Yeah, but how often do you see a refractive index of 17,621,052? For that matter, how often do you encounter a photon travelling slow enough that you could hope to see it actually moving? I think KT was looking for an observation a bit out of the ordinary.
Don’t forget, it is also related to the incidence angle. If you go straight in, you’re gonna come straight out. Also, remember that the angle of refraction is related to wavelength and they are working in the infra-red.
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The angle of the refracted beam is related to the angle of the incident beam (measured from a line perpendicular to the surface), by the equation
n_i * sin(theta_i) = n_r * sin(theta_r)
where n_i and n_r are the indices of refraction in the incident and refractive media, respectively, and theta_i and theta_r are the angles of incidence and refraction.
The BEC has an extremely large index of refraction, and the vacuum has index of refraction = 1. What this means is that the angle of refraction is extremely small compared to the angle of incidence. Therefore, no matter what the angle of incidence, the beam will enter the BEC pretty much perpendicularly.
All right now people, I don’t know if you’re really thinking what I think you’re thinking, but let’s all remember that we see photons only when they hit us in the eyeball. When light leaves the dense media we’ve been talking about, its speed increases. And since that dense media doesn’t exist in our eyeballs, we’re never going to see a photon at the super-low speeds. We always see light at the same speed; I don’t know what the speed of light through vitreous humour is, but that’s the speed.
Y’all seem to be thinking about a purely (and necessarily) hypothetical case whereby said 38 mph photon could carry a little flashlight and point it at us. The flashlight would send out photons at right angles to the vector of the flashlight-armed photon in the dense medium. As soon as the baby photons crawled to the edge of the medium, they could speed up and hit us in the eyeballs. Then we could see the (results of) the photon moving that slowly.
It’s necessarily a fictitious case cause photons don’t emit photons.
I don’t want to make people think like me, I want them to think like me of their own free will.
Maybe, but various atoms and molecules excited by photons, emit photons. Rather than each photon carrying a flashlight, to indicate its position as it moved through the BEC, imagine instead, that it is moving through a forest, and igniting the leaves as it goes.
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Before I got cut off, I meant to say that we’re still dealing in hypotheticals, but if you could excite certain atoms, without upsetting the BEC as a whole and you could differenciate between the illumination of the laser trap and the slow moving beam, who knows what you might be able to observe?
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That makes sense as a hypothetical, Stephen. We could watch a pattern of trees ignite as the incredibly slow photon touched them off, and we could find out more about the whole wave/particle thing that I never understood.
Interestingly enough, the speed of light in water is slow enough that scientists can accelerate particles to speeds faster than light in that medium.
When that happens, an interesting phenomena called “cherenkov effect” occurs. Even more interestingly enough, when the Starship Enterprise accelerates to warp speed, they show this Cherenkov Effect
I said that because I understand that–well, sound waves cannot travel through a vacuum–how can light waves? Unless there really is a hypothetical “ether” in outer space…
Smithsonian Magazine strikes again! I’m sure y’all are hearing about this because Smithsonian did an article about this recently.
The Smithsonian does a very good job of explaining how this works: Putting the Brakes on Light
Essentially sodium is being cooled down to such low temperatures that normal physics does (do?) not apply. Read the article, it’s fascinating.
It’s also the source of my new sig…
…in a state so nonintuitive it can only be called weird…
Well Dougie, to put it simply, a photon behaves like a wave and a particle. The particle/wave duality allows light to interact with constructive/destructive interference (like irridescence) while also imparting energy to solar cells. So, vacuum is no problem.
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Nope. Relativity proves that there is no “ether”. (Making up “ether” to explain something does no good when, even if there were an “ether”, it wouldn’t explain the way things actually are.)
Electromagnetic “waves” – just are.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
So basically a photon is its own medium of propagation.
mumble mumble Maxwell’s Equations mumble mumble wavicle mumble mumble compression wave in a medium versus the vibration of a packet of energy mumble mumble magnetic component balances against electrical component mumble mumble at right angles to its direction of motion mumble mumble
The lecture was for a general audience and mostly about atomic clocks. He showed a short video of what I understood to be a BEC trapped by lasers and a magnetic field. Computer-colorized, of course, so maybe they really don’t glow like light sabers. My physic is weak, so maybe it wasn’t a BEC, but it definitely was an image of super-cooled cesium atoms.
If anybody out there is interested and in the Wash. D.C. area, he’ll be giving a series of lectures about this next month at the Univ. of Maryland. He’s an entertaining speaker.
I recall someone asking how a laser could be used to cool something down. THe exact same question came up in my chem or physics class one or two years ago. I think the way it works is they wait until two molecules or atoms collide and one of them has almost no speed. Then they use the laser to getthe other one going really fast out of the system. THus, the system is cooler.
