"The future ain't what it used to be."

Light Propolsuion



Im Sure I read Somewhere that if it were Possible to Travel through Time that it would be required to travel the same or Greater speed than Light, So I were wondering if anybody else has any rough thoughts on Light Propulsion eg... + + or - - on a Maganet will repel, Is it Possible that Something could repel Light to an almost same fashion?

Just a stored thought
Light propulsion is a fact. A measured, demonstrated and verified reality.

If you were in space, holding a flashlight, it exerts a reaction force exactly opposite the direction of the beam that WOULD propel you in that opposite direction. Very, VERY weakly. It will EVENTUALLY accelerate you to c (hyothetically) IF: you have a VERY LONG time to wait (millenia) while it gets you there, AND your batteries don't run down. :)

Seriously, it DOES work this way but the force is SO WEAK from a flashlight you better have packed a LOT of lunches.

This mode of space travel has already been proposed in several forms. The latest I'm aware of is to construct a large (several kilometers in diameter) "light sail" and "push" it with a focused laser. I believe the latest design proposes a trip to Alpha Centauri (approx. 4 light years away) for a 10 year duration, one way. (Obviously if you get ENOUGH light force going against the given mass, it will accelerate quickly.) The light sail is do-able with current technology. Unfortunately the power required for the laser is almost equivalent to the Sun itself, so along with the proposal is the idea to build several mirrors to focus the Sunlight as a source for the laser power.
Re:Re:Light Propolsuion

About the statement on focusing the sun as a source of power. This is would not do much good as the intensity at the focal point would not be any greater than exsists at the surface of the sun. For example, using a magnifying glass to focus the sun done to a point will never do more than get hot. Also since the light will never be in phase, the light will "disipate" rapidly. Laser action is not accomplished by focusing light. A laser or light amplification by stimulated emission works by increasing the population in the N2 or greater state. This is most easily accomplished by a pulsed laser(a ruby laser). The most powerful lasers to date are chemical lasers.
Re:Re:Light Propulsion

Thanks for your reply, it opens another line of thought. When you mentioned that the light from the laser is weak & the Start would be slow, I wonder if the laser light could be stored & then delivered in higher doses, if that is possible & helpful then I would imagine that it would also be possible that enough could be stored for continual feeding of the panel. Also, the page you recomended is interesting....Thanks
Re:Re:Re:Light Propolsuion

I should clarify...

I never meant to say focusing the Sun would itself provide a stronger Laser. I am aware of how lasers are produced.

The plan, (which is not my idea by the way) uses mirrors to focus the Sun as a SOLAR POWER SOURCE for the Laser generator. The laser generator required to perform the aforementioned Laser "push" on the light sail requires an enormous amount of power. The logical place to get it, is from the Sun.

I'll try to find the site that has this plan and post it for everyone's reference.

Hope that clears up my point

Thanks for your comment.
> than the speed of light? I used to think the same but...

Travelling greater than the speed of light is a common theory in science fiction but if you think about it doesn't always seem so plausible.
By travelling faster than the speed of light it would theoretically possible to over-take the beams of light emmitted from an object it would appear that the object was moving backwards, however its all relative. Once you go back (even at the same speed) you will only end up back at the object with only a small variation of time. It's sort of like thinking that crossing the international date-line actually sends you back in time. You are simply at a different point reading a relative time. This is not the true meaning of time travel.
I think that when an object hits the speed of light it will disappear to the length contraction formula...
Re:> than the speed of light? I used to think the same but...

Please explain further about how an object appears to move backward if it exceeds the spead of light. thanks
Re:> But

If you were to travel say, Backwards from an object faster than the speed of Light, Overtaking the light beams that carry the objects image, how would you see it?


Re:> than the speed of light? I used to think the same but...

If I may interject here, I think James is correct and what he is reffering to is simply the fact that if you COULD travel faster than light, you would have to consider this:

A beam of light from some source, and YOU, take off simultaneously from points in proximity at precisely the same time.

YOU however accelerate ASAP to beyond the speed of light but are able to view the light beam as is processes in a parallel path in your vicinity. As you overtake the processing beam of light, does not the leading "edge" of it appear to be receding from you? i.e. - Travelling backwards?

This brings up an intersting question? How can you see a beam of light that is now no longer reaching you?

I think this is his point, (or one of them) in illustrating the impossibility of it all.

Am I right James?
But (again)

Once you stop the original waves of light will replay themselves to your vision, ie you are seeing something that has already happened(Granted you would need a pretty powerful telescope) however you would not be able to interact.

Well travelling faster than light you would be overtaking previous, lets say, frames of motion so that when you stop the images play all over again. I suppose saying you would see them backwards was only a theoretical asumption if the person kept passing out a light wave then overtaking, then stopping, then overtaking....