Transparent Filament
Transparent Filament
Urgent question on physics!!!10 points to intelligent answer!!?
We know that ,
If I were travelling on a train at 75kmph holding a loaded gun whose’ bullet speed is 75kmph and I shot it in the direction of my motion,the resultant speed of the bullet respective to ground will be 150kmph and 75kmph relative to the train.
So,does that happen to light speed?
ie,if I were in space where light speed is exactly 299452798m/s,travelling on a spaceship at some mere speed of 1000m/s holding a torch with no transparent fibre in front of the incandescent filament and I switch on the torch in the direction of my motion ,would the speed of the emitted photon alter or not??
Just to add a little. One of the foundations of relativity is that the speed of light in vacuum is the same for all observers regardless of their state of relative motion. Now we mere human beings are used to things on a small scale and at very tiny speeds so what you said about the bullet on the train seems reasonable and we think that maybe the same thing would happen with light. But not so. your calculation for the speed of the bullet relative to the ground is in error. The actual formula for adding velocities u and v (c being the speed of light) is:
V = [u + v]/[1 + u*v/c^2]
Now if u and v are very much smaller than c then u*v/c^2 will be very small and we can ignore it.
So in our human way of looking at things, it appears that speeds can simply be added together (as we are used to thinking):
V = u + v
Let us look at what this means for the bullet on the train.
The speed of light is about 3×10^5 km/s
Speed of the bullet and train is 75 km/h = 0.020833333 km/s
The ratios u/c and v/c = 6.94444E-08
And u*v/c^2 = 4.82253E-15
So the actual speed of the bullet relative to the ground is (I can use km/h here since u*v/c^2 is dimensionless).
V = [75 + 75]/[1 + 4.82253E-15]
V = 149.9999999999999
Very close to 150 but not exactly
Now go back to the velocty addition formula and take v to be the speed of light (we have a flashlight, torch, whatever).
V = [u + c]/[1 + u*c/c^2] = [u + c]/[1 + u/c]
V = c*[u + c]/[u + c] = c
So, if one of the velocities is the speed of light, then no matter what the speed of the light emitting device, the observed speed will always be the speed of light. One of the ways this has been confirmed is to accelerate elementary particles to very near the speed of light and then have them emit a photon. The speed of the photon is always 3×10^5 km/s. OK?
NOTE to awsheeeit. You are talking about something different. To a third person two objects can be seen as moving away from each other at faster than the speed of light. That is perfectly fine and reasonable. But if each of these guys shines a flashlight, no matter what direction, the third person will measure the speed of the photons from the flashlight as being 3×10^5 km/s. As einstein pointed out, it is the relative velocities of things that are important. Now to the people on the space ships moving away from each other, say at 3/4 the speed of light, they would see the other as moving away at:
V = [3/4 + 3/4]/[1 + (3/4)*(3/4)] = [6/4]/[1 + 9/16]
V = [6/4]/[25/16] = 24/25
at 24/25 the speed of light (just a little less than the speed of light). But the third guy would see the distance between them increasing at a rate of 3/4 + 3/4 = 6/4 or 3/2 the speed of light. You see distances between things can increase at over the speed of light but material objects can not move at or over the speed of light. It is just one of those peculiar things about the universe we live in.
If you want something odd to think about try this. Suppose there is a bomb guy who sets off a photon bomb that results in a spherical shell of light expanding outward from where he sets off the bomb (he is located at the point of detonation). Now common sense would tell you that he would see a shell of light expanding outwards in all directions from his location and that is right. Now suppose rocket guy comes flying along at 0.999 the speed of light and that he is passing right by bomb guy when the bomb is set off. What do you think rocket guy will see? Think abut it a little. He will see exactly what bomb guy sees. A spherical shell of light expanding outwards but from a point that is centered on and moving along with his rocket. And this is because light has the same speed to everyone.
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