We have all seen footage of astronauts floating freely in space, performing twists and turns that seem to defy gravity. As a result of these portrayals, many people believe that there is zero gravity in space. However, this statement could not be further from the truth. Gravity exists everywhere in the universe and is the most important force affecting all matter in space. In fact, without gravity, all matter would fly apart and everything would cease to exist.
Gravity is the attractive force between two objects at a fixed distance r. The strength of gravity is proportional to the mass of the two objects and inversely related the distance between them. A larger massed object has a greater gravitational force than a smaller massed object does which explains the difference between the gravitational field of the Earth and Moon. The force of gravity between two objects decreases rapidly at a rate of 1/r2. Thus, the gravitational force of two equal masses 1 meter apart is 100 times stronger than if the masses were 10 meters apart. Using the two parameters, mass and distance, we can understand how gravity operates in the universe and causes objects to appear as though they are experiencing zero gravity in space.
Earth’s gravitational pull is responsible for the moon’s orbit. Similarly, all planets, asteroids, and comets in our solar system orbit the sun due to this gravitational pull. The fact that celestial bodies millions of light years away orbit the sun debunks the myth of no gravity in space. The sun has a tremendous gravitational pull because it accounts for 99.86% of our solar system’s weight.
Why, then, are objects seemingly able to float freely in space despite the sun’s gravitational field? Remember, the force of gravity is dependent on the mass of two objects. The celestial bodies have enough mass to experience the gravitational pull of the sun. Objects with relatively little mass will experience less of the sun’s gravitational force than celestial bodies like Jupiter. In addition, small objects far from the sun experience a weaker gravitational force. Although gravity never reaches zero, it gets close.
The premise of Einstein’s theory of general relativity can be used to explain gravity in space. Imagine the universe as a two-dimensional sheet that represents the space-time fabric. If one were to place a ball with mass m on this sheet, it would create a depression that alters the space-time fabric. This distortion in gravity changes the progression of an object that passes through the depression. A ball with mass 2m will create a bigger depression and thus have a greater force of gravity acting upon it. The further an object is from the ball, the less it will experience the distortion or the ball’s gravitational field. Einstein’s theory postulates that any object with mass distorts space time, including humans. Although we barely dent the sheet, we create a small gravitational field around us. As long as there is matter in space, there is gravity.
The infamous astronomical phenomenon known as the black hole illustrates just how important gravity is in space. A black hole is a region in space so compact that light cannot escape it. Black holes are formed by dying stars that collapse under their own weight and form a core that is infinitely dense. In Einstein’s two-dimensional sheet analogy, a black hole is so compact that it creates a hole in the space time fabric instead of a dent. Any particle or wave, including light, is trapped by the enormous gravitational pull the black hole creates. The presence of black holes directly opposes the notion of zero gravity in space.
If all mass creates gravity in space, how did the notion of zero gravity originate? It has undoubtedly been fostered by the experiences of astronauts in space who seem weightless and are consequently described as experiencing zero gravity. This explanation cannot be true, especially so close to earth, where the gravitational field is strong and constantly pulling the spacecraft towards it. To understand the astronomer’s experiences, it is important to distinguish “weightlessness” from “zero-gravity.” Astronauts feel weightless because their shuttle is in a state of continuous free fall to the earth. However, the space shuttle never falls to the earth because it is traveling horizontally at about 18,000 km/hr, opposing the force of gravity. If the spacecraft was not moving quickly enough, it would fall prey to the effects of earth’s gravitational field and fall to the earth.
There is no such thing as zero gravity in space. Gravity is everywhere in the universe and manifests itself in black holes, celestial orbits, ocean tides, and even our own weight.