When it comes to physically exploring deep space, pretty much the slowest thing you could ever really do is send a towering hunk of metal weighing about a hundred tonnes into the sky above, thanks to a burning mass of rocket fuel – and yet, that's effectively where today's crewed space travel is at.
But one of the most mind-boggling proposals we've seen to get around these kinds of limitations is the prospect of sending postage stamp-sized spacecraft into space at extremely high speeds via laser propulsion.
And now, one of the researchers behind that project says the same photonics technology could not only transform space exploration as we know it – it could also overhaul the search for extra-terrestrial intelligence.
The idea is that advanced life forms – if they're actually out there and want to be found – could be using the exact same kind of 'directed energy' systems to be broadcasting their presence to us.
Physicist Philip Lubin from the University of California, Santa Barbara, says the type of laser propulsion system backed by Stephen Hawking to send a 'nanocraft' to Alpha Centauri in 20 years could enable us to pick up alien transmissions from anywhere in the Milky Way – and even beyond.
"If even one other civilisation existed in our galaxy and had a similar or more advanced level of directed-energy technology, we could detect 'them' anywhere in our galaxy with a very modest detection approach," said Lubin. "If we scale it up as we're doing with direct energy systems, how far could we detect a civilisation equivalent to ours? The answer becomes that the entire Universe is now open to us."
Describing the technique in a paper soon to be published in REACH – Reviews in Human Space Exploration, Lubin admits there's a lot of 'ifs' involved, but argues that recent advances in photonics at least make the search for laser transmissions now possible.
Likening photonic propulsion to using the force of water from a garden hose to push a ball forward, the physicist says you could basically send anything with the same approach: a small spacecraft, sure, but also a targeted signal between planets, solar systems, or even entire galaxies. If used for communication purposes, directed energy lasers are effectively the same thing as a lighthouse: sending a detectable beam outwards to let others know you're there.
"As a species we are evolving rapidly in photonics, the production and manipulation of light," he said. "In our paper, we propose a search strategy that will observe nearly 100 billion planets, allowing us to test our hypothesis that other similarly or more advanced civilisations with this same broadcast capability exist."
Of course, it's possible that the only life forms out there are simple bacteria or viruses that aren't capable of beaming such an advanced signal. But if any exist at our level of technological know-how – and they're not shy – looking for photonic transmissions could be a much more powerful tool than scanning for radio waves, and might help explain why we haven't detected any communications before.
"And you don't need a large telescope to begin these searches," said Lubin. "Put in context, and we would love to have people really think about this: you can literally go out with your camera from Costco, take pictures of the sky, and if you knew what you were doing you could mount a SETI search in your backyard. The lighthouse is that bright."