02/03/2017: How did dark matter come to matter?

The nature of dark matter is one of the most important open problems in today’s physics. When, how and why did scientists accept that most matter in the universe is actually invisible and unknown to us? An interdisciplinary collaboration of historians and physicists at the Institute of Physics, the GRAPPA Center of Excellence, and the Vossius Center has revisited these questions. Their results inform us about past and current practices in cosmology.

PhD student Jaco de Swart, astroparticle physicist Gianfranco Bertone and historian of science Jeroen van Dongen study the history of ‘how dark matter came to matter’. Their first results are published in an article in Nature Astronomy this week.

Forty years of darkness
Dark Matter has a long history. In the 1930s, first observations suggested that galaxies in clusters are moving so rapidly that their velocities cannot be understood by familiar and visible matter. Still, it took 40 years before consensus on this conclusion was reached. ‘[A] lot of things were not understood about masses of astronomical objects on the scales of galaxies and larger’, eminent physicist Jim Peebles recalled in an interview with Jaco de Swart. Peebles played a central role in the 1970s in convincing the scientific community that most of the matter in the universe is unknown to us: it is literally ‘dark’. But why did it take so long for scientists to realize this?

Cosmological turn
De Swart, Bertone and Van Dongen studied original sources, interviewed pioneering scientists and reconstructed the historical context of the dark matter hypothesis. In their paper, they show that newly observed phenomena, as well as institutional developments, partly driven by the Cold War, led astronomers and physicists to focus on cosmological problems. A quest to determine the mass density of the universe began: it is this mass density which decides the ultimate fate of the universe. In the search for the universe’s mass, galactic dynamics was finally taken to imply that 85% of the universe’s matter is missing.

History for the future
Collaborations between physicists, historians and philosophers are necessary to deepen our understanding of cosmology and dark matter. What kind of arguments and inferences are used in cosmology? When does data turn into evidence for astrophysicists? Answers to these questions will inform today’s heated debates on the nature of dark matter and the proper practice of cosmology.

How dark matter come to matter – Jaco de Swart, Gianfranco Bertone, and Jeroen van Dongen