light potential. questions

[Dylandrako]

this is a post with several question that all have to do with the various properties of light that i simply dont know.

 

1: light travels at approximately 299,792,000 miles per second. this has been proven oven time. however what has not been proven and my first question is, is this speed determined in space where very little to no resistance is or were these measurements take on earth where there is an atmosphere that the light has to travel through and if so what are the 2 measurements for these varying light situations?

 

2: to the current knowledge of the human populous, light is the fasted thing in the universe and it is impossible to travel faster than light. so my second question is has there already been a way to "harness" light and use it as a means of propulsion?

 

3: light is, like radio frequencies, a wave. we have been able to reproduce light for several hundreds of thousands of years using various means. my 3rd question is, is there a way to potentially speed up light to make it travel faster and further that it already does?

 

4: i remember when i was younger that light could be altered to change its course through water and other objects. my 4th question is, how exactly does this work, is it the light itself being pulled or pushed or is it the particles that the light is traveling through that is getting moved?

 

thanks for your time.

[John Cuthber]

" light travels at approximately 299,792,000 miles per second"

No, that's the speed in metres per second.

"is this speed determined in space where very little to no resistance is or were these measurements take on earth where there is an atmosphere that the light has to travel through and if so what are the 2 measurements for these varying light situations?"

Both have been measured it travels 1.000293 times slower in air.

 

"as there already been a way to "harness" light and use it as a means of propulsion? "

sort of. It's not been used much (if at all)

https://en.wikipedia.org/wiki/Solar_sail

 

"is there a way to potentially speed up light to make it travel faster and further that it already does?"

It already has an infinite range (unless it hits something, so "further" isn't an option and, as far as we know, there's no way to make it faster.

 

If I understand your last point correctly, it's related to the first (though I realise that's not obvious).

Does this help?

https://en.wikipedia.org/wiki/Refraction

[Dylandrako]

Thank you.

[swansont]

has there already been a way to "harness" light and use it as a means of propulsion?

 

Light has momentum, so reflection or emission will impart an impulse. It's small, though. One of the most dramatic uses is that you can slow atoms down by scattering photons off of them. Atoms are very light, and some transitions can scatter millions of photons per second, so you can get accelerations of hundreds of g's

[Dylandrako]

Light has momentum, so reflection or emission will impart an impulse. It's small, though. One of the most dramatic uses is that you can slow atoms down by scattering photons off of them. Atoms are very light, and some transitions can scatter millions of photons per second, so you can get accelerations of hundreds of g's

What exactly do you mean by transitions?

[swansont]

What exactly do you mean by transitions?

 

An excitation or de-excitation. And electron going to a different energy state in an atom, via absorption or emission of a photon. In Rb, for example, near-resonant light can cause the transition at 780 nm roughly every 100 ns. That's ten million transitions a second.

[Enthalpy]

Solar sails have been used - not very frequently...

 

Most were demonstrators just trying to unfurl the huge area needed to produce a significant thrust, and most failed to unfurl. Presently, Ikarus uses its propulsion by solar sail. Though, the size and mass make it still a demonstrator.

 

More ideas are needed, first to unfurl reliably a sail as hiuge and light as we know to produce presently

http://www.scienceforums.net/topic/78265-solar-sails-bits-and-pieces/

and then to produce sails even bigger and lighter than today's 7.5µm thin polymer films.

 

Mankind needs this technology for many missions impossible or inconvenient by other means: overfly the poles of the Sun, go near to it, change several times the orbit radius and inclination, put a payload in Mercury orbit... Presently, this effort is too small.

 

A very frequent use presently isn't exactly propulsion, but serves to keep the orientation of geosynchronous satellites. Two tilted panels at the ends of the solar arrays give for free a torque that passively keeps the panels towards the Sun, and the panel's motors at the satellite then align the body towards the Earth. This elegant method saves much fluid otherwise used to keep the orientation.