We may not be not the universe's first advanced civilization.

That's the conclusion of a recent revision of the famous 1961 Drake Equation, which estimates the number of intelligent civilizations in the universe.

Their new equation includes recent data from Nasa's Kepler satellite on the number of exoplanets that could harbour life.

Researchers also adapted the equation from being about the number of civilizations that exist now, to being about the probability of civilization being the only one that has ever existed.

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The Drake equation (top row) has proven to be a durable framework for research. But it is impossible to do anything more than guess at variables such as L, the probably longevity of other advanced civilizations. In new research, Adam Frank and Woodruff Sullivan offer a new equation (bottom row)

THE REVISED DRAKE EQUATION The Drake Equation is a seven-variable way of finding the chance of active civilisations existing beyond Earth. It takes into account factors like the rate of star formation, the amount of stars that could form planetary systems, the number potentially habitable planets in those systems. But it's now 55 years old, and doesn't include new information from astronomers on the likelihood of life existing on newly-discovered planets. Their new equation includes recent data from Nasa's Kepler satellite on the number of exoplanets that could harbour life. Researchers also adapted the equation from being about the number of civilisations that exist now, to being about the probability of civilisation being the only one that has ever existed. The study shows the odds of an advanced civilisation developing need to be less than one in 10 billion trillion for humans to be the only intelligent life in the universe. Advertisement

The study shows that unless the odds of advanced life evolving on a habitable planet are astonishingly low, then humankind is not the only advanced civilization to have lived.

In fact, the odds of an advanced civilization developing need to be less than one in 10 billion trillion for humans to be the only intelligent life in the universe.

But Kepler data places those odds much higher, which means technologically advanced aliens are likely to have existed at some point.

'The question of whether advanced civilizations exist elsewhere in the universe has always been vexed with three large uncertainties in the Drake equation,' said Adam Frank, professor of physics and astronomy at the University of Rochester and co-author of the paper.

'We've known for a long time approximately how many stars exist.

'We didn't know how many of those stars had planets that could potentially harbor life, how often life might evolve and lead to intelligent beings, and how long any civilizations might last before becoming extinct.'

'Thanks to Nasa's Kepler satellite and other searches, we now know that roughly one-fifth of stars have planets in 'habitable zones,' where temperatures could support life as we know it.

'So one of the three big uncertainties has now been constrained.'

Frank said that the third big question - how long civilizations might survive - is still completely unknown.

'The fact that humans have had rudimentary technology for roughly ten thousand years doesn't really tell us if other societies would last that long or perhaps much longer,' he explained.

But Frank and his co-author, Woodruff Sullivan of the astronomy department at the University of Washington, found they could eliminate that term altogether by simply expanding the question.

'Rather than asking how many civilizations may exist now, we ask 'are we the only technological species that has ever arisen?' said Sullivan.

Pictured is a plot of human population, total energy consumption and atmospheric CO2 concentration from 10,000 BCE to today. Scientists used data such as this to estimate how quickly a civilization might die out

'This shifted focus eliminates the uncertainty of the civilization lifetime question and allows us to address what we call the 'cosmic archaeological question' - how often in the history of the universe has life evolved to an advanced state?'

COULD 50 GALAXIES BE HIDING ADANCED ALIEN LIFE? Last year, scientists said they had found 50 galaxies that may contain intelligent alien races. These galaxies were found to be emitting 'unusually high' levels of radiation - possibly indicating 'the presence of a highly advanced civilisation.' Within these galaxies, the researchers said it was possible that an alien race could be harnessing the power of the stars - emitting huge amounts of noticeable heat in the process. The study was led by Dr Jason Wright from the Center for Exoplanets and Habitable Worlds at Penn State University in Pennsylvania. The Glimpsing Heat from Alien Technologies Survey (G-Hat), published in the Astrophysical Journal, details how the team thought they might see the infrared signature of a race far more advanced than ours. 'The idea behind our research is that, if an entire galaxy had been colonised by an advanced spacefaring civilisation, the energy produced by that civilisation's technologies would be detectable in mid-infrared wavelengths,' said Dr Wright. Advertisement

Rather than guessing at the odds of advanced life developing, they calculate the odds against it occurring in order for humanity to be the only advanced civilization.

With that, Frank and Sullivan then calculated the line between a universe where humanity has been the sole experiment in civilization and one where others have come before us.

'Of course, we have no idea how likely it is that an intelligent technological species will evolve on a given habitable planet,' says Frank.

'But using our method we can tell exactly how low that probability would have to be for us to be the only civilization the universe has produced.

'We call that the pessimism line. If the actual probability is greater than the pessimism line, then a technological species and civilization has likely happened before.'

Using this approach, Frank and Sullivan calculate how unlikely advanced life must be if there has never been another example among the universe's ten billion trillion stars, or even among our own Milky Way galaxy's hundred billion.

'One in 10 billion trillion is incredibly small,' says Frank. 'To me, this implies that other intelligent, technology producing species very likely have evolved before us.

'Think of it this way. Before our result you'd be considered a pessimist if you imagined the probability of evolving a civilization on a habitable planet were, say, one in a trillion.

'But even that guess, one chance in a trillion, implies that what has happened here on Earth with humanity has in fact happened about a 10 billion other times over cosmic history.'

The study shows the odds of an a civilisation developing need to be less than one in 10 billion trillion for humans to be the only intelligent life in the universe. Pictured is an artist's impression of an Earth-like planet

For smaller volumes the numbers are less extreme.

For example, another technological species likely has evolved on a habitable planet in our own Milky Way galaxy if the odds against it are better than one chance in 60 billion.

But if those numbers seem to give ammunition to the 'optimists' about the existence of alien civilizations,

Sullivan points out that the full Drake equation - which calculates the odds that other civilizations are around today - may give solace to the pessimists.

'The universe is more than 13 billion years old,' said Sullivan.

'That means that even if there have been a thousand civilizations in our own galaxy, if they live only as long as we have been around - roughly ten thousand years - then all of them are likely already extinct.

Their new equation includes recent data from Nasa's Kepler satellite on the number of exoplanets that could harbour life. Pictured is an artist's impression of the probe

'And others won't evolve until we are long gone. For us to have much chance of success in finding another 'contemporary' active technological civilization, on average they must last much longer than our present lifetime.'

'Given the vast distances between stars and the fixed speed of light we might never really be able to have a conversation with another civilization anyway,' said Frank.

'If they were 20,000 light years away then every exchange would take 40,000 years to go back and forth.'

But, as Frank and Sullivan point out, even if there aren't other civilizations in our galaxy to communicate with now, the new result still has a profound scientific and philosophical importance.

'From a fundamental perspective the question is 'has it ever happened anywhere before?'' said Frank.

Our result is the first time anyone has been able to set any empirical answer for that question and it is astonishingly likely that we are not the only time and place that an advance civilization has evolved.'