Monday, January 22, 2007

Fun with Gravity

What is gravity? One of the fundamental questions of physics, a force which affects our every move. Any successful theory seeking to explain the Universe must be able to explain gravity. To date there have been two successful theories of gravity (or gravitation).

The first, Newtons theory of gravity postulates that mass gives off a force that attracts other mass, this force decreases in strength as the inverse of the square of the distance between the two masses, such that

F = G*m1*m2 / r^2

This theory was incredibly successful in predicting the motions of planets, moons and other heavenly bodies, but it lacks a cause, no particle has been found that carries the gravitational force, a problem that Newton himself worried about, never quite being able to reconcile himself to this "action at a distance".

The second theory Einsteins General Relativityhas superseded Newton's theory for an important reason, it better reproduces the observations, especially in those regimes where gravity is strong. Einstein explained gravity as being due to mass curving space and time, so gravity is not a force pulling on a mass, it is a result of mass curving space/time such that what appears to be a straight path is actually curved, the moon follows a straight path but to an observer because of the curvature of space/time it appears to orbit the Earth. Of course this merely shifts the question, its now no longer a question of how gravity transmits force from one mass to another, but how does mass itself influence space/time? It is an active field of physics at present to try to answer this question.

The ADherents to Autodynamics believe that they have come up with a theory that explains the inverse square law of gravity naturally and whats more provides a physical explanation for it. This explanation is actually just a re-tread of a theory that was popular until the turn of the 19th century, the Le Sage theory of gravitation. I'll let the Autodynamics people to explain the theory (in which they use the term pico-graviton instead of Le Sage ultramundane corpuscle):
The Pico-Graviton (PG) is very similar to the concept called the "graviton". The concept of gravitons is that gravity is created by the "shadowing" affect. In affect, celestial bodies partially block the the flux of pico gravitons causing a low pressure area between the bodies. This pushes the bodies together.

The main difference between the pico-graviton and gravitons, is that pico-gravitons are somehow absorbed by mass. Most pico-gravitons push on the mass, but a very very tiny fraction are absorbed.
Now, there are many problems with this theory, as listed on this wikipedia page, go ahead its an interesting read. For now I think what would be more interesting that picking the overall theory apart (as the wiki article effectively does) would be to examine the logical inconsistencies in Autodynamics through this theory of gravitation. On this page the Autodynamics people explain their investigations of their version of the le Sage theory:
Using calculations for perihelion advance, he came up with the following numbers: the pico graviton has the mass of around 1x10-81 kilograms, and travels at around 27 times the speed of light. Another person in the SAA has claimed to find approximately the same values for the properties of the pico-graviton through completely different methods but the calculations have not be confirmed.
So the pico-graviton to explain the observations, must be both massive (as in it has some non-zero mass) and travel at superluminal velocities. Now this is a problem, even for Autodynamics, never mind the real world, on this page when talking about faster than light travel they state:
Autodynamics says that if E=mc^2 is correct, than no mass can accelerate beyond the speed of light. Why? Because in Autodynamics, mass moves by expending energy to push itself forward. According to current equations, all mass, no matter what the size could only result in a single photon going at the speed of light.
So far so good, they correctly point out that if E=mc^2 is true, then faster than light travel is impossible for massive objects even in Autodynamics. So for the pico-graviton to be real, and for it to match the observations, E=mc^2 must be false. Now lets just ignore for the moment the mountains of experimental data that show E=mc^2 to be true, lets just look deeper at the Autodynamics for a second. Specifically here. At the bottom of the page you will notice that the very same E=mc^2 has been used to derive the Autodynamics kinetic energy equations. Those very same kinetic energy equations that are supposed to explain amongst other things: muon decay, Compton effect, and nucleus-nucleus interactions.

So the question is, is E=mc^2 correct and hence the pico-graviton non-existent, or is E=mc^2 false and all of the AD "solutions" to atomic processes incorrect? A perfect example of why in Physics its usually impossible to change one "small" thing, everything is connected tweak one parameter to better fit some observations and you may well make the fit to other observations much worse. There are many other objections to the whole pico-graviton idea (especially the superluminal part), which I may get round to posting if I can sort out the maths.


IbaDaiRon said...

Still no response? How disappointing. :)

I noticed that Travis has responded to Will's latest post to the mailing list. I do so love a bit of the old ad hominem, you know?

Mark Norris said...

Indeed, I may well go and post the whole thing on their own discussion board and see what their explanation is.