# If it's 0 outside, how can it be twice as cold tomorrow?

Ever heard the joke of "if it's zero degrees today and twice as cold tomorrow, what's the forecasted temperature"?

It's a trick question because the Fahrenheit temperature scale is relative, and zero is a nebulous measurement based on what Daniel Fahrenheit decided was "as cold as it ever got in Denmark".  (And believe it or not, he's still right. The all time record low in Copenhagen is remains 0 degrees F). To truly know what is twice as cold, you have to use the Kelvin scale...

Kelvin uses the same increments as Celsius, only instead of setting 0 as the freezing point of water, Kelvin uses 0 as the coldest anything can possibly become -- also known as absolute zero.

Temperature is actually a measurement of average molecule movement. The faster the molecules move, the more energy is involved which gives the sensation of heat. At absolute zero, there is no molecule movement.

Outer space has an ambient average temperature of about 2 Kelvin (and you thought our spring was cold.)   Wikipedia says we've never been able to artificially make something get to absolute zero -- the closest is a fraction of a degree Kelvin. (But Seattle scientists have found getting the temperature to 28 during an evening commute in November while Monday Night Football is in town can bring I-405 to near zero molecule movement.)

0 Celsius is 273 degrees Kelvin, which makes the C to K conversion really simple -- just add 273 to Celsius. But for those of us using the wacky Fahrenheit scale, it's temperature, subtract 32, then divide by 1.9, then add back in 273 for K. Or just Google "Temperature Converter" and let Intel do the math for you.

So, back to our original joke, which might possibly get an award for longest route to go for a punch-line, if it's 0 degrees today, that means it's 255 degrees K.  Half of that is 127.7 degrees K, which converts back to about -230 degrees F.

So there you go. The answer is -230 degrees. Might want to keep the pets inside if that is truly the forecast.

For us though, it might feel twice as hot by the end of the week. OK, not literally since by the same doubling of Kelvin standards it would be about 550 degrees, but I'll bet 85-90 will feel boiling by some.

Tomorrow: Using changes in atmospheric pressure to understand why the chicken crossed the road.