the Lily star. What happens to that stream of water?



At the hose nozzle, the water follows your swing immediately. But out where the stream was impacting the Pansy star it drags behind the swing. And the faster you swing from the Pansy to the Lily star, the more the stream of water bows backward and drags behind. Why is this?



Because the water molecules coming from the nozzle travel at a finite speed, just like photons travel at a finite speed, the speed of light. So it takes some finite time for the water molecules out of that nozzle, that's now pointing at the Lily star, to finally reach the Lilies. Same deal for the laser beam. It takes a finite amount of time for the photons leaving the pointer to finally reach the other star.



There is no time dilation here as we with the laser pointer are the only reference frame involved. For there to be a dilation, there must be two different reference frames (e.g., Earth and a space ship) involved. In your case, we are measuring light speed relative to Earth... period.

Answer 2

There is no such thing as a perfectly stiff rod (even diamond, the hardest substance known would flex) so it would deform in such a way as to not violate relativity.



Here's a simpler example of what you are asking. We construct a perfectly stiff rod that reaches from Earth to Mars. This way when astronauts land there, we can have faster than light communication by tapping the rod up and down in morse code. Since it's a perfectly stiff rod, the signals (taps) are instantaneous!



The fallacy of course is again, there is NO SUCH THING as a perfectly stiff rod. So the signal will aways travel through the rod slower than the speed of light.

Answer 3

ok, adult adult males, all persons comprehend not something with mass can bypass gentle velocity; so enable's play "what if" besides. the respond is, gentle in a vacuum is going the value decrease lower back, the value of light in a vacuum, no count what or the placement. So the relative velocity W = V + C = C the placement V is the source and C is the gentle coming from the source. that is not legerdemain precise here, it is physics. Time and section alter on the source to maintain C at C no count what V there could be. C is invariant. and that's an spoke of fact of the Michelson Morley experiments that have been given AE thinking why. His answer grew to alter into that section and time adjust to keep C at C no count what; he revealed this by using way of certainty the particular concept of relativity in 1905. by using way of a delicate of hand mentioned because of the fact the Lorentz Transformation, we are able to prepare that W = (V + C)/(a million + VC/C^2) is the relative velocity of light C coming from a source at velocity V. So if that source is moving V = C (ok relax, that's what if), then the relative velocity is W = (C + C)/(a million + CC/C^2) = 2C/2 = C. And there you're. That gentle is moving at C and not C + C = 2C.

Answer 4

think of light, instead of a beam, as a series of balls or photons travelling at the speed of light. When you move the light source by any angle, a new stream of balls are required to create a beam. In this way, there is no arc of light created in the sky when you swing the laser point, since the photons don't have the time to reach that distance.

Answer 5

When you say, "swing the rod" you mean you would be changing its angular momentum. That takes energy. I don't know for sure, but I think that if you used the laws of relativity theory to work out how much energy you would need to make the tip travel that fast, it would turn out to be an infinite amount of energy. You simply could not swing it that fast.

Answer 6

You do need to remember that elastic response of any "rigid" body will propagate at its speed of sound, much more pokey slow than the speed of light.