The First Negative Absolute Temperature State for Moving Particles

reply to post by Phage


What are you referring to that was accomplished previously?

From MAX-PLANCK-GESELLSCHAFT:

. . . “We have thus created the first negative absolute temperature state for moving particles,” adds Braun.

Matter at negative absolute temperature has a whole range of astounding consequences: with its help, one could create heat engines such as combustion engines with an efficiency of more than 100%. 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 100 percent.

The achievement of the Munich physicists could additionally be interesting for cosmology . . .

reply to post by Mary Rose

I'm referring to experiments done in the early 1950s. In which negative temperatures were produced by manipulating the spin of atoms in crystals.
www.physics.umd.edu...

reply to post by Phage


Thanks!

reply to post by Phage


Does this mean that the following quote is off-base?

"We have created the first negative absolute temperature state for moving particles," said researcher Simon Braun at the University of Munich in Germany.

Originally posted by Phage
www.physics.umd.edu...

That .pdf from the University of Maryland physics department doesn't want to open for me and I tried searching their site but it didn't work. Do you have the title to the .pdf handy? (Maybe I could google it.)

reply to post by Mary Rose

No. The current work is different in that it involves "free" atoms, that's where the "moving particles" part comes into it.

reply to post by Mary Rose

Thermodynamics and Statistical Mechanics at Negative Absolute Temperatures

Originally posted by Phage
I'm not sure there is much in the way of practical implications since the conditions under which this was accomplished are quite contrived and it is a specialized case of what has been accomplished previously.

So, you disagree with this?

Originally posted by Mary Rose

From MAX-PLANCK-GESELLSCHAFT:

. . . Matter at negative absolute temperature has a whole range of astounding consequences: with its help, one could create heat engines such as combustion engines with an efficiency of more than 100%.

Originally posted by Phage
The title from Live Science is somewhat misleading. "Negative temperature" is not about producing temperatures below absolute zero.

The MAX-PLANCK-GESELLSCHAFT article did the same thing: "A temperature below absolute zero," followed by this sub-title: "Atoms at negative absolute temperature are the hottest systems in the world."

Maybe this experiment is showing the limitations of systems of measurement and scientific theories?