# Can absolute zero ever be measured?

1. Oct 5, 2012

### sirchick

Hey

I was wondering - is it physically impossible to make something absolute zero and then measure it to check if it was?

I often read that we bring things down to "close to absolute zero" but it never is the full way.

Is it because if human or electronic device, which ever it was that tried to measure the temperature of the object, would be giving off heat and always heat the object a tiny bit?

In affect - the only way to reach absolute zero would be only by not measuring temperature.

2. Oct 5, 2012

### Alkim

This could be so (I mean measurment affecting temperature) for quantum systems with very limited number of particles if temperature could be defined for a very small number of particles. However, temperature is a macroscopic function of the kinetic energy of a particle ensemble . The fewer the particles in a system, the more pronounced quantum effects are. For example, in the case of say a single electron, it is impossible to measure its velocity, energy or whatever property without affecting its magnitude. This is known as the uncertainty principle. Macroscopic systems are a different thing. Their temperature can be decreased as much as allowed by available technology, but never brought to zero since it is an asymptotic value. The reason is that even if you stop atom's Brownian motion, electrons can not be brought to complete halt.

Last edited: Oct 5, 2012
3. Oct 5, 2012

The third law of thermodynamics forbids reaching a temperature of zero with a finite number of cooling steps.

4. Oct 5, 2012

### phinds

you can't measure what doesn't exist

5. Oct 5, 2012

### sirchick

So absolute zero is impossible no matter how long the universe cools for ?

6. Oct 5, 2012

### phinds

That's a good question. I'm not sure about that one, but I AM sure that LONG before it gets there, there won't be any living things around to see it happen or measure it.

7. Oct 5, 2012

### sirchick

Do scientists believe absolute zero cannot be achieved then ? Or does it violate some physical law that we believe in =/

They always mention about the universe having a big freeze but they don't mention how cold it could theoretically get.

8. Oct 6, 2012

### Drakkith

Staff Emeritus
The temperature would approach absolute zero, but never reach it. Absolute zero isn't a barrier that can be broken. It is more like the speed of light. You can always approach it, but never reach or exceed it. It has to do with how energy is absorbed and emitted by a bulk material that we can assign a temperature to. It simply isn't possible to remove ALL thermal energy from an object OR keep it from absorbing any more once it reached that state. Neither are possible!

9. Oct 6, 2012

### Alkim

No, absolute zero cannot be achieved. However, very very low temperature (of the order of 10E-14 K) has been achieved in some systems (Bose-Einstein condensates) as well as negative temperature. However, in the latter case you should not imagine extreme cold but rather extreme hot. For more details see http://en.wikipedia.org/wiki/Negative_absolute_temperature

10. Oct 8, 2012

### snorkack

Ground state is equivalent to absolute sero.

Atoms and small molecules in ground state are common. The first excited state of electrons is usually quite high in energy.

The problem with creating and measuring macroscopic assemblies in or near ground state is phonons. While small wavelength phonons, representing oscillations of only a few atoms around bonds, carry high energy, phonons also include long wavelength ones. Slight mechanical distortion of a large part of a crystal or liquid would have large mass and mosest restoring force; therefore the first excited state would have extremely low energy. And these low energy phonons are hard to eliminate completely.

11. Oct 8, 2012

### mikeph

What is temperature? It is a property of a system that characterises its ability to transfer energy to something else that it is in thermal contact with. If something is (hypothetically) at 0 K, then that means it has no ability to transfer energy away. How can anyone verify a negative result such as this?