Science fiction stories that involve interstellar travel typically contain some method of faster-than-light travel. After all, the spaces between stars are incomprehensibly vast, and no conventional spacecraft could hope to cross these gulfs in anything resembling a timely manner. As such, stars in our own galaxy can feel impossibly distant.
Reasonably speaking, then, what’s the fastest we could get a spaceship moving in the real world? Physics, as we understand, doesn’t offer many promising ways to even get close to the speed of light, let alone exceed that rational upper limit on movement.
But could we find a way to accelerate up to a meaningful fraction of the speed of light?
Enter Freeman Dyson’s Theories
Freeman Dyson, well-known for his Dyson Sphere theory of deep-space megastructures, conceived of a highly advanced civilization that could harness the power of gravity to accelerate their ships to speeds that made interstellar travel feasible within an individuals’ lifetime.
How would they do this, you ask? Let’s talk about slingshot orbits.
In 1977, the Voyager mission used the gravity well of Jupiter for what is known as a “gravitational assist,” or a slingshot orbit. This is a process by which a craft uses a celestial body, like a planet or a star, to drop into a long, looping orbit that then has them exit on another vector with much more velocity.
According to Dyson’s research, a craft could exit a slingshot orbit up to twice the velocity of the celestial body used for the assist.
Going Bigger, Going Faster
Voyager used Jupiter as a springboard to launch itself deep into interstellar space, proving that such a maneuver was feasible. However, to truly put a dent in the time it takes to travel interstellar distances, a craft would need to use a much denser celestial body than a gas giant as its assist. That’s where the Dyson Slingshot comes into play.
Dyson conceived of a theoretical cosmic structure that a sufficiently advanced species could either discover or engineer for the express purpose of slinging their craft into space at high velocities. To be truly effective at interstellar travel, the structure would need to be an orbiting pair of neutron stars.
Binary Neutron Systems
A binary neutron system is two stars, locked in a death spiral on the verge of becoming black holes, held together only by their own neutron resistance. They are among the densest objects in the observable universe, and they orbit one another at an astonishing speed.
A ship with just the right trajectory could use the immense gravity field of such a binary system to accelerate up to a quarter of the speed of light.
This would make interstellar travel more than just feasible. It would allow a vessel to cross the gulfs between stars in a matter of decades instead of hundreds of thousands of years.
The Problems with the Dyson Slingshot
Of course, there are some issues preventing humanity from using a slingshot orbit to fling ourselves out into the cosmos. Firstly, there are no nearby neutron stars. There are certainly no nearby binary neutron star systems. In fact, there aren’t even any nearby binary star systems that could be accelerated into a neutron state.
The second problem with this theory is that the trajectory needed to actually receive a gravity assist from a pair of neutron stars would need to be exceedingly precise. One degree out of place, and your vessel could quickly become a plasmatic film coating the surface of one of the stars as it is pulled in by the gravity well.
Science Fact or Science Fiction?
The very existence of this theory gives credence to the otherwise outlandish notion of interstellar travel. One can envision a hyper-advanced alien species capable of transforming binary star systems they encounter into neutron systems to allow their ships to travel deeper into the cosmos.
They could use a relay of these systems to venture from one end of the galaxy to the other in a matter of centuries rather than millions of years. Such a society would have as close to a mastery of the stars as our current understanding of physics allows.