We have learned a lot about how the universe came to be what it is now, but we know very little about why the 13.8-billion-year process played out in the entirely improbable way that it did. Astrobiology has happily moved into this vacuum, and not only asks the question “Are we alone?” but also the question “How are we here at all?” This is the kind of question that is generally considered outside the realm of science. But in this case, where the whole astrobiology effort is anchored in the expectation that a universe that led to our existence is likely to give rise to other forms of life, that nonscientific question of “why?” is impossible to entirely disentangle from the traditional scientific question of “how?”
To think through this question, astrobiologists, like scientists in other areas, have had to consider why the universe we know is so exquisitely fine-tuned. The concept refers to the well-established fact that life could never have started and evolved if the laws of physics were not almost precisely what they are. The more scientists learn about the cosmos, the greater the fine-tuning appears to be. Fine-tuning can be dismissed as a tautology (of course life arises only under conditions conducive to life), it can be embraced as an argument for a Creator, it can be seen as a series of signposts directing scientists to the deepest, least understood logic of the universe. But however it is interpreted, fine-tuning is a significant reality of the universe.
Here are some prominent examples:
• At the level of the cosmos, gravity is the organizing force. Yet gravity is extraordinarily weak compared with the electrical forces that hold together electrons, protons, and neutrons in an atom. That weakness, physicists have determined, is absolutely essential to the existence of our universe. A strong gravity universe would not only keep life from growing larger than a small insect, but would also pack stars closer together and with that proximity most likely keep stable solar systems from ever forming. Here’s where the fine-tuning comes in: The ratio of the strength of the electrical forces in an atom compared with the force of gravity is 10 to the 26th. That’s 1,000,000,000,000,000,000,000,000,000,000,000,000. As Lord Martin Rees, England’s Astronomer Royal, described it, nothing as complex as humankind could have emerged if that number were even slightly smaller.
• The mass of a neutron in the center of an atom is 1.0013784 times heavier than the mass of a proton—in other words, they’re virtually the same. This ratio allows atoms to remain stable and for chemistry to occur between elements. But if the proton were the same 0.1 percent heavier than the neutron, then the whole system would fall apart and life (and chemistry) as we know it would be impossible.
• British astronomer Fred Hoyle found in 1952 that the processes that form carbon, the indispensable element of Earthly life, depend on an improbable coincidence. His calculations, which have subsequently been confirmed many times, led him to conclude that very little carbon would be produced in the stellar furnaces unless the carbon nucleus vibrated at the same frequency as the nucleus of another element involved in the reaction, beryllium. Nobody even knew when Hoyle made his prediction that carbon nuclei could vibrate at that kind of frequency, but they soon confirmed that it did. And carbon, it turns out, is not only essential for life as we know it, but its presence in interstellar space is needed to cool down clouds of gases created by the dying explosions of large stars. Without that cooling, far fewer new stars would be formed.
The standard model of particle physics, which explains how atoms work, has about twenty constants that, if changed to any even minute degree, would make matter, stars, and galaxies very different and life, to a greater or lesser extent, impossible. Another ten cosmic constants order the universe. Some of these forces overlap, and not all require precise fine-tuning. But several do, and must be fine-tuned to an accuracy of greater than 99 percent to make a universe capable of forming and supporting life. It all sounds quite far-fetched, but it nonetheless is reality.
Fine-tuning has been hotly debated by physicists and cosmologists in recent decades, but without any real resolution. Since the descriptions of these physical relationships and interactions are demonstrably true, then the issue is not to prove or disprove them, but rather to make sense of them. Somehow our universe formed with physical laws, chemistry, and cosmic forces that allow for life on Earth and, quite possibly, elsewhere. How did that happen? Why did it happen? The Canadian philosopher John Leslie perhaps best conveyed the dilemma posed by fine-tuning with this parable: A man is facing a firing squad and fifty expert marksmen are preparing to end his life. The word is given and many shots are fired. To his amazement, the target opens his eyes after the fusillade and discovers he is still alive. What happened? Either he was stupendously lucky and everyone missed, or the marksmen intentionally missed their mark. As biological creatures in a finely tuned universe, we are that man.
In the search for other explanations, the theory of the “multiverse” emerged in the 1980s as a seriously studied alternative, although it was proposed as far back as 1895 by philosopher William James. Many variations on the theory exist, but all posit that we live in one of many, perhaps an infinite number of universes. Just as the earth is minuscule in comparison to our sun, so too would our universe be a speck in the enormous collection of universes that exist beyond our ability to detect them. Under the multiverse theory, countless universes exist where the necessary forces did not combine in a way to allow for life, while leaving room for the possible formation of a universe like ours where they did. The theoretical logic is strong, but some scientists argue the multiverse idea is not actual science since it can’t be either verified or falsified now, and perhaps never will be. Since the multiverse presupposes universes in many different dimensions, at distances farther than the speed of light could travel in the 13.8 billion years of our universe, the ability to tease out the reflected presence of a second or third or billionth universe is absent. Until some way is found to detect another universe, the multiverse can only remain a plausible if unproven theory or, even worse, speculation—even though the number of physicists and cosmologists who embrace some variation of the theory grows ever larger.
Multiverse thinking—the attempt to address fine-tuning and other questions of theoretical and cosmological physics—proposes many different kinds of universes and dimensions. There’s the bubble universe theory, which assumes that our universe as well as numerous other universes were formed from a “bubble” of a “parent universe.” The many-worlds interpretation posits only one universe, but it splits into “many worlds” based on the logic of quantum mechanics. These worlds, however, cannot interact with each other. The so-called strong anthropic principle, in one of its interpretations, says that a range of different universes is necessary for the existence of our own. It also says, however, that the universe exists because we are here to observe its existence. None of these approaches has attracted anything close to a scientific consensus.
Theoretical physicist Lee Smolin, a founding professor of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, has sought to reconcile the concept of fine-tuning with science by using the idea of a cosmic natural selection. His best-known work, The Life of the Cosmos, makes the case that many of the seemingly fine-tuned aspects of the universe can be explained by a kind of cosmic Darwinism—one in which differing laws of physics in effect compete and change over time, allowing them to evolve in a way that leads to a finely tuned world. (I liked Smolin even better when I saw a video of a lecture he gave at his institute on the physics of the universe. The pointer he used was a clunky wooden hockey stick.)
Since the mid-1980s, when he studied biology as well as theoretical physics, Smolin’s pathway into understanding and working to resolve the fine-tuning problem has focused on the parallels he intuited between the two fields. Those perceived parallels led to his theory that the universe, like the Darwinian world of life on Earth, evolves under the pressure of natural selection. The rise of life and ultimately humans is not the goal of that cosmic process—any more than humans are the goal of Darwinian evolution—but it is a predictable offshoot. As Smolin explains it, the key is star creation. Not a new idea, but he adds a twist: that the very same processes that lead to the existence of long-lived stars happen to support the almost infinitely lengthy trail of processes essential to make biology possible. That mutuality of results is, he says, “an important clue for fundamental physics.” So too is the abundance of carbon dioxide and oxygen in the universe—not because it has anything to do with life per se, but because it helps accelerate or increase the formation of massive stars that then give rise to much greater molecular complexity, which in turn makes life possible far down the road. “So the universe,” he argues, “evolves in ways hospitable to life as part of natural selection, the movement towards a more complex universe.” Fine-tuning, in this interpretation, is the process by which more powerful, more fit laws of physics triumph over others, and life follows in the wake. Smolin said that he has tried to apply his cosmic natural selection theory to a single-universe model, but so far “couldn’t find an approach that didn’t yield predictions that disagree with experiment.”
This is a very short version of a long scientific story that includes a universe where the laws of physics can be different in disparate regions, where the existence of other universes is mathematically essential, and where black holes may be the key to the formation of those other universes. The idea that black holes, where the laws of physics fall apart under the pressure of concentrated gravity, might play a central role in the formation of new universes cannot be proven and has many detractors. But Smolin argues that black holes are nurseries for Big Bangs, that the collapsing in of matter into black holes leads directly to the formation of new universes on the other side. Each universe will have a different set of laws of physics that either can or cannot evolve into a structure that supports life.
Cosmic natural selection is a long way from being proven, but Smolin says it can indeed some day be proven or disproven, unlike other multiverse theories. Also, it offers an explanation of how fine-tuned physical laws and ultimately life could arise in a universe that isn’t “designed” to do either. It just happens, in a way similar to how a single-cell bacterium over the eons evolves into an elephant. The theory brings life into a scientific cosmology, and it extends astrobiology far into the cosmos. We also have a well established parallel to learn from—Darwinian evolution.
“A long time ago, your ancestors were fish,” writes Paul Davies, another iconoclastic physicist and cosmologist, British-born but now director of the Beyond Center for Fundamental Concepts at Arizona State University, where he writes prolifically about the logic of the universe and big-picture astrobiology. “Think how fish spawn countless eggs, and imagine the tiny, tiny fraction that survive and mature. Nevertheless, not one of your ancestors—not a single one—was a failed fish. What are the odds against this sequence of lucky accidents extending unbroken for billions of years, generation after generation? No human lottery would dare to offer such adverse odds. But here you are—a winner in the great Darwinian game of chance! Does this mean that there is something miraculous in the history of your ancestry? Not at all.”
Can’t the same be said of the ancestry of the Earth and its menagerie of life? Or of life elsewhere in the universe, or universes?
There is, however, an alternative view, one that involves a Creator, and it is held by some sophisticated scientists. A long tradition exists of attempting to support the existence of a Creator through science (Newton, Copernicus, and, more recently, Cambridge physicist-turned-Anglican cleric John Polkinghorne come to mind), but the track record has not been good. Nonetheless, Smolin, who certainly does not subscribe to the Creator view of the origin of the cosmos, suggested that I speak with South African theoretical physicist George Ellis, who does hold that position.
Ellis, born in 1939 and now retired from the University of Cape Town, has credibility because he coauthored a seminal book on cosmology with Stephen Hawking (The Large Scale Structure of Space–Time) and because he returned to South Africa after his studies at Cambridge University and joined the nonviolent wing of the fight against apartheid. Neither means he’s correct about the nature and meaning of fine-tuning, but he is nonetheless well regarded in the field. A practicing Quaker, he has published prolifically on cosmology, multiverses, and fine-tuning, and generally argues the following: The fine-tuning of the universe makes it likely that life in our universe is common, that no scientific proof has been offered (or probably ever can be offered) of the existence of universes beyond ours, and that the existence of multiverses is as much a question of belief as the existence of a Creator.
“The more we learn of the universe, the more we learn how great the fine-tuning really is,” he told me. “Since science cannot tell me that any of the various explanations for that reality is true or false, then a plausible hypothesis is that of a Creator. It’s not provable, but nothing else is, either.”
His long-ago collaborator, Stephen Hawking, sees the same fine-tuning and comes to a very different conclusion, one that did not sit well with some of the more religiously minded. In his 2010 book, The Grand Design, written with California Institute of Technology physicist Leonard Mlodinow, Hawking describes the universe (or universes) as ultimately understandable by science—a view shared by quite a few in the field.
“Our universe seems to be one of many, each with different laws. That multiverse idea is not a notion invented to account for the miracle of fine tuning. It is a consequence predicted by many theories in modern cosmology,” he writes. “As recent advances in cosmology suggest, the laws of gravity and quantum theory allow universes to appear spontaneously from nothing. Spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist. It is not necessary to invoke God to light the blue touch paper and set the universe going.”
A strong statement for sure, but notice how many qualifiers are written into even Hawking’s explanation. The issue is far from settled and few scientific challenges are as great as those posed by the fine-tuning of the universe. But few hold greater potential for explaining how and perhaps why we are here, and why other life-forms in the universe might be out there, too.
• • •
Just as astrobiology is inevitably drawn into the worlds of cosmological fine-tuning and multiverses, so too is it being pulled into an equally fantastical world here on Earth—that of a possible shadow biosphere that supports life with a different origin and different characteristics than our own. Science has never found any alternate life-forms, proponents say, not because they don’t exist, but because scientists have never looked for them.
That has begun to change. Nothing is for certain in their work, but a handful of researchers have made some intriguing discoveries that suggest a shadow biosphere just might be present. What began as a theory is now the subject of NASA-funded work at hypersalty, hyperalkaline Mono Lake in California, about one hundred miles north of Death Valley. A terminal lake that receives water from the nearby mountains, it has no outlets and so only loses water through evaporation (until the city of Los Angeles began siphoning off water in 1941). Mono Lake is known for the “tufa” columns of limestone that stand in its midst and give it a distinctly spooky quality, as well as a very unusual chemistry caused by its lack of outlet streams. That means elements and compounds that pass through other lakes and get dispersed into big rivers and later oceans stay put in Mono Lake and concentrate to abnormally high levels. Arsenic from the nearby Sierra Nevada flows into Mono Lake and stays—creating a toxic stew with arsenic levels seven hundred times higher than what the Environmental Protection Agency considers safe. Despite being a virulent poison for most living things, arsenic has emerged as the key element in shadow biosphere research. In fact, if the research holds up to the critiques it has attracted, it will represent the beginning of a new era of biology—one where the already fuzzy concept of life as we know it will get much fuzzier.
The main force behind the arsenic biosphere research is a thirty-three-year-old biochemistry whiz named Felisa Wolfe-Simon. She broke onto the NASA scientific scene in 2008 when she attended an exclusive Gordon Conference meeting on “The Origins of Life” and raised the possibility of life-forms on Earth with chemical makeups that are entirely incompatible with all other life that we know. At the time, she recalls with something between pride and dismay, her mane of dark hair was dyed bright pink, and she sported a number of piercings. That probably didn’t help her establish early credibility.
But over the next four years, she attracted the attention of a number of top scientists, ranging from biologists to cosmologists. She worked with geochemist Ariel Anbar at Arizona State University and he introduced her to Paul Davies, the unconventional physicist/astrobiologist (and prolific writer), who already had a strong interest in the “shadow biosphere.”
Davies has promoted the shadow biosphere idea for some time, as had University of Colorado philosopher and astrobiologist Carol Cleland, who actually coined the word. His argument is part scientific, part practical. Why spend billions on flying to distant planets in the hope of finding evidence of current or former life different from ours when it may well exist right under (or in) our own noses? Many origin-of-life scientists assume that life didn’t begin just once on Earth, but rather a number of times in similar but nonetheless distinct forms. The organisms that weren’t based on carbon, nitrogen, and phosphorus perhaps couldn’t compete as well and died out, or maybe remnant populations live undiscovered because nobody has ever looked for them. But now they’re looking.
Davies and Wolfe-Simon submitted a proposal on an arsenic-based shadow biosphere to the John Templeton Foundation in 2007, but the request was turned down. A prime reason why was that one of the reviewers, a senior arsenic specialist at the U.S. Geological Survey in California named Ron Oremland, didn’t believe there was sufficient reason to think the research would be successful. But Oremland was nonetheless intrigued. He had spent much of his career, after all, studying the interactions between arsenic compounds and surrounding biology, and he felt a little guilty that he had panned the proposal. He ran into Wolfe-Simon several more times in the next few years and then opened his USGS lab to her so she could focus on Mono Lake as the location for a possible shadow biosphere.
But that required outside funding, which ultimately came in the form of a fellowship from NASA’s Astrobiology Institute. She headed to California, started collecting mud from the lake, and began the tedious process of sifting and concentrating samples containing already high levels of arsenic. She then began to examine the microorganisms that made their living in the toxic environment, and found something unusual. All known living things on Earth contain the elements carbon, hydrogen, nitrogen, sulfur, oxygen, and phosphorus, which forms the backbone of all genetic material and, in the form of the molecule adenosine triphosphate, is essential for energy storage and transfers in cells. Yet it appeared that some of the microbes from Mono Lake could survive with little or no phosphorus in them, while having very high levels of arsenic.
Arsenic is chemically very similar to phosphorus, a downstairs neighbor in the table of elements, and its toxicity is in large part a function of the fact that other molecules initially mistake it for phosphorus and then are destroyed when the difference is revealed. But the microscopic Mono Lake organisms—from the domains of bacteria and archaea—not only withstood the arsenic but seemed to be possibly using it as a substitute for phosphorus, which, along with carbon, oxygen, hydrogen, and nitrogen, are the key and essential elements of life on Earth. Through months of lab work, Wolfe-Simon and Oremland grew Mono Lake samples with higher and higher levels of arsenic until they reached a point where arsenic had replaced a significant percentage of the phosphorus and arsenic levels were some forty thousand times the EPA safe level. Yet some microbes survived when fed glucose and vitamins, as evidenced by how the water slowly became cloudy with biological activity.
The samples were then sent to several of the nation’s best labs with the most sophisticated equipment for molecular-level testing, and the results were startling: The arsenic, they found, was incorporated into the genetic material (the DNA and RNA) of the cells as well as essential proteins and the cell membranes.
Word of the potentially ground-breaking discovery was first announced in an embargoed release from the journal Science, which was followed by the NASA public announcement of an upcoming press conference to discuss a finding that could have implications for extraterrestrial life. The news shot through the blogosphere, with detailed predictions of life on Jupiter’s moon Titan, or a new day in extraterrestrial research. Both Science and NASA remained silent for four days until the press conference, which by then was anticipated to be news on the scale of the 1995 Mars meteorite announcement or greater.
The press conference focused on the findings in the Science paper—that microbes from Mono Lake could be grown with lots of arsenic but virtually no phosphorus, and that sophisticated technology had been used to find that the arsenic was contained within the DNA and other essential genetic and life-supporting molecules of the microbe. While the result was remarkable, the larger take-home message was even more so. “We have cracked open the door to what is possible for life elsewhere in the universe,” Wolfe-Simon said. Ed Weiler, NASA’s associate administrator for the Science Mission Directorate, was not at the press conference but did add this in a formal release: “The definition of life has just expanded…. As we pursue our efforts to seek signs of life in the solar system, we have to think more broadly, more diversely, and consider life as we do not know it.”
The results were presented with the proper caveats—that they had to be confirmed and expanded upon—and respected chemist and astrobiologist Steve Benner was also onstage to make a strong case for the near impossibility of the substitution of arsenic for phosphorus in DNA. Arsenic breaks down quickly in water, he said, while phosphorus does not. So how could arsenic bonds hold up in an aqueous environment?
To say the scientific blogosphere was skeptical would be an extreme understatement. Some bloggers immediately attacked the research as incomplete or incompetent, and others concluded the results were simply impossible. Many dinged NASA for “hyping” the discovery, and the peer reviewers at Science were dismissed as compromised. Some of the critiques and challenges were sincere and based on science, but many were personal and nasty. The Mono Lake researchers had predicted a heated response, but they were taken aback by the venom. Perhaps they shouldn’t have been. History tells us that developments related to astrobiology and the search for extraterrestrial life bring out intense emotions. And NASA did put out a release the day of the press conference, saying that agency-funded “astrobiology research has changed the fundamental knowledge about what comprises all known life on Earth.” What was an historic and proud moment for NASA and the researchers was a red flag to many others.
For the first week, editors at Science and the researchers were silent except to say they would address challenges and critiques through the traditional peer review process. But after two weeks, the blogosphere was sufficiently livid that all felt the need to respond—to address some specific charges and to make clear that the microbes would be made available to anyone who wanted to test them in their own labs. In other words, they acknowledged the criticism but held their ground. Their research had been peer reviewed on several levels and so had already been challenged and challenged again. Nonetheless, Wolfe-Simon’s colleague at the U.S. Geological Survey, Ronald Oremland, joined a panel set up at an American Geophysical Union annual meeting specifically to discuss the controversy, as opposed to the science. An old-school scientist, who said he was trained to discuss his work in journals and at conferences rather than on the web, said he had not responded online because, “You can wind up in a Jerry Springer situation before you know it, with people throwing chairs.” But if the controversial research holds up and further investigation supports the finding that the arsenic really is woven into the microbes’ genetic material, then we’ll be in uncharted waters. Microbes with arsenic instead of phosphorus in their DNA backbones would not just represent another interesting discovery. The work of Wolfe-Simon and her team would open a new window into life—an alien life, if you will, right here on Earth.