Lawrence Jenkins wrote:
On Monday, 22 June 2015 09:44:02 UTC+1, Col wrote:
Yes.
We can throw spacecraft around planets and they always go where we
want them to, they don't crash into the planet or go flying off into
space in the wrong direction because somebdy got the equations wrong.
we know what the equations are. We can
'slingshot' spaceprobes around planets in order to accelerate them.
And lo and behold the probes end up where we want them.
Yes you can use the equations of Newtonian gravity and calculate
these trajectories with sufficient accuracy in the solar system,
but not in a strong gravitational field where you have to use the
more accurate theory of general relativity, where gravity is
modelled not as a force but as the curvature of spacetime.
I am well aware of the limitations of Newtonian physics.
How could we do that if the theory wasn't 'proven'?
Newtonian gravity was proven to be wrong ~100 years ago.
But only *wrong* where relativistic principles become significant.
Newtonian gravity works for us in most instances, and where it
doesn't we know how to calculate it.
Einstein didn't replace Newton's theories, he merely built upon them.
--
Col
Bolton, Lancashire
160m asl
Snow videos:
http://www.youtube.com/channel/UC3QvmL4UWBmHFMKWiwYm_gg
We know its there and always has been and we (not me) know how to
calculate its effects but that is a a far cry from understanding how
it works. If we (not me) knew how it worked then there is every
conceivable chance it could be negated making leaving this planet
with heavy pay loads and travel on earth in general, a darn sight
easier than it now. Anti gravity like fusion is another one of those
mysterious holy grails
When I said we know how it works I meant we have made observations
and devised theories to explain those observations.
And those theories *work*. We can accurately predict the future motion
of planets, spacecraft, apples etc based upon them.
I didn't mean that we know how it works on a much more fundamental
level, to the extent that we could build anti-gravity drives or whatever.
Perhaps saying we know how it 'behaves' rather than 'works' would have
been a better choice of word?
Nuclear fusion, eh?
Always 30 years away. Funny, it's been 30 years away for at least the last
60 years........
--
Col
Bolton, Lancashire
160m asl
Snow videos:
http://www.youtube.com/channel/UC3QvmL4UWBmHFMKWiwYm_gg