Most people have the good sense to stay away from the extreme cold.  The temperature drops below a certain point, and people do their best to warm up.  Maybe they drink some hot chocolate, maybe they throw on a sweater, maybe they huddle together to preserve bodily warmth.  Whatever it is they do, you can bet that trying to make the temperature even lower is not involved.

Then, there are scientists.  Specifically, there is a select group that takes a look at a cold temperature and thinks to themselves "-270 degrees Celsius?  We can make the temperature drop by at least another three degrees."  Literally. 

Absolute zero is the hypothetically lowest temperature possible, approximately -273.15 degrees Celsius, or 0 K (Kelvin).  To this point in our history, scientists have been unable achieve this temperature, but they have come within a hair's breadth of doing so (one has to go out to more than nine decimal places to see how far from 0 K scientists are).

Over the next two episodes, PBS's long-running science series, Nova, will take a look at just how low we can go, and how we got there.  Their latest special, "Absolute Zero" is divided into two hour-long looks at some people's obsession with the cold. 

First up, "Absolute Zero:  The Conquest of Cold."  Despite what its title may imply, this episode has very little to do with actual zero itself.  Instead, it looks at the history of lowering temperature, from the first air conditioner-type device (made in 17th century England), to the commercial harvesting of ice, to the centuries-long debate as to what actually makes something hot or cold anyway.

The episode works through history methodically and relies heavily on the recreation of events for illustrative purposes.  It does touch on the first scientist to theorize  about an absolute zero, but it is not until the second episode "Absolute Zero:  The Race for Absolute Zero" that absolute zero takes center stage.

In this second hour, which begins at the end of the 19th century and continues through the present day, scientists go from liquefying hydrogen (which happens at around 20 K) to less than a degree away from 0 K.