On 22/06/2015 09:44, Col wrote:
"RedAcer" wrote in message
...
On 21/06/15 15:02, Col wrote:
Dawlish wrote:
There's no 'right' and no wrong in science, as I've attested to on
here any times.there is no proof, though deniers want there to be.
The best you'll get is a consensus amongst scientists. In this case,
the consensus is huge, at 99.9% in the latest literature survey. What
does that suggest about CO2 being the major cause of global warming.

A good analogy is gravity. The theory of gravity is not proven and
never will be. However, if I was stood under a falling piano, I'd be
inclined to do my best to get out of the way. A denier, however would
be still telling anyone in hearing distance that the theory is a
bunch of crap. Right up to the end. ??

In the instance of gravity, how much proof do you want??

We know how it works,

Actually "how" is the one thing we really don't know. Hence the search
for the Higg's boson which might be the root cause of mass. We can make
exquisitely precise medium term computations of "what" using the
equations of motion but at present even proof of the solar systems long
term stability remains beyond our ability to prove mathematically.

Ovenden's conjecture comes the closest but even though most dynamicists
think it likely to be correct it is a long way short of a proof.

Testing whether inertial mass and gravitational mass are in fact the
same has taxed some of the best experimentalists on the planet.

Do we?

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 at an engineering level how to compute gravity in the solar
system but we have only a limited understanding of exactly why matter
has mass or what constitutes the majority of mass in the universe.

We cannot at present observe or detect dark matter but we can see strong
experimental evidence for it in the rotation curves of galaxies.

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.

There is actually a slight unexplained acceleration on the Voyager
probes (thought to be from asymmetric thermal radiation pressure).

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.

Actually GR *did* replace Newton's theories completely - it is a new
paradigm. Einstein's theories make the same predictions in the weak
field limit but the mechanism bending spacetime is entirely different.
Einstein started with the axiom that the laws of physics should be the
same for all observers in an inertial frame and then generalised it.

Newtonian gravity only works if you have have infinite speed action at a
distance so that a planet feels a gravitational force based on its
instantaneous position *without* any light time delay. This quirky
feature was always controversial and Leibnitz's primary line of attack.

--
Regards,
Martin Brown