The universe is expanding at an accelerating rate. This is a problem: The continuation of this will result in universe-wide cooling, eventually becoming too cold to sustain life. Ultimately, with heat evenly distributed across the cosmos, time itself will come to an end. Scientists trying to work out this expansion rate are essentially calculating the time until the universe ends.
As a new study uploaded to the arXiv server reveals, the most up-to-date measurement of universal expansion appears to be 8 percent greater than expected. This could mean that our knowledge of dark energy, the as-of-yet undetected force that is ripping our universe apart, is less robust than we think.
“I think that there is something in the standard cosmological model that we don't understand,” Adam Riess, an astrophysicist at Johns Hopkins University, co-discoverer of dark energy, and lead author on the new study, told Nature.
According to the study, the universe is expanding at a rate of 73 kilometers per second per megaparsec, not 67.3 as cosmological models of the universe have estimated (one megaparsec is equal to 3.26 million light-years). To directly measure this expansion rate, which is also known as the Hubble constant, they used distant objects known as “standard candles” to create the most robust measurement to date, they claim.
These are light sources like stars or supernovae of known absolute brightness, or “luminosity.” Their observed brightness will decrease as the universe expands, and by comparing this change to their luminosity, astronomers can work out by how much the universe has expanded over time.
That bright object in the bottom left is a Type 1a supernova, one of the objects used to work out the expansion rate of the universe. NASA/ESA
Despite the gravitational pull generated by ordinary matter, and the binding effect provided by dark matter, the universe has continued to expand at an accelerating rate since the Big Bang. Researchers assume this is down to the utterly mysterious dark energy, which makes up 68 percent of the universe.
Like dark matter, it hasn’t been directly detected, but its effects can be clearly seen: By all measures, something is pushing at the fabric of spacetime, forcing everything to move away from everything else. This new, higher estimate for the Hubble constant demonstrates just how powerful dark energy's repulsive force could be.
Astronomers are also keen to predict how the rate of universal expansion will change in the future. One way to do this is to look at how mass is distributed in the universe now, and compare this with how mass used to be distributed in the early universe. By using the European Space Agency’s Planck observatory, researchers are able to see the universe as it was 380,000 years after the Big Bang; consequently, they are able to predict how it will evolve.
This data can also be used to estimate what the expansion rate is right now. Each and every time a prediction is made using Planck’s data, it appears to slightly disagree with the Hubble constant. This latest paper, which uses two types of standard candles in 18 different galaxies, has now given the best estimate yet of the Hubble constant.
With an 8 percent greater expansion rate, the disagreement between Planck and the Hubble constant is now greater than ever, and the team isn't sure why. Dark matter’s binding effect could be weaker than predicted, or perhaps dark energy has become stronger in recent eons.
All in all, though, this new data means that, rather sadly, the universe will end faster than we previously thought.
