Sci-Fi Visions: Explaining the Modern Science Behind Futuristic Tropes

n the 1985 classic film Back to the Future, teenaged Marty McFly travels back in time and almost ruins his own future, accidentally disrupting his parents’ first meeting as teenagers. However, as one 2020 paper reports, Marty might not have been in much danger after all. Researchers at the University of Queensland argue that changes made in the past can’t dramatically alter the future. The theory calls Einstein’s theory of general relativity into question, since it theoretically allowed for an individual to go back in time and interact with a past self, potentially endangering their own future.

In the future, however, other sci-fi visions might creep closer to reality. Wormholes might help researchers discover a faster way to travel in space. Additional evidence is confirming the existence of a multiverse, otherwise known as alternative universes. And some physicists think that everything we experience in this world might be part of an elaborate video game rather than a biological world. These theories and others in modern theoretical physics bring science fiction to life. We will explain which of these theories (if any) will come closer to gaining evidence of existing in real life any time soon.

Traveling Through Time

The original theory that allowed for the possibility of time travel is Einstein’s theory of general relativity. Einstein’s theory was a big turning point in physics, turning Newton’s idea of fixed space and time on its head. The theory of general relativity basically challenges the assumption of gravity as an invisible force that merely brings objects together. In contrast, the theory of general relativity depicts gravity as “ a curving or warping of space.”

Objects with more mass can warp more space. For example, the Earth can warp space enough to bring a moon into its orbit, but the sun is massive enough to warp enough space to bring in eight planets with its gravitational pull. Gravity can also impact measurements of time in a process known as gravitational time dilation. NBC News Science explains the phenomenon with the following example. If your friends climbs a mountain, and you are still at the base of the mountain, your clock will be ticking slower on the ground than your friend’s clock on the peak. This is because of the difference in gravity between the two locations. When gravity is stronger, time moves slower, and this is because gravity curves space-time.

What might this all mean for time travel? Under general relativity, going back in time is theoretically possible. An extremely powerful gravitational field, such as a black hole, could potentially warp spacetime so much that it might turn back on itself. This could potentially create what is known as a “closed-time loop,” a loop of spacetime one could use to travel back in time. Within closed-time loops, a paradox is thought to exist—one where an individual could go back in time Marty McFly style and prevent their own existence.

However, the researchers from the University of Queensland aren’t convinced that such a paradox even exists. Their paper, “Reversible dynamics with closed time-like curves and freedom of choice” ultimately found that changes to events in the past couldn’t have large outcomes on events in the future. For example, if someone were to go back in time and prevent the COVID-19 patient zero from spreading the virus, they might contract the virus themselves. The idea is that the time travel paradox doesn’t exist because even if one event were to change, other events would shift to produce the same original outcome. If this theory is correct, those worried that time travel would allow someone to go back in time and kill their grandfather, preventing their own existence, have no reason to worry at all.

Through the Wormhole

According to NASA, other modes of time travel are possible with general relativity. For example, going faster than the speed of light in a vacuum might allow for time travel, though Einstein’s work shows that the object traveling would have to “have both [an] infinite mass and a length of (zero)” (it’s worth noting that Einstein’s original math shows that it is impossible for anything to move faster than the speed of light, but some modern day researchers think that it might someday be possible).

Additionally, something called a wormhole has many implications not just for time travel, but for interstellar travel. Wormholes act as a tunnel shortcut through space time. They connect two points in space that would otherwise be very far apart. Astrophysicist Sabrina Stierwalt says that wormholes are most commonly depicted by asking someone to imagine a piece of paper, then bending two points from opposite ends of the paper towards each other but not touching them. The piece of paper represents normal space, and the distance between the two ends of the paper once folded represents the shorter path between the two ends that might be traveled if a wormhole were to exist there.

The sci-fi solution to the time travel question ultimately has a few caveats. Though wormholes are theoretically possible, scientists have never been able to prove their existence. They have never been observed directly or indirectly in space. Further, even if wormholes did exist, they’d likely be very tiny, so small that a person couldn’t fit inside, much less a whole spaceship. Additionally, some physicists think that once we understand the laws of physics with more clarity, we will learn that time travel is not possible. Our current understanding of physics tells us that wormholes would have to be held open with exotic matter, a gravity-repelling substance whose properties are not fully understand. Since exotic matter usually exists only in particles, it is not yet known whether larger amounts can be assembled to form a wormhole.

Time-travel enthusiasts, however, need not despair just yet. Even though wormholes carry some technical complications, astrophysicist Eric Davis maintains that they’re our best shot at time travel. Wormholes connecting two points in spacetime arise as one potential solution to Einstein’s general relativity field equations. Further, Davis argues that there are several spacetime geometry solutions to current problems in physics that “exhibit time travel and/or have the properties of time machines.” According to Davis, “traversable wormholes imply time machines” which are “unavoidable in our physical dimensional space-time.” If Davis is right, and wormholes really exist, we might be able to travel in ways never before thought possible.

In a Parallel Universe

We might not be the only universe contemplating time travel. In fact, according to multiverse theory, we might not be the only universe, period. According to physicist Brian Greene, the universe might be vast and finite, or it might be vast and infinite. Even if the universe is infinitely large, there are only so many ways matter can be put together. So, if the universe is infinitely large, because matter can only be arranged in finite ways, there must be infinite parallel universes.

There are a number of different theories about the multiverse. Some theorists notice that some areas of the universe keeping inflating and expanding while others stay constant in size, suggesting a network of bubble universes across spacetime. Others posit the traditional parallel universe theory, noting that “with an infinite number of cosmic patches, the particle arrangements within them must repeat.”

The theory of parallel universes specifically rises from quantum theory. When the study of quantum physics began in the early 20th century, researchers started noticing that quantum particles behaved strangely. On the quantum level, particles seemed to arbitrarily switch forms. Photons, for example, the basic unit of light, can exist as particles or waves. In an idea known as the Heisenberg Uncertainty Principle, physicist Werner Heisenberg argued that we can determine the state of a quantum particle just by observation. Thus, if we aren’t observing a quantum particle, we don’t know all of the particle’s attributes, such as velocity or location, for certain.

The Heisenberg Uncertainly Principle prompted researchers to theorize that by observing a quantum object, we could affect its state. However, some researchers took this principle further and suggested that by measuring a quantum object, rather than pushing it into one state or the other, we actually cause a split in the universe. This is known as the Many-Worlds interpretation of quantum mechanics. According to proponents of the Many Worlds theory, when we observe a quantum object, we split the universe into two distinct universes to accommodate each of the observation outcomes. The Many Worlds theorem can mean that if a person was ever in a situation where they could have died, there exists a universe where they are dead, and the universe where they are alive. Essentially, the Many-Worlds theory offers an explanation for why parallel universes might exist.

If parallel universes do exist, we might face some technical difficulties if we tried to reach them. Within our universe, our vision is limited by the speed of light. Since light started traveling at the moment of the Big Bang 14 billion years ago, our vision is limited to 14 billion lights years away—a distance known as one Hubble Volume. The Hubble Volume limitation is the reason reaching a parallel universe is virtually impossible. We could only exchange communication within our own Hubble Volume, so sending or receiving a message to or from a parallel universe isn’t possible.

Of course, it’s always possible that parallel universes don’t exist at all. Some physicists point out that the finite age of the universe (14 billion years old) “limit(s) the number of possibilities for particles to rearrange themselves” within spacetime. Further, physicists who doubt the existence of parallel universes also point out that during the initial Big Bang expansion of the universe, the universe initially expanded exponentially because of a giant build-up of energy. That initial expansion has slowed, indicating perhaps that multiverses would have different rates of inflation and are thus less likely to be similar to our universe. Both of these ideas reduce the likelihood of parallel universes.

Is It All Just a Game?

Even more mind-blowing than the idea of parallel universes is the simulation hypothesis. In its simplest terms, the simulation hypothesis is that idea that we on Earth are living in an advanced civilization’s computer simulation. In a seminal 2003 paper, Oxford philosopher Nick Bostrom explained this hypothesis in detail. Bostrom assumed that at least of three possibilities had to be true. In one scenario, no civilization in the universe had ever survived long enough to create simulations. In the second scenario, the civilizations that reached this level of technological sophistication didn’t bother to create simulations. And in the final scenario, advanced civilizations have the ability to create several simulations and act on this ability, meaning that there are more simulated worlds than non-simulated worlds.

The simulation hypothesis sounds fantastical, but some physicists have tried to explain what elements of our physical world serve as likely evidence. First of all, some have commented the speed of light might act like the kinds of limitations in the video games we’ve played in our universe. Perhaps such a definite physical limitation, some argue, is meant to keep human “players” from leaving the “game” in this universe. Other researchers turn once again to quantum mechanics for an explanation. Computer scientist Rizwan Virk (who wrote the 2019 book The Simulation Hypothesis) notes that quantum mechanics is similar to a principle optimization feature within certain video games. Video games use an optimization technique sometimes which “only render that which is being observed.” In a first-person shooter game, this might look like only showing what would be visible from the point of view of the virtual camera. Virk says that if we are living in a simulation, quantum mechanics might be something like this – not showing these tiny particles in a definitive state as an optimization technique. In other words, it be the case that our alien programmers didn’t have the computer processing power to make us see and understand quantum behavior.

Virk also explains the history of progress in physics to defend the simulation hypothesis. The first wave of physics saw everything as the study of physical objects; the second wave saw everything as a field of probabilities. The third wave has come to understanding everything as information—i.e., everything we see is the result of pieces of information. Virk’s argument is that if everything isn’t physical and everything is instead information-based, that offers even more evidence for the simulation hypothesis.

However, Virk isn’t the only authority on simulation, and others in the field completely disagree with his hypotheses. In a 2017 paper published in Science Advances, theoretical physicists Zohar Ringel and Dmitry L. Kovrizhin argue that it’s mathematically impossible for us to be living in a computer simulation. The math to get to this conclusion is supposedly very complicated, but the takeaway is actually quite simple. In order to simulate the quantum mechanical system (the basis of nature), Ringel and Kovrihzhin argue that the simulator’s computer would need more processing power than can be built with all atoms in the universe. Of course, this doesn’t include the possibility that all of these calculations are part of the simulation. However, when Fast Company posed that question to Dr. Kovrizhin, he noted that though it was interesting, it was outside the realm of physics.

Modern physics is getting closer and closer to figuring out some of the most fantastic possibilities that have delighted science fiction fans for decades in real life. However, if you’re worried about your grandchild coming back to the past to kill you, or living a differ life in an alternate universe, or sweating about the possibilities for your character in this supposed elaborate video game we’re living in, you might not have to worry just yet. Science is still a long way away from making science fiction a reality.