Spring 2007 W. M. Keck Observatory 

 In this Issue:
 Systems Thinking
 The State of the
 Journey through the
 Above the Clouds

By Linda Copman

Photo: Saul Perlmutter.
“We live at an unusual time in history in that our rapid advance in technology has given us the opportunity to address truly fundamental questions about the world we live in, by making measurements and not just philosophizing. These are the kinds of questions that bring out the curious child in all of us — and thus bring people together from all backgrounds.” — Saul Perlmutter, co-winner of the 2006 Shaw Prize for Astronomy.

When Saul Perlmutter was a graduate student, he worked very near the Lawrence Berkeley Lab offices of Jerry Nelson and Terry Mast, who designed and engineered the Keck I telescope. “Each week I would hear about their latest successes and setbacks, and I watched as they realized this amazing new segmented-mirror telescope concept. At the time I didn’t know how much my research was going to depend on what they were doing,” recalls Perlmutter.

A few years later, Perlmutter and his team demonstrated a technique which enabled astronomers to find “batches,” on demand, of supernovae at cosmologically useful distances. This capability was critical to the study of cosmology, or the study of the origin, structure, and evolution of the universe. Here’s why: supernovae, or exploding stars, can be a few billion times more powerful than our Sun, and therefore very bright objects in the sky. One kind of supernova, “Type Ia,” is caused by the explosion of a white dwarf star and the characteristics of these supernovae are fairly consistent. They are very luminous, and they all have nearly the same power, “like car headlights,” explains Alex Filippenko, High-Z Supernova Search Team member.

Figure: Strategy to guarantee supernovae discovery. Courtesy of Saul Perlmutter.
By comparing the brightness of nearby supernovae with the brightness of distant supernovae, astronomers are able to determine the distance of the fainter objects. To do this, astronomers need to verify that they are observing the right kind of supernovae, or Type Ia supernovae. “With hours and hours of observations on the best previous telescope, we could begin to make a difficult case for a single supernova, but with the new much-larger Keck telescope we could quickly identify supernova after supernova, several per hour,” explains Perlmutter.

Astronomers obtained “spectra” of distant Type Ia supernovae using the Keck telescopes (which means that they separated the light from these objects into its component colors), in order to learn more about these objects, including their velocity in space. What they found was that very distant supernovae, viewed when the universe was two-thirds of its present age, are receding away from our planet more slowly than they had anticipated. Yet nearer supernovae, viewed at essentially the present time, are receding more rapidly. Thus, as the universe has expanded following the Big Bang, its expansion rate has accelerated over time.

Image: Courtesy of Saul Perlmutter.
Here’s what Brian Schmidt, leader of the High-Z Supernova Search Team, has to say about this unexpected discovery:

“Rather than measuring deceleration, we discovered acceleration — the universe was speeding up over time, and this meant it was made up of something we didn’t know about — something everyone now calls ‘dark energy.’ The big question now is — what is dark energy? — and we still haven’t a clue. Possibly it is what Einstein concocted back in 1917 to keep his equations from having the universe expand (or contract) - the ‘cosmological constant.’ This is an energy that Einstein’s equations allow to exist — and it is the energy of empty space. It would cause the universe to accelerate, but what we do not understand is why the energy of space would be what we measure today. So figuring out what dark energy is has become one of the big questions for astronomers and physicists today.”

Saul Perlmutter, leader of the competing Supernova Cosmology Project, adds:

“We set out to make a measurement of the expansion history of the universe, expecting to find out how much it has been slowing down (due to gravity) since the Big Bang. We thought that we might discover the ‘fate of the universe’ (an exciting goal!), since it was possible that the universe was slowing enough to come to a halt, collapse, and end in a ‘Big Crunch.’ What we found was a complete surprise, the universe was not slowing at all — its expansion has been speeding up.

This result has posed a new mystery: is there a new previously unknown component of our universe, a ‘dark energy’ that is accelerating the expansion? If so, it makes up most of the universe (about 75 percent). Alternatively, do we need a major revision to our understanding of gravity (Einstein’s General Relativity)? These exciting questions have led the physics and astrophysics communities to start entirely new projects, including a proposed dedicated space experiment specially designed to make the unusually precise cosmology measurements needed to explore the nature of the dark energy or the corrections to Einstein’s theory of gravity.”

Image: In 1916 Vesto Slipher observed about 50 nearby galaxies, spreading their light out using a prism, and recording the results onto film. The results confounded him and the other astronomers of the day. Almost every object he observed had its light stretched to redder colors, indicating essentially everything in the universe was moving away from us. Here we show the spectrum of a galaxy as Slipher would have seen it. The light is stretched in the bottom spectrum, so that the dark lines (the colors where elements such as sodium absorb light), are stretched to redder colors. Image and caption courtesy of Brian Schmidt.

Perlmutter’s and Schmidt’s teams made these groundbreaking discoveries about the history and fate of the universe simultaneously, working at different institutions in different parts of the world. For a list of Perlmutter’s team members, see here, and for a list of Schmidt’s team members, please click here. Both teams relied on the Keck telescopes for two things:
  1. To identify the right type of supernovae, Type Ia, and
  2. To determine how much the universe had expanded since the light from the supernova being studied was emitted.
Image: This plot shows the High-Z Supernova Search Team’s data. Across the bottom axis is distance (or equivalently time since the supernova exploded). The side axis shows change in the expansion rate from its current rate. As you can see, the points do not show the universe slowing down enough to eventually collapse. Furthermore, they do not even seem to show the universe coasting; rather they show that the universe is accelerating! Image and caption courtesy of Brian Schmidt.
“Keck — as the most powerful spectroscopic facility of its era — allowed us, for the first time, to take spectra of these distant exploding stars we were discovering, and thereby do 1) and 2) above. Without it, we just wouldn’t have had the information we needed to discover the accelerating Universe,” explains Schmidt.

The next steps are to quantify the expansion history of the universe and to determine how much the universe has been accelerating recently, compared with 2, 4, 6, or 8 billion years ago. These measurements will allow astronomers to better understand the nature of the "dark energy" that is driving the accelerated expansion.

And what of the competition among the scientific teams? This is a good thing, says Brian Schmidt:

“Saul’s team was our competition — and Saul played a similar role to me in his team. Having two teams work competitively on this research raised the whole standard. Everything we did we knew was going to be publicly scrutinized and judged in competition with Saul’s group. Both teams learned from the other’s successes, and we adopted a fairly similar strategy in the end. The competition also made us work more quickly — we had to ensure we were not scooped. We now work a bit more together toward our common goals, but not completely.

To solve a problem you need a group of people with a variety of skills. I believe in making collaborations to get the required skills needed to solve the problem, but I think science also needs to be competitive, or it drags to a standstill. I should say, by ‘competitive’ I mean supporting a diversity of teams and efforts to reach similar goals. I do not mean that software, data, etc., should be kept proprietary in the interests of competition. This is a terrible thing that I see microbiology falling into due to intellectual property issues. Eventually, this restriction of knowledge will slow progress down as everyone either reinvents the wheel or is prohibited from using the wheel due to intellectual property concerns. I have no prescription on how to work collaboratively. I just want to preserve diversity and keep science as open as possible, without barriers.”

Animation: Here is a toy model of the universe. Imagine if we expand it by five percent, and overlay the two images, centered on a galaxy near the center of the two pictures. As you can see, every galaxy appears to have moved away from the galaxy that we have centered the images on. Furthermore, the farther a galaxy is away from the center object, the farther it has moved in the expansion. This is exactly what Hubble saw. Another good part of this explanation is that everyone in the universe sees the same thing. Here we have centered the two pictures on a different galaxy. From this galaxy's perspective everything is moving away from it - it sees exactly the same thing as the previous galaxy. Original image and caption courtesy of Brian Schmidt.
UC Berkeley Astronomy professor Alex Filippenko was a member of both teams at one time. He first worked as part of Perlmutter’s team, and is now a member of Schmidt’s team. Filippenko was recently awarded the 2007 Richtmyer Memorial Award from the American Association of Physics Teachers for his research (including the discovery of the accelerating universe) and his ability to explain it to the general public. He also received the 2006 National Professor of the Year Award from the Carnegie Foundation for the Advancement of Teaching and the Council for Advancement and Support of Education in Washington, D.C. Filippenko is one of the most published and cited astronomers in the world, and he has also been recognized as one of its great teachers. When asked what qualities make a great astronomer, Filippenko replied as follows:

“Astronomers are driven by a deep desire to understand the structure and evolution of the universe, and the physical nature of its contents. We want to know how things work, and we want to determine our origins. Of course, we also want to do all this first, and best. The competition, and a genuine interest in figuring things out, compel us to excel.”

Image: This diagram reveals changes in the rate of expansion since the universe's birth 14 billion years ago. The more shallow the curve, the faster the rate of expansion. The curve changes noticeably about 5 billion years ago, when objects in the universe began flying apart as a faster rate. Astronomers theorize that the faster expansion rate is due to a mysterious, dark energy that is pushing galaxies apart. Credit for image: NASA/STSci/Ann Field.

But why should ordinary mortals care about the frontiers of cosmological research? Here’s why, explains Brian Schmidt: “Making discoveries in astronomy provides us as human beings a perspective of our place in the universe. The accelerating universe is especially profound, and it might be that there is a glaring error in our theories of gravity and how gravity interacts with things at the smallest scale via quantum mechanics. So it is just possible that understanding the accelerating universe might open up a window into how gravity and things on the atomic scale work together — and who knows where that might lead. It was the theory of quantum mechanics that opened up the possibilities of computers and the digital era . . .”

Read Brian Schmidt’s lecture, which he drafted upon acceptance of the 2006 Shaw Prize for Astronomy. The Shaw Prize honors individuals who have achieved a “significant breakthrough in academic and scientific research or application, and whose work has resulted in a positive and profound impact on humankind.” 

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