Scientists Create Rare Fifth Form of Matter in Space | Hacker News Reader

Scientists Create Rare Fifth Form of Matter in Space

livescience.com

47 pointsmotiw14 comments

Here's the Wikipedia article on laser cooling: https://en.wikipedia.org/wiki/Laser_cooling

Its explanation is a bit too surface level for me. Anyone have more details on the mechanism used for this experiment? Would they have used Doppler cooling like is sometimes done on Rb-85?

Author here. Yes, Doppler Cooling is the first step used in the experiment, in a Magneto Optical Trap [0]. It is followed by Polarization Gradient Cooling [1] to overcome the Doppler limit. Atoms are still way too "hot" after this step, so they are then transferred to a purely magnetical trap and cooled down further via forced evaporation [2].

[0] https://en.wikipedia.org/wiki/Magneto-optical_trap

[1] https://en.wikipedia.org/wiki/Sisyphus_cooling

[2] https://en.wikipedia.org/wiki/Evaporative_cooling_(atomic_ph...

Thanks!!

why does bombarding tightly-packed rubidium-87 atoms with lasers cool them to minus 273.15 degrees Celsius?

The simplest way to explain it is this:

Atoms can only absorb very specific and exact frequencies of light. But because the atoms are moving, the frequency of light, as seen by the atom, varies a lot.

If you only shine light that is slightly below the lowest frequency of light the atom can absorb, only those atoms that are moving toward the light (and thus "see" a slightly higher frequency) are able to absorb that light.

Then the atom emits that light - which is always at the exact frequency. In the process you basically "steal" energy from the atoms motion, and emit it back out as ever so slightly higher frequency light.

Since the atoms are now moving slower they are colder. You keep doing this until you've gotten as much out of the process as you can.

So do the moving atoms "see" different frequencies because of doppler effects, or something else?

Yes, doppler effect.

There are way more than five phases of matter...

Please do educate us.

The Bose-Einstein condensate that the article talks about is one of many low-temperature states. There are a few kinds of high-energy states too... the most famous ones being electron degenerate matter (found in white dwarfs) and neutron degenerate matter (found in neutron stars).

I think a good starting point is here: https://en.wikipedia.org/wiki/State_of_matter

Better link (which was found in your link):

https://en.wikipedia.org/wiki/List_of_states_of_matter

        When groups of atoms are cooled to such unfathomably low temperatures, they stop moving as individuals and meld into one big "super atom." Tens of thousands of atoms suddenly become indistinguishable from one another, slowly vibrating on a uniform wavelength that can, theoretically, pick up the tiniest gravitational disturbances around them.

Why should this be called "super atom", just because all atoms behave the same? If I have a bag of indistinguishable rice corns, they don't suddenly become a single "super rice corn".

> If I have a bag of indistinguishable rice corns

Ah, but they actually are distinguishable. If you checked them, their size will vary slightly, the exact position of the atoms making them up with be different, etc, etc.

If you tried, you would be able to find something different about every single grain of rice - even if you had to check at the atomic level.

The thing about this condensate is the atoms ARE truly indistinguishable. Their motion, energy, absolutely everything about this is exactly identical.

But what really makes them special is that they stay that way - they all move together. (At least until they get enough energy to break apart their bond.)

It's that last part that makes them into this "super atom" - they are all bonded together.

Atom means indivisible. Calling it a super molecule might seem like a better term, but it's not about the chemical nature of the substance.

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