Can you trap light indefinitely?

[ArcanaNoir]

Can you "trap" light indefinitely?

One of my fifth grade students wants to know if you can "trap" light. that is, can you let some light into a container and then seal it off, and let it out again some time later?

I'm not a physics major so I wasn't sure at all, but instinct tells me "no". That's supposing you could even get it in a container and seal the container in the first place. At first I'm thinking you can bounce light off a bazillion mirrors and so why couldn't you just keep doing that, but then I realized you basically have to have all the mirrors set up already, since you could never keep up with the speed of the light, leading me to suppose it doesn't matter how far the light goes, what matters is how long it is preserved. So in that case, it may dissipate almost instantly. But then, there's the light from far away planets from a long time ago. So, light does in fact have an appreciable "shelf-life". Of course, this light was extraordinarily bright at the origin and is now extraordinarily dim. So, maybe your "light in a jar" would become so dim that you couldn't see it anymore extremely quickly. The most problematic thing of all, I think, would be that you would only have an instant of light, since you could only capture that last instant before sealing the container. Any light that had entered the container previously would have worked its way out almost instantly. Even if you could "collect" more than an instant of light, the instant you released the light, it would ALL come out at practically the same time.

Well, it's all very impractical, but does the concept violate any laws? If not, what "practical constraints" would make the whole endeavor pointless? Please try to use basic language.

 

[Curl]

There are dozens of threads about this subject. Search "mirror box" or "light box".

 

[DaveC426913]

The short answer is no.

It's not a problem of being really quick. You could easily make a box large enough to trap the light inside.

The problem is that no mirror is perfectly reflective. It is not simply a practical constraint. No mirror can be perfectly reflective - even in principle. To reflect, the light must interact with the mirror. Ultimately (quickly) the light's energy will be absorbed into the mirrored walls of the box, resulting in heating up the box a tiny bit.

 

[I like Serena]

Hey Arcana!

What's this about you having students?
Did you make a career change?Oh, and here's a nice article about trapping light:
http://www.rsc.org/chemistryworld/News/2007/December/10120701.asp

'It was a chance discovery,' explained Mehta's colleague Rajesh Patel. While investigating the optical properties of their transparent fluid the researchers noticed that, in a certain magnetic field range, light scattering - both forward and backward - became zero. 'We thought the light got trapped inside,' said Patel. 'So, we switched off the laser [which was shining light through the system] and then the magnetic field, and there it was - a flash of colour lighting up our dark room.'

 

[e.bar.goum]

You can't trap light in a mirrored box, as there are no perfect mirrors (complicated dielectric mirrors can get to 99.999% reflectivity, but only for a very small region of the spectrum).

On the other hand, it is possible to "trap" light by slowing it down. If you can stop the light, you've trapped it. Indeed, this is crucial for the development of quantum memory.

 

[ehild]

The answer is "almost". You can reach reflectivity with internal total reflection much better than that of mirrors. There are optical resonators which trap light for a while. The lasers consist of such a resonator with a small opening on one of the end mirrors. Closing the output, the light is trapped. Think of fibre optics or other waveguides. The light is confined between the walls all along the length of the fibre or waveguide by the total reflection, and escapes at the open end. Of course, no surfaces are perfect, and no materials are completely free of absorption, so there will be some loss and the energy of the trapped light is dissipated sooner or later. But it is worth to show the students an experiment with a prism and laser pointer to demonstrate total reflection. With a prism of shape shown, at certain position and angle of the incident ray one can make the prism glow without any visible outgoing ray of light.

ehild

 

[ArcanaNoir]

These answers are great! Thank you. I did search some other threads like this, but the discussion was above my head. What you have posted here is exactly what I was looking for.

I haven't made a career change, I'm a teacher's aide during the day, stealth mathematician by night! I'll finally get to go to school full-time next year.

 

[Andy Resnick]

Echoing ehild, total internal reflection is used in optical fibers, which are nearly lossless at telecommunications wavelengths (0.2 dB/km). Cavity ring-down spectroscopy also uses high-finesse cavities (reflectivity = 0.9999 appears to be common).

These roughly translate to light 'trapped' for 1.6 ms (fiber, starting at a 100 dB SNR) and 12 us (CRDS, 1-meter long cavity).

 

[ehild]

Thank you Andy Resnick! Although that 1.6 ms is almost infinitely long with respect to the period of light, it is very short with respect to our lifespan But everything is relative...

ehild

 

[A.T.]

But then, there's the light from far away planets from a long time ago. So, light does in fact have an appreciable "shelf-life". Of course, this light was extraordinarily bright at the origin and is now extraordinarily dim.

The star light being dim has nothing to do with "shelf-life". The light doesn't decay with time, it just gets distributed over a huge area, and red shifted due to expansion.

You can trap light "locally" without reflection in orbit around a massive object. But these orbits are not stable.

 

[NascentOxygen]

One of my fifth grade students wants to know if you can "trap" light. that is, can you let some light into a container and then seal it off, and let it out again some time later?

Yes, researchers have been achieving that in just the last few years. But it's not quite as simple as capturing the beam in a mirrored lunchbox. But they claim to be able to stop a pulse of light and release it later at a time of their choosing. (They have been choosing what we would think of as very brief times, though, so far.)

http://anti-state.com/forum/index.php?board=5;action=display;threadid=21692

 

[ArcanaNoir]

The star light being dim has nothing to do with "shelf-life". The light doesn't decay with time, it just gets distributed over a huge area, and red shifted due to expansion.

Good point! Thank you for correcting me.

 

[silentbob14]

Nice question ;] I've been wondering about this for a while too.

 

[lenita24]

i guess light can be trapped on pictures, I assume that is how astronomers study the universe!. Also I would like to try to trap light on frozen water, may be very possible.

 

[Drakkith]

i guess light can be trapped on pictures, I assume that is how astronomers study the universe!. Also I would like to try to trap light on frozen water, may be very possible.

Pictures are either the result of a chemical reaction caused when light hits film, or the absorption of light by electrons in a digital sensor. Neither of these "trap light".

http://en.wikipedia.org/wiki/Photodetector

 

[Fieldwaveflow]

I wouldn't call it a lunch box

Metal is put on the backs of mirrors. It's like looking at the surface of atomic shells right?
So if someone where to put light on the inside of the shell it would be a light trap.
Maybe you could call fusion a way of constructing a "lunch box".

 

[Drakkith]

Metal is put on the backs of mirrors. It's like looking at the surface of atomic shells right?
So if someone where to put light on the inside of the shell it would be a light trap.
Maybe you could call fusion a way of constructing a "lunch box".

I'm not quite sure what you're trying to get at, but I don't think it works this way.

 

[Bobbywhy]

Until last week when I received my copy of Science News, August 10, 2013; Vol.184 #3 (p. 8) I would have answered the OP’s question just like everyone so far has.

But Wait! This article changes all that! Physicist Chia Wei Hsu and colleagues at MIT report in the July 11 Nature and summarized in Science News:

“A new type of mirror that reflects light perfectly has been constructed; a feat many scientists thought wasn’t possible. The mirror could find its way into powerful lasers and other devices.”

http://www.sciencenews.org/view/generic/id/351485/description/Perfect_mirror_debuts

 

[Drakkith]

Until last week when I received my copy of Science News, August 10, 2013; Vol.184 #3 (p. 8) I would have answered the OP’s question just like everyone so far has.

But Wait! This article changes all that! Physicist Chia Wei Hsu and colleagues at MIT report in the July 11 Nature and summarized in Science News:

“A new type of mirror that reflects light perfectly has been constructed; a feat many scientists thought wasn’t possible. The mirror could find its way into powerful lasers and other devices.”

http://www.sciencenews.org/view/generic/id/351485/description/Perfect_mirror_debuts

Note that this new mirror required that the light be at a specific angle, 35 degrees. I'm not sure you could design a container that could trap light indefinitely out of this. Yet.

 

[Fieldwaveflow]

Atoms are energy traps right?

I'm not quite sure what you're trying to get at, but I don't think it works this way.

If most atoms are perfect energy traps, as they appear to be, then a person would need to create an atom ("lunch box") to contain energy. One of the results of atomic fusion is an atom of increased mass. E=mc² shows that energy is contained in mass. With an increase in mass there is an increase in contained energy. So fusion is a way of creating a "lunch box".

If I were explain a perfect lunch box to a 5 year old I might not go into such details but possibly say "It would take a special lunch box that would need big, special machines to make."

 

[Drakkith]

If most atoms are perfect energy traps, as they appear to be, then a person would need to create an atom ("lunch box") to contain energy. One of the results of atomic fusion is an atom of increased mass. E=mc² shows that energy is contained in mass. With an increase in mass there is an increase in contained energy. So fusion is a way of creating a "lunch box".

I'm sorry, but none of this is correct.

Atoms are not perfect energy traps. They readily absorb and get rid of energy in a variety of ways.

[STRIKE]Fusion does NOT result in an atom of increased mass. It actually results in an atom of DECREASED mass. That's how you get energy from fusion. This missing mass is released as energy after fusion.[/STRIKE]

Went braindead... of course fusion results in a heavier atom.

 

[Fieldwaveflow]

fusion

Atoms are not perfect energy traps. They readily absorb and get rid of energy in a variety of ways.

I write of the inside of atom. The "lunch box"

Fusion does NOT result in an atom of increased mass. It actually results in an atom of DECREASED mass. That's how you get energy from fusion. This missing mass is released as energy after fusion.

Fission creates atoms of decreased mass. Fusion creates atoms of increased mass. A fusion "machine" may not be efficient in making the "lunch box" but it still contains light that was added to it.

 

[Drakkith]

I write of the inside of atom. The "lunch box"

I don't even know what this means.

Fission creates atoms of decreased mass. Fusion creates atoms of increased mass. A fusion "machine" may not be efficient in making the "lunch box" but it still contains light that was added to it.

Sorry, sorry, I misunderstood what you were saying. Of course the end product of fusion is more massive than before. However I don't see how light has anything to do with this.

 

[sophiecentaur]

Whether there is a mass increase or decrease will depend upon which product you are forming. Fusion of light nuclei results in a less massive product ('mass defect'), with energy released but you need energy to be input for fusion to produce elements heavier than Iron, giving an increase in mass. This accounts for the composition of 'early stars' (formed from only He and H) being limited to just the lighter elements. Afaiaa, you need a supernova (extreme energy situation) for the heavier elements to be formed and so the stars with heavy elements in them must have been formed from nebulae with 'second hand' materials.

 

[Drakkith]

Just so there's no confusion, the final product in fusion is ALWAYS more massive than either of the single elements that fused. The combined mass of the elements before they fused is more than the final product however, with the missing mass released as energy in the reaction. (Unless the final product is on the heavier side of the periodic table of course. Then it takes energy instead of releasing it)

 

[sophiecentaur]

Just so there's no confusion, the final product in fusion is ALWAYS more massive than either of the single elements that fused. The combined mass of the elements before they fused is more than the final product however, with the missing mass released as energy in the reaction. (Unless the final product is on the heavier side of the periodic table of course. Then it takes energy instead of releasing it)

If that were not true then the energy in or out would be unbelievable!

 

[BrettJimison]

Here is a report published by SLAC about trapping X ray photons. Not sure if anyone here has eluded to this paper yet: http://physics.aps.org/articles/v5/125

 

[astorboy-anmol]

Arcana, here's a video that you may like.

 

[Romulo Binuya]

Haroche won the Nobel prize for trapping photon. He used the shiniest mirror in the world at near absolute zero temperature, and yet he managed to trap photon for only a tenth of a second. So no, light as light can't be trapped indefinitely.

But light as energy is being trapped by plants through photosynthesis. Light energy is indefinitely trapped within the chemical bonds of the cellulose tissue of the plants, if you light up a matchstick you are technically liberating trapped light energy back into light again... what would the kids will think about that :D

 

[Bobbywhy]

Haroche won the Nobel prize for trapping photon. He used the shiniest mirror in the world at near absolute zero temperature, and yet he managed to trap photon for only a tenth of a second. So no, light as light can't be trapped indefinitely.

But light as energy is being trapped by plants through photosynthesis. Light energy is indefinitely trapped within the chemical bonds of the cellulose tissue of the plants, if you light up a matchstick you are technically liberating trapped light energy back into light again... what would the kids will think about that :D

It is important to notice the difference between "trap" the light and your suggestion that photons are trapped during photosynthesis. In the "trapping" we would capture a photon in a mirrored box and it would persist...it would reflect continuously.

But in photosynthesis photons are absorbed, not trapped. This absorption means they give up all their energy and disappear.

 

[Grace-low]

If you heat a box to red hot then open a hole and shine red light in from a red lamp. Then close that hole and open another hole red light will come out. I don't know how to make sure it is the light that you shine in though.

 

[Drakkith]

If you heat a box to red hot then open a hole and shine red light in from a red lamp. Then close that hole and open another hole red light will come out. I don't know how to make sure it is the light that you shine in though.

It will not be the same light. The speed of light is so quick that all of the red light you shone inside will be absorbed well before you can even close the first hole.

 

[Braincol]

If you had a sphere made of a material that took in light but didn't let it escape the sphere would the sphere heat up indefinitely? Resulting in infinite heat leading to infinite energy.

 

[DaveC426913]

If you had a sphere made of a material that took in light but didn't let it escape the sphere would the sphere heat up indefinitely? Resulting in infinite heat leading to infinite energy.

No.

The light is converted to heat. And it's limited to however much you put in.

 

[davenn]

If you had a sphere made of a material that took in light but didn't let it escape the sphere would the sphere heat up indefinitely? Resulting in infinite heat leading to infinite energy.

you also have to define your definition of "light" in your example
do you mean visible light ?

Any visible light absorbed by the sphere will heat it up, but that heat will be dissipated by some or all of the following ...
conduction, convection or E/M radiation ... IR ( infra-red) at lower frequencies (wavelengths)Dave