What Happens to Volume & Pressure at Absolute Zero?

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At absolute zero, which we denote by zero Kelvin, this is equal to approximately negative 273 degrees Celsius. Find out what happens to volume and pressure at absolute zero Kelvin with help from an applied physics professional in this free video clip.

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Hello. My name is Walter Unglaub, and this is what happens to volume and pressure at absolute zero. So at absolute zero which we denote by zero Kelvin, this is equal to approximately negative 273 degrees Celsius, we can begin by assuming the ideal gas law which states that pressure times volume is equal to number of particles times the Boltzmann constant KB times T, temperature. Now temperature is a thermodynamic quantity that is only truly physically meaningful when you have a large collection or ensembles of particles. So when T, the temperature goes to zero then this law breaks down as does a lot of thermodynamic quantities. In particular as the temperature starts to decrease we notice by experiments done on atoms, cooling them to temperatures close to zero Kelvin, that we can generate a new type of matter known as a Bose Einstein Condensate or BEC for short. And we do this by trapping a collection of atoms and some sort of optical potential for example, confining them with an external magnetic field and evaporating off the atoms that have the highest kinetic energies. And when this happens something interesting happens. All the atoms start to arrive at the ground state energy which is the lowest state energy and the wave functions begin to overlap. So you end up with a microscopic quantum mechanical entity. And because the ground state of these collection of atoms is not absolute zero, there will always be quantum mechanically some ground state energy which is greater than zero. You can not truly achieve absolute or zero Kelvin temperatures. But we do know that as the temperature decreases the pressure will decrease because these atoms are almost not moving at all and the volume will start to decrease rapidly as well. Because these atoms will have, will share a wave function and be able to almost coexist at the same point in space. They'll act as if they were Bose zones like photons for example. So we can make a prediction at least mathematically that if we truly had absolute zero that pressure and volume would disappear. And this would be tantamount to the atoms effectively not existing or interacting with their environment whatsoever. But because of quantum mechanics we know that this is physically impossible. My name is Walter Unglaub, and this is what happens to pressure and volume at absolute zero.

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