Perfectly reflective surfaces

I was thinking, If somehow we could create a perfectly reflective surface, create a sphere with it, couldnt we technically trap LIGHT inside of it? If a surface was perfectly reflective could it still be used as a solar sail since all the energy of the light is left completely the same after it is reflected?

I just got out of highschool so I really have no idea of the theories or anything behind this, so could someone with more knowlege explain if this is possible?

well, you are right, if and only if it were a perfectly reflective surface. However, in reality, some of the light energy gets converted to heat after every reflection (even a mirror is partially absorptive), and eventually the light dissapears.

It happens quite quickly because light travels at 3 x 10^8 (or something, cant remember exactly)

It whould be invisible from great distance and whould appear as a distotion close up being that you cant actaully see it because it is perfectly reflective

I guess they didn't teach you thermodynamics in HS :(

First off, note that talking about things that can't happen in physics (perfect reflectivity) is kinda like talking about a square triangle.  Since you start with a false premise, it's likely you'll end up with impossible conclusions.

Let us suppose I have a perfectly reflective sphere sitting here on my desk.  Furthermore, let us suppose that I insert a ray of light into the sphere, heading east.  The ray will hit the east wall of the sphere, and bounce back.

In order for momentum and energy to be conserved, two things will need to have happened.  First, the ball must have started to roll a little bit to the east.  Second, the "speed" of the photon (it's frequency in terms of wave theory) will need to have decreased.  Because the mass of the sphere is much much more than the "mass" of the photon, this is hardly noticable.

Still, this reflection wasn't a perfect one, because the wave has made a very minute red shift, but at least it conserved as much as physically possible.

So now this sphere is microscopically rolling eastward on my desk.  Assuming that it loses no velocity, then when the light ray bounces to hit the western wall of the sphere, the process will be reversed, and the sphere will remain stationary again untill the light returns to hit the east side of the sphere again, restarting the process.  The sphere will move in small eastward jerks while the ray inside goes from low energy to high energy.

Now, I have assumed that the interior of the sphere is a perfect vacuum.  I cannot really make the same assumption about the outside of the sphere.  It is on my desk, as it rolls eastward, it will bounce off with air particles and forces, which tend to turn it's kinetic energy into heat.  This is entropy in action.

Since the sphere has lost kinetic energy, the ray must red shift again in order to maintain momentum and energy conservation on the western bounce.

So if we take into account the fact that whatever the light propels will be affected by some sort of entropy, the light itself will lose energy and frequency with every bounce.  Eventually, it's just going to become a radio wave and fly out of the sphere.

So... as long as we're operating in a universe where this reflective surface is under the effect of forces that will convert it's kinetic energy to heat, you can't trap light inside a 'perfectly' reflective surface.

Furthermore, ignoring entropy, if light reflects off of any 'perfectly' reflective surface of non-infinite mass, the light will undergo a very small red shift in order to conserve momentum/energy.

I just wanked.

Also note that even though the mirror sphere might be such that you can see into the inside, it will appear all black even though there is a lot of light in there. This is because no light reaches out of the sphere and into your eyes.

Plus a perfect sphere is impossible to create, since pi is a non-terminating irrational number.

It's not really like you need a sphere though, you might use a cube or whatever you wish.

I like to use dildos.

How much energy do you suppose is lost when light bounces on a reflective surface? That is, since light travels in a straight path (rendering the sphere idea unnecessary) doesn't light that is being reflected hit light that is still going towards the reflective surface?

>>11

Do more research re: the particle-wave duality of light.

>>12
A trapped light wave will cancel itself out quickly

I am more interested in what kind of material one would use to create such a mirror. I think mercury would be a good substance to use. any thoughts?

>>14
Why would you want to use mercury? Hat wavelengths do you want to be perfectly reflected? Gold does a really good job around 700nm

>>13
100% fail for forgetting the 1st law of thermodynamics.

>>15
Well the hubble telescope uses a mercury mirror/

>>13
http://en.wikipedia.org/wiki/Laser
You have been learned. I hope you think about your failure, goto your room!

18get

fuck this, I'll just find "x"

20got

A NUMBER DIVISIBLE BY 10^(number of digits in last number -1)
DO I WIN??

Black Hole's Trap light

>>21

Well, depends on how you think of it.  If you take the "light is a particle" approach, then you could say that the event horizon is the precise point where gravity "pulling" the light in is the same as light's motivational force away from the black hole.

I, on the other hand, prefer the "wave" approach in this situation, where light is simply red-shifted into infinity at that point and physics, as we understand it, just stops working.

Of course, I'm getting my understanding from a book written in '96, and my understanding is incomplete at best.  I imagine a great many advances have taken place since then.

>>22
the event horizon is where time literally stops, according to einsteinian physics light would spend an eternity there, but stephen hawkling proved, somehow, that this is not the case and that blackholes somehow release this energy slowly over 10^50 years before the mass of the blackhole is low enough for it to rlease the rest of the energy at once.

I'm not sure how he came to that conclusion. This is where you take a course in theoretical physics.

bump

You could have flowers with perfectly reflective surfaces to shine light beams as weapons which would require some fancy vehicle to drive between their path.

>>5
How does it go from standing still to rolling eastward.  Wasn't there some kind of recoil when you fired the photon?

Unfortunately, I have a few questions for OP. What happens to the heat generated by the light photons after reflection and/or for that matter during the process of travel through a colder environment? You would have to maintain the temperature for the photons to continue their cycle of movement, but how do you balance that with it's needs? Do you know the needs of photonic perseverance? If something can be born, than it can decay and be destroyed. This is true because of some things being of a compounded nature and therefore having to balance between the two extremes in order to survive. That is why we need water at a level of 7 pH which is a perfect balance between 0 pH acid and 14 pH base. But what abouts nutrients to give burnable calories to our human muscles? What about sleep that the brain and muscles and heart need in order to slow down the life cycle in order to offset death? These are balance questions. What are the balance equations for photonic light? Answer that question and you have yourself a perpetual light rarefraction sphere. But of course, comming up with the details...I leave entirely up to you.
Btw, a movie character I look up to...L. :)
I guess that would make me...M. :P

inb4 3 year old thread

>>27
>>I have a few questions for OP

HA HA HA. He's probably already a junior in college by now.