In article ,
Richard Saam wrote:
wrote:
In article ,
Richard Saam wrote:

An interesting calculation.

Here is another for Pioneer Spacecraft deceleration 'a'

a ~ 2*Area*rho*c2 / M
~ 2*(58,965 cm2)*(6.38E-30 g/cm3)*(3E10 cm/sec)^2 /(241,000 g)
~ 2.8E10-9 cm/sec2 for Pioneer spacecraft


I haven't paid attention to the Pioneer anomaly stuff lately, so
I apologize if I'm just being stupid, but I don't see the physics
behind this relation. In particular, I don't see how c gets involved.
If you assume that the spacecraft is moving at velocity v through a cloud
of stationary particles that bounce elastically off of it whenever they hit
it, then you get a relation something like the above, but with v instead
of c. That makes a big difference, of course.

The conceptual physics is very simple.
Assume that space is a continuous medium
with mass critical density of 6.38E-30 g/cm^3 .
Then think of an object passing through it
defined something like a ram jet engine
(analogous to atmospheric oxygen intake)
which takes in this space medium with neglible effect (m v^2)
but which expells it as m c^2
with resultant thrust in the same direction as intake
resulting in object deceleration.

It's always embarrassing when something is described as "very simple"
and I still don't get it! I don't understand the model you're describing
in about half a dozen different ways. What does "expels it as m c^2" mean?
Why doesn't the final answer depend on the speed of the object through
the medium? Surely the faster the object is moving, the more of this
stuff it'll sweep up.

We're hypothesizing something like the Pioneer moving through a cloud
of particles, right? When a single particle of mass m strikes the
Pioneer, the *largest* impulse that can be imparted is surely 2mv,
where v is the relative speed of the particle and Pioneer. The total
mass of all such particles striking per second is something like rho A
v, so the total force would be 2 rho A v^2. So I get the same formula
as you have above, but with v instead of c. And that's bound to be an
overestimate, because not every particle imparts the maximum possible
impulse.

Your average calculated local density of 7 x 10^{-25} g/cm^3
is quite a bit higher than 30 x 6.38E-30 g/cm^3 or 2E-28 g/cm^3
but there still remains a conceptual mechanism
on how dark matter influences solar objects
according to their area/mass
(Pioneer some and planets negligible).
Perhaps the local dark matter density is on the order of
30 x 6.38E-30 g/cm3 or 2E-28 g/cm^3.


The calculation I did was based on well-measured Galactic dynamics.
If you want to get a different answer, you'll have to come up with a different
explanation for the motion of stars in the Galaxy.

I have replicated your calculations and they are right.
I think you will agree
there are potentially many components to Galactic dynamics.

I'm sorry; I'm missing your point yet again. The question I thought
we were talking about was, more or less, "what's the dark matter?" If
we're now talking about some component whose density is several orders
of magnitude less than the density implied from Galactic dynamics,
then more or less by definition we're not talking about the dark
matter.

I'm not sure I see the point of postulating that the solar system
contains some component of some unknown material with a density equal
to the critical density. We know that the density in the solar
neighborhood is orders of magnitude larger than that, so what problem
are we trying to solve by assuming such a component?

-Ted

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