In the seventies scientists decided to make computer models of the Milkyway Galaxy (that is where we live) and hit a bit of a snag with their calculations. Something was missing - it seems - the existing laws of gravity and formulaes we thought guided things like stars and light would mean that the galaxy would fly apart.
It was not the first time that science had to rethink its physics. In fact physics has evolved from a set of assumptions about the universe being a fairly linear understandable and predictable old thing to new understandings that indicate that up until quite recently we knew very little indeed.
Einstein changed the way we understood matter. Instead of a definite solid, it was now a dispersed lattice of atoms that sort of vibrate and seem like models of the solar system - and these systems clumped into molecules, seemingly following a pattern of natural analogy with galactic arrangements grouping billions of stars.
This had led to conclusions that had never taken into account that something had to be holding together these giant suns - rotating about an axis, the force would seem to natually disperse. Some kind of cosmic cement seemed to prevent this.
Much much vaster than the space between Earth and the Sun (Solar space), 93,000,000 miles approx - is the space between stars. The closest, Proxima Centauri is 4.3 light years away. 1 LY is approx 26 billion miles. The distance between stars is several orders of magnitude greater inside a galaxy. Being able to understand how huge a galaxy is itself presents a challenge. Now, the space between galaxies is again, an order of magnitude greater. Imagine throwing millions of frozen peas into the Pacific Ocean, how they disperse over a period of decades. May help to appreciate just how cold and huge intergalactic space is.
So, what is contained in these gaps? One theory is "dark matter", another is "dark energy". We used to think it was just a vast vacuum but the physics just say that is not the case. What does glue the pieces together appears to be gravity, a force that is exerted on an object in space seemingly by a larger object, another model is that gravity is the coercive electromagnetic environment dragging objects together like electro-magnetism.
The "dark matter" is not something that can be weighed or sliced up with a knife. It seems to me to be a way of explaining a discrete effect or bonding - the rules may be different in empty space - when there is no matter about, time hungers and creates an inert state that acts as a repelling force enveloping things with temporal resistance. This creates an equilibrium in which the real "exists".
