There are a number of parameters that we deal with in cosmology that have no dimensions; that is, they’re just numbers. And yet, there are a remarkable number of coincidences that just “happen to be that way” in our Universe.

Douglas Scott, in this paper, points out some of the more puzzling ones, including:

- The age of the Universe (13.7 billion years) is exactly three times the age of the Solar System (4.5 to 4.6 billion years).
- The dark matter fraction of the Universe (Omega
_{DM}=0.23 +/- 0.02) is equal to the Helium mass fraction (Y_{p}=0.238 +/- 0.010) of the baryons. - The Hubble constant (H
_{0}) times the age of the Universe (t_{0}) is exactly 1 (H_{0}t_{0}=1.03 +/- 0.04). - T
_{0}, the temperature of the cosmic microwave background, is exactly the triple point of water temperature divided by 100.

What does this mean? Let’s ask Douglas Scott:

Which of these turn out to be complete coincidence

remains to be seen. But perhaps one of them will be

the ‘smoking grail’ that cosmologists have been looking

for to lead us beyond vanilla ΛCDM into a whole new

ice-cream parlour of models.

In the absence of ice cream, then, this means absolutely nothing! (Although the coincidences are real, and feel free to quote me on them.) Happy April Fools’ Day!