AudioExploration:Dark Matter - Interview with Dr. David Spergel
Princeton theoretical astrophysicist David Spergel is an intellectual adventurer, driven by curiosity and a thirst to know the unknown. Professor Spergel's eclectic interests have taken him in diverse directions, from probing the nature of dark matter, through his instrumental role in mapping the Big Bang's imprint on the universe in the form of the cosmic microwave background radiation, to engineering technologies to directly detect earthlike extrasolar planets.
He focused much of his energy in the past few years on the Wilkinson Microwave Anisotropy Probe (WMAP). This satellite's data created a map of the universe as seen in microwave background radiation, which has been cooling unevenly in the 13.7 billion years since the Big Bang. The map reveals that only a small fraction of the mass of the universe is composed of the visible matter that makes up the stars and planets–the vast majority is dark matter. More recently Spergel has turned his attention to designing a new generation of instruments to visualize habitable, earthlike worlds in other solar systems. Travel along with David Spergel in his pursuit of the next big thing in this AudioExploration: Dark Matter.
Segment 1:The Laws of Physics Beat Out the Laws of Civics [Time 5:27]
A physicist's son—equally drawn towards physics, astronomy and law as a sophomore—is enchanted by the "elegant and striking description of our universe," general relativity. Going from Princeton and Oxford to Harvard, he asks "What would happen if dark matter were captured by the sun?"
Segment 2:The Importance of Being Audacious [Time 6:19]
Undaunted by inevitable setbacks of his constant exploration of new theoretical territory, Spergel follows where his curiosity leads—from dark matter interactions, to the texture and geometry of the universe and beyond—often finding that discarded strands of research become unexpectedly valuable in interesting ways years later.
Segment 3:WMAP looks back... 3.7 billion years [Time 6:35]
The leftover heat from the Big Bang fills the universe as microwave radiation, explains Spergel, but it pools unevenly. He helped design the experiment to detect the detailed patterns of this heat, the Wilkinson Microwave Anisotrophy Probe (WMAP, successor to COBE, the Cosmic Background Explorer satellite). Spergel describes all that WMAP has revealed and what that means about dark matter.
Segment 4: A Cold, Dark Matter [Time 6:21]
COBE showed that we have a universe made not just of atoms but of dark matter that can gravitate, says Spergel, strengthening the Cold Dark Matter model. WMAP bolsters it more and a theoretician gets experimental dirt under his fingernails.
Segment 5: Engineering a Left Turn [Time 6:24]
Spergel moves further into outer space engineering; the Yin & Yang of particle physics vs. cosmology and how the current of ideas is reversing its flow.
Segment 6: The Evolution of Dark Matter [Time 6:34]
Spergel takes us through the history of thought on dark matter: from Zwicky's first inklings, through super symmetry, and to the possibility that dark matter may be explained one day by a new physics we don't yet understand.
Segment 7: Detecting the Undetectable [Time 6:46]
From dark matter to finding earth-sized extrasolar planets—Spergel throws himself into another problem, balancing on a brand new cutting edge.
Credits: Interview with Dr. David Spergel for AccessScience AudioExploration: "Dark Matter" by Dorian Devins. Her previous work includes the National Academy of Sciences InterViews project and WFMU's Speakeasy. Podcast production by Jessa Forte Netting. Sound engineering by Neil Strachan of Tin Balloon Productions, New York, NY. Theme music by the Sacrosanct Wednesdays.
Five Year Microwave Sky The detailed, all-sky picture of the infant universe from three years of WMAP data. The image reveals 13.7 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies.
[Credit: NASA/WMAP Science Team]
Content of the Universe WMAP data reveals that its contents include 4.6% atoms, the building blocks of stars and planets. Dark matter comprises 23% of the universe. This matter, different from atoms, does not emit or absorb light. It has only been detected indirectly by its gravity. 72% of the universe is composed of "dark energy" that acts as a sort of an anti-gravity. This energy, distinct from dark matter, is responsible for the present-day acceleration of the universal expansion. (WMAP data is accurate to two digits, so the total of these numbers is not 100%.) This reflects the current limits of WMAP's ability to define Dark Matter and Dark Energy. [Credit: NASA/WMAP Science Team]
Timeline of the Universe A representation of the evolution of the universe over 13.7 billion years. The far left depicts the earliest moment we can now probe, when a period of "inflation" produced a burst of exponential growth in the universe. (Size is depicted by the vertical extent of the grid in this graphic.) For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. The afterglow light seen by WMAP was emitted about 380,000 years after inflation and has traversed the universe largely unimpeded since then. The conditions of earlier times are imprinted on this light; it also forms a backlight for later developments of the universe. [Credit: NASA/WMAP Science Team]
Terrestrial Planet Finder (TPF) Artist's concept of the Terrestrial Planet Finder (TPF) observatories. David Spergel is a member of Princeton's TPF research program, an interdepartmental effort to investigate the science and develop technologies to image extrasolar planets. The TPF mission will be explore the nearest 200 stars for evidence of Earthlike planets - planets within the habitable zone of the star that show evidence of life. [Credit: NASA/JPL]
Wavelengths from the Sky
How the WMAP sky image was created.
Starting with an overview of the Milky Way, we move into position to see the view from our location on Earth. Then we unwrap it into an oval for easy viewing. Finally, we view the scene as it appears in light at different points on the spectrum, from visible wavelengths down to the microwave. These varied wavelengths reveal the presence of different sources of radiation across the sky.
The sky's microwave radiation appears to be almost featureless until the contrast is increased to reveal the small variations in the Cosmic Microwave Background (CMB). The red band across the center of the sky image represents the strong radiation from our own galaxy, the Milky Way. The cooler blues and greens at the higher latitudes show the much larger portion of background radiation detectable in those areas.