5 reasons you should care about the discovery of gravitational waves

For the first time, scientists have found primordial gravitational waves — long-sought evidence of cosmic inflation theory.

Cosmic inflation suggests that the universe expanded at many times the speed of light a fraction of a second just after the Big Bang. These newly-discovered gravitational waves are ripples in space-time buried deep in the cosmic microwave background radiation, ancient light that permeated the known universe 380,000 years after the universe came into existence.

But why should we care? Here are five reasons the new cosmology findings announced Monday (March 17) should matter to Earthlings everywhere: 

5 Reasons You Should Care About the Discovery of Gravitational WavesInflation is the mysterious force that blew up the scale of the infant universe from sub-microscopic to gargantuan in a fraction of a second. See how cosmic inflation theory for the Big Bang and universe's expansion works in this Space.com infographic. (Image credit: By Karl Tate, Infographics Artist)

1) We all live in the universe

While this particular study might not have a huge practical impact on daily life, it does better explain our place in the universe.

By directly detecting gravitational waves for the first time, scientists now have more evidence for cosmic inflation — the theory that space-time expanded faster than the speed of light just after the Big Bang.

If scientists can nail down the nitty-gritty of cosmic inflation, they might be able to work backwards even further to find out what set off the Big Bang in the first place. [Cosmic Inflation and Gravitational Waves: Discovery Images]

2) … Well, make that a multiverse

The new results hint that our universe might just be one of many. According to some scientists, if cosmic inflation theory holds up, it would mean that the extreme expansion of space-time a fraction of a second after the Big Bang could have created small “bubbles” of universes in the fabric of the cosmos. Each of the universes could have their own weird laws of physics.

“In most of the models of inflation, if inflation is there, then the multiverse is there,” Stanford University theoretical physicist Andrei Linde, who wasn't involved in the new study, said a news conference Monday (March 17).

“It's possible to invent models of inflation that do not allow [a] multiverse, but it's difficult. Every experiment that brings better credence to inflationary theory brings us much closer to hints that the multiverse is real.

3) Testing the last untested part of Einstein's theory of general relativity

Gravitational waves were the last untested part of Albert Einstein's theory of general relativity.

Scientists had long predicted their existence, but these direct measurements show that they do, in fact exist.

The period of rapid cosmic inflation just after the Big Bang caused space-time to ripple, leaving its signature in the cosmic background radiation that can be seen throughout the universe.

4) Implications for grand unified theories

The new finding might also be a step closer to solving a major riddle in modern physics.

At the moment, the theory that describes huge things (general relativity) and the idea that describes tiny things (quantum mechanics) aren't compatible.

They both work on their separate scales, but when combined, they don’t play well together. If confirmed, the new study could move scientists closer to unifying those complicated theories.

“Right now, I think what we have are hints,” Marc Kamionkowski, a physics an astronomy professor at Johns Hopkins University who is unaffiliated with the study, said Monday.

“All we can tell now, is that the energy density is comparable to what you would expect from grand unified theories. We can't really say anything beyond that right now.

We can't say anything about the details about grand unified theories.

“In the future, if this signal is confirmed, and extended, we will have not only the energy density of the universe at one particular time during inflation, but at a multiple set of time,” he added. “We'll begin to learn something else about how inflation evolved, and then perhaps begin to learn more about the physics that had given rise to inflation.”

5) It narrows down the models of inflation … by a lot

The different models that can be used to describe how inflation worked in the early universe have been significantly limited by the new research, an exciting idea for physicists in the field, Kamionkowski said.

Ripples in Spacetime

“In a sweeping new book, Ripples in Spacetime: Einstein, Gravitational Waves, and the Future of Astronomy, prolific science writer Govert Schilling has achieved the fascinating trifecta of historical and scientific accuracy, a grand sense of wonder and curiosity, and brilliantly accessible storytelling…Ripples in Spacetime goes far beyond the gravitational wave story you've heard over the past few years…It belongs on the shelf of anyone interested in learning the scientific, historical, and personal stories behind some of the most incredible scientific advances of the 21st century. As our scientific progress continues, this book will serve as a reminder of how far we’ve already come, how we got there, and what we’re looking forward to with our most hopeful ambitions.”―Ethan Siegel, Forbes

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“A succinct, accessible, and remarkably timely survey of gravitational-wave astronomy as it developed over the past century…This book is a rare find…The book’s remarkable breadth and accessibility should make it the first piece of reading material for anyone―from high school students to policymakers―with an interest in gravitational waves…Ripples in Spacetime sets itself apart by putting the entire field into perspective―past, present, and future. It conveys a sense of awe about a century of scientific investment and achievement and a sense of excitement for what’s to come.”―Richard O’Shaughnessy, Physics Today

“Schilling gives us a lively and readable account of the [gravitational] waves’ discovery… Schilling underlines that this discovery is the opening of a new window on the universe, the beginning of a new branch of science.

Astronomers will no longer be limited to observing space through the waves of electricity and magnetism (for example, visible light) entering telescopes, but will be able to observe it through waves of gravity. Galileo would have been amazed.

”―Graham Farmelo, The Guardian

“A detailed account of the quest to detect gravitational waves.”―James Ryerson, New York Times Book Review

“Ripples in Spacetime provides a comprehensive and approachable guide to a complex subject.”―Monica Young, Sky & Telescope

“[Ripples in Spacetime] explains complex ideas clearly and entertainingly…It details the personalities, rivalries, collaborations, controversies, setbacks and successes of the century-long quest to test Einstein’s theories.

Bang up to date, the book describes science in progress and as a process: how ideas are developed and discoveries made and rejected or confirmed.

The best part for me was the detail the book goes into about the first detection and the meticulous protocols in place to scrutinize and eliminate every possible error. Schilling also looks ahead to what we can expect in this whole new field of astronomy.

This is a book for everyone who was as excited as I was when the [Laser Interferometer Gravitational-Wave Observatory] discovery first broke, but also for anyone who wants to know what all the fuss was about.”―Jenny Winder, BBC Sky at Night Magazine

“In September 2015, a new frontier in astronomy beckoned with the first direct detection of gravitational waves, confirming Albert Einstein's prediction almost a century before. Govert Schilling's deliciously nerdy grand tour takes us through compelling backstory, current research and future expectations.”―Barbara Kiser, Nature

“[Ripples in Spacetime] offers the reader a journey that goes beyond its title, exploring and connecting topics such as the cosmic-microwave background and its polarization, radioastronomy and pulsars, supernovae, primordial inflation, gamma-ray bursts and even dark energy… The book gives an interesting (and sometimes surprising) glimpse into the lives, aspirations and mutual interactions of the scientific pioneers in the field of gravitational waves.”―Guillermo Ballestero, CERN Courier

“A fascinating story of astronomy…Schilling walks readers through a lucid history of the universe, of general relativity, and of the bumpy search for Einstein’s last major unconfirmed prediction: the existence of gravitational waves…Schilling delivers a lively, expert, mostly comprehensible account, equal parts politics, personality, and science, of the search that ended two years ago…Schilling emphasizes that this is not simply another feather in Einstein’s cap, but a valuable new tool. The early universe was opaque to radiation until 380,000 years after the Big Bang, but gravity waves poured out from almost the beginning, so a new field of ‘gravitational wave astronomy’ can look back almost to the birth of the cosmos. An exciting history of the second great breakthrough of 21st-century physics.”―Kirkus Reviews (starred review)

“In this elegant and captivating book Govert Schilling takes us by the hand through a century of scientific adventures to one of the biggest discoveries of history.”―Robbert Dijkgraaf, Director and Leon Levy Professor, Institute for Advanced Study

Govert Schilling is an astronomy journalist and writer based in the Netherlands.

Martin Rees is a cosmologist and space scientist based in Cambridge, England. He holds the honorary title of Astronomer Royal.

Govert Schilling is an astronomy journalist and writer based in the Netherlands.

Explainer: what are gravitational waves?

Scientists working at the LIGO experiment in the US have for the first time detected elusive ripples in the fabric of space and time known as gravitational waves. There is no doubt that the finding is one of the most groundbreaking physics discoveries of the past 100 years. But what are they?

To best understand the phenomenon, let’s go back in time a few hundred years.

In 1687 when Isaac Newton published his Philosophiæ Naturalis Principia Mathematica, he thought of the gravitational force as an attractive force between two masses – be it the Earth and the Moon or two peas on a table top.

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However the nature of how this force was transmitted was less well understood at the time. Indeed the law of gravitation itself was not tested until British scientist Henry Cavendish did so in 1798, while measuring the density of the Earth.

Fast forward to 1916, when Einstein presented physicists with a new way of thinking about space, time and gravity. Building on work published in 1905, the theory of general relativity tied together that what we commonly consider to be separate entities – space and time – into what is now called “space-time”.

Space-time can be considered to be the fabric of the universe. That means everything that moves, moves through it. In this model, anything with mass distorts the space-time fabric. The larger the mass, the larger the distortion. And since every moving object moves through space-time, it will also follow the distortions caused by objects with big mass.

One way of thinking about this is to consider two children, one heavier than the other, playing on a trampoline. If we treat the surface of the trampoline as the fabric then the more massive child distorts the fabric more than the other.

If one child places a ball near the feet of the other then the ball will roll towards, or follow the distortion, towards their feet.

Similarly, when the Earth goes around the sun, the huge mass of the sun distorts the space around it, leaving our comparatively tiny planet following as “straight” a path as it can, but in a curved space. This is why it ends up orbiting the sun.

Trampolines: fun and educational. cotrim/pixabay

If we accept this simple analogy, then we have the basics of gravity. Moving on to gravitational waves is a small, but very important, step.

Let one of the children on the trampoline pull a heavy object across the surface. This creates a ripple on the surface that can be observed. Another way to visualise it is to consider moving your hand through water.

The ripples or waves spread out from their origin but quickly decay.

Any object moving through the space-time fabric causes waves or ripples in that fabric. Unfortunately, these ripples also disappear fairly quickly and only the most violent events produce distortions big enough to be detected on Earth.

To put this into perspective, two colliding black holes each with a mass of ten times that of our sun would result in a wave causing a distortion of 1% of the diameter of an atom when it reaches the Earth. On this scale, the distortion is of the order of a 0.

0000000000001m change in the diameter of the Earth compared to the 1m change due to a tidal bulge.

What can gravitational waves be used for?

Given that these ripples are so small and so difficult to detect, why have we made such an effort to find them – and why should we care about spotting them? Two immediate reasons come to mind (I’ll leave aside my own interest in simply wanting to know). One is that they were predicted by Einstein 100 years ago. Confirming the existence of gravitational waves therefore provides further strong observational support for his general theory of relativity.

In addition, the confirmation could open up new areas of physics such as gravitational-wave astronomy. By studying gravitational waves from the processes that emitted them – in this case two merging black holes – we could see intimate details of violent events in the cosmos.

LISA, a planned space-based laser interferometer, could study astrophysical sources of gravitational waves in detail. NASA

However, to make the most of such astronomy, it is best to place the detector in space. The Earth-based LIGO managed to catch gravitational waves using laser interferometry. This technique works by splitting a laser beam in two perpendicular directions and sending each down a long vacuum tunnel.

The two paths are then reflected back by mirrors to the point they started at, where a detector is placed. If the waves are disturbed by gravitational waves on their way, the recombined beams would be different from the original.

However, space-based interferometers planned for the next decade will use laser arms spanning up to a million kilometres.

Now that we know that they exist, the hope is that gravitational waves could open up the door to answering some of the biggest mysteries in science, such as what the majority of the universe is made of.

Only 5% of the universe is ordinary matter with 27% being dark matter and the remaining 68% being dark energy, with the latter two being called “dark” as we don’t understand what they are.

Gravitational waves may now provide a tool with which to probe these mysteries in a similar way that X-rays and MRI have allowed us to probe the human body.

Now read this by a scientist involved in the historic discovery

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5 reasons why you should care about the discovery of gravitational waves

Simulation of merging black holes showing gravitational waves. Wikimedia Commons
Last week marked the historic announcement of the first detection of gravitational waves.

  • A big press conference was held, and physicists around the world celebrated.
  • The discovery was even compared to Galileo looking through a telescope for the first time.

So why all the fanfare? Why are gravitational waves such a huge deal? 

REUTERS/NASA

Astronomers observe the universe across the electromagnetic spectrum, from X-ray and ultraviolet through optical and down to radio frequencies. Emission in each of these frequency ranges provides different information and thus a different perspective on our astronomical points of interest.

For example, we know that there are millions of stars clustered toward the center of our Galaxy which emit mostly at optical wavelengths, but there is also a lot of dust near the Galactic center as well.

So to study those dust-enshrouded stars, astronomers must observe them at either infrared wavelengths (where the dust emits) or radio wavelengths (which can penetrate through the dust more effectively than shorter optical wavelengths).

All of these wavelengths offer a unique perspective on the universe, but they are all the same kind of light, electromagnetic radiation, and so behave in similar, understood ways.

Gravitational waves are an entirely new phenomenon different from anything on the electromagnetic spectrum. In 1915, Albert Einstein proposed a radically different way of looking at gravity with his theory of general relativity.

Rather than thinking of gravity as a force pushing and pulling massive objects in different directions, he described gravity as being manifested in a curvature of spacetime.

In other words, the space (and time) around a massive object is curved, which then dictates how passing objects can move through that space.

This may sound crazy, but we can actually observe many of the effects predicted by Einstein’s theory.

For example, general relativity informs us that time passes more slowly by an ever so small margin down here on Earth than it does for GPS satellites in orbit, an effect known as time dilation, a result of the curvature of spacetime.

Without adjusting for this small time difference in our satellite communications, we would never get to where we are trying to go.

A consequence of the general relativity framework is that when objects accelerate through this warping of spacetime, they produce ripples known as gravitational waves. These waves propagate through space, compressing it in one direction and stretching it in another.

The frequencies predicted for these fluctuations are within the human hearing range. We can hear gravitational waves and already scientists and artists have teamed up to explore other artistic interpretations of their sound.

So why did it take 100 years to detect them? These ripples are tiny, on order of a thousandth of the size of a proton nucleus, so we need a pretty violent event to occur to produce enough of them for us to detect. We also need, of course, a very sensitive detector.

LIGO

To detect such tiny distortions in spacetime, physicists use a technique called laser interferometry.

A focused beam of light is sent in different directions to bounce back and forth between two sets of mirrors before being sent to a detector.

If a gravitational wave passes by the interferometer during all of this bouncing, the distance between the mirrors will change ever so slightly and this change will translate to a difference in the two signals as measured by the detector.

Not only is the signal from gravitational waves incredibly weak, there is also a significant amount of competing noise attempting to drown it out. To increase the detectability of such a signal against the background noise, the path the laser travels must be a long one.

The Laser Interferometer Gravitational-Wave Observatory (LIGO), the instrument that made the historic detection, is four kilometers long on each side.

The detectors are further suspended in the air in hopes of isolating the slightly faster wiggles due to gravitational waves from terrestrial interference.

What is the theory of gravitation now after the discovery of gravitational wave?

Godfrey Okoye University

Doshisha University

Saint Mary's College of California

COMSATS University Islamabad

Ministero dell'Istruzione, dell'Università e della Ricerca

Institute of Physics of the National Academy of Science of Ukraine

COMSATS University Islamabad

Progressive Science Institute

Institute of Physics of the National Academy of Science of Ukraine

Doshisha University

University of Tartu

Godfrey Okoye University

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