Why absolute zero is impossible

When applied to cooling, the question becomes how much work must be done and how large must the cooling reservoir be in order to cool an object to absolute zero 0 Kelvin, The physicists showed that cooling a system to absolute zero requires either an infinite amount of work or an infinite reservoir. This finding is in agreement with the widely accepted physical explanation of the unattainability of absolute zero: As the temperature approaches zero, the system's entropy disorder approaches zero, and it is not possible to prepare a system in a state of zero entropy in a finite number of steps.

The new result led the physicists to a second question: If we can't reach absolute zero, then how close can we get with finite time and resources? It turns out that the answer is closer than might be expected. The scientists showed that lower temperatures can be obtained with only a modest increase of resources.

Yet they also showed that there are limits here, as well. For example, a system cannot be cooled exponentially quickly, since this would result in a negative heat capacity , which is a physical impossibility.

One of the nice features of the new proof is that it applies not only to large, classical systems which traditional thermodynamics usually deals with , but also to quantum systems and to any conceivable type of cooling process. For this reason, the results have widespread theoretical implications.

Cooling to very low temperatures is a key component in many technologies, such as quantum computers, quantum simulations, and high-precision measurements. Understanding what it takes to get close to absolute zero could help guide the development and optimization of future cooling protocols for these applications.

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However, we do not guarantee individual replies due to the high volume of messages. This prompted Nernst to double down on his thinking and propose the second rule in , declaring absolute zero to be physically impossible. Together, these rules are now acknowledged as the third law of thermodynamics, and while this law appears to hold true, its foundations have always seemed a little rocky - when it comes to the laws of thermodynamics , the third one has been a bit of a black sheep.

In order to test how robust the assumptions of the third law of thermodynamics actually are in both classical and quantum systems , Masanes and his colleague Jonathan Oppenheim decided to test if it is mathematically possible to reach absolute zero when restricted to finite time and resources. Masanes compares this act of cooling to computation - we can watch a computer solve an algorithm and record how long it takes, and in the same way, we can actually calculate how long it takes for a system to be cooled to its theoretical limit because of the steps required to remove its heat.

You can think of cooling as effectively 'shovelling' out the existing heat in a system and depositing it into the surrounding environment. How much heat the system started with will determine how many steps it will take for you to shovel it all out, and the size of the 'reservoir' into which that heat is being deposited will also limit your cooling ability. In their experiment, the scientists first cool around a hundred thousand atoms in a vacuum chamber to a positive temperature of a few billionths of a Kelvin and capture them in optical traps made of laser beams.

The surrounding ultrahigh vacuum guarantees that the atoms are perfectly thermally insulated from the environment. The laser beams create a so-called optical lattice, in which the atoms are arranged regularly at lattice sites. In this lattice, the atoms can still move from site to site via the tunnel effect, yet their kinetic energy has an upper limit and therefore possesses the required upper energy limit.

Temperature, however, relates not only to kinetic energy, but to the total energy of the particles, which in this case includes interaction and potential energy. The system of the Munich and Garching researchers also sets a limit to both of these. The physicists then take the atoms to this upper boundary of the total energy — thus realising a negative temperature, at minus a few billionths of a kelvin. I f spheres possess a positive temperature and lie in a valley at minimum potential energy, this state is obviously stable — this is nature as we know it.

If the spheres are located on top of a hill at maximum potential energy, they will usually roll down and thereby convert their potential energy into kinetic energy. The energy limit therefore renders the system stable! This does not mean, however, that the law of energy conservation is violated.

Instead, the engine could not only absorb energy from the hotter medium, and thus do work, but, in contrast to the usual case, from the colder medium as well. At purely positive temperatures, the colder medium inevitably heats up in contrast, therefore absorbing a portion of the energy of the hot medium and thereby limits the efficiency.

If the hot medium has a negative temperature, it is possible to absorb energy from both media simultaneously. The work performed by the engine is therefore greater than the energy taken from the hotter medium alone — the efficiency is over percent.

The achievement of the Munich physicists could additionally be interesting for cosmology, since the thermodynamic behaviour of negative temperature exhibits parallels to so-called dark energy.

The reason has to do with the amount of work necessary to remove heat from a substance, which increases substantially the colder you try to go. To reach zero kelvins, you would require an infinite amount of work. And even if you could get there, quantum mechanics dictates that the atoms and molecules would still have some irreducible motion. At low enough temperatures, liquid helium, for example, morphs into a superfluid—a liquid that flows without the resistance of friction. Working at around just 1 to 10 millikelvins, or thousandths of a kelvin, the Cavendish team is in the process of surveying a variety of other materials that also show funky quantum behavior.

The journey towards absolute zero began in the early s when Guillaume Amontons contended that if temperature is the measure of heat in a system, then there must be a lowest possible temperature.

At Leiden University, Heike Kamerlingh Onnes and his colleagues raced against others around the world to develop techniques to liquify helium.

The cooling process itself is similar to what happens when you blow on hot cup of coffee to cool it down. As the person blows, the more chaotic, faster-moving coffee molecules are encouraged to evaporate and, therefore, move away from the cup. The molecules left behind are on average moving slower—consequently making the coffee a more drinkable temperature. Unlike everyday refrigerators that use vapor from inside the fridge, however, Onnes used helium in the gas state and hydrogen and oxygen in the liquid state to achieve low temperatures.

In doing so, the excess heat from the gaseous state dissipated and the system achieved a temperature merely six. This research won Onnes the Nobel Prize in