Re: Faster Than Light Travel - Reply

Donald Hosford writes:

@:) My favorite pet explanation of light, is it is a very tiny
@:) (quantum scale) object.

  Well others have answered this.  This is actually pretty well
understood already.  Light acts like a particle sometimes and like a
wave other times.  Actually all particles act like waves sometimes but
the more massive they get the less likely they are to act like waves.
Human beings act like waves but not very much because, quantum-wise,
we are extremely heavy.

@:) You can feel the sun shining on you.

  Well, you can definitely feel the heat of the Sun, but you can't
actually feel the light pressure.  Also you may have seen a
radiometer, a little glass bulb with four vanes inside that rotate
when you shine a light on them?  From what I hear that motive
principle in that case is actually heat.  The black sides of the vanes
get hot when light shines on them and heat the air next to them, which
expands and pushes on the vane.  The white sides stay cooler so the
vanes turn only in one direction.

  Light pressure is there, though, and has been used experimentally on
a few space probes.  It's never been used to actually propel a
spacecraft yet, though.  What you need is a big sheet of light
reflective material like aluminated (is that a word?) mylar.  Point
that at the Sun and the sun will push it away, pulling your spaceship
behind it.  You can also use a laser to push on the sail.

  Somebody asked why laser-propelled spaceship systems are always
depicted as having the laser on the ground - the answer is that you
can build a MUCH bigger laser on the ground.  By removing the engines
and fuel from your spacecraft you make is much, much lighter and it
can go much faster.  Plus you can use a much larger engine because you
have an entire planet to store it on.

-joachim