Relativity and a Solar Sail

I may be incorrect in saying this but I think that a spacecraft powered by a solar sail is flying on the stream of matter coming from a star called its solar wind and not actually be propelled by the light rays. Light has an infintesemal pressure meaning it could take years for starlight to accelerate even a negligible mass to a small velocity. I think you may need to revise the experiment to take this into account. Keep in mind I am not arguing the fact of the speed of c in a vacuum or any of the other constraints. I am questioning whether or not such a device could even work.

Mark Vitrone

If I am reading this question right the only important fact is the acceleration rate and not the power source. The question then is how far can the velcity be increased in a constant acceleration mode. Is this what you are asking or is the power process of importance?

Light is a wave within a medium. In order for the wave to have a push effect, the particles of the medium must possess the property of mass. Therefore your vehicle is traveling through the medium and the medium will have resistance to travel if a wave within it can push. You cannot decree that initial acceleration will be 1 gravity. The proper answer would come from actual experimentation.

Gregg Wilson

[Mac]
Without involving solar wind, light pressure and so on, your question reduces to:
"If a body is moving in a straight line with a constant acceleration for infinitely long time, what is the speed limit it could reach?"

The answer is, according to SR:
- the acceleration of a body depends on the force acting on it and its mass
- the instant speed of the body is the acceleration by the time elapsed
- the mass of the body increases with the speed, approaching infinity when the speed approaches c
- to maintain a constant acceleration, the force must increase too, approaching infinity

The mass increase with speed is confirmed beyond any doubt. No accelerator of elementary particles can work without taking into account this effect.

You can figure out by yourself what would be the speed limit for the body.

[Gregg]
The light medium, or ether, is somehow obsolete concept. It is known that the light is transverse wave - the classical dynamics states that such waves can exist only in solids. Considering the magnitude of the lightspeed, the ether must be a supersolid. Yet it has no detectable resistance effect on any moving mass body. This is the simpliest objection to the ether theory. Many experiments have been made to prove or disprove the ether existance. There are still debates about this, but the largely accepted opinion is the ether does not exist.

To learn how the light transports energy and impulse, please, refer to Poynting's work.

Hal, The limit of speed is not resolved by your explaination because the speed of light can't be reached within your perimeters. So, what happens when the rate of acceleration is maintained? I know it can't be maintained with your limits but what happens to the force when it can no longer increase the speed?

[Jim]
Nothing happens to the force, as it is a cause in this example, not effect. The acceleration becomes simply vanishingly small, but not zero. In prevision of your next objection - no matter how long you wait, you will never reach c. Let me give you an example - suppose you want to know the EXACT value of <img src=icon_pi.gif border=0 align=middle>. To achieve this, you have to calculate ALL digits behind the decimal point. It is known, that the sequence is infinite and never repeats. No matter how long you calculate - there is allways something that remains. It gets smaller and smaller at each step, but NEVER ZERO.