By Paul Rincon
The nature of this quirk, which allowed
Now, results from an experiment in Japan could help researchers solve the puzzle - one of the biggest in science.
It hinges on a difference in the way matter and antimatter particles behave.
The world that's familiar to us - including all the everyday objects we can touch - is made up of matter. The fundamental building blocks of matter are sub-atomic particles, such as electrons, quarks and neutrinos.
But matter has a shadowy counterpart called antimatter. Each sub-atomic particle of ordinary matter has a corresponding "antiparticle".
Today, there is far more matter than antimatter in the Universe. But it wasn't always this way.
The Big Bang should have created matter and antimatter in equal amounts.
"When particle physicists make new particles in accelerators, they always find that they produce particle-antiparticle pairs: for every negative electron, a positively charged positron (the electron's antimatter counterpart)," said Prof Lee Thompson from the University of Sheffield, a member of the 350-strong T2K collaboration, which includes a relatively large number of scientists from UK universities.
"So why isn't the universe 50% antimatter? This is a long-standing problem in cosmology - what happened to the antimatter?"
However, when a matter particle meets its antiparticle, they "annihilate" - disappear in a flash of energy.
During the first fractions of a second of the Big Bang, the hot, dense Universe was fizzing with particle-antiparticle pairs popping in and out of existence. Without some other, unknown mechanism at play, the Universe should contain nothing but leftover energy.
"It would be pretty boring and we wouldn't be here," Prof Stefan Söldner-Rembold, head of the particle physics group at the University of Manchester, told BBC News.
So what happened to tip the balance?
That's where the T2K experiment comes in. T2K is based
Researchers used the facility's detector to observe neutrinos and their antimatter counterparts,
As they travel through the Earth, the particles and antiparticles oscillate between different physical properties known as
Physicists think that finding a difference - or asymmetry - in the physical properties of neutrinos and antineutrinos might help us understand why matter is so prevalent compared with antimatter. This asymmetry is known as charge-conjugation and parity reversal (CP)
It is one of three necessary conditions, proposed by the Russian physicist Andrei Sakharov in 1967, that must be satisfied to produce matter and antimatter at different rates.
The result has also reached a level of statistical significance - called three-sigma - that's high enough to indicate that CP violation occurs in these particles.
The results have been published in the journal Nature.
"While CP violation involving quarks is experimentally well established, CP violation has never been observed for neutrinos," said Stefan Söldner-Rembold.
"The violation of CP symmetry is one of the (Sakharov) conditions for a matter-dominated Universe to exist, but the quark-driven effect is unfortunately much too small to explain why our Universe is mainly filled with matter.
"Discovering CP violation with neutrinos would be a great leap forward in understanding how the Universe was formed."
He said a theory called
The results from T2K "give strong hints" that the CP violation effect could be large for neutrinos.
This would mean that the next-generation neutrino experiment DUNE, which is currently being constructed in a mine in South Dakota, might detect the effect faster than expected. The international project is being hosted by the US Fermi National Accelerator Laboratory (Fermilab).
Prof Söldner-Rembold is a member of the DUNE scientific team and the collaboration's spokesperson. The experiment's detector will contain 70,000 tons of liquid argon buried one mile underground. It will be used to discover and measure CP violation with high precision.
He added that the T2K result still "requires a theoretical model which describes how you get from this effect at the beginning, to the Universe today".