We’re all time travelers.
Granted, we’re not very good at it. We’re only moving in one direction at a fixed rate — but we’re never in the same moment twice. And while time’s arrow seemingly puts spacetime second helpings out of reach, humans have a habit of breaking the rules.
What if we could do an about-face and discover what came before? Or push past our present pace to see what comes next? Astrophysicist Ron Mallett from the University of Connecticut says he’s got the theoretical receipts to take on time travel.
Wondering how to build a time machine? It takes just 4e2Q=X easy steps! Simple, right?
Not all time travel is created equal. While heading back into the past poses a host of problems — such as changing the course of history by altering key events, or encountering your past self and making choices that could lead to your non-existence in the present — moving forward is less complicated. Relatively speaking.
As with most things spacetime related, E=MC2 gets involved. Einstein’s equation articulates the interaction between energy and matter: Put simply, if matter goes fast enough, it becomes energy. It also becomes much more massive the closer it gets to the speed of light, providing a hard stop for objects trying to surpass this universal limit. But the theoretical framework that gave rise to this famous function — special relativity — also includes the fundamentals of future time travel.
Here’s how it works: The faster you go, the greater your mass. And the greater your mass, the greater your disruption of local space — and time. As a result, time passes more slowly for someone traveling near the speed of light than those of us back on Earth. As noted by Scientific American, a spaceship accelerating continuously at one g — equal to the value of gravitational acceleration at Earth’s surface, or 9.81 m/s2 — would approach the speed of light around the one-year mark. From the perspective of an astronaut on the ship, a trip to the center of our galaxy and back would take about 40 years. Upon returning home, however, our intrepid explorer might have trouble reporting their adventure to mission control, unless NASA was still up and running after 60,000 years.
Of course, it’s not quite that easy. The energy requirements for the acceleration described above would be “greater than a planetary mass,” and steering the ship at near-light speed might be problematic. Still, the basic science is there, though it’s worth mentioning a critical caveat: This isn’t the flash-forward in time we’re familiar with when Marty McFly hits 88 miles per hour in his DeLorean. Perceptually, both observer and actor see no change in the passage of time. Observationally, there’s a significant difference.
Fire Up the Flux Capacitor
Professor Mallet is looking the other direction, having spent the latter decades of his career looking for backward-facing loopholes. And while our equation for how to build a time machine is pure nonsense, he’s created one that posits the potential physics of actual travel through time.
By using a ring laser — what he describes as a “circulating beam of laser lights” — he believes its possible to bend both space and time. Do it right, and the machine should be able to bend time back on itself, creating a portal to the past. If this sounds vaguely familiar, it is — Mallett’s machine bears a striking similarity to the concept of spacetime wormholes: Theoretical tunnels of space and time that could let explorers travel across massive volumes of miles and moments in the blink of an eye. Professor Mallett has developed a prototype and hopes to conduct a feasibility study, even as he does more research into the potential mechanics of a time machine at scale.
Keeping the Lights On
Let’s get it out of the way right now: Professor Mallett’s time travel technology won’t head back into the past anytime soon. Information, rather than individuals, will make the trip and hopefully come out unscathed — but where? Or more accurately, when? This is another limitation of the Mallett machine: The farthest information can travel back in time is to the moment the machine was turned on. Turn it off, and you’d have to start over.
There’s also the issue of empirical verification. Let’s say the device turns on this year. You’d want continuous monitoring to ensure that if information arrived you’re ready to capture it and take appropriate action. But if it works, it makes sense that future scientists would send data back to the origin point — so information should arrive immediately after the device is turned on. Or should it?
Physicist Richard Muller doesn’t think so. He argues that the future doesn’t exist — meaning there are no scientists to send data back — and the past is literally a foreign country. For Muller, the intertwined nature of spacetime is responsible: “Every moment, the universe gets a little bigger, and there is a little more time, and it is this leading edge of time that we refer to as now.”
Because we’re on the leading edge of spacetime, nothing exists beyond it so there’s no one to send data back. But it’s all about perspective — what about the “us” of two years from now? If the machine is turned on in 2020, couldn’t scientists in 2022 use the device? Muller says this also isn’t possible because the machine doesn’t simply exist in another time — it exists in another spacetime. “To reverse time you would have to decrease, at least locally, the amount of space in the universe.” Not exactly an easy task.
Time, and Time Again
Whether Professor Mallet’s project works or not is worth watching, but it’s hardly the final word on time travel theory. Human effort to adjust the aim — or outright avoid — the arrow of time won’t stop just because the universe doesn’t like the idea. From pushing particles to near-light speed in high-powered accelerators to work on wormholes, efforts to both backtrack and fast-forward are scientifically inevitable.
Will time travel ever be a reality? In some form, probably. Are we on the road to a picnic in the past or a foray into the future? Don’t pack your bags just yet.