A new theory states that Dark Matter could be ordinary matter in a parallel universe.
The first stars illuminated the cold and dark primordial cosmos, then collapsed into black holes that together with Dark Matter formed galaxies and superclusters visible today.
How do we know that dark matter exists?
If a galaxy in another dimension were superimposed on our own, we would not be able to see it. It would be invisible, but we would feel its gravity. This could explain the existence of dark matter
Michio Kaku
We know that dark matter exists because we can see its gravitational effect on visible stars and galaxies.
Our galaxy, the Milky Way, could not have dragged enough matter to create its stars in the 13,8 billion years since the Big Bang without the presence of some invisible things held together by an equally invisible "glue".
The European Space Agency calculated that dark matter represents 26,8% of the mass energy of the Universe compared to 4,5% of normal "fermionic" matter. It means that dark matter exceeds ordinary matter by a factor of about six. Dark matter in packs, bags, cataracts. Free dark matter, ma'am.
Cosmology is approaching the next paradigm shift
One of the most astounding discoveries of the modern era is that the fabric of spacetime emerges from something somehow beneath it.
In an attempt to find the elusive quantum theory of gravity and merge quantum mechanics and general relativity, research has shown that spacetime emerges from (quantum) information processing in general.
Mirror universes

Most physicists and philosophers now adhere to the multiverse ontology, and quantum theory provides strong support for this worldview. Some physicists like Julian Barbour, Tim Koslowski e Flavio Markets they argue that for any confined particle system (an autonomous universe like ours) gravity will create a central point (they called it "Janus Point"). From this point on, time begins to flow in opposite directions.
Two other physicists (Sean Carroll of the California Institute of Technology in Pasadena e Alan Guth of MIT) work on a similar model based on entropy. A model that shows time moving in two different directions, in two mirror universes, from the Big Bang onwards.
In the ontological model that Alex Vikoulov is currently developing (the Cybernetic Theory of Mind) the Janus Point is equated with the concept of Omega Singularity. A convergent point of maximum computational capacity. The Omega singularity is a hypothetical projector of all possible timelines of the entire quantum multiverse.
What does this mean for dark matter?
From the above theories, it follows that dark matter could be ordinary matter in the "probabilistic space" of other dimensions that we do not see. With other stars, other life invisible to us. At least for our current level of development.
The "photon test"

These are not purely speculative hypotheses. On the subject of dark matter, these logics derive from the principles of quantum mechanics. For example Richard Feynman, Nobel Prize in Physics, discusses in his book "QED"(the situation of partially transmitted and partially reflected photons from a glass plate: a reflection of about 4%.
In other words, one out of every 24 photons will be reflected on average, and this also applies to a "one at a time" stream. Four percent, says Vikoulov, cannot be explained by statistical differences in photons (they are identical) or by random variations in the glass.
Something, says Vikoulov, is "driving" an average of 1 photon in every 24 to be reflected instead of being transmitted.
For more information: A. Vikoulov - The Physics of Time