Shpongle

I was reading a little while back (don't remember where, unfortunately), that there is no current fully-accepted theory of gravity, and that a lot of details still need to be worked out.

I'm wondering, is this true? How many different theories are there? And, if it is true, why is no one making a fuss about gravity being taught as fact in science class?

Corwin

Gravity doesn't contradict Genesis.... ergo the fundies don't get pissed off about it. Besides... even the stupidest of them can see that if you drop something, it falls.

As far as combining the theories.... the main issue is a quantum theory of gravity. (Explanation of gravity in quantum terms, which should be much more complete and accurate than the current relativistic description.) Whoever manages to figure that one out is going to have a nice new shiny gold medal with an old norwegian's profile stamped on it.

** edited to clarify **

Should have previewed first.

Relativity explains things one way, what we know of quantum mechanics explains them another. The two seem to be mutually exclusive, yet both work. Unifying the two and explaining the descrepancies (grand unified theory/quantum gravitation) is the goal.

Lobstrosity

There's one theory. It's called General Relativity. It works exceedingly well for anything macroscopic, however, as Corwin pointed out, it fails at the quantum level. General relativity requires space to be smooth, but quantum physics destroys this smoothness and produces singularities if you zoom in too far. Therefore meshing quantum mechanics with general relativity is somewhat of a problem. The solution to unifying the two might lie with Superstring Theory, in which elementary particles are no longer viewed as points but rather as loops of "string." These loops would have actual sizes (on the order of a Planck length) and thus would make it impossible to ever probe the universe on a level where the smoothness breaks down enough to cause the troubling singularities.

Shadowy Man

Whether or not a theory is complete may not reflect at all on its usefulness.

Lobstrosity mentioned General Relativity, which is obviously more complete than Newtonian gravity. However, for sending interplanetary probes to the outer planets, you only need Newtonian gravity.

Yes, there may be details to work out. And working out those details may result in a wildly new theory, but any new theory won't make old theories wrong in their regimes of usefulness. Quantum mechanics arose because there were some "details" to be worked out in classical mechanics, but QM doesn't negate classical mechanics completely, it just overrides it in certain regimes.

So, yes, gravity is a fact. And there are some theories that explain the way gravity works to very good precision in most cases. That should be taught in school.

Gleb

Correct me if I'm wrong here, but isn't it true that they haven't yet observed the graviton, the particle mediating the gravity?

Answerer

It is true but it doesn't mean that graviton doesn't exist.

malookiemaloo

This is the first I've heard that there was a problem re gravity.

Any chance of a brief synopsis for idiots for relativity and quantum?




m

Wyz_sub10

Yes, but we've observed gravity, it effects and limitations, etc. We've been able to develop a working theory of gravity that relates mass to distance, that allows for accurate predictions in the macro world, etc.

This makes the theory - a descriptor and predictor - quite appropriate for teaching.

Shpongle

But we still haven't actually seen gravity? How can they possibly teach something no one has ever seen?

At the very least, you'd think they'd put warning labels on text books.

MartinM

Quite right. It's clear to any thinking person that the planets are pushed round in their orbits by angels. This 'gravity' thing is just another atheistic attempt to deny God. The 'angels' theory should get equal time in schools - it does, after all, fit all the available data