Why is it believed that this ‘invisible’ stuff exists? If one were to measure the galaxies motions and then run the calculations using Newton’s laws for Gravitation or Motion it would result in a realization. The galaxies should just spin apart but they don’t seeming to indicate that there is some invisible matter or force or energy that holds it together. Of course this probably seemed more ridiculous earlier on, before the Hadron Collider went live in 2008.
In 1920 Ernest Rutherford proposed the neutron; in 1932 James Chadwick discovered it. In 1928 Dirac predicted the existence of anti-matter based on his famous “Dirac Equation”. It was 1955 when the anti-proton was discovered. In 1930 Wolfgang Pauli suggested that there was an unseen or invisible particle. He based this on measured energies and momenta of protons and electrons in the decay of a neutron. It wasn’t until 1956 when Frederick Reines and a team of physicists discovered the electron-antineutron. Also in 1964 a counting device was devised by Murray Gell-Mann and George Zweig that led to their explanation of hadrons which included what was later known as a “quark”. There were three different sorts offered – Up, Down, and Strange. These remained proposed until 1977 and 1995 though possibly were seen sooner but not recognized.
The point being offered is that what is invisible today is not necessarily invisible tomorrow.
A new theory has been developed by the Vanderbilt University Scientists and it is actually relatively simple. This theory is discussed in a paper entitled “ANAPOLE DARK MATTER” and in it is suggested that Dark Matter particles may be surrounded by a form of electromagnetism. This theory is different and simpler in its treatment of dark matter because instead of consisting entirely of unknowns, it makes use of ordinary electromagnetism. This model goes on to make predictions about the rate it would show up in the many matter detectors that are buried all over the world.
Following this concept the argument could be made that a type of propulsion to be considered for space travel would be one of Electromagnetism. (Electromagnetism is the principle of accelerating an object by the utilization of a flowing electrical current and magnetic fields.)
It is easier to accept the existence of this Dark Matter following the previous explanations. Understanding that invisible has existed as a constant in theories only to be later proven, it would seem that absence of evidence is not evidence of absence.