Astrophysicist Adam Riess shared the 2011 Nobel Prize in physics for research showing that the universe isn’t simply expanding (something we’ve known since Edwin Hubble's landmark 1929 paper) but that it's expanding at an accelerating rate.
Now Riess, along with an international team of collaborators, is back with surprising new research showing that the universe is expanding faster than predicted.
Based on observational data from the Hubble Space Telescope, the research indicates that a more accurate value of the Hubble constant (the term astronomers use for how fast the universe expands over time) is about 73 kilometers per second per megaparsec.
Or, if you prefer your astronomy in simple terms: The universe is expanding about 9 percent faster than we thought. That's so fast that the distance between cosmic objects will double in the next 9.8 billion years.
“I know this might not sound all that fast to most folks, but that is about 800 million years faster than we previously thought,” Riess, a 46-year-old professor at Johns Hopkins University, told The Huffington Post in an email.
What explains the new finding? What does it suggest about our understanding of the cosmos? In the email, Riess gave answers to these and other big questions:
How has our understanding of the expansion of the universe changed since Edwin Hubble?
The rate of expansion he measured was about seven times too fast and implied the universe was only about 2 billion years old. Now we are measuring to a couple of percent precision, and we know the universe is more like 13.5 billion years old. We also now know that the expansion is speeding up, which has given evidence for the existence of dark energy.
How do we know the universe is expanding?
When you look at 99.99999 percent of the galaxies around us, they are rushing away from us -- as evidenced by their large redshifts (like a Doppler shift). Either they don’t like us, or you realize that this is how it would look for any observer on any galaxy if the universe was expanding. Our eyes are not big enough to catch the faint light of distant, receding galaxies, nor are our eyes precise enough to measure the redshift of their light.
Beyond powerful telescopes like Hubble, what tools are used to measure the expansion of the universe?
Stars of various kinds, exploding and pulsating, provide astronomers like me with a cosmic lighthouse whose brightness reveals its distance. Analyzing so many stars and understanding what it says about the universe requires fast computers to do many calculations per second.
Do we know what causes the universe to expand?
The universe was expanding as a consequence of the event we call the Big Bang. After that, the ingredients of the universe play a role. Specifically, the dark energy in the universe has been the dominant feature in the last 5 billion years, causing the expansion to speed up. One interpretation of the new finding, though not the only one, is the dark energy is stronger or getting stronger than we thought. This would be surprising because a material with continually increasing energy (density) is somewhat at odds with other aspects of physics we hold near and dear.
What is the universe "expanding into"?
If the universe is infinite, which the best data suggests, it is not expanding into anything. It’s just getting bigger everywhere. What is bigger than infinity? Infinity+1. Admittedly, it is very hard to get our heads around infinity. It’s an important mathematical concept, but our minds balk when we try to imagine infinity in the real world.
How do you explain the discrepancy between your new value for the rate of expansion and the previous value?
Assuming that an error has not been made, it could be some additional wrinkle in the dark sector (dark matter, dark energy or dark radiation). Each of these components of the universe is quite veiled to us. We are perhaps quickest to attribute any anomaly to the behavior of dark energy simply because it is the most poorly understood part of the universe. Dark radiation, like neutrinos of a different type, is also a strong candidate, as these particles have always been elusive.
“On really dark nights I look up and am reminded that though we live our lives looking down, almost everything that ever was is up there. That thought really inspires me.”
- Adam Riess
What are the implications of your new research? Will the laws of cosmology need to be rewritten, as some have said?
I would say it's quite unlikely that the laws would change. Though it could change the inventory of the universe or the characteristics of some of the dark parts. In our way of thinking about this, our chief law is Einstein’s General Relativity, which has been so successful. We have no evidence for a violation there.
What is the ultimate fate of the universe?
It depends on the nature of dark energy, which is something we haven’t figured out yet. If you bet it would expand forever, you would get poor odds because that does seem like the most likely interpretation of the data at present.
Does thinking about the universe fill you with awe -- or is it just part of your work?
It does fill me with awe. But if you just keep thinking, “Wow…wow…wow,” you would never get anything done! I am able to separate the majesty of the universe from the cartography. It’s on the really dark nights when I look up and am reminded that though we live our lives looking down, almost everything that ever was is up there. That thought really inspires me.
Did you always want to be an astrophysicist? If you weren't a scientist, what would you be?
I have always viewed the world as a place to learn by experiments. Any occupation that involves that would appeal to me.
What's the biggest misconception nonscientists have about the universe?
That it’s incomprehensible. To quote Einstein: "The most incomprehensible thing about the universe is that it is comprehensible."
Note: Dr. Riess's answers have been lightly edited. A paper about his research is slated for publication in The Astrophysical Journal.
