Summary: We need a 3D map of the universe to see more than just the beginning of the universe
Original author and publication date: DOE Science News Source – December 6, 2019
Futurizonte Editor’s Note: It seems that everything we already know of the universe is just the beginning.
From the article:
One of the biggest mysteries in science began with a dying star.
It wasn’t any particular dying star so much as the idea of one. In the 1980s, Saul Perlmutter at the Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (LBNL) and his collaborators realized that they could use data about supernovae to research the history of the universe. Supernovae are extremely bright exploding stars that cast much of their mass out into space before they wink out.
Fortunately, Type Ia supernovae’s brightness is very consistent. Even when their actual brightness varies, it does so in a predictable way. By comparing measurements of how bright these supernovae appear in telescopes with their actual brightness, along with measurements of light from their home galaxies, scientists can figure out their age and distance from us. Using those, they can estimate how the universe has expanded over time.
Over the course of a decade, Perlmutter’s team collected enough data to look for a relationship between a supernova’s brightness and distance from Earth. They expected to see that very distant supernovae appear a bit brighter than they would in an expanding universe that wasn’t slowing in its growth.
The data revealed something else entirely.
The supernovae all looked dimmer than they should for their distance. At first, the scientists thought it was just a bizarre set of data. “When you see an amazing new result, your first thought isn’t ‘Eureka!’, it’s, ‘That’s an interesting looking graph,’” said Perlmutter. He and his team spent more than six months checking every aspect of the graph, looking for some aspect of the analysis that might be wrong.
In fact, it showed the opposite: The universe was expanding ever more quickly. The implication of this was dramatic. For the data to work with Einstein’s theory of general relativity – the foundation of astrophysics – 70 percent of the universe’s energy must be from some unknown source.
Something – a lot of something – was missing from our fundamental understanding of the universe.
As Perlmutter prepared for an upcoming conference, he made a series of changes to his plastic transparency slides to present the new results. “You are aware that it’s a very big, significant result, but that makes you even more careful,” he said. “By the time you say it in public, you have been working with it for so long that it doesn’t feel like a surprise to you.”
But for the audience, his 1998 talk made major waves. Not long after, a competing team presented the same result. In 2011, Perlmutter, Brian Schmidt, and Adam Riess received the Nobel Prize in physics for the discovery.
Because we don’t know what’s pushing the universe outward ever more quickly, “dark energy” is scientists’ shorthand for the mysterious process. To understand the history of our universe, researchers supported by the DOE Office of Science are collaborating with scientists around the globe to build elaborate 3D maps of space and time.
Considering the Possibilities
Whatever dark energy is, it’s weird. None of the possibilities fit scientists’ understanding of physics.
The first possibility is that it’s the “cosmological constant.” When Albert Einstein developed the equations describing general relativity, he assumed the universe was staying the same size. To counterbalance gravity pulling inward on the universe, he stuck in a variable, the cosmological constant, indicating something was pushing outward. When Edwin Hubble found that the universe was expanding, Einstein removed the constant. When they found there is a mysterious something pushing outward, scientists returned to Einstein’s idea. Unfortunately, the numbers from the experimental data are 10120 times smaller than the expectations for a cosmological constant in the equations.
There are two more possibilities. The second is that dark energy is an unknown form of energy that’s changed over time. The third possibility is that general relativity doesn’t explain what happens on the largest scales. Instead, it would be an approximation of an even more general theory. That would throw a wrench into one of our most successful pillars of astrophysics.
More than Just the Beginning of the Universe
Figuring out how the structure of the universe has changed over time can help scientists determine if dark energy is constant or not.
Scientists already know what the universe looked like in its early days, about 10 billion years ago. They’ve studied the cosmic microwave background, a set of faint heat signatures left over from that time. From examining this lingering radiation, scientists can work out the patterns of density and radiation way back then.