The universe has a lithium problem

February 20, 2017 by Evan Gough, Universe Today
The universe has a lithium problem
This illustration shows the evolution of the Universe, from the Big Bang on the left, to modern times on the right. Credit: NASA

Over the past decades, scientists have wrestled with a problem involving the Big Bang Theory. The Big Bang Theory suggests that there should be three times as much lithium as we can observe. Why is there such a discrepancy between prediction and observation?

To get into that problem, let's back up a bit.

The Big Bang Theory (BBT) is well-supported by multiple lines of evidence and theory. It's widely accepted as the explanation for how the started. Three key pieces of evidence support the BBT:

  • observations of the cosmic microwave background
  • our growing understanding of the large-scale structure of the universe
  • rough agreement between calculations and observations of the abundance of primordial light (Do NOT attempt to say this three times in rapid succession!)

But the BBT still has some niggling questions.

The missing lithium problem is centred around the earliest stages of the universe: from about 10 seconds to 20 minutes after the Big Bang. The universe was super hot and it was expanding rapidly. This was the beginning of what's called the Photon Epoch.

At that time, atomic nuclei formed through nucleosynthesis. But the extreme heat that dominated the universe prevented the nuclei from combining with electrons to form atoms. The universe was a plasma of nuclei, electrons, and photons.

Only the lightest nuclei were formed during this time, including most of the helium in the universe, and small amounts of other light nuclides, like deuterium and our friend lithium. For the most part, heavier elements weren't formed until stars appeared, and took on the role of nucleosynthesis.

The problem is that our understanding of the Big Bang tells us that there should be three times as much lithium as there is. The BBT gets it right when it comes to other primordial nuclei. Our observations of primordial helium and deuterium match the BBT's predictions. So far, scientists haven't been able to resolve this inconsistency.

But a new paper from researchers in China may have solved the puzzle.

One assumption in Big Bang nucleosynthesis is that all of the nuclei are in thermodynamic equilibrium, and that their velocities conform to what's called the classical Maxwell-Boltzmann distribution. But the Maxwell-Boltzmann describes what happens in what is called an ideal gas. Real gases can behave differently, and this is what the researchers propose: that nuclei in the plasma of the early photon period of the universe behaved slightly differently than thought.

This graphics shows the distribution of early primordial light elements in the Universe by time and temperature. Temperature along the top, time along the bottom, and abundance on the side. Credit: Hou et al. 2017

The authors applied what is known as non-extensive statistics to solve the problem. In the graph above, the dotted lines of the author's model predict a lower abundance of the beryllium isotope. This is key, since beryllium decays into lithium. Also key is that the resulting amount of lithium, and of the other lighter nuclei, now all conform to the amounts predicted by the Maxwell-Boltzmann distribution. It's a eureka moment for cosmology aficionados.

What this all means is scientists can now accurately predict the abundance in the primordial universe of the three primordial nuclei: helium, deuterium, and lithium. Without any discrepancy, and without any missing .

This is how science grinds away at problems, and if the authors of the paper are correct, then it further validates the Big Bang Theory, and brings us one step closer to understanding how our universe was formed.

The universe has a lithium problem
The decay chains of primordial light nuclei in the early days of the Universe. Notice the thin red arrows between Beryllium and Lithium at 10-13, the earliest time shown on this chart. Credit: Chou et. al.

Explore further: Physicists reveal the role of diffusion in the early universe

Related Stories

Physicists reveal the role of diffusion in the early universe

September 22, 2016

Scientists from the Space Research Institute of the Russian Academy of Sciences (IKI RAS), the Moscow Institute of Physics and Technology (MIPT), and the Max Planck Institute for Astrophysics (MPA) have shown that diffusion ...

Measurement at Big Bang conditions confirms lithium problem

August 27, 2014

The field of astrophysics has a stubborn problem and it's called lithium. The quantities of lithium predicted to have resulted from the Big Bang are not actually present in stars. But the calculations are correct – a fact ...

When was the first light in the universe?

November 7, 2016

The speed of light gives us an amazing tool for studying the universe. Because light only travels a mere 300,000 kilometers per second, when we see distant objects, we're looking back in time.

Recommended for you

NASA telescope studies quirky comet 45P

November 22, 2017

When comet 45P zipped past Earth early in 2017, researchers observing from NASA's Infrared Telescope Facility, or IRTF, in Hawai'i gave the long-time trekker a thorough astronomical checkup. The results help fill in crucial ...

Uncovering the origins of galaxies' halos

November 21, 2017

Using the Subaru Telescope atop Maunakea, researchers have identified 11 dwarf galaxies and two star-containing halos in the outer region of a large spiral galaxy 25 million light-years away from Earth. The findings, published ...

Cassini image mosaic: A farewell to Saturn

November 21, 2017

In a fitting farewell to the planet that had been its home for over 13 years, the Cassini spacecraft took one last, lingering look at Saturn and its splendid rings during the final leg of its journey and snapped a series ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

RNP
not rated yet Feb 20, 2017
An open access copy of the paper can be found here: https://arxiv.org...4149.pdf

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.