Our Cosmic Patch
|NGC 1999, a nebula in the constellation Orion. Like fog around a street lamp, a reflection nebula shines only because the light from an embedded source illuminates its dust; the nebula does not emit any visible light of its own. |
Britain’s Astronomer Royal, Martin Rees , took time from his busy schedule to talk with Astrobiology Magazine’s Chief Editor and Executive Producer, Helen Matsos. His three-part interview considers a broad range of alternative planetary futures, while highlighting today’s changes in one of the oldest sciences, astronomy.
Martin Rees earned his degrees in mathematics and astronomy at the University of Cambridge , where he is currently professor of cosmology and astrophysics and Master of Trinity College. Director of the Institute of Astronomy at Cambridge, he has also been a professor at Sussex University. He has been Britain’s Astronomer Royal since 1995. He has modeled quasars and has made important contributions to the theories of galaxy formation, galaxy clustering, and the origin of the cosmic background radiation. His early study of the distribution of quasars helped discredit the steady state cosmological theory. He was one of the first to propose that enormous black holes power the quasars. He has investigated the anthropic principle, the idea that we find the universe the way it is because if it were much different we would not be here to examine it, and the question of whether ours is one of a multitude of "universes." He has written nine books . Through his public speaking and writing he has made the Universe a more familiar place for everyone.
Helen Matsos (HM): I was recently at a gathering of scientists, including notables such as Mitchell Feigenbaum, Oliver Sacks, and Neil deGrasse Tyson, and discovered you are much admired among this group. For instance, Neil referred to you as one of the last great gentleman astronomers of our time.
Martin Rees (MR): (laughs) Does he mean it as compliment or not?
HM: Maybe he was referring to your title of Astronomer Royal. My understanding is that this role dates back to 1675, and was established to rectify the tables of star motion used for navigation. I’m wondering what’s the modern-day relevance of this role.
MR: The quaint antique title indeed goes back to 1675, when the Royal Observatory was set up in Greenwich and the person in charge was given this title. The reason there is a title of Astronomer Royal, but no Chemist Royal or Physicist Royal, is that those other sciences were not professionalized and supported by governments until much later. Astronomy is one of the oldest sciences — perhaps the oldest after medicine – and may be the first to do more good than harm.
But in the last 50 years, British astronomy has been making use of telescopes overseas with clearer skies, and the Greenwich Observatory is now essentially a museum. The title of Astronomer Royal was made an honorary title given to a senior academic astronomer. So my "day job" is being a professor at Cambridge University, and the title is purely honorary.
|Charles Darwin (1809-1882)|
HM: Britain has such a rich history of supporting science and producing brilliant scientific minds. For instance, we’re sitting here in Cambridge, looking across the green to where Isaac Newton worked and lived. What is Britain’s role in the field of science today?
Circumstances are rather different today, because government support is now more important than private patronage. But in the UK, you still have a strong tradition in science, partly because the British government has been more enlightened than many other European governments in providing a growing science budget. We hope to be able to maintain our competitiveness with the United States. We’re much smaller, of course, but in terms of quality we can be a world force in science.
HM: In your book, "Just Six Numbers," you say there are six numbers that dictate the state of the universe, and that if any one of them were slightly different, then life as we know it would be impossible. Are any of your numbers related to ones in the Drake equation, which calculates the probability of life in the universe?
|The Ring Nebula. 2,000 light years distant in the direction of the constellation, Lyra, the ring is formed in the late stages of the inner star’s life, when it sheds a thick and expanding outer gas layer. Credit: NASA Hubble HST|
MR: We don’t really know the likelihood of life because the uncertainties in the Drake equation, which still are still very large, are the probabilities that life gets started given the right kind of initial soup. Astronomers can’t say whether life is likely or unlikely, because the most uncertain terms in the Drake Equation are the terms biologists have to solve for us.
HM: Then what can astronomers predict based on your six numbers?
MR: Astronomers can say what the necessary conditions are for life, but not the sufficient ones. In order for life to develop, there have to be habitats in the universe that are stable, are warmed by a star, and contain not just hydrogen but all the elements in the periodic table, like oxygen, carbon, and phosphorus, that are important for life.
In the last few decades, astronomers and cosmologists have been able to understand how our physical universe has evolved over nearly fourteen billion years, from its beginnings to the so-called big bang to its present state with galaxies, stars, and planets. We are starting to understand how stars and galaxies formed as the cosmos cooled down from its hot initial state. Those first stars were fueled by the same process of an H-bomb: the conversion of hydrogen to helium. Then even hotter stars fused helium into carbon, oxygen, and the rest of the periodic table.
Every atom on Earth was forged in an ancient star that completed its life more than four and a half billion years ago. Those ancient stars exploded, throwing debris back into interstellar gas. Our solar system condensed from interstellar clouds contaminated by the debris from earlier stars. So we are literally the ashes of long dead stars, or, if you are less romantic, we are the nuclear waste from fuel that made those ancient stars shine. On the basis of this hypothesis, we can understand why oxygen and carbon are common but gold and uranium are rare, and how they came to exist in our solar system.
|The early Sun was half its current luminosity. |
HM: So your six numbers are setting the physical parameters for life to occur in the universe?
MR: We can understand how stars and planets formed, and how they came to contain all the basic elements necessary for life. So setting the scene for the origin of life is something we do understand better. Then biologists take over, and biology is a harder subject than physics and astronomy, because what makes things hard to understand is not how big they are but how complicated they are. As I said in one of my books, an insect is more complex than a star. A star is basically a large ball of gas held together by gravity, while even the smallest insect has layer upon layer of structure and is a far greater challenge to understand.
In a universe where the basic governing physical laws were different, these processes couldn’t have happened. If gravity were too strong, then you couldn’t have long-lived, stable stars, because gravity would crush everything. If the forces within the atomic nucleus were too strong, then hydrogen would not exist. If those nuclear forces were too weak, then only hydrogen would exist, and not the other elements.
So it does seem that there are various ways in which the laws of physics are fine-tuned, and the same is true of the universe itself. You could imagine a universe that expanded so fast that gravity could never pull together proto-galaxies or proto-stars. Or a universe that expanded so slowly, it collapsed before there’d been time for anything much to happen. You could imagine a universe that contained no atoms at all — just dark matter and dark energy. So in order to provide the pre-conditions for any kind of life or complexity, our universe had to be set up and governed by rather special laws.
|"…an insect is more complex than a star..and is a far greater challenge to understand ." –M. Rees |
This leads to another mystery, a mystery that physicists address rather than biologists, which is the nature of the physical laws. Are there equations that can define those laws exactly, and give us the mass of the electron, or the strength of different forces? Or will we never have such a thing? Could it be that the strength of these forces is some kind of environmental accident?
One idea many of us are pursuing is a grander concept of the physical world. Over history we’ve gone from thinking of our solar system as being the center of the universe, to our galaxy being the center, to the present consensus that our big bang gave rise to zillions of galaxies. Some of us now think that perhaps we have to go a step further — that the big bang wasn’t the only one.
HM: There could be other universes…
MR: There could other universes separate from ours, other big bangs maybe separated by an extra-spatial dimension, or different in other ways. If that’s the case, then it’s possible that those different universes would be governed by somewhat different physical laws.
Some physicists believe this is true. If so, then the fine-tuning of our universe occasions no surprise. If there were not merely zillions of galaxies in the aftermath of our big bang, but there were actually zillions of other big bangs, each governed by different laws, then some would have laws with the capricious forms and basic number values to allow complex life and evolution. Most of the universes would be sterile or stillborn. In this grander context, there will still be basic laws of nature, but they’d be at a deeper level.
What we traditionally call the "laws of nature" — the "laws" that determine the so-called "physical constants" — could then be just parochial bylaws in our cosmic patch.