Brett: There’s another example like this. You can do this with a saucepan at home. Put a beaker of water on a heat source, then put a thermometer into that water and turn on your heat source. As time passes, record the temperature of the water.
You’ll notice the temperature of water increase. So long as the heat source is relatively constant, the temperature rise will be relatively constant as well. After one minute, the temperature might go from 20°C to 30°C. Imagine every minute it climbs by another 10°C.
Naval: But at some point, it’s going to stall when it hits the boiling point.
Brett: Precisely. Now, if you’re an inductivist—or even a Bayesian reasoner—and you don’t know anything about the boiling temperature and what phenomena happen at that temperature, you can join all of those lovely lines into a perfectly diagonal straight line and extrapolate off into infinity.
According to your Bayesian reasoning and your induction, after two hours we should assume that the temperature of that water will be 1,000°C. But, of course, this is completely false. Once the water starts boiling, it stays at its boiling temperature. We get a plateau at about 100°C that remains there until all the water boils away.
There’s no possible way of knowing this without first doing the experiment or having already guessed via some explanatory means what was going to happen. No method of recording all of these data points and extrapolating off into the future could ever have given you the correct answer. The correct answer can only come from creativity.
Notice that science is not about predicting where the trend starts and where the trend goes.
To explain what’s going on with the water, we’d refer to the particles and how, as the temperature increases, the kinetic energy of the particles starts to increase. This means the velocity of the particles is increasing. Eventually, particles in the liquid state achieve escape velocity from the rest of the liquid. At this point, we have boiling.
That escape velocity—the technical term is latent heat—requires energy. For this reason, we can have heating of water without a temperature increase.
That’s what science is, that whole complicated story about how the particles are moving faster. It’s not about trends and predictions; it’s about explanations.
Only once we have the explanation can we make the prediction.