Led by Nobel Laureate Adam Riess of the Space Telescope Science Institute and Johns Hopkins University, the research team developed new, more accurate techniques for measuring the ever-increasing size of the cosmos.
It measured stars and supernovae commonly used as "cosmic yardsticks": 2,400 Cepheid stars (in 19 different galaxies), which pulsate in a way that allows scientists to compare their true brightness to their apparent brightness and figure out how far away they are, and 300 Type Ia supernovae, which flare with a brightness so reliable it can be used to measure distance.
The calculations, which will be published in an upcoming edition of the Astrophysical Journal, estimate the rate of expansion to be 45.5 miles per second per megaparsec (3.26 million light-years). That means that the distance between cosmic objects will double in another 9.8 billion years.
And the more we learn, the less we know.
“If you really believe our number — and we have shed blood, sweat and tears to get our measurement right and to accurately understand the uncertainties — then it leads to the conclusion that there is a problem with predictions based on measurements of the cosmic microwave background radiation, the leftover glow from the Big Bang,” study co-author Alex Filippenko of UC Berkeley said in a statement.
“If we know the initial amounts of stuff in the universe, such as dark energy and dark matter, and we have the physics correct, then you can go from a measurement at the time shortly after the big bang and use that understanding to predict how fast the universe should be expanding today,” Riess said in a statement. “However, if this discrepancy holds up, it appears we may not have the right understanding, and it changes how big the Hubble constant should be today.”
Riess and his colleagues believe there must be some way to marry the two estimates — some obvious data we're missing or misunderstanding. It could be that dark energy is pushing galaxies apart faster than we think it is. Or that dark matter has some kind of properties we understand even less than its other properties. Maybe some undiscovered "dark radiation" — subatomic particles like the neutrino — was present during the big bang, and we've yet to add it to the expansion equation. Or Einstein’s general theory of relativity isn't quite right. If these measurements are confirmed by other scientists, something's gotta give.
“You start at two ends, and you expect to meet in the middle if all of your drawings are right and your measurements are right,” Riess said. “But now the ends are not quite meeting in the middle and we want to know why.”
It's a reminder of just how mysterious most of the universe is to us: Scientists estimate that some 95 percent of the cosmos is made up of substances like dark energy, dark matter and dark radiation — things we know only by the forces they exert on our galaxies.