What will be the speed of light?

[Sanket Karnik]

Hi friends! I was reading a book in which it was mentioned that the speed of light does not changes if we move towards its source or move away from it. Now the question comes in my mind as follows;
suppose a space shuttle is moving in space with velocity almost equal to that of light. It has two headlights. what aill be the speed of light from those headlights? will speed of space shuttle get added to it? if not then what will be the distance traveled by the light coming from the headlights?

 

[Ryan_m_b]

Hi friends! I was reading a book in which it was mentioned that the speed of light does not changes if we move towards its source or move away from it. Now the question comes in my mind as follows;
suppose a space shuttle is moving in space with velocity almost equal to that of light. It has two headlights. what aill be the speed of light from those headlights? will speed of space shuttle get added to it? if not then what will be the distance traveled by the light coming from the headlights?

Welcome to PF! The speed of light is always the same, hence being a constant.

If you were traveling at .9C (thats 90% of the speed of light) and you turned on your headlights the light would travel at the same speed regardless of how fast you were going.

IIRC this is covered by special relativity

 

[0xDEADBEEF]

The true formula how to add speeds is this one:

$$v_3=\frac{v_1+v_2}{1+\frac{v_1v_2}{c^2}}$$

You see that the lower part is normally (for normal human speeds) very close to one and this is why people thought for a long time that velocities simply add.

 

[DaveC426913]

suppose a space shuttle is moving in space with velocity almost equal to that of light. It has two headlights. what aill be the speed of light from those headlights? will speed of space shuttle get added to it? if not then what will be the distance traveled by the light coming from the headlights?

The head lights will send out rays of light at the speed of light as measured from inside the space shuttle. They will also be measured as the speed of light from outside, say, on Earth.

How? Time dilation.

(With very round numbers. No time to get exact.)
The shuttle is moving at a significant fraction of c, therefore its occupants are time-dilated. In the time the light travels one light second, and the space shuttle has traveled .9 light seconds, the shuttle's occupants have only experienced one tenth of a second, so they should measure the light as having traveled only 1/10 of a light second. After a full second they will have seen it travel a full light second beyond their nose.

 

[mishrashubham]

At the risk of sounding like a broken record, I would say that this question should be added to the FAQ (I have seen at least three threads in the past two weeks asking a similar question about exceeding the speed of light).

 

[phinds]

At the risk of sounding like a broken record, I would say that this question should be added to the FAQ (I have seen at least three threads in the past two weeks asking a similar question about exceeding the speed of light).

I second that and would add that there ought to be several such items in the thread and label it something like INCREDIBLY BASIC COSMOLOGICAL CONCEPTS