Retell Lecture

Can we never get to absolute zero? What a wonderful question. I wish I had a wonderful answer to go with it. Here is the problem, there is actually a law of physics called the third law of thermodynamics, that says you cannot get to the absolutely zero. We don' t really know it’s true, but we are pretty sure it is for the following reason: every time you think of some way of cooling something down a little bit, it means you try to get energy out of that thing and make the temperature lower. Well if you can get energy out, usually there is a way that the energy can go in as well. And that always means there is a competition between taking the energy out and putting the energy in. Now you can try to make it, so you are favoring getting energy out, but you can’t completely stop the energy from going in and that means you might be able to get colder and colder, but you won' t be able to get all the way to absolute zero. Could we go back to my power point, because I think that one of these slides will illustrate that point a little bit better. Yes, here, remember the logarithmic thermometer? There is no zero on this logarithmic thermometer, just keeps going down, you make it a fact of 10 colder, you' re not a zero. You make it a fact of 10 colder, you’re still not a zero. You make it a fact of 10 colder, you' re still not a zero. So, you start a million of a degree, now you are 10 million of a degree, now you are 100 million of a degree. Now you are billions of a degree. You never get to zero that way. You get closer and closer, but you never get to zero. So that’s why we cannot get to absolute zero.