On 3/9/2018 6:10 PM, John Clark wrote:
On Fri, Mar 9, 2018 at 6:22 PM, Russell Standish
<[email protected] <mailto:[email protected]>>wrote:
Hi Russell
/> Alan was claiming that motion of a free particle along a
geodesic was an unjustified assumption in relativity./
But its not unjustified or an assumption if that's the way we observe
things move, and it is.
/> If he were asking why is momentum conserved, then one could
answer it along the lines of Vic Stenger's symmetries,
utilising Noether's theorem./
Yes but Noether's theorem couldn't be invoked and the conservation of
momentum produced from it unless there was a symmetry, in this case
the fact that the laws of physics are the same at all points in space.
Someone could then ask why that is, and at this time the best answer
we could give is that’s just what we observe. As far as I can see it
is not a logical necessity, physics could have been different from one
place to another but we see that is not the case.
If that were the case then we would look for some other variable(s) that
would account for the difference in order to arrive at a more
comprehensive theory that, with the new variable(s), made the theory the
same both places. The idea of physics as a fundamental theory is that
it should be the same at all times and places. So if it's not, we
either look for a better theory or (temporarily) give up and call the
variations "geography". As my friend Vic Stenger put it, physics
assumes POVI, Point Of View Invariance.
Brent
And Einstein said mass/energy tells spacetime how to curve and
spacetime tells mass/energy how to move, but if this were not true it
would contradict observations but not produce any logical self
contradictions that I know about. In physics if you keep asking
recursive "why is that?” questions eventually you'll come to a brute
fact. Put it another way, I don't think the laws of physics could be
derived from pure logic alone regardless of how intelligent you are,
that's why we need observation.
John K Clark
--
You received this message because you are subscribed to the Google
Groups "Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to [email protected]
<mailto:[email protected]>.
To post to this group, send email to [email protected]
<mailto:[email protected]>.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
