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Astrophysicist Brandon Carter's long-standing argument against finding intelligent extraterrestrial life has been roundly challenged by a team of Serbian researchers led by Milan Ćirković.
Carter's theory assumed set timescales for two processes: the life cycle of a star and the emergence of complex life. By statistically combining the two Carter concluded that complex life takes longer to emerge than the life-friendly duration of most stars -- with the implication being that intelligence is excruciatingly rare in the Galaxy and we may be alone.
Not satisfied with this conclusion, Ćirković and colleagues Branislav Vukotić and Ivana Dragićević are now disputing these assumptions. In their Astrobiology paper, "Galactic Punctuated Equilibrium: How to Undermine Carter's Anthropic Argument in Astrobiology," they contend that there is no reason to assume life evolves only gradually. They argue life could evolve in fits and starts - mirroring an evolutionary theory called punctuated equilibrium.
The abstract of their paper reads,
Our approach is based on relaxing hidden uniformitarian assumptions and considering instead a dynamical succession of evolutionary regimes governed by both global (Galaxy-wide) and local (planet- or planetary system–limited) regulation mechanisms. Notably, our increased understanding of the nature of supernovae, gamma-ray bursts, and strong coupling between the Solar System and the Galaxy, and the theories of “punctuated equilibria” and “macroevolutionary regimes” are in full accordance with the regulation-mechanism picture. The application of this particular strategy highlights the limits of application of Carter's argument and indicates that, in the real universe, its applicability conditions are not satisfied. We conclude that drawing far-reaching conclusions about the scarcity of extraterrestrial intelligence and the prospects of our efforts to detect it on the basis of this argument is unwarranted.
In plain English, the conditions in the Universe required for the emergence of intelligent life have only recently been established (in cosmological scales). Prior to 'recent times', universal mechanisms were in place to continually thwart the evolutionary development of intelligence, namely through gamma-ray bursts, super novae and other forms of nastiness. Occasional catastrophic events have been resetting the "astrobiological clock" of regions of the Galaxy causing biospheres to start over. "Earth may be rare in time, not in space," they say. They also note that the rate of evolution is intimately connected with a planet's environment, such as the kind of radiation its star emits.
This is why the authors reject a strict uniformitarian approach; the Universe is not the same now as it was in the past.
And importantly, given the possibility that the conditions for intelligence to emerge are now in place, we shouldn't give up hope about our chances of discovering extraterrestrial life.
Originally posted by DaMod
It is impossible to determine how life would develop / evolve elsewhere without any test cases (aka other inhabited worlds).
Let's pause for a moment and look at the numbers.
Recent figures place the total number of stars in the Milky way at an astounding three trillion. I don't need to tell you that that is a huge number. But given how poor the human mind is at groking large figures I'm going to play with this number for a bit:
3 trillion fully expressed is 3,000,000,000,000 (12 zeros)
As an exponent it can be expressed as 3 x 1012
Re-phrased, it is 3 thousand billions, or 3 million millions
Which necessarily leads to this question: given such a ginormous figure, what does it mean to be rare?
Even if the Earth is a one in a million occurrence, that means there are still 3 million Earthlike planets in the Galaxy (assuming one Earthlike planet per star). Does that qualify as rare? Not in my books.
If, on the other hand, the Earth is a one in a billion occurrence, then there are only 3,000 Earths in the galaxy. That sounds a bit more rare to me -- but one in a billion!? Seriously?
We also have to remember that the 3 trillion stars only accounts for what exists right now in the Milky Way. There have been well over a billion trillion stars in our past Universe. As Charles Lineweaver has noted, planets began forming in our Galaxy as long as 9 billion years ago. We are relative newcomers to the Galaxy.
Our Biophilic Universe
But all this numerological speculation might be moot. We're overlooking the mounting evidence indicating that we live in a universe exceedingly friendly to life. What we see in the physical laws and condition of the universe runs contrary to the expectations of the Rare Earthers.
Indeed, we are discovering that the Galaxy is littered with planets. Scientists have already cataloged 321 extrasolar planets -- a number that increases by a factor of 60 with each passing year. Yes, many of these are are so-called "hot Jupiters," but the possibility that their satellites could be habitable cannot be ruled out. Many of these systems have stable circumstellar habitable zones.
And shockingly, the first Earthlike planet was discovered in 2007 orbiting the red star Gilese 581. It's only 20 light-years away, 1.5 times the diameter of Earth, is suspected to have water and an atmosphere, and its temperature fluctuates between 0 and 40 degrees Celsius.
If we are one in a billion, then, and considering that there are only 0.004 stars per cubic light-year, what are the odds that another Earthlike planet is a mere 20 light-years away?
Indeed, given all this evidence, the Rare Earthers are starting to come under attack. Leading the charge these days is Alan Boss who recently published, The Crowded Universe. Boss estimates that there may be billions of Earthlike planets in the Milky Way alone. "I make the argument throughout the book that we already know that Earths are likely to be incredibly common—every solar-type star probably has a few Earth-like planets, or something very close to it," says Boss. "To my mind, at least, if one has so many habitable worlds sitting around for five billion or 10 billion years, it's almost inevitable that something's going to start growing on the majority of them."
And it gets worse for the Rare Earthers. They also have to contend with the conclusions of astrobiologists.
It's a myth, for example, that it took life a long time to get going on Earth. In reality it was quite the oppoite. Our planet formed over 4.6 billion years ago and rocks began to appear many millions of years later. Life emerged relatively quickly thereafter some 600 million years after the formation of rocks. It's almost as if life couldn't wait to get going once the conditions were right.
We also live in a highly fertile Galaxy that's friendly to extremophiles. The Panspermia hypothesis suggests that 'life seeds' have been strewn throughout the Galaxy; evidence exists that some grains of material on Earth have come from beyond our solar system.
Recent experiments have shown that microorganisms can survive dormancy for long periods of time and under space conditions. We also now know that rocks can travel from Mars to Earth and that simple life is much more resilient to environmental stress than previously imagined. Consequently, biological diversity is probably much larger than conventionally assumed.
Google Video Link
The integers that are plugged into this equation are often subject to wide interpretation and can differ significantly from scientist to scientist. Even the slightest change can result in vastly different answers. Part of the problem is that our understanding of cosmology and astrobiology is rapidly changing and there is often very little consensus among specialists as to what the variables might be.
Consequently, the Drake formula relies on 'stabs in the dark.' This makes it highly imprecise and unscientific. The margin of error is far beyond what should be considered acceptable or meaningful.
No accounting for cosmological development or time
Another major problem of the Drake Equation is that it does not account for two rather important variables: cosmological developmental phases and time (see Cirkovic, "The Temporal Aspect of the Drake Equation and SETI").
More specifically, it does not take into consideration such factors as the age of the Galaxy, the time at which intelligence first emerged, or the presence of physiochemical variables necessary for the presence of life (such as metallicity required to form planets). The equation assumes a sort of cosmological uniformity rather than a dynamic and ever changing universe.
For example, the equation asks us to guess the number of Earth-like planets, but it does not ask us when there were Earth-like planets. And intelligence itself may have been present as long as 2 to 4.5 billion years ago.
The Galaxy's extreme age and the potential for intelligence to have emerged at disparate points in time leaves an absurdly narrow window for detecting radio signals. The distances and time-scales in question are mind-boggingly vast. SETI, under its current model, is conducting an incredibly futile search.
Which leads to the next problem, that of quantifying the number of radio emitting civilizations. I'm sure that back in the 1960's it made a lot of sense to think of radio capability as a fairly advanced and ubiquitous means of communication, and by consequence, an excellent way to detect the presence and frequency of extraterrestrial civilizations.
But time has proven this assumption wrong. Our radio window is quickly closing and it will only be a matter of time before Earth stops transmitting these types of signals -- at least unintentionally (active SETI is a proactive attempt to contact ETI's with radio signals).
Due to this revelation, the entire equation as a means to both classify and quantify certain types of civilizations becomes quite meaningless and arbitrary. At best, it's a way of searching for a very narrow class of civilizations under very specific and constrained conditions.
Rather, SETI should continue to redefine the ways in which ETI's could be detected. They should try to predict future means of communication (like quantum communication schemes) and ways to identify these signals. They should also look for artificial objects such as megascale engineering and artificial calling cards (see Arnold, "Transit Lightcurve Signatures of Artificial Objects").
The future of advanced intelligence
Although possibly outside the auspices of this discussion, the Drake Equation does not account for the presence of post-radio capable civilizations, particularly post-Singularity machine intelligences. This is a problem because of what these types of civilizations might be capable of.
The equation is used to determine the number of radio capable civilizations as they conduct their business on their home planet. Again, this is a vary narrow view of ETI's and the space of all possible advanced civilizational types. Moreover, it does not account for any migratory tendency that advanced civs may have.
The Drake Equation does not tell us about exponential civilizational growth on account of Von Neumann probe disbursement. It does not tell us where advanced ETI's may be dwelling or what they're up to (e.g. Are they outside the Galaxy? Do they live inside Jupiter Brains? Do they phase shift outside of what we regard as habitable space? etc.). This is a serious shortcoming because the answers to these questions should help us determine not just where we should be looking, but they can also provide us with insight as to the makeup of advanced intelligence life and our own potential trajectory.
In other words, post-Singularity ETI's may represent the most common mode of existence for late-stage civilizations. And that's who we should be looking for rather than radio transmitting civs.
Originally posted by DrumsRfun
Nice to see science back it up but in my opinion it is very arrogant to think we are the only life in the universe.