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Killer slug
Sep12-07, 01:24 PM
is it possible to catch light particals and have them push you along in some kind of space ship, and if you could would it be the speed of light
Morga
Sep12-07, 02:25 PM
No, but apparently swans make good propulsion for early space craft. Light particles or "Photons" are packets of energy that you can't catch. If you were to try and "grab" one with your hand and catch a ride you may be disappointed. Traveling at light speed is impossible for such a large mass as yourself, but seriously swans all the way...
russ_watters
Sep12-07, 03:08 PM
Actually, every time a photon hits you and you absorb it, you have "caught" it. And when you do, it transfers its momentum to you. So yes, you could propel a spaceship that way (actually, reflecting them is better...), but you'd need an enormous solar sail to catch enough photons to be useful. And no, you could never reach the speed of light. You could get arbitrarily close to it, though.

Anyway, look here: http://en.wikipedia.org/wiki/Solar_sail
HallsofIvy
Sep12-07, 03:18 PM
"swans"? Is that a technical term.

"Light Sails" have long been a staple of science fiction. I don't know if NASA is doing any research but it would certainly been possible.
jobyts
Sep12-07, 04:40 PM
Why is the speed of light limited to 3*10^8 m/s? What is blocking it from going faster than that?
lanman
Sep12-07, 07:55 PM
The speed of lights is an absolute maximum to speed, because it is the rate at which time flows. The digits it is expressed as are based on our units of measurement.
russ_watters
Sep12-07, 09:43 PM
The speed of light is not the rate at which time flows.

The speed of light is a dictated by the permeability and permittivity of space, as a consequence of Maxwell's equations.
prasannapakkiam
Sep13-07, 05:07 AM
Well Watters has explained it clearly...
lanman
Sep13-07, 07:58 AM
it is the rate at which time flows.

Not sure where I heard that...
genneth
Sep13-07, 08:10 AM
Not sure where I heard that...

In a sense, c is the conversion rate between space and time. In many theoretical papers, "natural" units are adopted, where c = 1, \hbar = 1, etc. So that mass, length, time are all inter-convertible without changing the number.
jobyts
Sep13-07, 05:07 PM
The speed of light is a dictated by the permeability and permittivity of space, as a consequence of Maxwell's equations.

From the speed of light, did we derive the permeability and permittivity of space, or is it the other way?

Can anyone explain permeability and permittivity of space in simpler terms? I googled those keywords, but gave me pages with lots of greek symbols, which I used to understand in the past, for a short period in my life.
Loren Booda
Sep13-07, 06:44 PM
I would think that the definition of c, the speed of light, would rely somewhat on the Higgs field - that which endows mass upon particles. Massless particles travel at the speed of light, massive ones at less than c.
russ_watters
Sep13-07, 10:15 PM
From the speed of light, did we derive the permeability and permittivity of space, or is it the other way? If I understand the history correctly, I think they were measured about the same time the first accurate measurements of the speed of light were being taken (by Michelson). So the speed of light was separately measured and calculated and found to be the same value. Can anyone explain permeability and permittivity of space in simpler terms? I googled those keywords, but gave me pages with lots of greek symbols, which I used to understand in the past, for a short period in my life. Basically, the resistance to passing magnetic and electric fields.