If Al was travelling at the speed of light & he saw Jill also travelling at the speed of light & they collided

Question

wouldn't they collide at twice the speed of light? If not why not ?

Answer 1

the question is absolutely wrong as no body can travel with the speed of light in accordance with Einstein theory of relativity.

Answer 2

1. Nothing with mass can travel at the speed of light so this is impossible.
2. Particles without mass can only travel at the speed of light.
3. Time does not exist for anything moving at the speed of light so seeing something is impossible.
4. You are using the equation v(collision) = v1 + v2 which is just an approximation to the correct equation. This approximation works well at low velocities but becomes less and less usefull as velocity approaches the speed of light.

Points 1,2 and 3 are especially important - every time you see a speed of light related question make sure it passes these tests.

(and for the pedantic feel free to add 'in a vacuum' as appropriate )

I am going to wimp out of the full description and fall back to that old standby of wikkipedia.
http://en.wikipedia.org/wiki/Special_relativity

Answer 3

The answer might be more philosophical than scientific.

The only way Al and Jill could be travelling at the speed of light would be for them to each have no mass.

And objects with no mass (are they even objects at that point?) can't really collide.

Like aiming 2 flashlights at each other. Can photons collide? I don't think they can.

Answer 4

First of all, neither could possibly travel at the speed of light, but let's assume they could get to within 99% or so. Even at that speed each would see the other approaching at *less* than the speed of light - that's just the way things are in the universe, which Einstein proved in 1905.

An observer looking at both of them racing toward each other from the side, however, would see each person traveling at 0.99c and collide at 1.98c, but that 1.98c is not an actual, physical speed experienced by anyone.

The speed of light in a vacuum is *always* observed to be 186,000 mi/sec (300,000 km/sec) from any point of view. Einstein figured out that for this to hold, space and time themselves must actually change at high enough speeds.

Anything with mass that went as fast as light would see time slowed to zero (and the equivalent, space shrunk to zero thickness so it could go anywhere instantaneously), its own thickness shrunk to zero, and its mass increase to infinity. Since these are all physical impossibilities, the conclusion is that no mass can even reach the speed of light, much less exceed it.

Answer 5

As someone else said, this is unanswerable because no one could travel at the speed of light. However, since nothing can happen at twice the speed of light (whether a collision or something travelling) then the answer is probably no, I should think.

Answer 6

You coaching replaced into incorrect about all skill having mass. Radiation, or mild waves contain no mass. some human beings argue that it has an 'effective mass' given by technique of a few of the E=hf (engery=plank's consistent situations the frequency), yet that remains debated. Reguardless, mild has no mass, and it really is the reason it may commute @ the speed of sunshine c. you're fantastic about accelerating a partlice in direction of the speed of sunshine ought to require limitless quantity of skill. once you're truly intrested seem @ Lorentz ameliorations, and also you may see the extremely person-friendly why something with mass can not attain the speed of sunshine.

Answer 7

Relative velocity on impact = c= speed of light
You need to take into account time dilation which increases as their velocities increase (as observed by each)
the formula for addition of velocities v = v1+v2/(1+(v1*v2/c^2))
When v1,v2 < Also Al and Jill would have to have zero mass because as v increases, m increases
m= m0/sqrt(1-(v/c)^2)
So as v>c m> infinity!

Answer 8

I think you are right, they would collide at twice the speed of light.

Their combined speed would be twice the speed of light.

Answer 9

First of all, they could not see each other because in order to do so there would have to be a means of "seeing" that would be faster than light. Their relative speeds would be additive.

Answer 10

Yes they would. [speed of light] x [2] ouch, that would hurt.