The night sky taunts astronomers. Filled with countless points of light and visions of deep cosmic beauty, it tempts us to reach out into the cosmos. Yet most of it, almost everything we see, remains far beyond our grasp.
That’s not to say we haven’t tried. Since the dawn of the space age probes have succeeded in reaching most of our solar system. We’ve travelled to the Moon, seen Jupiter up close, passed through the rings of Saturn and gone beyond, to the frozen edge of interstellar space.
Even with these successes, though, the stars have always been out of reach — but perhaps not out of our imaginations. Several dreamers have thought up ways to reach Alpha Centauri, the closest star to our own. Some imagine star ships voyaging for millennia through the depths of space. Others wonder if we could warp the very fabric of the Universe, travelling through the galaxy at the speed of light.
These ideas are impractical, at least for now. And even if we were to launch a probe towards Alpha Centauri tomorrow, using the very latest technology, it would be obsolete long before arrival. Other probes built with futuristic propulsion systems would undoubtedly overtake it during its thousand year voyage. Better, then, to wait for technology to advance, and leave the stars to our dreams for now.
One billionaire disagrees with this sentiment. Yuri Milner believes that we are on the cusp of developing technology that would put nearby stars in reach. So sure is he in his belief, in fact, that he has committed a decent chunk of his fortune towards developing this vision of the future. His project, Breakthrough Starshot, might sound like the typical delusions of a clueless tech billionaire. But maybe not. Yuri Milner has a track record, and it is impressive.
In his youth, spent in the USSR, Milner was a physicist. He studied at one of the leading Soviet research centres, but, deciding not to continue in physics, turned to business. He went first to America, studying at the Wharton School, and then took a job at the World Bank.
While he was gone, Russia underwent profound change. The collapse of the Soviet Union and the end of communism opened up new opportunities for those willing to grab them. At the same time another revolution was happening in America — the dawn of the Internet. For Milner, now back in Russia, the future lay at crux of the two revolutions.
Ten years and a string of successful start-ups later, Milner returned to America as a wealthy man. He invested in two new firms promising a new revolution — Facebook and GroupOn, and quickly made another fortune. His wealth allowed him to pursue other interests — especially the fundamental sciences. In 2012, after a move to California, he established the Breakthrough Prize, dedicated to ground breaking research.
Unlike the formal Nobel Prize ceremonies the award-givings of the Breakthrough Prize are glitzy Hollywood affairs. Crowds of billionaires and celebrities attend the events, which, with millions of dollars in prize money, have become the largest scientific prizes in the world.
Three years after launching the Breakthrough Prize Milner followed up with Breakthrough Initiatives. Again the project was star-studded, with Stephen Hawking leading the announcements. The ceremony launched three programmes— Listen, Message and Starshot. All, in some way, relate to humanity’s place in the wider universe.
Listen and Message focus on the hunt for signs of alien civilization, and on finding ways to contact them. As part of Breakthrough Listen, Milner has invested one hundred million dollars into a series of new astronomical observatories. These are dedicated to searching for alien signals, similar to the older SETI projects.
Traditional searches for alien signals have focused on hunting for deliberate radio signals sent by aliens. But the approach suffers from many drawbacks. For one, the search space is enormous. A signal could come from any direction, broadcast on any frequency, at any time. The chances of finding one by luck are astronomically small. Despite decades of searching, no confirmed alien signal has ever been found.
To overcome these problems, Breakthrough Listen has changed the approach. Instead of radio waves, the project is also focusing on laser signals, which an advanced civilization may prefer for communications. Non-deliberate signals are also included in the search. We may, for example, see flashes of light from igniting spacecraft engines, or signs of engineering projects reshaping entire solar systems.
Two recent events caught the attention of alien hunters — strange light patterns coming from Boyajian’s Star, and the brief presence of Oumuamua, an asteroid of interstellar origin passing through the Solar System. Breakthrough Listen dedicated resources towards the two objects. In both cases the search focused on artificial signals, either laser or radio based. Nothing of interest has been discovered so far, but Milner is already preparing for the next strange discovery.
With such a track record, Milner’s ambitions to reach the stars may seem a little less outlandish. Even so, it’s hard not to be impressed by the scope of his ambition. Starshot, the third leg of the Breakthrough Initiatives, looks at nothing less than reaching the stars.
Milner’s approach is to build a fleet of tiny spacecraft, each less than an inch across and weighing a few ounces. Intense lasers will power the probes to a fifth of the speed of light — putting a dozen stars with fifty years journey time from Earth.
The small mass of the proposed spacecraft is vital. Lightweight probes need much less time and energy to reach high speeds, and are cheaper to build. In principle Milner could construct thousands of spacecraft for the price of a normal Mars-bound probe.
That mass production is vital — high speed interstellar flight is incredibly dangerous. At close to the speed of light even a collision with a single grain of dust can result in an enormous explosion. By sending a large enough fleet Breakthrough Starshot hope that at least one would be lucky enough to survive the journey.
Spacecraft usually need to carry heavy fuel with them. Opportunities for refuelling in space are rare, so a probe must ensure it has enough fuel before launching. This is hard for tiny nanoships — which can barely carry any fuel at all. Instead Milner wants to equip them with solar sails, allowing them to use sunlight as fuel.
A solar sail is basically a large mirror. Place one in space, and it will slowly start moving away from the Sun. This effect, caused by sunlight bouncing off reflective surfaces, provides a small, but steady, acceleration. Researchers have already flown several experimental missions, but the force of sunlight is so weak that solar sails have found little practical use so far.
Milner’s plan is to replace sunlight with something much more powerful: intense lasers. With a powerful enough laser, studies suggest sails a few feet across could reach a fifth of the speed of light. The solar sail turns out to solve another problem too — they can be used as antennas to send signals back to Earth.
In principle all this sounds possible, although much of the technology is still in the development phase. Progress is needed in solar sails, in communications, in laser technology, and in miniaturisation.
Even with the technology, the engineering effort required is immense. The lasers needed to power the nanoships would be the biggest ever built. Each would need its own power station, and would use as much electricity as a small city.
The problems don’t end there. The sails must be extremely reflective — otherwise the intense laser beams would vaporise the small ships. We don’t yet have materials that can do that, and we don’t even understand physics well enough to say if such materials are possible.
The powerful lasers required are another problem. Such intense lasers, if they were ever built, could become dangerous weapons. Capable of burning entire cities, they would undoubtedly be watched carefully by military powers. If they were ever seized for use in war, the consequences could be horrific.
These, though, are problems for the future. Milner’s current aim is to kick-start the research, and get smart people thinking about what is possible. To that end Milner is considering other exploration projects that may return useful data.
In his sights are the various water worlds discovered in recent years in the outer Solar System. Scientists have recently speculated that some of these places — notably Europa and Enceladus — may host primitive life forms. Until now missions to such places have been funded by national agencies like NASA or ESA. Milner thinks he might be able to fund a cheap scientific mission to one, perhaps Enceladus, himself.
In this kind of mission the real benefits of Breakthrough Starshot can be seen. Even if the science and engineering needed to power tiny spacecraft to nearby stars turns out to be infeasible, it could perhaps be adapted. Smaller lasers, and less advanced probes, could be used to reach the outer solar system. At the moment reaching distant plants like Neptune can take decades. Laser powered solar sails could cut that travel time drastically.
The nature of space exploration is already shifting. Space agencies are planning a new generation of missions utilising ever smaller satellites. Could the next step see them truly embrace miniaturisation? Could we soon fill the solar system with fleets of laser powered nanoships? If we do, we will win unprecedented views of our neighbouring worlds, and maybe, just maybe, find alien life.