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Michael81
2009-May-15, 03:52 AM
Ok, I was listening to your questions show for April 30 and had a question about one of your answers. The question that you answered was about turning a flashlight on while going to speed of light. Pamela said that if you could go the speed of light and if you could turn the flashlight on while going to speed of light that the flashlight would just sit there and be a flashlight and no light would come out. My question is if we take the same situation of 'ifs' by flying through space at light speed and turning on a flashlight while going the speed of light and taking pamela's answer that the flashlight would just sit there and do nothing then since it is not giving off any light, and therefore using it energy, would the batteries theoretically last forever since they weren't being used? and if they would die where would the energy go?

I am thinking that the light would still be leaving the flashlight but you in the spacecraft couldn't see it because you were moving just as fast as the light coming out of it, but again if the flashlight itself is traveling just as fast as the light trying to come out of itself then would the energy just continue the loop back into the battery without expending any of it into another form...

Fazor
2009-May-15, 01:57 PM
I'm surprised there's not an answer to this yet. But the answer you described goes against my understanding of light.

Disclaimer: I'm probably among the least qualified people 'round these parts to answer this.

But my understanding is that, regardless of the speed of the object giving off light, the light will travel at the speed of light relative to the observer. Thus, you on your light-speed ship would still see the light as normal, and an outside observer would see the light traveling at the speed of light as well (not the speed of light + the speed of light).

Granted, an outside observer would see both ship and light at the same speed, thus the light would likely be obstructed by the ship.

If nothing else, maybe my post will help draw the attention of someone who can answer better than I did. ;)

robross
2009-May-15, 10:50 PM
I'm surprised there's not an answer to this yet. But the answer you described goes against my understanding of light.

Disclaimer: I'm probably among the least qualified people 'round these parts to answer this.

But my understanding is that, regardless of the speed of the object giving off light, the light will travel at the speed of light relative to the observer. Thus, you on your light-speed ship would still see the light as normal, and an outside observer would see the light traveling at the speed of light as well (not the speed of light + the speed of light).

Granted, an outside observer would see both ship and light at the same speed, thus the light would likely be obstructed by the ship.

If nothing else, maybe my post will help draw the attention of someone who can answer better than I did. ;)

The problem with some of these thought experiments is that people make assumptions about moving at the speed of light without dealing with some of the repercussions of those assumptions. In our universe, matter cannot travel at the speed of light. So just thinking up a thought experiment that starts "say you were in a spaceship going at the speed of light" is already fraught with real problems. They mentioned the issue with *time*. At c, you would experience NO time. Thus, you could not do anything, like turn on a flashlight. Traveling at very close to the speed of light makes your thought experiment well-behaved again, and you can do things like turn on a flashlight and watch the light from it travel at the speed of light.

Rob

Empyre
2009-May-16, 02:40 AM
What if the flashlight was already on when you reached the speed of light? Well, the flashlight would also experience no time, and thus give off no light.