When Will the Lights in the Night Sky Blink Off Forever?

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Deep space, captured by the Hubble Space Telescope. NASA/ESA

At some dreary point in the far distant future, the universe will continue to expand until everything is so far apart that the last visible twinkle in the night sky will get snuffed out forever.

That will be a dark day indeed. Fortunately, though, it's a day that's not likely to come for trillions of years.

In fact, scientists at Clemson University have just made the most precise measurement yet of exactly when that day of darkening will probably happen, thanks to state-of-the-art technologies and techniques all brought together in unison for the first time, reports Phys.org.

"Cosmology is about understanding the evolution of our universe — how it evolved in the past, what it is doing now and what will happen in the future," said Marco Ajello, associate professor in physics and astronomy at Clemson. "Our team analyzed data obtained from both orbiting and ground-based telescopes to come up with one of the newest measurements yet of how quickly the universe is expanding."

For the study, the team took aim at the Hubble Constant, a calculation named after famed American astronomer Edwin Hubble that is intended to describe the rate at which the universe is expanding. Hubble himself originally estimated the number to be around 500 kilometers per second per megaparsec (a megaparsec is equivalent to about 3.26 million light-years), but the number has been fiddled with significantly over the years as our instruments for measuring it have improved.

Even with our improved instruments, though, calculating the Hubble Constant has proven to be an elusive venture. We had narrowed it down to between 50 and 100 kilometers per second per megaparsec, but that was far from precise.

Now this new effort by the Clemson team might have finally pinpointed the number, however. What made this effort different was the availability of the latest gamma-ray attenuation data from the Fermi Gamma-ray Space Telescope and Imaging Atmospheric Cherenkov Telescopes. Gamma rays are the most energetic form of light, which makes them particularly useful as benchmarks for making more scrupulous measurements.

So what did the Clemson team settle on? According to their data, the universe's rate of expansion is approximately 67.5 kilometers per second per megaparsec.

In other words, we've got some time until the lights go out. If you consider that our universe is only a tad under 14 billion years old, the idea that we've still got trillions of years of starry nights ahead of us is a comforting one, even if the omnipresent darkness is inevitable.

Nailing down the Hubble Constant isn't just a fun fact, though. It's crucial information for understanding how our universe works, and perhaps even one day helping answer why things are as they are, as opposed to being some other way. For instance, while we can observe that the universe is expanding at an accelerated rate, we're still at a loss to explain why this expansion is happening in the first place.

This is the mystery of "dark energy," which is the term we use to describe the puzzling force that is pushing everything apart. We don't know what dark energy is... yet. But the more precisely we measure the Hubble Constant, the better equipped we will become at testing our theories about dark energy.

So this research by the Clemson scientists is a major advance forward.

"Our understanding of these fundamental constants has defined the universe as we now know it. When our understanding of laws becomes more precise, our definition of the universe also becomes more precise, which leads to new insights and discoveries," said professor Dieter Hartmann, a member of the team.

The study was published in The Astrophysical Journal.