Light slowed down to 38 mph

http://www.news.harvard.edu/gazette/2007/02.08/99-hau.html

by aliasaria • 17 years ago

124 39 17 years ago

news.harvard.edu

timf• 17 years ago

The 38mph result was from 11 years ago, the title of this (2007) article is "Light and matter united" and it's far more startling...

> She and her team made a light pulse disappear from one cold cloud then retrieved it from another cloud nearby. In the process, light was converted into matter then back into light.

froo• 17 years ago

"She and her team made a light pulse disappear from one cold cloud then retrieved it from another cloud nearby. In the process, light was converted into matter then back into light."

When I first read that, the only response I had was "Beam me up Scotty"

I think it was more of a stunned response than anything. Mind = Blown.

Herring2• 17 years ago

Photon number isn't conserved.

Bjartr2• 17 years ago

More accurate, to my layman's interpretation, would be to say that light was converted to information, encoded in existing matter, then converted back to light. Saying it was converted to matter seems to imply that new matter was created in the process which doesn't appear to be the case.

TallGuyShort2• 17 years ago

Unless light and matter consist of the same fundamental building blocks. During nuclear tests they've found that a tiny amount of matter actually disappears (which may SOUND like it violates the Law of Conservation of Matter), but it's actually believed that that tiny amount of matter was converted into an enormous amount of electromagnetic energy (hence e=mc^2) (i.e. light, for all intents and purposes).

If that's true, then this experiment is probably just reversing the process. The light is converted into a tiny amount of matter that's barely detectable (that 'fingerprint' - possibly just a tiny amount of matter that's slightly different from the matter around it), and can be converted back into energy easily.

Personally, my theory is that once we get down to more and more subatomic particles, we're going to start seeing that it has more and more properties in common with electromagnetic radiation. Electromagnetic radiation itself consists of a magnetic 'part' and an electro 'part', and if you coiled enough of it together millions and millions of times in a certain state, maybe you'd have an atomic particle that contained a phenomenal amount of energy, and a tiny amount of mass.

smhinsey2• 17 years ago

This reminds me of something that I think I first read about in Michio Kaku's book Physics of the Impossible where a Bose-Einstein condensate was used as a medium for "teleportation". I believe in his book he referred to the experiment referenced here. http://www.physorg.com/news102681027.html

They are careful to note that it is a transmission of information rather than photons. It sounds like this experiment is similar, but I am certainly not qualified to comment authoritatively on that.

ricaurte2• 17 years ago

It would make sense that teleportation (or perceived teleportation) would be possible from it, since all matter is is stored information. Now the question is if matter is the only way to store information aside from light. If this is so, then if you reduced an object or human to its light representation, you would be able to travel at the speed of light, but no faster, which would be perceived teleportation - I'm assuming teleportation is instantaneous whereas going the speed of light is not. Hopefully no one would slow you down in the meant time.

smhinsey2• 17 years ago

I think that what you've described is essentially the basis for the Australian "teleportation" idea. They distinguish it from quantum entanglement approaches which could theoretically (or not, depends on who you ask) transmit the information faster than light.

jpeterson• 17 years ago

Maybe I'm dense, but I don't see how this experiment shows that the original light beam was affected in any way. Seems to me that the original light beam etched information onto the "cold atomic cloud", and then later an entirely new beam of light (with identical properties) was emitted (or reflected) from the laser blast's impact on this "etching".

How can they reach the conclusion that the original light beam itself was altered from this experiment?

noonespecial2• 17 years ago

They mislabeled the event when they said that the light was "converted" into matter. This is sad because I think many people will miss the greatness of what was really done because of it. A large (long) beam of light (everything about it) was stored in a very small amount of matter, then recreated exactly. It wasn't light like what was there before, diffracted from new light (like a hologram), it was the same light.

Once this becomes practical, we have practically infinite data storage, not to mention the underpinnings of computing with pure light, so perhaps practically infinite computational speed as well.

ars2• 17 years ago

Saying "the same" about light (and other subatomic particles) is meaningless. If the have the same state, then are the same, in the sense that they are indistinguishable.

So it was "just like" what was there, but not "the same" photon in the sense the photon did not exist for a while, and was recreated. And at the same time it was also "the same" photon, in the sense that the before and after photons are not distinguishable.

It should be noted that the "no cloning" theorem adds a twist: It says you can not copy a photon. This means that the matter that stored the photon can not be induced to create another one (like a hologram does).

So in that sense it was the "same" photon - because you can only ever create the original, and no additionals.

pjvandehaar• 17 years ago

So if you could figure out just how much storage, you could use Moore's law to figure out just when this will become practical? If "nearly infinite", then this will likely never happen (unless you go with the "accelerating returns").

ljlolel• 17 years ago

"then later an entirely new beam of light (with identical properties) "

I think, if you understand quantum physics, it's meaningless to say that it's a "new beam of light with identical properties." If it "has the same properties", then it is the "same beam of light." It doesn't just look the same. It is the same in a physical (and meta-physical?) sense.

Then again, I don't really understand quantum physics, so I might be misunderstanding this. I'm telling you what I picked up from Eliezer Yudkowsky's series on quantum electrodynamics.

Perhaps a physicist can elaborate?

rdtsc• 17 years ago

it's meaningless to say that it's a "new beam of light with identical properties."

You can think of it as information (bits). The same information that was encoded was decoded later.

It is not as if photons are items on the macro scale, that were somehow labeled (for example, photon #134), then disappeared and reappeared and the scientists compared the label and proclaimed that its the same photon (#134).

sp332• 17 years ago

What's amazing about this case is that all of the quantum states were maintained as well. The light maintained entanglement with other photons. This is not something that could happen by simply storing information and retrieving it later.

Currently, quantum encryption setups require a fiber optic cable to reach all the way from the sender to the recipient, because repeaters would destroy the entanglement. But with this device, you could store the data in a Bose-Einstein condensate, ship it to the destination, then read the data back out.

pra• 17 years ago

the key phrase here is "Despite all the intriguing possibilities, "there are no immediate practical uses," Hau admits."

The experiment and its results are intriguing nevertheless.

zmimon• 17 years ago

The article seems very loose with its terminology which makes it really confusing. For example:

> Albert Einstein and just about every other physicist insisted that light travels 186,000 miles a second in free space, and that it can't be speeded-up or slowed down. But in 1998, Hau, for the first time in history, slowed light to 38 miles an hour, about the speed of rush-hour traffic.

Hau did not slow down light in free space so this has nothing to do with Einstein's statement.

What I would like to know is, is underlying fundamental mechanism here similar to or the same as what we know as refraction? From all the descriptions it sounds awfully similar, other than the extreme(!) nature of the slowdown.

ars2• 17 years ago

Yes. It's the same, just on a more extreme level.

Light can NOT be slowed down - at all! What happens with refraction is the light is absorbed by matter, then re-emitted, over and over, which effectively slows it down.

In this case the material that absorbed the light takes a very long time to re-emit it.

diederikm• 17 years ago

Check out this great docu http://www.pbs.org/wgbh/nova/zero/ witch shows more of the Bose-Einstein condensate.

laut• 17 years ago

Not just 60km/h, it was completely stopped. It was on (Danish) TV years ago.

finebanana• 17 years ago

This is way beyond my head, but I can fell the awesomeness!

tjic• 17 years ago

> For the first time in history, this gives science a way to control light with matter and vice versa.

Typical bad science writing.

Mirrors have existed before this year...

eru• 17 years ago

Though mirrors are not too good at the vice versa part.

bdr• 17 years ago

Ever heard of vanity? ;)

nebula• 17 years ago

<quote>Einstein and just about every other physicist insisted that light travels 186,000 miles a second in free space, and that it can't be speeded-up or slowed down. But in 1998, Hau, for the first time in history, slowed light to 38 miles an hour, about the speed of rush-hour traffic. <quote>

I wouldn't have been surprised if a newspaper journalist used dramatization that indicated as if Einstein is proven wrong. I didn't expect that kind of dramatization when reporting scientific matters on news.harvard.

Of course, Einstein is still right. All these experiments slow down the speed of light when it's traveling in special matter at special temperatures. Constant speed of light in free space is a necessary condition for Theory of Relativity be correct. If that condition is found to be incorrect, our current understanding of the universe completely goes for a toss;

Locke16892• 17 years ago

Indeed. To be even more specific, the reason why it is slowed down is because of absorption and re-emittance of particles of light (photons). If you go down the the extremely small scale, what you will actually see is a photon moving at the speed of light, colliding with an atom, being absorbed by an electron, then re-emitted on the other side. Repeat this process ad nauseam and the constant absorption/re-emittance will slow down the speed of light to a varying degree. Most importantly, however, is that the c is constant in free space.

rawr• 17 years ago

This is sure to revolutionize all communications done at 460 degrees below zero Fahrenheit!

cunard-n• 17 years ago

Thanks for posting this. count one more in the mind=blown camp!

Light slowed down to 38 mph

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