This *Speed-of Light* thing - I'm still trying to get my head round it. For instance:-?

Question

Imagine that you are in the vacuum of Space. You observe a particle passing you at near to the speed of light (C).
You then observe another one passing you also at near C, but travelling in the opposite direction.
If both occurrences just happened to happen at the same time, there would be a collision; right.

1) Newton would calculate the closing velocity to be the sum of both speeds; in this case almost 2xC

2) Einstein would say 1xC (as nothing can travel faster than C)and so the Newtonian answer must be wrong.

Therefore the nagging Q is: -
Wouldn't the two particles have to "Know" that a light-speed collision is about to occur so that they can slow down sufficiently to satisfy Einstein?

Answer 1

ermm...obviously light "collides"/crosses paths all the time, constantly in fact as every light source is "emiting" photons in Every direction (unless a full cutoff shade is properly directing the light to the ground and preventing Up-light night sky polution :P Dark Sky Society shameless plug :P ).

Thing is light (photons) works confusingly as if they are both particles and waves, they pass through the double slit experiment like particles, and they pass "through" each other like waves...waves don't "collide".

And ya, light is screwwy stuff when you try to wrap your head around the "point of view" problem.

Good luck with that.

Answer 2

The observer you call "you" would indeed observe a closing speed of almost 2c (if the two particles were photons, the closing speed would be 2c exactly).

An observer riding on particle 1 would observe particle 2 approaching at nearly c.

An observer riding on particle 2 would observe particle 1 approaching at nearly c.

I learnt this stuff by reading "Basic concepts in Relativity and Early Quantum Theory" by Resnick & Halliday. The mathematics of special relativity is very easy - you only need to understand basic algebra and what a square root is! The concepts are surprising though - for example, there is no absolute time, you can make two clocks go out of synch simply by moving one of them - so you need to think imaginatively and ditch some "common sense" ideas in order to understand special relativity reasonably well. I'm not sure if anyone has fully appreciated the implications of relativity, but physicists have worked out what happens to measurements of time, mass, distance and speed, when different observers are moving relative to each other. I'm not sure if anyone has fully thought through what a "measurement of time" or a "measurement of distance" actually is.

Answer 3

You are forgetting that relativity depends on frame of reference and you are describing three: one for each particle and another for the observer. The observer has no special status. It is entirely consistent for each particle to see the other as moving at near the speed of light, while the outside observer sees two moving near the speed of light in opposite directions.

As a note, those particles are very unlikely to collide because the cross-section for a collision will be tiny at such speeds... they won't be close together long enough to collide with significant probability. This is the effect that gives rise to the "Bragg peak."

Aloha

Answer 4

No. In the frame of reference of either particle, the other particle will be moving at less than the speed of light. neither has to 'slow down' in order to have a speed less than light. The whole point of relativity is that things like velocity depend on the observer's frame of reference. There is no such thing as absolute motion. In *your* reference frame, the closing velocity will be close to 2c, and if you do the calculations of the energy of the collision, that 2c never enters the picture.

Answer 5

This question is related to "theory of relativity" and eintstein gave that concept. The particle's relative velocity would be 2C but einstein also says that no particle can reach the speed of light.


as e=mc^2
it implies that> m=e/c^2

As mass of a particle is near to infinity when a particle reaches speed of light the collision might distroy the whole world if it happens. Maybe the whole solar system.

Hence two particles can reach the speed of light and their relative speed will be near to 2C at that time With the both of their masses reaching near to infinity. It is possible.

Answer 6

Lets imagine this high speed collision is about to take place; the electromagnetic radiation is of the same wavelength for each part(they have the same mass) you have managed to alter time to "observe" the collision, you have altered your size you are now much smaller than what you are observing. the angle of incidence between the two rays is zero degrees.

The two masses meet head on. their mass is subatomic so the laws we associate with atomic level collisions are different, the collision will not result in a conversion of energy. That leaves them one option they have to bounce off each other, they have the same subatomic mass, same angle of incidence, they bounce and return the same direction they came, at the same speed.

In effect it will appear that the two parts pass through each other, but we have altered time so we can see that they actually bouncing off each other.

Answer 7

They need not know, a ferrari can travel at 200 mph lets say thats its max speed. If two ferraris travelling at 200 mph collide, does it necessitate either of the cars to slow down.

No ..... think of those two photons in a similar way. It is not even breaking einsteins law as each of them are still travelling at the speed 'c'.

Answer 8

Sorry, you're off. Time unquestionably strikes on the comparable fee, somewhat. What I propose is that in case you have been with the clock that become shifting close to gentle velocity(if it unquestionably moved at gentle velocity it would convert to uncooked means and be lost.. as a clock) it would look as though in easy terms 10 seconds had surpassed ( you will possibly in easy terms age 10 seconds ), yet on the earth your twin might age lots extra. that is unquestionably difficult to entice close the "why" of this, yet while the neatest talkin monkey that ever lived believed it(Einstein) we small brainers are purely gonna could settle for it. the unusual section is that in case you went for a journey at close to gentle velocity for say a 12 months, the human race might in all probability wreck itself on your absence( it would be like a pair thousand years later or so....).all human beings you be attentive to could have perished of previous age, whether we controlled to stay alive as a race.

Answer 9

neither of the particles is itself travelling faster than the speed of light. therefor there is no slowing down to be done.

Answer 10

a good couple of questions are
1. if u were driving a var that was moving at the speed of light and u turned on the head lights. would they shine?

2. what is the speed of heavy?