What holds galaxies together?

These are some of the things we know about galaxies

• They are clusters of stars, gas, and other rocky and gassy stuff like planets and asteroids, plus black holes.
• They are mostly shaped like a fried egg: disk shaped with a significant bulge towards the centre.
• They are huge: Most galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years)
• They are separated by even huger distances of empty space on the order of millions of parsecs (or megaparsecs).
• And they rotate. Our galaxy, the Milky Way, rotates about once every 200 million years.

And here's the problem. Simply stated, there is not enough observable mass in the galaxies for its gravity to hold the galaxy together. They should fly apart. For the stars and other stuff in the galaxy to orbit around the centre of the galaxy like the moon rotates around the earth or the earth rotates around the sun, there has to be much more mass in the galaxy than we can find. A lot more. About 25% more.

But since they do, and we can't see the extra mass, and the only stuff that we know of that contains mass is matter, the scientists have named the missing matter "Dark Matter". And

But maybe they are looking at the problem from the wrong angle.

Think about water.

At the molecular level, we think of water as being made up of molecules, and all of the chemistry of water is based upon this molecular model.  Atoms of hydrogen and oxygen are bound together and react with other molecules. They have mass, they vibrate and move around. As Ice, they still vibrate but their movement is much more restricted to lattice structure. As water vapour, they are unconstrained and move around freely.  

At the particle level, the atoms are made up of subatomic particles: protons, neutrons and electrons which can be used to explain electricity, magnetism and X-rays and nuclear fission.

At an even smaller scale, they can be considered as gluons, quarks etc which can explain quantum stuff, which I don't know enough about to describe.

But at a larger scale, water behaves like a fluid. Nothing to do with molecules, but small parcels with mass, volume, velocity, viscosity, temperature etc. which can be used to model the behaviour of water on a human scale, through pipes, as sea waves and being driven by propellers.

Water molecules are spaced about  10-7 metres.

Electrons are around  10-11 metres from the centre of the atom

I'm not sure of the spacing of gluons but I suspect it's much smaller

Water is considered as a fluid at scales of millimetres and above, i.e 10-3 plus

The point is that depending on the scale of our observation, we are totally comfortable using totally different and incompatible models to describe and understand the nature of water.

Now, on a human scale, of metres and kilometres, galaxies are colossal. Their diameters are measured in thousands of parsecs, or 3x1019 metres and their separations are millions of parsecs or 1022 metres.  

At this super-colossal scale of intergalactic space, could we consider galaxies as a fluid? At the "molecular level" we can see that they are made up of stars, planets, asteroids, black holes, gas etc, moving apparently randomly but according to their local gravitational fields, but when viewed from a macroscopic level at a scale of 1015-20 greater than human scale, could we consider galaxies not as individual stars etc, but as a colossal blob of fluid in empty space?

Now let's think about vortices for a minute.

We are familiar with vortices in nature:  the bath water spinning down the plughole, the dust devil, cyclone,  or tornado spinning hot air up into the clouds. In all these cases, the fluid, water or air is rotating in the horizontal plane and the matter is being swept vertically - down in the bath and up in the air. In vector analysis, this vertical sweeping is named a "sink" (after the plug-hole is suspect).  In these cases the sink is perpendicular to the horizontal plane of rotation. This is the nature of vortices in nature. Indeed this is a tenet of Maxwell's circulation theory: Vorticity, Γ, is perpendicular to the plane of the circulation.

Here's where the argument gets quirky.

As we know, modern physics views space as a 4-dimensional space-time continuum, three dimensions of distance and the 4th, of time. By definition the three space dimensions are orthogonal, i.e  perpendicular to each other. It can be concluded that time is orthogonal to the space dimensions.

I wonder if, whilst rotating in two dimensions vortices actually have a sink not only in the other space dimension, but also in the other time dimension as well?

But such a blob of fluid, like water, does not behave like that. Experiments with water in the microgravity of the space station clearly shows that water doesn't spin into a disk. When a blob of water in microgravity is made to spin, it does become a bit flattened, but we've never seen them become a disk. That's because the blob is being constrained by surface tension. I'm pretty sure if in microgravity you spin a blob of water fast enough, the surface tension will eventually be insufficient to provide the centripetal force and the blob will disintegrate.

But, maybe, at the super-colossal scale of galaxies, they do spin like that, so maybe there's something about the scale that solves that problem?

So, here's the crux of the theory:

In a natural vortex, like  a tornado or the bath water, the rotation is in a two spatial dimension plane.and the sink is in the third dimension (up/down). Maybe, for the colossal system of a galaxy, (3x1013 times the size of the largest vortex in the known universe, Jupiter's Red Spot) the sink is not in the third spatial dimension, but the fourth dimension: time.

Maybe "Dark Matter" is now as unnecessary as the 19th Century need for "ether".