
Light slowed down to 38 mph - aliasaria
http://www.news.harvard.edu/gazette/2007/02.08/99-hau.html
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timf
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._

~~~
Bjartr
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.

~~~
TallGuyShort
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.

~~~
Bluem00
My physics is a little rusty, so please forgive me if I'm wrong. I think the
law you're referring to is the Law of Conservation of _Mass_. As energy has
mass and subatomic particles have mass, you can convert back and forth between
them all day (good luck with that), and never violate it. In particular,
Einstein's E=mc^2 is applicable here.

It was a surprise to me to find that the term 'matter' is actually poorly
defined. At least according to Wikipedia.

~~~
TallGuyShort
Ah yes - I did mean conservation of mass, thank you.

I think most people use 'matter' to refer to the regular objects we interact
with that are composed of atoms, and that's how I intended to use it in the
above post. However, if I had my way, electromagnetic radiation would also be
consider 'matter', because it's the same stuff, just a different form.

>> As energy has mass

Is that generally accepted, btw? Because I've always heard people talk about
light as having no mass, and it never made sense, because that what I
understood e=mc^2 to represent. I think it does have mass, it's just so minute
(smaller than anything we know by such an order of magnitude that the speed of
light squared is used to express it) that it doesn't seem like it.

~~~
roundsquare
I'm no expert, but my understanding is a little different. Its not that energy
"has" mass but that energy and mass are two different forms of the same thing,
i.e. they are equivalent. If some process is able to convert mass to energy
then you could find out much mass you'd get but multiplying the energy by c^2
(hence E = mc^2).

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jpeterson
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?

~~~
noonespecial
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.

~~~
ars
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.

~~~
noonespecial
True, true. Saying a lot of things about subatomic particles is meaningless.
Their behavior doesn't map to english very well. The point is that that
information could be stored in the beam basically at the photon level, trapped
in matter, and then pulled out later. That's as cool as ultracold atoms.

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nebula
<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;

~~~
Locke1689
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.

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smhinsey
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.

~~~
ricaurte
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.

~~~
smhinsey
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.

~~~
Bjartr
As described in the article linked the speed of the teleportation is limited
by the speed of the signal beam which is necessarily capped at c.

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zmimon
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.

~~~
ars
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.

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

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

~~~
bdr
Ever heard of vanity? ;)

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

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

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pra
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.

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

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

