Fast-than-light travel, instantaneous communication, terraforming. Science fiction relies on imaginative physics ideas to enrich its stories. Some of these are pure fiction, while others are closer to fact than you might expect. Which is which?
Faster-than-light travel probably won’t work
Perhaps no concept is more foundational to modern space fiction than that of faster-than-light (FTL) travel. After all, exploring a galaxy even at lightspeed takes prohibitively long for any narrative. In the time it takes the Enterprise to travel to a new planet each episode, any characters not on the ship have aged and died.
The proposed mechanics of FTL vary across sci-fi properties, but many authors (George Lucas, Douglas Adams, Martha Wells, CJ Cherryh…) use the vocabulary of wormholes and hyperspace. Both of these refer to real, physical solutions to Einstein’s equations.
In fact, many physicists suspect that if we fully understood gravity, these solutions would be impossible. Einstein’s equations fail to describe gravity at the atomic scale, for example. A theory that encompasses quantum gravity as well as macroscopic gravity might make wormholes impossible.
Right now, though, Einstein’s equations are the best we have. And while they allow wormholes, further calculations suggest that it’s probably impossible to travel through them. This might be a good thing, considering the eldritch horror of getting stuck in hyperspace, as depicted in CJ Cherryh’s haunting sci-fi novel Port Eternity, where a spaceship drifts forever through hyperspace darkness while unknown creatures knock on the walls.
But there is a property that uses an FTL mechanism closer to reality: Star Trek. In fact, physicist Miguel Alcubierre cited Star Trek in his seminal paper on an object now known as an Alcubierre drive. This shortens the space in front of a ship in the same way gravitational waves do. With an Alcubierre drive, a spaceship doesn’t actually move faster than light, and so doesn’t violate any laws of general relativity.
The catch? How to make a machine that can contract and expand spacetime. Alcubierre showed that it fits mathematically into Einstein’s laws, but only if it uses matter with negative mass as fuel. Right now, most physicists suspect such peculiar matter does not exist.
Still, Star Trek gets closer to feasible FTL than most other sci-fi properties. Take that, Star Wars.
The front page of the NYT on May 4, 1935, dramatized Einstein’s philosophical concerns with quantum entanglement, often proposed as a tool for FTL communication. His co-author leaked their upcoming paper on quantum to the NYT, and Einstein reportedly never spoke to him again. Photo: Wikimedia Commons
FTL communication is also a no-go
Very few pieces of space fiction depict worlds without faster-than-light travel. The first book in the peculiar Bobiverse novels, whose major characters are all clones of one human-turned-AI, does show its protagonist colonizing the universe without FTL, but the process takes centuries. In Cixin Liu’s novel The Three Body Problem (now a Netflix series), humans buy precious time to prepare for an alien invasion thanks to the aliens’ sub-light travel speed. And in the early Ender’s Game novels, the eponymous Ender spends enough time on sub-light spaceships that he’s still alive 2,000 years after the first book, thanks to time dilation — at which point he is universally reviled.
All of these authors, though, cave on the point of FTL communication. Despite the laws of physics being just as firm on superluminal Zoom as they are about superluminal spaceships, the allure of real-time conversations seems too much for science fiction authors not to take advantage of.
When authors try to work in FTL communication, they often appeal to the phenomenon of quantum entanglement — where particles become linked together so that they share the same fate, no matter how far apart they are. Entanglement is so bizarre that Einstein, in the throes of his philosophical war on quantum mechanics, famously called it “spooky action at a distance.”
Quantum mechanics predicts that two particles can be connected so that any measurement of one also tells you the state of the other. For instance, imagine an atom with zero intrinsic angular momentum, or spin, decays into two smaller particles. We measure one of them and find that it’s spin points in the upward direction. Since we started with no spin, we know that the other particle’s spin has to cancel this out. It must have a downward spin.
The pioneer of quantum photonics, John Stewart Bell, described entanglement in reference to a quirky coworker of his, Reinhold Bertlmann. “Dr. Bertlmann likes to wear two socks of different colors. Which color he will have on a given foot on a given day is quite unpredictable,” wrote Bell, in an excellent and accessible essay on entanglement. But when you see, illustration below, that the first sock is pink, you can already be sure that the second sock is not pink.”
Mr. Bertlmann’s socks and the nature of reality, or Fig. 1 from Bell’s essay on entanglement. Photo: JS Bell
Bertlmann’s socks, of course, are simpler than quantum entanglement. If you turn around and give his socks a moment, they won’t randomly switch color. Quantum systems, though, do. You can measure one decayed particle at 9 am, find that it has a downward spin, and then come back after lunch only to find its spin has switched direction. The one thing you know is that at each point, the other particle will have the opposite spin.
It’s surprisingly easy to test this in a lab. Entangled photons and electrons are bizarre, but totally real. Physicists have even managed to entangle millimeter-sized diamonds.
If whatever happens to one particle affects the other, Einstein reasoned with skepticism, then wouldn’t entanglement allow FTL communication? For instance, the pure act of measuring a quantum system collapses it into a classical system, without all the mucky probabilistic behaviors of quantum.
Say the Greek hero Theseus has one half of an entangled quantum system and gives the other to his father. They agree that if Theseus survives his fight against the Minotaur, he will measure his half of the system, thereby collapsing the half in the care of his father into a classical system as well. The transfer of information is instantaneous. Theseus enacts spooky action at a distance.
But there’s a problem. In order to check whether his half of the entangled system has collapsed, Theseus’ father has to measure it. Doing so would collapse it. His father has no way of knowing whether Theseus’ observation or his own has changed the system. No matter what, it looks as though Theseus lives. This goes to show that if the ancient Greeks had only had quantum theory, everything would have turned out all right for Theseus’ father.
Collapsing a quantum state is only one of many proposed mechanisms for FTL communication via entanglement. But the “no-signaling theorem,” provable with relatively simple mathematics, outlaws all of them. The very act of measurement breaks the entanglement, and each half of the system joins its surrounding environment, independent of the other half. Trying to communicate across quantum entanglement is like sending a letter via a beautiful, fast carrier pigeon that happens to drop dead if you tie anything to its feet.
Terraforming is not instantaneous
In Star Trek II: The Wrath of Khan, the enigmatic antagonist searches for a terraforming mechanism called the Genesis Device, which remakes planets in minutes. No such device exists, and no serious physicists or biologists propose to make one.
But the idea of turning a lifeless planet into a life-bearing one does have legs. The core questions of astrobiology are: How does life form, and how rare is it? Research on these topics naturally leads to the suggestion, either as a thought experiment or a policy proposal, that we attempt to create it ourselves.
We’ve reported before on proposals to breed specialized microbes capable of surviving on Mars and eventually giving rise to algae. But perhaps the biggest barrier to Martian terraforming relies not on biologists but on physicists to solve it. Life on Earth only exists because of our planet’s magnetic field, and Mars has none.
Every second, tens of thousands of dangerous particles pummel our atmosphere. Called cosmic rays, these particles — primarily electrons and light atoms — originate in the Sun, in the explosive deaths of stars, and even in distant black holes. Their births are violent. They accelerate to nearly the speed of light and shoot through anything in their way like a bullet.
That includes human cells. But fortunately, the Earth’s magnetic field gently ushers cosmic rays to the Poles, where they either cascade down to Earth or join the solar wind. Unless you’re a researcher at the Amundsen-Scott South Pole Station, you don’t have to worry about cosmic rays.
But you would on Mars. So would any hopeful plant life trying to get a foothold on the red planet. Physicists, however, are already tackling the issue of an artificial Martian magnetic field. One team found that “the most feasible design is to encircle Mars with a superconducting wire with a loop radius of about 3,400 km” and running a current through it to create a magnetic field. Making this wire would only require mining 0.1% of Olympus Mons(!)
Both the microbial and the magnetic components of terraforming are potentially feasible. But neither one is the instant Genesis Device from Star Trek. Granting algae a toehold on Mars would take decades, and full-fledged forests would come centuries later. And no matter how we would create a magnetic field for a planet, it would take massive amounts of labor.
Real-life terraforming
Terraforming research has picked up in recent decades, as climate change looms ever-larger in the minds of many scientists. It’s tempting to hear the phrase, “There is no Planet B,” and ask: But what if there was?
There could be. But terraforming a new planet, while feasible, would be slow and painstaking.
In fact, terraforming is already occurring in small controlled experiments on Earth. Scientists have begun using salt-based aerosols to deflect sunlight. After successful tests, one team has even begun using them over the fragile, floundering Great Barrier Reef.
Experiments like these are deeply controversial but are gaining traction as the effects of climate change become more apparent.
Solar-deflection aerosol engines look like something out of the planet-creation scene in The Hitchhiker’s Guide to the Galaxy. But they’re real, and unlike in Hitchhiker’s Guide, they’re happening on the only Earth we have.
Aerosol scientist Daniel Harrison and technician Stuart Maclennan operate their aerosol machine over the Great Barrier Reef. Photo: Adam Ferguson
