Science and Technology
G Waves— A Time Travelling Aphotic Warning
An important step towards solving Einstein’s final riddle
A ‘Blast from the Past’
On 11th February 2016, a trailblazer swashbuckled its way into known observational astronomy: G Waves were finally detected by the LIGO and Virgo collaboration, in the United States. This distortion was named GW150914 (GW for G Waves and the date of observation, 14th September 2015). These G Waves were thought to be released by a binary black hole merger, located approximately 1.4 billion light-years away in the Southern Celestial Hemisphere. The work took place under David Reitze, famed laser physicist and the executive director of LIGO.
In order to record and hear them, these waves were converted to sound waves. To everyone’s surprise, a resonating hum, followed by minuscule blipping sounds similar to small pebbles being dropped into a pond was heard. After breaking some eggs, the widespread excitement fizzled out after hearing a diminutive sound. “Was this a waste of time and taxpayers’ money?” — some may ask. Let us delve into this newfangled, yet defining part of space.
The G stands for…
G Waves (gravitational waves, not gravity waves) are 4-dimensional distortions, which momentarily warp the space-time curvature. They propagate from their source at the speed of light and can take billions of years to be observed.
Clueless yet?
These distortions are caused when two massive bodies, such as a couple of black holes, collide with each other or come into the range of bodies like neutron stars. GW150914 was caused by the inward spiral and the merging of a binary black hole system. These temporary celestial warpings are also formed when a star explodes asymmetrically, causing shock heating of the circumstellar region. This explosion is known as a supernova.
Still feel like this going over your head? Let us get down to Earth.
The fundamentals of the space-time fabric
We know that film projectors and zoopraxiscope work on the fixed rate of frames per second, due to which, we see the horses galloping and a man running. We take the latter case, wherein the person is moving from one point to another.
Consider two people, Max and Andrew. Max uses a laser to illuminate in one direction towards Andrew who is driving a Beetle towards Max, making sure Max is not roadkill. This scene is shown as panels, running at a certain rate of frames per second. This whole sequence of animation is viewed in panels and stacked one behind the other. These infinite numbers of panels when glued together, they both and the light form separate loci of their positions (which are called world lines, in space-time scenario). In the perspective of Max, we see the straight world line of Max and the slanted world line of Andrew with the world line of light at an angle to the horizontal. But to the perspective of Andrew, the latter occurs. However, we see the angle of the world line of the light to the horizontal remains the same. This is because light travels at a constant speed always, denoted by the fixed angle.
This comparison is made by the Lorentz transformation, which makes up the heart of special relativity. According to this method, the light world line is squeezed and rotated, such that the speed of light is always constant. This was the brainchild of Albert Einstein, marked into history more than a century ago.
This concept is applied when gravity is inserted in the space-time fabric. We do know that according to Newton’s law of gravitation, the attractive force exerted by an object on another is proportional to the product of their masses and inversely proportional to the square of the distance between them. Let us take a simple example.
When we put a bowling ball on a spongy mattress and a marble near it, the marble rapidly rolls towards the bowling ball due to the depression formed. Our space-time fabric works similarly. Every celestial object makes a dent on the space-time fabric, and the revolution of artificial satellites can be compared to rolling a marble at a constant rate inside a large bowl.
Sounds good on paper, but do these theories exist in real life?
The space-time model can be applied in the collision of black holes, where they combine into a single world line.
The line of motion was as such wherein the two black holes spiraled into each other. The duo combined to form a massive ripple across space, which caused expansion and contraction, albeit at a microscopic rate.
We know that gravitational forces are the weakest interaction forces. So, with the astronomical distances between Earth and the binary systems of a black hole, it is not easy to observe them properly. When combined with various interferences by anthropogenic activities, it is near impossible to observe these with meagre instruments. As a result, LIGOs (Laser Interferometer Gravitational-Wave Observatories) were used.
What are LIGOs?
LIGOs are considered the world’s largest gravitational wave observatories, to date. They are currently located at two places in the US (Hanford, Washington, and Livingston, Louisiana; located in isolated places in order to observe these G Waves without interference and noise, and in order to rule out terrestrial disturbances, if any). These observatories are L-shaped, whose arms are about four kilometers long. These observatories are also located in Pisa, Italy (Virgo).
LIGOs are also called Blind astronomical observatories and are called so for a reason. Unlike other optical or radio telescopes, LIGOs are used to observe G Waves, which are not a part of the electromagnetic spectrum. So, they are not round or dish-shaped, like radio telescope dishes, as they do not collect light from stars and other luminous bodies.
The rudimentary components for this observatory involve a pair of mirrors, two light beams, and interferometers, etc. Lasers of the wavelength of 1064 nm (infrared) are selected, with less space for error. The working principle behind them is that when the G Wave passes through Earth, the length of one light beam or laser travelling through an arm contract while the latter expands. The latter is also possible. Then another reference light beam is sent, on both the arms respectively, towards the giant, polished-to-the-finesse mirrors, which makes these expansions and contractions. These mirrors are stranded above the ground by the thickness of a thumb. They occur alternatively in each arm; for example, if one arm gets longer, the latter gets shorter. This is called Differential Arm Motion. This is visible in the first place, due to the difference in time taken by the reference light beam to travel the changed length of the four-kilometer tube, which is measured in the scale of ten-thousandth of the width of the proton. The time difference is calculated with reference to the curvature of the Earth, at the building which is located at the epicentre of this L-shaped structure.
The interferometers used in LIGOs are of Michelson-type, which produce interference fringes, by splitting a beam of monochromatic light, so that one beam strikes a fixed mirror and the other beam hits a mobile mirror. They have low-temperature sensitivity.
The arrangement above is surrounded by cylindrical concrete tubes in a vacuum. Also, it is isolated from vibration and seismic activity, by active damping systems that use permanent magnet actuators and quadruple pendulum systems. This is done for achieving accuracy and to avoid anomalies in calculations.
“What does this have to do with our mundane routine?”
The technology we currently possess cannot analyze the amount of data, given by the vast ocean of space. These waves show proof of Einstein’s Theory of Relativity. With the discovery of these G Waves, predictions of binary black hole systems and their orbits, or supernovae of stars can be made relatively easier and efficient.
This would give us a fourth angle of the triangle to our view towards gravity and would reduce our reliance on Electromagnetic Waves, like X-rays emitted from those systems in space which cause lots of aberrations in the observed values. As their calculations are time-consuming, detecting the accelerations of these humongous waves is easier, as these can be found even in the absence of light. These waves can also give answers to the mystery of the expanding Universe. It can also give an insight into the black hole binary systems and the monstrous and elusive magnetars, which are formations of neutron stars from supernovae. These magnetars produce ginormous magnetic fields of 0.1 trillion Tesla.
Perhaps we can finally find a way to go back to the past and solve our school assignment on time. Or can we?
