3D Map Of Universe Gives Scientists A Clearer Picture Of The Cosmos … And New Questions
A decades-long project called the Sloan Digital Sky Survey has produced a new 3D map of the universe, the largest ever created. Cosmologist Kyle Dawson of the University of Utah is the principal investigator for the survey’s latest iteration, the extended Baryon Oscillation Spectroscopic Survey, or eBOSS.
Dawson says that what makes this map unique is its third dimension — a clearer representation of the distance between objects like galaxies and quasars. And because light travels at a fixed speed, that means it’s not only showing us distant objects, but those objects appear as they were billions of years ago. It’s literally showing the past.
Caroline Ballard: What does this map show that scientists haven’t seen before?
Kyle Dawson: Our map shows large swaths of cosmic time that scientists haven't really been able to study in detail before. Namely, it's a period of time something like 8 to 11 billion years ago or 6 to 11 billion years ago, which is very, very hard to map out because it's so far away in distance. The objects are therefore much fainter and it's a much more rigorous and time consuming process to map out that part of the universe. And there's a lot of physics in that epoch of time from objects that are that far away that we can provide unique insight into.
CB: The map showed some discrepancies where the science and the math we have on the expansion rate of the universe don't quite add up with the model you've created. What's going on there?
KD: One of the primary questions in cosmology for years and decades has been how fast is the universe is expanding? Why is it expanding? And how is that expansion changed with time? So one of those key components is what's happening at this very instant. What is the expansion rate today? You can measure it by looking at objects in our galaxy, looking at galaxies a little further away and building up your understanding of distances. That's been done by several other groups, and they find a fairly high value for the expansion rate — something like a value of 74 and the units are kilometers per second per megaparsec.
We take a different approach, and this is where the tension lies. Instead of making simple measurements by building up a ruler one inch to two inches to six inches to a foot, we go the opposite direction. We look to the other side of the universe, calibrate our ruler and then work back. The two measurements should wind up in the same place.
[For example], if I have opposing quarterbacks on opposite ends of the football field, they both throw the ball from one end of the field to the other. You calculate the trajectory. You know exactly how fast the ball is moving. You’ve both measured what is a meter. You both calculate that it should land a hundred yards away. It should work out and the ball should land on exactly the other end zone. What happens is that it doesn't — when we throw the ball it lands on the 90 yard line.
We come up with a very different measurement of the current expansion rate that's about 10% lower. And what may be the discrepancy is that we disagree on what is the definition of a meter or a yard. And that would be very exciting. It means there's likely to be some new type of physics that we weren't aware of. Maybe a new type of particle or new type of field. Something that was present in the early universe that affected how we would define the definition of a meter in a way that's unexpected to us. And that would be a very exciting result.
CB: What are some of the applications for scientists in using this map?
KD: The applications for science are getting us a better understanding of the absolute fundamental model of physics. One of our goals in cosmology and in physics is to figure out what are the true laws that govern the universe? What is the law of gravity, for example? Did Einstein's theory of general relativity describe the whole universe or does it fail at certain regimes? We also want to understand the properties of the particles like neutrinos. What is their fundamental mass? And we also want to understand what are the different energy components in the universe and why are they there and what is their physical property?
One of the biggest questions in terms of understanding the energy of the universe is what is this thing called dark energy that causes an effect in universal expansion that's opposite to that of matter. Rather than causing the universe to want to slow down in its expansion under gravity, this dark energy causes the universe to accelerate. That is not something that can be explained in any simple physical model, and that's something that we're fundamentally trying to understand. And the only way to do so is by exploring the cosmos.
Caroline Ballard hosts All Things Considered at KUER. Follow them on Twitter @cballardnews