Is Time Travel Possible?
How many times have you said, “If I could do that again, I would do it differently"? From time to time, when something does not go according to plan, I often wish I had said or done something differently. When mistakes happen, a common thought of mine often occurs: "What if I could build a time machine to go back in time and change a decision I made to cause it to go right instead of wrong?"
The late Stephen Hawking, a world-renowned cosmologist, believed time travel or temporal displacement to be possible. Many other physicists agree, but the main problem with moving through time is that it requires a lot of energy, especially if one wants to send something such as a human either forward or backward in time. It is, however, very possible to do this with subatomic particles in an accelerator, as we will learn later.
A Timely Definition
From a physicist’s viewpoint, time is defined as one of the four dimensions in our physical world. Everything that exists in the universe has length, width, height, and the fourth dimension called time. When we are moving around in the world, we always move within these four dimensions, and everything in the universe moves with us, down to the atoms and subatomic particles that comprise matter.
Time is, in essence, the existence of something in the universe. Time is basically another dimension in length. Look at it this way; each one of us will be around for 70 to 100 years, the pyramids have existed for about a couple thousand years or more, and the Earth and sun will exist for a few billion years more. In this case, we are measuring a type of length by using time.
Mass and Time Connection
Physicists have known for a while that time slows down near massive objects. It was clarified in Einstein’s 1916 paper on special relativity that mass put a drag on the flow of time. This is called the time dilation effect. Think of time as water flowing in a river. The speed of the flowing water slows down around large boulders in the river.
Time Slows Down Near the Pyramid of Giza
This phenomenon is happening all the time on Earth when tourists are standing near the giant Pyramid of Giza in Egypt. This pyramid is the most massive structure on the planet with an estimated mass of 40 million tons. Time slows down near the monument due to its large mass, but the effect is small. To put the effect into perspective, we can exaggerate it by using an observer looking at the pyramid. This individual would see people moving slower near the pyramid, and if he or she were to look out toward the desert, they would see people moving at a faster pace. In this exaggerated scenario, if the individual stood by the monument long enough, he or she would emerge a few minutes, hours, or even a day into the future depending on how long he or she stood. The time dilation is taking effect as the time away from the pyramid is zooming by faster than the time near the pyramid.
This drag on time also occurs near the Earth's surface. Time moves slower on the surface of Earth compared to the flow of time measured at a distance of 100 or even 200 miles outside of its atmosphere. This is because Earth is a massive object and causes space near it to curve. This theory (discovered by Einstein) was proven many years ago with a specially designed gyroscope-equipped satellite.
Satellites Are Programmed to Correct Time Dilation
In fact, there is more proof of this dilation effect taking place literally every second of the day just above our heads. The precise clocks on the 31 global positioning satellites (GPS) circling the Earth experience the dilation effect. Time is moving faster in space with respect to time on Earth because the satellites are further away from the massive body of the Earth. The distance between the satellites and Earth's surfaces causes a time dilation effect.
The effect is very small, but it is enough to throw the clocks on each satellite off by about one-billionth of a second every day. Due to the dilation effect, the positions measured on the Earth’s surface may be thrown off by 6 miles a day from the perspective of the satellite. Fortunately, there is a built-in correction program on each satellite to correct this time error.
Time Moves Very Slowly Near Black Holes
Physicists know that the effect of time dilation near a massive object can be significantly amplified if we could fly a spacecraft near the most immense object in the universe—a black hole (Mother Nature’s time machine). For a spacecraft to approach a black hole, everything must be done correctly. Astronauts in the spacecraft must move toward the black hole at the right speed and trajectory to avoid being drawn into it.
If done correctly, the astronauts in the spacecraft circling the black hole would experience this slower passing of time. Those away from the black hole would experience time moving at twice the speed compared to the astronauts in the spacecraft. If the astronauts stayed near the black hole for one year, people back on Earth would have already experienced two years. Obviously, traveling to a black hole would not be a practical way to travel into the future because too much time and energy is needed to achieve any significant time travel into the future. However, there is a more straightforward approach to traveling into the future, and that is speed.
Speed and Time Connection
Another aspect from Einstein’s paper on special relativity states that the time slows down to an observer approaching the speed of light. Particle physicists prove this theory at the CERN particle accelerator facility in Geneva, Switzerland. It is here where subatomic particles are accelerated to velocities near the speed of light in a tube buried underground in a circular tunnel that is 16.8-miles in length.
The CERN Particle Accelerator Increases the Lifespan of Particles
To study a very short-lived subatomic particle called a pi-meson (which has a lifespan lasting only 25 billionths of a second), the particles in the CERN particle accelerator are accelerated to 99.99% the speed of light. About a trillion of these particles are placed in the circular accelerator and are accelerated from 0 to 60,000 miles per hour in a few seconds with powerful magnets. The particles continue to accelerate until they are traveling at 99.99% the speed of light. At this speed, the particles are moving around the 16.8-mile circular accelerator 10,000 times per second, and the lifespan of the particles last 30 times longer due to the time dilation effect at speeds near the speed of light.
Train Traveling at the Speed of Light
This same scenario can be done with a train traveling close to the speed of light on Earth. This would be a challenging task to accomplish. If it were possible, imagine about 200 to 300 passengers board a train for a trip into the future. This is a one-way trip in which you cannot return.
The doors close and the train begins to accelerate slowly on a 25,000-mile track circling the Earth. The train continues to accelerate until it reaches a speed close to the speed of light. Once there, the train will be orbiting the Earth seven times a second. To an observer outside the train (granted he is able to see the passengers), the passengers will appear to be moving very slowly due to the time dilation effect.
If this train continued at this speed going around and around and finally coming to a stop after one week, one hundred years would have gone by for the people who are not on the train. The passengers on the train will only see one week go by. They will be 100 years into the future once they step off the train. The problem with this scenario is that it would require a lot of power, energy, advanced technology, and manpower to accomplish, but would work if it could be done.
A Trip to Space
This scenario could be done in space as well with the use of an enormous spaceship. The problem here is that the ship would once again require a lot of fuel and manpower. Also, the ship would have to travel out of the galaxy to achieve the same effect because it will take the ship almost four years just to reach 90% of the speed of light. By that time, it would be just passing the nearest star, Alpha Centauri (about four light years from Earth). The other obvious problem is that flying a ship at the speed of light would be a one-way trip. Passengers would not be coming back from this trip.
Finally, the Time Paradox
Cosmologists and physicists believe there is one thing you cannot do in time travel; you cannot travel back to the past. Yet, this seems to be what everybody wants to do with a time machine (if they had one). Traveling back in time is impossible, and I will explain why.
You cannot have "effect" before "cause." In other words, you cannot see the effect before its cause—it simply doesn’t make sense. Here is an example: Imagine a scientist had assembled a gun to shoot himself in the past. Now, let’s say he invented a time machine to open a portal that allows the scientist to travel approximately one minute back in time to shoot himself before he assembles the gun. Therefore, the scientist shoots his past self and his past self dies before he assembles the gun. Who fired the shot? It doesn’t make sense; it's a paradox. This is an example of the way all events progress in the universe—cause, then effect—not the other way around. Another way of understanding the cause and effect is that the future is the “effect” and the present and past is the “cause." Unfortunately, you will not be able to go back in time to witness the Wright brothers taking off at Kitty Hawk, North Carolina, for their first flight, nor experience when the first pyramids were built.
Time Travel in Science Fiction Movies
There are many shows and movies depicting time travel, such as the sci-fi classic, Time Machine, or the TV series of the '60s, “The Time Tunnel." More recent movies include The Time Traveler’s Wife and the Back to the Future trilogy. These shows and films were all wonderful, but they never quite accomplished explaining the significant amount of power needed to send something back and forth across the time continuum.
The sets in sci-fi movies and television shows will often use fancy pieces of equipment such as lights, dials, and gauges to dramatize the power of time travel. Often, the actor or actress who is time traveling will "disappear" in the blink-of-an-eye. Today, physicists can explain how it is possible to go through time by reason of Einstein’s papers on relativity, which focused on particle physics and black holes.
© 2011 Melvin Porter