By Dr. Gary Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
Suppose we found a way past the engine and fuel problems of space travel discussed in Part II. Still, a peculiar byproduct of Einstein’s Theory of General Relativity presents another quandary. Now, the physics of general relativity are quite elaborate and complex, but in short, Einstein posited that as things speed up (relative to an inertial reference frame), time begins to slow down. Einstein called this effect “time dilation.”
The concept of time dilation sounds absurd, but it has been empirically tested and confirmed beyond any shadow of doubt. At the speeds we travel on the surface of the Earth — cars, trains, and planes — the time rate change is unnoticeable. However, at speeds much closer to that of light, the difference can be substantial.
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Imagine taking a trip in a spaceship that lasts several years. When you return to Earth, 100 or more years has passed. This would not be an illusion or a trick; it would actually happen if we could travel fast enough.
The Only Efficient Way to Make Interstellar Trips Is with Near-Light Speeds
Therein lies a dilemma. If we decide to make interstellar trips, the only efficient way to do so is with near-light speeds. However, if we travel at such speeds we pay the price of time dilation. For example, a spaceship that is capable of reaching 99.9 percent of light speed could take a group of humans to our nearest star Alpha Centauri in about four years. The return trip would take another four years. But although our travelers would only be eight years older upon their return, on Earth nearly 179 years would have passed. Everyone they left back home would be long dead. Thus, time dilation doesn’t prevent us from going, per se, but it does present some serious implications for those who go and those who stay.
Time dilation could theoretically be overcome if we could harness the ability to generate and control wormholes — tears in the space-time continuum that would hypothetically allow us to travel instantly from one part of our universe to another part without the effects of time dilation. However, again, wormholes are theoretical. And even if they exist, the amount of energy required to open and maintain them is estimated to rival that of supermassive black holes at the centers of galaxies like our own. By the time we would be able to generate that much power, interstellar travel will likely be child’s play.
Another Challenge to Interstellar Travel Is the Hostility to Spacecraft and Life Aboard
Another challenge to interstellar travel is the hostility of the interstellar medium to spacecraft and to any life aboard. The Voyager I space probe recently transitioned out of the heliosphere and into the interstellar medium. The heliosphere is the boundary at which the sun’s solar wind ends and deep space begins.
The Sun’s solar wind prevents a lot of dangerous cosmic rays from entering our solar system and striking the planets. Some cosmic rays are as powerful as a bullet fired from a rifle. Once we move beyond this heliospheric boundary, spaceships would be completely exposed to these dangers. Therefore, thick armor plating would be needed to prevent hull breaches and other damage from these rays. Or some type of active electromagnetic shielding (a la Star Trek) would be required.
Shielding, like Wormholes, Is Theoretically Possible but Is Not within our Current Technological Reach
Active shielding, like a wormhole, is theoretically possible. But it isn’t within our current technological reach. So if we were to journey beyond our solar system tomorrow, armor plating would be the only option. The drawback is such plating would be heavy, and would further exacerbate the fuel and propulsion problems because even more of both would be required.
Assuming we solve the cosmic radiation problem, deep space — not unlike space just beyond Earth’s atmosphere — is still hostile to life. It is inhospitably cold, and there is no oxygen, no water, no food, and no air pressure. Thus, in addition to power for propulsion, interstellar spacecraft would have to include life support systems that could last for years. These systems would include hydroponic gardens, water filtration systems, carbon/oxygen exchangers, heating systems, and illumination.
There is also a plethora of other factors to consider, many of which we can only speculate about because the longest a human has ever spent in space is currently a little over a year, aboard the International Space Station (ISS).
For example, we know that humans can survive short stints in space without gravity. But muscles and bones atrophy quickly in Zero G, so astronauts aboard the ISS use tension straps to simulate gravitational forces when they run on treadmills to stay fit. On years-long or decades-long voyages, it would likely be necessary to create long-lasting artificial gravity. This much is readily achievable through centripetal force in a rotating spacecraft, but this also adds to the complexity of such missions.
Another potential factor of concern would be circadian rhythms and the human body’s need for a consistent sense of day/night patterns to maintain homeostasis. This too could be resolved with artificial lighting to simulate day/night patterns on Earth.
Can the Human Mind Remain Healthy in Small Spaces over Very Long Periods of Time?
Perhaps the biggest unknown is whether the human mind can remain healthy with only a few other humans in small spaces over very long periods of time. Psycho-social studies are currently trying to determine these dynamics. But evidence from other quasi-isolated environments — such as prisons, submarines, and monasteries — suggests that serious mental and social deterioration may be a real problem.
There are significant and compelling reasons to pursue travel to other stars and their planets. Despite some enormous obstacles, such travel is within the realm of possibility. However, it is not likely our species will achieve extended space travel for several more generations of significant space flight research and development. We should, therefore, continue to press forward with spaceflight innovation in hopes of one day reaching the stars.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a JD in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.