If you want to know why astrophysics is a sizzling science, read this book.
I see that there are a number of reviews here on Amazon, which I think is great. It shows that people care about the big questions-- what's the Universe made of? How do we know?
The review by Paul Preuss is particularly interesting. "Snarky" "virulent" "rancorous" Wow! Who knew science was so much fun?
Preuss doesn't reveal until the 27th paragraph that he is the Press Officer at the Lawrence Berkeley Lab whose job over the past decade has been to press the case for recognition of the work on dark energy done by scientists at his institution. There's nothing dishonorable about putting the best face on the work done by people at the Lab, whether it involves super-heavy elements, the Cosmic Microwave Background, or cosmic acceleration. After all, somebody has to make the case for science in a media atmosphere of Lady Gaga and the cat in the dumpster. But it would be asking too much for a person in his position to give a completely balanced account of a scientific discovery, like the discovery of cosmic acceleration, that took place over time and at many places, as described in the spellbinding new book by Richard Panek, The 4% Universe .
To avoid a similar gaffe, I should tell the reader right up front that I am the same Robert Kirshner referred to in Panek's excellent book. Not always with admiration, but he's not perfect and neither am I. The important thing is that all of the people in this book, and many left out, got to discover something big and wonderful about the universe in which we live. Panek is an excellent guide to that adventure.
Panek is a talented writer, a diligent researcher, and his book The 4% Universe is an exciting account of one of the most revolutionary discoveries in physical science. Great science is bigger than any of us. If you want a complementary perspective on these events, I can't recommend a better book than "The Extravagant Universe: exploding stars, dark energy, and the accelerating universe." It's by me, and I am a participant in the events, but I tried hard to stick to the facts. It's from 2002, still in print, and available in Spanish, Portuguese, Japanese and Czech.
The Extravagant Universe: Exploding Stars, Dark Energy, and the Accelerating Cosmos (Princeton Science Library)In his Amazon review of Panek's book, Preuss offers his own version of the story starting (as if that were the start of the discovery of cosmic acceleration) with the establishment of the Center for Particle Astrophysics at Berkeley by the National Science Foundation. Preuss asserts without any evidence that I was opposed to the Supernova Cosmology Project (SCP) "from the moment I heard about it." I think I'm the only witness on this matter. It ain't so. I thought this project could be a good thing, and gave a talk at the opening symposium for the Center describing how you could use supernovae to find out how much the universe is slowing down. Little did I know it was speeding up! The LBL team asked me more than once to join the project. The Center for Particle Astrophysics asked me to serve on their External Advisory Committee. I would not waste my time to fly across the country to sit in darkened windowless rooms to watch hours of powerpoint presentations if I thought the project was not worth doing. The Center for Particle Astrophysics, with its healthy engagement with astrophysics, may be the place where Preuss first encountered the idea that supernovae could be used to measure the universe, but this idea has deep roots in astronomy, as sketched by Panek in The 4% Universe .
After Fritz Zwicky pioneered methods for finding supernovae through monthly searches in the dark of the moon, Walter Baade showed that the supernovae we now call Type Ia, the thermonuclear detonation of white dwarf stars, could be used to measure cosmic expansion. If supernovae all had the same intrinsic brightness, then you could judge their distances by their apparent brightness. If you also measured the redshift for the supernova, or its host galaxy, you could use the plot of distance against redshift to measure the history of cosmic expansion. This was clearly understood in the 1930s! In 1968, Charlie Kowal, who worked for Zwicky at Caltech, compiled the world's data and published an article in The Astronomical Journal that showed thermonuclear supernovae were pretty good standard candles with a scatter of about 60% in brightness. Kowal speculated that distances to individual objects might eventually be known to 5-10%. What's more, Kowal said, "It may even be possible to determine the second-order term in the redshift-magnitude relation when light curves become available for very distant supernovae." In plain english, that means he was thinking about using supernovae to gather evidence for the cosmic deceleration that everyone expected to see due to the effects of gravity. This is the measurement that, to everyone's surprise, showed evidence for cosmic acceleration when it was finally published in 1998.
Along the way in 1979, Gustav Tammann, working with Allan Sandage, showed how you could use the Hubble Space Telescope to measure distant supernovae and establish whether or not the universe was decelerating. But first, some important astronomical aspects of the supernovae needed to be sorted out. It turns out that mixed in with the thermonuclear explosions were some imposters-- supernovae that resembled SN Ia, but got their energy from the gravitational collapse of their cores. Astronomers, including me, began to get this straightened out in 1985.
Another complication comes from the thermonuclear supernovae. Preuss says about the 1990 establishment of the SCP "the physicists believed, {thermonuclear supernovae were} very similar in their brightness. " I don't know if that is accurate about the beliefs of physicists, but it certainly is not true about supernovae. Mark Phillips (later a member of the High-Z Team) began to see in 1986 that there's a factor of 3 in the range of intrinsic brightness of Type Ia supernovae. If you don't develop a method to compensate for this, to sort out the 75 watt bulbs from the 25 watters, you will make a mess of estimating distances from brightness. Physicists did not have a monopoly on understanding supernovae as tools for measuring the history of cosmic expansion, and in the early 1990s it was clear we all needed to learn more about the variety of supernovae from astronomical observations of nearby objects. My own team at Harvard worked hard on this aspect of the problem.
Methods for working out how to find supernovae with digital detectors were pioneered by a group of Danish astronomers in 1988. Their goal was to measure cosmic deceleration. There's no question that the LBL team later worked out their own way to detect supernovae in digital images of the sky, and they profited from the rapid technical advances in detectors and computers after 1988, but this was not a problem for which astronomers were waiting for intervention from superior beings, having already done it. More important was making precise observations of the supernova brightness through more than one filter. If you do not do this, you cannot, even in principle, tell the difference between supernovae that are dimmed by cosmic acceleration and supernovae that are dimmed by obscuring dust. The SCP made their earliest observations through only one filter. As Panek describes, I counseled them to do this measurement correctly. Maybe that's why Preuss thinks I was opposed to the project. But that's not right. I was only opposed to them making bad inferences from inadequate data.
In his review of The 4% Universe, Preuss says:
"With an initial small sample the SCP did indeed make bad guesses about the universe's weight and shape. But in 1994 they started collecting Type Ia supernovae by the fistful, having developed and applied methods that should have been obvious -- particularly to doubting astronomers."
The way this is written, a reader might think that those early "bad guesses" were made before 1994. In fact, the SCP reported these results at conferences in 1996 and published them in 1997. As for the "doubting astronomers" who seem like such dolts-- Danish astronomers were discovering supernovae in 1988 and by 1995 our High-Z supernova team, led by Brian Schmidt, was finding distant supernovae to go along with our nearby samples and making our own observations with carefully selected pairs of filters as imagined by Nick Suntzeff. This is the program that led to a good outcome in 1998.
As Panek makes clear, the early work from the SCP, led by Saul Perlmutter, was not "bad guesses", it was wrong. It claimed to rule out accelerating cosmologies. This was a small data set. Maybe the problem was bad luck. Maybe the problem was flaws in the way the observations were carried out and analyzed. Later observations by Saul's team were technically much better, and gave a different result, which makes me think the latter is more likely. But in 1996 and 1997, the LBL team was saying that supernovae showed there was no cosmic acceleration, and no need for dark energy. Theorists were frustrated. To some of them, dark energy would help fit all the pieces of cosmology together. But the SCP resolutely said the opposite. Cosmologist Mike Turner is quoted by Panek (on p.148) as saying (in jest!) at a 1996 conference in Princeton, "I don't think Saul is that stupid.
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