interstellar travel and light speed

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The myths and reality about interstellar travel

Is reaching alien planets outside our Solar System actually possible, and if so, how would it work?

Science fiction writers and moviemakers have shown us countless visions of humanity spread out across the Universe, so you might be forgiven for thinking that we’ve already got this in the bag. Unfortunately, we still have more than a few technical limitations to overcome – like the laws of physics as we understand them – before we can start colonising new worlds beyond our Solar System and galaxy.

That said, several privately funded or volunteer initiatives such as the Tau Zero Foundation , Project Icarus and Breakthrough Starshot have emerged in recent years, each hoping to bring us a little bit closer to reaching across the cosmos. The discovery in August of an Earth-sized planet orbiting our nearest star has also raised fresh hopes about visiting an alien world.

Interstellar spacecraft will be one of the topics discussed at BBC Future’s World-Changing Ideas Summit in Sydney in November . Is travelling to other galaxies possible? And if so, what kinds of spacecraft might we need to achieve it? Read on to get up to (warp) speed:

WHERE WOULD WE GO?

Where wouldn’t we go? There are more stars in the Universe than there are grains of sand on Earth – around 70,000,000,000,000,000,000,000 – and billions of these are estimated to have one to three planets in the so-called ‘Goldilocks’ zone: not too hot, not too cold .

As we’re just starting out, the best contender so far is our nearest stellar neighbour – the triple star system of Alpha Centauri, 4.37 light-years away. This year, astronomers at the European Southern Observatory discovered an Earth-sized planet orbiting Alpha Centauri’s red dwarf star Proxima Centauri . The planet, named Proxima b, is at least 1.3 times the mass of the Earth but has a very tight orbit around Proxima Centauri, taking just 11 Earth days to complete the trip. What has astronomers and exoplanet hunters especially hot under the collar is that this planet is in the right temperature range for liquid water, which is a useful proxy for habitability.

The downside is we don’t know if it has an atmosphere, and given its closeness to Proxima Centauri – closer than the orbit of Mercury around our Sun – it would likely be exposed to dangerous solar flares and radiation. It is also tidally-locked, which means the planet always presents the same face to its star; something that would completely alter our notions of night and day.

HOW WOULD WE GET THERE?

That’s the $64 trillion question.

Upcoming event

The BBC's World-Changing Ideas Summit

This story is part of a series inspired by the subjects and speakers appearing at BBC Future’s World-Changing Ideas Summit in Sydney on 15 November. Find out more about the inspiring people coming to the meeting , including:

• Researcher Rachel Armstrong on organic spacecraft
• BBC TV presenter  Michael Mosley  on the future of food and health
• Uber’s  Kevin Corti  on the hidden patterns of transport
• Scientist and TV presenter Emma Johnston on 'blue engineering'
• Astronauts  Ron Garan  and  Andrew Thomas

 + many more

Breakthrough Starshot – a $100 million initiative privately funded by Russian billionaires Yuri and Julia Milner – is focusing on propelling a tiny unmanned probe by hitting its extremely lightweight sail with a powerful Earth-based laser . The idea is that if the spacecraft is small enough – and we’re talking barely a gram – and the sail light enough, the impact of the laser will be enough to gradually accelerate the craft to around one-fifth of the speed of light, taking it to Alpha Centauri in around 20 years.

The Milners are counting on miniaturisation technologies to enable this tiny craft to carry a camera, thrusters, a power supply, communication and navigation equipment so it can report on what it sees as it flashes past Proxima b. Hopefully the news will be good, because that will lay the foundation for the next and more difficult stage of interstellar travel: people-moving.

WHAT ABOUT WARP DRIVE?

Star Trek made it all look so easy, but everything we currently know about the laws of physics tells us that faster-than-light travel – or even travel at the speed of light – is not possible . Not that science is throwing in the towel. Inspired by another propulsion system that has captured the imagine of science fiction creators, Nasa’s Evolutionary Xenon Thruster project is developing an ion engine which is hoped to accelerate a spacecraft to speeds up to 90,000mph (145,000km/h) using only a fraction of the fuel of a conventional rocket .

But even at those speeds, we won’t be getting far out of the Solar System within a single generation of spacefarers. Until we work out how to warp time and space, interstellar travel is going to be a very slow boat to the future. It might even be better to think of that travel period as the end itself, rather than a means to an end.

HOW WOULD WE SURVIVE ON AN INTERSTELLAR VOYAGE?

Warp drives and ion propulsion are all very sexy, but they’re not much use if our interstellar voyagers starve, dehydrate or suffocate long before they even leave our own Solar System. Researcher Rachel Armstrong, who will be presenting at BBC Future’s World-Changing Ideas Summit in Sydney in November, argues we need to start thinking about the ecosystem that interstellar humanity will occupy out there in between the stars. “We’re moving from an industrial view of reality to an ecological view of reality,” she says.

As professor of experimental architecture at the University of Newcastle in the UK, Armstrong talks about ‘worlding’: “it’s about the inhabitation of spaces, not just the design of an iconic object,” she says. The inside of a spacecraft or space-station today is sterile, and industrial, she argues. Armstrong believes we instead need to think ecologically about our vessels – about the vegetation that is grown, and even the kinds of soils we take with us. In the future, she envisages giant biomes, full of organic life, not the cold, metal boxes of today .

CAN'T WE JUST SLEEP ALL THE WAY THERE?

Cryosleep, hibernation or some form of stasis are favoured solutions to the prickly problem of how to keep people alive on a voyage that might take longer than a human lifespan (a subject explored in the upcoming movie Passengers ). A facility full of cryopreserved bodies and heads at the Alcor Life Extension Foundation are testament to human optimism that we will one work out how to safely freeze and thaw humans , but again, no such technology currently exists.

One suggestion, which is explored in movies such as Interstellar and books such as Neal Stephenson’s Seveneves, is to send frozen embryos that could – presumably – survive those hardships by virtue of not needing to eat, drink or breathe. But this raises the very ‘chicken and egg’ problem of who would raise these fledgling humans when they arrive at their destination.

SO, WILL IT ACTUALLY HAPPEN?

Probably not in the lifetime of anyone old enough to read this article, but in the longer term, there’s cause for optimism. “From the outset of human existence we’ve looked up at the stars and projected our hopes and fears, anxieties and dreams there,” says Armstrong. And with the launch of projects to tackle the engineering, such as Breakthrough Starshot, “this is no longer just a dream, this is an experiment now”.

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