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Beyond Einstein — the video

ALBERT EINSTEIN’S THEORIES rank among humanity’s greatest achievements, and sparked the scientific revolution of the 20th Century.

In their attempts to understand how space, time and matter are connected, Einstein and his successors made three predictions:

First, that space is expanding from a Big Bang.

Second, that black holes exist—these extremely dense places in the universe where space and time are tied into contorted knots and where time itself stops.

And third, that there is some kind of energy pulling the universe apart.

These three predictions seemed so far-fetched, that everyone, including Einstein himself, thought they were unlikely.

Yet incredibly, all three have turned out to be true.

This is where NASA’s Beyond Einstein programme begins. Using advanced space-based technology to explore these three questions, NASA and its partners begin the next revolution in our understanding of the universe.

NASA’s Beyond Einstein programme is poised to complete Einstein’s legacy—and ultimately unravel the mysteries of the Universe.

Adapted from information issued by NASA / Goddard Space Flight Centre.

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It’s official – dark energy is real!

Visualisation of dark energy

Cosmic wrestling match. In this artist's visualisation, dark energy is represented in purple and gravity in green. Dark energy is a uniform force that now dominates over the effects of gravity in the cosmos. Courtesy NASA / JPL-Caltech.

A SURVEY OF MORE THAN 200,000 GALAXIES led by Australian astronomers has shown that ‘dark energy’ is real and not a mistake in Einstein’s theory of gravity.

The finding is conveyed in two papers led by Dr Chris Blake from Swinburne University’s Centre for Astrophysics and Supercomputing, which will be published in the Monthly Notices of the Royal Astronomical Society.

Using the Anglo-Australian Telescope, 26 astronomers contributed to the ‘WiggleZ Dark Energy Survey’ that mapped the distribution of galaxies over an unprecedented volume of the Universe.

Because light takes so long to reach Earth, it was the equivalent of looking seven billion years back in time—more than half way back to the Big Bang.

The survey, which took four years to complete, aimed to measure the properties of ‘dark energy’ a concept first cast by Einstein in his original Theory of General Relativity. The scientist included the idea in his original equations, but later changed his mind, calling the inclusion “his greatest blunder”.

However, in the late 1990s when astronomers began to realise that the Universe was expanding at an accelerating rate, the concept of ‘dark energy’ was revived. This was done by measuring the brightness of distant supernovae—exploding stars.

Diagram illustrating cosmic standard candles and standard rulers

This diagram illustrates two methods that astronomers use to measure how fast the universe is expanding—the "standard candle" method, which involves studying exploded stars in galaxies, and the "standard ruler" method, which involves studying the distances between pairs of galaxies. Courtesy NASA / JPL-Caltech.

“The acceleration was a shocking discovery, because it showed we have a lot more to learn about physics,” Dr Blake said. “Astronomers began to think that Einstein’s blunder wasn’t a blunder at all, and that the Universe really was filled with a new kind of energy that was causing it to expand at an increasing speed.”

Einstein vindicated

The WiggleZ (pronounces ‘wiggles’) project has now used two other kinds of observations to provide an independent check on the supernovae results. One measured the pattern of how galaxies are distributed in space and the other measured how quickly clusters of galaxies formed over time.

Both tests have confirmed the reality of dark energy.

“WiggleZ says dark energy is real,” said Dr Blake. “Einstein remains untoppled.”

According to Professor Warrick Couch, Director of Swinburne’s Centre for Astrophysics and Supercomputing, confirming the existence of the anti-gravity agent is a significant step forward in understanding the Universe.

“Although the exact physics required to explain dark energy still remains a mystery, knowing that dark energy exists has advanced astronomers’ understanding of the origin, evolution and fate of the Universe,” he said.

According to one of the survey’s leaders, Professor Michael Drinkwater from the University of Queensland, the researchers have broken new ground. “This is the first individual galaxy survey to span such a long stretch of cosmic time,” he said.

The WiggleZ observations were possible due to a powerful spectrograph attached to the Anglo-Australian Telescope. The spectrograph was able to make measurements at the super-efficient rate of 392 galaxies an hour, despite the galaxies being located halfway to the edge of the observable Universe.

“WiggleZ has been a success because we have an instrument attached to the telescope, a spectrograph, that is one of the best in the world for large galaxy surveys of this kind,” said Professor Matthew Colless, director of the Australian Astronomical Observatory.

The WiggleZ survey involved 18 Australian astronomers, including 10 from Swinburne University of Technology. It was led by Dr Chris Blake, Professor Warrick Couch and Professor Karl Glazebrook from Swinburne and Professor Michael Drinkwater from the University of Queensland.

Adapted from information issued by AAO / Swinburne University of Technology.

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Dark energy dilemma

PHYSICISTS CAN’T SEE IT and don’t know much about what it is, but they think dark energy makes up 70 percent of the universe. In this video, Professor Saul Perlmutter, one of the world’s leading scientists trying to understand dark energy, explains the role it plays in causing our universe to expand.

Adapted from information issued by Lawrence Berkeley National Laboratory / KQEDondemand.

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Hubble bursts dark energy bubble

Galaxy NGC 5584

Galaxy NGC 5584 was one of eight galaxies astronomers studied to measure the universe's expansion rate. Two special kinds of stars—Type Ia supernovae and Cepheid variable stars—were used as "cosmic yardsticks", due to their predictable brightnesses.

  • Our universe seems to be expanding faster and faster with time
  • ‘Dark energy’ proposed as an explanation, but its nature remains a mystery
  • Hubble observations have ruled out one dark energy hypothesis

ASTRONOMERS USING NASA’s Hubble Space Telescope have ruled out one explanation for the nature of dark energy after recalculating the expansion rate of the universe to unprecedented accuracy.

The universe appears to be expanding at an increasing rate. Some think this is because it is filled with a ‘dark energy’ that works in the opposite way to gravity.

An alternative to that hypothesis is that an enormous ‘bubble’ of relatively empty space eight billion light-years wide surrounds our galactic neighbourhood.

If we lived near the centre of this void, observations of galaxies being pushed away from each other at accelerating speeds would be an illusion.

This hypothesis has now been invalidated because astronomers have refined their understanding of the universe’s present expansion rate.

“We are using the new camera on Hubble like a policeman’s radar gun to catch the universe speeding,” said Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University, and leader of the science team. “It looks more like it’s dark energy that’s pressing the [accelerator] pedal.”

Portion of NGC 5584 with Cepheid locations marked

A portion of galaxy NGC 5584 with the location of Cepheid variable stars marked.

The observations helped determine a figure for the universe’s current expansion rate to an uncertainty of just 3.3 percent. The new measurement reduces the error margin by 30 percent over Hubble’s previous best measurement in 2009.

Cosmic yardsticks

Riess’ team first had to determine accurate distances to galaxies near and far from Earth, and then compare those distances with the speed at which the galaxies are apparently receding because of the expansion of space.

They used those two values to calculate the Hubble constant, the number that relates the speed at which a galaxy appears to recede to its distance from the Milky Way.

Because we cannot physically measure the distances to galaxies, astronomers have to find stars or other objects that serve as reliable cosmic yardsticks. These are objects with known intrinsic brightness—brightness that hasn’t been dimmed by distance, an atmosphere or interstellar dust. Their distances, therefore, can be inferred by comparing their intrinsic brightness with their apparent brightness as seen from Earth.

To calculate long distances, Riess’ team chose a special class of exploding star called Type Ia supernovae. These stellar blasts all have similar luminosity and are brilliant enough to be seen far across the universe.

By cross-correlating the apparent brightness of Type Ia supernovae with pulsating Cepheid stars (another class of stars whose intrinsic brightness is known), the team could accurately gauge the distances to Type Ia supernovae in far-flung galaxies.

WFC3

Hubble's latest camera, the Wide Field Camera 3, was instrumental in the research.

Bubble is burst

By using the sharpness of Hubble’s new Wide Field Camera 3 (WFC3) to study more stars in visible and near-infrared light, the team eliminated systematic errors introduced by comparing measurements from different telescopes.

“WFC3 is the best camera ever flown on Hubble for making these measurements, improving the precision of prior measurements in a small fraction of the time it previously took,” said Lucas Macri, a collaborator on the Supernova Ho for the Equation of State (SHOES) Team from Texas A&M in College Station.

Knowing the precise value of the universe’s expansion rate further restricts the range of dark energy’s strength and helps astronomers tighten up their estimates of other cosmic properties, including the universe’s shape and its roster of neutrinos, or ghostly particles, that filled the early cosmos.

“Thomas Edison once said ‘every wrong attempt discarded is a step forward,’ and this principle still governs how scientists approach the mysteries of the cosmos,” said Jon Morse, astrophysics division director at NASA Headquarters in Washington.

“By falsifying the bubble hypothesis of the accelerating expansion, NASA missions like Hubble bring us closer to the ultimate goal of understanding this remarkable property of our universe.”

Adapted from information issued by STScI. NGC 5584 image credit: NASA / ESA / A. Riess (STScI/JHU), L. Macri (Texas A&M University) / Hubble Heritage Team (STScI/AURA). NGC 5584 illustrations credit: NASA / ESA / L. Frattare (STScI) / Z. Levay (STScI).

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Hubble confirms the universe is expanding faster

A map showing the expected location of dark matter withing a region of deep space

A map showing the expected location of dark matter withing a region of deep space

A new study led by European scientists presents the most comprehensive analysis of data from the most ambitious survey ever undertaken by the NASA/ESA Hubble Space Telescope.

The researchers have, for the first time ever, used Hubble data to probe the effects of the natural gravitational “weak lenses” in space and characterise the expansion of the Universe.

A group of astronomers, led by Tim Schrabback of the Leiden Observatory, conducted an intensive study of over 446,000 galaxies within the COSMOS field, the result of the largest survey ever conducted with Hubble. In making the COSMOS survey, Hubble photographed 575 slightly overlapping views of the same part of the Universe using the Advanced Camera for Surveys (ACS) onboard Hubble. It took nearly 1,000 hours of observations.

In addition to the Hubble data, researchers used redshift data from ground-based telescopes to assign distances to 194,000 of the galaxies surveyed (out to a redshift of 5).

“The sheer number of galaxies included in this type of analysis is unprecedented, but more important is the wealth of information we could obtain about the invisible structures in the Universe from this exceptional dataset,” says Patrick Simon from Edinburgh University.

An illustration showing how Hubble looks back in time to "map" evolving dark matter

Hubble looks back in time to "map" evolving dark matter by splitting the background galaxy population into discrete epochs of time (like cutting through rock strata). By measuring the redshift of the "lensing" galaxies used to map the dark matter distribution, scientists can put them into different time/distance "slices".

In particular, the astronomers could “weigh” the large-scale matter distribution in space over large distances. To do this, they made use of the fact that this information is encoded in the distorted shapes of distant galaxies, a phenomenon referred to as weak gravitational lensing.

Using complex algorithms, the team led by Schrabback has improved the standard method and obtained galaxy shape measurements to an unprecedented precision. The results of the study will be published in an upcoming issue of Astronomy and Astrophysics.

The meticulousness and scale of this study enables an independent confirmation that the expansion of the Universe is accelerated by an additional, mysterious component named dark energy. A handful of other such independent confirmations exist.

Astronomers compared real observations with two predictions – one for a dark matter-dominated universe, the other one dominated by dark energy.

COSMOS Project Astronomers compared real observations with two simulations – one for a dark matter-dominated universe, the other one dominated by dark energy. The dark energy one is the closest match.

Scientists need to know how the formation of clumps of matter evolved in the history of the Universe to determine how the gravitational force, which holds matter together, and dark energy, which pulls it apart by accelerating the expansion of the Universe, have affected them.

“Dark energy affects our measurements for two reasons. First, when it is present, galaxy clusters grow more slowly, and secondly, it changes the way the Universe expands, leading to more distant — and more efficiently lensed — galaxies. Our analysis is sensitive to both effects,” says co-author Benjamin Joachimi from the University of Bonn.

“Our study also provides an additional confirmation for Einstein’s theory of general relativity, which predicts how the lensing signal depends on redshift,” adds co-investigator Martin Kilbinger from the Institut d’Astrophysique de Paris and the Excellence Cluster Universe.

The large number of galaxies included in this study, along with information on their redshifts is leading to a clearer map of how, exactly, part of the Universe is laid out; it helps us see its galactic inhabitants and how they are distributed.

“With more accurate information about the distances to the galaxies, we can measure the distribution of the matter between them and us more accurately,” notes co-investigator Jan Hartlap from the University of Bonn.

“Before, most of the studies were done in 2D, like taking a chest X-ray. Our study is more like a 3D reconstruction of the skeleton from a CT scan. On top of that, we are able to watch the skeleton of dark matter mature from the Universe’s youth to the present,” comments William High from Harvard University, another co-author.

Image credits: NASA, ESA, J. Hartlap (University of Bonn), P. Simon (University of Bonn) and T. Schrabback (Leiden Observatory)