Kate Becker The Visible Universe
Kate Becker The Visible Universe

Imagine that you're an engineer. (Actual engineers: skip this step and move on to the next one.) You want to send a spacecraft to another star. It's a long trip, and you'd like to still be alive when the ship gets there, so you need a way to get it going fast: close to the speed of light would be great, you think. But you don't want to weigh the ship down with heavy propellant.

Did I mention that you are a technologically-advanced alien?

Since you're an alien, you have access to power sources that make Earth's best and brightest lasers look like a kid's nightlight. You also have advanced nanomaterials that you use to make super lightweight foil fabrics, just hundreds of atoms thick. Heck, your underwear is made of the stuff. (You may be an alien, but you still have your dignity.)

So what do you do?

You make a giant nanofabric sail and strap it to your spaceship. Then you power up a beam of light — perhaps a laser, perhaps something that gives off energy all across the electromagnetic rainbow — point it at the sail and let the pressure blow on the "light sail" until, gradually, your ship builds up the velocity it needs to get to the nearest star some time before your AAARP (that's the Alien AARP) membership card arrives in the mail.

Now, imagine that you're a human astronomer. You may be stuck on Earth, but you like to dream about ways to send spacecraft to other stars. Maybe you even chair the advisory committee for a plucky project called Breakthrough Starshot, which is putting $100 million into building up the technology required to sail postage-stamp-sized "nanocrafts," accelerated by an array of synchronized laser beams, to Alpha Centauri.


Because you are an astronomer, you are aware of a mystery blooming within your field: The unexplained origin of fast radio bursts, or FRBs, which are, as their name suggests, very brief bursts of radio waves. They are extremely powerful, last just milliseconds, and seem to be coming from beyond our galaxy. What's causing them? Astronomers are still guessing.

But if you happen to be that human astronomer we were speaking of — and, by the way, your name is Avi Loeb, and you are chair of the Harvard astronomy department — you might get together with your Harvard colleague Manasvi Lingam and try to connect these two scientifically juicy dots to make one very speculative hypothesis: Perhaps FRBs are actually the power source for alien light sails, momentarily pointing Earthward as they nudge their spaceships from star to star.

Lingam and Loeb figured that, to make a radio transmitter capable of generating FRB-style signals, aliens might harness solar energy and beam it out using a planet-sized collector and transmitter. A set-up like this could propel an enormous spaceship — "an 'interstellar ark' or 'world ship' of sorts," they write — through space.

It's a diverting long shot. But it's also testable, Lingam and Loeb point out. Lightsails would cast a shadow across the beam that drives them, and that shadow should leave a measurable impression on the radio signal astronomers detect at Earth. Fewer than two dozen FRBs have been recorded so far, but as the tally grows — and it will, especially with a much-anticipated new telescope called CHIME (Canadian Hydrogen Intensity Mapping Experiment) coming online — astronomers will have more opportunities to scrutinize the signals for these lightsail shadows.

The odds that this wild hypothesis will turn out to be right probably compare unfavorably with my odds of winning the lottery tomorrow. But you don't always play the lottery to win. Sometimes you play just for fun, and the thrill of dreaming: What if?

Kate Becker is a science writer living in Boston. Contact her at spacecrafty.com, or connect via facebook.com/katembecker or twitter.com/kmbecker.