On the 14th of September, 2015, scientists working at two LIGO (Laser Inferometer Gravitational wave Observatory) stations in Washington and Louisiana detected what would later be confirmed as the gravitational waves of two orbiting binary black holes, colliding and coalescing into one greater, stable black hole. To a physicist, it is one of the most important confirmations of modern times. To the everyday layman…what are gravitational waves? What even happened? Is it important?
This article is here to enlighten you all on the implications of this discovery; as a student with a love for all things Physics, I hope you will find the knowledge of interest! In order to explain how important the confirmation is, some introductory knowledge must be imparted, beginning with knowledge on how the detectors work.
In two research stations in America are two sets of perpendicular laser emitters, spaced 4km from each other. Using precise analysis of the interference pattern of the waves (which should normally cancel out, and produce no light), disturbances in physical matter can be measured on an extremely small scale. When a significant gravitational wave disturbance occurs, it causes the distance between the two laser emitters to change, meaning the laser beams no longer ‘cancel out’ but produce a modicum of a reflected beam; the intensity of the beam is directly linked to the intensity of the gravitational wave, as it stretches and compresses matter. As such, the detector demonstrates a direct effect of Einstein’s Theory of Relativity.
Einstein, in 1915, proposed the theory of general relativity, which dictated, among many other points, that physical space is connected by a gravitational field that warps and undulates, based upon mass. As such, extremely large or dense objects (such as black holes or stars) should curve and distort space more significantly than smaller objects, causing objects to be stretched and squashed proportionally. Orbiting objects should therefore create a ‘wave’ of gravitational space-time influence. However, this only occurs on an atomic scale on Earth because the most powerful sources of gravitational waves are so far from us; even so, they should still, theoretically, be measurable. However, Einstein lacked the technology in 1916 to prove his idea of gravitational, but about hundred years later, the apparatus to measure gravitational field strength would finally be accurate enough to measure changes in the gravitational field; so accurate, it can measure a change in distance equal to the width of the human hair, over a distance of four light years (equivalent to 94,608,000,000,000,00 metres!).
Speaking to Doctor David Burton, a theoretical physicist with experience working with fluid dynamics, plasma physics and particle theory, alongside gravitational physics at Lancaster University, I gained a physicist’s insight into this discovery. Surprisingly, he informed me that “there are several different aspects of general relativity that have already been detected”. The main reason why scientists are so excited is because this was an example of the first ‘concrete’ evidence of gravitational waves. “There already was indirect evidence for gravitational waves coming from binary pulsars. It was to do with the change in the orbital period due to gravitational wave emission…That’s been known since the late 1970’s”. Despite this, the confirmation is important, because it means that we’ll “have a completely new way of doing astronomy… essentially all of astronomy has relied upon electromagnetic radiation using photons as opposed to the gravitational field…it’s a different way of seeing the universe, and gravitational waves propagate a lot further, less impeded than electromagnetic waves…[meaning] you get a completely different view of what’s going on [in the universe]”.
The amazing fact about this was that it barely scratches the surface of a whole new area of astronomy; the newly upgraded LIGO detectors picked this data when it was first run! A space mission under the name eLISA aims to place gravitational wave detectors in space, so that we can analyse shorter wavelengths, meaning we can view more subtle changes in the gravitational space-time field, and hence analyse more well-hidden phenomena.
The implications of the success of such technology are astounding. Ever since Galileo first constructed the telescope, we have been using the electromagnetic spectrum to view the heavens. The electromagnetic spectrum is a scale of the wavelength of different waves, and is grouped into radio waves, microwaves, infra-red (heat), the visible light spectrum, ultra-violet, x-rays and gamma rays, each section of the spectrum holding unique properties, but sharing the same fundamental structure. We have used all of these in the analysis and study of the universe, and now we have the tools to breach a new, gravitational spectrum. Gravitational waves will allow us to be able to see further into the heart of the Universe, and not only better understand phenomena such as black holes, but also potentially discover new mechanisms and forces behaving within the confines of reality. We are taking yet another step into our great Universe; it may be a much more wondrous place to look into, in the years to come.