Lightspeed Vehicles

Umm, before I learn anything about the topic, what is the constraint on lightspeed vehicles?

I know we aren't even close to creating lightspeed vehicles; it takes many years to get to mars with the current technology. Going at half of light speed would still make some kind of solar empire possible, and it would certainly dare some brave souls to colonize the closer stars.


In space, there is no gravity or friction, so it seems that one could keep accelerating an object until it was very close to the speed of light (since light speed cannot be achieved by objects of mass).

However, kinetic energy is mass x veloctiy^2 , so once you are going very fast it takes enormous amounts of energy to go faster. There is surely more to this (probably relativistic), since according to that simple formula one could go faster than light (however enormous the energy cost). So, it is relativistic effects that make it impossible to go as fast as light or faster.



An interesting thought that struck me is that at light-speed time stops. So if a person got onto a light-speed spacecraft he could go anywhere and back only to find that millions of years have passed. This simple fact should also prevent anything from going faster than light. Its simple-

If you have an internal source of energy (an engine), it will stop running at the speed of light since time does not pass. The closer you get to the speed of light, the slower the engine will be running, and the less power it will be producing. Because the space around spacecraft still obeys laws of physics, it will continue exerting friction on the spacecraft until it is going slower than light-speed when the engine starts working again.

But this same fact also means the engine does not consume fuel at light speed, only to maintain near-lightspeed.

 

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Inside the space ship you wouldn't notice anything strange, but the amount of time that passes during that 1,000,000 year journey will seem to not have passed at all. Meaning that if you are burning a simple kerosene lamp on board, it will effectively stop burning for 1,000,000 years, its power dropping to near zero. On board you won't notice it, but any observer will not be able to see the flame because it is not burning (and thus not emitting photons).

Space isn't a perfect vacuum so there will always be some friction. I suppose it is negligible for solar activity, but once you go past light speed it may become more apparent.



Our rockets still only move a fraction of light speed, even with their enormous fuel tanks. What gives?



I have read a science fiction story where the method of propelling a rocket to near light speed was using an enormous battery of lasers. The lasers would have to remain stationary, while the space ship would be in the beam path. The beam would supply the energy for further acceleration.

 

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Here is another thought that struck me as interesting-
The amount of thermal radiation increases as the speed of the vehicle approaches light-speed... This is another form of breaking/friction associated with light-speed spacecraft.
Both are ideas relating relativity to thermal radiation.

1. As the vehicle is moving close to the speed of light, the blue shift continues to produce more energy than usual. This is not exactly cancelled out by the red shift, I don't think, and here is why I don't think so-
If you have a sheet of paper travelling slower than lightspeed at a temperature above the cosmic background, the two sides will be emitting close to the same amount of energy [with one side facing 'forwards' and the other 'backwards', relative to motion]. If this sheet of paper accelerates closer to the speed of light, there will be a doppler shift and the forward facing side will radiate more energy than the backwards facing side. However, the backwards facing side can at the very least radiate 0 watts while the forward facing side can at most radiate infinity. This way, the amount of energy radiate is increased close to light-speed.

2. However, due to the dilation of time, thermal radiation will also decrease. At light speed time will not be passing, and so thermal radiation should not be emitted because thermal radiation is the product of oscillating charges, which will no longer oscillate.

I don't know, but perhaps these two effects cancel each other out. Either way, it seems that planck's laws are violated because of the blueshift.. also, close to the speed of light one of sides of the sheet of paper will be radiating far more energy than the other. This in itself should contribute to a braking process since momentum of photons is dependent on frequency.

The fundamental question is- do relativistic effects disturb planck's law? Do objects emit fewer high-energy photons on the 'forward' side than low-energy photons on the 'backward' side? Is the amount of energy radiated on the two sides of a near light-speed object always the same? An object in motion tends to stay in motion??

 

thought this was interesting:

http://www.msnbc.msn.com/id/31665236/

 

Interesting. I figure faster than light spaceships will utilize both near light-speed and some kind of space time distortion technique like the Alcubierre Drive.