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Coldest Place in the Universe 1

For a long time, we didn't have any way to measure heat or temperature. We've been able to do it for only around 4 centuries - and just recently we discovered the coldest place in the natural Universe.

A few thousand years ago, the Greek thinkers talked about Fundamental Qualities, like Heat and Cold and Dry and Wet. If you combined them in different ways, you could make the four Elements of Earth, Water, Air and Fire. So for example, Earth was Dry and Cold, while Fire was Dry and Hot. But nobody could actually measure temperature.

In 1603, Galileo had already built an instrument called a "thermoscope". It could indicate temperature by measuring the expansion of air as it heated up. By the 1630s, scientists had already developed a thermometer - it measured temperature by having a liquid expanding inside glass.

We measure temperature in degrees because of Giovanfrancesco Sagredo, who was both a follower of Galileo and instrument-maker for the famous House of Medici. Now a circle has 360 degrees. Giovanfrancesco divided his thermometer scale into 360 individual marks like a circle - and so scientists just followed his lead and started calling the individual marks on the thermometer, degrees.

The scientists soon ran into the problem of how to calibrate their thermometers from one town to another, or from one country to another. So they came up with the idea of a Fixed Point, that anybody anywhere in the world could measure and get the same result for. These Fixed Points included the freezing point of water, the boiling point of water, and obscure and local measurements like the temperature in the deepest cellar of the Paris Observatory, or the maximum summer temperature in your home country whether it be Italy, or elsewhere. Isaac Newton suggested as a Fixed Point the hottest bath a man could withstand, without having to stir the water with his hands. But the boiling and freezing points of water were the obvious choices for Fixed Points, and soon everybody started using them.

Most of the world measures temperatures in Celsius degrees (also called Centigrade degrees). This is a scale named after Anders Celsius, who lived from 1701 to 1744. But some parts of the world use the Fahrenheit scale named after Daniel Gabriel Fahrenheit, who lived from 1686 to 1736. A Celsius degree is 1.8 times bigger than a Fahrenheit degree. Water freezes into ice at 0ºC (which corresponds to 32ºF), while liquid water boils into steam at 100ºC (which corresponds to 212ºF). Just as an aside, the Celsius and Fahrenheit scales meet at -40 - so -40ºF is the same temperature as -40ºC. (Scientists think that it's really funny, when they give the temperature as -40, to leave off the C or the F.)

If you're going to measure really low temperatures, it gets messy talking about minus 200-and-something degrees C, so the scientists switch over to the Kelvin Scale. You don't call them Kelvin degrees, just Kelvins. One Kelvin is the same size as a Celsius degree. So the Kelvin scale is like the Celsius scale, but offset with a lower zero point. Absolute zero is Zero Kelvin, which is -273.15ºC, or 273.15 degrees colder than the freezing point of liquid water into ice. This is the absolute coldest temperature possible, and we've never ever got to it. In fact, Quantum Mechanics suggests that we can never get to it.

Now probably the hottest temperature ever experienced in the entire known Universe happened with the Big Bang, and the temperature back then was 1030ºC, or one million million million million million degrees. The hottest temperature we've ever been able to achieve in a laboratory was at Fermilab in the American midwest, where they briefly reached a temperature of 1014ºC (100 million million degrees). A nuclear explosion, and the centre of our Sun, are around the same temperature of about 10 millionºC. The centre of the Earth and the boiling of tungsten are around 5,750ºC, which is around 500 degrees hotter than the surface of the Sun. The hottest temperature reliably measured on the surface of the Earth was in Lybia in 1922 with a reading of 58ºC.

If you keep heading down the scale, water freezes at 0ºC while mercury freezes at -39ºC. The average surface temperature of Mars is around -49ºC, while the coldest temperature ever measured on the surface of the Earth is -89ºC. This was measured at the Russian Vostok Base in Antarctica, in 1983.

The coldest temperature that our scientists have ever generated is one ten thousandth of one millionth of a degree above Absolute Zero, and this was achieved at the Helsinki Technical University. The average temperature of the entire Universe is around 2.73 Kelvin, or 2.73ºC above Absolute Zero. And the coldest place that we've ever found in space is the Boomerang Nebula, and that's even colder - and that's what I'll talk about, next time...

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