# Speed of light through moving liquid

1. Jul 14, 2010

### Grips

If light travels at a certain speed through fiber-optic cable, would the light get to its destination faster if the fiber-optic cable was actually a liquid, and the liquid had a substantial velocity in the same direction as the light?

2. Jul 14, 2010

### FawkesCa

no, becasue light is a constant, no matter the medium. you cant PUSH a photon or pull it faster, because light will always be going 300,000 km/s. i already said this once, but ill say it again.
if youre on a spaceship going around at 100,000 km/s (1/3 of C) observers on the ground will see light going 2/3 faster than your ship. but to observers on the ship, light will still be going 300,000 km/s.
hope that helped

Last edited: Jul 14, 2010
3. Jul 14, 2010

### Grips

So if the spaceship is fitted with a powerful laser-beam and is shooting at a target (enemy mother-ship that is sitting still), and I am observing from afar, will the spaceship see the laser hit the mother-ship before I would observe it hitting the mother-ship?

4. Jul 14, 2010

### Grips

You also mention that you can't push a photon or pull it faster... but you can deflect it, right?

5. Jul 14, 2010

### FawkesCa

techincally speaking...yes, since the light would have less distance to travel from the ship being hit than to where you are sitting. Brian Greene addressed this in The Elegant Universe. a light is exactly in between to people on a train is turned on. observers outside on a train would see light hit one person before the other (becasue the one person is heading toward the light while another is heading away from it), but inside each person would see the light hit them at the same time.

and yes, you can deflect it, but it wouldnt speed it up.

6. Jul 14, 2010

### Staff: Mentor

Yes. Because the speed of light (phase velocity) through the medium is less than c.

7. Jul 14, 2010

### FawkesCa

i think the point to the question however, is can it transmit information. and it cant. i think

8. Jul 14, 2010

### Grips

Yes, that is the point, is there potential improvement in the speed of information through optical cables.

9. Jul 14, 2010

### FawkesCa

of course there is room for improvemnt. just not with our current technology. but thats why we ask these questions. once we verify the Higgs field and possibly "distort" it, daily trips to Alpha Centuri may be possible.

10. Jul 14, 2010

### Staff: Mentor

Can a beam of light transmit information? Sure.
Yes. (Not practical, of course.)

11. Jul 14, 2010

### FawkesCa

that wasnt what i meant. i meant transmit information through a phase velocity faster than light.

12. Jul 14, 2010

### Glen Bartusch

unfortunately, the crackpots always make the Science Advisors go away... :(

13. Jul 14, 2010

### Staff: Mentor

You are not really specific about what you are comparing to by the word "faster". I think that FawkesCa read your question as comparing to the speed of light in vacuum and Doc Al read it as comparing to the speed of light in a stationary fluid.

The speed of light in a vacuum is faster than the speed of light in any transparent medium regardless of the motion of the medium. However, the speed of light is faster in a transparent fluid going with the flow than in the same fluid going against the flow. This was the subject of a famous experiment by Fizeau in 1851: http://en.wikipedia.org/wiki/Fizeau_experiment

14. Jul 14, 2010

### morrobay

experiment with regard to the aether, the misconception that light propagates in a medium.

15. Jul 14, 2010

### FawkesCa

thanks. that was what i was trying to say... just not as elequently.

16. Jul 15, 2010

### Staff: Mentor

Light going through a medium--such as a fiber optic cable--is quite different that light going through a vacuum, as in the Michelson-Morley experiment. Read about Fizeau's experiments, as referenced by DaleSpam.

17. Jul 15, 2010

### morrobay

Sorry for the non thinking post , and I do know the difference .