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Physicists Slow the speed of Light

LordOfWizards

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#1
Physicists Slow Speed of Light

Since the "Non-constant speed of light" thread showed up I did some digging and found this.
This involves using the Bose-Einstein condensate state of matter to slow light down (a lot!)

There was a recent movie that used the Bose-Einstein condensate state of matter (idea) to create an army of strange (other-worldly) beings. Spectral: Spectral (2016) - IMDb
 
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#2
I imagine that the light isn't actually moving any slower than normal, but way the light is normally absorbed into the electron shell of atoms and then released has been slowed down to a crawl by matter that is essentially at zero Kelvin.

I don't know if the condensate has a much different density than normal matter, as that would also slow things down, but I don't imagine it has.

Cool article!
 

LordOfWizards

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#3
From the article:

"An entirely new state of matter, first observed four years ago (article was written in 1999), has made this possible. When atoms become packed super-closely together at super-low temperatures and super-high vacuum, they lose their identity as individual particles and act like a single super-
atom with characteristics similar to a laser."

So, if I am reading this correctly, the condensate is incredibly dense compared to "normal" matter.
 
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#4
From the article:

"An entirely new state of matter, first observed four years ago (article was written in 1999), has made this possible. When atoms become packed super-closely together at super-low temperatures and super-high vacuum, they lose their identity as individual particles and act like a single super-
atom with characteristics similar to a laser."

So, if I am reading this correctly, the condensate is incredibly dense compared to "normal" matter.
I've never gotten the impression that the condensate takes up less volume than the atoms it replaced, just that you can't detect individual atom anymore.
 

LordOfWizards

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#5
I researched the question, and didn't find any absolute answer to whether BEC is more dense than normal matter. They keep describing it as a new "state" of matter. Here is one example:

"Just as there is a maximum threshold of energy above which atomic matter as we know it can't exist, there is a minimum threshold of energy below which atoms no longer behave in the ways we expect. Atoms become excited when their energy increases. In an analogous way, atoms become "de-excited" when their energy decreases. As atoms approach absolute zero, they become sluggish and ultimately condense into an additional physical state called a Bose Einstein Condensate (BEC). Consider a balloon filled with steam, the gaseous state of water. Cool it down to room temperature and it will contain a small puddle of water inside it. Put it in a freezer and that water will solidify into ice. It's easy to visualize the atoms in steam moving around fast and bumping into each other, or atoms sliding around one another in liquid water, but there is no visible motion within a block of ice. Yet, undetectable to our eyes, there is. As the water freezes into ice, the atoms get close enough and slow down enough to form attractive chemical bonds with each other. In the case of water ice, they create a three-dimensional lattice. The type of bond arrangement depends on the kinds of atoms involved. No matter what the solid material is, the bonds hold the atoms more or less in place but they don't stop the atoms from jiggling about, like a runner jogging in place. This jiggling or oscillating motion, averaged over the material, is what we perceive as its heat or temperature. Lets say we cool our balloon down much further inside a special box that removes energy. The oscillations, on average, will slow down. Eventually, the ice will theoretically get so cold that the atoms no longer oscillate at all. At this point it has reached absolute zero, a temperature measured as - 273.15°C or - 459°F or 0K. I say theoretically because it is not possible in practice to remove all the energy from a system (we are treating our balloon as a physical system). Scientists are finding ways to get very close to absolute zero, and as they do, matter begins to act very strangely. In theory, the ice in our balloon could transform from a solid into a BEC, and when it does it will exhibit some very interesting properties." from this site.
 

Vertigo

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#6
From the article:

"An entirely new state of matter, first observed four years ago (article was written in 1999), has made this possible. When atoms become packed super-closely together at super-low temperatures and super-high vacuum, they lose their identity as individual particles and act like a single super-
atom with characteristics similar to a laser."

So, if I am reading this correctly, the condensate is incredibly dense compared to "normal" matter.
I'm struggling to understand that statement. How can you have atoms "packed super-closely together" and at the same time being a "super-high vacuum"? Seems to me those two have to be mutually exclusive?

Also, and again maybe I'm missing something here, but I thought we have long been able to slow the speed of light down; isn't that what causes refraction? The whole issue of the limiting/constant speed of light is just referencing the speed of light in vacuum isn't it?
 

Brian G Turner

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#7
I thought we have long been able to slow the speed of light down; isn't that what causes refraction? The whole issue of the limiting/constant speed of light is just referencing the speed of light in vacuum isn't it?
I suspect a headline about exploring the refractive index of a Bose-Einstein condensate would have less mass appeal. :)
 

Venusian Broon

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#8
I'm struggling to understand that statement. How can you have atoms "packed super-closely together" and at the same time being a "super-high vacuum"? Seems to me those two have to be mutually exclusive?

Also, and again maybe I'm missing something here, but I thought we have long been able to slow the speed of light down; isn't that what causes refraction? The whole issue of the limiting/constant speed of light is just referencing the speed of light in vacuum isn't it?
I believe most Bose-Einstein condensates are made from cooling a gas of extremely low density. When the temperature is low enough a BEC will form and the atoms rather than acting as Fermions will instead behave like Bosons - in particular they many will occupy the same quantum state, something Fermions are not 'allowed' to do. Hence the reason it's called the 'fifth state of matter'.

As the term condensate suggests, a BEC will be much denser than a gas (after all they have to be in each others physical vicinity to interact and form bosonic pairs etc...) And I guess it will leave, after it's condensation, a super-high vacuum around it :)

Yes we've been manipulating the speed of light in materials for a long time - as you say it's refraction! Of course it's not that the light really slows down, but its the interaction between the light and atoms that causes the apparent reduction in speed.
 

Vertigo

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#9
Ah so what they're saying is that once the atoms have condensed out they will now be a, well, non-gas 'condensate' within a super high vacuum?
 

Venusian Broon

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#10
Ah so what they're saying is that once the atoms have condensed out they will now be a, well, non-gas 'condensate' within a super high vacuum?
Actually reading the sentence now :lol:, I think they are describing the density of the original gas - which from Wikipedia is described as having to be "about one-hundred-thousandth the density of normal air" for a BEC

Other sources state that an ultra high vacuum are pressures below 10^-6 or 10^-7 Pa, for your information.

So I assume they are technically in a high vacuum first to make the BEC.

Think of the transition between water vapour to water, the gaseous water vapour will fill any container it's held in, but as you lower the temperature the atoms will prefer to link together forming a liquid. So as you form a BEC the atoms condense together in a similar way.
 

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