2,442 total views
The coldest place on Earth… The bottom of the ocean? Antarctica perhaps? Room A521, Physics Building, Lancaster University? You’d be forgiven for getting this wrong. Most people, students and staff alike, walk around campus completely unaware that they’re perhaps no more than 500ft away from one of the world’s leading Ultra Low Temperature laboratories. Lancaster University actually holds the world-record for the coldest temperature ever reached; a chilly 0.000006 Kelvin (or about -273⁰C to you and I). That alone is definitely an achievement worth bragging about, but how have they managed this? And perhaps more importantly, why have they bothered?
Believe it or not, ‘coldness’ does not go on forever. Temperature is related to the energy inside a substance and there is an Absolute zero value of temperature (zero Kelvin) which represents zero internal energy; it is impossible for anything to be colder than this value. Below certain temperatures substances begin to lose ‘degrees of freedom’, for example water turning into ice; below 0⁰C, it no longer flows. The colder a substance gets, the simpler it becomes to study; just as measuring a block of ice with a tape measure is easier than measuring a block of water. This brings us to one of the main reasons why low-temperature physics is useful; it makes very complex situations easier to understand and quantify. Another reason is that at these extremely low temperatures matter begins to take on some very peculiar properties, Helium becomes a super-fluid with zero viscosity and can crawl up walls or creep into spaces which are only the size of an atom.
In the lab at Lancaster, there are three cryostats (big fridges) which vary in size, cryo meaning ‘icy cold’ and stat meaning ‘stable’. Each of these are cooled by roughly the same process. The cooling process begins like that of a conventional refrigerator; a substance with a low boiling point is compressed into a liquid, the liquid is then allowed to expand and evaporate, absorbing energy from its surroundings as it does so and therefore causing the surroundings to cool down. In the cyrostats, liquid helium is used, which has a boiling point of a mere -269⁰C. To bring the temperature down those last few degrees, a more complex process is used called demagnetisation which, as its name suggests, involves applying a strong magnetic field to a metal (copper in this case) cooling it down and then demagnetising it. To get back to its original state, the copper is forced to absorb energy from its surroundings cooling them as low as -273⁰C.
There are two main experiments running at Lancaster as the moment, the first involves cooling Helium-3 (a rare isotope of helium) until all its different states are ‘frozen out’ and it behaves simply like one large molecule. Helium-3 is used because of its incredibly low melting point and because of certain properties which make it behave more interestingly than Helium-4 (the helium used to fill balloons). When Helium-3 is cooled to 0.0001 Kelvin, it is a super-fluid and takes on the simplest form that it is possible for it to be in. In this state it can be used to study several different phenomena.
One application is related to the rapidly developing field of nanotechnology; the manipulation of matter on an atomic scale, which is being used heavily at the moment to help develop new and better materials and devices with a vast range of applications from medicine to mobile phones. When you’re trying to manipulate atoms at nano-scale (around 1×10−9 m) the effects of quantum mechanics (a complex and poorly understood area of physics) are very prominent. These quantum mechanical effects can be frozen out at low temperatures and manipulating nanotechnology instantly becomes much simpler and much more similar to dealing with everyday macroscopic objects we’re more familiar with.
Another interesting phenomenon is that in this state, the Helium-3 has properties remarkably similar to the theorised structure of the metric of the universe (the structure of space-time) and for this reason can be used as a tool in the study of cosmology (the study of the origin and evolution of the universe). Cosmological theories are notoriously difficult to test due to the impossibility of re-creating scales and conditions present in the early universe. Super-fluid helium-3 can provide a solution to this problem by modelling the different ways space-time may have behaved and warped as the universe evolved.
Perhaps the most exciting results these experiments can achieve are the ones that no physicist has predicted. Like high speed, high temperature, or small scale physics; low temperature physics is pushing at the boundaries of science as we know it. Humans have never investigated temperatures this low before, and we just don’t know what weird and wonderful phenomena we might discover.
Is it safe? Is all this talk of the structure of the universe making you think Large Hadron Collider and destruction of the earth? Worry not, as one of the leading research supervisors Prof. G R Pickett informed me, the biggest danger is falling down the three metre hole. Helium gas is extremely safe and inert.
Is it worth it? I’m sure you can imagine how much an experiment on this scale might cost, Helium-3 is extremely rare, and the technology needed to create and maintain the temperature in addition to the technology needed to make the observations during experiments is very advanced and very pricey. If the uses I’ve described here haven’t convinced you, however, remember that this is the very frontier of science research – we simply do not know what we’re going to find. The same could have been said about the people researching into the composition of atoms, yet without that research, we’d never have reaped the benefits of nuclear physics.
So next time you take a stroll past the Physics department just pause to consider, whilst you’re stood there sipping your Greggs coffee, that there are people in that building growing ever closer to unlocking the secrets of the Universe. And appreciate how warm you really are.