# Faster than light

1. Feb 9, 2004

### Blueshift5

Hello out there!
This is my first post so I am ready for lots of answers. I have heard from several sources that astronomers studying the area around black holes have discovered particals being shot away faster than the speed of light. I have always understood that nothing can go faster than light, but maybe I am not up to date with the exciting world of changing physics. Thanks.

2. Feb 9, 2004

### chroot

Staff Emeritus
No one has ever observed anything moving faster than light to date. Can you provide a reference to where you read this?

- Warren

3. Feb 9, 2004

### Blueshift5

My science teacher briefly mentioned it in class and I think I might have seen it at Astronomy.com. Of course when he said this I had to tell him it was impossible at the moment, but he seemed really sure about himself, so since this went against my current understanding. I thought I would post and see if anyone knew for sure if this was ever discovered. Thanks.

4. Feb 9, 2004

### chroot

Staff Emeritus
Well, your science teacher is not correct. He may be referring to the so-called "superluminal quasar jets," but they are not really going faster than light -- it's just a geometric illusion.

- Warren

5. Feb 9, 2004

### Blueshift5

Thank you. I will let him know cause he wanted me to prove that it was impossible .

6. Feb 9, 2004

### chroot

Staff Emeritus
You cannot prove that it is impossible. Scientific theories do not work that way. All you can do is provide a preponderance of evidence in favor of a theory -- but no theory is ever "proven."

- Warren

7. Feb 9, 2004

### Blueshift5

Another to add to my arsenal.

8. Feb 10, 2004

### Chi Meson

I just wanted to interject an example of how a "faster than light" illusion can be created:

Think of a pair of scissors. Open them, then as you close them notice the point at which the two blades meet. See how it appears to be a point that moves? But there is nothing that is actually moving as fast as the illusion of this "point of contact."

I can't remember if this is directly related to the "superluminous quasar jets," but I know it has been used to explain some astronomical "faster than light" observations.

9. Feb 10, 2004

### rocketcity

I would say the easiest way to 'prove' to your teacher that matter cannot travel faster than light would be to point out that the relativistic energy of a particle is

$$E = \gamma*m*c^2$$

where

$$\gamma = 1/(1-v^2/c^2)^{0.5}$$

The Taylor series expansion for this expression can be approximated by, for low speeds, E = mc^2 + (1/2)mv^2 -- where the second term is called the kinetic energy of a particle and the first term is Einstein's 'magical' energy. In reality, both terms together form an approximation of the total "kinetic" (i.e., 'because of motion') energy of the particle.

Using the real equation for E, though, you'd never make the mistake of thinking that something massive could ever acquire a speed of greater than c. Just plug in v = c and see how much energy it would take to make a particle of (rest) mass m go that fast: you get mc^2 divided by zero, which is infinity.

There's not enough energy in a black hole to make even one nucleon exceed the speed of light, let alone continuous streams of superluminal particles.

But, as others have pointed out, this 'proof' is based on the assumption that the relativistic equations are valid. A good scientist would never claim to be sure about *anything* in the real world--there's always the chance that the current theory will be refined or even refuted.

P

moderator edit: fixed TeX

Last edited by a moderator: Feb 10, 2004
10. Feb 10, 2004

### rocketcity

[removed LaTex gripe]

Last edited: Feb 11, 2004