Editor’s Note: This is the fourth installment of a five part series about the technologies of yesterday’s science fiction becoming the reality of tomorrow. The first installment on flying cars can be viewed here, the second installment on invisibility cloaks can be viewed here, and the third installment on teleportation can be viewed here.
As I sit here writing this article, I’m travelling into the future at a rate of one second per second. But time does not always flow at a constant rate. Time is relative. Gravitational time dilation, which is part of Einstein’s theory and has been experimentally proven, explains the difference in elapsed time between two events as measured by observers differently situated from gravitational masses. For example, the closer a clock is to a source of gravitation, the slower it will show time as passing.
Because we live on the surface of the earth, our planet’s gravitational pull slows the passage of time from our perspective. On the other hand, global positioning satellites orbiting around the planet accrue an extra third of a billionth of a second daily because they are further from the source of gravitation. Now, obviously such minute differences in time don’t mean anything. But, a massive and gravitationally potent object, such as a black hole, could cause very extreme time dilation. The incredible mass of a black hole combined with an infinitely dense point at its center allow it to exert a gravitational force that is so strong that even light can’t escape. For example, supermassive black hole Sagittarius A, which is located in the center of the Milky Way Galaxy, has the mass of four million suns! If you were somehow able to circle around this black hole without falling in you’d experience time at about half the earth-rate. Orbit this object for 10 years and you’d come back to earth to find that 20 years have passed. You’ve successfully travelled into the future!
Speed also plays a role in the passage of time. The faster you go, the slower time will pass. Light travels at almost 300,000 meters per second. Although theory tells us that nothing can exceed the speed of light, if you were able to hop on a train travelling at 99.9% of this speed, then only one year would pass onboard for every 223 years back at the train station. Again, in very real terms, you have taken a journey into the future.
Obviously we currently don’t have the means to orbit a black hole nor the ability to harness the energy required to travel at almost the speed of light. But the point is, the ability to effectively travel into the future is scientific fact. Perhaps several more decades of technological advancement will yield the capacity to do so.
Although travelling into the future is a fairly simple scientific concept, travelling into the past and rewriting history is a more complicated story. Nothing in Einstein’s theory restricts travelling back in time. But, the law of causality tells us that time only flows forward. One event causes another in the never-ending stream of forward-moving time. Certain paradoxes involving time travel into the past violate reality as we know it. For example, take the case of the grandfather paradox. If you were to hop in your time machine in the year 2014, travel back to 1930, and kill your grandfather before he ever had your father, meaning you were never born, then were you ever able to travel back in time in the first place?
Some scientists have put forth theories that would eliminate any paradoxes of backwards time travel. One is the post-selected theory of time travel. This explanation states that certain quantum variations will occur around a paradoxical situation. Take the grandfather paradox again. This theory states that if you were to attempt to kill your grandfather, then somehow he would survive. Maybe the gun malfunctions, or maybe he survives the gunshot wound.
Another explanation involves the ever-increasing-in-popularity many-worlds interpretation. This theory states that every possible quantum event actually occurs in all possible ways in different universes. Thus, history is constantly branching into an infinite number of parallel universes. In relation to the grandfather paradox, the time traveller would end up successfully killing his grandfather in a parallel universe. The traveller would therefore never exist in this universe. However, his prior existence in the original universe would be unaltered.
So if one of these paradox-eliminating-theories is indeed true would we then be able to travel back in time? Well, some physicists theorize that there may be a means to do so. Einstein’s theory of relativity allows for the existence of wormholes due to the fact that any mass will curve space-time. Two equal masses placed in different parts of the universe could curve space-time to the point where they connect and a tunnel is formed.
World-renowned astrophysicist Stephen Hawking believes that wormholes do exist. Just as no 3-D object is completely flat or solid (everything has wrinkles and crevices at the microscopic level), the fourth dimension of space-time also contains wrinkles. At the smallest scale, an environment smaller than even atoms, wormholes that are just a billion-trillionth-trillionths of a centimeter in size constantly form, disappear, and re-form. These wormholes actually do connect two separate places and different times.
Unfortunately, these wormholes are too small for us to see and obviously pass through. But, some scientists believe that technology could eventually give us the ability to capture, stabilize, and enlarge these wormholes to the point that we can use them as portals into a different time. This is purely speculative but certainly an idea that could seem more realistic in the decades and centuries to come.
In summary, any wannabe time traveller would need quantities of energy beyond our current capabilities. But advancements in energy and the advancement of human civilization go hand in hand. The earliest humans had only caloric energy gained from food as well as the kinetic energy of their own muscles to rely on. Fast-forward through history though and humans began to harness energy sources outside of their body. First, it was the energy of domesticated animals, water and wind. In the 18th century, the introduction of steam power began a new era for human civilization. Then came electricity fueled by coal and oil. In the 20th century, the introduction of nuclear power was displayed by the creation of atomic weapons.
My point is, we are constantly finding better and more efficient sources of energy. The world will not run on electric and nuclear power for the rest of history. New sources of energy will emerge and imagining the implications of these new forms of energy is beyond our current comprehension.