How do gravitational waves affect humans? Gravitational waves: the most important thing about a colossal discovery

On February 11, 2016, an international group of scientists, including from Russia, at a press conference in Washington announced a discovery that sooner or later will change the development of civilization. It was possible to prove in practice gravitational waves or waves of space-time. Their existence was predicted 100 years ago by Albert Einstein in his.

No one doubts that this discovery will be awarded the Nobel Prize. Scientists are in no hurry to talk about its practical application. But they remind us that until quite recently, humanity also did not know what to do with electromagnetic waves, which ultimately led to a real scientific and technological revolution.

What are gravitational waves in simple terms

Gravity and universal gravitation are one and the same thing. Gravitational waves are one of the solutions to GPV. They must spread at the speed of light. It is emitted by any body moving with variable acceleration.

For example, it rotates in its orbit with variable acceleration directed towards the star. And this acceleration is constantly changing. The solar system emits energy on the order of several kilowatts in gravitational waves. This is an insignificant amount, comparable to 3 old color TVs.

Another thing is two pulsars (neutron stars) orbiting each other. They rotate in very close orbits. Such a “couple” was discovered by astrophysicists and observed for a long time. The objects were ready to fall on each other, which indirectly indicated that pulsars emit space-time waves, that is, energy in their field.

Gravity is the force of gravity. We are drawn to the earth. And the essence of a gravitational wave is a change in this field, which is extremely weak when it reaches us. For example, take the water level in a reservoir. The gravitational field strength is the acceleration of free fall at a specific point. A wave runs across our pond, and suddenly the acceleration of free fall changes, just a little.

Such experiments began in the 60s of the last century. At that time, they came up with this: they hung a huge aluminum cylinder, cooled to avoid internal thermal fluctuations. And they waited for a wave from a collision, for example, of two massive black holes to suddenly reach us. The researchers were full of enthusiasm and said that the entire globe could be affected by a gravitational wave coming from outer space. The planet will begin to vibrate, and these seismic waves (compression, shear, and surface waves) can be studied.

An important article about the device in simple terms, and how the Americans and LIGO stole the idea of ​​Soviet scientists and built introferometers that made the discovery possible. Nobody talks about it, everyone is silent!

By the way, gravitational radiation is more interesting from the position of cosmic microwave background radiation, which they are trying to find by changing the spectrum of electromagnetic radiation. CMB and electromagnetic radiation appeared 700 thousand years after the Big Bang, then during the expansion of the universe, filled with hot gas with traveling shock waves, which later turned into galaxies. In this case, naturally, a gigantic, mind-boggling number of space-time waves should have been emitted, affecting the wavelength of the cosmic microwave background radiation, which at that time was still optical. Russian astrophysicist Sazhin writes and regularly publishes articles on this topic.

Misinterpretation of the discovery of gravitational waves

“A mirror hangs, a gravitational wave acts on it, and it begins to oscillate. And even the most insignificant fluctuations with an amplitude less than the size of an atomic nucleus are noticed by instruments” - such an incorrect interpretation, for example, is used in the Wikipedia article. Don’t be lazy, find an article by Soviet scientists from 1962.

First, the mirror must be massive in order to feel the "ripples". Secondly, it must be cooled to almost absolute zero (Kelvin) to avoid its own thermal fluctuations. Most likely, not only in the 21st century, but in general it will never be possible to detect an elementary particle - the carrier of gravitational waves:

Yesterday, the world was shocked by a sensation: scientists finally discovered gravitational waves, the existence of which Einstein predicted a hundred years ago. This is a breakthrough. Distortion of space-time (these are gravitational waves - now we’ll explain what’s what) was discovered at the LIGO observatory, and one of its founders is - who do you think? - Kip Thorne, author of the book.

We tell you why the discovery of gravitational waves is so important, what Mark Zuckerberg said and, of course, share the story from the first person. Kip Thorne, like no one else, knows how the project works, what makes it unusual and what significance LIGO has for humanity. Yes, yes, everything is so serious.

Discovery of gravitational waves

The scientific world will forever remember the date February 11, 2016. On this day, participants in the LIGO project announced: after so many futile attempts, gravitational waves had been found. This is reality. In fact, they were discovered a little earlier: in September 2015, but yesterday the discovery was officially recognized. The Guardian believes that scientists will certainly receive the Nobel Prize in Physics.

The cause of gravitational waves is the collision of two black holes, which occurred already... a billion light years from Earth. Can you imagine how huge our Universe is! Since black holes are very massive bodies, they send ripples through space-time, distorting it slightly. So waves appear, similar to those that spread from a stone thrown into the water.

This is how you can imagine gravitational waves coming to the Earth, for example, from a wormhole. Drawing from the book “Interstellar. Science behind the scenes"

The resulting vibrations were converted into sound. Interestingly, the signal from gravitational waves arrives at approximately the same frequency as our speech. So we can hear with our own ears how black holes collide. Listen to what gravitational waves sound like.

And guess what? More recently, black holes are not structured as previously thought. But there was no evidence at all that they exist in principle. And now there is. Black holes really “live” in the Universe.

This is what scientists believe a catastrophe looks like—a merger of black holes.

On February 11, a grandiose conference was held, which brought together more than a thousand scientists from 15 countries. Russian scientists were also present. And, of course, there was Kip Thorne. “This discovery is the beginning of an amazing, magnificent quest for people: the search and exploration of the curved side of the Universe - objects and phenomena created from distorted space-time. Black hole collisions and gravitational waves are our first remarkable examples,” said Kip Thorne.

The search for gravitational waves has been one of the main problems in physics. Now they have been found. And Einstein's genius is confirmed again.

In October, we interviewed Sergei Popov, a Russian astrophysicist and famous popularizer of science. He looked like he was looking into water! In the fall: “It seems to me that we are now on the threshold of new discoveries, which is primarily associated with the work of the LIGO and VIRGO gravitational wave detectors (Kip Thorne made a major contribution to the creation of the LIGO project).” Amazing, right?

Gravitational waves, wave detectors and LIGO

Well, now for a little physics. For those who really want to understand what gravitational waves are. Here's an artistic depiction of the tendex lines of two black holes orbiting each other, counterclockwise, and then colliding. Tendex lines generate tidal gravity. Let's move on. The lines, which emanate from the two points furthest apart from each other on the surfaces of a pair of black holes, stretch everything in their path, including the artist’s friend in the drawing. The lines emanating from the collision area compress everything.

As the holes rotate around one another, they carry along their tendex lines, which resemble streams of water from a spinning sprinkler on a lawn. In the picture from the book “Interstellar. Science behind the scenes" - a pair of black holes that collide, rotating around each other counterclockwise, and their tendex lines.

Black holes merge into one big hole; it is deformed and rotates counterclockwise, dragging tendex lines with it. A stationary observer far from the hole will feel vibrations as the tendex lines pass through him: stretching, then compression, then stretching - the tendex lines have become a gravitational wave. As the waves propagate, the black hole's deformation gradually decreases, and the waves also weaken.

When these waves reach the Earth, they look like the one shown at the top of the figure below. They stretch in one direction and compress in the other. The extensions and contractions fluctuate (from red right-left, to blue right-left, to red right-left, etc.) as the waves pass through the detector at the bottom of the figure.

Gravitational waves passing through the LIGO detector.

The detector consists of four large mirrors (40 kilograms, 34 centimeters in diameter), which are attached to the ends of two perpendicular pipes, called detector arms. Tendex lines of gravitational waves stretch one arm, while compressing the second, and then, on the contrary, compress the first and stretch the second. And so again and again. As the length of the arms changes periodically, the mirrors shift relative to each other, and these displacements are tracked using laser beams in a way called interferometry. Hence the name LIGO: Laser Interferometer Gravitational-Wave Observatory.

LIGO control center, from where they send commands to the detector and monitor the received signals. LIGO's gravity detectors are located in Hanford, Washington, and Livingston, Louisiana. Photo from the book “Interstellar. Science behind the scenes"

Now LIGO is an international project involving 900 scientists from different countries, with headquarters located at the California Institute of Technology.

The Curved Side of the Universe

Black holes, wormholes, singularities, gravitational anomalies and higher order dimensions are associated with curvatures of space and time. That's why Kip Thorne calls them "the twisted side of the universe." Humanity still has very little experimental and observational data from the curved side of the Universe. This is why we pay so much attention to gravitational waves: they are made of curved space and provide the most accessible way for us to explore the curved side.

Imagine if you only saw the ocean when it was calm. You wouldn't know about currents, whirlpools and storm waves. This is reminiscent of our current knowledge of the curvature of space and time.

We know almost nothing about how curved space and curved time behave "in a storm" - when the shape of space fluctuates violently and when the speed of time fluctuates. This is an incredibly alluring frontier of knowledge. Scientist John Wheeler coined the term "geometrodynamics" for these changes.

Of particular interest in the field of geometrodynamics is the collision of two black holes.

Collision of two non-rotating black holes. Model from the book “Interstellar. Science behind the scenes"

The picture above shows the moment when two black holes collide. Just such an event allowed scientists to record gravitational waves. This model is built for non-rotating black holes. Top: orbits and shadows of holes, as seen from our Universe. Middle: curved space and time, as seen from the bulk (multidimensional hyperspace); The arrows show how space is involved in movement, and the changing colors show how time is bent. Bottom: The shape of the emitted gravitational waves.

Gravitational waves from the Big Bang

Over to Kip Thorne. “In 1975, Leonid Grischuk, my good friend from Russia, made a sensational statement. He said that at the moment of the Big Bang many gravitational waves arose, and the mechanism of their origin (previously unknown) was as follows: quantum fluctuations (random fluctuations - editor's note) gravitational fields during the Big Bang were greatly enhanced by the initial expansion of the Universe and thus became the original gravitational waves. These waves, if detected, could tell us what happened at the birth of our Universe."

If scientists find the primordial gravitational waves, we will know how the Universe began.

People have solved far all the mysteries of the Universe. There's more to come.

In subsequent years, as our understanding of the Big Bang improved, it became obvious that these primordial waves must be strong at wavelengths commensurate with the size of the visible Universe, that is, at lengths of billions of light years. Can you imagine how much this is?.. And at the wavelengths that LIGO detectors cover (hundreds and thousands of kilometers), the waves will most likely be too weak to be recognized.

Jamie Bock's team built the BICEP2 apparatus, with which the trace of the original gravitational waves was discovered. The device located at the North Pole is shown here during twilight, which occurs there only twice a year.

BICEP2 device. Image from the book Interstellar. Science behind the scenes"

It is surrounded by shields that shield the device from radiation from the surrounding ice cover. In the upper right corner there is a trace discovered in the cosmic microwave background radiation - a polarization pattern. Electric field lines are directed along short light strokes.

Trace of the beginning of the universe

In the early nineties, cosmologists realized that these gravitational waves, billions of light years long, must have left a unique trace in the electromagnetic waves that fill the Universe - the so-called cosmic microwave background, or cosmic microwave background radiation. This began the search for the Holy Grail. After all, if we detect this trace and deduce from it the properties of the original gravitational waves, we can find out how the Universe was born.

In March 2014, while Kip Thorne was writing this book, the team of Jamie Bok, a cosmologist at Caltech whose office is next door to Thorne's, finally discovered this trace in the cosmic microwave background radiation.

This is an absolutely amazing discovery, but there is one controversial point: the trace found by Jamie's team could have been caused by something other than gravitational waves.

If a trace of the gravitational waves that arose during the Big Bang is indeed found, it means that a cosmological discovery has occurred on a level that happens perhaps once every half century. It gives you a chance to touch the events that occurred a trillionth of a trillionth of a trillionth of a second after the birth of the Universe.

This discovery confirms theories that the expansion of the Universe at that moment was extremely fast, in the slang of cosmologists - inflationary fast. And heralds the advent of a new era in cosmology.

Gravitational waves and Interstellar

Yesterday, at a conference on the discovery of gravitational waves, Valery Mitrofanov, head of the Moscow LIGO collaboration of scientists, which includes 8 scientists from Moscow State University, noted that the plot of the film “Interstellar,” although fantastic, is not so far from reality. And all because Kip Thorne was the scientific consultant. Thorne himself expressed hope that he believes in future manned flights to a black hole. They may not happen as soon as we would like, but today it is much more real than it was before.

The day is not too far off when people will leave the confines of our galaxy.

The event stirred the minds of millions of people. The notorious Mark Zuckerberg wrote: “The discovery of gravitational waves is the biggest discovery in modern science. Albert Einstein is one of my heroes, which is why I took the discovery so personally. A century ago, within the framework of the General Theory of Relativity (GTR), he predicted the existence of gravitational waves. But they are so small to detect that it has come to look for them in the origins of events such as the Big Bang, stellar explosions and black hole collisions. When scientists analyze the data obtained, a completely new view of space will open before us. And perhaps this will shed light on the origin of the Universe, the birth and development of black holes. It is very inspiring to think about how many lives and efforts have gone into unveiling this mystery of the Universe. This breakthrough was made possible thanks to the talent of brilliant scientists and engineers, people of different nationalities, as well as the latest computer technologies that have appeared only recently. Congratulations to everyone involved. Einstein would be proud of you."

This is the speech. And this is a person who is simply interested in science. One can imagine what a storm of emotions overwhelmed the scientists who contributed to the discovery. It seems that we have witnessed a new era, friends. This is amazing.

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The official day of discovery (detection) of gravitational waves is February 11, 2016. It was then, at a press conference held in Washington, that the leaders of the LIGO collaboration announced that a team of researchers had managed to record this phenomenon for the first time in human history.

Prophecies of the great Einstein

The fact that gravitational waves exist was suggested by Albert Einstein at the beginning of the last century (1916) within the framework of his General Theory of Relativity (GTR). One can only marvel at the brilliant abilities of the famous physicist, who, with a minimum of real data, was able to draw such far-reaching conclusions. Among many other predicted physical phenomena that were confirmed in the next century (slowing down the flow of time, changing the direction of electromagnetic radiation in gravitational fields, etc.), it was not possible to practically detect the presence of this type of wave interaction of bodies until recently.

Is gravity an illusion?

In general, in the light of the Theory of Relativity, gravity can hardly be called a force. disturbances or curvatures of the space-time continuum. A good example to illustrate this postulate is a stretched piece of fabric. Under the weight of a massive object placed on such a surface, a depression is formed. Other objects, when moving near this anomaly, will change the trajectory of their movement, as if being “attracted”. And the greater the weight of the object (the greater the diameter and depth of the curvature), the higher the “force of attraction”. As it moves across the fabric, one can observe the appearance of diverging “ripples”.

Something similar happens in outer space. Any rapidly moving massive matter is a source of fluctuations in the density of space and time. A gravitational wave with a significant amplitude is formed by bodies with extremely large masses or when moving with enormous accelerations.

Physical characteristics

Fluctuations in the space-time metric manifest themselves as changes in the gravitational field. This phenomenon is otherwise called space-time ripples. The gravitational wave affects the encountered bodies and objects, compressing and stretching them. The magnitude of the deformation is very insignificant - about 10 -21 from the original size. The whole difficulty of detecting this phenomenon was that researchers needed to learn how to measure and record such changes using appropriate equipment. The power of gravitational radiation is also extremely small - for the entire solar system it is several kilowatts.

The speed of propagation of gravitational waves depends slightly on the properties of the conducting medium. The amplitude of oscillations gradually decreases with distance from the source, but never reaches zero. The frequency ranges from several tens to hundreds of hertz. The speed of gravitational waves in the interstellar medium approaches the speed of light.

Circumstantial evidence

The first theoretical confirmation of the existence of gravitational waves was obtained by the American astronomer Joseph Taylor and his assistant Russell Hulse in 1974. Studying the vastness of the Universe using the Arecibo Observatory radio telescope (Puerto Rico), researchers discovered the pulsar PSR B1913+16, which is a binary system of neutron stars rotating around a common center of mass with a constant angular velocity (a rather rare case). Every year the circulation period, originally 3.75 hours, is reduced by 70 ms. This value is fully consistent with the conclusions from the general relativity equations, which predict an increase in the rotation speed of such systems due to the expenditure of energy on the generation of gravitational waves. Subsequently, several double pulsars and white dwarfs with similar behavior were discovered. Radio astronomers D. Taylor and R. Hulse were awarded the Nobel Prize in Physics in 1993 for discovering new possibilities for studying gravitational fields.

Escaping gravitational wave

The first announcement about the detection of gravitational waves came from University of Maryland scientist Joseph Weber (USA) in 1969. For these purposes, he used two gravitational antennas of his own design, separated by a distance of two kilometers. The resonant detector was a well-vibration-insulated solid two-meter aluminum cylinder equipped with sensitive piezoelectric sensors. The amplitude of the oscillations allegedly recorded by Weber turned out to be more than a million times higher than the expected value. Attempts by other scientists to repeat the “success” of the American physicist using similar equipment did not bring positive results. A few years later, Weber’s work in this area was recognized as untenable, but gave impetus to the development of the “gravitational boom”, which attracted many specialists to this area of ​​research. By the way, Joseph Weber himself was sure until the end of his days that he received gravitational waves.

Improving receiving equipment

In the 70s, scientist Bill Fairbank (USA) developed the design of a gravitational wave antenna, cooled using SQUIDS - ultra-sensitive magnetometers. The technologies existing at that time did not allow the inventor to see his product realized in “metal”.

The Auriga gravitational detector at the National Legnar Laboratory (Padua, Italy) is designed using this principle. The design is based on an aluminum-magnesium cylinder, 3 meters long and 0.6 m in diameter. The receiving device weighing 2.3 tons is suspended in an insulated vacuum chamber cooled almost to absolute zero. To record and detect shocks, an auxiliary kilogram resonator and a computer-based measuring complex are used. The stated sensitivity of the equipment is 10 -20.

Interferometers

The operation of interference detectors of gravitational waves is based on the same principles on which the Michelson interferometer operates. The laser beam emitted by the source is divided into two streams. After multiple reflections and travels along the arms of the device, the flows are again brought together, and based on the final one, it is judged whether any disturbances (for example, a gravitational wave) affected the course of the rays. Similar equipment has been created in many countries:

• GEO 600 (Hannover, Germany). The length of the vacuum tunnels is 600 meters.
• TAMA (Japan) with shoulders of 300 m.
• VIRGO (Pisa, Italy) is a joint French-Italian project launched in 2007 with three kilometers of tunnels.
• LIGO (USA, Pacific Coast), which has been hunting for gravitational waves since 2002.

The latter is worth considering in more detail.

LIGO Advanced

The project was created on the initiative of scientists from the Massachusetts and California Institutes of Technology. It includes two observatories, separated by 3 thousand km, in and Washington (the cities of Livingston and Hanford) with three identical interferometers. The length of perpendicular vacuum tunnels is 4 thousand meters. These are the largest such structures currently in operation. Until 2011, numerous attempts to detect gravitational waves did not bring any results. The significant modernization carried out (Advanced LIGO) increased the sensitivity of the equipment in the range of 300-500 Hz by more than five times, and in the low-frequency region (up to 60 Hz) by almost an order of magnitude, reaching the coveted value of 10 -21. The updated project started in September 2015, and the efforts of more than a thousand collaboration employees were rewarded with the results obtained.

Gravitational waves detected

On September 14, 2015, advanced LIGO detectors, with an interval of 7 ms, recorded gravitational waves reaching our planet from the largest phenomenon that occurred on the outskirts of the observable Universe - the merger of two large black holes with masses 29 and 36 times greater than the mass of the Sun. During the process, which took place more than 1.3 billion years ago, about three solar masses of matter were consumed in a matter of fractions of a second by emitting gravitational waves. The recorded initial frequency of gravitational waves was 35 Hz, and the maximum peak value reached 250 Hz.

The results obtained were repeatedly subjected to comprehensive verification and processing, and alternative interpretations of the data obtained were carefully eliminated. Finally, last year the direct registration of the phenomenon predicted by Einstein was announced to the world community.

A fact illustrating the titanic work of researchers: the amplitude of fluctuations in the size of the interferometer arms was 10 -19 m - this value is the same number of times smaller than the diameter of an atom, as the atom itself is smaller than an orange.

Future prospects

The discovery once again confirms that the General Theory of Relativity is not just a set of abstract formulas, but a fundamentally new look at the essence of gravitational waves and gravity in general.

In further research, scientists have high hopes for the ELSA project: the creation of a giant orbital interferometer with arms of about 5 million km, capable of detecting even minor disturbances in gravitational fields. Activation of work in this direction can tell a lot of new things about the main stages of the development of the Universe, about processes that are difficult or impossible to observe in traditional ranges. There is no doubt that black holes, whose gravitational waves will be detected in the future, will tell a lot about their nature.

To study the cosmic microwave background radiation, which can tell us about the first moments of our world after the Big Bang, more sensitive space instruments will be required. Such a project exists ( Big Bang Observer), but its implementation, according to experts, is possible no earlier than in 30-40 years.

Astrophysicists have confirmed the existence of gravitational waves, the existence of which was predicted by Albert Einstein about 100 years ago. They were detected using detectors at the LIGO gravitational wave observatory, which is located in the United States.

For the first time in history, humanity has recorded gravitational waves - vibrations of space-time that came to Earth from the collision of two black holes that occurred far in the Universe. Russian scientists also contributed to this discovery. On Thursday, researchers talk about their discovery around the world - in Washington, London, Paris, Berlin and other cities, including Moscow.

The photo shows a simulation of a black hole collision

At a press conference at the Rambler&Co office, Valery Mitrofanov, head of the Russian part of the LIGO collaboration, announced the discovery of gravitational waves:

“We were honored to participate in this project and present the results to you. I will now tell you the meaning of the discovery in Russian. We've seen some great pictures of LIGO detectors in the US. The distance between them is 3000 km. Under the influence of a gravitational wave, one of the detectors shifted, after which we discovered them. At first we saw just noise on the computer, and then the mass of the Hamford detectors began to rock. After calculating the data obtained, we were able to determine that it was the black holes that collided at a distance of 1.3 billion. light years away. The signal was very clear, it came out of the noise very clearly. Many people told us that we were lucky, but nature gave us such a gift. Gravitational waves have been discovered, that’s for sure.”

Astrophysicists have confirmed rumors that they were able to detect gravitational waves using detectors at the LIGO gravitational wave observatory. This discovery will allow humanity to make significant progress in understanding how the Universe works.

The discovery occurred on September 14, 2015 simultaneously with two detectors in Washington and Louisiana. The signal arrived at the detectors as a result of the collision of two black holes. It took scientists so long to verify that it was the gravitational waves that were the product of the collision.

The collision of the holes occurred at a speed of about half the speed of light, which is approximately 150,792,458 m/s.

“Newtonian gravity was described in flat space, and Einstein transferred it to the plane of time and assumed that it bends it. Gravitational interaction is very weak. On Earth, experiments to create gravitational waves are impossible. They were discovered only after the merger of black holes. The detector shifted, just imagine, by 10 to -19 meters. You can't feel it with your hands. Only with the help of very precise instruments. How to do this? The laser beam with which the shift was recorded was unique in nature. LIGO's second generation laser gravity antenna became operational in 2015. The sensitivity makes it possible to detect gravitational disturbances approximately once a month. This is advanced world and American science; there is nothing more accurate in the world. We hope that it will be able to overcome the Standard Quantum Sensitivity Limit,” explained the discovery Sergei Vyatchanin, employee of the Physics Department of Moscow State University and the LIGO collaboration.

The standard quantum limit (SQL) in quantum mechanics is a limitation imposed on the accuracy of a continuous or repeatedly repeated measurement of any quantity described by an operator that does not commute with itself at different times. Predicted in 1967 by V.B. Braginsky, and the term Standard Quantum Limit (SQL) was proposed later by Thorne. The SKP is closely related to the Heisenberg uncertainty relation.

Summing up, Valery Mitrofanov spoke about plans for further research:

“This discovery is the beginning of a new gravitational wave astronomy. Through the channel of gravitational waves we expect to learn more about the Universe. We know the composition of only 5% of matter, the rest is a mystery. Gravity detectors will allow you to see the sky in “gravitational waves.” In the future, we hope to see the beginning of everything, that is, the relic radiation of the Big Bang, and understand what exactly happened then.”

Gravitational waves were first proposed by Albert Einstein in 1916, almost exactly 100 years ago. The equation for waves is a consequence of the equations of the theory of relativity and is not derived in the simplest way.

Canadian theoretical physicist Clifford Burgess previously published a letter saying the observatory detected gravitational radiation caused by the merger of a binary system of black holes with masses of 36 and 29 solar masses into an object with a mass of 62 solar masses. The collision and asymmetrical gravitational collapse last a fraction of a second, and during this time energy amounting to up to 50 percent of the mass of the system is lost into gravitational radiation - ripples in space-time.

A gravitational wave is a wave of gravity generated in most theories of gravitation by the movement of gravitating bodies with variable acceleration. Due to the relative weakness of gravitational forces (compared to others), these waves should have a very small magnitude, difficult to register. Their existence was predicted about a century ago by Albert Einstein.

The key difference is that while sound needs a medium to travel through, gravitational waves move the medium - in this case, spacetime itself. “They literally crush and stretch the fabric of spacetime,” says Chiara Mingarelli, a gravitational wave astrophysicist at Caltech. To our ears, the waves detected by LIGO will sound like a gurgle.

How exactly will this revolution take place? LIGO currently has two detectors that act as "ears" for scientists, and there will be more detectors in the future. And if LIGO was the first to discover, it certainly won't be the only one. There are many types of gravitational waves. In fact, there is a whole spectrum of them, just as there are different types of light, with different wavelengths, in the electromagnetic spectrum. Therefore, other collaborations will begin the hunt for waves with a frequency that LIGO is not designed for.

Mingarelli works with the NanoGRAV (North American Nanohertz Gravitational Wave Observatory) collaboration, part of a large international consortium that includes the European Pulsar Timing Array and the Parkes Pulsar Timing Array in Australia. As the name suggests, NanoGRAV scientists hunt low-frequency gravitational waves in the 1 to 10 nanohertz regime; LIGO's sensitivity is in the kilohertz (audible) part of the spectrum, looking for very long wavelengths.


The collaboration draws on pulsar data collected by the Arecibo Observatory in Puerto Rico and the Green Bank Telescope in West Virginia. Pulsars are rapidly spinning neutron stars that form when stars more massive than the Sun explode and collapse into themselves. They spin faster and faster as they are compressed, just as a weight at the end of a rope spins faster the shorter the rope gets.

They also emit powerful bursts of radiation as they spin, like a beacon, which are detected as pulses of light on Earth. And this periodic rotation is extremely accurate - almost as accurate as an atomic clock. This makes them ideal cosmic gravitational wave detectors. The first indirect evidence came from the study of pulsars in 1974, when Joseph Taylor Jr. and Russell Hulse discovered that a pulsar orbiting a neutron star slowly contracts over time, an effect that would be expected if it were converting some of its mass into energy in the form of gravitational waves.

In the case of NanoGRAV, the smoking gun will be a kind of flicker. The pulses must arrive at the same time, but if they are hit by a gravitational wave, they will arrive a little earlier or later, since space-time will compress or stretch as the wave passes.

Pulsar time grid arrays are especially sensitive to gravitational waves produced by the merger of supermassive black holes a billion to ten billion times the mass of our Sun, such as those that lurk at the center of the most massive galaxies. If two such galaxies merge, the holes at their centers will also merge and emit gravitational waves. “LIGO sees the very end of the merger, when the pairs are very close,” says Mingarelli. “With the help of MRVs, we could see them at the beginning of the spiral phase, when they are just entering each other’s orbit.”

And there is also the LISA (Laser Interferometer Space Antenna) space mission. Earth-based LIGO is excellent at detecting gravitational waves equivalent to parts of the audible sound spectrum - like those produced by our merging black holes. But many interesting sources of these waves produce low frequencies. So physicists must go into space to discover them. The main objective of the current LISA Pathfinder() mission is to test the detector's performance. “With LIGO, you can stop the instrument, open the vacuum, and fix everything,” says Scott Hughes of MIT. “But you can’t open anything in space.” We’ll have to do it right right away for it to work properly.”

LISA's goal is simple: Using laser interferometers, the spacecraft will attempt to accurately measure the relative position of two 1.8-inch gold-platinum cubes in free fall. Placed in separate electrode boxes 15 inches apart, the test objects will be protected from solar wind and other external forces so that it will be possible to detect the tiny movement caused by gravitational waves (hopefully).

Finally, there are two experiments designed to search for the imprints left by primordial gravitational waves in the cosmic microwave background radiation (the afterglow of the Big Bang): BICEP2 and the Planck mission. BICEP2 announced its detection in 2014, but it turned out that the signal was fake (cosmic dust is to blame).

Both collaborations continue the hunt in hopes of shedding light on the early history of our Universe - and hopefully confirming inflationary theory's key predictions. This theory predicted that soon after its birth, the Universe experienced rapid growth, which could not help but leave powerful gravitational waves that remained imprinted in the cosmic microwave background radiation in the form of special light waves (polarization).

Each of the four gravitational wave modes will give astronomers four new windows onto the Universe.

But we know what you're thinking: time to fire up the warp drive, guys! Will LIGO's discovery help build the Death Star next week? Of course not. But the better we understand gravity, the more we will understand how to build these things. After all, this is the job of scientists, this is how they earn their living. By understanding how the Universe works, we can rely more on our abilities.