Photo by: NASA/JPL

NASA/JPL

Is Interstellar Travel Really Possible?

Listen folks, I love a good sci-fi movie as much as anyone. Cruising around the galaxy, finding weird stuff, and blowing up aliens--it’s all good. But just because a writer can come up with something, it doesn’t make it possible. I’m sorry to say that we’re going to be bound to our solar system for a really, really long time. As in, probably forever.

June 03, 2021

Let’s get some perspective. The nearest star to Earth (which is also home to a small rocky world!) is Proxima Centauri, which sits a little less than 4 light-years away. Four. That’s doesn’t sound like a lot, does it? Imagine making a scale model of our solar system. Let’s say in that scale model you put the Earth three feet away from the Sun. In that scale model, Proxima Centauri would sit about 200 miles away.

It took one of our fastest spacecraft, New Horizons, traveling 36,000 miles per hour nearly a decade just to reach Pluto. If it were pointed at Proxima Centuari (and it’s not), cruising at that speed it would get to visit our nearest neighbor in about 25,000 years.

That’s a long trip.

The New Horizons mission is helping us understand worlds at the edge of our solar system by making the first reconnaissance of the dwarf planet Pluto and by venturing deeper into the distant, mysterious Kuiper Belt – a relic of solar system formation.

Photo by: NASA

NASA

The New Horizons mission is helping us understand worlds at the edge of our solar system by making the first reconnaissance of the dwarf planet Pluto and by venturing deeper into the distant, mysterious Kuiper Belt – a relic of solar system formation.

If you want to visit another star system in any reasonable amount of time, you need to go fast. To go fast, you need a lot of energy. And that’s what makes interstellar travel so dang hard.

One proposed for an interstellar spacecraft is called the Starshot Initiative, which aims to shoot a super-powerful laser on a lightsail (a giant nearly perfectly reflecting membrane), using the energy from the light to propel the spacecraft to a tenth the speed of light. That would enable it to reach Proxima in less than half a century.

To make this work, the laser would have to use all the energy from every single nuclear reactor in the United States at once. And it would have to operate for 10 minutes, which is about a quadrillion times longer than we’ve ever operated our most powerful lasers).

Oh, right, and the spacecraft could weigh no more than a paperclip.

Artist's rendering of a four-quadrant solar sail propulsion system.

Photo by: NASA

NASA

Artist's rendering of a four-quadrant solar sail propulsion system.

Nothing about the Starshot is physically impossible. Just really, really difficult and expensive…and using technology that is decades, if not centuries, away from coming to fruition (assuming we even want to develop that kind of technology in the first place).

Sure, there are more fanciful ideas out there, like building wormholes or warp drives. And while those concepts do have their roots in legit physics (most notably, general relativity, our modern understanding of the force of gravity), the reality of their near impossibility is also rooted in physics. If you ever want to build a wormhole or warp drive, you first need to find yourself a healthy amount of negative mass. By which I mean matter that has negative weight. If that sound weird, it’s because it is: we have no evidence that anything with negative mass actually exists in our universe, and we have very good reasons to suspect it can’t.

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I’ll be the first to admit that we don’t know everything there is to know about the physics of the universe, and that technology has a way of quickly going from infeasible to commonplace. So I’m not going to say that interstellar travel is truly impossible…but I’m also not going to hold my breath.

Paul M. Sutter

Paul M. Sutter is an astrophysicist at Stony Brook University and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.

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