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Your understanding is actually pretty good (lines up with mine, at least), and I liked your explanation except for the needlessly conversational tone. Basically

Your understanding is actually pretty good (lines up with mine, at least), and I liked your explanation except for the needlessly conversational tone. Basically by only cutting things out: > We used a crystal that is normally opaque (not see-through) and fired laser beams at it [which] made it see-through but only for a narrow range of light frequencies (e.g. a filter that only allows one colour of light through). [Then] we made [the crystal] see-through with the laser, shone some of that colour light in and turned off the laser so that it's no longer see-through. We trapped light!

amirmc 13y ago
> "... except for the needlessly conversational tone." Yes, I agree it's not necessary to get the basic information across but it was definitely a lot more fun to write that way! If I were really writing piece for an article or blog post I'd take a lot more care and probably consider using better analogies.
- TeMPOraL 13y ago
  > Yes, I agree it's not necessary to get the basic information across but it was definitely a lot more fun to write that way! I agree; for me, "conversational tone" is usually much more fun to write, and much more fun to read. I find it a sign of a good understanding of the topic if one can phrase his explenation in a conversational tone. You have to know your stuff well to be able to correctly express complicated ideas in simple terms.
  - alanctgardner2 13y ago
    'Tone' may have been the wrong word. Obviously he understands, he did explain it well. I was just trying to point out that he added a bunch of noise under the guise of being conversational. Cutting out the noise makes it concise will remaining accessible - I don't think my edits actually changed the tone.
    - rangibaby 13y ago
      Less is more. > http://www.amazon.com/Writing-Works-Communicate-Effectively-Business/dp/0060956437 http://www.amazon.com/Writing-Works-Communicate-Effectively-...
bilbo0s 13y ago
This may be a dumb question... but how are they able to validate that the light was stopped for one minute? They switched the crystal to opaque... and time passed... until the light exited the crystal??? How much time? How did they validate the light left the crystal? Did they have to do anything to induce the light to leave? If they did, why couldn't this storage crystal hold the light indefinitely... until we trigger the release state? Sorry if these are dumb questions, just can't really figure that part of it out. I understand the crystal going from opaque, to color filter, to opaque... that is essentially the "writer". How does the "Reader" work?
- alanctgardner2 13y ago
  This is based on my fuzzy knowledge of quantum physics: - electrons exist at varying levels of excitement "around" a molecule. These states are discrete; an electron can only have certain values of energy - photons can "collide" with electrons and impart more energy, provided the photon's energy (correlated to the wavelength of light) plus the electron's existing energy puts it into an allowable state - when an electron falls back from a high energy state to a low energy state it will emit a photon - crystals have low electron mobility; it's hard for an electron with a lot of energy to escape from a molecule. The molecules also don't move within the lattice. - in this experiment, the first laser raises the electrons to a higher energy state, where this new state + the wavelength of the light is also an allowable state - the second laser excites the electrons into an even higher state. These electrons can't escape from their position (they're fixed in space), but they encode the energy of the second laser. When the first laser goes away, the distance the electrons now have to fall back to their natural (ground) state is very large, so it takes some time. This is what limits how long you can keep the light "stopped" for. -the 'Reader' is just a photodiode (or a hemisphere of them) which emits electricity when hit by a photon. So you pulse laser #2, then wait for the diodes to 'light up', which means they've been hit by light. The 1 minute figure is the time between turning laser #2 on and seeing the diodes turn on.
  - netshade 13y ago
    I don't have enough background knowledge to ascertain if this is the correct understanding of the problem, but this explanation reads very well, and is the best 'mechanical' explanation I've seen in this thread so far. Thank you.
e3pi 13y ago
I liked and agreed with your description and particularly the transparent reading of your `conversational tone'. There's a career for you editing mathematics journals my friend.

amirmc 13y ago

> "... except for the needlessly conversational tone." Yes, I agree it's not necessary to get the basic information across but it was definitely a lot more fun to write that way! If I were really writing piece for an article or blog post I'd take a lot more care and probably consider using better analogies.

TeMPOraL 13y ago
> Yes, I agree it's not necessary to get the basic information across but it was definitely a lot more fun to write that way! I agree; for me, "conversational tone" is usually much more fun to write, and much more fun to read. I find it a sign of a good understanding of the topic if one can phrase his explenation in a conversational tone. You have to know your stuff well to be able to correctly express complicated ideas in simple terms.
- alanctgardner2 13y ago
  'Tone' may have been the wrong word. Obviously he understands, he did explain it well. I was just trying to point out that he added a bunch of noise under the guise of being conversational. Cutting out the noise makes it concise will remaining accessible - I don't think my edits actually changed the tone.
  - rangibaby 13y ago
    Less is more. > http://www.amazon.com/Writing-Works-Communicate-Effectively-Business/dp/0060956437 http://www.amazon.com/Writing-Works-Communicate-Effectively-...

bilbo0s 13y ago

This may be a dumb question... but how are they able to validate that the light was stopped for one minute? They switched the crystal to opaque... and time passed... until the light exited the crystal??? How much time? How did they validate the light left the crystal? Did they have to do anything to induce the light to leave? If they did, why couldn't this storage crystal hold the light indefinitely... until we trigger the release state? Sorry if these are dumb questions, just can't really figure that part of it out. I understand the crystal going from opaque, to color filter, to opaque... that is essentially the "writer". How does the "Reader" work?

alanctgardner2 13y ago
This is based on my fuzzy knowledge of quantum physics: - electrons exist at varying levels of excitement "around" a molecule. These states are discrete; an electron can only have certain values of energy - photons can "collide" with electrons and impart more energy, provided the photon's energy (correlated to the wavelength of light) plus the electron's existing energy puts it into an allowable state - when an electron falls back from a high energy state to a low energy state it will emit a photon - crystals have low electron mobility; it's hard for an electron with a lot of energy to escape from a molecule. The molecules also don't move within the lattice. - in this experiment, the first laser raises the electrons to a higher energy state, where this new state + the wavelength of the light is also an allowable state - the second laser excites the electrons into an even higher state. These electrons can't escape from their position (they're fixed in space), but they encode the energy of the second laser. When the first laser goes away, the distance the electrons now have to fall back to their natural (ground) state is very large, so it takes some time. This is what limits how long you can keep the light "stopped" for. -the 'Reader' is just a photodiode (or a hemisphere of them) which emits electricity when hit by a photon. So you pulse laser #2, then wait for the diodes to 'light up', which means they've been hit by light. The 1 minute figure is the time between turning laser #2 on and seeing the diodes turn on.
- netshade 13y ago
  I don't have enough background knowledge to ascertain if this is the correct understanding of the problem, but this explanation reads very well, and is the best 'mechanical' explanation I've seen in this thread so far. Thank you.

e3pi 13y ago

I liked and agreed with your description and particularly the transparent reading of your `conversational tone'. There's a career for you editing mathematics journals my friend.