You Ain’t Seen Nothing Yet…

This is the week the Nobel Prizes are announced, and today is the day (at least in New Zealand; first place in the world to see the light, as the tourist people say) the Physics prize is announced. And this year the odds-on favourite will be LIGO and the discovery of gravitational waves.

It is possible that the famously cautious Nobel committee will wait another year but their biggest debate may be exactly which people should get the nod, as the prize can only be split three ways. At one point the LIGO experiment was driven by “the troika” of Rainer Weiss, Kip Thorne and Ronald Drever which would have simplified matters. However, Drever was sidelined early in the process and died this year, rendering him definitively ineligible and leaving an empty chair. One candidate to fill it is Barry Barish who is credited with laying the much of the groundwork for the overall LIGO collaboration but there is no shortage of claimants.

This gets to the heart of a dilemma with prizes and the Nobel in particular, thanks to the almost infinite prestige it confers upon winners and the iron rule that it can be shared only three ways: we award accolades to individuals for what are ultimately the accomplishments of a community. One solution would to give prizes to ideas; there is often debate about who should win the prize but it is rare to hear deep disagreement as to what should win the prize. Nor do we honour the often unsung heroes who make the community tick. [My proposal for a George Bailey Prize has gone nowhere, however. C’est la vie.]

But ahead of the big reveal, here are a few quick thoughts: 

  • Since I am in New Zealand, it would be remiss of me not to mention my compatriot Roy Kerr, who solved the Einstein field equations for spinning black holes in 1963. A black hole born in a merger inherits the spin of it progenitors so the end-stages of the events detected by LIGO are expected to match the “Kerr metric”, and the detailed signals appear to confirm this. For whatever reason, the smart money is not backing Kerr but it would be a pleasant surprise if he gets a phone call from Stockholm late this evening, and not undeserved. (Local time!) That said, gravitational wave observations are not yet sufficiently sensitive to confirm that the final state is exactly described by Kerr’s solution, which is probably enough to prevent a major antipodean celebration later tonight. 
  • Gravitational waves have already been the subject of a Nobel Prize. In 1993 Hulse and Taylor were honoured for discovering a binary neutron star whose mutual orbit is slowly contracting; this behaviour is exactly consistent with energy carried away by gravitational waves emitted by this system. These gravitational waves are far too weak to detect directly on Earth, but more than enough for a win.
  • Hulse was a student and Taylor his supervisor. Neutron stars themselves were first detected via the discovery of pulsars in the 1960s. Jocelyn Bell‘s work as a PhD student was key to this earlier breakthrough but she (in)famously missed out on the prize awarded to her supervisor. So an empty slot this year could be used to correct this shameful mistake, but sadly that is also an unlikely result.
  • A key test of any scientific discovery is an independent confirmation. LIGO has two detectors but they were built by the same team from the same design and work in tandem. However, the latest detection (just last week) was the first in which the European VIRGO instrument also played an important role so that announcement should put many remaining qualms about LIGO’s discovery to rest.
  • And, in fact, the LIGO-VIRGO news came as something of an anti-climax since many people were expecting an announcement of the first detection of two neutron stars merging into a single black hole. Unlike black holes, colliding neutron stars produce a strong burst of energy at wavelengths ranging from gamma rays down to optical and below, providing an exquisite opportunity to complement gravitational wave observations with conventional telescopes. Stay tuned on that one. 

As it happens, I have been teaching about gravitational waves over the last few weeks. At the University of Auckland (where I am Head of the Department of Physics, or “Chair”, in North American parlance) we were grappling with a paradox at the heart of all physics programmes: we like to think of physics as a cutting edge discipline but the foundational material we teach to undergraduates has almost all been known for decades or centuries. In fact, even “modern physics”, quantum mechanics and relativity, was itself developed in the 1920s, and is perhaps “modern” in the same way that Virginia Woolf and TS Eliot are “modernist writers”.

Our solution to this dilemma was to develop a second year / sophomore course we called “Frontiers of Physics“, which treats cutting edge topics but assumes only introductory physics. This comes at the cost of the finer details, but in the case of gravitational waves you can get a lot of traction with the key ideas of energy conservation, the wave equation, the interference of light beams, and a little special relativity. This year is the first time we have taught the course and gravitational waves have truly been ripped from the headlines: I had to change my lectures to keep up with breaking news from LIGO and discoveries in black hole physics. And I couldn’t be happier. 

CODA: The header image is from the Simulating Extreme Spacetimes (SXS) Project. And this post was edited a little to clarify the reasons why Roy Kerr is not tipped to win the Prize today. (Thanks to Christopher Berry for comments on Twitter about this.)