Physicists at the LIGO (Laser Interferometric Gravitational Observatory) first discovered gravitational waves - disturbances of space-time predicted a hundred years ago by the creator of the general theory of relativity, Albert Einstein. About the opening during a live broadcast organized by Lenta.ru and Moscow state university(MSU) named after M.V. Lomonosov, scientists from the Faculty of Physics, participants in the international LIGO collaboration. Lenta.ru talked to one of them, Russian physicist Sergei Vyatchanin.

What are gravitational waves?

According to Newton's law of universal gravitation, two bodies are attracted to each other with a force inversely proportional to the square of the distance between them. This theory describes, for example, the rotation of the Earth and the Moon in flat space and universal time. Einstein, having developed the special theory of relativity, realized that time and space are one substance, and proposed a general theory of relativity - a theory of gravity based on the fact that gravity manifests itself as the curvature of space-time that matter creates.

Doctor of Physical and Mathematical Sciences Sergei Vyatchanin has headed the Department of Oscillation Physics of the Physics Faculty of Moscow State University since 2012. Scientific interests focused on the study of quantum non-perturbative measurements, laser gravitational wave antennas, dissipation mechanisms, fundamental noise and nonlinear optical effects. The scientist collaborated with the California Institute of Technology in the USA and the Max Planck Society in Germany.

You can imagine an elastic circle. If you throw a light ball at it, it will roll in a straight line. If you put a heavy apple in the center of the circle, the trajectory will bend. From the equations of general relativity, Einstein immediately learned that gravitational waves are possible. But at that time (at the beginning of the twentieth century) the effect was considered extremely weak. You could say that gravitational waves are ripples in space-time. The bad thing is that this is an extremely weak interaction.

If we take similar (electromagnetic) waves, then there was the experiment of Hertz, who placed the emitter in one corner of the room and the receiver in the other. This doesn't work with gravitational waves. Too weak interaction. We can only rely on astrophysical catastrophes.

How does a gravity antenna work?

There is a Fabry-Perot interferometer, two masses separated by four kilometers. The distance between the masses is controlled. If the wave comes from above, the distance changes slightly.

Is gravitational disturbance essentially a distortion of the metric?

You can say that. Mathematics describes this as a slight curvature of space. Herzenstein and Pustovoit proposed using a laser to detect gravitational waves in 1962. It was such a Soviet article, a fantasy... Great, but still a flight of fancy. The Americans thought and decided in the 1990s (Kip Thorne, Ronald Drever and Rainer Weiss) to make a laser gravitational antenna. Moreover, two antennas are required, since if there are events, it is necessary to use a coincidence scheme. And then it all began. It's a long story. We have been cooperating with Caltech since 1992, and switched to a formal contractual basis in 1998.

Don't you think that the reality of gravitational waves was beyond doubt?

In general, the scientific community was confident that they existed, and it was a matter of time to discover them. Hulse and Taylor were awarded the Nobel Prize for the actual discovery of gravitational waves. What did they do? There are double stars - pulsars. Since they spin, they emit gravitational waves. We cannot observe them. But if they emit gravitational waves, they give off energy. This means that their rotation is slowing down, as if due to friction. The stars move closer to each other and a change in frequency can be seen. They looked - and saw (in 1974 - approx. "Tapes.ru"). This is indirect evidence of the existence of gravitational waves.

Now - direct?

Now - direct. A signal arrived and was registered on two detectors.

Is the reliability high?

It's enough to open.

What is the contribution of Russian scientists to this experiment?

Key. In initial LIGO (an early version of the antenna - approx. "Tapes.ru") ten-kilogram masses were used, and they hung on steel threads. Our scientist Braginsky already expressed the idea of ​​​​using quartz threads. A paper was published that proved that quartz filaments make much less noise. And now the masses (in advanced LIGO, a modern installation - approx. "Tapes.ru") hang on quartz threads.

The second contribution is experimental and related to charges. The masses, separated by four kilometers, need to be somehow adjusted using electrostatic activators. This system is better than the magnetic one that was used previously, but it senses the charge. In particular, every second a huge number of particles - muons - pass through a person’s palm, which can leave a charge. Now they are struggling with this problem. Our group (Valery Mitrofanov and Leonid Prokhorov) is participating in this experimentally and has become significantly more experienced.

In the early 2000s, there was an idea to use sapphire filaments in advanced LIGO, since formally sapphire has a higher quality factor. Why is it important? The higher the quality factor, the less noise. This general rule. Our group calculated the so-called thermoelastic noise and showed that it is still better to use quartz rather than sapphire.

And one more thing. The sensitivity of the gravitational antenna is close to the quantum limit. There is the so-called standard quantum limit: if you measure a coordinate, then according to the Heisenberg uncertainty principle you immediately perturb it. If you continuously measure a coordinate, then you are perturbing it all the time. It is not good to measure the coordinate very accurately: there will be a large reverse fluctuation effect. This was shown in 1968 by Braginsky. Calculated for LIGO. It turned out that for initial LIGO the sensitivity is approximately ten times higher than the standard quantum limit.

The hope now is that advanced LIGO will reach the standard quantum limit. Maybe it will go down. This is actually a dream. Can you imagine this? You will have a quantum macroscopic device: two heavy masses at a distance of four kilometers.

Gravitational waves were detected on September 14, 2015 at 05:51 a.m. Eastern Daylight Time (13:51 Moscow time) at the twin detectors of the LIGO Laser Interferometer Gravitational-Wave Observatory located in Livingston (Louisiana) and Hanford (Washington State). ) in the USA. The LIGO detectors detected relative variations of ten to the minus 19 meters (roughly equal to the ratio of the diameter of an atom to the diameter of an apple) of pairs of test masses spaced four kilometers apart. The disturbances are generated by a pair of black holes (29 and 36 times heavier than the Sun) in the last fractions of a second before they merge into a more massive rotating gravitational object (62 times heavier than the Sun). In a fraction of a second, three solar masses turned into gravitational waves, the maximum radiation power of which was about 50 times greater than from the entire visible Universe. The merger of black holes occurred 1.3 billion years ago (this is how long it took for the gravitational disturbance to reach the Earth). Analyzing the moments of arrival of the signals (the detector in Livingston recorded the event seven milliseconds earlier than the detector in Hanford), scientists assumed that the source of the signal was located in the southern hemisphere. The scientists submitted their results for publication in the journal Physical Review Letters.

At first glance, this is not very compatible.

This is what is paradoxical. That is, it turns out to be fantastic. It seems to smack of charlatanism, but in reality it’s not, everything is honest. But for now these are dreams. The standard quantum limit has not been reached. There you still need to work and work. But it is already clear that it is close.

Is there any hope that this will happen?

Yes. The standard quantum limit needs to be overcome, and our group has been involved in developing methods for how to do this. These are the so-called quantum non-perturbing measurements, what specific measurement scheme is needed - this or that... After all, when you study theoretically, calculations cost nothing, and experimentation is expensive. LIGO achieved an accuracy of ten to minus 19 meters.

Let's remember children's example. If we reduce the Earth to the size of an orange, and then reduce it by the same amount, we get the size of an atom. So, if we reduce the atom by the same amount, then we get ten meters to the minus 19 degree. This is crazy stuff. This is an achievement of civilization.

It's very important, yes. So what does the discovery of gravitational waves mean for science? It is believed that this could change the observational methods of astronomy.

What do we have? Astronomy in the usual range. Radio telescopes, infrared telescopes, X-ray observatories.

Is everything in the electromagnetic ranges?

Yes. In addition, there are neutrino observatories. There is registration of cosmic particles. This is another channel of information. If the gravitational antenna produces astrophysical information, then researchers will have at their disposal several observation channels at once, through which they can test the theory. Many cosmological theories have been proposed, competing with each other. It will be possible to weed out something. For example, when the Higgs boson was discovered at the Large Hadron Collider, several theories immediately fell away.

That is, this will contribute to the selection of working cosmological models. Another question. Is it possible to use a gravitational antenna to accurately measure the accelerated expansion of the Universe?

So far the sensitivity is very low.

What about in the future?

In the future, it can also be used to measure the relict gravitational background. But any experimenter will tell you: “Ay-yay!” That is, this is still a long way off. God grant that we register an astrophysical catastrophe.

Black hole collision...

Yes. After all, this is a disaster. God forbid you end up there. We wouldn't exist. And here is such a background... For now... “they feed the hopes of the young, they give joy to the elders.”

Could the discovery of gravitational waves provide further evidence of the existence of black holes? After all, there are still those who do not believe that they exist.

Yes. How do they work at LIGO? The signal is being recorded, to explain which scientists develop patterns and compare them with observational data. A collision of neutron stars, a neutron star falls into a black hole, a supernova explosion, a black hole merges with a black hole... We will change parameters, for example, the mass ratio, the initial moment... What should we see? Recording is in progress, and at the moment of the signal the performance of the templates is assessed. If the pattern designed for the collision of two black holes matched the signal, then that's proof. But not absolute.

Is there no better explanation? Is the discovery of gravitational waves most simply explained by the collision of black holes?

At the moment - yes. The scientific community now believes that it was a merger of black holes. But a collective community is the opinion of many, a consensus. Of course, if some new factors arise, it can be abandoned.

When will it be possible to detect gravitational waves from less massive objects? Doesn't this mean that new and more sensitive observatories need to be built?

There is a program next generation LIGO. This is the second one. There will be a third. There are a lot of options there. You can increase the distance, increase the power, and the suspension. Now all this is being discussed. At the brainstorming level. If the observation of a gravitational signal is confirmed, it will be easier to obtain money to improve the observatory.

Is there a boom in the construction of gravitational observatories?

Don't know. It's expensive (LIGO cost about $370 million - approx. "Tapes.ru"). After all, the Americans offered Australia to build in Southern Hemisphere antenna and agreed to provide all equipment for this. Australia refused. Too expensive toy. The maintenance of the observatory would take up the entire scientific budget of the country.

Is Russia financially involved in LIGO?

We cooperate with the Americans. What will happen next is unclear. So far we have good relations with scientists, but politicians rule everything... Therefore, we need to watch. They appreciate us. We deliver results that are truly up to par. But they are not the ones who decide whether to be friends with Russia or not.

Unfortunately, yes.

This is life, let's wait.

The LIGO observatory is funded by the US National Science Foundation. Research at LIGO is carried out as part of a collaboration of the same name by more than a thousand scientists from the United States and 14 other countries, including Russia, represented by two groups from Moscow State University and the Institute of Applied Physics Russian Academy Sciences (Nizhny Novgorod).

Are there any plans to build a gravitational observatory in Russia?

Not planned yet. In the 1980s, the Sternberg State Astronomical Institute of Moscow State University wanted to build the same gravitational antenna in the Baksan Gorge, only on a smaller scale. But perestroika came, and everything was covered with a copper basin for a long time. Now the traffic police of Moscow State University is trying to do something, but so far the antenna has not worked...

What else can you try to check using a gravitational antenna?

The validity of the theory of gravity. After all, most existing theories are based on Einstein's theory.

No one can refute it yet.

She occupies a leading position. Alternative theories are designed in such a way that they basically lead to the same experimental consequences as it does. And this is natural. Therefore, we need new facts that would sweep away incorrect theories.

Briefly, how would you formulate the meaning of the discovery?

In fact, gravitational astronomy began. And for the first time, the waves of space curvature were hooked. Not indirectly, but directly. A person admires himself: what a son of a bitch I am!

, 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! “David Reitze, executive director of the 1,000-person research team, announced 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 Earth, they have stretched and compressed every kilometer of space by a tiny fraction of the diameter of an 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, the scientists measured changes in the length of these systems 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 of 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 University of Arkansas theoretical physicist 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 of dark matter that we can't easily detect 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.”

The intensity of passions

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 data collection officially began.

The detectors were being tested after an upgrade that lasted five years and cost $200 million. They are equipped with new mirror suspensions for noise reduction and an active feedback system to suppress extraneous vibrations in real time. The upgrade gave the improved observatory a higher level of sensitivity than the old LIGO, which between 2002 and 2010 detected “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 email. 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.

False claims in the search for gravitational waves have been made repeatedly since the late 1960s, when Joseph Weber of the University of Maryland thought he had discovered resonant vibrations in an aluminum cylinder containing sensors in response to the 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 this 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 guess." During the old observatory's operation, simulated signals were surreptitiously inserted into data streams to test the response, without most of the team knowing about it. When Krauss learned from a knowledgeable source 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 detection at 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. Stay tuned for more 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

Einstein's equations of general relativity 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 landmark work written in 1918, he showed what objects could do this: dumbbell-shaped systems that rotate on two axes simultaneously, such as binaries and supernovae that explode 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 wasn't until 1957 that Richard Feynman put the matter to rest by demonstrating in a thought experiment that if gravitational waves existed, they could 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 desk-sized resonant detectors from aluminum and placed them in different locations. 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 understand 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 will detect gravitational waves?” And then I came up with an idea that I call the conceptual basis of 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 the 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, the two light waves are reflected from the 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 talking 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 myriad problems in preparation for the practical experiment. The trio created LIGO in 1984, and once prototypes were built and collaboration began within an ever-expanding team, they received $100 million in funding from the National Science Foundation in the early 1990s. 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, atmospheric pressure, lightning, the appearance of 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 when the lasers and mirrors are completely isolated and stabilized, “strange things happen all the time,” says Marco Cavaglià, deputy press secretary for the LIGO project. Scientists must track these "goldfish", "ghosts", "obscure sea monsters" and other extraneous vibrational phenomena, finding out their source in order to eliminate it. One difficult incident occurred during the testing phase, said LIGO research scientist 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 telecom 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 are they produced by collisions within dense star clusters? “These are just two guesses, I believe there will be more when everyone calms down,” Weiss says. As LIGO's upcoming work begins to accumulate new statistics, scientists will begin to listen to the stories the cosmos whispers to them about the origins of black holes.

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 from foreign media and do not reflect the position of the InoSMI editorial staff.

The discovery of gravitational waves became the main scientific sensation of 2016. Anton Pervushin explains what this discovery means, why we had to wait a hundred years for it, and why it does not overturn our ideas about the universe, but, on the contrary, confirms them.

One hundred years ago, in 1916, the great Albert Einstein published the first articles on the General Theory of Relativity (GTR). They showed that gravity is caused by the deformation of space-time itself under the influence of mass. Let's try to describe this clearly. If a metal ball lies on a soft surface, a dent will form underneath it. And the heavier the ball, the deeper and more extensive the dent. So outer space, and time at the same time, “sinks” under the mass of planets, stars and galaxies.

Although some scientists were hostile to Einstein's theory, it had important quality: could predict real observable effects, namely the deformation of space-time near massive celestial bodies. Actually, the General Theory of Relativity appeared as an attempt to explain the observed shift in the perihelion of Mercury. At that time, this phenomenon was explained by the influence of an unknown planet near the Sun; they even came up with a name for it - Vulcan. Using Einstein's formulas, it was possible to explain and mathematically describe this shift without inventing any Vulcan.

The non-existent Vulcan as imagined by the artist

The theory required other confirmations, and they were soon received. In 1919, Arthur Eddington, while observing the next solar eclipse, was able to register the deflection of the rays of stars passing close to our luminary - exactly as predicted by General Relativity.

During the 20th century, many other experiments were conducted that directly or indirectly confirmed the theory. For example, the effect of gravitational lensing was discovered, when the radiation of distant objects is amplified or divided due to large masses in its path. The search for gravitational lenses gave rise to a whole direction in astronomy after in 1979, British scientists discovered not one quasar, but two identical ones, in photographs of the quasar QSO 0957+16.

There is even more clear evidence - the so-called “Einstein Cross”. It is in the form of a cross of four objects with a lensing galaxy in the center that we observe the quasar QSO 2237+0305, located in the constellation Pegasus at a distance of 8 billion light years from us.

"Einstein Cross", photo by NASA. In fact, this is one quasar, simply distorted by a gravitational lens

Moreover, it was possible to confirm two more effects predicted by General Relativity: time dilation in a gravitational field and a weak curvature of space-time created by the Earth. Direct evidence of their existence was obtained using the Gravity Probe spacecraft launched in 1976 and 2004.

After all this, it was already possible to confidently say that Einstein’s theory works and has practical application. All that remained was to record the gravitational waves she predicted, which arise in space-time when a massive body moves, like ripples on water. Although they are very faint, they can be detected when observing objects with enormous mass: quasars, galaxies, black holes. Indirect evidence of their existence has appeared since the early 1990s. And now the long-awaited opening took place.

More precisely, it was done on September 14, 2015, but it took five months to process the results. And just yesterday, February 11, 2016, scientists from international project LIGO Scientific Collaboration was able to officially announce that they were able to detect gravitational waves using two laser interferometric gravitational-wave observatories located in the states of Louisiana and Washington. These waves were formed as a result of the collision of two black holes, which occurred 1.3 billion years ago.

Washington State Gravity Observatory

Today this discovery is written about in enthusiastic terms as a scientific sensation. However, contrary to what some enthusiastic commentators claim, it is not capable of “changing the world.” Quite the opposite: the predicted effect once again proves that our ideas about the Universe, formed a hundred years ago thanks to Einstein, will remain unchanged for now.

So the discovery will not bring us new technologies such as anti-gravity engines, which science fiction lovers and space exploration enthusiasts dream about. Indeed, within the framework of the modern version of the General Theory of Relativity, such engines are simply impossible.

1.3 billion years ago, far, far from Earth, solar system and even our Galaxy, two black holes came extremely close, one with a mass of 29 Suns, and the other with a mass of 36. 20 milliseconds - elusively short for a person - and they merge into one large black hole, and the excess energy released during the collision causes space-time to go ripples from the site of a cosmic catastrophe. On September 14, 2015, at 13:51 Moscow time, this wave reached the Earth and caused the mirrors of gravitational telescopes spaced four kilometers apart near the American cities of Livingston and Hanford to vibrate.

True, it fluctuates just a little, almost imperceptibly: with an amplitude of 10 -19 m (this is so many times smaller size atom, how much smaller an orange is than our entire planet). A sophisticated optical design for detecting such disturbances, measurements on the verge of the quantum limit of accuracy, decades theoretical works and several months of careful checks of the results. On February 11, at press conferences in Washington, Moscow, London, Paris and other cities, physicists from the international LIGO collaboration announced: humanity has detected gravitational waves for the first time and this cannot be a mistake. Ahead of us are gravitational telescopes, new physics and, who knows, maybe even a new reality.

What is it?

Let's imagine a stretched fabric and several stones different weights, which we will put on it. The heavier the stone, the more it pushes through the fabric - in the same way, massive gravitational objects, according to Einstein’s theory of relativity, push through the fabric of space-time enveloping our world (more precisely, this fabric is our world, but that’s not about that now).

The easiest way to explain the impact of massive objects on space-time is through the example of black holes - they are so compact and heavy that they push space-time to the colossal depths of billions of millions of Mariana Trenches.

Even time in their vicinity begins to flow more slowly, and all the objects that fall into the giant funnel can no longer come out. Stars, dust, light quanta - everything remains trapped forever.

But what will happen if we not only put the stones, but also start rotating them? There will be ripples of folds across the fabric. Likewise, massive gravitational objects moving with variable acceleration generate spreading ripples in space-time around them - the same gravitational waves predicted by Albert Einstein a hundred years ago.

What emits gravitational waves?

Gravitational waves are emitted by any object that has mass and moves with variable acceleration - from a rotating black hole to a braking car and the reader of this text (it’s unlikely that you look at the screen without blinking - and here it is, acceleration). It’s just that gravitational waves from the last two objects cause such modest fluctuations in space that from the modern point of view quantum physics they simply cannot be registered.

Therefore, physicists hoped to find gravitational waves only from massive objects moving with very large differences in acceleration. More precisely, from a pair of such objects - simply according to Newton’s second law, if one heavy body moves with a large variable acceleration, then there must be a large force “setting” this movement. The easiest way for this force to appear is from the influence of some massive object nearby. Ideal candidates for such pairs of heavyweights are colliding galaxies and binary systems of black holes or neutron stars “living” together.

Haven't they really tried to find gravitational waves before?

We tried, and more than once. Some of the first experiments to detect gravitational waves were carried out back in the 70s at the Physics Faculty of Moscow State University in a group led by Professor Vladimir Braginsky. Then the device installed in the basement of the building seemed to register a signal, strong and stably repeated every evening. A sensation was brewing. The holiday was ruined by Braginsky himself, who realized that the device was recording seismic noise from the friendly entry of several trams into a nearby depot.

Researchers from the international BICEP collaboration were much less careful than Soviet physicists. Last year, they announced irrefutable traces of gravitational waves in the cosmic microwave background radiation, preserved from the first moments after the Big Bang. But the sensational antiquity turned out to be a mistake: when processing the data, scientists did not take into account the influence of cosmic dust.

Repeated attempts to detect gravitational waves have been made using other gravitational telescopes, including detectors from the LIGO collaboration.

What is LIGO and gravitational telescopes anyway?

LIGO (Laser Interferometer Gravitational-Wave Observatory) is the name of the observatory and at the same time an international collaboration of scientists from 14 countries. Russia is represented in LIGO by two scientific teams: the group of Alexander Sergeev from the Institute of Applied Physics of the Russian Academy of Sciences (Nizhny Novgorod) and the group led by Valery Mitrofanov, a professor at the Faculty of Physics at Moscow State University. The latter, by the way, was headed by the same Vladimir Braginsky until recently.

LIGO as an observatory has a detector and two interferometers: one installed in Livingston (Louisiana, USA), and the other in Hanford (Washington State, USA). Gravitational waves travel at the speed of light, and therefore the signal arrived at them with only a slight delay of 10 milliseconds.

The interferometers themselves are large L-shaped antennas with arms of four km each. Inside they contain high-quality optical circuits (that is, with low level extraneous noise) into which laser beams are launched. Under the influence of a gravitational wave, one shoulder should compress, and the other, on the contrary, should stretch. As a result, the laser beams travel slightly different distances along the arms and reach the exit with a small gap between them. Having come out, they come together again and form an interference pattern, according to the characteristics of which it is possible to reconstruct how the antenna arms changed and what was the gravitational wave that caused all this.

The LIGO observatory began its work back in 2002, but then its accuracy was not enough to register gravitational waves. In 2010, LIGO was closed for modernization and started working again only in 2014 (Advanced LIGO). Each design element was literally honed to the limit: for example, the mirrors between which the laser beams run (they are installed at the ends of each arm) were manufactured in a special factory. The European collaboration VIRGO built a similar telescope in parallel with LIGO, but it was not operational in September last year.

What signal did the scientists register?

This is what Valery Mitrofanov says. “At first there was a constant background noise, and suddenly at some point the test masses of the detector, those same mirrors, began to sway with a certain frequency. Then - once, and a break. Moreover, the signal was sent to two detectors at once: first, the gravitational wave approached one, and then, with a slight delay, to the other.”

The frequency of the signal was 150 Hz (it was with this frequency and amplitude of 10 -19 m that the mirrors oscillated, which became closer and then further away from each other), and after processing, its cause was found: the merger of two black holes at a distance of 1.3 billion light years years from Earth. The mass of one of them was equal to 29 solar masses, and the other - 36. The mass of the resulting black hole turned out to be slightly less: the lack of energy of three solar masses was just emitted during the collision in the form of gravitational waves.

The luminosity (that is, the total energy emitted) of this flare was 50 times greater than the luminosity of the entire visible Universe. If it were light and not gravity, observable space would become dazzlingly bright.

Luminosity? Frequency? I'm completely confused

Once again: scientists saw gravitational waves. This is not light (that is electromagnetic waves, or coupled vibrations of magnetic and electric fields propagating in space), and not sound (mechanical vibrations in a solid, liquid or gaseous medium, that is, propagating waves of high/low pressure). It’s just that all these phenomena (light, sound and gravity) can be described by the same equations and terms of wave physics.

Thus, each wave has an oscillation frequency, measured in hertz (Hz). Human hearing is capable of perceiving sounds at a frequency of 20 hertz - 20 kilohertz. The frequency of the incoming gravitational wave was 150 Hz, but this does not mean that it can be heard if you listen very carefully. At a press conference in Washington, scientists even turned on an alarming sound from this collision somewhere unimaginably far away, but it was just a beautiful interpretation of what would have happened if the researchers had registered not a gravitational wave, but exactly the same one in all parameters (frequency, amplitude, form) sound wave.

It's the same with luminosity. It is simply a term for determining the intensity of the radiation flux, used in an unusual but correct context. For example, in the case of light bulbs: the more intensely they emit, the brighter they glow, and the greater their luminosity. For colliding black holes: the greater their mass and the sharper their acceleration, the more powerful gravitational waves they will launch into space. Why then did this event of 50 luminosities of the Universe not compress the entire planet Earth into an accordion, but only shake the complexly arranged mirrors with some otherworldly breeze? But because gravitational interaction is much weaker than electromagnetic interaction (which is why it is so difficult to detect) - so much so that we only notice our attraction to the Earth, but, for example, not to century-old oak, no matter how close we come to him.

Could this be a mistake?

Scientists are 100% confident in their findings. At the same time, they have already had false positives before, but outsiders never found out about it, so from the point of view of accuracy they can definitely be trusted.

“Firstly, this is a direct method for recording gravitational waves,” says Valery Mitrofanov. “And secondly, the results coincided with the predictions of the theorists. We had a pattern of the gravitational wave signal from the merger of two black holes calculated using quantum physics. The signal was registered only if it fell into this pattern - this is what happened on September 14, and it is thanks to this pattern that we can reconstruct the masses of holes."

By the way, a leak of information about the imminent announcement of results appeared in mid-September. Then many discussed that, among other things, the signal could simply be mixed into the data by the scientists controlling the project to check its readiness. Now all participants in the collaboration unequivocally deny this possibility: the event did not occur during the operational launch of the system, but during a test and engineering one, in which false “injections” are not expected according to the instructions.

Did Russia participate?

Yes. As already mentioned, two laboratories from Moscow and Nizhny Novgorod are participating in the LIGO collaboration from Russia. They developed the design of a telescope (for example, Russian physicists proposed hanging mirrors on quartz threads instead of steel, which reduced extraneous noise in the system) and struggled with quantum effects that distort the signals of ultra-sensitive antennas.

“We have obtained a quantum device of macroscopic dimensions,” says MSU professor Sergei Vyatchanin. “This is the ultimate achievement of civilization at the moment: LIGO has almost reached the quantum limit of measurements. We were able to detect the displacement of two macroscopic objects weighing several kilograms and separated by several kilometers, with an accuracy predicted by Heisenberg's quantum uncertainty."

One of the initiators of the project, Professor Emeritus of the California Institute of Technology Kip Thorne, especially notes the contribution of our physicists to research. According to him, it was Vladimir Braginsky, a recognized world expert in the field of quantum gravity, who was the first to suggest looking for gravitational waves from black holes and was the first to draw attention to the need to take into account quantum effects in measurements.

Let's go upward. First, scientists hope to acquire a third gravitational telescope for their system, which will no longer be located on Earth, but in space. Then, based on the characteristic delays of gravitational wave signals, researchers will be able to reconstruct the exact position of the sources - just as you can now find out your exact position on Earth by exchanging signals with three GPS satellites.

“This is the beginning of a new, gravitational-wave astronomy,” says Valery Mitrofanov. — Ancient people observed the Universe only in visible light. Then X-ray telescopes, radio telescopes, gamma-ray telescopes, neutrino observations appeared, and now we will see the sky in gravitational waves, which, by the way, are not screened by anything.”

“These waves cannot be stopped by any matter, and with them we will be able to understand much more about the Universe than we do now. And there are many mysteries—for example, the mystery of dark matter.”

In addition, a gravitational telescope can scan the entire sky at once: it does not need to be tuned to a specific point in space or to one frequency. Therefore, in the future, many unique astrophysical events will be first recorded precisely by the gravitational telescope - it will be able to determine exact location objects, and then other surveillance tools will be configured using this data.

Not without this. Now scientists hope to see relic gravitational waves - the same ones that began to spread throughout the Universe almost immediately after the Big Bang.
“This will allow us to look into the very beginning of time,” says MSU professor Farit Khalili. “Gravitational interaction was the first to stop interacting with matter, and therefore the observation of cosmic microwave background radiation may make it possible to marry gravitational interactions with electromagnetic ones.”

The professor talks about the long-standing dream of physicists - the development of a coherent theory of quantum gravity, within the framework of which both electromagnetic and gravitational interactions are described using unified terms and equations. The maximum task on this path is the “theory of everything” or, as it is also called, the theory of the great unification. It combines all four well-known physical interactions(besides gravitational and electromagnetic there are also weak and strong interactions, explaining the existence of elementary particles).

Einstein's theory of relativity should also become part of such a theory. “We will be able to look into the area where the general theory of relativity ends, since it predicts a singularity in a black hole,” says MSU professor Igor Bilenko. “Perhaps we will see a new physics that includes general relativity as one of its components, one of its special cases.”

Finally, something from this feast may fall to us, ordinary people who do not dream of a grand unified theory. “When Hertz discovered electromagnetic waves, he had no idea that this would lead to power lines, mobile phones and the Internet,” says MSU Associate Professor Sergei Strygin. “Perhaps humanity will someday learn not only to detect gravitational waves, but also to use them for their own purposes.”

What will it be? Transmission of information through time, as in the film “Interstellar”, for which Kip Thorne was the scientific consultant? Time travel? Something incredibly crazy? We can’t predict anything yet—we can only wait and watch.

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, which were confirmed in the next century (slowing down the flow of time, changing the direction of electromagnetic radiation in gravitational fields, etc.), until recently it was not possible to practically detect the presence of this type of wave interaction between bodies.

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 A stretched piece of fabric can serve as an illustration of this postulate. 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 what more weight object (the larger the diameter and depth of 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 double system of neutron stars orbiting general center mass with constant angular velocity(quite a 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 positive results didn't bring it. 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 Legnara Laboratory (Padua, Italy) is based on 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. Emitted by a source laser beam 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 fundamentally new look on 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.