Two beams of light from opposite directions meet...at what speed?

Answer 1

The beams will travel with the speed of light in vacuum(air), but if the medium is something else, then the speed of light will decrease.

Answer 2

If you are watching, you see both beams approaching the meeting point at the speed of light (in whatever medium it is), so the closing speed of the two beams is twice the speed of light, as far as you are concerned. Although Einstein said that nothing can travel faster than light, that does not prevent two things closing at a higher speed in the eyes of a detached observer, as no "thing" is actually travelling faster than light. However, when it comes to working out how each light beam experiences the "collision", of course relativity has to be taken into account. If you were driving at (almost) the speed of light at night, then light from the headlamps of a car coming the other way would, as far as you are concerned, reach your eyes at exactly the speed of light, not at (almost) twice the speed of light.

Answer 3

Interesting question. Put another way: From the "point of view" of Beam A, how fast is Beam B travelling? Hard to answer, because no time (at all) passes from the point of view of a beam of light; so the concept of "speed" is meaningless.

If you're willing to drop the speed a little, it's more meaningful. Say two spaceships approach each other, each going at 99% of the speed of light (as seen by some 3rd party). At what speed do they meet?

The answer: they meet at about 99.995% of the speed of light.

When you're adding very high velocities, you can't use the usual formula "V1 + V2". You have to use this formula instead:

(V1 + V2)/(1 + V1•V2/c²)

If you analyze that formula, you'll see that the answer is always less than c, provided that V1 and V2 are both less than c.

The formula actually works perfectly well for slow velocities too; but in that case, the answer is almost exactly the same as "V1 + V2".

Answer 4

We cannot measure the speed of light other than C what ever is the observer’s speed.

The speed of light in any direction is a constant and is independent of the motion of observer.

You cannot measure the speed relative to an observer’s speed.

The result is you cannot move with the speed of light.

However if your speed is less than C, you cannot measure the speed of light relative to your speed and you will measure it again as a constant.

You have to correct your length time and mass so as to measure the speed as C and only C.

Answer 5

The speed of light is 186,282.397 miles per second in a vacuum, so it seems natural they should collide at double that: 372,564.794 miles per second.
However, Einstein's theory of relativity states that nothing can moves faster than the speed of light (so this violates that) and that the speed of light is the same for everyone no matter how fast you are travelling. So how can this be?
Our good friend Einstein also answers this for us. When something is moving at very high speeds time appears to slow down according to the point of view of an observer. He even gave us a nice equation based on Pythagorus' theorum:
Time taken to travel certain distance = Time passing on moving object / sqroot(1 - speed of moving object squared/speed of light squared).
So this means that from the point of view of one photon, time is passing normally for it, but time is completely stopped on the other photon so it is travelling at 186,000 miles per infinity, i.e. not moving. The same applies from the point of view of the other photon. So from the point of view of either, the speed is exactly the speed of light.
These laws only apply to speeds observed from one of the photons or any of the other moving objects.
From the point of view of someone who is "still" or moving comparitively slowly, the collision would look like twice the speed of light, as it is simply the addition of the speeds of the light beams' speeds, not the speed of any one beam. For example if I walk towards a light beam, I would experience the collision as the speed of light plus my speed only a teeny weeny bit less because of the speed at which I was travelling towards it means it looks the tiniest bit slower.
Hope this helps.

Answer 6

the previous answer is actual. It sounds unusual, however the perceived velocity of an merchandise relies upon on what reference physique you're watching the article from. A table certain observer will see each and every muon shifting at 0.9c, yet in the reference physique of one of the the muons, the different one would be shifting at 0.9944751c as Helene pronounced.

Answer 7

the speed of light

Answer 8

As seen by any observer, the leftward ray travels at c and the rightward ray travels at c. So the distance between them closes at 2c.

But neither body itself ever travels at 2c, or at any speed greater than c.

Edit: Despite the thumbs-down, this is the correct response. Lots of people don't understand relativity, even though they might think they do. There is also NO "point of view" -- NONE!!! --- of the photon; no observer can ever observe a photon at rest. Anyone who claims to tell you about what the collision looks like to a photon is incorrect, because no observer can ever be "on" or traveling with the photon.

Answer 9

186,000 miles per second.

The speed of light is constant, and therefore you do not double the speed of two beams of light that are approaching each other.

Answer 10

They don't meet. They pass through each other at c. I know that's hard to understand, but relativity gets weird at that speed.