Our place in the universe is a conundrum - life on Earth evolved to create a technologically-savvy race that is now looking for other technologically-savvy intelligences populating our galaxy. But there's a problem; it looks like humanity is the only "intelligent" species in our little corner of the universe - what gives?
This question forms the basis of the Fermi Paradox: given the age of the universe and the apparent high probability of life evolving on other planets orbiting other stars, where are all the smart aliens?
Has Kepler Discovered an Alien Megastructure?
According to a new study based on data collected by the NASA/ESA Hubble Space Telescope and NASA's Kepler Space Telescope, it might be that Earth (and all life on it) is an early bloomer. By extension, the logical progression from this new study is that we're not hearing from advanced alien civilizations because, in short, the universe hasn't had the time to spawn many more habitable worlds.
The study, which focuses purely on the likelihood of the evolution of habitable worlds (and not speculation of alien intelligence, the Fermi Paradox implication is my own), finds that when our planet was born from our young sun's protoplanetary disk some 4.6 billion years ago, it was born into an era when only "8 percent of the potentially habitable planets that will ever form in the universe existed." This means that the universe has 92 percent to go until it runs out of the necessary material to produce the stars that go on to produce planets, some of which will be small and rocky and orbit in just the right location for life (as we know it) to thrive.
"Our main motivation was understanding the Earth's place in the context of the rest of the universe," said Peter Behroozi of the Space Telescope Science Institute (STScI) in Baltimore, Md., "Compared to all the planets that will ever form in the universe, the Earth is actually quite early."
Hubble has shown astronomers that young galaxies were churning out stars at a fast rate some 10 billion years ago. However, the quantity of hydrogen and helium involved in stellar production was low compared with the amount of these star-forming gases that exist today.
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"There is enough remaining material (after the Big Bang) to produce even more planets in the future, in the Milky Way and beyond," said Molly Peeples, also of STScI.
By combining this knowledge from Hubble with exoplanetary data from Kepler, the researchers were able to form a picture of the habitable planet potential of our galaxy and use it as a model for the number of other habitable worlds existing throughout the cosmos.
Since Kepler started taking data in 2009, we've been introduced to a menagerie of small rocky worlds orbiting sun-like stars. Some of these thousands of worlds orbit their stars within the habitable zone - the region surrounding a star that's not too hot and not too cold to allow liquid water to persist on its surface. By extrapolating from Kepler's comparatively small dataset, astronomers have predicted that there should be around 1 billion Earth-sized worlds orbiting within their stars' habitable zones in the Milky Way. If we consider there are 100 billion galaxies in the observable universe, there's a huge number of habitable, Earth-sized worlds throughout the cosmos.
And the universe, according to this new theoretical study, has only just started in the planetary production business. The last star isn't expected to fizzle out for another 100 trillion years (when the universe will continue toward its perpetual march to "heat death"), so there's lots of time left.
Kepler's ‘Bizarre' Signal Sparks Alien Intelligence Speculation
With the help of these observations, the researchers predict that Earth 2.0 (i.e. rocky planets of Earth-like dimensions orbiting within their stars' habitable zones) will most likely pop up inside giant galaxy clusters or dwarf galaxies where reservoirs of star-forming (and therefore planet-forming) gases are known to reside. Alas, the Milky Way's planet-forming days are numbered, as much of these gases have already been consumed during our galaxy's heady "starburst" days.
Noted by the researchers is that the advantage of being an "early" civilization evolving at this time of universal evolution is that we have the awesome opportunity to study the early stages of cosmic evolution, using space telescopes (such as Hubble) to see the early formation of galaxies and witness observable evidence for the Big Bang. For any future civilization in a trillion years time, the universe will look very different than it does now - fewer galaxies will be visible and the earliest evidence for the Big Bang (such as the cosmic microwave background radiation) will have further ebbed away.
It's interesting to ponder how an intelligent alien civilization will interpret a more mature, perpetually expanding universe lacking the cues to its origin that we take for granted today. Would they assume, lacking contradictory evidence, that the universe has always existed? And that just because the universe is expanding, it doesn't mean there had to be a Big Bang?
A Mathematical Twist on the Fermi Paradox
Of course, this is just a fun thought experiment; predicting the existence of a future alien intelligence, let alone how they may interpret their cosmic environment, is presumptuous at best. But it does pose an existential problem beyond the Fermi Paradox. If the Earth is an early bloomer, and humanity is one of the first intelligent civilizations to pop up in a universe of infinite possibilities, how might our civilization unfold?
Who knows, but it seems the universe has the boundless potential to form new worlds and new life (and new intelligences) that will potentially form long after humanity and life on Earth has come and gone, eventually succumbing to the inevitable death of our sun in about 5 billion years time. This study serves to remind us that our time as an intelligent life form in the universe is fleeting, and it seems many more intelligences will evolve long after we are gone.
Despite the occasional report of an extraterrestrial sighting, be it through a microscope revealing curious shapes in a meteorite or a photo of wispy lights taken at the blurry end of a camera lens, aliens have yet to make contact with humans. Even the White House yesterday put out a statement declaring that the federal government "has no evidence that any life exists outside our planet, or that an extraterrestrial presence has contacted or engaged any member of the human race." Humans may not yet have encountered life outside of our planet, but many scientists see it as an inevitability. In 1960, astronomer Frank Drake came up with the now eponymous equation which provided an estimate of the number of civilizations in our galaxy. Although scientists continue to debate the application of his formula as well as alternatives, Drake's own solution to the equation is 10,000 civilizations, suggesting intelligent, technologically advanced life outside our planet is common. How these different civilizations, including our own, find each other is an important question for anyone here on Earth looking for extraterrestrials. Explore how aliens might stumble upon our planet -- and how we might actually spot them first.
ARE UFOS ALIEN? NO!
Before we can began to search the skies, we have to start by narrowing down our options. Sticking within our own galaxy is a good start, since we're more likely to spot a neighbor closer to us than one further away. Astronomers may also elect to focus their attention on stars closer to the center of the Milky Way, where 90 percent of its stars are clustered. Furthermore, the stars here are a billion times older than the sun, giving life more time to develop biologically and technologically. Many stars are unsuitable for nurturing life, and even stars that do have the appropriate "spectral type" may host exoplanets inhospitable to life due to their location relative to their parent star, size or composition. These criteria would not only help us find aliens, but also help them find us. After all, Earth would stand out as a hospitable planet, according to a paper published in 2007 in Astrophysical Journal.
If aliens are looking for us, they're scanning the same, vast, dark and mostly empty expanse of space that we are. It's a good thing then that we're leaving the lights on to make it easier to find us. According to Abraham Loeb, of Harvard University and Edwin Turner, from Princeton University, by scanning the skies for artificial illumination as opposed to naturally occurring light sources, both human and extraterrestrial astronomers might be able to find signs of life. Existing telescopes would be able to see a city the size of Tokyo as far as the edges of our solar system.
CITY LIGHTS COULD REVEAL ET
For more than 25 years, the SETI Institute has been scouring the skies for signs of alien life. However, long before the institute was established, scientists have tried to catch a communication signal from another world. Scientists looking for alien signals use a combination of optical and radio telescopes, such as the one seen here. Dropping in on a signal without knowing the source of the communication is the tricky part, however, and researchers narrow down their search by targeting specific kinds of stars. With their citizen science program, SETI@home, the institute has enlisted three million additional observers analyzing data for traces of an alien signal.
MAN LOOKS FOR ALIENS, LOSES JOB
Have aliens already stopped by for a visit, even though we weren't at the door to meet them? If they have, shouldn't they have left something behind? An artificial object of alien origin could be lurking in our solar system without our knowledge. As Discovery News' Ray Villard explains: "In a paper published in the 1960s, Carl Sagan, using the Drake Equation, statistically estimated that Earth might be visited every few tens of thousands of years by an extraterrestrial civilization." Further out beyond our solar system, aliens may have left what essentially amount to interstellar billboards large enough to be seen by, say, a planet-hunting telescope like Kepler. These last two scenarios, of course, envision an extremely technologically advanced civilization well beyond the engineering capabilities of humankind. At the same time, humans have sent spacecraft beyond the solar system, including Pioneer 10 and 11 as well as Voyager 1 and 2. All of these spacecraft are equipped with what are essentially calling cards for the human race -- small plaques in the case of the Pioneer spacecraft and golden records for the Voyager spacecraft (seen here).
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Humans may rely primarily on fossil fuels as their primary means of energy, but that doesn't mean extraterrestrials in a far off civilization have the same power source. Solar power could be one option, though not quite with the same black panels we use on Earth. A super civilization could even tap into a black hole to meet its energy needs. If aliens are tapping to these cosmic bodies, that should make them all the more detectable from Earth. How would we know whether an alien race was relying on a black hole as a source of energy? As Discovery News' Ray Villard explains: "Tell-tale evidence would come from measurements that showed the black hole weighed less than 3.5 solar masses. That's the minimum mass for crushing matter into a black hole via a supernova core-collapse."
In one of the most unusual -- and highly unlikely -- first-contact scenarios, aliens would be able to recognize us by the level of greenhouse gas emissions we pump into our atmosphere. Not only that, according to a hypothesis put forward by researchers affiliated with NASA and Pennsylvania State University (though not directly tied with either institution), but aliens may use that as cause to wipe out the human race. In this bizarre set of circumstance, aliens view human advancement as a destructive force spiraling out of control. To avoid the threat of a future adversary, extraterrestrials clear out the competition.
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