Originally posted by buddhasystem
Full stop. Experiment is the criterion of truth. We've got plenty. They match our theory that planets move according to gravity, and we need to
sometimes include corrections due to relativity for more precision (Mercury orbit being one).
please stop saying that gravity has been tested, gravity has never been directly tested. You are speaking as if you have found the illusive graviton,
or as if you have found out
why gravity causes mass to attract, no-one knows that. Your statement that gravity has been tested is
exactly what is wrong with modern astronomy. Gravity (or the force that is currently thought to be caused only by the attraction of mass, i should
say) is
unbelievably weak, which makes testing its exact nature nearly impossible without the other forces interfering with the experiment.
Maybe my previous post did not explain it enough for you to understand what i was trying to say. Let me elaborate further.
Newton's Law of Gravity is one of the most useful mathematical formulae ever devised. This little formula has made space travel and the exploration
of the Solar System possible. It made satellites possible. . . . Scientists use this little formula to gain an understanding of galaxies far away, and
indeed the behaviour of the universe as a whole. It is now more than 300 years since Newton devised this little formula; and we still do now know what
causes gravity.
Newtonian gravity is accurately measured and proven with the bounds of the solar system. However, Newtonian gravity remains untested in other areas.
All we have is a formula. This formula has been used to determine the mass of the Earth. This is based on the concept that for each mass of M inside
the Earth, it exerts and attractive force of F. We do not know the valid range for Newtonian gravity. Inside Newton's formula is G. G is the
"universal gravitational constant". It is assumed, and assumed is the correct word here, that each mass of M exerts the same force of F regardless
of where in the universe it may be placed. How did newton work out this assumption? he certainly could not test it back then. It is also assumed that
each mass of M exerts the same force F whether it lies on the surface of a planet or star or whether it be deep inside the body.
This assumption rules out the very real possibility that particles near the surface of a body in space might exert a force greater (or less) than
those deep down. Its also rules out the very real possibility that other EM forces that are much stronger than gravity can effect these particles. The
key to all of our gravity is the mass of the Earth. If the mass of the Earth is wrong, then so are our estimates for those of other bodies. If the
mass of the Earth has been overstated, then it follows that the masses of all other bodies in the solar system have also been overstated.
How can we be sure that the Earth really has the mass accorded it by Newtonian gravity? As gravity is so unbelievably weak, is an experiment using two
lead balls really representative of the entire Earth? No, of course not, that is probably down to EM forces in the first place, not gravity. There are
electrical forces to account for, magnetic forces and (obviously) electromagnetic forces, that are a lot stronger than gravity, that the current
theory does not take into account.
There are a number of odd facts that you can draw from Newtons (now ancient) theory of gravity. Either Newton was an absolute genius and worked all of
this out nearly perfectly hundreds of years ago, or his theory has been made to fit with the current forces attributed to gravity. Newtons idea of
gravity is that all mass attracts equally, a simple idea, that is very hard to disprove due to the weakness of gravity.
I would point out that a lot of what we think we know about space is also based on special assumptions in gravity. If gravity turns out to not to work
exactly how it is thought it would mean that the mass of earth is wrong, and so to every other body in space. That throws a lot of modern astronomy
out of the window, it would also render things like gravitational lensing and dark matter pointless.
Over all these years you would expect that someone would have tested that gravity is due exclusively to the equal attraction of mass. This could be
easily tested by measuring gravity at depths in the earth to see if the strength of the gravitational field drops off proportionally as you descend.
According to newtons theory, at the centre of every spherical body in space there is
absolutely zero gravity, as it cancels out in all
directions. (see newtons shell theorem;
en.wikipedia.org...)
So as you descend it should decrease at a roughly constant rate, until you get to the centre where you will be completely weightless. Surprisingly,
no-one seems to have tested it. They probably have tested it somewhere, but the results probably did not agree with newtons theory, and so it would
not be accepted for any journal. If you could find any data on this, i would greatly appreciate it, i certainly cant find any info on gravity at
depths. All journals seem to be surprisingly silent when it comes to ways of confirming certain aspects of newtons theory of gravitation.
I hope that clears some of the misconceptions about the force that has been
hypothesized to be due to the attraction of mass, ie.
Gravity.
[edit on 4-1-2008 by ZeuZZ]