理论是解释，不是预测Theories Are Explanations, Not Predictions
Brett：还有一个类似的例子。你在家用一个炖锅就能做。把一个装有水的烧杯放在热源上，再把一支温度计放进水里，然后打开热源。随着时间推移，记录水的温度。
你会注意到水的温度在升高。只要热源相对稳定，温度的上升也会相对稳定。一分钟后，温度可能从20°C升到30°C。想象一下，之后每一分钟它都再爬升10°C。
Naval：但在某个时刻，当它到达沸点时就会停滞下来。
Brett：正是如此。现在，如果你是一个归纳主义者——甚至是一个贝叶斯推理者——而你对沸点以及在那个温度下会发生什么现象一无所知，你就可以把那些漂亮的数据点连成一条完美的对角线，然后向外推至无穷。
根据你的贝叶斯推理和归纳，两小时后，我们应该假设那杯水的温度会是1,000°C。但当然，这完全错了。一旦水开始沸腾，它就保持在沸点温度。我们会得到一个大约在100°C的平台期，一直保持到所有的水烧干为止。
除非先做这个实验，或者已经通过某种解释性的方式猜到了将要发生什么，否则根本没有办法知道这一点。任何记录所有这些数据点并向外推至未来的方法，都不可能给你正确的答案。正确的答案只能来自创造力。
注意，科学并不是关于预测趋势从哪里开始、要往哪里去。
要解释水发生了什么，我们要谈到粒子：随着温度升高，粒子的动能开始增加，这意味着粒子的速度在加快。最终，处于液态的粒子达到了脱离其余液体的逃逸速度。在这一点上，我们就得到了沸腾。
那种逃逸速度——技术术语叫潜热——需要能量。正因如此，我们可以给水加热而温度却不升高。
这才是科学的本质：那整个关于粒子如何运动得更快的复杂故事。它不是关于趋势和预测，而是关于解释。
只有当我们有了解释，我们才能做出预测。
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.