Bill Spight wrote:Look. You are a merchant who accepts bitcoins and you know that, come Tuesday, everybody's bitcoin holdings will increase by 1%. You know this, perhaps, because you hold a few bitcoins yourself. In any event, it is your business to know it. Do you keep your prices in bitcoins the same, or do you raise them by 1%?
I might do either! You can't just speculate about these things. It depends on whether people are going to try to buy more goods as a result, or not. If consumer confidence is high, then if everyone gets an extra 1% of their holdings, then I will expect them to spend most of it, so if I can increase my stock easily I'll raise prices a little, and if not I'll absorb the whole extra demand by hiking my prices. On the other hand, if I think everyone is worried about losing their jobs and is going to save the money for a rainy day - and as a result I'm already dealing with an inventory overhang, then all that's going to happen if I raise my prices is my rivals will get all of the business.
Bill Spight wrote:Also, the "doctrine of immaculate transfer" argument does not cut it with me. In a collision of billiard balls, both momentum (mv) and energy (mv^2) are conserved. (A conservation law is an identity.) Without going into details, typically the kinetic energy in the motion of the balls after the collision is less than before the collision. What happens to it? On earth typically most of it is dissipated in sound waves, which is why we hear the click of the balls. On the moon, with no atmosphere to carry sound waves, my guess is that the balls would heat up. Even on earth, when billiard balls were made of celluloid, sometimes they would explode.
Now, it is true that the conservation of energy identity does not tell us exactly what will happen with the extra energy. But what would you think of a physicist who claimed that it did not express a causal relationship?
This is a great example. I could, by assuming that two billiard balls have the same mass and velocity before and after their collision (albeit in opposite directions), prove to you that in my thought-experiment the collision is silent. However, that would be a very poor guide to what actually happens when the balls collide. If we want to use the accounting identity to make a causal prediction, we actually need a causal theory about how we get the energy from one side of the equation to the other side of the equation (at minimum, a theory of whether billiard ball collisions are elastic or inelastic).