# Brainstorm: Is absolute zero relative

• B
• unix101os
I just realized that I am wrong about everything I just said. If you consider a collection of particles moving at different velocitie...In summary, the conversation discusses the concept of absolute zero and the coldest temperature ever reached in a lab which was 0.006K according to Google. The idea of absolute zero being unattainable is explored, and the conversation delves into the definition of temperature and its relation to an observer's frame of reference. The importance of considering a system of multiple particles and their random motion in determining temperature is also mentioned.
unix101os
I know that absolute zero is impossible to achieve but we can get close. According to google the coldest temperature ever reached in a lab was 0.006K. Do you think this is because while the atoms are moving very slow relative to the observer they are still moving at the velocity of Earth's rotation + orbit + solar systems velocity + galactic velocity and so on?

I could be (probably am lol) mistaken but my understanding is that absolute zero would occur when there is no atomic motion relative to the environment being measured. For instance, if you're studying it in a lab's self-contained unit the Earth's rotation would be irrelevant to the temperature reading because all of the physical elements of your test are being affected by the Earth's rotation in the same way, relative to each other.

I think you should:
1. reexamine what your understanding of how temperature is defined (and tell us!)
2. decide what those velocities you mentioned are measured against (and tell us!)

@XZ923 's answer already provided some clues, but give it a go anyway.

unix101os said:
Do you think this is because...
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?

Lord Jestocost
unix101os said:
According to google the coldest temperature ever reached in a lab was 0.006K.

Well, that's just completely wrong. It's much, much colder. Less than a microkelvin.

Bandersnatch said:
I think you should:
1. reexamine what your understanding of how temperature is defined (and tell us!)
2. decide what those velocities you mentioned are measured against (and tell us!)

Well, that's just completely wrong. It's much, much colder. Less than a microkelvin.
do you have a reference?

unix101os said:
do you have a reference?

6 mK is about the lowest temperature you can reach with a commercial dilution refrigerator with not load. There are many ways to reach temperatures lower than that; for big objects (several kg) you can e.g. use adiabatic demagnetisation to get down tot a few tens of microkelvin.
Laser cooling of gases can get you down to temperatures much lower than that.

I have often wondered whether a logarithmic temperature scale wouldn't be more sensible, sort of like decibel. Then again that would require a "reference temperature", and that would be arbitrary.

rumborak said:
I have often wondered whether a logarithmic temperature scale wouldn't be more sensible, sort of like decibel.

Nothing stops people from adopting one - like pH. The fact that they haven't suggests its not useful.

As a general comment, lack of use is not a particularly good indicator of usefulness. I don't think anyone disputes the usefulness of the metric system, despite its lack of use in the US.

the difference, however, is that nobody uses a logarithmic temperature scale whereas only the Americans don't use the metric system. so the comparison is kinda apples and oranges.

f95toli said:
Laser cooling of gases can get you down to temperatures much lower than that.
The temperature of Bose-Einstein condensates is in the nK range. I haven't kept track of the most recent results, but a group at the University of Alberta claims to have reached 40 nK.

From: https://www.universetoday.com/8861/coldest-temperature-ever-created/

Since the 1995 breakthrough, many groups have routinely reached nanokelvin temperatures; with three nanokelvin as the lowest temperature recorded. The new record set by the MIT group is 500 picokelvin or six times lower.

At such low temperatures, atoms cannot be kept in physical containers, because they would stick to the walls. Also, no known container can be cooled to such temperatures. To circumvent this problem, magnets surround the atoms, which keeps the gaseous cloud confined without touching it. To reach the record-low temperatures, the researchers invented a novel way of confining atoms, which they call a “gravito-magnetic trap.” The magnetic fields acted together with gravitational forces to keep the atoms trapped.

DrClaude
Bandersnatch said:
I think you should:
1. reexamine what your understanding of how temperature is defined (and tell us!)
2. decide what those velocities you mentioned are measured against (and tell us!)

@XZ923 's answer already provided some clues, but give it a go anyway.

1. Temperature is defined by the amount of movement of atoms
2. I guess those velocities would only be observed by someone outside out galaxy.

I would say that temperature is absolutely dependent on the observers frame of reference.

unix101os said:
1. Temperature is defined by the amount of movement of atoms
2. I guess those velocities would only be observed by someone outside out galaxy.

I would say that temperature is absolutely dependent on the observers frame of reference.

As far as I know, temperature only applies to a system of multiple particles/atoms, not to single ones. A moving observer would see all of those particles moving with higher speed than the lab observer sees them, but this doesn't matter, as temperature is not defined solely in terms of the velocity of each particle. See Nugatory's link for more info.

unix101os said:
Do you think this is because while the atoms are moving very slow relative to the observer they are still moving at the velocity of Earth's rotation + orbit + solar systems velocity + galactic velocity and so on?
I was always under the impression that the motion associated with temperature is essentially random. The Mean Kinetic Energy refers to the Energy that would be involved in random collisions with other bodies in the vicinity it would correspond to the Standard Deviation of their velocities and the component due to motion of a planet or a galaxy system would have a very low standard deviation and would not actually contribute to the 'thermal' motion.

There is a parallel with the way people want to discuss the De Broglie wavelength of a motor car at 60mph. A motor car is not a quantum object so the calculation is nonsensical, in a similar way.

unix101os
Just to throw a wrench into things, there is such a concept as negative temperature on the Kelvin scale, experimentally achieved briefly in the lab. For example, cooling down a material to absolute zero and then changing an internal magnetic field and RF waves can reduce the entropy further by changing the statistical population of spins away from 50/50, resulting in a "negative" temperature.

Anachronist said:
For example, cooling down a material to absolute zero and then changing an internal magnetic field and RF waves can reduce the entropy further by changing the statistical population of spins away from 50/50, resulting in a "negative" temperature.
This is not correct. A two-level system with a spin population of 50/50 corresponds to an infinite temperature. Heating that system such that the excited state becomes more populated than the ground state will reduce the entropy, leading to a negative temperature. Hence, negative temperatures correspond to hotter systems than positive temperatures. You will find many threads on PF discussing this.

My prior post in response to Anachronist got deleted, and I got a warning from Nugatory for posting "noise" -- I'm grateful that I didn't yet get banned -- here's a link to a wiki article on the topic of negative temperature: https://en.wikipedia.org/wiki/Negative_temperature

Anachronist said:
Yes, that's the same article I linked in my post above. -A
I didn't notice that you had already posted that link (for obvious reasons, I can't/don't pay full regard to every link I encounter) -- after reading that article, I found some of the implications it posed regarding the second law of thermodynamics to be to me thought-provoking ...

Hello

This is a very interesting question :)

@sophiecentaur : in this case... quantum behavior may arise, as in the case of the specific heat below the Einstein temperature* (which can be room temperature). I remember that for the treatment of the Born paradox**, one of the DeWitt's firsts articles about the topic said that quantum may arise since the amount of expected radiation was pretty small.

I think that the first question would be "how the temperature is defined in relativity" ***. You can suppose that the temperature is invariant for every observer**** (this would answer the original question), or that the entropy is invariant (since the entropy is defined from the number of occupied states).

As far as I know (I may be wrong), the main problem is that in relativity the 3rd law of Newton doesn't work (there is no "instant" interaction), and all mechanical interpretations of Thermodynamics have no-sense (in relativity) since they may violate the causality principle.

To sum up: there is a theoretical work which says that in an accelerated frame (SR) or in a gravitational field (GR) you can see a thermal bath due to acceleration/gravitation (Unruh/Hawking effect); but experiments are needed to validate the theoretical work.

Regards,
ORF
* For example, the Einstein temperature of quartz is pretty high. https://en.wikipedia.org/wiki/Einstein_solid#Heat_capacity_.28microcanonical_ensemble.29
**** Covariant Maxwell distribution (invariant T): https://en.wikipedia.org/wiki/Maxwell–Jüttner_distribution

unix101os and sophiecentaur

## 1. What is absolute zero and how is it related to temperature?

Absolute zero is the theoretical lowest possible temperature at which all molecular motion stops. It is equivalent to 0 Kelvin or -273.15 degrees Celsius. It is considered the baseline for measuring temperature, with all other temperatures being relative to absolute zero.

## 2. Is absolute zero truly achievable?

In theory, yes, absolute zero is achievable through various cooling methods such as adiabatic demagnetization or laser cooling. However, it has never been reached in an experiment as it is practically impossible to completely remove all molecular motion from a system.

## 3. How does absolute zero affect the behavior of matter?

At absolute zero, matter reaches its minimum energy level and all molecular motion stops. This causes materials to become extremely brittle and lose all electrical resistance, among other unique properties. It also allows for the study of quantum mechanics and the behavior of matter at the most basic level.

## 4. Is absolute zero the same for all substances?

No, absolute zero is not the same for all substances. Different materials have different properties and require different methods to reach absolute zero. For example, helium reaches absolute zero at a lower temperature than water.

## 5. How does absolute zero relate to the concept of entropy?

Entropy is a measure of disorder or randomness in a system. At absolute zero, molecular motion ceases and disorder is minimized, resulting in a state of zero entropy. As temperature increases, so does entropy, as molecular motion and disorder increase.

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