Sean, if you really want to shake things up, join the growing number of scientists who realize “string” is the wrong path to quantum gravity.

Tissa (#55), to emphasise the point implied in my final paragraph, stars in a galaxy do *not* orbit their galaxy as one would predict from Newton’s laws assuming theirs is the only mass in the galaxy. So your argument is based on a false premise, specifically your point 9.

Read the Wikipedia article http://en.wikipedia.org/wiki/Galaxy_rotation_problem

I’m not entirely clear how cosmologists exclude the possibility of enough non-stellar material to account for observed orbits. But this stuff, especially gas and ice and dust, absorbs and reflects radiation. So presumably the amount present can be deduced from spectrographic data and the amount infered by this and other means is insufficient for the job.

In any case, dark mass and energy is apparently needed to make up the total amound of mass-energy which the Standard Model predicts must have been formed in the Big Bang. Ordinary matter falls far short of what is required.

OK, now let’s do one with N in the billions of equal billionth parts of the mass of the combined Earth-Moon system.

> 7) Now we will use some magic, we will make 90% of the N bodies
> invisible, and call them Dark Matter!
> 8).What do you think would happen to the 10% that are still visible?
> 9).You guessed! they will keep moving as before and still obey
> Newtonian Law’s with no velocity discrepancies.

This time let the magic be to make the Earth invisible and call it Dark Matter. Then an alien observer on Mars, say, observing the moon through a telescope for several months would see it perform bizarre cyclic motions superimposed on its orbit of the Sun.

As this motion would not certainly not be Newtonian, they would be able to correctly predict the large invisible mass sufficient to cause the combined centre of mass of that and the Moon to orbit along the approved Newtonian ellipse.

It’s the same with stellar rotation rates – The dark mass is needed to restore Newtonian sanity to observations in conflict with it when only visible mass is taken into account. Somehow you’ve put the cart before the horse.

A Dark Matter thought experiment.

1) Dark Matter was invented to augment the observed motion of
real visible matter, right? right!
2) Dark Matter interacts with real matter via gravitational forces
only, right? right!
3) Dark Matter too interacts with Dark Matter gravitationally
right? right!
4) Therefore Dark Matter must take part in the orbital dynamics
of the system, right? right!
5) The only difference is that Dark Matter cannot be seen, other
wise, it takes part in the gravitational dynamics of the system,
which is purely Newtonian motion, right? right!

Now that we agree, let us do a pure thought experiment.
Let us do an N-Body simulation, where N will be in the billions.

6) All N Bodies will therefore do a Newtonian Samba. Each of the
N Bodies will clearly have rotational motion velocities defined
by Newton’s laws. Therefore only Newton’s Law accounts for
their motions.
7) Now we will use some magic, we will make 90% of the N bodies
invisible, and call them Dark Matter!
8).What do you think would happen to the 10% that are still visible?
9).You guessed! they will keep moving as before and still obey
Newtonian Law’s with no velocity discrepancies.
10)Moral of the story is, Dark Matter don’t matter.
11)There must be another way! I have a hypothesis for another
alternative to Dark Matter at cosmicdarkmatter.com.

/Tissa Perera

I have been to Ned Wright’s tutorial several times over the years, but I find the assumption not only there but also generally (running the film backwards) is that the universe began as an extreme density region. Whatever the inferred history prior to the CMB, all that is “known” is that it is emitted from a hydrogen plasma at 3000 K (correct?). How it got to be that way is what I question. In other words it could be either cooling down or heating up. There seems to be no consideration of a heating up scenario. I think this is for reasons of the historical growth of physics, e.g. bodies of matter, conservation of mass-energy.

Re the balloon analogy, I dimly understand the mathematicians have a special sense of 2D and 3D, sphere and ball. It is difficult to ignore the interior of the ball, I wonder how the mathematicians do it. But the key to my idea is in your sentence, “The space will just keep expanding, and of course there is no “rubber” that will break.” If the initial condition is spatial expansion, the universal expansion rate will be dictated at the moment of expansion. The “spatial field” will expand at its full potential, which it cannot alter without breaking its own natural law (or our understanding of the constancy of natural laws in our frame). The initial condition therefore dictates a constant expansion rate and immediately invokes space and time measurement, including added volume per unit of existing volume of the ball.

The thing is that, after a very short time, for every added unit of constant radial expansion the added volume is less than the natural law (initial condition) requires. That is, each unit of existing volume adds less and less new volume as the ball expands at its limit. In other words, if every ‘point’ within the expanding field replicates the initial condition of the field itself, there is not enough space within the field to absorb the expansion potential – even while the field is expanding at its full potential at its ‘edge’. So although there is no rubber that will break, the initial condition of constant expansion rate produces pressure inside the ball. I am told that rotation is a degree of freedom. So rotation absorbs the pressure. I think it would have to be rotation on the equivalent of three axes in order to absorb pressure from all directions. It also has the effect that space in the rotating region does not expand. If you go by Planck times and Planck lengths and rotation rate of c applied to ~10^23 hertz frequency for protons and ~10^20 hertz frequency for electrons, I calculated something like 10^64 particles would be created in one second. Each non-expanding region forms effectively a zero point for the spatial field, so the working of the natural law restarts from an effective zero radius with each matter particle created. Then the cycle repeats itself, constantly creating new matter just inside the edge of the ball, but I think with larger intervals, so you end up with dense regions of matter and voids. Large enough voids may create pressure and rotation, i.e. dark matter.

$latex
\nabla_\mu T^{\mu\nu}~=~0,
$

but there is no conservation principle for energy in cosmology!

The expansion of the universe is likened to a baloon blowing up, but of course in three dimensions instead of two. However, ignore the idea that this sphere encloses a higher dimensional region or a ball. The space will just keep expanding, and of course there is no “rubber” that will break. I think Sean posted the Ned Wright’s cosmology website. There is a lot of good stuff there which can help anyone understand some of this stuff.

Lawrence B. Crowell

I am of two minds about whether to continue. In view of your last post just read, I don’t expect an answer but I will give this one last try. What I already wrote was:

Thank you for your concern, but I cheer up by laughing at myself!
I notice the term Lambda above. I wonder what your interpretation of Lambda is. More broadly, I wonder about gravitational instability and the feature of a limited amount of mass-energy in the universe. NASA says the universe is supposed to have “released” all its mass-energy within a certain time, which requires a kind of mass-energy “bank” – once all the mass-energy is withdrawn from the bank, there is no more. Yet at the same time there is an entity whose influence increases (dark energy).

However, what if the universe is not the inflation-powered surface of a balloon, but the volume inside the balloon, expanding at a constant rate powered by a positive energy density, creating positive pressure, in turn creating matter which absorbs the local pressure resulting in local non-expansion (perceived as gravitational attraction/spacetime curvature), followed by further expansion (perhaps perceived as accelerated expansion depending on frame), pressure inside the surface, and further matter creation, in cycles? No need for rho crit., Lambda, etc. since the system stabilizes itself by cyclical matter creation.

When you quit laughing, how about a round of “Row, row, row your boat. . . .”?

Lawrence B. Crowell

Yes, I second that. He does a cracking good job here, much appreciated, and doubtless in other forums besides. What’s more he’s written several books on physics, as a quick search on Amazon reveals.