FRONTLINES FAST CLASS
By JOHN D. CUNNINGHAM, S.J., PhD Associate professor, department of physics
The big questions
Fr. John Cunningham, PhD, has spent much of his academic career chasing heavy quarks and cosmic rays in elemen- tary particle research. Currently his research interests center on astrophysics, where he and a team of other scientists are tracking down supernovae. In this Fast Class, he takes on some of cosmology’s biggest questions and breaks them down for those of us who are not astrophysicists.
How old is the universe?
The universe exploded into being with the Big Bang, which happened some 14 billion years ago.
How do we know that the universe is expanding?
What was there before the Big Bang?
We are not sure. The Big Bang seems to be not only the start of energy and matter, but of time.
How big is the universe?
We are not exactly sure, but we do know that it’s expanding. And it was recently proven that it’s expand- ing at a faster rate than previously understood.
In 1929, Edwin Hubble (after whom the Hubble Space Telescope is named) studied distant galaxies and discovered that their velocities were greater the further away they were from Earth. With that discovery, many came to realize that the universe was a radically dynamic place, rather than a “static” one. But he wasn’t done there. By studying the light emitted by those distant galaxies, Hubble discovered that the stars were moving farther away from Earth in every di- rection, thus proving that the universe was expanding outward. Hubble proposed that the rate of expansion of the universe was constant. But astrophysicists now conclude that the universe’s rate of expansion is actually increasing or accelerating.
How do we know that the expansion is accelerating?
This is actually quite recent—the 2011 Nobel Prize in Physics was awarded to three scientists for this very discovery. It starts with supernovae, which are the explosions that occur as a mas- sive star dies. There is a certain type of supernova that emits roughly the same amount of brightness every time. If you know that you are observing this type of supernova, and you measure how bright it appears to you on earth, then you can determine how far away the supernova is.
The trio that won the Nobel Prize compared the observed brightness of nearby supernovae with more dis- tant ones and found—to everyone’s surprise, including their own—that the distant supernovae were dimmer than expected. They were so dim, and growing more so, that the most logical conclusion is that they were farther away, and not only that, but that they were moving farther away at an accel- erating speed.
12 LOYOLA UNIVERSITY CHICAGO
NASA /
HUBBLESITE.ORG
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