"One is a measurement of how fast the universe is expanding today, as we see it", Riess added.
Astronomers previously estimated that the chances that the discrepancy is a fluke is about 1 in 3,000, but the new, more precise data reveal that the possibility of a fluke is only 1 in 100,000.
He said: "This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke".
In the study, Riess and his SH0ES (Supernovae, H0, for the Equation of State) Team studied light from 70 stars in the Large Magellanic Cloud, our neighboring galaxy, with a new method that involved capturing quick images of these stars. Because these stars brighten and dim at predictable rates, and the periods of these variations give us their luminosity and hence distance, astronomers use them as cosmic mileposts. The old method of measuring the stars was time-consuming because the Hubble could only observe one star for every 90-minute orbit around the Earth. The research effort, led by professor Adam Riess of The Johns Hopkins University, used data gathered by NASA's Hubble Space Telescope to pin down the rate at which the Universe is ballooning.
The Hubble measures expansion through the close monitoring of stars known as Cepheids, which are seen as "cosmic yardsticks".
The Hubble astronomers then combined their result with another set of observations, made by the Araucaria Project, a collaboration between astronomers from institutions in Chile, the USA, and Europe. Instead, as Hubble astronomers continue to "tighten the bolts" on the accuracy of their measurements, the discordant values remain stubbornly at odds.
Riess said: "This disparity could not plausibly occur just by chance". 'We are measuring something fundamentally different.
This latest research by Reiss and team has reduced the uncertainty in their Hubble constant value to an unprecedented 1.9 percent - that is a significant improvement from a previous estimate past year which had the uncertainty set at 2.4 percent.
So, what could explain this discrepancy?
What they found directly contradicts predictions made based on observations from the European Space Agency's Planck satellite, which measured the speed of the universe 380,000 years after the Big Bang. Findings showed the universe is expanding about 9 percent faster than it should be-indicating that there is something missing from the cosmological models that help explain what happened after the Big Bang. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding.
One explanation for the mismatch involves an unexpected appearance of dark energy in the young universe, which is thought to now comprise 70% of the universe's contents.
Most astronomers around the globe agree that it is the reason for the acceleration of the Universe's growth.
In a study published in the Astrophysical Journal, researchers suggest that these revelations highlight the need for new knowledge and theories to understand the changing cosmos. The existence of this "early dark energy" could account for the tension between the two Hubble constant values, Riess said. An alternative explanation might be that dark matter interacts more strongly with ordinary matter than previously thought.
Cosmologists characterize the universe's expansion in a simple law known as Hubble's Law, named after Edwin Hubble, who first observed that the universe is in constant expansion after studying the Doppler shift of retreating nebulae.
However, when you calculate the Hubble Constant from CMB/Planck data, you get a different figure altogether; 67.4 km/sec/Mpc, with a tiny uncertainty of less than a percent.