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Is the Universe Expanding Faster Than We Thought?

Hubble Data Provides New Insight.

by Amy Thompson
Jun 4 2016, 3:00pm

Image: NASA/ESA/A. Field (STScI)/A. Riess (JHU)

The idea that the Universe is expanding is nothing new. It's been expanding since the Big Bang—some 13.7 billion years ago. However, according to new research, it's expanding at a much faster rate than previously thought.

The findings will be published in the upcoming edition of the Astrophysical Journal, and a pre-print is available here.

Adam Riess of Johns Hopkins University and the Space Telescope Science Institute is a Nobel laureate and lead author on the paper, which details how his team measured the rate of expansion with a higher degree of precision. The new measurements show the Universe is expanding at a rate of 45.5 miles (73.2 kilometers) per second per megaparsec (one megaparsec is equivalent to 3.26 million light-years)—that's a whopping 5-9 percent faster than previous calculations.

So what does this new rate of expansion mean? It tells us that over the next 9.8 billion years, the distance between our galaxy and our closest cosmic neighbors will double. It may not seem like much, but on a cosmological scale, this is a big discrepancy.

Riess is known for his expertise on the subject as he shared the 2011 Nobel prize in physics by discovering that the Universe is expanding at an accelerating rate, which led to the discovery of dark energy. Now he's taken his work one step further by developing a more accurate way to measure the rate of expansion (aka the Hubble constant).

To do this, Riess and his team broke out the cosmic yardsticks; meaning they used the Hubble Space Telescope to measure the movements of over 2400 stars and 300 Type 1a supernovae, spread across 19 distant galaxies. Acting as cosmic mile markers, these stars (known as Cepheid variable stars) and supernovae each have a known brightness that allows astronomers to measure how far away they are with incredible precision.

The team then compared the distances to the expansion of space—a value calculated by measuring how light is stretched as galaxies move away from the Earth—to determine how fast the universe is expanding.

Previous estimates of the Hubble constant (named for the renowned astronomer Edwin Hubble) relied on measurements of the cosmic microwave background—leftover radiation from the Big Bang. Both NASA and ESA have examined the afterglow of the cosmic explosion that spawned our existence, and two separate missions have yielded lower, slightly different expansion rates (5 and 9 percent respectively).

"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 explained in a statement.

It's important to note that the new findings still need to be independently verified. However, if this discrepancy holds up, it could indicate we don't really understand all the processes at work.

"Maybe the universe is tricking us, or our understanding of the universe isn't complete," says Alex Filippenko, co-author and astronomy professor at UC Berkeley.

Image: NASA/ESA/A. Field (STScI)/A. Riess (JHU)

According to the team, there are multiple reasons why we are seeing a discrepancy. One explanation could be dark energy. The mysterious force is thought to drive the expansion, but could also do so with ever-increasing strength. If true, then in about 20 billion years, dark energy could even rip apart the entire Universe.

Or perhaps, this is evidence that a new type of subatomic particle that was zipping around the early Universe at light speeds (a fourth neutrino flavor perhaps) and is affecting the rate of expansion.

Or this could even be a sign that some of Einstein's theories are still incomplete.

"This surprising finding may be an important clue to understanding those mysterious parts of the universe that make up 95 percent of everything and don't emit light, such as dark energy, dark matter, and dark radiation," Riess explained in a statement.

"We know so little about the dark parts of the universe," added Lucas Macri of Texas A&M University and key collaborator on the study. "It's important to measure how they push and pull on space over cosmic history."

The team is excited to see where this goes. New observatories coming online soon (like Gaia) will help to reconcile the discrepancy in the data.

However it plays out, one thing is certain: as technology improves, so do our measurements and ultimately our understanding of the Universe.

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Johns Hopkins University
Adam Riess