On 10/20/2016 11:40 AM, dlzc wrote:
Dear Yousuf Khan:

On Wednesday, October 19, 2016 at 11:46:24 PM UTC-7, Yousuf Khan
wrote:
On 10/16/2016 1:05 PM, dlzc wrote:
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.

At a *much* lower luminosity. Remember, they use luminosity,
essentially watts, and calibrate to normal-mass-present.

Well obviously they did that because humans naturally favor those
wavelengths that we can see. We also didn't take into account the higher
frequency UV, X-ray, and gamma scales. These higher frequency radiation
would be higher luminosity than visible light.

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.

Even dwarf spiral galaxies need Dark Matter, however. And they have
a few billion stars. This should be doable soon.

Yes, if we can start to model a full dwarf galaxy soon, then we're
likely going to find out the real differences between a GR model and a
Newtonian model.

GR really kicks in: - to handle light, - to handle advancement of
perihelion (for close objects), - to handle gravitational radiation.

The main idea of GR is the spacetime curvature vs. the simple
inverse-squared distance relationship. The spacetime curvature may not
always equal the inverse-squared law, even at large distances. Maybe
especially at very large distances, such as galactic size ranges. There
were already attempts to model GR over larger scales, such as TeVeS.

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

Remove the *serious* errors of (normal-mass / luminosity)
calibration, and then see if you think a further 5 or 10% (max)
correction is necessary.

I don't really think finding more mass is going to make a difference
here. What I think is really going to make the difference is a new way
model the curvature of spacetime with the existing mass. I think when GR
is iterated over many self-dependent iterations, it will result in some
surprising relationships that we hadn't expected to see. Quantum
computing will make this task a lot easier.

One example is in the movie Interstellar. This is where they fed GR
equations into a movie graphics computer, and came up with an image of a
blackhole that nobody imagined in their own heads. The computer had no
preconceived notions of what it should see, it just ate the input data,
ran the equations, can came up with an output image.

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.

But GR (like Newton), is a classical solution. GR simplifies to
Newton, under the right circumstances, circumstances suitable to
galaxies "in the large".

Classical problems can still be solved through quantum qubits. In fact,
classical physics could be thought to emerge from macroscopic quantum
interactions. So far, we've only been considering the macroscopic
effects themselves, but no one has attempted to build up to a classical
solution from a series of quantum solutions.

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.

There is no significant rotation in a globular cluster, so the normal
mass present, is explained by microlensing, and other methods that
apply equally well to a spiral's nucleus, or a globular cluster
(expected to be ancient cores of spiral galaxies).

There has to be rotation in a globular cluster, stars don't just stand
in place with all of that gravity between them without there being
curved motion.

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?

We *know* it is still a classical theory, however.

Being a classical theory doesn't make it the same as Newton's gravity,
it's quite a significant departure from Newton, just as Newton was a
departure from Aristotle's gravity.

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.

Amen. Absolutely "dark" too, just not very massive, and in order to
stay in the halo (as we observe), would have to be moving damned
slowly... so would have to be too numerous to be all of Dark Matter.

Well, let's look at it practically. The Milky Way by itself is 100,000
LY across on its disk, probably 1 million LY across on its halo. So
neutrinos released now from the various stars of the galaxy will remain
within the borders of the galaxy for between 100,000 to 1 million years.
Enough time to remain a part of the galaxy's mass. Even photons will do
the same. So there's a large amount of time that energy will remain
within the borders of a galaxy, and even larger amount of time that
it'll remain within the borders of a galactic cluster or supercluster.
Now that we have detected gravitational waves, there's another even more
humongous source of energy (converting several solar masses into energy
at a time) that we know travels at only the speed of light. So lots of
energy stays locked into regions just due to the slow passage of time.

Yousuf Khan