Physicists at the LIGO observatory (Laser Interferometric Gravitational Observatory) for the first time gravitational waves - disturbances of space-time predicted a hundred years ago by the creator general theory relativity by Albert Einstein. About the opening during a live broadcast organized by Lenta.ru and Moscow state university(MSU) named after M.V. Lomonosov, scientists Faculty of Physics, members of 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 special theory relativity, realized that time and space are one substance, and proposed the 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 Californian 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 it's extreme 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 like this Soviet article, 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. This 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?
Generally, science community was sure that they existed, and discovering them was a matter of time. Hulse and Taylor were awarded the Nobel Prize for the actual discovery of gravitational waves. What did they do? Eat 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 further. 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 recorded 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 USA. The LIGO detectors detected relative fluctuations of ten to the minus 19 meters (this is approximately equal to the ratio of the diameter of an atom to the diameter of an apple) of pairs of test masses separated by four kilometers. 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 Livingston detector recorded the event seven milliseconds earlier than the Hanford detector), scientists assumed that the signal source 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.
This is 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. Registration available 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 facilitate the selection of workers 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 the parameters, for example the mass ratio, starting 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.
No better explanation No? Is the discovery of gravitational waves most simply explained by the collision of black holes?
On this 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 next generation program called 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 level brainstorming. 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 National scientific foundation USA. 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, the majority existing theories 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!
Yesterday, the world was shocked by a sensation: scientists finally discovered gravitational waves, the existence of which Einstein predicted a hundred years ago. This is a breakthrough. Distortion of space-time (these are gravitational waves - now we’ll explain what’s what) was discovered at the LIGO observatory, and one of its founders is - who do you think? - Kip Thorne, author of the book.
We tell you why the discovery of gravitational waves is so important, what Mark Zuckerberg said and, of course, share the story from the first person. Kip Thorne, like no one else, knows how the project works, what makes it unusual and what significance LIGO has for humanity. Yes, yes, everything is so serious.
Discovery of gravitational waves
The scientific world will forever remember the date February 11, 2016. On this day, participants in the LIGO project announced: after so many futile attempts, gravitational waves had been found. This is reality. In fact, they were discovered a little earlier: in September 2015, but yesterday the discovery was officially recognized. IN The Guardian believe that scientists will certainly receive the Nobel Prize in Physics.
The cause of gravitational waves is the collision of two black holes, which occurred already... a billion light years from Earth. Can you imagine how huge our Universe is! Since black holes are very massive bodies, they send ripples through space-time, distorting it slightly. So waves appear, similar to those that spread from a stone thrown into the water.
This is how you can imagine gravitational waves coming to the Earth, for example, from a wormhole. Drawing from the book “Interstellar. Science behind the scenes"
The resulting vibrations were converted into sound. Interestingly, the signal from gravitational waves arrives at approximately the same frequency as our speech. So we can hear with our own ears how black holes collide. Listen to what gravitational waves sound like.
And guess what? More recently, black holes are not structured as previously thought. But there was no evidence at all that they exist in principle. And now there is. Black holes really “live” in the Universe.
This is what scientists believe a catastrophe looks like—a merger of black holes.
On February 11, a grandiose conference took place, which brought together more than a thousand scientists from 15 countries. Russian scientists were also present. And, of course, there was Kip Thorne. “This discovery is the beginning of an amazing, magnificent quest for people: the search and exploration of the curved side of the Universe - objects and phenomena created from distorted space-time. Black hole collisions and gravitational waves are our first remarkable examples,” said Kip Thorne.
The search for gravitational waves has been one of the main problems in physics. Now they have been found. And Einstein's genius is confirmed again.
In October, we interviewed Sergei Popov, a Russian astrophysicist and famous popularizer of science. He looked like he was looking into water! In the fall: “It seems to me that we are now on the threshold of new discoveries, which is primarily associated with the work of the LIGO and VIRGO gravitational wave detectors (Kip Thorne made a major contribution to the creation of the LIGO project).” Amazing, right?
Gravitational waves, wave detectors and LIGO
Well, now for a little physics. For those who really want to understand what gravitational waves are. Here's an artistic depiction of the tendex lines of two black holes orbiting each other, counterclockwise, and then colliding. Tendex lines generate tidal gravity. Go ahead. The lines, which emanate from the two points furthest apart from each other on the surfaces of a pair of black holes, stretch everything in their path, including the artist’s friend in the drawing. The lines emanating from the collision area compress everything.
As the holes rotate around one another, they carry along their tendex lines, which resemble streams of water from a spinning sprinkler on a lawn. In the picture from the book “Interstellar. Science behind the scenes" - a pair of black holes that collide, rotating around each other counterclockwise, and their tendex lines.
Black holes merge into one big hole; it is deformed and rotates counterclockwise, dragging tendex lines with it. A stationary observer far from the hole will feel vibrations as the tendex lines pass through him: stretching, then compression, then stretching - the tendex lines have become a gravitational wave. As the waves propagate, the black hole's deformation gradually decreases, and the waves also weaken.
When these waves reach the Earth, they look like the one shown at the top of the figure below. They stretch in one direction and compress in the other. The extensions and compressions oscillate (from red right-left, to blue right-left, to red right-left, etc.) as the waves pass through the detector at the bottom of the figure.
Gravitational waves passing through the LIGO detector.
The detector consists of four large mirrors (40 kilograms, 34 centimeters in diameter), which are attached to the ends of two perpendicular pipes, called detector arms. Tendex lines of gravitational waves stretch one arm, while compressing the second, and then, on the contrary, compress the first and stretch the second. And so again and again. As the length of the arms changes periodically, the mirrors move relative to each other, and these movements are tracked using laser beams in a way called interferometry. Hence the name LIGO: Laser Interferometer Gravitational-Wave Observatory.
LIGO control center, from where they send commands to the detector and monitor the received signals. Gravity detectors LIGOs are located in Hanford, Washington and Livingston, Louisiana. Photo from the book “Interstellar. Science behind the scenes"
Now LIGO is an international project in which 900 scientists from different countries, with headquarters located at the California Institute of Technology.
The Curved Side of the Universe
Black holes, wormholes, singularities, gravitational anomalies and dimensions higher order associated with the curvature of space and time. That's why Kip Thorne calls them "the twisted side of the universe." Humanity still has very little experimental and observational data from the curved side of the Universe. This is why we pay so much attention to gravitational waves: they are made of curved space and provide the most accessible way for us to explore the curved side.
Imagine if you only saw the ocean when it was calm. You wouldn't know about currents, whirlpools and storm waves. This is reminiscent of our current knowledge of the curvature of space and time.
We know almost nothing about how curved space and curved time behave "in a storm" - when the shape of space fluctuates violently and when the speed of time fluctuates. This is an incredibly alluring frontier of knowledge. Scientist John Wheeler coined the term "geometrodynamics" for these changes.
Of particular interest in the field of geometrodynamics is the collision of two black holes.
Collision of two non-rotating black holes. Model from the book “Interstellar. Science behind the scenes"
The picture above shows the moment when two black holes collide. Just such an event allowed scientists to record gravitational waves. This model is built for non-rotating black holes. Top: orbits and shadows of holes, as seen from our Universe. Middle: curved space and time, as seen from the bulk (multidimensional hyperspace); The arrows show how space is involved in movement, and the changing colors show how time is bent. Bottom: The shape of the emitted gravitational waves.
Gravitational waves from the Big Bang
Over to Kip Thorne. “In 1975, Leonid Grischuk, my good friend from Russia, made a sensational statement. He said that at the moment big bang many gravitational waves arose, and the mechanism of their occurrence (previously unknown) was as follows: quantum fluctuations (random fluctuations - editor's note) gravitational field During the Big Bang, they were amplified many times over by the initial expansion of the Universe and thus became the original gravitational waves. These waves, if detected, could tell us what happened at the birth of our Universe."
If scientists find the primordial gravitational waves, we will know how the Universe began.
People have solved far all the mysteries of the Universe. There's more to come.
In subsequent years, as our understanding of the Big Bang improved, it became obvious that these primordial waves must be strong at wavelengths commensurate with the size of the visible Universe, that is, at lengths of billions of light years. Can you imagine how much this is?.. And at the wavelengths that LIGO detectors cover (hundreds and thousands of kilometers), the waves will most likely be too weak to be recognized.
Jamie Bock's team built the BICEP2 apparatus, with which the trace of the original gravitational waves was discovered. The device located at the North Pole is shown here during twilight, which occurs there only twice a year.
BICEP2 device. Image from the book Interstellar. Science behind the scenes"
It is surrounded by shields that shield the device from radiation from the surrounding ice cover. On the right top corner shows a trace discovered in the cosmic microwave background radiation - a polarization pattern. Lines electric field directed along short light strokes.
Trace of the beginning of the universe
In the early nineties, cosmologists realized that these gravitational waves, billions of light years long, must have left a unique trace in the electromagnetic waves that fill the Universe - the so-called cosmic microwave background, or cosmic microwave background radiation. This began the search for the Holy Grail. After all, if we detect this trace and deduce from it the properties of the original gravitational waves, we can find out how the Universe was born.
In March 2014, while Kip Thorne was writing this book, the team of Jamie Bok, a cosmologist at Caltech whose office is next door to Thorne's, finally discovered this trace in the cosmic microwave background radiation.
This is an absolutely amazing discovery, but there is one controversial point: the trace found by Jamie's team could have been caused by something other than gravitational waves.
If a trace of the gravitational waves that arose during the Big Bang is indeed found, it means that a cosmological discovery has occurred on a level that happens perhaps once every half century. It gives you a chance to touch the events that occurred a trillionth of a trillionth of a trillionth of a second after the birth of the Universe.
This discovery confirms theories that the expansion of the Universe at that moment was extremely fast, in the slang of cosmologists - inflationary fast. And heralds the advent of a new era in cosmology.
Gravitational waves and Interstellar
Yesterday, at a conference on the discovery of gravitational waves, Valery Mitrofanov, head of the Moscow LIGO collaboration of scientists, which includes 8 scientists from Moscow State University, noted that the plot of the film “Interstellar,” although fantastic, is not so far from reality. And all because Kip Thorne was the scientific consultant. Thorne himself expressed hope that he believes in future manned flights to a black hole. They may not happen as soon as we would like, but today it is much more real than it was before.
The day is not too far off when people will leave the confines of our galaxy.
The event stirred the minds of millions of people. The notorious Mark Zuckerberg wrote: “The detection of gravitational waves is the most big discovery V modern science. Albert Einstein is one of my heroes, which is why I took the discovery so personally. A century ago, within the framework of the General Theory of Relativity (GTR), he predicted the existence of gravitational waves. But they are so small to detect that it has come to look for them in the origins of events such as the Big Bang, stellar explosions and black hole collisions. When scientists analyze the data obtained, a perfect A New Look to space. And perhaps this will shed light on the origin of the Universe, the birth and development of black holes. It is very inspiring to think about how many lives and efforts have gone into unveiling this mystery of the Universe. This breakthrough became possible thanks to the talent of brilliant scientists and engineers, people different nationalities, as well as the latest computer technologies, which appeared only recently. Congratulations to everyone involved. Einstein would be proud of you."
This is the speech. And this is a person who is simply interested in science. One can imagine what a storm of emotions overwhelmed the scientists who contributed to the discovery. It seems we have witnessed a new era, friends. This is amazing.
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February 11, 2016 will forever go down in history. On this day one of the greatest scientific discoveries recent times - predicted almost a hundred years ago by Albert Einstein's general theory of relativity. Ripples in the fabric of space-time, which distort space and time around it, have reached Earth and have been directly detected for the first time.
"We are opening new era- era of gravitational wave astronomy. This can be compared to the advent of the telescope or radio astronomy. We have a new tool for studying the Universe,” says one of the LIGO project participants, head of the Coherent Microoptics and Radio Photonics group at the Russian Quantum Center (RCC), Mikhail Gorodetsky.
The international project LIGO (Laser Interferometer Gravitational-Wave Observatory), a laser interferometer gravitational-wave observatory, was launched in 1992 and now involves scientists from 15 countries. From the very beginning, the experiments involved Russian physicists, including scientific groups under the guidance of professor of the Faculty of Physics of Moscow State University Valery Mitrofanov.
Today Valery Mitrofanov and other prominent Russian physicists took part in a press conference at which they spoke in detail about the discovery. Below is a video recording of the press conference. Professor Mitrofanov speaks first, first he comments in live broadcast from Washington. Sensational news was officially announced there, rumors about which had been circulating for several weeks.
Then Valery Mitrofanov himself explained briefly technical side How the experiment went:
“The signal was caught from two black holes, which are located at a distance of about 1.3 billion light years from us. The holes revolved around each other and eventually merged into one. The gravitational waves signaled this with a burst, which was recorded by the detectors. It is important to emphasize that this is a direct recording of waves, not an indirect one. For indirect, the Nobel Prize was awarded in 1993. The detectors picked up a signal at 10 minus 19 degrees of a meter. It is today extreme precision measurements that have so far been achieved on Earth.As for the contribution of Russian scientists, this is, first of all, the creation of systems that make it possible to isolate such a weak signal from a background of noise. The task, frankly speaking, is extremely difficult.”
The black holes had a mass of approximately 30 solar masses each and rotated around each other at a frequency of 150 Hz. The post-merger mass was three solar masses less than the sum of the pre-merger masses: the remaining energy was emitted in the form of gravitational waves.
Having reached the Earth, gravitational waves began to distort our space-time. Accordingly, the distance between the antenna elements of the LIGO observatory began to periodically change, which was recorded by laser beam detectors.
Gravitational waves were recorded on September 14, 2015 at 13:51 Moscow time.
"This ultimate achievement human civilization, said MSU professor Sergei Vyatchanin. - LIGO has almost reached the quantum measurement limit. It was possible to register the displacement of two macroscopic objects weighing several kilograms and separated by several kilometers with an accuracy predicted by Heisenberg’s quantum uncertainty.”
“Now we have only two detectors, but even with them we will be able to determine the masses of objects, and estimate them based on the delay time approximate position in the sky,” said one of the authors of the discovery, scientific director of the Russian Quantum Center, professor at Moscow State University Mikhail Gorodetsky. “For two antennas, the localization is not very good - there is some arc in the sky, but when the third European gravitational antenna is fully operational, we will be able to determine the position of the sources quite accurately using the triangulation method.”
L-shaped antenna and LIGO observatory in Louisiana
By the way, it was Russian physicists who proposed hanging the mirrors on quartz threads instead of steel (laser beams were reflected from the mirrors in each four-kilometer arm of the L-shaped interferometer), which reduced extraneous noise in the system. Without this, the discovery would hardly have taken place.
Video recording of the press conference
Gravitational waves - artist's rendering
Gravitational waves are disturbances of the space-time metric that break away from the source and propagate like waves (the so-called “space-time ripples”).
In general relativity and most others modern theories In gravity, gravitational waves are generated by the motion of massive bodies with variable acceleration. Gravitational waves propagate freely in space at the speed of light. Due to the relative weakness gravitational forces(compared to others) these waves have a very small magnitude, which is difficult to register.
Polarized gravitational wave
Gravitational waves are predicted by the general theory of relativity (GR), and many others. They were first directly detected in September 2015 by two twin detectors, which detected gravitational waves, likely resulting from the merger of two and the formation of one more massive rotating black hole. Indirect evidence of their existence has been known since the 1970s - General Relativity predicts rates of convergence that coincide with observations tight systems due to the loss of energy due to the emission of gravitational waves. Direct registration of gravitational waves and their use to determine the parameters of astrophysical processes is important task modern physics and astronomy.
Within the framework of general relativity, gravitational waves are described by solutions of wave-type Einstein equations, which represent a perturbation of the space-time metric moving at the speed of light (in the linear approximation). The manifestation of this indignation should be, in particular, periodic change distances between two freely falling (that is, not influenced by any forces) test masses. Amplitude h gravitational wave is a dimensionless quantity - a relative change in distance. The predicted maximum amplitudes of gravitational waves from astrophysical objects (for example, compact binary systems) and phenomena (explosions, mergers, captures by black holes, etc.) when measured are very small ( h=10 −18 -10 −23). A weak (linear) gravitational wave, according to the general theory of relativity, transfers energy and momentum, moves at the speed of light, is transverse, quadrupole and is described by two independent components located at an angle of 45° to each other (has two directions of polarization).
Different theories predict the speed of propagation of gravitational waves differently. In general relativity, it is equal to the speed of light (in the linear approximation). In other theories of gravity, it can take any value, including infinity. According to the first registration of gravitational waves, their dispersion turned out to be compatible with a massless graviton, and the speed was estimated as equal to speed Sveta.
Generation of gravitational waves
A system of two neutron stars creates ripples in spacetime
A gravitational wave is emitted by any matter moving with asymmetric acceleration. For a wave of significant amplitude to occur, extremely large mass emitter and/or huge accelerations, the amplitude of the gravitational wave is directly proportional first derivative of acceleration and the mass of the generator, that is ~ . However, if an object is moving at an accelerated rate, this means that some force is acting on it from another object. In turn, this other object experiences reverse action(according to Newton’s 3rd law), it turns out that m 1 a 1 = − m 2 a 2 . It turns out that two objects emit gravitational waves only in pairs, and as a result of interference they are mutually canceled out almost completely. That's why gravitational radiation in the general theory of relativity, the multipolarity always has the character of at least quadrupole radiation. In addition, for non-relativistic emitters in the expression for the radiation intensity there is a small parameter where is the gravitational radius of the emitter, r- its characteristic size, T - characteristic period movements, c- speed of light in vacuum.
Most strong sources gravitational waves are:
- colliding (giant masses, very small accelerations),
- gravitational collapse dual system compact objects(colossal accelerations at quite large mass). As private and most interesting case- merger of neutron stars. In such a system, the gravitational-wave luminosity is close to the maximum Planck luminosity possible in nature.
Gravitational waves emitted by a two-body system
Two bodies moving in circular orbits around general center masses
Two gravitational bound body with the masses m 1 and m 2, moving non-relativistically ( v << c) in circular orbits around their common center of mass at a distance r from each other, emit gravitational waves of the following energy, on average over the period:
As a result, the system loses energy, which leads to the convergence of bodies, that is, to a decrease in the distance between them. Speed of approach of bodies:
For the Solar System, for example, the greatest gravitational radiation is produced by the and subsystem. The power of this radiation is approximately 5 kilowatts. Thus, the energy lost by the Solar System to gravitational radiation per year is completely negligible compared to the characteristic kinetic energy of bodies.
Gravitational collapse of a binary system
Any double star, when its components rotate around a common center of mass, loses energy (as assumed - due to the emission of gravitational waves) and, in the end, merges together. But for ordinary, non-compact, double stars, this process takes a very long time, much longer than the present age. If a compact binary system consists of a pair of neutron stars, black holes, or a combination of both, then the merger can occur within several million years. First, the objects come closer together, and their period of revolution decreases. Then, at the final stage, a collision and asymmetric gravitational collapse occurs. This process lasts a fraction of a second, and during this time energy is lost into gravitational radiation, which, according to some estimates, amounts to more than 50% of the mass of the system.
Basic exact solutions of Einstein's equations for gravitational waves
Bondi-Pirani-Robinson body waves
These waves are described by a metric of the form . If we introduce a variable and a function, then from the general relativity equations we obtain the equation
Takeno Metric
has the form , -functions satisfy the same equation.
Rosen metric
Where to satisfy
Perez metric
Wherein
Cylindrical Einstein-Rosen waves
In cylindrical coordinates, such waves have the form and are executed
Registration of gravitational waves
Registration of gravitational waves is quite difficult due to the weakness of the latter (small distortion of the metric). The devices for registering them are gravitational wave detectors. Attempts to detect gravitational waves have been made since the late 1960s. Gravitational waves of detectable amplitude are born during the collapse of a binary. Similar events occur in the surrounding area approximately once a decade.
On the other hand, the general theory of relativity predicts the acceleration of the mutual rotation of binary stars due to the loss of energy in the emission of gravitational waves, and this effect is reliably recorded in several known systems of binary compact objects (in particular, pulsars with compact companions). In 1993, “for the discovery of a new type of pulsar, which provided new opportunities in the study of gravity” to the discoverers of the first double pulsar PSR B1913+16, Russell Hulse and Joseph Taylor Jr. was awarded the Nobel Prize in Physics. The acceleration of rotation observed in this system completely coincides with the predictions of general relativity for the emission of gravitational waves. The same phenomenon was recorded in several other cases: for the pulsars PSR J0737-3039, PSR J0437-4715, SDSS J065133.338+284423.37 (usually abbreviated J0651) and the system of binary RX J0806. For example, the distance between the two components A and B of the first binary star of the two pulsars PSR J0737-3039 decreases by about 2.5 inches (6.35 cm) per day due to energy loss to gravitational waves, and this occurs in agreement with general relativity . All these data are interpreted as indirect confirmation of the existence of gravitational waves.
According to estimates, the strongest and most frequent sources of gravitational waves for gravitational telescopes and antennas are catastrophes associated with the collapse of binary systems in nearby galaxies. It is expected that in the near future several similar events per year will be recorded on improved gravitational detectors, distorting the metric in the vicinity by 10 −21 -10 −23 . The first observations of an optical-metric parametric resonance signal, which makes it possible to detect the effect of gravitational waves from periodic sources such as a close binary on the radiation of cosmic masers, may have been obtained at the radio astronomical observatory of the Russian Academy of Sciences, Pushchino.
Another possibility of detecting the background of gravitational waves filling the Universe is high-precision timing of distant pulsars - analysis of the arrival time of their pulses, which characteristically changes under the influence of gravitational waves passing through the space between the Earth and the pulsar. Estimates for 2013 indicate that timing accuracy needs to be improved by about one order of magnitude to detect background waves from multiple sources in our Universe, a task that could be accomplished before the end of the decade.
According to modern concepts, our Universe is filled with relic gravitational waves that appeared in the first moments after. Their registration will make it possible to obtain information about the processes at the beginning of the birth of the Universe. On March 17, 2014 at 20:00 Moscow time at the Harvard-Smithsonian Center for Astrophysics, an American group of researchers working on the BICEP 2 project announced the detection of non-zero tensor disturbances in the early Universe by the polarization of the cosmic microwave background radiation, which is also the discovery of these relict gravitational waves . However, almost immediately this result was disputed, since, as it turned out, the contribution was not properly taken into account. One of the authors, J. M. Kovats ( Kovac J. M.), admitted that “the participants and science journalists were a bit hasty in interpreting and reporting the data from the BICEP2 experiment.”
Experimental confirmation of the existence
The first recorded gravitational wave signal. On the left is data from the detector in Hanford (H1), on the right - in Livingston (L1). Time is counted from September 14, 2015, 09:50:45 UTC. To visualize the signal, it is filtered with a frequency filter with a passband of 35-350 Hertz to suppress large fluctuations outside the high sensitivity range of the detectors; band-stop filters were also used to suppress the noise of the installations themselves. Top row: voltages h in the detectors. GW150914 first arrived at L1 and 6 9 +0 5 −0 4 ms later to H1; For visual comparison, data from H1 are shown in the L1 graph in reversed and time-shifted form (to account for the relative orientation of the detectors). Second row: voltages h from the gravitational wave signal, passed through the same 35-350 Hz bandpass filter. The solid line is the result of numerical relativity for a system with parameters compatible with those found based on the study of the GW150914 signal, obtained by two independent codes with a resulting match of 99.9. The gray thick lines are the 90% confidence regions of the waveform reconstructed from the detector data by two different methods. The dark gray line models the expected signals from the merger of black holes, the light gray line does not use astrophysical models, but represents the signal as a linear combination of sinusoidal-Gaussian wavelets. The reconstructions overlap by 94%. Third row: Residual errors after extracting the filtered prediction of the numerical relativity signal from the filtered signal of the detectors. Bottom row: A representation of the voltage frequency map, showing the increase in the dominant frequency of the signal over time.
February 11, 2016 by the LIGO and VIRGO collaborations. The merger signal of two black holes with an amplitude at maximum of about 10 −21 was recorded on September 14, 2015 at 9:51 UTC by two LIGO detectors in Hanford and Livingston, 7 milliseconds apart, in the region of maximum signal amplitude (0.2 seconds) combined the signal-to-noise ratio was 24:1. The signal was designated GW150914. The shape of the signal matches the prediction of general relativity for the merger of two black holes with masses of 36 and 29 solar masses; the resulting black hole should have a mass of 62 solar and a rotation parameter a= 0.67. The distance to the source is about 1.3 billion, the energy emitted in tenths of a second in the merger is the equivalent of about 3 solar masses.
Story
The history of the term “gravitational wave” itself, the theoretical and experimental search for these waves, as well as their use for studying phenomena inaccessible to other methods.
- 1900 - Lorentz suggested that gravity “...can spread at a speed no greater than the speed of light”;
- 1905 - Poincaré first introduced the term gravitational wave (onde gravifique). Poincaré, on a qualitative level, removed the established objections of Laplace and showed that the corrections associated with gravitational waves to the generally accepted Newtonian laws of gravity are canceled out, thus the assumption of the existence of gravitational waves does not contradict observations;
- 1916 - Einstein showed that, within the framework of general relativity, a mechanical system will transfer energy to gravitational waves and, roughly speaking, any rotation relative to fixed stars must sooner or later stop, although, of course, under normal conditions, energy losses of the order of magnitude are negligible and practically not measurable (in In this work, he also mistakenly believed that a mechanical system that constantly maintains spherical symmetry can emit gravitational waves);
- 1918 - Einstein derived a quadrupole formula in which the emission of gravitational waves turns out to be an effect of order , thereby correcting the error in his previous work (an error remained in the coefficient, the wave energy is 2 times less);
- 1923 - Eddington - questioned the physical reality of gravitational waves "...propagating...at the speed of thought." In 1934, when preparing the Russian translation of his monograph “The Theory of Relativity,” Eddington added several chapters, including chapters with two options for calculating energy losses by a rotating rod, but noted that the methods used for approximate calculations of general relativity, in his opinion, are not applicable to gravitationally bound systems , so doubts remain;
- 1937 - Einstein, together with Rosen, investigated cylindrical wave solutions to the exact equations of the gravitational field. During the course of these studies, they began to doubt that gravitational waves may be an artifact of approximate solutions of the general relativity equations (correspondence regarding a review of the article “Do gravitational waves exist?” by Einstein and Rosen is known). Later, he found an error in his reasoning; the final version of the article with fundamental changes was published in the Journal of the Franklin Institute;
- 1957 - Herman Bondi and Richard Feynman proposed the “beaded cane” thought experiment in which they substantiated the existence of physical consequences of gravitational waves in general relativity;
- 1962 - Vladislav Pustovoit and Mikhail Herzenstein described the principles of using interferometers to detect long-wave gravitational waves;
- 1964 - Philip Peters and John Matthew theoretically described gravitational waves emitted by binary systems;
- 1969 - Joseph Weber, founder of gravitational wave astronomy, reports the detection of gravitational waves using a resonant detector - a mechanical gravitational antenna. These reports give rise to a rapid growth of work in this direction, in particular, Rainier Weiss, one of the founders of the LIGO project, began experiments at that time. To date (2015), no one has been able to obtain reliable confirmation of these events;
- 1978 - Joseph Taylor reported the detection of gravitational radiation in the binary pulsar system PSR B1913+16. Joseph Taylor and Russell Hulse's research earned them the 1993 Nobel Prize in Physics. As of early 2015, three post-Keplerian parameters, including period reduction due to gravitational wave emission, had been measured for at least 8 such systems;
- 2002 - Sergey Kopeikin and Edward Fomalont used ultra-long-baseline radio wave interferometry to measure the deflection of light in the gravitational field of Jupiter in dynamics, which for a certain class of hypothetical extensions of general relativity makes it possible to estimate the speed of gravity - the difference from the speed of light should not exceed 20% (this interpretation does not generally accepted);
- 2006 - the international team of Martha Bourgay (Parkes Observatory, Australia) reported significantly more accurate confirmation of general relativity and its correspondence to the magnitude of gravitational wave radiation in the system of two pulsars PSR J0737-3039A/B;
- 2014 - Astronomers at the Harvard-Smithsonian Center for Astrophysics (BICEP) reported the detection of primordial gravitational waves while measuring fluctuations in the cosmic microwave background radiation. At the moment (2016), the detected fluctuations are considered not to be of relict origin, but are explained by the emission of dust in the Galaxy;
- 2016 - international LIGO team reported the detection of the gravitational wave transit event GW150914. For the first time, direct observation of interacting massive bodies in ultra-strong gravitational fields with ultra-high relative velocities (< 1,2 × R s , v/c >0.5), which made it possible to verify the correctness of general relativity with an accuracy of several post-Newtonian terms of high orders. The measured dispersion of gravitational waves does not contradict previous measurements of dispersion and upper limit mass of the hypothetical graviton (< 1,2 × 10 −22 эВ), если он в некотором гипотетическом расширении ОТО будет существовать.
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 solutions to GPV. They must spread at the speed of light. It is emitted by any body moving with variable acceleration.
For example, it rotates in its orbit with variable acceleration directed towards the star. And this acceleration is constantly changing. 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). They rotate 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. Gravitational field strength - 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 of electromagnetic radiation. Relic and electromagnetic radiation appeared 700 thousand years after the Big Bang, then during the 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 needs to be cooled to almost absolute zero(in 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 elementary particle— carrier of gravitational waves: