Searching for Vibrations from the Big Bang

Watson Lecture Preview

For a brief instant after the Big Bang, the universe went through a period of rapid expansion during which space itself was flung apart faster than the speed of light. This "inflationary epoch" sowed the gravitational seeds that formed galaxies and clusters of galaxies. Its echoes linger as fluctuations imprinted on the so-called cosmic microwave background radiation—the Big Bang's glow, which pervades the universe today.

For the last 15 years, James J. (Jamie) Bock, a professor of physics at Caltech and a senior research scientist at JPL, has been searching for a distinctive polarization pattern in the background that gravitational waves from the epoch of inflation may have produced. At 8 p.m. on Wednesday, May 6, 2015, in Caltech's Beckman Auditorium, Bock will discuss how this hunt has led to instruments at the South Pole, on stratospheric balloons, and in outer space. Admission is free.

 

Q: What do you do?

A: I study the early universe empirically, which is often a good approach in a field where we continue to make discoveries driven by new data. My lab builds experiments that address a particular problem is cosmology. Starting out, we think, "What would be the perfect instrument to go after this question?" and that often leads to a new approach. We've been working on the search for B-mode polarization in the microwave background since the year 2000, shortly after theorists came up with the idea that such a polarization signal might be the best way to look for gravitational waves from the era of inflation.

Einstein's equations say that gravitational waves—they stretch and squeeze space and propagate at the speed of light—also have a "handedness." It is similar to how light waves can have a left-handed or a right-handed state. If you look at the cosmic microwave background's polarization across the sky, you can ask yourself, "Which parts of that pattern will look the same in a mirror? Which parts will look different?" The B-mode pattern is the part of the pattern that looks different in a mirror. You can see similar handedness in the brushstrokes of Vincent van Gogh's The Starry Night. A B-mode pattern has to originate from a source that has a handedness, such as gravitational waves. So we're mapping the microwave background to find such a pattern, which in turn will tell us more about how inflation occurred.

 

Q: How do you map polarization?

A: We use detectors called superconducting polarimeters, which are focal plane array detectors developed at JPL. Sometimes, when you figure out the instrument you need, there is a key technology yet to be invented. We dreamed up the basic concept for these detectors in 1999, and JPL has taken them from this initial idea to a fully mature technology.

We previously developed detectors that looked like a spider's web to map temperature variations in the background. These devices were quite successful and flew on the BOOMERanG experiment on a high-altitude balloon and on the Planck satellite in space. However we could see that we needed a completely new approach to map polarization, which led us to superconducting polarimeters. This development is a bit like going from analog film to digital photography. Except here we are literally printing out miniature cameras—the lens, filter, film and a polarizer—on a chip. The detector uses a superconducting thermometer to detect the energy from the background.

The cosmic microwave background means we have to carry out our measurements where microwaves are not strongly affected by the earth's atmosphere. Water vapor copiously absorbs microwave energy. The ideal site from the ground for us is the Antarctic Plateau, where the air is cold and very, very dry. Our observing season at the South Pole begins when the sun goes down for the six-month Antarctic winter, when the air is the driest.

 

Q: How did you get into this line of work?

A: I was a fan of Carl Sagan when I was growing up, and I also really liked a BBC show called Connections, hosted by James Burke. Connections explored the unexpected twists and turns that led to revolutions in technology and science. These often started with a desire to make money or build a new weapon, but that impetus then spawned new technologies, and new ways to use them, that would go off in directions you would never have expected. There's an element of that here—we're using the principles of superconductivity as the best way to explore the very early universe!

As a graduate student at Berkeley I discovered a certain satisfaction in designing instruments developed for a particular purpose, building and testing them, and seeing them actually work. This is hard to explain unless you have actually done it, but maybe the closest analogy is finishing an advanced project in high school shop class. The process definitely requires some patience and determination due to all the steps involved, but once you've built something new, and it works, you want to do it again.

Finally, I am constantly amazed that we can learn so much about something so deeply fundamental as the beginnings of the universe with a small team of scientists. We hunt for imprints from inflation with a team of highly motivated graduate students and postdocs. Our program is exploring the universe some 10–32 seconds after the Big Bang, and the fact that that era is accessible right now, today, if you can just develop the means to do it—well, that is pretty amazing. The early universe is not only knowable, it's within grasp. We live in a special time in history in which we are learning the answers, and some of those answers recently have been deeply surprising. I can't think of anything more exciting than that!

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

Written by Douglas Smith

Caltech Media Relations