Main Difference – Gravity Waves vs Gravitational Waves
The terms “gravity waves” and “gravitational waves” are two commonly confused terms in physics. Gravity waves are generated in fluid mediums or on interfaces between two fluid mediums. On the other hand, gravitational waves are produced by cosmological phenomena in the universe. This is the main difference between gravity waves and gravitational waves. Gravity waves can be easily detected on the Earth whereas gravitational waves could not be detected until 14 September 2015. The concept of gravity waves isn’t complex whereas the concept of gravitational waves is complex. The generation of gravity waves can be easily explained in fluid dynamics whereas the generation of gravitational waves isn’t easy to understand. So, as you can see, these two terms have totally different meanings. This article attempts to give you a better understanding of those differences.
What are Gravity Waves
When a fluid particle or a cluster of particles moves on an interface of two fluids (between a body of water and air) or into a region of the fluid with a different density, the gravity tries to restore the lost equilibrium by replacing and repositioning some fluid particles at suitable places. This attempt of the gravity generates oscillations and oscillate about the equilibrium state, known as gravity waves or buoyancy waves. The gravity waves that are generated at interfaces between a water body and air are called surface gravity waves whereas the gravity waves that are generated within the water bodies (sea, ponds and lakes) are called internal gravity waves.
Surface gravity waves
What are Gravitational Waves
The existence of the gravitational waves was first suggested by Albert Einstein in 1916, yet scientists were unable to detect them until 14 September 2015. There were many arguments, even among some major stream scientists, about the existence of gravitational waves. A team of researchers at LIGO (Laser Interferometer Gravitational-wave Observatory) announced in September 2015 that they have detected gravitational waves in the fabric of space-time coordinate system. According to the researchers at LIGO, the gravitational waves they have detected were generated when two black holes merged to create a single giant black hole.
The theory of general relativity predicts that a system of two black holes that are orbiting around each other releases their energy as gravitational waves. So, the system loses its energy causing them to come closer. This process takes billions of years and during the final fraction of a second, the two black holes strike against each other and creates a single giant black hole. As a result of this tremendous cosmological strike, a portion of the mass of the system is converted into energy and propagates through space as gravitational waves. The amount of the mass that converted into energy is given by the famous Einstein’s equation, E=mc2.
Difference Between Gravity Waves and Gravitational Waves
Fundamental Nature:
Gravity waves: Gravity waves are mechanical waves.
Gravitational waves: Gravitational waves are not mechanical waves.
Origins:
Gravity waves: Surface gravity waves such as ocean waves are frequently produced on water surfaces by winds. The waves that produce when a stone is dropped into a pond or lake are also surface gravity waves. Tides are also surface waves created by the attraction of the sun or the moon. In addition, underwater earthquakes create surface gravity waves called tsunamis.
Internal gravity waves are produced in fluids. An example of internal gravity waves is mountain waves that generate when the wind passes over a mountain. In addition, whenever the buoyancy pushes air up, the gravity pulls it back down to restore the equilibrium and, as a result of this reaction, internal gravity waves are produced in air. The same thing happens in water bodies such as oceans and lakes. The essential requirement for internal gravity waves is an existence of a continuously or discontinuously changing density of the fluid. In general, in the water bodies, the temperature and the salinity change with the depth and therefore, the density varies from layer to layer within the fluid. The density of the atmosphere also varies due to several reasons.
Gravitational waves: According to the theory of relativity, any accelerating or decelerating object that isn’t spherically or cylindrically symmetrical generates gravitational waves. In addition, irregularly shaped spinning stars and binary systems of black holes, neutron stars or black hole- neutron star that are orbiting around each other also generate gravitational waves. Gravitational waves are produced by cosmological explosions such as supernova explosions or gamma ray bursts (GBR) according to some astrophysicists.
Scientific Explanations & Theories:
Gravity waves: Fluid dynamics can be used to explain gravity waves.
Gravitational waves: The theory of general relativity predicts the existence and formation of gravity waves.
Speed:
Gravity waves: The speed varies. The maximum speed may be around 100ms-1.
Gravitational waves: Travels with the speed of light.
Energy associated with the waves:
Gravity waves: Gravity waves transfer energy through matter.
Gravitational waves: Gravitational waves carry energy away through empty space or matter.
Detection:
Gravity waves: Some types of gravity waves such as ocean tides can be seen with naked eye. But there are some types of gravity waves that cannot be seen with the naked eye. However, they can be detected and mapped using satellite data or other instruments.
Gravitational waves: Physicists were able to detect gravitational waves on the 14 September 2015 for the first time with the help of signals recorded by LIGO.
Importance of detecting:
Gravity waves: Detection of gravity waves is very important in weather forecasting and disaster management.
Gravitational waves: Physicists believe that the gravitational waves can penetrate any cosmological barrier. So, gravitational waves carry very important cosmological information, and they will reveal the secrets of the universe.
Medium for propagation:
Gravity waves: Gravity waves need a medium for propagation as they are mechanical waves. They are produced in fluids and propagate within fluids.
Gravitational waves: Gravitational waves don’t need a medium for propagation as they aren’t mechanical waves.
Attenuation by physical barriers:
Gravity waves: Gravity waves are attenuated significantly by physical barriers.
Gravitational waves: The attenuation of gravitational waves when they pass through physical barriers is negligible.
Image Courtesy:
“Wind wave” by Brocken Inaglory – Own work, (GFDL) via Commons Wikimedia
“History of the universe” by Yinweichen – Own work (CC BY-SA 3.0) via Commons Wikimedia
