2020-11-12

Recently, physicists reproduced the nuclear reaction of the Big Bang and confirmed the Big Bang model

By yqqlm yqqlm
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  • The physicists of the Italian Underground Nuclear Astrophysics Laboratory A beam of protons (pink) was emitted from a deuterium target and the fusion rate was measured.

In a hidden laboratory in Italy, physicists recreated the universeThe nuclear reaction that occurred two to three minutes after the Big Bang. Their reaction rate measurement results were published in the journal Nature yesterday, and they identified the most uncertain factor in a series of steps called the Big Bang nuclear fusion (the Big Bang nuclear fusion produced the first atomic nucleus in the universe) .

According to Ryan Cook, an astrophysicist at Durham University in the United Kingdom, the researchers were”ecstatic” at the result.”There will be many people interested in particle physics, nuclear physics, cosmology and astronomy,” he said.

The reaction involves deuterium, which is a isotope of hydrogen. It is composed of a proton and a neutron, which fused in the first three minutes of the universe. Most of the deuterium quickly fused into heavier, more stable elements, such as helium and lithium. But some”live to today”. Brian Fields, an astrophysicist at the University of Illinois at Urbana-Champaign, said,”We have a few grams of deuterium in our body, and they come from the Big Bang.”

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The exact amount of deuterium left reveals key details in the first few minutes, including protons And the density of neutrons, and how quickly they separate during the expansion of the universe. Carlo Gustavino, a nuclear astrophysicist at the Italian National Institute of Nuclear Physics, said that deuterium is”a special super witness of that era.”

But physicists can only infer this information if they know the rate at which deuterium and protons fusion form the isotope helium-3. New measurements in collaboration with the Underground Nuclear Astrophysics Laboratory (LUNA) have determined this rate.

The earliest detector in the universe

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The production of deuterium is the first step in the Big Bang nuclear fusion, when the universe is still super hot but rapidly cooled by protons and neutrons During the”soup”, a series of nuclear reactions took place.

Since the 1940s, nuclear physicists have developed a series of chain equations that describe how various isotopes of hydrogen, helium, and lithium combine to form nuclei. How to fuse and absorb protons and neutrons (heavier elements are formed in the interior of stars a long time later). Since then, researchers have tested most aspects of these equations in the laboratory by replicating primitive nuclear reactions.

In the process, they made important discoveries. These calculations first provided some evidence for the existence of dark matter in the 1970s. The Big Bang nuclear fusion also enabled physicists to predict the number of different types of neutrinos, which helped drive the expansion of the universe.

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  • The cosmic microwave background radiation map, the first Look

But in the past ten years, uncertainty about whether deuterium is likely to absorb protons and transform into helium-3 has made the universe’s first few minutes The scene became blurred. Most importantly, this uncertainty prevents physicists from comparing this picture with what the universe looked like 380,000 years after the Big Bang. 380,000 years after the Big Bang, the universe had cooled enough to allow electrons to start moving around the nucleus. This process releases radiation called the cosmic microwave background, providing a”snapshot” of the universe at that time.

Cosmologists hope to check whether the density of the universe changes from one cycle to another as expected based on their evolutionary model of the universe. If the two pictures are inconsistent,”understanding this will be very, very important,” Cook said. Solutions to stubborn cosmic problems (such as the nature of dark matter) can be found in this gap, or in the first signs of new foreign particles.”From a minute or two after the Big Bang to hundreds of thousands of years after the Big Bang, many things can happen,” Cook said.

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The most important The reaction rate of deuterium allows researchers to make such comparisons, but it is very difficult to measure the reaction rate of deuterium. Because this is simulating the big bang in a controlled way in the laboratory! The last time a physicist tried to measure was in 1997. Since then, observations of the cosmic microwave background have become more and more accurate, which has put pressure on physicists who study the Big Bang nuclear fusion.

In 2014, Cook and his co-authors accurately measured the abundance of deuterium in the universe through observations of distant gas clouds. However, to convert this abundance into an accurate prediction of the density of the original material, they need to better measure the deuterium reaction rate. A pure theoretical estimate released in 2016 is inconsistent with laboratory measurements in 1997, which further increases the difficulty of research.

“This is a very messy situation,” said Gustavino, a member of the LUNA cooperative.”At this point, I have become more active about cooperation… because Luna can accurately measure this reaction.”

A rare The combination of

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measure Part of the challenge with the ease of deuterium and proton fusion is that this reaction does not occur frequently under laboratory conditions. Every second, the LUNA experiment emits 100 trillion protons to a deuterium target. Fusion occurs only a few times a day.

What’s more difficult is that the cosmic rays continuously falling on the surface of the earth can simulate the signal generated by the deuterium reaction.”For this reason, we are in an underground laboratory, and because of the rock coverage, we can benefit from’avoiding the interference of cosmic rays,'” Francesca Cavana said. She and Sandra Zavatarelli led the data collection and analysis of LUNA.

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in three years For a long time, the scientists worked in shifts in a laboratory deep in the Great Sasso Mountain in Italy for up to a week.”It’s exciting because you really feel like you are in science,” Cavanagh said. As they collect more and more data, the pressure from the wider physics community is also increasing.”There are many expectations; there are many expectations,” they said.

It turns out that the team’s latest measurement results may disappoint cosmologists who are looking for”cracks” in the universe model.

One ​​small step

The measured rate (that is, the temperature during the original nuclear fusion period The rate at which deuterium and protons fused to form helium-3 within the range) fell between the theoretical prediction in 2016 and the measurement in 1997. More importantly, when physicists input this rate into the Big Bang nuclear fusion equation, their predicted raw material density and cosmic expansion rate are very consistent with observations of the cosmic microwave background 380,000 years later.

“It essentially tells us that so far, the standard model of cosmology is completely correct,” Aliota said. This in itself closes the gap that the next-generation universe model must adapt. Experts say that the results can even rule out certain dark matter theories.

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This is better than support The evidence for the strange new cosmic composition is even more exciting. But Aliota said that in this era of precision astronomy, this is a”small step” for scientists. Fields agreed,”We have been trying to do better in prediction, measurement and observation.”

The next generation of cosmic microwave background measurement is coming soon. technology. At the same time, as people have a better understanding of the behavior of deuterium, the uncertainty of other primitive nuclear reactions and element abundance becomes more urgent.

According to Field, a long-standing”big bang nuclear fusion effect” is a prediction of the density of matter calculated from deuterium and the cosmic microwave background. The lithium content should be three times more than what we actually observed. There are still many unknown factors, and what will happen in the future will be very interesting.