By the end of this century, says astrophysicist Martin Rees, we should be able to ask whether or not we live in a multiverse, and how much variety of the laws of physics its constituent ‘universes’ display. The answer to this question, says Rees, “will determine how we should interpret the ‘biofriendly’ universe in which we live (sharing it with any aliens with whom we might one day make contact).”
The same fundamental laws of physics apply throughout the entire domain we can survey with telescopes. Were that not so—were atoms ‘anarchic’ in their behavior—we’d have made no progress in understanding the observable universe. But this observable domain, says Rees, may not be all of physical reality; some cosmologists speculate that ‘our’ big bang wasn’t the only one—that physical reality is grand enough to encompass an entire ‘multiverse’.
Even conservative astronomers, concludes Rees, “are confident that the volume of space-time within range of our telescopes—what astronomers have traditionally called ‘the universe’—is only a tiny fraction of the aftermath of the big bang. We’d expect far more galaxies located beyond the horizon, unobservable, each of which (along with any intelligences it hosts) will evolve rather like our own.”
The Physics of Life
Following the laws of physics, Charles Cockell suggests that life on Earth might be a template for life in the universe, adhering to a standard model of constants or equations of life. Cockell, an astrobiologist at the University of Edinburgh and Director of the UK Center for Astrobiology and author of The Equations of Life: How Physics Shapes Evolution, views the topic of life’s construction through the lens of an observer who is trying to understand how life on Earth can serve as a test case for possible life elsewhere in the universe.
No matter how different the conditions on distant worlds, all presumably have the same laws of physics — from quantum mechanics to thermodynamics and the laws of gravity, reports the New York Times. And life, as Cockell puts it, is simply living matter, “material capable of reproducing and evolving.” If there is biology elsewhere in the universe, we would find it strikingly familiar not only in appearance but down to the carbon-based machinery in its cells.
There are equations and rules that are not limited to living systems that underlie the way that life operates. These equations are consistent, so far as we can tell, anywhere in the universe. To understand what life might look like elsewhere, it is critical that we have a thorough understanding of how it works here.
Replaying the Tape of Evolution
Rerun the tape of evolution, and DNA, RNA, ATP, the Krebs cycle — the rigmarole of Biology 101 — would probably arise again, here or in distant worlds, writes George Johnson in the New York Times: Single cells would then join together, seeking the advantages of metazoan life, until before you know it something like the earthly menagerie would come to be.
The laws of biology, according to Cockell, mimic the physical laws that are the same everyplace –gravity, for instance, is omnipresent, not exclusive to our solar system. Restrictions are everywhere –organic molecules, on Earth or elsewhere, still disintegrate at high temperatures, deactivate at low ones. Certain ingredients are indispensable for life –carbon is the optimal element to assemble burgeoning life; water is the ideal solvent to shuttle it.
“If he’s correct,” wrote Darby Dyar, Senior Scientist, Planetary Science Institute and Chair of NASA’s Venus Exploration Analysis Committee, wrote in an email to The Daily Galaxy, “then the “tape of evolution” would likely have run on our nearest neighbor, Venus, where current evidence suggests liquid oceans (and very Earth-like conditions) were present for roughly 3 billion years. Moreover, recent discoveries of exoplanets at Venus-like distances from their stars also become highly likely candidates for hosting such an environment.”
“The laws of physics channel living creatures into restricted shapes,” Cockell says. “They narrow the scope of evolution. Alien life may have many similarities to life here.”
Our Perceptions are Earth Centric
“Cockell’s hypothesis is a bit more subtle than comes across in many popular reports”, wrote Steven Benner, at the Foundation for Applied Molecular Evolution in Florida in an email to The Daily Galaxy. “The laws of physics are certainly universal, and with equal certainty constrain the forms that life might take. However, in this year, in this century, our perception of those laws and those forms remains horribly “Earth-centric”. We talk about water and DNA and proteins, because that is where we live. Yet many, perhaps most, Earth-like rocky planets have other solvents, the sulfuric acid of Venus or the methane of Titan. Because we do not live in acids or hydrocarbons, the chemical logics that might operate in these environments are not well explored by us.
‘Weird’ is in the Eye of the Beholder”
“Indeed, while ‘weird’ is in the eye of the beholder” continues Benner, synthetic biologists who make alternative forms of matter that might work there are astonished at how much our Earthling imagination has limited our view of what those ‘forms’ might be. And I would be far more comfortable in accepting the equations of today’s physics if they could tell us convincingly, for example, what constitutes 90% of the gravitational mass in the galaxy.”
Not Universal Outside Our Solar System
In an email to The Daily Galaxy, Georgia Tech biochemist and Director of The Center for the Origin of Life, Loren Dean Williams wrote that “I am not sure I am the best person for this because I disagree with the hypothesis that earth’s biopolymers or metabolism are universal to life outside our solar system. The idea that the DNA, RNA, and protein would arise elsewhere in the universe is an example of a type of error that is so common that it merits a name, the “evolution = optimization error”. A trait or process or characteristic that has arisen from evolution appears to be perfect – but it never is. Your wrist might appear to be perfect; you can play a violin or do karate or write with a pen. But evolution is path dependent. The bones in your wrist evolved from the bones of the fin of our fish ancestor and are contingent on their very specific history. If different evolutionary forces acted on our fish ancestor, you could have a different wrist. And incredibly, it would appear perfect.
“Similarly (in my view) biopolymers chemically evolved from simpler organic molecules and are products of their history (which we don’t know a lot about),” Williams continued. “A more rapidly spinning planet, a different pattern of impacts, a different chemical inventory, or a different temperature profile during chemical evolution might have produced a different set of biopolymers. And these alternative biopolymers would appear perfect. Some would propose that they were universal to all life in the universe. I think they would be wrong.”
“In general, I share the views expressed by Cockell about the origin of life on other planetary bodies, particularly if they share geological, chemical and physical characteristics of Earth,” wrote University of Washington astrobiologist John A Baross in an email to The Daily Galaxy. “The specific properties of Earth life that are also likely to be universal for life on an Earth-like planet include carbon- based macromolecules, dependence on metals and trace-elements, the use of chemical or light as the energy sources for metabolism, and very likely a dependence on water as the solvent to carry out oxidation and reduction reactions,” continues Baross. “There are many reasons that carbon-based life should be emphasized: it is one of the most abundant elements in the universe and has been recorded in meteorites, comets and interplanetary dust. Also, many of the organic compounds used by life are synthesized abiotically on Earth under a wide range of environmental conditions. Would carbon-based life elsewhere have similar biochemistries to Earth life?
“There is some evidence that there are “rules of organic chemistry” that would imply either favoring or presupposing specific chemical reactions and macromolecular structures,” concludes Baross. “The origin of life elsewhere, given the contingency of evolution, could result in the selection of different organisms and ecosystems than are found on Earth. However, they are likely to share similar biochemical characteristics and perhaps phenotypes with Earth organisms. The possibility of life on a planetary body that is unlike Earth, is another issue that we can only speculate about.”
Contingency vs. Convergence
Woodward W. Fischer, professor of geobiology at the California Institute of Technology wrote in an email to The Daily Galaxy: “I’m reminded of the classic arguments that would take place between Steve Gould and Simon Conway Morris about the importance of the roles of contingency vs. convergence in evolution. Gould was impressed by how life is shaped by the rare chance events like the bollide impact that hit the Yucatan sixty five million years ago and wiped out the non-avian dinosaurs, leaving ecological room for a radiation of mammals in its wake. Without this singular event, one might argue that the rise of mammals and their importance in terrestrial ecosystems might not have ever taken place. Conway Morris was taken by convergence in evolution—flight, for example, was invented many times in biology (insects, birds, bats, squirrels, etc.); just evolve an aerodynamic control surface and you can fly. So he argued that you could run the tape of life again and get more-or-less the same result: intelligent bipedal apes. Cockell’s conjecture is very much in family with these convergence arguments.
“But I think it’s important to consider that there are good examples of both contingency/singularities in the history of life on Earth,” Fischer continues. “The singularities stand out—biological processes that are absolutely critical for the modern biosphere like oxygenic photosynthesis evolved once in 4+ billion years of evolution on Earth, and it took 2 billion years for it to emerge. Even though our planet is bathed in sunlight and water (the two substrates needed for oxygenic photosynthesis), it only evolved once. Because it’s a singularity we can’t presume that it would happen with certainty. We also don’t know why it took so long to evolve—presumably part of the reason is that it’s a challenging chemical task. But when O2 became abundant from photosynthesis, biology evolved many ways of breathing and using O2 in metabolism—convergence. So O2 was a good thing for life (in the long run) and easy for the biosphere to figure out how to access. That is to say we have examples of both end-member styles of evolution being important. And that also makes it hard to evaluate with certainty the question of if life were to emerge elsewhere does it have to play by the same molecular and metabolic rules that life on Earth does.”
The Daily Galaxy, Avi Shporer, Research Scientist, MIT Kavli Institute for Astrophysics and Space Research via John A. Baross, Darby Dar, Woodward W. Fischer, Loren Dean Williams, New York Times, and Rees, Martin. On the Future (Kindle Edition p. 186)
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