On 10/16/2016 1:05 PM, dlzc wrote:
Dear Yousuf Khan:

On Saturday, October 15, 2016 at 10:45:21 PM UTC-7, Yousuf Khan
wrote: ...
Maybe the issue here is not to find a new modification of
Newtonian gravity, but perhaps our reliance on still using
Newtonian gravity even 100 years after we found a better theory of
gravity might be the problem here?

I find it more likely that a nearly 100 year old assumption that
luminosity is directly proportional to the amount of mass present,
when it has long been known that luminosity drops off rapidly with
surface temperature. If you have cooler objects, they simply don't
put out as much light... especially in the visible light bands.

But they do still glow in the cooler invisible light bands like IR and
microwave and radio.

We're still using Newtonian gravity after all of these years,
because it's frankly much easier to calculate with than General
Relativity.

Paper on this subject for a "simple" galaxy, and evaluating the
possible error between Newtonian gravity-as-a-force and GR, and in
that galaxy, it is a 1% (or so) error, not the necessary 300% error.

That's the point I'm trying to make, they are using "simple" galaxy
models, rather than full galaxy models.

But in a many-body system such as stars in a galaxy or galaxies in
a universe, those simple inverse-distance squared relationships
simply don't work out anymore?

They do work out "well enough", for simple gravitation.

But we are "blind as bats" at these scales, and have a full
complement of "flatlander fallacies" that we have to divest
ourselves of.

So then we're basically agreeing on this. Newtonian gravity might be one
of those flatlander fallacies.

We're still using Newtonian gravity in this day and age because we
still don't have computers strong enough to do a GR calculation
for an entire galaxy.

False. The amount of computer time might still be abysmally long
for an interesting galaxy, but it would still be doable. After all,
Nature does this math in real time...

Nature has its own entire universe-sized quantum computer to work with.
We can barely put two qubits together yet.

Using even our strongest supercomputers we can do perhaps a
simulation of only a few million stars in a galaxy using GR, but
our galaxy contains perhaps as much as 400 billion stars, so we
keep approximating with Newton.

Yet, even small spirals show a need for Dark Matter. Globular
clusters, essentially don't.

Then we need to investigate where the globular clusters differ from
dwarf galaxies.

If one day we can do a full simulation of the Milky Way with all
of its entire 400 billion stars, then likely we'll see surprising
results coming out of GR that are inconsistent with Newton, and
then we'll be finally shaken of our illusion that Newton is "still
good enough".

Maybe. But the speeds and curvature on something the size of a
galaxy, even the Milky Way, should present minimal error in using
Newton.

Well, that's been our assumption all along hasn't it? Maybe our
assumption is wrong?

Now what I wonder is, if the "perfectly mirrored, massless box,
containing photons", which has rest mass, exists between a star and
the gases/dust/planets that give that star a background temperature
higher than the CMBR. So some Dark Matter (probably less than 1%)
might still be photons in transit between intersystem objects...?

Or even neutrinos.

Yousuf Khan