# Is a photonic-boom possible?

1. Dec 8, 2003

### matthewfullhart

is a "photonic-boom" possible?

ok, so I'm sitting in class one day, and my physics teacher is talking about light... and since we had just finished up a section on sound, I was wondering whether there is such an effect as a "light-boom"

that is to say, if we were to have a spaceship that could go exactly at the speed of light, and we attached a flashlight to the front of the ship, could we not cause the buildup of light rays much the same as we can with sound and airplanes? if so, couldn't we make a gigantic weapon with this? let's say that there's life on a planet near alpha centauri, and we go to war with them... couldn't we just send out a ship with a big flashlight on the front, cause the buildup of light particles over the span of 4.3 years, and then decelerate just before hitting the planet? 4.3 years of light would definitely do some amount of damage to their planet, even if it's just blinding everyone on the surface...

I asked my teacher this, and he said something to the effect of "no, because of time dialation." I realize his point, but that makes me wonder how the red shift works, if this effect doesn't...

If anyone knows why this can/can't occur, could you please tell me? it's been bugging me.

2. Dec 8, 2003

### HallsofIvy

A "buildup" relative to what? In any case, the speed of light relative to any reference is the speed of light. If you were standing on the bridge of such a space ship (I'm going to assume moving at 99.9% the speed of light relative to a given planet. If you say "moving at the speed of light" you are rejecting relativity and there is no way to answer your question.) you would see the light rays moving away from you at speed c. If you were standing on that planet watching the ship go by, you would see the light rays moving away from it at speed c. No buildup.

3. Dec 8, 2003

### lethe

the electromagnetic analogue of the sonic boom does indeed occur. it is called Čerenkov radiation.

Last edited: Dec 8, 2003
4. Dec 8, 2003

### NateTG

It's impractical (but possible) to create a light shockwave. There are several different methods for doing this.

The method you describe is a bit silly because it would be easier, more efficient, and more damaging to simply accelerate a projectile and let it run into the planet.

Shining a light forward, is inefficient because light loses intensity with the distance cubed, so it's better to keep the projectile solid so that all of the energy in the projectile can be used.

5. Dec 8, 2003

### mathman

There is a phenomenom called Cerenekov radiation, which is caused by particles entering a medium, travelling faster than the speed of light of the medium. The result is a radiation pattern similar to supersonic shock waves.