J.--If you want to talk science, or discuss speculative ideas about science (that's allowed, even welcome, on the Zone); you're going to have to adhere to some simple rules of scientific discourse.

All terms must be rigorously defined, in terms of others that have also been rigorously defined. In normal conversation, we throw about terms like mass, weight, density, force, power, energy, momenutm, impulse and so on, but these mean little in everyday speech. In elementary physics, these terms have very specific definitions. Without these definitions, we do not know what we are talking about, and we cannot construct mathematical formulations to check our thinking.

In the humanities, particularly in politics, history, economics, sociology, psychology, we are pretty much forced to use intuitive and anecdotal nomenclature, often improvised on the spot. For example, we may speak of the "force of public opinion", or "artistic energy", or "intellectual power" and we all have a vague idea of what we're talking about. In physics we have to be much more precise and formal so we can use our math. This gives science its great power, but also establishes its severe limitations. This is why scientific logic is often so clumsy and incomplete (if not downright misleading) when applied to the humanities and behavioral/social sciences.

In Newtonian physics, all terminology derives from axiomatic concepts which we all accept, but which we must remember, are just axioms; they are instinctive and psychological. In other words, we made them up. These concepts are mass, space, time and electric charge (which we will not talk about here). The units of these four items are the kilogram, meter, second and Coulomb (kg,m,s,C), but we will talk only about the first three. All the physical concepts involved in Newtonian mechanics are derived mathematically from these fundamental axiomatic definitions. There are some mathematical embellishments I'm glossing over here, but this is the meat of the matter.

Velocity = space/time (m/s)
Acceleration = velocity/time
Momentum = mass x velocity
Force = mass x acceleration The unit of force is the Newton = kg x m/s/s
Energy = Force x space. The unit of energy is the Joule = Newton x m = (kg x m/s/s) x m = kg x (m/s)**2
Power = Energy/time. The unit of power is the Watt.

Another way of defining Energy is 1/2 x mass x velocity**2 or 1/2 kg x (m/s)**2 You will note this gives the result in the same units (Joules) as our other definition, mass x velocity squared. The "1/2" comes from the calculus we have to use to describe moving bodies.

The reason we go through all this trouble in defining things so carefully is that force, momentum and energy have been shown by experiment to have wonderful properties: They are conserved in all physical systems: the Conservation Laws. This is even the case where we are talking about things like chemical or electrical or heat energy. The amount of momentum and energy in any closed physical system remains constant, it never changes. This allows us a check in all our speculations and calculations. In Newtonian Mechanics (In the Einstein world it gets a bit more complicated) keeping track of the energy and momentum allows to determine whether certain reactions are even possible.

Experiment and experience has shown us that Forces always occur in opposing pairs (for every action there is an equal and opposite reaction). For example, the force of the hot gasses expelled out a rocket motor is equal and opposite to the force acting on the rocket which moves it forward. The two forces cancel out. That force acting on the rocket over a certain distance adds to its energy, which is exactly half of the energy that was chemically locked up in the fuel. The other half goes into heating up the rocket exhaust. All of these complex relations interact in very simple and wonderful ways in all physical systems throughout nature. And if you take the trouble to properly define your terms calculating all these interactions and their effects is very simple because you have rules which tell you exactly how to play the game.

These facts also hold true in the relativistic universe, although there are some interesting wrinkles I didn't want to bring up here. For example, Einstein showed us mass and energy are intimately related, they are two aspects of the same thing (That's what E = Mc**2 actually means in English.) Hre also showed us space and time are different aspects of the same thing thing, they are not separate. He also demonstrated that space and time can change, and only the speed of light is always the same. The simple definitions of Classical Mechanics I listed above gave us no clue about this. You see, our rules are not a property of reality, we make them up. They have a psychological origin. They come from our brain, not from nature. And sometimes different rules can give you the same results, or even better results.

This doesn't mean you can just think something up and it will work. You always have to go back to nature and see if it works better, or if it works at all. We have three kinds of rules that work, Classical Mechanics, Relativity, and Quantum Physics. But none of them works in all cases. I think we're just getting started.