Doe Science news source
The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
  • 2017-06-23 08:05:15
  • Article ID: 676945

Our Expanding Universe: Delving Into Dark Energy

Space is expanding ever more rapidly and scientists are researching dark energy to understand why

The universe is growing a little bigger, a little faster, every day.

And scientists don’t know why.

If this continues, almost all other galaxies will be so far away from us that one day, we won’t be able to spot them with even the most sophisticated equipment. In fact, we’ll only be able to spot a few cosmic objects outside of the Milky Way. Fortunately, this won’t happen for billions of years.

But it’s not supposed to be this way – at least according to theory. Based on the fact that gravity pulls galaxies together, Albert Einstein’s theory predicted that the universe should be expanding more slowly over time. But in 1998, astrophysicists were quite surprised when their observations showed that the universe was expanding ever faster. Astrophysicists call this phenomenon “cosmic acceleration.”

“Whatever is driving cosmic acceleration is likely to dominate the future evolution of the universe,” said Josh Frieman, a researcher at the Department of Energy’s (DOE) Fermilab and director of the Dark Energy Survey.

While astrophysicists know little about it, they often use “dark energy” as shorthand for the cause of this expansion. Based on its effects, they estimate dark energy could make up 70 percent of the combined mass and energy of the universe. Something unknown that both lies outside our current understanding of the laws of physics and is the major influence on the growth of the universe adds up to one of the biggest mysteries in physics. DOE’s Office of Science is supporting a number of projects to investigate dark energy to better understand this phenomenon.

 

The Start of the Universe

Before scientists can understand what is causing the universe to expand now, they need to know what happened in the past. The energy from the Big Bang drove the universe’s early expansion. Since then, gravity and dark energy have engaged in a cosmic tug of war. Gravity pulls galaxies closer together; dark energy pushes them apart. Whether the universe is expanding or contracting depends on which force dominates, gravity or dark energy.

Just after the Big Bang, the universe was much smaller and composed of an extremely high-energy plasma. This plasma was vastly different from anything today. It was so dense that it trapped all energy, including light. Unlike the current universe, which has expanses of “empty” space dotted by dense galaxies of stars, this plasma was nearly evenly distributed across that ancient universe.

As the universe expanded and became less dense, it cooled. In a blip in cosmic time, protons and electrons combined to form neutral hydrogen atoms. When that happened, light was able to stream out into the universe to form what is now known as the “cosmic microwave background.” Today’s instruments that detect the cosmic microwave background provide scientists with a view of that early universe.

Back then, gravity was the major force that influenced the structure of the universe. It slowed the rate of expansion and made it possible for matter to coalesce. Eventually, the first stars appeared about 400 million years after the Big Bang. Over the next several billion years, larger and larger structures formed: galaxies and galaxy clusters, containing billions to quadrillions (a million billion) of stars. While these cosmic objects formed, the space between galaxies continued to expand, but at an ever slower rate thanks to gravitational attraction.

But somewhere between 3 and 7 billion years after the Big Bang, something happened: instead of the expansion slowing down, it sped up. Dark energy started to have a bigger influence than gravity. The expansion has been accelerating ever since.

Scientists used three different types of evidence to work out this history of the universe. The original evidence in 1998 came from observations of a specific type of supernova. Two other types of evidence in the early 2000s provided further support.

 “It was this sudden avalanche of results through cosmology,” said Eric Linder, a Lawrence Berkeley National Laboratory researcher and Office of Science Cosmic Frontier program manager.

Now, scientists estimate that galaxies are getting 0.007 percent further away from each other every million years. But they still don’t know why.

 

What is Dark Energy?

“Cosmic acceleration really points to something fundamentally different about how the forces of the universe work,” said Daniel Eisenstein, a Harvard University researcher and former director of the Sloan Digital Sky Survey. “We know of four major forces: gravity, electromagnetism, and the weak and strong forces. And none of those forces can explain cosmic acceleration.”

So far, the evidence has spurred two competing theories.

The leading theory is that dark energy is the “cosmological constant,” a concept Albert Einstein created in 1917 to balance his equations to describe a universe in equilibrium. Without this cosmological constant to offset gravity, a finite universe would collapse into itself.

Today, scientists think the constant may represent the energy of the vacuum of space. Instead of being “empty,” this would mean space is actually exerting pressure on cosmic objects. If this idea is correct, the distribution of dark energy should be the same everywhere.

All of the observations fit this idea - so far. But there’s a major issue. The theoretical equations and the physical measurements don’t match. When researchers calculate the cosmological constant using standard physics, they end up with a number that is off by a huge amount: 1 X 10120 (1 with 120 zeroes following it).

“It’s hard to make a math error that big,” joked Frieman.

That major difference between observation and theory suggests that astrophysicists do not yet fully understand the origin of the cosmological constant, even if it is the cause of cosmic acceleration.

The other possibility is that “dark energy” is the wrong label altogether. A competing theory posits that the universe is expanding ever more rapidly because gravity acts differently at very large scales from what Einstein’s theory predicts. While there’s less evidence for this theory than that for the cosmological constant, it’s still a possibility.

 

The Biggest Maps of the Universe

To collect evidence that can prove or disprove these theories, scientists are creating a visual history of the universe’s expansion. These maps will allow astrophysicists to see dark energy’s effects over time. Finding that the structure of the universe changed in a way that’s consistent with the cosmological constant’s influence would provide strong evidence for that theory.

There are two types of surveys: imaging and spectroscopic. The Dark Energy Survey and Large Synoptic Survey Telescope (LSST) are imaging surveys, while the Baryon Oscillation Spectroscopic Survey (part of the Sloan Digital Sky Survey), eBOSS, and the Dark Energy Spectroscopic Instrument are spectroscopic.

Imaging surveys use giant cameras – some the size of cars – to take photos of the night sky. The farther away the object, the longer the light has taken to reach us. Taking pictures of galaxies, galaxy clusters, and supernovae at various distances shows how the distribution of matter has changed over time. The Dark Energy Survey, which started collecting data in 2013, has already photographed more than 300 million galaxies. By the time it finishes in 2018, it will have taken pictures of about one-eighth of the entire night sky. The LSST will further expand what we know. When it starts in 2022, the LSST will use the world’s largest digital camera to take pictures of 20 billion galaxies.

“That is an amazing number. It could be 10% of all of the galaxies in the observable universe,” said Steve Kahn, a professor of physics at Stanford University and LSST project director.

However, these imaging surveys miss a key data point – how fast the Milky Way and other galaxies are moving away from each other. But spectroscopic surveys that capture light outside the visual spectrum can provide that information. They can also more accurately estimate how far away galaxies are. Put together, this information allows astrophysicists to look back in time.

The Baryon Oscillation Spectroscopic Survey (BOSS), part of the larger Sloan Digital Sky Survey, was one of the biggest projects to take, as the name implies, a spectroscopic approach. It mapped more than 1.2 million galaxies and quasars.

However, there’s a major gap in BOSS’s data. It could measure what was going on 5 billion years ago using bright galaxies and 10 billion years ago using bright quasars. But it had nothing about what was going on in-between. Unfortunately, this time period is most likely when dark energy started dominating.

“Seven billion years ago, dark energy starts to really dominate and push the universe apart more rapidly. So we’re making these maps now that span that whole distance. We start in the backyard of the Milky Way, our own galaxy, and we go out to 7 billion light years,” said David Schlegel, a Berkeley Lab researcher who is the BOSS principal investigator. That 7 billion light years spans the time from when the light was originally emitted to it reaching our telescopes today. 

Two new projects are filling that gap: the eBOSS survey and the Dark Energy Spectroscopic Instrument (DESI). eBOSS will target the missing time span from 5 to 7 billion years ago. DESI will go back even further – 11 billion light years. Even though the dark energy was weaker then relative to gravity, surveying a larger volume of space will allow scientists to make even more precise measurements. DESI will also collect 10 times more data than BOSS. When it starts taking observations in 2019, it will measure light from 35 million galaxies and quasars.

 “We now realize that the majority of … the universe is stuff that we’ll never be able to directly measure using experiments here on Earth. We have to infer their properties by looking to the cosmos,” said Rachel Bean, a researcher at Cornell University who is the spokesperson for the LSST Dark Energy Science Collaboration. Solving the mystery of the galaxies rushing away from each other, “really does present a formidable challenge in physics. We have a lot of work to do.”

 The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit http://science.energy.gov.

Shannon Brescher Shea is a Senior Writer/Editor in the Office of Science, shannon.shea@science.doe.gov.

X
X
X
  • Filters

  • × Clear Filters

A New Optimization Model Could Bring Higher Solar-Power Integration

With numerous installations of solar power systems for residential homes at or near the distribution site, there is a challenge to balance supply and demand to make these intermittent energy sources reliable. Demand response is one promising way to increase operational flexibility and energy efficiency, and researchers in Malaysia have incorporated DR scenarios in case studies based on 100 urban low-voltage network samples to learn more. They report their findings in this week's Journal of Renewable and Sustainable Energy.

Making Polymer Chemistry 'Click'

A team including Berkeley Lab scientists has developed a faster and easier way to make a class of sulfur-containing plastics that will lower the cost of large-scale production.

Imaging Technology Reveals Copper Is Key to Meeting Future Food and Energy Needs

For the first time, Cornell University researchers are using imaging capabilities at the Cornell High Energy Synchrotron Source (CHESS) to explore how copper affects plant fertility. The work could provide key insights into how plants can be bred for better performance in marginal soils.

PPPL Researchers Perform First Basic Physics Simulation of the Impact of Recycled Atoms on Plasma Turbulence

Article describes simulation of impact of recycled atoms on plasma turbulence.

"Hindcasting" Study Investigates the Extreme 2013 Colorado Flood

Using a publicly available climate model, Berkeley Lab researchers "hindcast" the conditions that led to the Sept. 9-16, 2013 flooding around Boulder, Colo. and found that climate change attributed to human activity made the storm much more severe than would otherwise have occurred.

Ultrathin Device Harvests Electricity From Human Motion

Imagine slipping into a jacket, shirt or skirt that powers your cell phone, fitness tracker and other personal electronic devices as you walk, wave and even when you are sitting down. A new, ultrathin energy harvesting system developed at Vanderbilt University's Nanomaterials and Energy Devices Laboratory has the potential to do just that.

Energy-Efficient Accelerator Was 50 Years in the Making

With the introduction of CBETA, the Cornell-Brookhaven ERL Test Accelerator, Cornell University and Brookhaven National Laboratory scientists are following up on the concept of energy-recovering particle accelerators first introduced by physicist Maury Tigner at Cornell more than 50 years ago.

Scientists Program Yeast to Turn Plant Sugars into Biodiesel

Redox metabolism was engineered in Yarrowia lipolytica to increase the availability of reducing molecules needed for lipid production.

Soils Could Release Much More Carbon than Expected as Climate Warms

Deeper soil layers are more sensitive to warming than previously thought.

3-D Models Help Scientists Gauge Flood Impact

Using one of the world's most powerful supercomputers--Titan, the 27-petaflop Cray XK7 at the Oak Ridge Leadership Computing Facility (OLCF)--a University of Iowa team performed one of the first highly resolved, 3-D, volume-of-fluid Reynolds-averaged Navier-Stokes (RANS) simulations of a dam break in a natural environment. The simulation allowed the team to map precise water levels for actual flood events over time.


  • Filters

  • × Clear Filters

DOE User Facilities Join Forces to Tackle Biology's Big Data

Through the "Facilities Integrating Collaborations for User Science" (FICUS) initiative, 6 proposals have been selected to participate in a new partnership between the DOE Joint Genome Institute and the National Energy Research Scientific Computing Center, both U.S. Department of Energy user facilities at Lawrence Berkeley National Laboratory.

Qubitekk Licenses ORNL Single-Photon Source Approach for Quantum Encryption

Qubitekk has non-exclusively licensed an Oak Ridge National Laboratory-developed method to produce quantum light particles, known as photons, in a controlled, deterministic manner that promises improved speed and security when sharing encrypted data.

Construction of Massive Neutrino Experiment Kicks Off a Mile Underground

A new era in international particle physics research officially began July 21 with a unique groundbreaking held a mile underground at the Sanford Underground Research Facility in South Dakota. Dignitaries, scientists and engineers from around the world marked the start of construction of a massive international experiment that could change our understanding of the universe. The Long-Baseline Neutrino Facility (LBNF) will house the international Deep Underground Neutrino Experiment (DUNE), which will be built and operated by roughly 1,000 scientists and engineers from 30 countries.

Construction Begins on International Mega-Science Experiment to Understand Neutrinos

In a unique groundbreaking ceremony held this afternoon at the Sanford Underground Research Facility in Lead, South Dakota, a group of dignitaries, scientists and engineers from around the world marked the start of construction of a massive international experiment that could change our understanding of the universe. The Long-Baseline Neutrino Facility (LBNF) will house the international Deep Underground Neutrino Experiment (DUNE), which will be built and operated by a group of roughly 1,000 scientists and engineers from 30 countries.

Buchanan Named Deputy for Science and Technology at Oak Ridge National Laboratory

Michelle Buchanan, an accomplished scientific leader and researcher, has been appointed Deputy for Science and Technology at the Department of Energy's Oak Ridge National Laboratory by new Lab Director Thomas Zacharia.

Neutrino Project to Fuel Particle Physics Research

Over the next decade, 800,000 tons of rock will be excavated from the former Homestake Mine in Lead, South Dakota, to accommodate a particle detector filled with 70,000 tons of liquid argon cooled to -300 degrees Fahrenheit to study neutrinos beamed from Fermilab in Illinois. It's called the Deep Underground Neutrino Experiment.

Berkeley Lab to Lead Multimillion-Dollar Geothermal Energy Project

The Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) will lead a new $9 million project aimed at removing technical barriers to commercialization of enhanced geothermal systems (EGS), a clean energy technology with the potential to power 100 million American homes.

PNNL Scientist Ruby Leung Appointed a Battelle Fellow

Ruby Leung of the Department of Energy's Pacific Northwest National Laboratory has been named a Battelle Fellow -- the highest recognition from Battelle for leadership and accomplishment in science. She is one of eight Battelle fellows at PNNL.

Gu and Paranthaman Named ORNL Corporate Fellows

Researchers Baohua Gu and Parans Paranthaman have been named Corporate Fellows of the Department of Energy's Oak Ridge National Laboratory.

DOE Funds Center for Bioenergy Innovation at ORNL to Accelerate Biofuels, Bioproducts Research

The DOE has announced funding for new research centers to accelerate the development of specialty plants and processes for a new generation of biofuels and bioproducts.


  • Filters

  • × Clear Filters

Quantum Computing Building Blocks

Scientists invented an approach to creating ordered patterns of nitrogen-vacancy centers in diamonds, a promising approach to storing and computing quantum data.

Scientists Program Yeast to Turn Plant Sugars into Biodiesel

Redox metabolism was engineered in Yarrowia lipolytica to increase the availability of reducing molecules needed for lipid production.

Soils Could Release Much More Carbon than Expected as Climate Warms

Deeper soil layers are more sensitive to warming than previously thought.

Weaving a Fermented Path to Nylons

Microbial enzymes create precursors of nylon while avoiding harsh chemicals and energy-demanding heat.

Loosening of Lignocellulose: Switchgrass and Success in Sugar Release

Using a genetically modified line of switchgrass, scientists reduced plant cell wall recalcitrance while increasing sugar release over three generations.

Extending the Life of Lithium-Ion Batteries

Scientists offer new insights into how the source of electrons in batteries fails.

Unraveling the Molecular Complexity of Cellular Machines and Environmental Processes

State-of-the-art mass spectrometer delivers unprecedented capability to scientists.

Speeding Up Catalysts for Energy Storage

Researchers develop the fastest synthetic catalyst for producing hydrogen gas, potentially leading to a new environmentally friendly, affordable fuel.

Watching Neutrons Flow

Like water, neutrons seek their own level, and watching how they flow may teach us about how the chemical elements were made.

FIONA to Take on the Periodic Table's Heavyweights

FIONA (For the Identification Of Nuclide A) is a newly installed device designed to measure the mass numbers of individual atoms of heavy and superheavy elements. FIONA will let researchers learn about the shape and structure of heavy nuclei, guide the search for new elements, and offer better measurements for nuclear fission and related processes.


Spotlight

Saturday May 20, 2017, 12:05 PM

Rensselaer Polytechnic Institute Graduates Urged to Embrace Change at 211th Commencement

Rensselaer Polytechnic Institute (RPI)

Monday May 15, 2017, 01:05 PM

ORNL, University of Tennessee Launch New Doctoral Program in Data Science

Oak Ridge National Laboratory

Friday April 07, 2017, 11:05 AM

Champions in Science: Profile of Jonathan Kirzner

Department of Energy, Office of Science

Wednesday April 05, 2017, 12:05 PM

High-Schooler Solves College-Level Security Puzzle From Argonne, Sparks Interest in Career

Argonne National Laboratory

Tuesday March 28, 2017, 12:05 PM

Champions in Science: Profile of Jenica Jacobi

Department of Energy, Office of Science

Friday March 24, 2017, 10:40 AM

Great Neck South High School Wins Regional Science Bowl at Brookhaven Lab

Brookhaven National Laboratory

Wednesday February 15, 2017, 04:05 PM

Middle Schoolers Test Their Knowledge at Science Bowl Competition

Argonne National Laboratory

Friday January 27, 2017, 04:00 PM

Haslam Visits ORNL to Highlight State's Role in Discovering Tennessine

Oak Ridge National Laboratory

Tuesday November 08, 2016, 12:05 PM

Internship Program Helps Foster Development of Future Nuclear Scientists

Oak Ridge National Laboratory

Friday May 13, 2016, 04:05 PM

More Than 12,000 Explore Jefferson Lab During April 30 Open House

Thomas Jefferson National Accelerator Facility

Monday April 25, 2016, 05:05 PM

Giving Back to National Science Bowl

Ames Laboratory

Friday March 25, 2016, 12:05 PM

NMSU Undergrad Tackles 3D Particle Scattering Animations After Receiving JSA Research Assistantship

Thomas Jefferson National Accelerator Facility

Tuesday February 02, 2016, 10:05 AM

Shannon Greco: A Self-Described "STEM Education Zealot"

Princeton Plasma Physics Laboratory

Monday November 16, 2015, 04:05 PM

Rare Earths for Life: An 85th Birthday Visit with Mr. Rare Earth

Ames Laboratory

Tuesday October 20, 2015, 01:05 PM

Meet Robert Palomino: 'Give Everything a Shot!'

Brookhaven National Laboratory

Tuesday April 22, 2014, 11:30 AM

University of Utah Makes Solar Accessible

University of Utah

Wednesday March 06, 2013, 03:40 PM

Student Innovator at Rensselaer Polytechnic Institute Seeks Brighter, Smarter, and More Efficient LEDs

Rensselaer Polytechnic Institute (RPI)

Friday November 16, 2012, 10:00 AM

Texas Tech Energy Commerce Students, Community Light up Tent City

Texas Tech University

Wednesday November 23, 2011, 10:45 AM

Don't Get 'Frosted' Over Heating Your Home This Winter

Temple University

Wednesday July 06, 2011, 06:00 PM

New Research Center To Tackle Critical Challenges Related to Aircraft Design, Wind Energy, Smart Buildings

Rensselaer Polytechnic Institute (RPI)

Friday April 22, 2011, 09:00 AM

First Polymer Solar-Thermal Device Heats Home, Saves Money

Wake Forest University

Friday April 15, 2011, 12:25 PM

Like Superman, American University Will Get Its Energy from the Sun

American University

Thursday February 10, 2011, 05:00 PM

ARRA Grant to Help Fund Seminary Building Green Roof

University of Chicago

Tuesday December 07, 2010, 05:00 PM

UC San Diego Installing 2.8 Megawatt Fuel Cell to Anchor Energy Innovation Park

University of California San Diego

Monday November 01, 2010, 12:50 PM

Rensselaer Smart Lighting Engineering Research Center Announces First Deployment of New Technology on Campus

Rensselaer Polytechnic Institute (RPI)

Friday September 10, 2010, 12:40 PM

Ithaca College Will Host Regional Clean Energy Summit

Ithaca College

Tuesday July 27, 2010, 10:30 AM

Texas Governor Announces $8.4 Million Award to Create Renewable Energy Institute

Texas Tech University

Friday May 07, 2010, 04:20 PM

Creighton University to Offer New Alternative Energy Program

Creighton University

Wednesday May 05, 2010, 09:30 AM

National Engineering Program Seeks Subject Matter Experts in Energy

JETS Junior Engineering Technical Society

Wednesday April 21, 2010, 12:30 PM

Students Using Solar Power To Create Sustainable Solutions for Haiti, Peru

Rensselaer Polytechnic Institute (RPI)

Wednesday March 03, 2010, 07:00 PM

Helping Hydrogen: Student Inventor Tackles Challenge of Hydrogen Storage

Rensselaer Polytechnic Institute (RPI)

Thursday February 04, 2010, 02:00 PM

Turning Exercise into Electricity

Furman University

Thursday November 12, 2009, 12:45 PM

Campus Leaders Showing the Way to a Sustainable, Clean Energy Future

National Wildlife Federation (NWF)

Tuesday November 03, 2009, 04:20 PM

Furman University Receives $2.5 Million DOE Grant for Geothermal Project

Furman University

Thursday September 17, 2009, 02:45 PM

Could Sorghum Become a Significant Alternative Fuel Source?

Salisbury University

Wednesday September 16, 2009, 11:15 AM

Students Navigating the Hudson River With Hydrogen Fuel Cells

Rensselaer Polytechnic Institute (RPI)

Wednesday September 16, 2009, 10:00 AM

College Presidents Flock to D.C., Urge Senate to Pass Clean Energy Bill

National Wildlife Federation (NWF)

Wednesday July 01, 2009, 04:15 PM

Northeastern Announces New Professional Master's in Energy Systems

Northeastern University

Friday October 12, 2007, 09:35 AM

Kansas Rural Schools To Receive Wind Turbines

Kansas State University

Thursday August 17, 2006, 05:30 PM

High Gas Prices Here to Stay, Says Engineering Professor

Rowan University

Wednesday May 17, 2006, 06:45 PM

Time Use Expert's 7-Year Fight for Better Gas Mileage

University of Maryland, College Park





Showing results

0-4 Of 2215