Tuesday, 14 June 2016

The Coolest Stuff in the Universe – Approaching Absolute Zero

The Coolest Stuff in the Universe – Approaching Absolute Zero
We went to a lecture a while back (March 15, 2016), at the University of Alberta, by Nobel laureate Dr. William Phillips, of NINST (National Institute of Technology), in the U.S.. He is also a professor at the University of Maryland. The professor's Nobel was for work in “laser cooling”, a technique used to bring the temperature of certain gases down to very close to absolute zero.

Time and Motion

One of the key reasons for wanting to cool matter down to very low temperatures, is to make more accurate clocks. We measure time via motion – that can be anything from:
  • the motion of the Earth around the sun (year),
  • to the motion of the moon around the Earth (month),
  • to the swing of a pendulum (seconds),
  • to the oscillations of a spring (less than a second),
  • to the oscillations of atoms (millionths of a second).
The random thermal motion that we call heat makes it difficult to measure time with great precision, so by eliminating as much of this heat as possible, we can measure time more accurately.
Another way that motion affects time, is via Einstein's equations of special relativity. As the saying goes, “moving clocks run slow”. At the highest levels of accuracy, we use devices such as atomic clocks, so we are interested in the realm of the very small, when we talk about cooling matter to these very low temperatures, millions of a degree above absolute zero. When using atoms as clocks, it is helpful to keep the state of motion of the atoms as low as possible, and thus it is necessary to keep the “clock” as cool as possible.
One might wonder if these esoteric concerns of physicists have any practical effect on everyday society. In fact they do, in an application that is vital to the entire world - the geographical positioning system or GPS. Positions on Earth are determined via the timing of signals from multiple satellites, so extreme precision in timing is needed to produce extreme precision in geographical positioning. Super accurate clocks are also needed to efficiently coordinate computer networks, as well as for various types of advanced scientific research (particle physics, astrophysics).

Temperatures and Cooling

Getting back to temperatures and cooling, the professor (who was quite a showman), demonstrated how the temperature regime at which we humans live (about 290 Kelvin) is quite special. Via the use of a fair bit of liquid nitrogen (77 Kelvin), he showed how matter's characteristics change, when cooled down far below our special temperature range. Here are a few examples:
  • Inflated balloons collapsed to pancake thinness after immersion in liquid nitrogen, then re-inflated after being re-exposed to room temperature. In fact, several popped, perhaps because of the strain on the rubber, caused by the temperature changes.

  • Carnation flowers froze to rigidity after being immersed in the liquid nitrogen, and then the petals shattered after being withdrawn and given a sharp blow.

  • Rubber balls go from bouncy before immersion, to smashy afterwards.

  • After pouring liquid nitrogen into a plastic bottle, then sealing it tightly, the bottle was placed under an overturned wastepaper basket. After some minutes, the pressure of the warming nitrogen burst the bottle, which was safely under the wastepaper basket, and the gas then blew the overturned basket to the ceiling. Quite a show, that was (no picture, though)

  • And, of course, just the act of spilling liquid nitrogen on the floor was “pretty cool”, as it quickly boils off in a dramatic display of vapour.
But liquid nitrogen only takes you only part of the way to absolute zero , which is the theoretically coldest temperature that can be achieved. All motion stops at that point (strictly not true, due to quantum mechanical effects). Liquid nitrogen is 77, on the Kelvin scale. A number of other atoms can be used, whose liquid or solid states are at much lower temperatures, helium for example, which gets to a few degrees above absolute zero. Most of this initial cooling is via evaporative cooling.
But how do you cool matter to temperatures barely above absolute zero? One way is through the technique of laser cooling. In fact, Professor Philloips won the Nobel for his work on laser cooling.
The principle behind this, is to use radiation pressure to slow down atoms of a gas (usually cesium). This is the same effect as that produced by the sun's light on a comet's tail, causing the gas molecules to stream away from the sun, as they are boiled off, while in the inner solar system.
To cool gas (slow down the atoms), laser light is pumped into the gas, so as to resonate at the natural vibration frequency of the atoms. Doppler shifted atoms can be selected for cooling, with different laser frequencies. When the atoms absorb the appropriate frequency of radiation, they are slowed down, somewhat like marbles in a viscous fluid. This has been given the nickname “optical molasses”.

Of course, when the radiation is re-emitted, the atoms speed up (gain heat). But this emmission process is in random directions, while the absorbtion that slows the atoms can be tuned in one direction. The cumulative effect allows the process to lead to very low temperatures.
For example, sodium atoms can be cooled to 240 micro-Kelvins via this method. Even lower temperatures have been acheived, such as 700 nano-degrees (billionths of a Kelvin). At the lowest temperatured, the atoms might only be moving at speeds on the order of a centimeter per second, rather than the hundreds of meters per second typical of gases at “normal” temperatures. But that's not the end – Bose-Einstein condensates have been used to get to even lower temperatures, less than one nano-degree above absolute zero.
It is worth noting that the coldest “natural temperature” is about 3 degrees Kelvin, the residual background heat from the big bang. So, short of what aliens might be doing, this really is the coolest stuff in the universe.
Atoms can both be cooled and trapped this way. Magnetic containment is also used, to keep the atoms from warming as they would interact with normal conainers. The professor showd the audience an example of a toy that uses magnetic levitation, to keep a gyroscope suspended in mid-air, to give a concrete demonstration of this phenomenon.

Between laser cooling and magnetic containment, atomic clocks have been made that are accurate to one part in 10 to the -18. That is equivalent to one second every 10 billion years, which is about the estimated current age of the observable universe.

It is hard to imagine a need for even more timing accuracy, though I imagine there is such a need, and the professor and his team (and others) are working on the problem right now. 

Source:  https://uofa.ualberta.ca/physics/about-the-department/events/time-einstein-and-the-coolest-stuff-in-the-universe


Science is cool (especially the science of super-cooling matter), but so is Science Fiction. So, you should consider reading the books described below. :)

The Witches’ Stones Series

The Witches' Stones, Book 1 - Rescue from the Planet of the Amartos

Young Earth woman and spaceship mechanic, Sarah Mackenzie, has unwittingly triggered a vast source of energy, the Witches' Stones,  via her psychic abilities, of which she was unaware.  She becomes the focal point of a desperate contest between the authoritarian galactic power, known as The Organization, and the democratic Earth-based galactic power, known as The Terran Confederation.  The Organization wants to capture her, and utilize her powers to create a super-weapon; the Terra Confederation wants to prevent that at all costs.  The mysterious psychic aliens, the Witches of Kordea also become involved, as they see her as a possible threat, or a possible ally, for the safety of their own world.

A small but fast scout-ship, with its pilot and an agent of the Terra Confederation, Coryn Leigh, are sent to rescue her from a distant planet at the very edge of the galaxy, near space claimed by The Organization.  Battles, physical and mental, whirl around the young woman, as the agent and pilot strive at all costs to keep her from the clutches of the Organization.

The Witches' Stones, Book 2 - Love and Intrigue, Under the Seven Moons of Kordea

Sarah has taken refuge on the planet of Kordea, where she is also learning how to control her psychic abilities, through the tutelage of the Witches of Kordea.  Coryn Leigh has now taken up the position of Confederation diplomat to the Kordeans, but he is also charged with keeping the Mackenzie girl safe at all costs.  During their time on the planet, an attraction between them grows, though they try to deny it, to themselves and each other.
But The Organization has plans of its own, including threatening the destruction of the planet Kordea, via destabalizing the orbit of Lina, one of its many moons.  The Organization proves that its threats are in deadly earnest, so, ultimately Sarah, Coryn and the Witches of Kordea must take the fight to the enemy.  Thus is borne a dangerous mission, to  a planet where their foe has based the weapon that threatens Kordea, and ultimately, the balance of power throughout the galaxy.  Sarah and Coryn agree that the machine must be destroyed, even at the possible cost of their own lives and growing love.

The Witches' Stones, Book 3 - Revenge of the Catspaw

Sarah and Coryn have become married, under the traditions of the Witches of Kordea.  But the marriage is performed by the Eldest of the most important coven, a rare honour, that comes with a blessing and a curse.  The slow working out of this blessing and curse forms the backdrop to the story.

Having come so close to their goal of enhancing their weaponry via Witches' Stone power, The Organization will not give up.  In order to lure Sarah into their trap, and thus have her become their Catspaw (someone who is forced into helping another, against their will) they need bait, and Coryn becomes the bait.  He also comes under the domination of a particularly nasty Elite of The Organization, one "Evil Evilla" Copoz.

Sarah, and a picked group of companions, must re-enter The Organization space, this time to the very heart of the empire, to rescue her husband, as he has done for her in the past.  They do so at great peril, but nothing can stop the terrible Revenge of the Catspaw.

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