# What is the highest temperature in the known universe, and can we reach it

(ORDO NEWS) — From what we know about our universe, the lowest possible temperature is “absolute” zero degrees Kelvin, or -273.15 degrees Celsius. What about the hottest possible temperature?

Physics doesn’t quite understand what the absolute hottest of hot temperatures looks like, but, theoretically speaking, such a thing exists – or at least once existed. It’s called the Planck temperature, but like everything in life, it’s not that simple.

What is temperature?

The first thing that may come to mind when thinking about temperature is a description of the amount of heat that an object contains. Or, for that matter, does not.

Heat, or thermal energy, is an important part of the explanation. Our intuitive understanding of heat is that it flows from higher temperature sources to lower temperature sources, much like a cup of tea cools when we blow on it.

In physics terms, thermal energy is more like an average of random motions in a system, usually between particles such as atoms and molecules.

Place two objects with different amounts of thermal energy close enough to touch, and the random motions combine until both objects come into balance. As a form of energy, heat is measured in units of joules.

Temperature, on the other hand, describes the transfer of energy from hotter regions to colder regions, at least in theory.

It is usually described as a scale in units such as Kelvin, Celsius, or Fahrenheit. The flame of a candle may be hot compared to an iceberg, but the amount of heat energy in a heated wick will not matter much if it is placed against a mountain of frozen water.

What is absolute zero?

Absolute zero is temperature, that is, a measure of the relative transfer of thermal energy. Theoretically, it marks the point on the temperature scale when, according to the laws of thermodynamics, thermal energy can no longer be removed from the system.

From a practical point of view, this exact point remains out of reach forever. But we can get tantalizingly close: All we need are ways to reduce the average amount of thermal energy distributed between the particles of the system, perhaps with lasers or a suitable magnetic field.

But in the end, there is always an energy averaging that leaves the temperature a fraction above the theoretical limit of what can be extracted.

What is the highest possible temperature?

If absolute zero places a limit on how much heat we can take from a system, it makes sense that there is also a limit on how much heat we can put into the system. And there is. In fact, there are several limits, depending on which particular system is in question.

One limit is the Planck temperature of 1.417 x 1032 Kelvin (or 141 million million million million million million degrees). This is what people often refer to as “absolute temperature”.

Nothing in the modern universe comes close to such temperatures, but they existed for a brief moment at the dawn of time.

In that fraction of a second one unit of Planck time, in fact when the universe was only one Planck length, the random motion of its contents was as extreme as could possibly be.

If it were even hotter, then forces such as electromagnetism and nuclear forces would equal the force of gravity.

To explain what this looks like requires physics that we don’t yet know, but that combines what we know about quantum mechanics with Einstein’s general theory of relativity.

These are also quite specific conditions. Time and space will never again be so limited. Today, the best the universe is capable of is the measly few trillion degrees we create when we knock atoms together in a collider.

The opposite of absolute zero

But there is another way of looking at heat that turns the whole question of temperature on its head.

Remember that thermal energy describes the average amount of movement between parts of a system. Only a small percentage of particles flying randomly around the system is enough to consider it “hot”.

What happens if we reverse this state and get much more lightning particles than sluggish ones? This is what physicists call the inverted Maxwell-Boltzmann distribution, and oddly enough, it is described by values ​​below absolute zero.

This strange system seems to cross out all the rules of physics. Not only do we quantify it as a negative value relative to absolute zero, it is technically hotter than any positive value. Literally hotter than hot.

Like a quirk of statistics, it’s not something we could find in any natural corner of the universe. On the one hand, this requires an infinite amount of energy, and even more.

But that doesn’t mean we can’t break the rules a little and create something similar. In 2013, physicists from the Ludwig Maximilian University in Munich and the Max Planck Institute for Quantum Optics in Germany demonstrated this possibility; they have used atomic gases under very specific conditions which impose their own upper energy limits.

The result was a stable system of particles with so much kinetic energy that it couldn’t be pushed in anymore. The only way to describe this particular system is to use a temperature scale that goes into the negative Kelvin, or a few billionths of a degree below absolute zero.

Such a bizarre state could theoretically absorb thermal energy not only from hotter, but also from colder spaces, which made it a real monster of extreme temperatures.

In this diabolical corner of the universe, a machine could operate at over 100 percent efficiency, powered by both hot and cold, as if spitting on the laws of thermodynamics.

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