Universe expanding faster than expected, Nasa data confirms

Discovery could require astronomers to work out ‘new physics’

Andrew Griffin
Thursday 25 April 2019 14:19 BST
Nasa celebrates Hubble’s 29th year in orbit

The universe is expanding considerably faster than it should be, Nasa has confirmed.

The space agency’s Hubble Space Telescope shows that it is growing about 9 per cent faster than had been expected, based on the trajectory it started with shortly after the Big Bang, according to astronomers.

While such a discrepancy had already been suggested, the new measurements reduce the chance this is a mistake to just one in 100,000.

Such a confirmation could require astronomers to find new physics theories to explain the universe‘s strange behaviour.

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 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 unexpectedlythe 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 analyse 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 clearer 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 can observe the conditions of the early 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.

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