Temperature is one of those fundamental concepts that, despite our daily experience, easily gets us confused. And that’s not just true for non-experts. Temperature has been a crucial scientific concept for centuries and understanding its limits impacts us far beyond pure science.
It all comes down (pardon the pun) to thermodynamics, the study of energy, temperature, heat, and work and their relationship to each other. The four laws (from zero to third) are so fundamental that they appear in completely different disciplines. And people have spent their lives trying to refute them, without success.
The zero law asserts that temperature is an important empirical parameter and that thermal equilibrium is a transitive relationship. Thus, if object A and object B are in thermal equilibrium with object C, they are also in thermal equilibrium with each other. This is like saying that thermometers are indeed an accurate way of measuring things, and if we say yesterday was X degrees and then we say today is also X degrees, that means both days had the same temperature.
One of our favorite analogies for the other three laws is to imagine the universe as a gambling table. The first law is the conservation of energy and this is equivalent to knowing that you cannot win at this table because you cannot create something out of nothing. The second law tells us that you can’t even draw. No system is 100% efficient and entropy always increases in an isolated system. Sorry, perpetual motion machine fans, that can’t be done.
The third says you can’t leave the table. You can’t choose not to play this game. You are subject to the laws of thermodynamics wherever you go and these laws suggest that there is an ultimate lowest possible temperature: absolute zero.
What is absolute zero?
The temperature of an object or substance is due to the movement of its molecules. The hotter it is, the more the molecules tremble. As energy is removed from a system by thermodynamic processes (as in a refrigerator for example), the molecules slow down.
And that’s where absolute zero comes in. There will be a point where the molecules are still, motionless. There’s no way to slow them down any further. No other lower temperature can be reached.
The value of absolute zero is −273.15°C (−459.67°F) or simply 0 Kelvin in the International System of Units scale. The record for the coldest temperature ever reached was broken just over a year ago when rubidium gas cooled to 38 picokelvins (3.8 * 10-11 K), really just a fraction above absolute zero.
What is the hottest temperature in the Universe?
Humans like symmetry, so if there is a lower limit, is there also an upper limit? Well, things are not so clear cut when it comes to how hot something can be. The hottest temperature ever created in the lab was 5 trillion kelvins. It was created in the Large Hadron Collider and it was the temperature of the Universe moments after the Big Bang.
But can you go hotter than that? It could be possible for sure. When it comes to hottest physics, we’ve yet to find anything as strict as absolute zero. Absolute heat has several possibilities, it could be 10,000 times hotter than what we have achieved in particle colliders for example. But it’s not strict.
The only limit that can be found in physics depends on the so-called Planck scale. This set of measurement units depends exclusively on physical constants and tends to signal where physics as we know it breaks down. The Planck temperature is equivalent to 1.4 x 1032 K. That’s 100 billion billion times what you can get in a particle accelerator. Scientists don’t believe it’s possible to get hotter than this, but the true limit could be much lower.
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