In February this year, astronomers made a monumental discovery. Almost a hundred years after their prediction by Albert Einstein, scientists finally discovered gravitational waves - "ripples in space-time", illuminated by the radiation of two merging black holes. This observation was a very clear confirmation of Einstein's general theory of relativity, but at the same time this event was bold proof that the laws of this theory cease to work as soon as they reach the event horizon of black holes.
Since February this year, the Laser Interferometric Gravitational Wave Observatory (LIGO) has seen gravitational waves a total of three times. Researchers have finally taken a close look at the findings and now claim to have found evidence of so-called "echoes" within waves that challenge Einstein's predictions of black holes.
These statements are currently published in the scientific online library ArXiv.org, where they can be analyzed by other members of the physicist community before being presented to peer review. Therefore, there is a very real likelihood that fresh facts will be found within the framework of an outside look at the data on observations of these echoes. In addition, the evidence presented was provided with an accuracy of 5 Sigma, which is the gold standard in the world of physics. This means that in 3.5 million there is one possibility that the observations are pure coincidence.
However, if other studies show that this "echo" is actually present, then for physics it will be a huge event. Previously, it has been suggested that the laws of general relativity are crumbled to smithereens when approaching the center of black holes, but this discovery will show that the laws also stop working at the boundaries of these space-time phenomena. If this is so, then this may be the beginning of the birth of the laws of a completely new physics.
“The discovery of LIGO and other organizations in perspective offers an amazing opportunity to explore new physical laws,” says Steve Giddings, a black hole researcher at the University of California, Santa Barbara, who was not involved in the study described today.
If the echoes turn out to be a dummy, then general relativity will only need to pass just another test. For decades, physicists have tried to tweak black holes into this theory, trying to find ways that would integrate it with quantum mechanics, but Einstein's theory has been doing well until now.
But before we continue with the discussion, let's understand what these echoes are and how they relate to general relativity.
It all comes down to the so-called information paradox of black holes. According to Einstein's theory, everything that crosses the event horizon of black holes should disappear, leaving nothing behind. In the traditional sense, this means that nothing, not even light, is able to get out of a black hole (hence, by the way, the name of this object).
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Recently, scientists have been greatly puzzled by testing this theory. Indeed, according to the laws of quantum mechanics, matter absorbed by a black hole can actually leave a trail in the form of information. So how can the event horizon be simultaneously described both from the point of view of general relativity (everything is destroyed after crossing its boundaries), and from the point of view of quantum mechanics (from the object, its information remains)?
This question is one of the most difficult in modern physics, and scientists still cannot find an answer to it.
One suggested explanation is the 2012 firewall hypothesis, which suggests that there are rings of highly charged particles around the event horizon, which incinerate any matter that passes through them.
Physicist Stephen Hawking has a different assumption. He believes that black holes can be surrounded by soft "hair" (hair is, of course, used here as a metaphor). These "hairs" represent low-charge quantum disturbances and store in themselves signatures (information, if you will) of everything that once fell into a black hole.
Regardless of which hypothesis you are more inclined to, their main message is the same: instead of the clean event horizon predicted by general relativity, the boundaries of black holes can be much more complex and blurry than we imagined. And the main problem here was that we did not have the opportunity to somehow verify these assumptions. Until LIGO detected gravitational waves.
Now, with the data on hand, an international team of researchers is proposing a way to find out what is happening around black holes. According to the new assumption, if the event horizons of black holes do not really lend themselves to the laws of general relativity, then echoes should remain after the initial gravitational waves.
According to the researchers, it will be possible to detect them thanks to the “hairs” surrounding the black hole, which are in a state of excitement and behave at this moment like mirrors. They capture some of the gravitational waves escaping the black hole, envelop them, transmitting some of their state of perturbation, and then can be detected by instruments like LIGO.
According to the scientists' calculations, these echoes could be detected using LIGO 0.1 and 0.3 seconds after the initial release of the gravitational wave. And - lo and behold! Scientists have become witnesses of this! Moreover, the event was observed not only within the framework of the first detection of gravitational waves in February this year, but also within the framework of all three observations of gravitational waves this year.
It should, of course, be understood that the three events can hardly be called reliable statistical data. So while the possibility remains that these echoes were some kind of background noise (1 in 270 cases, or 2.9 Sigma error), further observations will help researchers build a more solid evidence base.
“The good news is that the clarity and sensitivity of LIGO will be significantly improved soon, so we have a firmer opportunity over the next two years to confirm or deny these observations,” said lead researcher Niaesh Afshordi.
Even if the echoes can be confirmed, they will not answer the question of what level of fuzziness the boundaries of black holes have. Therefore, the solution of the information paradox has been postponed for now. So far, one thing is clear: one of the most important discoveries in physics this year has become even more tempting.
NIKOLAY KHIZHNYAK