# I Absolute zero temperature is impossible to achieve?

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1. Nov 24, 2017

Just a general musing. Could absolute zero ever be physically possible or is it like the speed of light but for an inverse reason? The speed of light take infinite energy to achieve. So therefore is impossible because the energy put into the system adds mass. This is not noticeable at slower speeds but I would imagine the speed vs mass converts more and more to mass and your speed increase becomes less and less the faster you go, thus preventing you from ever reaching the speed of light. I have learned in calculus that one of the definitions of Zero is 1/infinity. Could this mean that absolute zero is impossible because it takes an infinite amount of energy removal to reduce the molecular motion to zero? And the issue with energy removal is the greater the difference between ambient energy and the energy of a system is the harder it becomes to remove said system energy to the point it becomes infinitely hard to remove the system energy.
Thanks

2. Nov 24, 2017

### phinds

The answer is no, but I don't remember the specifics --- this has been asked and answered MANY times here on PF so I suggest a forum search for the details.

3. Nov 24, 2017

Thank you for your answer. I did do a forum search and I worded my question poorly. I was aware of not being able to get to absolute zero. I was just wondering on the possible why. I will see if I can search a bit deeper and dig up the why.

4. Nov 25, 2017

### Staff: Mentor

The way to cool an object to temperature $T$ is to put it in contact with something colder than $T$. (Putting it in contact with an object whose temperature is exactly $T$ won't do the trick because as heat flows from the warmer object to the colder object, the colder one warms up so we end up with the two objects in equilibrium at a temperature higher than $T$).

So to cool an object to absolute zero you need something colder than absolute zero. And where are you going to find that?

5. Nov 26, 2017

So how does laser calling work? I was under the impression they could use lasers to cool an object with no physical contact. https://en.m.wikipedia.org/wiki/Laser_cooling

6. Nov 26, 2017

### jerromyjon

That depends if you consider "an atom absorbing and emitting photons" as physical contact... or magnetic fields manipulating atoms in
Magnetic refrigeration
So the only way you could hypothetically remove "all" contact from an atom is to surround it with atoms at absolute zero which don't exist.

7. Nov 26, 2017

### willem2

This seems to imply that refrigerators aren't possible. You can get lower than the temperature of the environment. The third law of thermodynamics implies that you can only reduce the absolute temperature in a single cooling stage by a constant factor. This was already known for a lot of cooling methods, but a rigorous proof of this was only given this year. http://www.nature.com/articles/ncomms14538