According to a recent study, the signals we send out, like radio waves and city lights, could reach faraway planets. However, because space is so vast, these signals would take thousands or even millions of years to get there. So, if aliens are watching, they would be seeing our past, not our present.
However, alien civilizations with more advanced telescopes might already be able to spot us. “It’s totally feasible that there’s alien astronomers that have built a 100m (330ft) space telescope that could be seeing us right now,” says the BBC.
Astronomers have deduced what alien scientists might see when they gaze at the Milky Way from afar. The new results suggest our home galaxy is unusual but not unique, at least when it comes to chemistry.
The study says that the signals we send out, like radio waves and city lights, might reach faraway planets. But because space is so huge, these signals would take thousands or even millions of years to get there. So, if aliens are watching, they would be seeing our past, not our present.
The classic Fermi paradox makes for very interesting analysis. There are some very compelling theories on why we haven’t been visited by or been made aware of other intelligent life forms out there if there are potentially over a 100 billion Earth-like planets out there.
To understand these theories, there are certain concepts and theories one needs to be familiar with: Kardashev Scale, Drake’s Equation, Great Filter, and the Wow! Signal. This is a longish answer, but bear with me while I get to it. I took a fair bit of help from this Wait But Why post to give my answer a skeleton. Tim’s done a great job of it and I’d encourage everyone to read it. I’ve added a lot of extra information, I hope you find it relevant.
First of all, how do you define alien life? Hardcore weirdos like in our famous movies or ant like creatures we can hardly see even if we zoom in on a body’s surface, or better still, microbial organisms? For the purposes of this answer and for aliens to contact us — for them to contact us — let us assume they are “intelligent”. Which brings us to, how do we define intelligent life and what if there’s life more intelligent than us?
Types of Intelligent Civlizations
The first thing we need to understand is the Kardashev Scale. The Kardashev scale measures the technological advancement of a civilization based on the amount of energy it has at its disposal. There are three types of civilizations: Type 1, where a civilization is technologically capable of using all the energy sources on its planet (Carl Sagan puts us at 0.7, Michio Kaku says we might become Type 1 in about 200 years); Type 2, a civilization with enough technology to harness energy from its system’s host star; and Type 3, a civilization capable of harnessing the power of its galaxy and thereby colonizing the galaxy. All these Types are used broadly while talking about colonization in space and the ability to terraform and mine other planets.
Why do we talk about these civilization types? Are they some form of measurement for future technological advancement? Not necessarily. Our Universe is 13.77 billion years old. Our Solar System is 4.6 billion years old. The Earth is about 4.54 billion years old. There are planets outside our Solar System that are more than twice as old as Earth. Even if out of the 100 billion Earth-like planets, only 1% have the right conditions to harbor life, we still have about 1000000000 planets
On paper, some of these 1000000000 planets could easily be sustaining Type 2 or even Type 3 civilizations. But in reality, are they? If these civilizations indeed do exist, why have they not contacted us? Or have they contacted us? In fact, can they theoretically even exist at all? Is it even possible, there might not be any other civilizations at all?
Let’s simplify these questions and break them down into three: 1) that life either doesn’t exist or is of lower intelligence than us, making it hard for them to contact us, 2) there are Type2 and Type3 civilizations, but they choose not to contact us or are contacting us and we can’t recognize them, and 3) we have been contacted and we know it. There are ample theories to explain the former two scenarios, and one piece of evidence for the third:
Origin of Life on Earth
Life arose on Earth from non-living organic compounds about 3.8 billion years ago: 700 million years after the Earth formed. We have proof of this in the form of sedimentary rocks in Isua, Greenland (the oldest known sedimentary rocks) that show evidence of life; and from the famous Miller–Urey experiment. This leads us to believe that planets that are older than us have had ample time to a) create conditions enough to sustain life, and b) have and contain civilizations more advanced than us. But there’s more to it than just that.
The Great Filter
The Great Filter is a filtering event that exists somewhere in the journey from abiogenesis to Type 3 civilization which prevents civilizations as a group — or lifeforms, really — to reach Type 3. Simply put, it’s a filter that is so catastrophic to civilizations, it simply wipes them out. However, by an extremely rare occurrence, one or some civilizations might cross it to advance further.
In recent years, astronomers have discovered more than 2,500 planets orbiting other stars by observing the subtle dimming of light as these exoplanets pass in front of their host stars. Wells wondered if alien scientists on some distant world might be doing exactly same thing but in the opposite direction: pointing a telescope our way and noting the flickering of starlight caused by our very own Earth as it “transits” the sun.
Wells sifted through astronomical catalogs and identified nine known exoplanets in one of the celestial sweet spots from which an Earth transit would be visible.
Alas, it seems unlikely that any of these worlds could be home to alien skywatchers looking our way. Most are Jupiter-sized gas-ball worlds so hot that they’re unlikely to harbor life.
But it turns out there’s more to the story
We can observe the transit of a faraway planet only if, by pure chance, it and its host sun are perfectly aligned with Earth — what Wells calls “a very low-probability alignment.” Statistically speaking, however, Wells knew there should be a whole crowd of relatively nearby planets in the sweet-spot regions — hundreds of them, probably — just not angled properly from our point of view. They could see us, but we can’t see them.
Even if the planets are aligned almost right, we could be missing out — staring past cozy, Earthlike exoplanets orbiting alongside those hot Jupiter-sized worlds. Unfortunately for any aliens, they face the exact same challenge. An E.T. astronomer might detect Jupiter while overlooking Earth entirely.
After crunching the numbers, Wells and his collaborators estimated that, in addition to the nine hot gas-ball worlds (and many more similarly unpromising neighbors), there are 10 potentially habitable worlds located where Earth would be visible to any aliens there using the kinds of telescopes and related equipment that we now use.
And experts say there’s no reason to assume that E.T.’s astronomy tools are as primitive as our own.
“An alien civilization is unlikely to be technological lock-step with us,” says David Kipping, a Columbia University astronomer who is known as a leading planet hunter. “Most likely they are either far less or far more technologically advanced. They may have used the transit method for a while but since moved on to more advanced techniques.”
If so, all bets are off about where Earth-spying aliens might be located. They could be watching us from any part of the sky. And depending on the level of their technology, they could know a fair bit about us.
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Some scientists have speculated that extraterrestrials could detect industrial chemicals in Earth’s atmosphere or the glow of artificial lights at night, revealing that our planet has a technological civilization. If the E.T.s are less than 100 light-years away, our radio broadcasts will have had time to reach them.
“And if the aliens have really huge optical telescopes, it’s conceivable they might see structures such as the highway systems or cities,” says Seth Shostak of the SETI Institute, which is dedicated to the search for intelligent life beyond Earth.
Astronomers here on this planet are working hard to achieve those kinds of capabilities. They’ve proposed building the Habitable Exoplanet Imaging Mission (HabEx) as a successor to the Hubble Space Telescope. With a mirror up to 32 feet across and specialized technology to single out the dim glow of distant planets, HabEx would be capable of detecting Earthlike worlds around nearby stars and scanning them for signs of water, as well as for potential indicators of life like oxygen and methane gas.HabEx Vehicle – StarshadeNASA / JPL-Caltech
If approved by early next decade, HabEx could launch by the end of the 2030s.
At that point, humans, too, would be liberated from the limitations of transits, capable of finding Earthlike planets all around without relying on the luck of a happy alignment. Even then, though, there’s no guarantee that we’d be able to detect the same aliens who could already be looking at us. Maybe they don’t want to be found.
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“Advanced civilizations would have no trouble cloaking even the very signatures of life on their planet from our current telescopes by using a simple laser system,” Kipping says. “Our remote-sensing abilities, impressive as they may seem, could be quite basic and easily thwarted.”
Someday, maybe, extraterrestrials really will make contact. But it may not happen until they like what they see.
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