Scientists have produced their most precise measurement yet of the rate at which the early Universe was expanding.
They find that some three billion years after the Big Bang, the cosmos was pushing itself apart by another 1% every 44 million years.
It is the latest result to come from the Baryon Oscillation Spectroscopic Survey (BOSS).
The international group clocks the expansion by making detailed maps of the distribution of matter in space.
The hope is such studies can provide further insights on "dark energy".
This is the mysterious force that appears today to be driving the cosmos apart ever more quickly.
What is interesting about the new result is that the BOSS-measured expansion rate 10 billion years ago is quite a bit slower than that expected from the standard model of cosmology.
"This is the most precise measurement that's ever been done, and all I'll say at the moment is that there is a tension there," explained Dr Matthew Pieri, a BOSS team-member from Portsmouth University, UK.
"We expected to see the Universe expanding faster than what we found.
"The disagreement could still be a statistical fluke, or it could be be that the Universe was different to how we thought it was, but we'll have to explore this further to find out."
Theory holds that the Universe has been on a rollercoaster-like ride.
From the Big Bang 13.8 billion years ago, it expanded rapidly - but that expansion decelerated in the first few billion years under the constraining influence of gravity.
Then, some six billion years ago, the cosmos started to speed up again under the influence, scientists suspect, of dark energy.
The BOSS group has determined both the near and far expansion rates.
And while the near values fit very well with expected numbers, it is the new result for the far Universe that is the cause of some head-scratching.
Two largely independent measurements have been made.
One is to map the distribution of quasars, which are extremely luminous, distant galaxies.
The second measure involves using the light from those quasars to pinpoint the positions of clouds of hydrogen gas along the line of sight to Earth. In both instances, the BOSS team is probing so-called baryon acoustic oscillations (BAOs).
These refer to the pressure-driven waves that passed through the post-Big-Bang Universe and which subsequently became frozen into the distribution of matter once it had cooled to a sufficient level.