# Speed of light

1. Sep 6, 2007

### Swatje

This might be a stupid question, but I've been thinking about it.

Let's say, we make a visit to CERN particle accelerator... They accelerate a particle (or a football) to about 298 thousand km/s. (c = 300 thousand rounded). And then I accelerate a particle, or something else, to about 3000 km/s. And at the exact same moment, they move in opposite direction, so their relative speed is faster than 300 thousand km/s.

Is this possible?

Sorry if it's a stupid question...

Francis.

2. Sep 6, 2007

### neutrino

If you add them using the rules of Galilean relativity, then you will get answer that suggests the particle should be travelling at a speed greater than c. But it is observed that the rules of Galilean relativity does not work at speeds close to c.*

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel.html#c1

*Actually, the Einstein velocity-composition rule gives the 'right' answer in all cases, but at low speeds, the differences between Galilean and Einsteinian are negligible.

3. Sep 6, 2007

### Swatje

Wow thanks alot for that website!