Retirement looms in a few weeks, after 30 years plus one day of government service. (Want to see my résumé? Just ask!) Interviews for the next job have already begun. As part of the process one potential employer requested a half-hour briefing on a "technical topic". I decided to talk about the work I did in the late 1970s on astrophysics and general relativity, and what progress has been made in the field. But as I warned the audience at the beginning of the presentation:

A few years ago I started running marathons and ultramarathons. I'm slow, so it takes me a long time. In 2004, during my first 50-miler, a friend who was with me made the mistake of asking me about gravitational waves. We were near mile 17 when I began a version of this talk. About six hours and 25 miles later he dropped out without finishing the race. He blamed blisters and knee pain — but I think it was my lecture. Today we'll see how long you all survive!

For busy people here's the "bottom line up front" summary:

• No confirmed direct detection ... but strong indirect evidence
• Better understanding of sources
• Five orders of magnitude improvement in detector sensitivity
• Significant spin-offs in sensor technology
• Good chance of successful detection within the decade

The talk itself generally followed this outline:

• What are gravitational waves, anyway?
  • "Ripples in Spacetime"
  • Free-space solutions to Einstein field equations
  • Like electromagnetic waves, but ...
    • displace masses, not charges
    • no dipoles (no negative mass)
    • nonlinear (when strong)
• What good are GW?
  • Unique windows into hard-to-observe phenomena (similar to radio astronomy and neutrino astronomy)
  • Tests of general relativity
  • Drivers for new sensor and signal processing technology developments
• Sources
  • Early universe (analogous to cosmological microwave background)
  • Supernova or other stellar collapses
  • Black hole or neutron star collisions
  • Binary star systems
  • Rotating/precessing neutron stars
• Observations
  • Weber bar events (1960s-70s)
  • Binary pulsar orbital decay
  • Negative results (upper bounds)
• Detectors
  • Resonant bars
  • Earth-based laser interferometers (LIGO, ...)
  • Space-based interferometers (LISA, ...)
• Prospects, Implications, Applications
  • Astronomical & Cosmological
  • Sensors & Signal Processing

Mercifully for my audience, we ran out of time before the end ...

_{(cf. As If So Many Minutes for 50-miler anecdote, and on the substantive-historical front see Relativity Plus Astrophysics, Ni and Me, Pulsar Waves, Soft Outside Crunchy Center, Spinning Sources, Cherished Beliefs, ...) - ^z - 2011-07-15}