Just a passing thought; if you put a flashlight in space and turned it on, would it speed up because of the light it emmits since light has mass?

And if it does, then what stops it from surpassing the speed of light? That was a concept I did not understand. It makes sense that if you had enough fuel, then a rocket could just go faster and faster until it runs out of fuel. Why would it suddenly stop going faster when it reaches the speed of light?

Originally posted by WindWip
And if it does, then what stops it from surpassing the speed of light? That was a concept I did not understand. It makes sense that if you had enough fuel, then a rocket could just go faster and faster until it runs out of fuel. Why would it suddenly stop going faster when it reaches the speed of light?
The answer is surprisinly simple and, in fact, you already know it. It's Einstein's famous equation, e=mc². e is energy, m is mass, and c is the speed of light, which is a constant. If you know basic algebra, it would make sense that as e increases, m must increase as well. As m gets bigger and bigger, the energy required for m increases as well. As we approach the speed of light, m approaches infinity. So does e! So it would take an infinite amount of energy to go the speed of light.

And I don't think photons have mass.

Originally posted by WindWip
Just a passing thought; if you put a flashlight in space and turned it on, would it speed up because of the light it emmits since light has mass?

Theoretically yes, since light does have mass, the flashlight would begin to accelerate but the acceleration would be incredibly small and would likely be offset by even the slightest gravitational influences. In an absolute vacuum however, you would see some acceleration.

And if it does, then what stops it from surpassing the speed of light?

Well, the batteries would die of course!

Sorry...couldn't resist.

That was a concept I did not understand. It makes sense that if you had enough fuel, then a rocket could just go faster and faster until it runs out of fuel. Why would it suddenly stop going faster when it reaches the speed of light?

Don't feel bad about not understanding. Nobody does understand what happens to objects as they approach the speed of light. Einstein theorized about it but spent the last years of his life trying to improve upon his theories to answer some of these questions.

Part of the problem is because a stationary observer, watching an object traveling that fast, gets a distorted view of events. Another part of the problem is terminology. We are using our limited senses, and terminology based on those senses, to describe phenomena that are outside our ability to understand, much less describe with any accuracy.

Einsteins theories say that the speed of light is constant, and that the speed of light is an upper limit to how fast objects can travel. I believe that it is true as far as it goes. Objects are limited to the speed of light within the four dimensions we can observe, but I see no reason to believe that this speed limit holds true outside of these four dimensions. As Borg said, Einstein's equation E=mc^2 suggests that it would take an infinite amount of energy to accelerate beyond the speed of light, but is that a limitation of nature, or is that a limitation of our mathematics?

I had a physics teacher pose the following problem once:

"How would you put a 10-foot long pole into a 5-foot long box, without bending the pole?"

The answer is, you would move the pole into the box at something approaching the speed of light. According to Einsteins theories, as the pole approaches the speed of light, it will get shorter. That is, it would appear shorter to someone standing next to the box. All motion is relative to the observer. The corollary would seem to be that if you were riding on the pole, the box would appear longer.

Let's try it with your rocket flashlight. You are standing on the moon while this flashlight, with me riding on it, flys by approaching the speed of light (C). To you the flashlight is getting shorter and shorter, until it hits (C) and now it is infinitely short, i.e. it has no dimension of length anymore. Also, time slows down on the flashlight as I approach (C), relative to you on the moon, so when the flashlight hits (C), time no longer flows at all for me on the flashlight, from your vantage point on the moon. You, on the moon, would see me almost hitting (C) for an infinite amount of time, but never quite getting there. I, on the flashlight, would see you grow older and die in the blink of an eye and eventually when I hit (C) time would seem to fly by at an infinite speed.

What does this mean? I don't know, and I'm not sure that we can know such things. It is difficult, if not impossible, to describe events that happen between two objects that lose all common frames of reference. It would appear that if you were to somehow exceed (C), you would pass out of the four dimensions that we can perceive and into a different realm altogether. What that realm would be is beyond my ability to comprehend, but I do know that for an oberver on the moon, watching me fly past and hitting (C), if they were to try to describe what happened to me, the terms where and when, would have no meaning any longer. I would be outside of the dimensions described by those terms. I don't know if it's possible to exceed the speed of light, but I do think we have not yet achieved the ability to understand what might happen if you did. Perhaps we never will.

Originally posted by BorgHunter
And I don't think photons have mass.

Well, I thought they did, since the Michaelson-morley experiment proved that light was affected by gravity. It turns out that physicists generally consider photons to be "massless", but they do have energy. Which in some cases is equivalent to having mass. Another problem with terminology I think. See link.

Let it soak in that the above formula contains the speed of light squared.
Not the speed of light.
If your spacecraft traveling at the speed of light had headlights would they shine ahead at the speed of light or not .
In the above case the craft speed of light would be the zero point and the lights would shine foreward.
To surpass the speed of light you must first reach this zero point.
Surpassing the speed of light will only be accomplished with the projection of human thought. My personal experiments lead me to this conclusion.
I do not personally believe it will be accomplished by mechanical means.
When Einstein came up with his theories he did not take into account molecular vibration within the mass.I have found no papers of a study on this.For simple example look thru a stopped fan in an area where a blade is blocking your view. Turn on the fan and the faster the blades turn they seem to disappear no longer blocking your view. You are looking thru the space between the blades.
The same would happen when the molecules in a solid object began to become excited and vibrate at the speed of light. You would see thru the space between the molecules. Hence destroying the theory that two solid objects cannot occupy the same space at the same time.

I think you meant to ask if you were in space traveling at the speed of light and you turned on a flashlight what would happen.

Well, I thought they did, since the Michaelson-morley experiment proved that light was affected by gravity. It turns out that physicists generally consider photons to be "massless", but they do have energy.
They are energy. They bend do to gravity, it is due to the mass of an object. The mass of the object puts a "dent" in the space/time around it, curving it. Since, light travels within our space/time it also has to bend with it. That is why it bends. "Gravity" is a relative term that applies very little anymore.

I think you meant to ask if you were in space traveling at the speed of light and you turned on a flashlight what would happen.
Theoretically it would move with you. But I thought that there had been some research into the area that lignt isn't constant and it slows and speeds depending on where it is, such as slowing down near massive objects. Thus it should be able to move faster with enough energy and less mass. I'd only heard things about that, not any proof though.