Interstellar Travel

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.

Voyager 2 a space probe that has reached interstellar space

The Universal Law of Gravitation

  Newton’s universal law of gravitation is a fundamental aspect of modern science. The law states that every mass is attracted to every other mass through a force known as gravity. The strength of the gravitational force between any two objects is directly proportional to the product of their masses, which means that increasing the mass of one object increases the gravitational force between both objects. The force of gravity between two objects is also inversely proportional to the the square of the distance between two objects, therefore the force of gravity decreases as the distance between the two masses increases. Newton’s law of gravity extends to Kepler’s laws, as the inverse square law for gravity leads directly to elliptical orbits for planets orbiting the Sun. Newton showed that two objects attracted by gravity both orbit their common center of mass, which is the point representing the average position of mass between the two objects. For example, in a binary star system with both stars of equal mass, the center of mass lies directly between the two objects therefore the stars would orbit around themselves. However, in our Solar System, since the Sun is so much more massive than planets, the center of mass between the Sun and any planet lies inside the Sun, and as a result the planets orbit around the Sun. Prior to Newton, many people saw Kepler’s planetary model for our Solar System as just another theory. By explaining Kepler’s complex laws in terms of basic laws of physics, Newton was able fully legitimize Kepler’s theory and thus convince the world of a heliocentric Solar System.

Objects Orbit Their Common Center of Mass