# The light passing lane

1. Sep 20, 2014

### David Cate

Here is the setup. We have a laser (supplement any type here) that constantly beams information packets in sequential order. If that beam was suddenly bounced off of a FORWARD moving mirror, traveling 7 times the speed of sound, would the protons, light waves and or information packets overtake the original set initially projected???? ie. Would 1111 2222 3333 4444 5555 turn into 1111 2222 5555 4444 3333 ??

2. Sep 20, 2014

### Orodruin

Staff Emeritus
It is not really clear to me what your setup looks like, which direction do you define as "forward" and who is receiving the signals? Typically, in one dimension, you will not be able to change the order of pulses by just bouncing off different mirrors regardless of how they move. You can just make them arrive with longer or shorter intervals in between just as you can red or blue shift the light.

3. Sep 20, 2014

### Staff: Mentor

Protons? Do you mean photons?

There is no way to overtake light in vacuum. I don't understand how your signal would bounce of a mirror that is slower than those photons, but all the mirror could do is change the frequency and direction of the light, not the speed.

4. Sep 20, 2014

### Staff: Mentor

No, they would not over take the previous light since it all moves at the same speed.

5. Sep 20, 2014

### David Cate

Would secondary information ever overtake the first transmissions, even if mirrors were traveling toward the laser at a much faster speed? If a blue shift occurred, would it slow down the secondary packet transmission speed? I'm just find it difficult grasping a constant under these variables .... affecting both waves and particles. (see attachment)

6. Sep 20, 2014

### David Cate

mmm what if the mirrors were replaced with a reflective magnetic field ??

7. Sep 21, 2014

### Orodruin

Staff Emeritus
First off, the speed of sound is not a good reference as it would be different in different materials. In addition, the speed of sound is very slow compared to the speed of light, which means that the light would be red/blue shifted by a small amount only.

In fact, it is a relatively simple exercise to figure out that you cannot change the order of the signals in this way. All you need to do is to ask and answer the following questions: When does a given light pulse hit the mirror? Based on this, when does it reach the observer? What you need to apply is just basic kinematics and the fact that the speed of light is constant and equal to c.

8. Sep 21, 2014

### Staff: Mentor

The original poster's question has been answered.

9. Sep 21, 2014

### Staff: Mentor

I already answered this. No. The speed of light is c regardless of any reflection or Doppler shift.