The missing mass problem has been with us many decades now. Going on a century if you start counting from the work of Oort and Zwicky in the 1930s. Not quite a half a century if we date it from the 1970s when most of the relevant scientific community started to take it seriously. Either way, that’s a very long time for a major problem to go unsolved in physics.

A Philosophical Approach to MOND is a new book by David Merritt. This is a major development in the both the science of cosmology and astrophysics, on the one hand, and the philosophy and history of science on the other. It should be required reading for anyone interested in any of these topics.

The distance scale is fundamental to cosmology. How big is the universe? is pretty much the first question we ask when we look at the Big Picture. The primary yardstick we use to describe the scale of the universe is Hubble’s constant: the H ₀ in v = H ₀ D that relates the recession velocity (redshift) of a galaxy to its distance. More generally, this is the current expansion rate of the universe.

Britain and America are two nations divided by a common language. attributed to George Bernard Shaw Physics and Astronomy are two fields divided by a common interest in how the universe works. There is a considerable amount of overlap between some sub-fields of these subjects, and practically none at all in others.

There is a tendency when teaching science to oversimplify its history for the sake of getting on with the science.

There are two basic approaches to cosmology: start at redshift zero and work outwards in space, or start at the beginning of time and work forward. The latter approach is generally favored by theorists, as much of the physics of the early universe follows a “clean” thermal progression, cooling adiabatically as it expands.

I have had the misfortune to encounter many terms for psychological dysfunction in many venues. Cognitive dissonance, confirmation bias, the Dunning-Kruger effect – I have witnessed them all, all too often, both in the context of science and elsewhere. Those of us who are trained as scientists are still human: though we fancy ourselves immune, we are still subject to the same cognitive foibles as everyone else.

Reading Merritt’s paper on the philosophy of cosmology, I was struck by a particular quote from Lakatos: A research programme is said to be progressing as long as its theoretical growth anticipates its empirical growth, that is as long as it keeps predicting novel facts with some success (“progressive problemshift”); it is stagnating if its theoretical growth lags behind its empirical growth, that is as long as it gives only post-hoc

Casertano et al. have used Gaia to provide a small but important update in the debate over the value of the Hubble Constant. The ESA Gaia mission is measuring parallaxes for billions of stars. This is fundamental data that will advance astronomy in many ways, no doubt settling long standing problems but also raising new ones – or complicating existing ones.

It has been proposal season for the Hubble Space Telescope, so many astronomers have been busy with that. I am no exception. Talking to others, it is clear that there remain many more excellent Hubble projects than available observing time. So I haven’t written here for a bit, and I have other tasks to get on with. I did get requests for a report on the last conference I went to, Beyond WIMPs: from Theory to Detection.