In 2015, a group of scientists made headlines when they announced the first-ever detection of gravitational waves. Detecting gravitational waves is a technological feat in and of itself, yet their detection also offers scientists an entirely new way of looking at the universe. What are gravity waves, and how are they produced?
What Is Gravity?
Any discussion on gravity waves must also include a description of gravity. Most of us are likely aware that gravity is the force between objects with mass. The strength of gravity is dependent upon how massive an object is. Gravity is the weakest force in the universe, yet it operates on the largest scales, so it is the most apparent force in the universe. Isaac Newton was the first scientist to describe the law of gravity, changing humanity’s perception of the cosmos forever. Isaac Newton showed that every object of mass possesses a gravitational force, with the strength of that force being directly related to the mass of an object. Newton explained why apples fall to the Earth, why the moon orbits the Earth, and why all the planets orbit the sun. However, Newton was unable actually to explain what gravity is. It is a force between objects, yet what causes things to generate a gravitational pull? Even Newton himself admitted he was unable to define gravity truly.
The true nature of gravity would remain unknown until Albert Einstein published his theory of General Relativity in 1916. Einstein improved upon Newton’s description of gravity by explaining precisely what gravity is and how it is produced. According to General Relativity, space itself is dynamic. Rather than being a static place, space behaves like a fabric, bending and warping around objects with mass. The force of gravity is the warping of space. For example, the sun warps the space around, kind of like putting an indent in the very fabric of space. The planets travel along with warped space and orbit the sun. The higher an object’s mass, the more intensely it warps the fabric of space. General Relativity explained what gravity is and how it is generated, yet it also predicted the existence of gravity waves.
How Waves Are Generated
The process by which gravity waves are generated is similar to how ocean waves and wind waves are generated. Waves are produced when fluid is displaced from a state of equilibrium. A wave is created when that fluid tries to position itself back into equilibrium. In outer space, space behaves like a fluid, and objects of mass warping the fabric of space can displace that fluid from a state of balance. When space tries to restore its state of equilibrium, gravity waves are produced. Any object with mass that warps space can generate gravity waves, yet most gravity waves are too weak for current technology to detect. So far, scientists have only been able to detect gravity waves produced by some of the most extreme events in the cosmos, such as a black hole or neutron star collisions. In 2015, using the LIGO gravitational wave observatory, scientists could detect gravitational waves produced by the collision of two black holes. When two black holes collide, the amount of energy generated creates ripples in the fabric of space, sending them outwards as gravity waves. Interestingly, gravity waves move at the speed of light, something Einstein had proposed in General Relativity. Newton believed that the force of gravity was instantaneous. According to Newton’s law of gravity, if the sun were to disappear suddenly, all of the planets would immediately stop orbiting. According to Einstein, however, nothing can move faster than the speed of light, including the force of gravity. Light takes about eight minutes to reach the Earth from the sun, and so if the sun were to vanish suddenly, it would take eight minutes for the Earth to stop orbiting the sun. Thus, gravity waves move at the speed of light.
Another Way Of Seeing The Universe
For all of human history, the universe has only been observable with light. Light reflected off or emitted by objects eventually reaches our eyes, allowing our brains to create an image of what we’re seeing. Light is information that is relayed from our eyes to our brain. Gravity waves offer us a potentially new way of seeing the universe. Scientists can use gravity waves to create a picture of what generated them, allowing us to see the universe in an entirely new way. As of yet, technology is not yet sensitive enough to detect gravity waves in large numbers, yet as technology advances, we may one day be able to see the universe in gravity waves.