What is the single most important notion in physical theory that the layman should understand?

Question

...assuming the layman had the time and resources to master the neccessary math, etc.

Answer 1

That empirical observations are the sole arbiter of truth in science - a theory is not even meaningful unless and until it makes specific, testable predictions about what you will and will not see. And if the predictions do not match reality, it does not matter how elegant it is or how much you want the theory to be true, the theory is wrong. If the predictions do match, then the theory _might_ be true, but you are not relieved of the burden of continuing to test it at every scale and in every new environment, because science can only discover new theories by testing things and finding out what doesn't work. While you didn't ask, the second most important notion in science that people should understand is that scientists understand the first principle - when a scientist makes a proclamation like "humans share a common ancestor with all other animals," they're not just talking out of their asses, or giving you their particular religous beliefs, and they especially are not trying to lend vermissilitude to the notion that there's no god (although there is, in fact, no god, most scientists have yet to recognize that fact) - they are making that pronouncement because the theory of evolution makes specific predictions about what you will and won't find in animals (i.e. you will find organs in closely related animals that share similarities in form unrelated to their similarities in function), the fossil record (i.e. you will find intermediate forms between related species A and B prior to the emergence of A and B and not after it), and genes (one of the major predictions of evolutionary theory was that genes would exist in the first place - prior to it it was a matter of sheer guesswork whether the differences in species could actually be inherited), and every time one of these predictions has been tested (which would constitute many millions of tests, at least), it has turned out to be correct.

Answer 2

It's the notion that 'physical theory' is worth understanding. You can learn a huge amount of science with high school math or less. You can learn the scientific method. You can learn how to think, to reason. You can learn how science came to be known, and the mistakes made along the way. Understanding how things work can help keep you from making some really bad decisions. It's a good way to learn the mental skills that can help you solve problems and accomplish things in nearly any field.

Answer 3

"... assuming the layman had the time and resources to master the neccessary math, etc", a theoretical physicist might answer:

Follow the path of least action!
Follow the path of maximal aging!
Explore all paths!

That's it.

Answer 4

I think that if people had the capability to understand the premise and experiemental support for big bang theory and evolution then there'd be a lot less stupid creationist lunacy and religious fundamentalism.

Remember that fundamental religious nutcases have been killing each other (and innocent people who got in the way) over whose god is better for thousands of years. No scientist has killed another scientist (or a whole lot of innocents) because he thought his theory was better. To my mind no religion would mean lots more sanity and a lot less killing.

Answer 5

BY FAR, the most universal truth of physics and most important is conservation of energy. This principal is as simple as "Work = the integral of X dot dx" to much more difficult thermo dynamic applications. It is also good for all aspects of life an philosophy...you can't get something for nothing.

Answer 6

That an object at rest has a tendency to remain at rest, and an object in motion has a tendency to remain in motion unless acted upon by an outside force (Newton). In other words - keep the ball rolling, don't be lazy and you will need to prod things along to get the job done.

Answer 7

Gravity.

Answer 8

Energy can neither be created nor destroyed

Answer 9

God.