Yes, it's even hotter than a Dunedin summer

"Hot" is not a word one would usually associate with a Dunedin summer.

But it's an appropriate description of recent weather, when the temperature has been nudging 30degC.

Even so, we're still a little way from New Zealand's record temperature of 42.4degC in Rangiora in 1973, and quite some distance from Earth's highest air temperature, a truly hot 57.8degC in Libya nearly 90 years ago.

But these numbers pale into insignificance when compared with the 4,000,000,000,000 (four trillion) degC temperature recently attained by researchers at Brookhaven National Laboratory in the United States.

Indeed, this is not only the highest temperature ever reached on planet Earth; it's also (apparently) the highest temperature in the Universe since the Big Bang.

This extraordinary temperature resulted from the collision of gold ions (an ion is any chemical species which bears a positive or negative charge) moving at nearly the speed of light, and led to the production of what is called a "quark-gluon plasma".

This is an unusual state of matter in which the normal constituents of the atomic nucleus, protons and neutrons, break down into their component subatomic particles called (surprise, surprise) quarks and gluons, which at this temperature behave as a liquid.

Such a liquid is thought to have been formed in the first instants of the Big Bang, and this is the reason such research is being pursued.

This then begs the question: "Is there any such thing as the hottest possible temperature?"

My guess is that the answer is yes, but I don't know, and I'm not sure that anyone really does.

However, we do know for certain that there is a lowest possible temperature, and by comparison with the number above, it's not really all that low.

It may surprise you to know that it's impossible to get any colder than a mere -273.15degC, a temperature called absolute zero.

And the reason for this is all to do with the fundamentals of heat itself.

What is heat? The Oxford English Dictionary offers the helpful definition "the quality of being hot" which doesn't really tell you a lot.

In scientific terms, heat is a manifestation of motion.

The atomic and molecular components of everything we see around us are in constant motion; gas molecules are whizzing around at hundreds of metres per second in the air, water molecules constantly jostle and push past each other, while even the atoms and molecules in solids, which are confined to fixed positions, are always vibrating.

All of these motions we experience as heat.

However, when we cool down substances, the atomic and molecular motion becomes less and less, and we eventually reach a temperature at which all motion stops.

That temperature is absolute zero, and it's simply impossible to get any colder.

In fact, it's actually impossible to reach absolute zero.

We can approach it extremely closely (the record is a few trillionths of a degree above absolute zero) but to actually get there would violate the Third Law of Thermodynamics, which would then probably require the Universe to be rewritten.

Hopefully, our winter temperatures this year won't plumb these depths.

• Dr Blackman is an associate professor in the chemistry department at the University of Otago.