[Alan McDougall (OP)]

Hi,

3 Dark matter
TAKE our best understanding of gravity, apply it to the way galaxies spin, and you'll quickly see the problem: the galaxies should be falling apart. Galactic matter orbits around a central point because its mutual gravitational attraction creates centripetal forces. But there is not enough mass in the galaxies to produce the observed spin.

Vera Rubin, an astronomer working at the Carnegie Institution's department of terrestrial magnetism in Washington DC, spotted this anomaly in the late 1970s. The best response from physicists was to suggest there is more stuff out there than we can see. The trouble was, nobody could explain what this "dark matter" was.
And they still can't. Although researchers have made many suggestions about what kind of particles might make up dark matter, there is no consensus. It's an embarrassing hole in our understanding. Astronomical observations suggest that dark matter must make up about 90 per cent of the mass in the universe, yet we are astonishingly ignorant what that 90 per cent is.

[Soul Surfer]

It is perfectly logical that there will be both bosons and fermions that only interact gravitationally since all other sorts of particles exist so to a certain extent one would expect there to be some dark matter and dark energy in the universe the big surprise is that now we have measured the universe well enough to estimate the amount of dark matter and dark energy that there is so much of it.

The interesting and difficult problem will be detecting these particles and understanding where they fit in the models.  This may yet prove to be beyond the reach of mankind.