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When theoretical physicists like myself say that we're studying why the universe exists, we sound like philosophers. But new data collected by researchers using Japan's has revealed insights into that very question.

in particle physics suggest that for all the matter created at the universe's conception, an equal amount of antimatter should have been created alongside it. Antimatter, like matter, has mass and takes up space. However, antimatter particles exhibit the opposite properties of their corresponding matter particles.

When pieces of matter and antimatter collide, they , leaving behind only energy. The puzzling thing about theories that predict the creation of an equal balance of matter and antimatter is that if they were true, the two would have totally annihilated each other, leaving the universe empty. So there must have been more matter than antimatter at the birth of the universe, because the universe isn't empty—it's full of stuff that's made of matter like galaxies, stars and planets. A little bit of antimatter , but it is very rare.

As a , I'm interested in this so-called . In our , my collaborators and I found that the telescope's new measurement of the amount and type of helium in faraway galaxies may offer a solution to this long-standing mystery.

After the Big Bang

In the first milliseconds after the Big Bang, the universe was hot, dense and full of elementary particles like protons, neutrons and electrons . Also present in this pool of particles were neutrinos, which are very tiny, weakly interacting particles, and antineutrinos, their antimatter counterparts.

Â鶹ÒùÔºicists believe that just one second after the Big Bang, the nuclei of light elements like hydrogen and helium began to form. This process is known as . The nuclei formed were about , plus small amounts of heavier nuclei.

The physics community's on the formation of these nuclei tells us that neutrinos and antineutrinos played a fundamental role in the creation of, in particular, helium nuclei.

Helium creation in the early universe happened in a two-step process. First, neutrons and protons converted from one to the other in a involving neutrinos and antineutrinos. As the universe cooled, these processes stopped and the .

As theoretical physicists, we can create models to test how the ratio of protons to neutrons depends on the relative number of neutrinos and antineutrinos in the early universe. If , then our models show more protons and fewer neutrons would exist as a result.

As the universe cooled, hydrogen, helium and other elements . Helium is made up of two protons and two neutrons, and hydrogen is just one proton and no neutrons. So the fewer the neutrons available in the early universe, the less helium would be produced.

Because the nuclei formed during Big Bang Nucleosynthesis , scientists can infer how many neutrinos and antineutrinos were present during the early universe. They do this by looking specifically at galaxies that are rich in light elements like hydrogen and helium.

A clue in helium

Last year, the Subaru Collaboration—a group of Japanese scientists working on the Subaru telescope—released data on far outside of our own that are almost exclusively made up of hydrogen and helium.

Using a technique that allows researchers to distinguish different elements from one another based on the wavelengths of light observed in the telescope, the Subaru scientists determined exactly how much helium exists in each of these 10 galaxies. Importantly, they found less helium than the previously accepted theory predicted.

With this new result, my collaborators and I worked backward to find the necessary to produce the helium abundance found in the data. Think back to your ninth grade math class when you were asked to solve for "X" in an equation. What my team did was essentially the more sophisticated version of that, where our "X" was the number of neutrinos or antineutrinos.

The previously accepted theory predicted that there should be the same number of neutrinos and antineutrinos in the early universe. However, when we tweaked this theory to give us a prediction that matched the new data set, the number of neutrinos was greater than the number of antineutrinos.

What does it all mean?

This analysis of new helium-rich galaxy data has a far-reaching consequence—it can be used to explain the asymmetry between matter and antimatter. The Subaru data points us directly to a source for that imbalance: neutrinos. In this study, my collaborators and I proved that this new measurement of helium is consistent with there being more neutrinos then antineutrinos in the early universe. Through , the asymmetry in the neutrinos could propagate into an asymmetry in all matter.

The result of our study is a common type of result in the theoretical physics world. Basically, we discovered a viable way in which the matter-antimatter asymmetry could have been produced, but that doesn't mean it definitely was produced in that way. The fact that the data fits with our theory is a hint that the theory we've proposed might be the correct one, but this fact alone doesn't mean that it is.

So, are these tiny little neutrinos the key to answering the age old question, "Why does anything exist?" According to this new research, they just might be.

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