Scientists at Harvard University have recently suggested that intelligent life forms in another galaxy may have used interstellar spacecraft billions of years ago. Their paper, co-authored by Manasvi Lingam and Abraham Loeb and entitled ‘Fast Radio Bursts from Extragalactic Light Sails’, has just been published in The Astrophysical Journal, and can be read for free here.
Lingam and Loeb’s paper suggests that some fast radio bursts (FRBs), which were discovered in 2007, may have been caused by aliens powering interstellar spacecraft. This idea was first suggested in 2014.
FRBs are bursts of light in the radio spectrum that we have found emanating from other galaxies. They are unlike other bursts that have previously been found and scientists generally thought that they were made by one-off events like when a neutron star collapses into a black hole, however in 2012, eleven FRB were shown to come from the same location, showing that whatever was causing these bursts we not destroyed by them[5a].
The 2012 FRBs were found to be located in a dwarf galaxy that is about 3.2 billion light years away. This means it has taken the light about 3.2 billion years to reach us, and so the beams were originally sent when the Earth was just over a billion years old, before the atmosphere contained oxygen, and well before the first multicellular life had formed.
Just over a dozen other FRBs have been discovered in other galaxies, but these do not repeat and so it is thought that these are more likely to be natural.
No one knows what’s creating them, and suggestions include the idea that they come from magnetars – extremely magnetic neuron stars[5b] – or flaring main-sequence stars. It is certainly possible that they have a natural origin that we don’t yet fully understand, and this has been the case for every strange extraterrestrial signal scientists have found so far, but it is also possible that they are artificial.
Lingam and Loeb look at what this artificial beam could be for, and what we can expect to happen next if this were true. They showed that bursts like this could be caused by light transmitted from a planet, which could be used to power a solar sail. Solar sails are sails that are pushed by light in space in a similar way to how boat-sails are pushed by the wind in the atmosphere. Both can be used to power ships.
Lingam and Loeb found that bursts like those found in FRBs could be created if the light burst was generated on a rocky planet about twice the size of the Earth in order to power a sail carrying almost a million tonnes. This is a mass about 20 times the size of a large cruise ship. They showed that it was possible to build a device like this if it was cooled with water, and that these sails should be able to achieve relativistic speeds.
In order to work, the beam would be on continuously, and we would see flashes of it as it moves relative to the Earth.
Lingam and Loeb suggest that a device like this can be used to carry passengers between stars or possibly even across galaxies. It’s also possible that they are used as ‘beacons’ to broadcast their location or for some purpose that we don’t understand.
While their ideas seem extremely speculative, Lingam and Loeb’s hypothesis is scientific because it can be falsified. This means they show how it could be proven wrong.
Lingam and Loeb claim that their theory can be tested by looking at the shape of the pulse of light from FRBs, where the sail would cast a shadow on the beam. Calculations show that an FRB appears in each galaxy every few hundred years and Lingam and Loeb suggest that a repeating FRB in our galaxy would not only be spectacular, but should be close enough to allows us to get a much better grasp on its origin. They also suggest that as our technology advances, we will be able to find evidence of lower energy solar sails.
Lingam and Loeb suggest that we should use systems like Breakthrough Listen in order to search for evidence of alien life in the vicinity of FRBs. If we were to send them a message, however, then it would take billions of years to get there, and billions of years for them to send a message back.