In many science fiction movies, spaceships race through the galaxy at extremely high speeds, seemingly ignoring many of nature’s laws that govern our universe. With what we know about the universe right now, it is impossible for any object to travel faster than the speed of light. Any man made object has not reached speeds even close to the speed of light, as the five planetary probes that we have launched to eventually travel among the stars move at speeds less than 1/10,000 of the speed of light. Alpha Centauri is the closest star system to Earth, but it is still a staggering 4.3 light years away. Therefore, at the rate that these probes are traveling, it would take each of these probes at least 100,000 to reach Alpha Centauri, but their trajectories won’t take them anywhere close to it. Rather, these probes will simply continue their journey through interstellar space for millions or billions of years to come.
If we wanted to travel to other stars within human lifetimes, we would need starships that are able to travel at speeds close to the speed of light. In order to do this, we would need entirely new types of engines built to travel at such high speeds. Similarly, spaceships traveling at such high speeds would require new types of shielding to protect crew members from instant death, as a spaceship traveling through interstellar space near the speed of light would be bombarded by billions of deadly high-energy cosmic rays. Even if we were able to accomplish this, we would still be met with other significant challenges. According to Einstein’s theory of relativity, time moves much slower to an object traveling near the speed of light. For instance, a starship embarking on a 50-light-year round trip to the star Vega would only take crew members about 2 years, but more than 50 years would have passed on Earth while they were gone. While the crew would have only aged two years, they would return to a considerably different world that they left. Therefore, it is clear that we are years away from interstellar space travel within human lifetimes, and even if are able to accomplish this we would still face other immense challenges.
We hear about aliens all the time, whether in books or movies or tv shows, and this leads us to ponder our own existence. Are we alone, or is there other life out there? This is a question that has plagued mankind since begun exploring interstellar space, and started looking for life in our own Solar System. If it turns out that life is actually out there, it is natural to wonder if there is other intelligent life in the universe. Would there be other human civilizations, or is Earth the only planet in the entire universe that harbors intelligent life, and we really are all alone. And even if there are other human civilizations out there, how would we find them? Scientists now speculate that we might be able to detect other civilizations simply by listening for signals that they are sending into interstellar space. By this method, efforts to search for extraterrestrial intelligence can only succeed if advanced civilizations are broadcasting signals right now.
The astronomer Frank Drake wrote a simple equation that summarizes factors that would determine the number of civilizations we might be able to contact. This equation, known formally as the Drake equation, gives us a simple way to calculate the number of civilizations in our galaxy that are sending signals into outer space. The Drake equation relates the number of possibly habitable planets in our galaxy, fraction of habitable planets that actually have life, fraction of life-bearing planets on which a civilization capable of interstellar communication has arisen at some time, and the fraction of life-bearing planets that are communicating now. In short, the Drake equation tells us how many civilizations we could possibly contact right now. Because we do not actually know how many possibly habitable planets there are in our galaxy, we cannot accurately calculate the number of civilizations that are communicating right now. However, the Drake equation is still useful as it relates all of the factors necessary for us to determine the number of communicating civilizations, and we can therefore make a general estimate of the number of civilizations we could possibly contact today.