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 Nobel Prize. Scientists are in no hurry to talk about it 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 gravity- It is the same. Gravitational waves are one of the OTS solutions. 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. 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 rotating around each other ( neutron stars s). 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. Tension gravitational field— acceleration 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 all Earth may experience the effects of a gravitational wave arriving from outer space. The planet will begin to vibrate, and these seismic waves (compression, shear, and surface waves) can be studied.

Important article about the device in simple language, 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 electromagnetic radiation. CMB and electromagnetic radiation appeared 700 thousand years after big bang, then in the process of expansion of the universe, filled with hot gas with running 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 in amplitude smaller size 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.

Firstly, 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:

Valentin Nikolaevich Rudenko shares the story of his visit to the city of Cascina (Italy), where he spent a week on the then just built “gravitational antenna” - the Michelson optical interferometer. On the way to the destination, the taxi driver asks why the installation was built. “People here think it’s for talking to God,” the driver admits.

– What are gravitational waves?

– A gravitational wave is one of the “carriers of astrophysical information.” There are visible channels of astrophysical information; telescopes play a special role in “distant vision”. Astronomers have also mastered low-frequency channels - microwave and infrared, and high-frequency channels - X-ray and gamma. In addition to electromagnetic radiation, we can detect streams of particles from Space. For this purpose, neutrino telescopes are used - large-sized detectors of cosmic neutrinos - particles that weakly interact with matter and are therefore difficult to register. Almost all theoretically predicted and laboratory-studied types of “carriers of astrophysical information” have been reliably mastered in practice. The exception was gravity - the most weak interaction in a microcosm and the most powerful force in the macrocosm.

Gravity is geometry. Gravitational waves are geometric waves, that is, waves that change the geometric characteristics of space when they pass through that space. Roughly speaking, these are waves that deform space. Strain is the relative change in the distance between two points. Gravitational radiation differs from all other types of radiation precisely in that it is geometric.

– Did Einstein predict gravitational waves?

– Formally, it is believed that gravitational waves were predicted by Einstein as one of the consequences of his general theory of relativity, but in fact their existence becomes obvious already in the special theory of relativity.

The theory of relativity suggests that due to gravitational attraction gravitational collapse is possible, that is, the contraction of an object as a result of collapse, roughly speaking, to a point. Then the gravity is so strong that light cannot even escape from it, so such an object is figuratively called a black hole.

– What is the peculiarity gravitational interaction?

A feature of gravitational interaction is the principle of equivalence. According to it, the dynamic response of a test body in a gravitational field does not depend on the mass of this body. Simply put, all bodies fall with the same acceleration.

Gravitational interaction is the weakest we know today.

– Who was the first to try to catch a gravitational wave?

– The gravitational wave experiment was first conducted by Joseph Weber from the University of Maryland (USA). He created a gravitational detector, which is now kept in the Smithsonian Museum in Washington. In 1968-1972, Joe Weber conducted a series of observations on a pair of spatially separated detectors, trying to isolate cases of "coincidences". The coincidence technique is borrowed from nuclear physics. Low statistical significance gravitational signals received by Weber caused a critical attitude towards the results of the experiment: there was no confidence that it was possible to detect gravitational waves. Subsequently, scientists tried to increase the sensitivity of Weber-type detectors. It took 45 years to develop a detector whose sensitivity was adequate to the astrophysical forecast.

During the start of the experiment, many other experiments took place before fixation; impulses were recorded during this period, but their intensity was too low.

– Why was the signal fixation not announced immediately?

– Gravitational waves were recorded back in September 2015. But even if a coincidence was recorded, before announcing it, it is necessary to prove that it is not accidental. The signal taken from any antenna always contains noise bursts (short-term bursts), and one of them can accidentally occur simultaneously with a noise burst on another antenna. It is possible to prove that the coincidence was not accidental only with the help of statistical estimates.

– Why are discoveries in the field of gravitational waves so important?

– The ability to register the relict gravitational background and measure its characteristics, such as density, temperature, etc., allows us to approach the beginning of the universe.

What's attractive is that gravitational radiation is difficult to detect because it interacts very weakly with matter. But, thanks to this same property, it passes without absorption from the objects most distant from us with the most mysterious, from the point of view of matter, properties.

We can say that gravitational radiation passes without distortion. The most ambitious goal is to study the gravitational radiation that was separated from the primordial matter in the Big Bang Theory, which was created at the creation of the Universe.

– Does the discovery of gravitational waves rule out quantum theory?

The theory of gravity assumes the existence of gravitational collapse, that is, the contraction of massive objects to a point. At the same time, the quantum theory developed by the Copenhagen School suggests that, thanks to the uncertainty principle, it is impossible to simultaneously indicate exactly such parameters as the coordinate, speed and momentum of a body. There is an uncertainty principle here; it is impossible to determine the exact trajectory, because the trajectory is both a coordinate and a speed, etc. It is only possible to determine a certain conditional confidence corridor within the limits of this error, which is associated with the principles of uncertainty. Quantum theory categorically denies the possibility of point objects, but describes them in a statistically probabilistic manner: it does not specifically indicate coordinates, but indicates the probability that it has certain coordinates.

The question of unifying quantum theory and the theory of gravity is one of the fundamental questions of creating a unified field theory.

They continue to work on it now, and the words “ quantum gravity” mean a completely advanced area of ​​science, the border of knowledge and ignorance, where all the theorists of the world are now working.

– What can the discovery bring in the future?

Gravitational waves must inevitably lie in the foundation modern science as one of the components of our knowledge. They play a significant role in the evolution of the Universe and with the help of these waves the Universe should be studied. The discovery contributes to the general development of science and culture.

If you decide to go beyond the scope of today's science, then it is permissible to imagine gravitational telecommunication lines, jet devices using gravitational radiation, gravitational-wave introscopy devices.

– Do gravitational waves have anything to do with extrasensory perception and telepathy?

Dont Have. The effects described are the effects quantum world, optics effects.

Interviewed by Anna Utkina

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 have seen beautiful 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 it? 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.

Standard Quantum Limit (SQL) quantum mechanics- a limitation imposed on the accuracy of a continuous or repeatedly repeated measurement of any quantity described by an operator who does not commute with himself 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.

A hundred years after the theoretical prediction made by Albert Einstein within the framework of the general theory of relativity, scientists were able to confirm the existence of gravitational waves. The era of a fundamentally new method for studying deep space—gravitational wave astronomy—begins.

There are different discoveries. There are random ones, they are common in astronomy. There are not entirely accidental ones, made as a result of a thorough “combing of the area,” such as the discovery of Uranus by William Herschel. There are serendipal ones - when they were looking for one thing and found another: for example, they discovered America. But special place In science, planned discoveries occupy the forefront. They are based on a clear theoretical prediction. What is predicted is sought primarily in order to confirm the theory. Such discoveries include the discovery of the Higgs boson at the Large Hadron Collider and the detection of gravitational waves using the laser interferometer gravitational-wave observatory LIGO. But in order to register some phenomenon predicted by the theory, you need to have a pretty good understanding of what exactly and where to look, as well as what tools are needed for this.

Gravitational waves are traditionally called a prediction of the general theory of relativity (GTR), and this is indeed so (although now such waves exist in all models that are alternative to or complementary to GTR). The appearance of waves is caused by the finiteness of the speed of propagation of gravitational interaction (in general relativity this speed is exactly equal to the speed of light). Such waves are disturbances in space-time propagating from a source. For gravitational waves to occur, the source must pulsate or move at an accelerated rate, but in a certain way. Let's say movements with perfect spherical or cylindrical symmetry are not suitable. There are quite a lot of such sources, but often they have a small mass, insufficient to generate a powerful signal. After all, gravity is the weakest of the four fundamental interactions, so it is very difficult to register a gravitational signal. In addition, for registration it is necessary that the signal changes quickly over time, that is, it has a sufficiently high frequency. Otherwise, we will not be able to register it, since the changes will be too slow. This means that the objects must also be compact.

Initially, great enthusiasm was generated by supernova explosions that occur in galaxies like ours every few decades. This means that if we can achieve a sensitivity that allows us to see a signal from a distance of several million light years, we can count on several signals per year. But later it turned out that initial estimates of the power of energy release in the form of gravitational waves during a supernova explosion were too optimistic, and such a weak signal could only be detected if a supernova had broken out in our Galaxy.

Another massive option compact objects, committing fast movements, - neutron stars or black holes. We can see either the process of their formation, or the process of interaction with each other. The last stages of the collapse of stellar cores, leading to the formation of compact objects, as well as the last stages of the merger of neutron stars and black holes, have a duration of the order of several milliseconds (which corresponds to a frequency of hundreds of hertz) - just what is needed. In this case, a lot of energy is released, including (and sometimes mainly) in the form of gravitational waves, since massive compact bodies make certain rapid movements. These are our ideal sources.

True, supernovae erupt in the Galaxy once every few decades, mergers of neutron stars occur once every couple of tens of thousands of years, and black holes merge with each other even less often. But the signal is much more powerful, and its characteristics can be calculated quite accurately. But now we need to be able to see the signal from a distance of several hundred million light years in order to cover several tens of thousands of galaxies and detect several signals in a year.

Having decided on the sources, we will begin to design the detector. To do this, you need to understand what a gravitational wave does. Without going into detail, we can say that the passage of a gravitational wave causes a tidal force (ordinary lunar or solar tides are a separate phenomenon, and gravitational waves have nothing to do with it). So you can take, for example, a metal cylinder, equip it with sensors and study its vibrations. This is not difficult, which is why such installations began to be made half a century ago (they are also available in Russia; now an improved detector developed by Valentin Rudenko’s team from the SAI MSU is being installed in the Baksan underground laboratory). The problem is that such a device will see the signal without any gravitational waves. There are a lot of noises that are difficult to deal with. It is possible (and has been done!) to install the detector underground, try to isolate it, cool it to low temperatures, but still, in order to exceed the noise level, a very powerful gravitational wave signal would be needed. But powerful signals come rarely.

Therefore, the choice was made in favor of another scheme, which was put forward in 1962 by Vladislav Pustovoit and Mikhail Herzenstein. In an article published in JETP (Journal of Experimental and Theoretical Physics), they proposed using a Michelson interferometer to detect gravitational waves. The laser beam runs between the mirrors in the two arms of the interferometer, and then the beams from different arms are added. By analyzing the result of beam interference, the relative change in arm lengths can be measured. This is very precise measurements, so if you beat the noise, you can achieve fantastic sensitivity.

In the early 1990s, it was decided to build several detectors using this design. The first to go into operation were relatively small installations, GEO600 in Europe and TAMA300 in Japan (the numbers correspond to the length of the arms in meters) to test the technology. But the main players were to be the LIGO installations in the USA and VIRGO in Europe. The size of these instruments is already measured in kilometers, and the final planned sensitivity should allow seeing dozens, if not hundreds of events per year.

Why are multiple devices needed? Primarily for cross-validation, since there are local noises (e.g. seismic). Simultaneous recording of the signal in the northwestern United States and Italy would be excellent evidence of its external origin. But there is a second reason: gravitational wave detectors are very poor at determining the direction to the source. But if there are several detectors spaced apart, it will be possible to indicate the direction quite accurately.

Laser giants

In their original form, the LIGO detectors were built in 2002, and the VIRGO detectors in 2003. According to the plan, this was only the first stage. All installations worked for several years, and in 2010-2011 they were stopped for modifications, and then reached the planned level. high sensitivity. The LIGO detectors were the first to operate in September 2015, VIRGO should join in the second half of 2016, and from this stage the sensitivity allows us to hope for recording at least several events per year.

After LIGO began operating, the expected burst rate was approximately one event per month. Astrophysicists estimated in advance that the first expected events would be black hole mergers. This is due to the fact that black holes are usually ten times heavier than neutron stars, the signal is more powerful, and it is “visible” from long distances, which more than compensates for the lower rate of events per galaxy. Fortunately, we didn't have to wait long. On September 14, 2015, both installations registered an almost identical signal, named GW150914.

With pretty help simple analysis data such as black hole masses, signal strength, and distance to the source can be obtained. The mass and size of black holes are related very simply and well in a known manner, and from the signal frequency one can immediately estimate the size of the energy release region. IN in this case the size indicated that a black hole with a mass of more than 60 solar masses was formed from two holes with a mass of 25-30 and 35-40 solar masses. Knowing this data, you can get full energy splash. Almost three solar masses were converted into gravitational radiation. This corresponds to the luminosity of 1023 solar luminosities - approximately the same amount as all the stars in the visible part of the Universe emit during this time (hundredths of a second). And from the known energy and magnitude of the measured signal, the distance is obtained. Large mass merged bodies made it possible to register an event that occurred in a distant galaxy: the signal took approximately 1.3 billion years to reach us.

More detailed analysis allows us to clarify the mass ratio of black holes and understand how they rotated around their axis, as well as determine some other parameters. In addition, the signal from two installations makes it possible to approximately determine the direction of the burst. Unfortunately, the accuracy here is not very high yet, but with the commissioning of the updated VIRGO it will increase. And in a few years, the Japanese KAGRA detector will begin to receive signals. Then one of the LIGO detectors (there were originally three, one of the installations was dual) will be assembled in India, and it is expected that many dozens of events will be recorded per year.

The era of new astronomy

On this moment most important result LIGO's work is confirmation of the existence of gravitational waves. In addition, the very first burst made it possible to improve the restrictions on the mass of the graviton (in general relativity it has zero mass), as well as to more strongly limit the difference between the speed of propagation of gravity and the speed of light. But scientists hope that already in 2016 they will be able to obtain a lot of new astrophysical data using LIGO and VIRGO.

First, data from gravitational wave observatories provide a new avenue for studying black holes. If previously it was only possible to observe the flows of matter in the vicinity of these objects, now you can directly “see” the process of merging and “calming” the resulting black hole, how its horizon fluctuates, taking on its final shape (determined by rotation). Probably, until the discovery of Hawking evaporation of black holes (for now this process remains a hypothesis), the study of mergers will provide better direct information about them.

Secondly, observations of neutron star mergers will yield a lot of new, extremely necessary information about these objects. For the first time, we will be able to study neutron stars the way physicists study particles: watching them collide to understand how they work inside. The mystery of the structure of the interiors of neutron stars worries both astrophysicists and physicists. Our understanding of nuclear physics and the behavior of matter at ultrahigh densities is incomplete without resolving this issue. It is likely that gravitational wave observations will play a key role here.

It is believed that neutron star mergers are responsible for short cosmological gamma-ray bursts. In rare cases, it will be possible to simultaneously observe an event both in the gamma range and on gravitational wave detectors (the rarity is due to the fact that, firstly, the gamma signal is concentrated into a very narrow beam, and it is not always directed at us, but secondly, we will not register gravitational waves from very distant events). Apparently, it will take several years of observation to be able to see this (although, as usual, you may be lucky and it will happen today). Then, among other things, we will be able to very accurately compare the speed of gravity with the speed of light.

Thus, laser interferometers together will work as a single gravitational-wave telescope, bringing new knowledge to both astrophysicists and physicists. Well, sooner or later a well-deserved Nobel Prize will be awarded for the discovery of the first bursts and their analysis.

2197
, USA
© REUTERS, Handout

Gravitational waves are finally discovered

Popular Science

Oscillations in space-time are discovered a century after Einstein predicted them. Begins new era in astronomy.

Scientists have discovered fluctuations in space-time caused by the merger of black holes. This happened a hundred years after Albert Einstein predicted these “gravitational waves” in his general theory of relativity, and a hundred years after physicists began searching for them.

This landmark discovery was announced today by researchers from the Laser Interferometer Gravitational-Wave Observatory (LIGO). They confirmed rumors that had surrounded the analysis of the first set of data they collected for months. Astrophysicists say the discovery of gravitational waves provides new insights into the universe and the ability to recognize distant events that cannot be seen with optical telescopes, but can be felt and even heard as their faint vibrations reach us through space.

“We have detected gravitational waves. We did it!" - announced the executive director scientific team of one thousand people David Reitze, speaking today at a press conference in Washington at the National Science Foundation.

Gravitational waves are perhaps the most elusive phenomenon of Einstein's predictions, and the scientist debated this topic with his contemporaries for decades. According to his theory, space and time form stretchable matter, which bends under the influence of heavy objects. To feel gravity means to fall into the bends of this matter. But can this space-time tremble like the skin of a drum? Einstein was confused; he didn't know what his equations meant. And he changed his point of view several times. But even the most staunch supporters of his theory believed that gravitational waves were in any case too weak to be observed. They cascade outward after certain cataclysms, and as they move, they alternately stretch and compress space-time. But by the time these waves reach the Earth, they stretch and compress every kilometer of space by an insignificant share diameter of the atomic nucleus.

© REUTERS, Hangout LIGO Observatory detector in Hanford, Washington

Detecting these waves required patience and caution. The LIGO observatory fired laser beams back and forth along the four-kilometer (4-kilometer) angled arms of two detectors, one in Hanford, Washington, and the other in Livingston, Louisiana. This was done in search of coincident expansions and contractions of these systems during the passage of gravitational waves. Using state-of-the-art stabilizers, vacuum instruments and thousands of sensors, scientists measured changes in the length of these systems that were as small as one thousandth the size of a proton. Such sensitivity of instruments was unthinkable a hundred years ago. It seemed incredible even in 1968, when Rainer Weiss from the Massachusetts Institute of Technology conceived an experiment called LIGO.

“It is a great miracle that in the end they succeeded. They were able to detect these tiny vibrations!” - said theoretical physicist from the University of Arkansas, Daniel Kennefick, who wrote the 2007 book Traveling at the Speed ​​of Thought: Einstein and the Quest for Gravitational Waves (Traveling at the speed of thought. Einstein and the search for gravitational waves).

This discovery marked the beginning of a new era of gravitational wave astronomy. The hope is that we will have better understanding of the formation, composition and galactic role of black holes—those super-dense balls of mass that bend space-time so dramatically that not even light can escape. When black holes come close to each other and merge, they produce a pulse signal—space-time oscillations that increase in amplitude and tone before ending abruptly. Those signals that the observatory can record are in the audio range - however, they are too weak to be heard by the naked ear. You can recreate this sound by running your fingers over the piano keys. “Start with the lowest note and work your way up to the third octave,” Weiss said. "That's what we hear."

Physicists are already surprised by the number and strength of signals that have been recorded so far. This means there are more black holes in the world than previously thought. “We were lucky, but I always counted on that kind of luck,” said astrophysicist Kip Thorne, who works at the California Institute of Technology and created LIGO with Weiss and Ronald Drever, also at Caltech. “This usually happens when a completely new window opens in the universe.”

By listening to gravitational waves, we can form completely different ideas about space, and perhaps discover unimaginable cosmic phenomena.

“I can compare this to the first time we pointed a telescope into the sky,” said theoretical astrophysicist Janna Levin of Barnard College, Columbia University. “People realized that there was something there and that it could be seen, but they could not predict the incredible range of possibilities that exist in the universe.” Likewise, Levine noted, the discovery of gravitational waves could show that the universe is “full dark matter, which we cannot easily determine with a telescope.”

The story of the discovery of the first gravitational wave began on a Monday morning in September, and it began with a bang. The signal was so clear and loud that Weiss thought: “No, this is nonsense, nothing will come of it.”

Intensity of emotions

That first gravitational wave swept through the upgraded LIGO's detectors—first at Livingston and seven milliseconds later at Hanford—during a simulation run early on September 14, two days before official start data collection.

The detectors were being tested after an upgrade that lasted five years and cost $200 million. They were equipped with new mirror suspensions for noise reduction and an active feedback to suppress extraneous vibrations in real time. The modernization gave the improved observatory more high level sensitivity compared to the old LIGO, which between 2002 and 2010 found “absolute and pure zero,” as Weiss put it.

When the powerful signal arrived in September, scientists in Europe, where it was morning at that moment, began hastily bombarding their American colleagues with messages over e-mail. When the rest of the group woke up, the news spread very quickly. According to Weiss, almost everyone was skeptical, especially when they saw the signal. It was a true textbook classic, which is why some people thought it was a fake.

The search for gravitational waves has been flawed many times since the late 1960s, when Joseph Weber of the University of Maryland thought he had discovered resonant vibrations in an aluminum cylinder with sensors in response to waves. In 2014, an experiment called BICEP2 announced the discovery of primordial gravitational waves—spacetime ripples from the Big Bang that have now stretched out and become permanently frozen in the geometry of the universe. Scientists from the BICEP2 team announced their discovery with great fanfare, but then their results were subjected to independent verification, during which it turned out that they were wrong and that the signal came from cosmic dust.

When Arizona State University cosmologist Lawrence Krauss heard about the LIGO team's discovery, he initially thought it was a "blind hoax." During the operation of the old observatory, simulated signals were surreptitiously inserted into data streams to test the response, and most of The team didn't know about it. When Krauss is from knowledgeable source Having learned that this time it was not a “blind throw in,” he could hardly contain his joyful excitement.

On September 25, he told his 200,000 Twitter followers: “Rumors of a gravitational wave being detected by the LIGO detector. Amazing if true. I’ll give you the details if it’s not a fake.” This is followed by an entry from January 11: “Previous rumors about LIGO have been confirmed by independent sources. Follow the news. Perhaps gravitational waves have been discovered!”

The official position of scientists was this: do not talk about the received signal until there is one hundred percent certainty. Thorne, bound hand and foot by this obligation to secrecy, did not even say anything to his wife. “I celebrated alone,” he said. To begin with, the scientists decided to go back to the very beginning and analyze everything down to the smallest detail in order to find out how the signal propagated through thousands of measurement channels of various detectors, and to understand whether there was anything strange at the moment the signal was detected. They didn't find anything unusual. They also excluded hackers, who would have had the best knowledge of the thousands of data streams in the experiment. “Even when a team does blind throw-ins, they are not perfect enough and leave a lot of marks,” Thorne said. “But there were no traces here.”

In the following weeks, they heard another, weaker signal.

Scientists analyzed the first two signals, and more and more new ones arrived. They presented their research in the journal Physical Review Letters in January. This issue is published online today. According to their estimates, the statistical significance of the first, most powerful signal exceeds 5-sigma, which means that the researchers are 99.9999% confident in its authenticity.

Listening to gravity

Equations general relativity Einstein's theories are so complex that it took most physicists 40 years to agree: yes, gravitational waves exist, and they can be detected - even theoretically.

At first, Einstein thought that objects could not release energy in the form of gravitational radiation, but then he changed his point of view. In his historical work, written in 1918, he showed which objects could do this: dumbbell-shaped systems that simultaneously rotate around two axes, such as double and supernovae, exploding like firecrackers. They can generate waves in space-time.

© REUTERS, Handout Computer model, illustrating the nature of gravitational waves in the Solar System

But Einstein and his colleagues continued to hesitate. Some physicists argued that even if waves existed, the world would vibrate along with them, and it would be impossible to sense them. It was only in 1957 that Richard Feynman closed this question by demonstrating thought experiment that if gravitational waves exist, they can theoretically be detected. But no one knew how common these dumbbell-shaped systems were in outer space, or how strong or weak the resulting waves were. “Ultimately the question was: Will we ever be able to detect them?” said Kennefick.

In 1968, Rainer Weiss was a young professor at MIT and was assigned to teach a course on general relativity. Being an experimentalist, he knew little about it, but suddenly news appeared about Weber's discovery of gravitational waves. Weber built three resonant detectors from aluminum, the size of desk and placed them in different American states. Now he reported that all three detectors detected “the sound of gravitational waves.”

Weiss's students were asked to explain the nature of gravitational waves and express their opinion on the message. Studying the details, he was amazed at the complexity of the mathematical calculations. “I couldn’t figure out what the hell Weber was doing, how the sensors interacted with the gravitational wave. I sat for a long time and asked myself: “What is the most primitive thing I can come up with that would detect gravitational waves?” And then an idea came into my head, which I call conceptual basis LIGO."

Imagine three objects in spacetime, say mirrors at the corners of a triangle. “Send a light signal from one to the other,” Weber said. “See how long it takes to move from one mass to another, and check if the time has changed.” It turns out, the scientist noted, this can be done quickly. “I assigned this to my students as a research assignment. Literally the entire group was able to make these calculations.”

In subsequent years, as other researchers tried to replicate the results of Weber's resonance detector experiment but continually failed (it is unclear what he observed, but it was not gravitational waves), Weiss began preparing a much more precise and ambitious experiment: a gravitational-wave interferometer. The laser beam is reflected from three mirrors installed in the shape of the letter “L” and forms two beams. The interval between the peaks and troughs of light waves precisely indicates the length of the legs of the letter "L", which create the X and Y axes of spacetime. When the scale is stationary, two light waves reflected from corners and cancel each other out. The signal in the detector is zero. But if a gravitational wave passes through the Earth, it stretches the length of one arm of the letter “L” and compresses the length of the other (and vice versa in turn). The mismatch of the two light beams creates a signal in the detector, indicating slight fluctuations in space-time.

At first, fellow physicists expressed skepticism, but the experiment soon gained support from Thorne, whose team of theorists at Caltech was studying black holes and other potential sources of gravitational waves, as well as the signals they generate. Thorne was inspired by Weber's experiment and similar efforts by Russian scientists. After speaking with Weiss at a conference in 1975, “I began to believe that detection of gravitational waves would be successful,” Thorne said. “And I wanted Caltech to be a part of it, too.” He arranged for the institute to hire Scottish experimentalist Ronald Dreaver, who also said he would build a gravitational-wave interferometer. Over time, Thorne, Driver, and Weiss began to work as a team, each solving their share of the countless problems in preparation for the practical experiment. The trio created LIGO in 1984, and when prototypes were built and collaboration began within an ever-expanding team, they received from the National scientific foundation$100 million in funding. Blueprints were drawn up for the construction of a pair of giant L-shaped detectors. A decade later, the detectors started working.

At Hanford and Livingston, at the center of each of the four-kilometer detector arms there is a vacuum, thanks to which the laser, its beam and mirrors are maximally isolated from the constant vibrations of the planet. To be even more on the safe side, LIGO scientists monitor their detectors as they operate with thousands of instruments, measuring everything they can: seismic activity, Atmosphere pressure, lightning, appearance cosmic rays, vibration of equipment, sounds in the area of ​​the laser beam, and so on. They then filter their data from this extraneous background noise. Perhaps the main thing is that they have two detectors, and this allows them to compare the received data, checking them for the presence of matching signals.

Context

Gravitational waves: completed what Einstein started in Bern

SwissInfo 02/13/2016

How black holes die

Medium 10/19/2014
Inside the vacuum created, even with the lasers and mirrors completely isolated and stabilized, “strange things happen all the time,” says Marco Cavaglià, LIGO deputy spokesman. Scientists must track these "goldfish", "ghosts", "obscure sea monsters" and other extraneous vibrational phenomena, finding out their source in order to eliminate it. One hard case occurred during the testing phase, said LIGO researcher Jessica McIver, who studies such extraneous signals and interference. A series of periodic single-frequency noises often appeared among the data. When she and her colleagues converted the vibrations from the mirrors into audio files, “the phone could be clearly heard ringing,” McIver said. “It turned out that it was the communications advertisers making phone calls inside the laser room.”

Over the next two years, scientists will continue to improve the sensitivity of LIGO's upgraded Laser Interferometer Gravitational-Wave Observatory detectors. And in Italy, a third interferometer called Advanced Virgo will begin operating. One of the answers that the data will help provide is how black holes form. Are they a product of the collapse of the earliest massive stars, or do they appear as a result of collisions within dense star clusters? “These are just two guesses, I believe there will be more when everyone calms down,” Weiss says. When during upcoming work LIGO will begin to accumulate new statistical data, scientists will begin to listen to stories about the origin of black holes that the cosmos will whisper to them.

Judging by its shape and size, the first, loudest pulse originated 1.3 billion light-years from where, after an eternity of slow dance, two black holes, each about 30 times the mass of the sun, finally merged under the influence of mutual gravitational attraction. The black holes were circling faster and faster, like a whirlpool, gradually getting closer. Then the merger occurred, and in the blink of an eye they released gravitational waves with an energy comparable to that of three Suns. This merger was the most powerful energetic phenomenon ever recorded.

“It’s like we’ve never seen the ocean during a storm,” Thorne said. He has been waiting for this storm in spacetime since the 1960s. The feeling Thorne felt as those waves rolled in wasn't exactly excitement, he says. It was something else: a feeling of deep satisfaction.

InoSMI materials contain assessments exclusively of foreign media and do not reflect the position of the InoSMI editorial staff.