Dark matter filaments bridge the space between galaxies in this false-color map. The locations of bright galaxies are shown by the white regions and the presence of a dark matter filament bridging the galaxies is shown in red. Image via RAS/ S. Epps & M. Hudson / University of Waterloo. Dark Matter, it's what the universe is made of. When I started all this I had a good idea what Dark Energy was. I do not have a good idea for Dark Matter. My best guess is that the cosmos is full of dark/black matter. There are some powerful gravitational forces out there and what we do know about Dark Matter and Black Holes is that they interact only via gravity. My theory of the Big Bang assumes that a cosmic scale black hole or colliding binary destabilised and exploded. All matter both dark and light, all radiation and energy came from this explosion. So both dark and light (baryonic) matter came out of this black hole. Now let's run the clock forward. The future for our stars is that they will either collapse into a black hole or those little red dwarfs will eventually be absorbed by the very large black holes in our galaxies. Those galaxies already beyond or close to the edge of our observable universe are been drawn out by cosmic gravity aka Dark Energy. So what’s going to happen to them? They are heading out into even more massive cosmic black holes. The photons heading out of our universe will find a home in one of those black holes one day. The traffic is all one way. Whatever is inside a black hole is the basic stuff of the universe. All matter will end up in this state eventually. A small aside. It is said that nothing escapes a black hole. Not true. Gravity escapes black holes. I’ll come back to this later when I discuss a unified theory of forces and quantum gravity. The cosmos, present company excepted, is just black holes and gravity. If that was the end of the story we would not be pondering these questions. Once in a while one of these big lumps of dark matter gets so big that it explodes. Could be many causes. The energy released from this catastrophic event explodes the dark matter out into space. Some of the dark matter is energised or excited by the massive energy and heat generated. Quarks, protons, neutrons and then atoms are formed. Now beyond the massive gravitational forces inside the black hole they are stable. Now we have light matter. Now run the usual story of the Big Bang, cooling,opaque plasma, recombination, stars, lots of light and galaxies. In the course of time though all this stuff returns back to black holes. A cosmic cycle from Dark Matter creating our universe and returning to Dark Matter. It’s almost a certainty that this cycle has and will be repeated throughout the cosmos for ever. So what is Dark Matter.? What does it ‘look’ like? My guess is that it is in the form of black holes. When the Big Bang happened most of the Dark Matter in the black hole exploded out into space. At the core where the pressure and energy of the explosion was generated the light matter of the universe was created, in the proportion of 1/6th of Dark Matter. That is one route. However, it is quite possible that dark matter retains its dense structure at masses well below solar masses. Stellar mass black holes may have a core structure similar to neutron stars. Once you get to supermassive black holes it is very possible that there is a major change. An analogy would be glad to liquid to solid. Inside the fierce gravity of a cosmic scale black hole the structural change could be such that the dense form is retained even through the Big Bang explosion. If so then Dark Matter could be a much smaller particle, tiny, heavy but without any interaction with light matter. I prefer the black hole scenario. If so we had trillions of black holes in the early universe from stellar mass up to Great Attractor size This would help to explain the supermassive black holes we are finding in the early universe. Also explains the early formation of galaxies. Perhaps the ‘Great Attractor’ is a big chunk of the Big Bang black hole or maybe it is another black hole which was close when the Bang happened. In my lifetime we have moved from disbelief in black holes to finding evidence for them everywhere and more and more often. Maybe it is WIMPS but we have been looking for them for many years. My best wishes to the WIMP hunters. My bet is that just like Dark Energy the solution is simple, they just have not seen it yet. To all you astronomers out there doing all the hard graft, please keep looking for those black holes and for those gravitational waves from beyond our universe. The universe is much bigger than we think but it really is quite simple. It is all about gravity, the “weak force”. And please hurry up because I don’t have much time left as I approach my 3 score and 10. Finally some quotes I like from the internet. ‘Not everyone believes, as these researchers do, that primordial black holes and dark matter could be one and the same. But as Kamionkowski told Science in 2017:’ "It’s a nutty idea, but every idea of what dark matter might be is a nutty idea." Originally published on Live Science. “On dark matter, I think it’s much less clear. For a long time, the most popular candidate was this thing called the WIMP, or a Weakly Interacting Massive Particle. That idea is still popular and totally possible, but a lot of the particles that could be that kind of dark matter are already ruled out. The other really compelling candidate is a subatomic particle called the axion. People are just getting to a place where they’re able to start searching for these particles that we think are going to be extremely difficult to detect. It’s also possible that dark matter might surprise us, that it’s some new kind of particle that we don’t have the techniques to look for yet.” —Adam Hadhazy, Fall 2017 “We’re not sure our current way of thinking [about the universe] is correct because it essentially requires us to make stuff up, namely dark matter and dark energy.” —Scott Dodelson Also Dodelson: “We’re living in an era of cognitive dissonance. There is all this cosmological evidence for the existence of dark matter, but over the last 30 years, we’ve run all these experiments and haven’t found it. My bet is that we’re looking at things all wrong. Someone who’s 8 years old today is going to come around and figure out how to make sense of all the data without evoking mysterious new substances.” How about a 68 years old?