The space agency’s Hubble Space Telescope shows that it is growing about 9 percent faster than we had expected, based on the trajectory it started with shortly after the big bang, according to astronomers.
While such a discrepancy was already suggested, the new measurements reduce the chance we are mistaken to just 1 in 100,000.
Such a confirmation could require astronomers to find new physics to explain the universe’s strange behavior.
“This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke. This is not what we expected,” says Adam Riess, Bloomberg distinguished professor of physics and astronomy at The Johns Hopkins University, Nobel laureate and the project’s leader.
The speed of the universe’s expansion, known as the Hubble constant, is a central part of physics and our understanding of the universe. But it has repeatedly been observed to behave unexpectedly – the more astronomers find out about it, the more wrong it appears – in ways that have forced scientists to wonder whether our assumptions about it had been wrong.
The new study confirms that speculation and requires further work to explain how exactly the universe is growing.
The research saw Professor Riess and his team analyze light from 70 stars in a galaxy near ours, known as the Large Magellanic Cloud, using a new method that allowed them to capture the stars quickly. The stars they observed are called Cepheid variables and change brightness predictably, allowing them to be used to measure intergalactic distances.
The new method allowed the researchers to measure many more of those stars far more quickly. Normally, Hubble can only look at one star each time it takes one of its 90-minute orbits around Earth, but the new method allowed it to see dozens in that same time.
Using that data, the researchers were able to confirm our understanding of the “cosmic distance ladder”, which allows us to determine distances throughout the universe. And they were able to use the information to calculate the Hubble constant and see how fast the cosmos is expanding.
The more precise that understanding became, the more clear it was that the speed was not in line with what they expected. Scientists have made predictions of the Hubble constant based on data from the European Space Agency’s Planck satellite, which captured the expansion of the universe just 380,000 years after it came into existence.
The two numbers did not match up. That led scientists to think that there must be something missing in their understanding of how the beginning and current universe match up.
“This is not just two experiments disagreeing,” Riess explained. “We are measuring something fundamentally different. One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding.
“If these values don’t agree, there becomes a very strong likelihood that we’re missing something in the cosmological model that connects the two eras.”
Professor Riess and his team are not able to say why such a difference exists. They hope to work to refine it, even more, allowing them to get rid of any further uncertainty about the Hubble constant.