About Me

I am an associate professor at the Research Center for the Early Universe on the Hongo campus of the University of Tokyo.  I am a member of KAGRA and of the LIGO Scientific Collaboration, and work primarily on searches for gravitational waves from the mergers of compact objects like neutron stars and black holes.

I did my undergraduate studies at York University at the north end of Toronto where I received a Bachelor of Science in Physics.  From there I moved to Edmonton where I attended graduate school at the University of Alberta where I worked on problems related to structure formation in the very early universe with my supervisor Prof. Don Page, and received a Doctorate of Philosophy in Physics.

After graduate school I lived in Milwaukee, Wisconsin, where I was a postdoctoral researcher with the gravity group in the Physics Department of the University of Wisconsin-Milwaukee.  If you drink beer and/or drive a motorcycle (I do both) you should visit Milwaukee.  Some people know that I moved from Edmonton to Milwaukee in a big yellow school bus, but that's a story for another time.  After Milwaukee I was a senior postdoctoral researcher with the LIGO Laboratory at Caltech.  My Caltech e-mail address was kipp@caltech.edu, not to be confused with kip@caltech.edu, a totally different person.  The house I rented in Pasadena came complete with a very young feral cat living under the floor whom I adopted.  She and I then moved to Toronto where we lived with my partner, Catherine, and a big brown cat we found at the Humane Society, while I worked as a senior research associate at the Canadian Institute for Theoretical Astrophysics on the St. George campus of the University of Toronto.  Now my partner and I live in both Toronto and Tokyo, and depend on our kind families for cat-sitting while we are in Japan.

Astrophysics and Experimental Gravity

One of the predictions of General Relativity is that the acceleration of a gravitating body will, generally, cause waves of spacetime curvature to radiate away from the body, retarding its movement and carrying energy away with them.  This is very much like the phenomenon of electromagnetic wave generation by the acceleration of an electric charge.  Because gravitational waves originate in the movement of mass and momentum, not electric charges and currents, they carry with them fundamentally different information about the objects that created them.  Furthermore, the most powerful sources of gravitational waves are likely to be black holes and other compact objects with very strong gravitational fields, objects which are not necessarily strong sources of electromagnetic waves (light and radio).  Lastly just about everything there is is nearly completely transparent to gravitational waves, which means they can pass unimpeded and unmolested through dense dust clouds, plasmas, even the fireball of the big bang.  Altogether, observing gravitational waves promises to open a window into some of the most exotic and inaccessible domains of the natural world.

Unfortunately, like everything else in the universe we, too, are nearly transparent to gravitational waves and that makes it very difficult to detect them since they can happily pass right through us, the Earth, and pretty much anything we can build, without registering at all.  That can't stop us from trying, though!  Starting in the 1960's, people began building devices in the hopes of detecting this new form of radiation.  The early attempts were unsuccessful but now we are on the verge of what we hope will, finally, be the dawn of gravitational-wave astronomy.

Starting in the late 1990's, kilometre-scale laser interferometers began being constructed at several locations around the world: GEO600, Virgo, Kagra, and the three antennas of LIGO.  The first generation of these antennas proved unsuccessful at detecting gravitational radiation, but they did achieve the design goals laid out in their original proposals which has enabled the second generation of these facilities to be built, the so-called Advanced detectors.  The two Advanced LIGO antennas are now operational and are expected to begin observing the sky this coming summer or early fall.

The most promising source of detectable gravitational waves is the near-by collision of a pair of neutron stars.  PSR B1913+16, also known as the Hulse-Taylor binary pulsar, is one of several systems in which a pair of neutron stars are orbiting close enough to one another that gravitational radiation will cause their orbit to decay and the two stars to collide (in the case of PSR B1913+16) in about 300 million years.  If that sounds like a long time, consider how short a time that is in astronomical or even just geological terms.  Knowing that such systems exist that can decay on such a short time scale, even just a small number of them, gives us a hint at the rate at which collisions between such objects should occur.  Such an analysis suggests that the first generation of gravitational-wave antennas had, maybe, even odds of a discovery integrated over the duration of their operation.  The second generation of antennas entering operation right now will, it is hoped, see 1000 times more space than the first generation of antennas, making observations of binary neutron star collisions a regular occurrence.

Many things can be learned from observing a binary neutron star collision, but many more things will likely require future, third-generation, antennas to reveal; antennas like the Einstein Telescope.  In the short term, measuring the rate of binary neutron star collisions (just the rate) already will tell us many things.  For example, from the rate we can infer what fraction of the energy density of the Universe is in the form of gravitational waves from such collisions, and when combined with other bounds on how much that can be in total it puts constraints on the amount of gravitational-wave energy that can be left over from inflation, which in turn tells us about the conditions in the Universe during that very early time.  One of the most persistently mysterious phenomena in the Universe is the gamma-ray burst, or GRB.  (when you see something's name is, really, just a description of what it looks like that tells you when an astronomer has no idea what it is).  GRBs come in two types:  short and long (again, descriptions of appearance).  The long type are believed to be supernovae and the short type are believed to be the collisions of pairs of neutron stars.  If we can observe a GRB or another optical phenomenon believed to be associated with a GRB in association with gravitational waves from a binary neutron star collision, that will be very strong evidence that short GRBs are, in fact, the collisions of pairs of neutron stars.  Seeing the association at all immediately tells one very important thing:  gravitational waves travel at the same speed as light, which is a very important theoretical question to settle.&nbps; What kind of light is seen (radio, optical, gamma ray or X ray), what polarization the gravitational waves have, and the time delay seen between the arrival of the light and of the gravitational waves, then begins to fill in our picture of the physics of these extreme collision events.

Making an association between an electromagnetic transient signal and a gravitational wave observation is aided by being able to claim to have detected a gravitational wave very quickly after the data has been collected.  My work, specifically, is the design, construction, and operation of a data analysis system capable of comparing the data streams from LIGO and Virgo to enormous banks of template waveforms very quickly and producing detection claims within tens of seconds.  This work has been very successful, the analysis pipeline is nearly complete, and I am now considering the problem of connecting our anticipated gravitational-wave observations to other electromagnetic transients.  Please poke around the rest of this web site for more information.

Last updated 2016-05-06.

Peter Papadakos