The age of the Universe is crucial in cosmology. Find out how a new study casts doubt on the conventional wisdom concerning when the Big Bang took place.
We’ve had a slew of science fiction and comic book films and programs over the past few years. We’ve seen Guardians of the Galaxy, the Hitch Hikers Guide to the Galaxy and new editions to the Star Wars and the Star Trek franchise.
All these stories are preoccupied with galaxies in one form or another. Star Wars takes place in “a galaxy far, far away.” Star Trek consists of the adventures of Star Fleet, which is part of a federation of planets throughout our galaxy.
The stories all presuppose that we all know what galaxies are. It’s hard to realize that, just a hundred years ago, nobody knew that the Universe consists of billions of separate galaxies. Until 1924, scientists thought that our galaxy was the entire Universe.
Hubble Discovered that Andromeda Was Another Galaxy
Edwin Hubble discovered that Andromeda wasn’t a simple gas nebula, but another galaxy similar to the Milky Way but separate from it. He also told the public that there were countless other galaxies as well.
As he continued to study these other galaxies, Hubble made another paradigm-shifting discovery. He found that most of the galaxies were moving away from us. Not only that, but the further away the galaxies were, the faster they were travelling away.
The reason the galaxies are all moving away from each other is that the Universe itself is expanding. In honour of these discoveries, scientists call the rate at which the Universe is increasing in size the Hubble Constant.
A Key Factor in Estimating the Age of the Universe
The Hubble Constant is a crucial factor in estimating the age of the Universe. Suppose we know how fast the Universe is expanding. In that case, we can work backwards and imagine the Universe contracting back until it was all in one place.
Then, based on the rate of expansion, they can determine how much time has passed since the inflation began. The challenge is pinning down precisely what that Hubble Constant number is.
Cosmologists know that the expansion rate is very roughly in the neighbourhood of 70 kilometres per second per megaparsec. I say “roughly” because estimates range between 68 km/s/Mpsc and 74 km/s/Mpsc.
Were Confident That Age of Universe is 13.8 Billion Years
As anyone who watched the Big Bang Theory sitcom knows, the expert consensus is that “nearly 14 billion years ago, expansion started. Wait!” To be exact, cosmologists have been reasonably confident that the age of the Universe is very close to 13.8 billion years.
Now a new study from the University of Oregon is challenging that number. The Astronomical Journal has published the results of a study led by Professor Jim Schombert.
Professor Schombert and his team used data from the Spitzer Telescope to benchmark more accurate distances to 50 galaxies. Then they used those figures to determine the distances to 90 more galaxies.
More Accurate Distances to 50 Galaxies
Astronomers can tell a lot of things about a star just by looking at it with a telescope. Frustratingly, they can’t say how far away it is that way.
Instead, they have to come up with specific categories of reference stars whose brightness and other characteristics are very consistent. They can calculate how far away these guide stars are. Then they use a kind of ladder technique to word stepwise and get the distances to galaxies and other distant objects.
Professor Schombert explains, “The distance scale problem, as it is known, is incredibly difficult because the distances to galaxies are vast and the signposts for their distances are faint and hard to calibrate.” To address this, Schombert and his colleagues created a new mathematical model.
New Estimate for Hubble Constant at 75.1
Using these new measurements and equations, the team believes that they can better account for the rotational curves of spiral galaxies and their mass. They’ve come up with a new estimate for the Hubble Constant at 75.1 km/s/Mpsc.
The margin of error on their calculation is 2.3, so the real value could be 72.8 to 77.4. This figure is consistent with other measurements, but it’s a little on the high side compared to the others.
It stands to reason that if the expansion is faster than we had realized, the Universe must be younger. The age of the Universe based on this new study is 12.6 billion years.
Rule Out Any Estimates Below 70
The team also found that, based on their statistical analysis, cosmologists should rule out any estimates of the Hubble Constant that fall below 70 km/s/Mpsc. That has some important implications.
There’s a school of thought that we can measure the Hubble Constant based on the Cosmic Microwave Background. That’s the energy left over from the Big Bang that we can still detect as static in the background of radio signals.
Scientists who have estimated the Hubble Constant that way have always had results closer to 67 km/s/Mpsc. Scientists have been frustrated because as they refined the two techniques for measuring the Hubble Constant and the age of the Universe, the numbers didn’t move any closer together.
Cosmic Microwave Background Model Inaccurate?
If the team from the University of Oregon is right, the calculations based on the cosmic microwave background are inaccurate. Cosmologists need to take a hard look at why that might be.
It’s looking like that we’re closing in on a Hubble Constant in or around the mid-seventies. The result of that is that the age of the Universe is younger than everyone thought.
The age of the Universe is itself a benchmark for many other things. For example, if we can determine the age of a celestial body, then based on the age of the Universe, we can tell how soon the object formed after the Big Bang.
Answers to a Wide Range of Astronomical Questions
Doing this with a range of astronomical targets gives us a sense of the sequence in which the Universe formed right up to the present day. Having an accurate narrative about each phase that the Universe has gone through provides answers to a wide range of astronomical questions.
Professor Schombert and his team are presenting their findings with a great deal of humility. He explained, “Our resulting value is on the high side of the different schools of cosmology, signalling that our understanding of the physics of the Universe is incomplete with the hope of new physics in the future.”
We always have more to learn if we dare to know.
UO physicist tweaks the age of the universe with new approach
Using the Baryonic Tully-Fisher Relation to Measure H o
The 5 Big Questions We Need Cosmology to Answer
Are We Inside a Hubble Bubble?
Hubble Constant: How Fast Are We Going?
Originally published at https://daretoknow.ca on August 10, 2020.