杏吧原创

The truth is out there (Image: Universal/Everett/REX)

A report that bursts of radio waves from the distant universe exhibit a weird mathematical pattern have freshly raised hopes that ET might be signalling us. But what鈥檚 really behind it? Here鈥檚 our ET FAQ.

1. Is this the first time we think we might have found aliens?
Nope, there have been several false alarms. The most famous is the 72-second Wow! signal, so called because an eager astronomer wrote 鈥淲ow!鈥� next to it on a printout from the Ohio State Big Ear Telescope in 1977. It didn鈥檛 seem to be of this Earth, but it was never seen again.

A few years before that, astronomer Jocelyn Bell thought she may have found the beep-beep-beep of 鈥渓ittle green men鈥� when she had actually discovered , the rapidly rotating corpses of stars that sweep a lighthouse-like beam of radiation as they spin. In the 70s, astronomers thought a Citizen鈥檚 Band radio could be ET, and flagged the as a possible signal in the 90s. But their double, triple and quadruple-checking rules meant they found the real culprits before making any announcements.

SETI software now weeds out false alarms pretty fast on its own, and there haven鈥檛 been any major maybes in more than a decade 鈥� until now, perhaps.

2. Could the bursts have natural causes?
Fast radio bursts could have a natural, rather than an artificial, flavour. If a star in our galaxy had a massive flare-up, and the radiation had to tunnel through a bunch of cast-off plasma, the signal could look like it came from much farther away.

Also, if two white dwarf stars 鈥� the kind of dead sphere our sun will turn into in a few billion years 鈥� crash into each other, they explode in a supernova. That blast could release a fast radio burst.

Then there are neutron stars. If two neutron stars 鈥� the dense cores of collapsed stars 鈥� are about to collide, they might release a radio burst right before they violently merge into one. Alternatively, some neutron stars are so massive that they should have collapsed into black holes, but are rotating too fast to do so. If one of these slows down, it will finally form a black hole, maybe blasting out a burst before it disappears forever.

Still, these don鈥檛 account for the fast radio bursts鈥� pattern according to any physics we know now.

3. How will we figure out if the creepy pattern is real or not?
First, scientists will have to discover more bursts using lots of different telescopes. Based on how much of the sky telescopes stared at and for how long before we found the 10 known bursts, scientists estimate that 10,000 bursts happen every day. Watching the whole sky all the time we鈥檇 catch every one of them, but right now we make discoveries when a scope happens to be pointed at the right place at the right time.

Either these new bursts will fit within the same pattern, adding to the eeriness, or they won鈥檛. If not, case closed. But, assuming they match up, we can see if they fit any earthly patterns, like appearing at the same parts of the day-night cycle or aligned with our seconds or minutes, which might imply an earthly origin. This may already be throwing some water on the discovery: the researchers published an on 30 March suggesting that the signals might arrive according to UTC times, which aliens are unlikely to know about.

4. If it鈥檚 really a signal from ET, how will we know what they鈥檙e saying?
Google Translate! Just kidding. For the bursts we鈥檝e already seen, we鈥檒l have to dig around in the existing data 鈥� which tells us how strong the radio waves were, at which frequencies, at what times 鈥� and see if anything is encoded besides 187.5. In the future, we could try to record more information about the bursts, to see if extra signals are embedded.

Some SETI scientists think it could take us centuries to decode any message we received. We won鈥檛 have a common language, a common culture, or even common sensory organs. For a while, we may have to be happy to assume they鈥檙e just saying 鈥淗ello!鈥�

5. How else can we find ET?
Rogue radio broadcasts are the traditional signs astronomers look for from aliens 鈥� basically because these are the easiest to spot 鈥� and specifically, those from known exoplanet systems. The currently does this sort of work from northern California. But search options expand as our technology gets better. As astronomer Jill Tarter is fond of saying, 鈥淪ETI scientists always reserve the right to get smarter.鈥�

We could also look for signs of atmospheric and light pollution on other planets, to see if ET is as environmentally unfriendly as we are. We can look for that, as far as we know, the universe doesn鈥檛 create naturally, but which humans 鈥� and perhaps aliens 鈥� can generate. And aliens who harness their star鈥檚 energy in a super-evolved version of solar panels called a Dyson sphere would leave a heat signature we could see from far away.

6. What is the most likely explanation?
The only thing we know for sure about fast radio bursts 鈥� and this potential pattern 鈥� is that they鈥檙e telling us we don鈥檛 understand something about the universe. Maybe what we don鈥檛 understand is that we have cosmic cousins. But more likely, we鈥檙e missing something fundamental about how pulsars work or what our own satellites are doing. Either we鈥檒l learn something about physics, or we鈥檒l learn something about interstellar biology. It鈥檚 win-win.