In 1905 Einstein formalized his theory of special relativity. According to this theory, the speed of light is not only a constant, but also the universal speed limit. Theories proposing how one could travel faster than the speed of light have been put forth, ranging from wormholes to tesseracts to time travel. Some of these theories take advantage of additional dimensions that we cannot see. But how realistic are these suggestions? Are there more than three dimensions? Is it possible to travel faster than light? What is a wormhole and how would it allow us to travel great distances in a short amount of time?
If you’re already a Star Wars fan, you know that the stories take place in a galaxy far, far away, so the laws of physics should still apply. On the other hand, these are obviously works of fiction; is there any point in applying those laws? My book makes the case that is is both fun and worthwhile to do so for a range of Star Wars technologies, including the one of its most important: hyperspace.
In Star Wars, hyperspace is extra-dimensional space through which ships can travel so as to move across the galaxy faster than would be allowed by traveling through real space. In order to do this, a ship must be equipped with a hyperdrive. But going to hyperspace is not without its dangers. “Traveling through hyperspace ain’t like dusting crops,” as Han Solo explains. “Without precise calculations we could fly right through a star or bounce too close to a supernova.” With such severe risks, it is important to rely upon hyperdrive computers.
The physics of Star Wars
Hyperspace is, in theory, a set of extra dimensions beyond the three that we experience daily. These extra dimensions are able to connect distant points in real space. This allows for faster-than-light speeds (in a sense). For example, consider the flight from Tatooine to Alderaan. If Owen turned on a laser pointed directly at Alderaan (and we assume that there are no obstructions and the beam will stay accurately aimed enough to be detectable at Alderaan) at the same moment the Millennium Falcon jumped into hyperspace, the Millennium Falcon would arrive before the laser beam reached Alderaan. It seems as if the Millennium Falcon traveled “faster than light.”
There are problems with this theoretical explanation. One is the idea that cause and effect rely on things happening in a particular order. More simply, for one event to cause a second event, the first event must happen before the second. That seems easy enough and unrelated to hyperspace, but the concept of simultaneity throws a wrench into everything.
Consider the following: you are sitting on a chair next to a high-speed railroad track, and you decide to launch two fireworks at the same time, one on either side. From your perspective, they launch at precisely the same moment. If your friend were to ride on a train traveling close to the speed of light as the fireworks were launched, that friend would see the fireworks launch at different times. An event that is simultaneous for you would not be simultaneous for your friend. Similarly, you could launch the fireworks at different times such that in your friend’s reference frame they launch simultaneously.
The catch is, if your friend’s train were to travel faster than the speed of light, the order in which the fireworks launch will appear different to you (as a stationary observer) versus your friend (as an observer traveling faster than light).
You may think, well, fireworks are a silly example. Who cares if you disagree on the order in which the fireworks were launched? However, this thought experiment shows us the interrelationship between speed and the sequence of events. The laws of physics don’t care what those events are. Imagine firing a blaster (event 1) and the bolt hitting the target (event 2). Or reading a book (event 1) and telling a friend about what you read (event 2). As you can see, the order in which these events happen would be nonsensical when reversed. Technically, it would be possible for the Millennium Falcon to fly faster than light past Alderaan as it explodes and arrive at the Death Star in time to stop the weapon from firing in the first place.
There are ways in which traveling through hyperspace would not require a violation of relativity. There are ways in which traveling through hyperspace would not require a violation of relativity, though. The idea that two points in real space are connected by a “tunnel” taking advantage of additional dimensions is not unheard of in physics theories. These connections between points in space-time are called wormholes. Here’s how a wormhole works: Hold a piece of paper in front of you and fold it in half. Now take a pencil (or other sharp object) and poke a hole through the folded paper. Now imagine that an ant wants to walk from one side of the paper to the other. If it walks along the surface of the paper, it will have to walk all the way up and around the fold. On the other hand, if the ant walks through the hole, it can get from one side of the paper to the other much faster. The ant itself never traveled faster; it just made it from one location to the other faster.
Whereas the paper is a two-dimensional surface, three-dimensional space as we understand it could be folded through a fourth dimension to create connections between two points. Because our minds have only ever experienced three-dimensional space, this is impossible to visualize fully. Still, if a hyperdrive were able to distort space-time such that it warped and created a hole between Tatooine and Alderaan, traveling through hyperspace would not violate any laws of physics. It would just require tremendous amounts of energy to accomplish these jumps.
The physics of real life
This probably all sounds fantastical; something that couldn’t happen in reality. As far as experimentally verified physics is concerned, that’s true. There are theories, though, that indicate there could be additional dimensions of reality yet undiscovered. Perhaps the best-known example of this is string theory. At this time, there are five different formalizations of string theory, all of which cannot be falsified by current data. M-theory is a possible unification of all string theories according to which each individual string theory is a special example of the generalized M-theory.
There are theories that indicate there could be additional dimensions of reality yet undiscovered. The basic premise of all string theories is that everything in the universe is made up of tiny strings, which are either wrapped in a loop or exist in a straight line. Just as strings on a guitar oscillate in particular ways to make notes in a song, the strings making up the universe oscillate in different ways to create subatomic particles.
One of the other ideas of string theory is that there are more than the three spatial dimensions and one-time dimension that we know. Depending on the specific formulation of string theory you are referencing, there are different proposed numbers of dimensions. For instance, in bosonic string theory, there are a proposed twenty-six dimensions.
So where are these extra dimensions? Why can we not see them or experience them? Like most things involved with physics on the border of human knowledge, we use analogies to describe the results. Imagine that you are an astronaut in the International Space Station looking down at New York City. You will be able to see the grid of streets lit up at night. From your perspective, the streets will look like one-dimensional lines; things can go along them, but there is no width to go across them. Having been on a street, you know that you can walk across a street (not just go along it) and that you could even jump up and down while crossing the street, but from space you are too far away to see those details. Similarly, on our human-sized scale, we may be so far away from these compact dimensions that we cannot see the intricacies of them.
These dimensions are often described in terms of what is known as the Planck length. Some people suggest that this is the shortest possible length. The Planck length can be visualized in this way: Look at the width of a human hair. This is about a tenth of a millimeter across. If this hair were scaled up to be the size of the observable universe (about 1027 meters across), in the scaled-up version the Planck length would be the width of a human hair. Another way of saying this is that a human hair is about 1031 Planck lengths across. That is ten million times the number of stars in the observable universe.