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30 September 2002 @ 10:58 am
Thought for today  
Nothing is ever created by divine power out of nothing.
Nature resolves everything into its component atoms and never reduces anything to nothing.
-Lucretius, On the Nature of the Universe

Quantum Mechanics describes for us a world wherein matter is constantly being created and destroyed. Vacuum diagrams show intricate examples of this phenomena. It took us this long to find out that the universe does not strictly adhere to persistence of matter, but we have found another persistence; persistence of energy. According to this principle, energy can neither be created nor destroyed, and the amount of energy in a system is constant. Under this model, energy doesn't "become" matter. Rather, matter is seen as one form of energy.

Mind you, the concept of persistence of energy seems to be true by definition. One particularly ugly (IMNSHO, of course) hack to justify this is the concept of "potential energy". If a roughly spherical rock is sitting at the top of a hill, it is said to have "gravitational potential energy" to represent the energy that would be involved in the rock running down the hill. Similarly, we have the concept of "electromagnetic potential energy", which is useful for describing electromagnetic effects. It seems to me that the concept of potential energy is a hack to satisfy the principle of persistence of energy, but it is a very useful hack. The equations balance in elegant ways, and the concept of "potential energy" has led to useful results.
 
 
 
Jim: karandraswarpdragon on September 30th, 2002 11:55 am (UTC)
I'm not sure potential energy is such a hack. A boulder sitting on a hill is being pulled down by gravity even as it's at rest. Move it a couple feet and it'll go rolling at such a speed, but it's being acted on by the same force that was acting on it as it sat there.
St. Sean the Amusedseanb on September 30th, 2002 03:58 pm (UTC)
True, the boulder gains kinetic energy as it rolls down the hill with (largely, but not exactly) the same forces acting on it. I see two ways to represent that gain in kinetic energy:
1) The energy already existed in some other form, and was somehow converted into kinetic energy.
2) The energy was somehow created due to the unbalanced forces acting on the boulder.

The ONLY way to arrive at the conclusion of "potential energy" is to assume that conservation of energy is true. The only way conservation of energy can be true is by using the concept of "potential energy".

Due to this circular dependancy, I will persist in seeing the concept of "potential energy" as an amusing, useful, and elegant hack.