The Stars Are Too Far Away For Mortals.

Why immortality, not faster-than-light travel, may be the true price of becoming an interstellar species.

Imagine being offered a place aboard humanity's first interstellar spacecraft. Another sun awaits, but everyone you love may be gone before you reach it. Would you still go?

This is less a scientific question than an intensely personal one. Your answer depends on the life you have built and the people you love here on Earth. Put like that, it is hard to imagine anyone accepting the ticket. Yet humanity's story has always been one of discovery, often at a formidable personal cost.

Why Explorers Have Always Paid a Price

What persuaded Polynesians in 3000 BCE to sail thousands of miles across the open Pacific? Exploration was deeply woven into their spiritual and social systems. Navigators enjoyed elite status, and discovering new lands brought enormous prestige to them and their families.

The Real Math of Reaching Alpha Centauri

Early explorers might spend years away from home, but travelling to the stars belongs to another category entirely. Our nearest neighbouring star system, Alpha Centauri, is so distant that even light takes about 4.3 years to cross the gap. Let us be honest: with contemporary propulsion, interstellar travel without faster than light is not a journey that fits into a human life. A chemically powered rocket launch, followed by planetary gravity assists, could give a spacecraft an outward speed of roughly 17 kilometres per second, as Voyager 1 has achieved. The engineering is realistic. Unfortunately, so is the resulting journey time: approximately 77,000 years.

Science Fiction's Favourite Cheat: Faster-Than-Light Travel

This is awkward news for any science-fiction writer with a galactic empire to run. The heroes still need to save the day, preferably within a couple of years rather than several millennia. So what is science fiction's favourite escape route? The answer is wonderfully convenient: break the laws of nature until the journey fits the plot. To make interstellar adventures manageable, we need to cross light-years in days. Enter the warp drive, the mysterious leap through hyperspace, or the obligingly positioned wormhole. The machinery varies, but the requirement does not: we must travel faster than light. So why can't we? Unfortunately, we have the wrong universe. Physicists call flat spacetime Minkowski space, and it comes with an awkward constraint: faster-than-light travel can allow the order of cause and effect to be reversed.

The Physics Problem With Breaking the Speed Limit

Let us follow that thought into its natural habitat: the time-travel paradox. Suppose a traveller visits the past and prevents their grandfather from having children. The traveller is then never born, which makes it rather difficult to explain who made the journey.

The Back to the Future films turn this problem into excellent entertainment: the hero meddles with the past, returns to find an altered present, then heads back again to arrange a future more to his liking. In this version of time travel, once you start changing events, even by doing something as innocent as breathing the air, you create a new timeline, and everything is up for grabs. A new world branches off at that moment. Science offers no tidy resolution here. Our local theory of gravity admits solutions containing so-called “closed timelike curves”, which connect a traveller's future with their own past. One response is to invoke a many-worlds picture; another is to reject such solutions as unphysical, excluding scenarios that produce the grandfather paradox.

The film 12 Monkeys explores a world in which history refuses to be rewritten. In a future ravaged by a virus, a convict is sent into the past to gather information that might help those still struggling with its consequences. He is not supposed to interfere: the future has already happened, and trying to change it would be futile. Nevertheless, he becomes determined to stop the virus, and meets his end before he can alter its course.

What are we really doing here? We desperately want galactic civilisations to play out their dramas within our brief human lifespans, and we are prepared to break the universe to make the timetable work.

What If We Changed the Traveller Instead?

I would like to suggest a different bargain: what if we changed the traveller instead?

What would a traveller built for the journey between the stars need? They would need a body that does not age, with extraordinary powers of healing and endurance to withstand millennia of hazards, including radiation. They would need a mind capable of surviving centuries of isolation aboard a tiny spacecraft. And they would need to accept that Earth might be unrecognisable by the time they returned. Seen in this light, immortality looks less like the happy ending promised by eternal youth and more like an evolutionary step. An immortal traveller could reach the stars, but would repeatedly lose friends, family, languages and entire civilisations along the way. Would such beings still call themselves human, or would they have evolved into something entirely different?

Immortality in First Light Rising

In my novel First Light Rising, Tom Wright stops ageing at twenty-four. To the governments pursuing him, he is a medical miracle and a strategic asset. Measured against the distances between the stars, however, his condition may have an entirely different purpose. As the world approaches war over the secret of immortality Tom may carry, Saskia Sorensen, his long-time confidant, brokers a truce. She proposes sending him on an interstellar mission, with one condition: he must not return to Earth for 150 years.

Humanity may not become interstellar by building faster machines. Instead, the first true spacefarers may be humans, or beings, whose relationship with time has fundamentally changed.

If immortality gave you the stars but took away everyone you loved, would you consider it a gift, or the price of admission?

Frequently Asked Questions

How long would it take to reach Alpha Centauri with current propulsion?

Using speeds comparable to Voyager 1, roughly 17 kilometres per second, a spacecraft would take approximately 77,000 years to reach Alpha Centauri, far beyond any human lifespan.

Why can't anything travel faster than the speed of light?

Physicists describe our universe using what is called Minkowski spacetime, which imposes the speed of light as an absolute limit. Travelling faster than light would allow cause and effect to be reversed, creating logical paradoxes rather than just engineering challenges.

What is the grandfather paradox in time travel?

The grandfather paradox describes a scenario where a time traveller prevents their own grandfather from having children, making the traveller's own existence, and the journey itself, logically impossible.

Could an immortal human actually survive an interstellar journey?

In theory, a body immune to ageing and radiation damage, paired with a mind able to endure centuries of isolation, solves the timescale problem that makes interstellar travel without faster-than-light impossible for ordinary humans. Whether such a being would still be considered human is a separate question.

Related reading: The Flow of Time and Immortality.