What are gravitational waves and how were they detected?
Ariel R
Gravitational waves were first theorized by Albert Einstein when he released his General Theory of relativity in 1916 and were not detected until nearly 100 years later in 2015. [1] They are signatures of the most violent and catastrophic events which the universe has to offer, such as the collision of two black holes. [2] Despite this, by the time they reach the earth their effect was predicted to be infinitesimal and ‘vanishingly small’. Einstein thus thought that they were practically impossible to detect. [3] But what precisely are these cataclysmic yet faded waves? How were they detected? And what are the implications of their detection? These topics and more should hopefully be made clear by this essay.
A common definition of gravitational waves is that they are ‘ripples in spacetime caused by an asymmetric accelerating body’. [4] This technically dense definition can be broken down for ease of understanding. ‘Spacetime’ is the combination of the 3 dimensions (x, y and z) in addition to time to make a four-dimensional concept. This spacetime is typically represented as a two-dimensional sheet as we cannot think in more than 3 dimensions. This sheet acts almost like a fabric which can be morphed by objects being placed on it, with heavier objects such as black holes morphing spacetime more (see fig.1). [4] This effect of morphing spacetime is how gravity is understood to work, as the path of an object follows the curvature of spacetime (see fig. 2). Asymmetric objects include things such as planets and moons, as they have surface imperfections and are not perfectly spherical. An asymmetric object may also include a binary system consisting of two objects orbiting each other such as two black holes or neutron stars. The final piece of the definition which needs to be broken down is ‘accelerating’. An accelerating object is one which constantly changes its speed and/or one which constantly changes direction (acceleration is a vector quantity, and so is affected by changes in both speed and direction). This means that an object which is spinning is accelerating as from the perspective of one point on the object as is always changing direction and thus accelerating.
Figure 1: Spacetime being increasingly warped by more massive objects. Credit: University Of Cincinnati
Figure 2
These three ideas all combine into forming ‘ripples’ in spacetime. If you were to have a symmetrical object accelerating in spacetime the shape of the observed spacetime well will not visibly change. Due to the object being symmetrical, no matter its orientation, the spacetime well formed will not change
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