How do you draw a black hole? Upcoming talk at HSS in Montreal

On Friday (November 5) I’ll be presenting some of my work on the history of General Relativity (GR) at the History of Science Society annual meeting in Montreal as part of a panel on Black Holes and Quantum Mechanics (1:30–3:10, Salon B–Level 4). I did my bachelor’s degree at McGill, so I’m really excited to get back to the city, and see some of my old friends and professors.

How to draw a black hole? Errrr...

My talk asks how we can explain the revival of the study of GR that started in the mid-1950s and built strongly into the 1970s. One explanation has been that new observational and experimental evidence made the field more reputable—closer to the real world than the realm of high theory.

New experimental included Pound and Rebka’s 1959 confirmation of the gravitational redshift of light at Harvard, and Joseph Weber’s 1968 announcement that he had detected gravity waves at the University of Maryland. New observational evidence included the discover of “quasi stellar objects” (now called quasars) as strong radio sources in 1959, the discovery of pulsars in 1967, and the measurement of the ~3K Cosmic Microwave Background radiation.

But this can’t be the whole story. First off, because this GR revival started before 1959, and the exciting work on black holes got going before 1967. Secondly, because the increase of energy in the field was in both high theory and observation. Thirdly, the communities of astrophysics and GR theory were reasonably distinct. (And, current `Relativists’ and Cosmologists benefit from casting the modern revival of their field in terms of solid observations and experiments; not in terms of theoretical advances.) I think the root of this revival came from theorists, and in particular the importation of new techniques from mathematics into physics.

In particular, I’m interested in Roger Penrose’s application of topology to GR, and the diagrams that went along with them. Penrose shook up the field in 1965 when he proved that any sufficiently-large star that collapses must create a singularity. Previously, it was known that a perfectly spherically symmetric star would create a singularity. But, physicists reasoned that because no star is actually spherically symmetric, the singularity could be avoided. (And at the time, there were no computers to approximate the non-symmetric situations.) But Penrose proved that whatever the shape, singularities must form.

This is an exciting and challenging idea—something that make you reconsider your understanding of space-time. When Penrose and Stephen Hawking extended the stellar collapse to cosmological situations in 1970, questions became bigger.

All this would be attractive to students, fueling the development of the field. Moreover, because topology was a relatively well-developed field in mathematics, aspiring physicists knew that there would be a lot of interesting results just from applying the new tools.

But in addition to these sorts of draws, I think that Penrose’s diagrammatic representations of the universes of black holes (representations of solutions of the Einstein Equations) made it easier to approach the subject. GR involves intricate mathematics, and a diagram of the entire system keeps you connected to the physical situation. It allows you to reason about the connections between different regions of space-time, for instance. (See for instance Brandon Carter (1966)).

When this work was incorporated into Misner, Thorne, and Wheeler’s Gravitation, students (and post docs, and young professors) knew that learning this material would help them understand GR and put them in a position where generalizations from homework problems are publishable results. I think this goes a long way to explaining the “Renaissance” of General Relativity.  And, it provides insight into what it means to think with diagrams and also the relationship between research and pedagogy in physics.

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