The United States Space Force has released a recruitment video on Twitter. The 11th Combatant Command in the Department of Defense featured a 30-second clip to garner interest from individuals who may wish to enlist. Yet, we have not learned how to pursue interstellar space travel.
The recruitment video for the United States Space Force (USSF) begins with a narrator saying, “Some people look to the stars and ask, ‘What if?’ Our job is to have an answer.” Footage of astronauts, engineers, and computer screens follows, ending with the tagline, “Maybe your purpose on this planet isn’t on this planet.” The video was tweeted by the official USSF Twitter account, accompanied by a link that redirects to the official United States Air Force website.
The possibilities are exciting, but before signing up for the Space Force, it may help to brush up on the realities of space travel.
Distances in Outer Space
One of the main challenges facing humans who wish to travel to other star systems is the sheer distance from our solar system to the thousands of exoplanets that orbit stars outside of our solar system. In order to consider this distance, it helps to use a scale model, with the distance from the Earth to the Sun constituting the common unit of measurement one astronomical unit (AU).
“Say the scale between the Sun and the Earth is four feet,” said Dr. Laird Close, Professor of Astronomy and Astrophysics at The University of Arizona. “The Sun should be closer to the size of a marble and the Earth would be more like the head of a pin. If this is one AU, four feet, then the distance to the nearest star is 210 miles away.”
The speed of light, Dr. Close said, is about six trillion miles per year. If we were to travel at the speed of light, it would take eight minutes to journey from the Earth to the Sun. If we wished to travel to the nearest star, Proxima Centauri, at the speed of light, it would take 4.2 years. Unfortunately, humanity has not yet discovered how to travel so quickly.
“The rockets that were used in the Apollo program that were pretty quick, it took some three days to get to the Moon,” Dr. Close said. “A rocket like that at those speeds would take you 900,000 years to get to the nearest star system. What if you went even faster, like the Voyager spacecraft, which has already left our solar system? If you traveled at those speeds, which is some 37,000 miles per hour […] it would still take 80,000 years just to go from our Sun to our nearest neighbor.”
Faster than Light Travel
Traveling more quickly than the speed of light would solve the problem of interstellar space travel. Doing so would be rather difficult.
“Einstein’s special theory of relativity predicts and calls out that nothing can exceed the speed of light; however, there is a sort of loophole,” Dr. Close said. “Special relativity applies when space-time is flat; when it is curved, the theory only applies locally—that is, over the very immediate region of where the spaceship is. If you actually can curve space-time, like how it’s curved around a black hole or a star, then you have some loopholes around so-called ‘faster than light travel.'”
Dr. Close presented an analogy of imagining space-time as a sheet of paper. If the paper is bent over in half, two distant points on the paper are brought together. Unfortunately, bending space-time like this would be incredibly difficult.
“A variant on this is the idea of a wormhole,” he said. “In a wormhole you have two points, like the Earth and Sirius, a star that is quite far away. By conventional space travel it would take an awful long time to get there, but if you can make a wormhole which creates a bending of conventional space-time, you create a so-called “hyperspace,” and you could pop from the Earth and very quickly, effectively, fall through the wormhole and pop out near the star Sirius.”
Until wormholes or other methods of bending space-time can be put into practice, Space Force may have to settle for protecting us in our own solar system.
Dr. Laird Close contributed to this article. Dr. Close is Professor of Astronomy and Astrophysics at The University of Arizona. He earned his Ph.D. in Adaptive Optics from the renowned University of Arizona Astronomy Department where he now teaches.