Oh it's still fascinating stuff even if I almost failed Algebra II, but then you gotta talk about the general and special theories of relativity and that gets into words is all.
CGP Grey is great, but that video doesn't have much to do with science. This one, however, relates to both science and poop. Two of my favorite things!
There is so much wrong with that article. PopSci at it's worst. Right off the bat they start with the completely false (but taught in highschool) notion that "An object's temperature is a measure of how much its atoms move".
TL;DR Temperature is defined by how Entropy changes when you add energy to a system. It is basic freshman level physics to devise systems that have "negative" temperature. These researchers just managed to make a working version of such a hypothetical system.
So the short answer is the new system sets an upper limit (read: max amount of entropy) on temperature, and as you go down entropy is taken out of the system, with limitless order, rather than normal, where there's a lower limit (no entropy) and no upper limit on how much entropy can be in the system?
So the short answer is the new system sets an upper limit (read: max amount of entropy) on temperature, and as you go down entropy is taken out of the system, with limitless order, rather than normal, where there's a lower limit (no entropy) and no upper limit on how much entropy can be in the system?
Not quite. The system has a maximum *energy*. This means that as you heat it up and particles occupy higher and higher energy states at some point entropy is maximised (when all energy states are evenly occupied). Untill this point entropy has increased as you put energy into the system (meaning positive temperature).
If you continue to put energy into the system there are no higer energy states to occupy so the particles will start to bunch up against the upper limit. This will result in a less even distribution -> Entropy is going down with increase in energy -> negative temperature.
So you go from
1) Particles bunched up in the low energu states (low entropy) 2) Particles evenly distributed (max entropy) 3) Particles bunched up in the high energy states (low entropy)
as you increase the energy of the system. Since
Temp = (change of energy) / (change of entropy) = (positive number) / (negative number) = negative number
you get negative temperatures in regime 3) even though you continue to put energy into the system.
These kind of systems (upper limit on energy) were first devised and built in the early 50's, this time was the first time it was done with a gas of cold atoms, hence the publication in Science.
If you continue to put energy into the system there are no higer energy states to occupy so the particles will start to bunch up against the upper limit. This will result in a less even distribution -> Entropy is going down with increase in energy -> negative temperature.
So you go from
1) Particles bunched up in the low energu states (low entropy) 2) Particles evenly distributed (max entropy) 3) Particles bunched up in the high energy states (low entropy)
as you increase the energy of the system. Since
Temp = (change of energy) / (change of entropy) = (positive number) / (negative number) = negative number
you get negative temperatures in regime 3) even though you continue to put energy into the system.
Also notable is that in regime 2) temperature is infinite, since the change in entropy is 0. This also means that temperatures of positive infinity and negative infinity are the same thing (just from different directions).
As an aside, since he's been on GeekNights before and is therefore an absolute authority, here's Adam Becker's explanation of negative absolute temperatures: What's Cooler Than Being Cool?
Comments
http://web.mit.edu/newsoffice/2012/mit-researchers-discover-a-new-kind-of-magnetism-1219.html
Even Wikiedia does better than that.
TL;DR Temperature is defined by how Entropy changes when you add energy to a system. It is basic freshman level physics to devise systems that have "negative" temperature. These researchers just managed to make a working version of such a hypothetical system.
If you continue to put energy into the system there are no higer energy states to occupy so the particles will start to bunch up against the upper limit. This will result in a less even distribution -> Entropy is going down with increase in energy -> negative temperature.
So you go from
1) Particles bunched up in the low energu states (low entropy)
2) Particles evenly distributed (max entropy)
3) Particles bunched up in the high energy states (low entropy)
as you increase the energy of the system. Since
Temp = (change of energy) / (change of entropy) = (positive number) / (negative number) = negative number
you get negative temperatures in regime 3) even though you continue to put energy into the system.
These kind of systems (upper limit on energy) were first devised and built in the early 50's, this time was the first time it was done with a gas of cold atoms, hence the publication in Science.
As an aside, since he's been on GeekNights before and is therefore an absolute authority, here's Adam Becker's explanation of negative absolute temperatures:
What's Cooler Than Being Cool?