Episode 27: Death and Heat Death with Cory Doctorow

Okay So. 


It’s this super-popular idea (which is good) which is often misunderstood (which is bad). It’s the reason an icecube melts in a glass of warm water. It’s the reason you can’t get an engine which is 100% efficient.

Our guest today is the author, blogger, and Wikipedia article subject Cory Doctorow. I got him onto the show by promising that I could explain death to his child. He did not realize two things: 1. you should not ever let me explain anything to your children, 2. I would spend most of the time explaining thermodynamics.

anyway, it’s a lovely show!  If you listen past the end music, you’ll hear us trying to tell him how to explain death to a child.

Physicists: Jocelyn Read, Miles Steininger

Intro Music: Ted Leo and the Pharmacists 

Exit Music: John Vanderslice 

Transcript: Ep_27_Death_And_Heat_Death

Cory asks an interesting question during the show, and only as I edited the show did I realize that it’s got a really pertinent answer. He asked us how evaporative cooling works. the answer is: Entropy and statistical mechanics. I don’t know why i forgot  to tell him. anyway, here’s how it works (copied and pasted from an email I wrote. forgive the punctuation)

Imagine that you have a brick, and it’s 50 degrees C, and you pour some water on it, so the water temperature is 50 degrees C.

here’s where statistical mechanics and entropy come in.

the description of the water being 50C is NOT a description of the energy of each and every molecule in the body of liquid. it’s the average energy. So, among the molecules composing the puddle of water, some have an energy above 50C, some will have an energy lower than 50C. Indeed, some will even have an energy above 100C.

If those particular molecules are near the surface of the puddle, they can break away and turn into vapour.

so a body of water will always have SOME molecules which are evaporating away from it, even if the temperature is well below the boiling temperature.

So, because the temperature of the puddle is the average energy of the molecules, when the high energy molecules leave, the average energy decreases.

Like a rich person taking their money and moving it into the bahamas or something.

incidentally, a puddle of water in a closed room will usually reach an equilibrium. just as some water will evaporate, some of the water vapour will be statistically cold enough to condense.

so a puddle of water will cool until there’s enough vapour above it to make an equilibrium.

so what happens if you put a fan up to a puddle of water?

by blowing fresh air over the water (or the kid who just got out of the pool) you’re keeping the water from being in equilibrium with the air around it, and the puddle of water will just keep cooling due to statistical evaporation.


6 thoughts on “Episode 27: Death and Heat Death with Cory Doctorow

  1. I think we do our children a disservice by candy coating death. It doesn’t matter if it’s by saying we all go to heaven (or Kevin), or look for some loophole so you can tell them they will live for ever, both are dishonest. The later is just as dishonest as the first because there is no proof or evidence that this will happen.

    Instead tell them that yes, everything that lives must die. It’s likely she will live a long time, a very long time considering how long her ancestors lived not too long ago. And for that reason she should take care of her body and mind, and experience life to it’s fullest. That she only has once change to make a difference in the world, and although she may not change the world, everything she does will have an effect and helping the least of people or animals will make the world a better place.

    Protecting your children from the concept of death does them a disservice because they may not take threats to their own lives seriously and sooner or later they WILL find out you lied. It’s inevitable. If you can’t tell your children the truth on the more important things in life, then whats the point in telling them anything?

  2. I just found this website, so I’m still just catching up. Your podcasts are fantastic. I love it and I love all your physicist bench. Jocelyn is hot too!

  3. Also, in the wheel water example: I’m not sure if I’m clear on that.

    Is the reason that you can’t get 100% efficiency because the waters potential energy would fall into the bucket and push it down, but if hundred percent of the potential energy were used to push the wheel, there would be no more potential energy for the water to continue falling? Am I close?

    In other words, is the idea of 100% efficiency a nonsense question, like trying to divide by zero or trying to catch up with the horizon. It just doesn’t make sense?

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