Expansion of Universe accelerating


How long has the Universe been accelerating?

“The Universe has been accelerating for the past six billion years, and if we had come along sooner than that, we might never have considered an option beyond the three possibilities our intuition would have led us to. Instead, we get to perceive and draw conclusions about the Universe exactly as it is, and that’s perhaps the greatest reward of all.”

One of the biggest surprises in our understanding of the Universe came at the end of the 20th century, when we discovered that the Universe wasn’t just expanding, but that the expansion was accelerating. That means the fate of our Universe is a cold, lonely and isolated one, but it’s a fate that we wouldn’t have uncovered if we were born when the Universe was just half its current age. By understanding the Universe’s expansion history and determining what the different components are that it’s made of, we can figure out exactly how long the Universe has been accelerating. We find that dark energy rose to prominence some 7.8 billion years ago, and the Universe has been accelerating for the last 6 billion years. As the acceleration continues, more and more galaxies become unreachable from our perspective, even at the speed of light; that number’s already up to 97% of the galaxies in our visible Universe.

Is Dark Energy Evaporating Dark Matter?

Scientists at the University of Rome and Portsmouth recently published a paper which describes dark matter slowly being engulfed by dark energy.

Dark matter is almost completely undetectable matter that astronomers and cosmologists have calculated to exist within our universe, hence the name “dark”. Whereas dark energy is an accepted model of energy that permeates all matter and space, and is responsible for the acceleration of the expansion of the universe (to find out more about the two, click on the links above)

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Scale of Universe Measured with 1-Percent Accuracy

An ultraprecise new galaxy map is shedding light on the properties of dark energy, the mysterious force thought to be responsible for the universe’s accelerating expansion.

Image: An artist’s concept of the latest, highly accurate measurement of the universe from the Baryon Oscillation Spectroscopic Survey. The spheres show the current size of the “baryon acoustic oscillations” (BAOs) from the early universe, which have helped to set the distribution of galaxies that we see in the universe today. BAOs can be used as a “standard ruler” (white line) to measure the distances to all the galaxies in the universe. Credit: Zosia Rostomian, Lawrence Berkeley National Laboratory

A team of researchers working with the Baryon Oscillation Spectroscopic Survey (BOSS) has determined the distances to galaxies more than 6 billion light-years away to within 1 percent accuracy — an unprecedented measurement.

“There are not many things in our daily lives that we know to 1-percent accuracy,” David Schlegel, a physicist at Lawrence Berkeley National Laboratory and the principal investigator of BOSS, said in a statement. “I now know the size of the universe better than I know the size of my house.”

Major Discovery: ‘Smoking Gun’ for Universe’s Incredible Big Bang Expansion Found

Wow. Astronomers say this could be “the most important discovery since the discovery that the expansion of the universe is accelerating.”

Astronomers have found the first direct evidence of cosmic inflation, the theorized dramatic expansion of the universe that put the “bang” in the Big Bang 13.8 billion years ago, new research suggests.

If it holds up, the landmark discovery — which also confirms the existence of hypothesized ripples in space-time known as gravitational waves — would give researchers a much better understanding of the Big Bang and its immediate aftermath.


Reality is a set of ideas that predicts the observations we make.

-Brian Schmidt, an Australian National University cosmology professor, speaking about “The Astronomical Revolution” on June 24, 2014, at the Euroscience Open Forum. Schmidt is a winner of the 2011 Nobel Prize for Physics based on his work uncovering the accelerating expansion of the universe.

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Could a new type of supernova eliminate dark energy?

“Imagine you had a box of candles that you thought were all identical to one another: you could light them up, put them all at different distances, and immediately, just from measuring the brightness you saw, know how far away they are. That’s the idea behind a standard candle in astronomy, and why type Ia supernovae are so powerful.

But now, imagine that these candle flames aren’t all the same brightness! Suddenly, some are a little brighter and some are a little dimmer; you have two classes of candles, and while you might have more of the brighter ones close by, you might have more of the dimmer ones far away. That’s what we think we’ve just discovered with supernovae: there are actually two separate classes of them, where one’s a little brighter in the blue/UV, and one’s a little brighter in the red/IR, and the light curves they follow are slightly different. This might mean that, at high redshifts (large distances), the supernovae themselves are actually intrinsically fainter, and not that they’re farther away.”

Back in the 1990s, scientists were quite surprised to find that when they measured the brightness and redshifts of distant supernovae, they appeared fainter than one would expect, leading us to conclude that the Universe was expanding at an accelerating rate to push them farther away. But a 2015 study put forth a possibility that many scientists dreaded: that perhaps these distant supernovae were intrinsically different from the ones we had observed nearby. Would that potentially eliminate the need for dark energy altogether? Or would it simply change ever-so-slightly the amount and properties of dark energy we required to explain modern cosmology? A full analysis shows that dark energy is here to stay, regardless of the supernova data.

“They’re like, ‘Sir, there’s something in your bag.’

I said, ‘Yes, I think it’s this box.’

They said, ‘What’s in the box?’

I said, ‘a large gold medal,’ as one does.

So they opened it up and they said, ‘What’s it made out of?’

I said, ‘gold.’

And they’re like, ‘Uhhhh. Who gave this to you?’

‘The King of Sweden.’

‘Why did he give this to you?’

‘Because I helped discover the expansion rate of the universe was accelerating.’


Brian Schmidt, 2011 Nobel Prize winner in Physics, explaining his Nobel Prize to the TSA agents inspecting it on his flight to see his grandmother in Fargo.

Today, in conversations I will never have ….


What’s the difference between dark matter and dark energy?

Mathematically speaking, matter and energy are two very different things, right? Is dark energy actually anything like energy, or is it just called that because it’s easier for a non-physicist to think of it like that?

Asked by punk-rock-shark


That is an excellent question, particularly because it covers a subject scientists don’t completely understand. Although dark energy accounts for roughly 68% of the universe, we are not really sure what dark energy is. According to Einstein, it is something (not necessarily an actual material “thing”) that exists in the sense of the cosmological constant. Einstein also theorizes that dark matter permeates space, meaning that it isn’t diluted as space expands. According to other theories, dark energy permeates space and acts like a fluid with negative gravity. So yeah…we aren’t really sure about what dark energy is. We have a pretty decent idea of what its job is though. The accelerated expansion of the universe is usually attributed to dark energy. So dark energy isn’t “energy” in the same sense we think of potential or kinetic energy; however, it is energy in the sense that it is conserved.

Dark matter (some 27% of the universe) is somewhat more understood. It is

a type of matter that does not emit or reflect light (so yeah, it’s black), and it isn’t found as “clouds” of matter, like ordinary matter is. We call this type of matter non-baryonic, meaning that it is not made up of baryons (a type of subatomic particle). Dark matter is different from antimatter, because we do not see any of the effects of matter-antimatter annihilation (like gamma ray emission). Mathematically speaking, matter and energy are actually pretty similar. I mean, both quarks (constituent of matter) and leptons (constituent of energy) are fermions (a type of subatomic particle), thus following the same principles (most of the time). Also, there is an equivalence between the two, namely the mass-energy equivalence, which states that

where Er is the relativistic energy, and m0 the relativistic mass (relativistic meaning that it can vary with the frame of reference, or velocity of the observer) . If we make certain considerations, we get E=mc^2 from here. Sources: NASA: “Dark Energy, Dark Matter - NASA Science.”Dark Energy, Dark Matter - NASA Science. N.p., n.d. Web. 1 Sept. 2014. <http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/>. How Stuff Works: Lamb, Robert. “What are Dark Matter and Dark Energy?.”HowStuffWorks. HowStuffWorks.com, n.d. Web. 2 Sept. 2014. <http://science.howstuffworks.com/dictionary/astronomy-terms/dark-matter-dark-energy.htm>.

Answered by Demian L., Expert Leader Edited by Margaret G.
Why Type Ia Supernovae Continue to Burn Bright

Three years after its explosion, a type Ia supernova continues to shine more brightly than expected, new research finds. The observations, made with the Hubble Space Telescope and published today in The Astrophysical Journal, suggest that powerful explosions like this one produce a heavy form of cobalt that gives the heat from nuclear decay an energy boost.

The work could help researchers pinpoint the parents of type Ia supernovae and reveal the mechanics behind these events. These particular types of stellar explosions are frequently used to measure distances to faraway galaxies, and have grown more important to the field in recent decades, after they were used to demonstrate that expansion of the universe is accelerating. But researchers still have many questions about the phenomenon.

“We still do not know exactly what type of star system explodes as a type Ia supernova or how the explosion takes place,“ said lead author Or Graur, a research associate in the American Museum of Natural History’s Department of Astrophysics and a postdoctoral researcher at New York University. "A lot of research has gone into these two questions, but the answers are still elusive.”

Current research suggests that type Ia supernovae begin in binary star systems, where two stars orbit one another, and where at least one star is a white dwarf. The explosion is the result of a thermonuclear chain reaction, which produces vast quantities of heavy elements. The light that researchers see when a type Ia supernova explodes comes from the radioactive decay of these elements, notably when an isotope of nickel (56Ni) decays into an isotope of cobalt (56Co) and then into a stable isotope of iron (56Fe).

Read the full story on the Museum blog. 


How certain are we of the Universe’s ‘Big Freeze’ fate?

“In the end, all we can go off of is what we’ve measured, and admit that the possibilities of what’s uncertain could go in any number of directions. Dark energy appears consistent with a cosmological constant, and there’s no reason to doubt this simplest of models in describing it. But if dark energy gets stronger over time, or if that exponent turns out to be a positive number (even if it’s a small positive number), our Universe might end in a Big Rip instead, where the fabric of space gets torn apart. It’s possible that dark energy may change over time and reverse sign, leading to a Big Crunch instead. Or it’s possible that dark energy may increase in strength and undergo a phase transition, giving rise to a Big Bang once again, and restarting our “cyclical” Universe.”

The discovery of the accelerated expansion of the Universe – and of dark energy behind it – in 1998 was one of the biggest physics revolutions of our lifetime. By measuring these distant galaxies and how their distances and redshifts scale in the Universe, we were able to determine that despite everything we knew about matter and radiation, there was an additional force at play, and it caused distant galaxies to accelerate away from us. The data is now good enough to determine that dark energy is extremely close, if not identical, to the predictions of a cosmological constant. But there are still other theoretical possibilities that are admissible, even if they aren’t favored. Perhaps in the coming decades, we’ll find out that the ‘Big Freeze’ isn’t necessarily where we’re headed in the distant future?

Why do we think most of the universe is missing?

About 380,000 years after the big bang, the universe cooled enough to allow protons and electrons to combine to form neutral hydrogen atoms. This is called ‘recombination.’ Photons that had previously bounced around between free protons and electrons suddenly had nowhere to go and were released, flooding the universe with cosmic background radiation.

As the universe expanded over the next 13.8 billion years, this radiation cooled further and now takes the form of microwaves and infra-red radiation. Its temperature is incredibly uniform across the sky, but it does show some very small differences, of just a few hundredths of a degree.

These variations are consistent with the most widely accepted model of the big bang. Detailed analysis using this model suggests that 68% of the mass-energy of the universe today consists of dark energy, the energy of ‘empty’ space. Dark energy is responsible for accelerating the expansion of the universe, as shown by analysis of very distant supernovae. About 27% is dark matter, an invisible form of matter detectable only through its gravitational effects. Nobody known what dark matter is, but there is some hope that experiments at CERN’s Large Hadron Collider may provide some clues.

About 5% is ordinary matter, or what we used to think of as ‘the universe’ not so very long ago. The universe is mostly missing.

You can learn more about this missing universe via Origins: The Scientific Story of Creation by Jim Baggott, or by following #BaggottOrigins across social media.

Image: ‘Our universe,’ by NASA, ESA, M.J. Jee and H. Ford. Public domain via Wikimedia Commons.

Supernova SN 2014J explodes

New data from NASA’s Chandra X-ray Observatory has provided stringent constraints on the environment around one of the closest supernovas discovered in decades. The Chandra results provide insight into possible cause of the explosion, as described in our press release. On January 21, 2014, astronomers witnessed a supernova soon after it exploded in the Messier 82, or M82, galaxy. Telescopes across the globe and in space turned their attention to study this newly exploded star, including Chandra.  Astronomers determined that this supernova, dubbed SN 2014J, belongs to a class of explosions called “Type Ia” supernovas. These supernovas are used as cosmic distance-markers and played a key role in the discovery of the Universe’s accelerated expansion, which has been attributed to the effects of dark energy.  Scientists think that all Type Ia supernovas involve the detonation of a white dwarf. One important question is whether the fuse on the explosion is lit when the white dwarf pulls too much material from a companion star like the Sun, or when two white dwarf stars merge. This image contains Chandra data, where low, medium, and high-energy X-rays are red, green, and blue respectively. The boxes in the bottom of the image show close-up views of the region around the supernova in data taken prior to the explosion (left), as well as data gathered on February 3, 2014, after the supernova went off (right).  The lack  of the detection of X-rays detected by Chandra is an important clue for astronomers looking for the exact mechanism of how this star exploded. The non-detection of X-rays reveals that the region around the site of the supernova explosion is relatively devoid of material. This finding is a critical clue to the origin of the explosion. Astronomers expect that if a white dwarf exploded because it had been steadily collecting matter from a companion star prior to exploding, the mass transfer process would not be 100% efficient, and the white dwarf would be immersed in a cloud of gas. If a significant amount of material were surrounding the doomed star, the blast wave generated by the supernova would have struck it by the time of the Chandra observation, producing a bright X-ray source. Since they do not detect any X-rays, the researchers determined that the region around SN 2014J is exceptionally clean. A viable candidate for the cause of SN 2014J must explain the relatively gas-free environment around the star prior to the explosion.  One possibility is the merger of two white dwarf stars, in which case there might have been little mass transfer and pollution of the environment before the explosion. Another is that several smaller eruptions on the surface of the white dwarf cleared the region prior to the supernova.  Further observations a few hundred days after the explosion could shed light on the amount of gas in a larger volume, and help decide between these and other scenarios.

Image credit: NASA/CXC/SAO/R.Margutti et al


Could dark energy be caused by frozen neutrinos?

“Since its discovery in 1998, the accelerated expansion has lacked a compelling, simple explanation that didn’t hypothesize a completely new set of forces, properties or interactions. If you wanted a scalar field — a quintessence model — it had to be finely tuned. But in a very clever paper just submitted yesterday by Fergus Simpson, Raul Jimenez, Carlos Pena-Garay, and Licia Verde, they note that if a generic scalar field couples to the neutrinos we have in our Universe, that fine-tuning goes away, and that scalar field will automatically begin behaving as a cosmological constant: as energy inherent to space itself.”

The accelerated expansion of our Universe was one of the biggest surprise discoveries of all-time, and something that still lacks a good physical explanation. While many models of dark energy exist, it remains a completely phenomenological study: everything appears consistent with a cosmological constant, but nothing appears to be a good motivator for why the Universe should have one. Until now, that is! In a new paper by Fergus Simpson, Raul Jimenez, Carlos Pena-Garay and Licia Verde, they note that any generic scalar field that couples to the neutrino sector would dynamically and stably give rise to a type of dark energy that’s indistinguishable from what we’ve observed. The huge advance is that this scenario doesn’t require any fine-tuning, thanks to this dark energy arising from neutrinos “freezing,” or becoming non-relativistic. In addition, there are experimental signatures to look for to confirm it, too, in the form of neutrinoless double-beta decay!

One trillion, trillion, trillion years from now, the accelerating expansion of the universe will have disintegrated the fabric of matter itself, terminating the possibility of embodiment. Every star in the universe will have burnt out, plunging the cosmos into a state of absolute darkness and leaving behind nothing but spent husks of collapsed matter. All free matter, whether on planetary surfaces or in interstellar space, will have decayed, eradicating any remnants of life…. The stellar corpses littering the empty universe will evaporate into a brief hailstorm of elementary particles. Atoms themselves will cease to exist. Only the implacable gravitational expansion will continue, driven by the currently inexplicable force called ‘dark energy’, which will keep pushing the extinguished universe deeper and deeper into an eternal and unfathomable blackness.
—  Ray Brassier, Nihil Unbound

Scale of Universe Measured with 1-Percent Accuracy

An ultraprecise new galaxy map is shedding light on the properties of dark energy, the mysterious force thought to be responsible for the universe’s accelerating expansion.

A team of researchers working with the Baryon Oscillation Spectroscopic Survey (BOSS) has determined the distances to galaxies more than 6 billion light-years away to within 1 percent accuracy — an unprecedented measurement.

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Gravity may have saved the universe after the Big Bang
London, UK (SPX) Nov 20, 2014
External image
New research by a team of European physicists could explain why the universe did not collapse immediately after the Big Bang. Studies of the Higgs particle - discovered at CERN in 2012 and responsible for giving mass to all particles - have suggested that the production of Higgs particles during the accelerating expansion of the very early universe (inflation) should have led to instability and
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Light that travels through space encounters many obstacles, one of which is the danger that it will get scattered by interstellar dust.

These images, compiled by Bob Franke, show you what we see when we look at the globular cluster M71 and its color if you were to see it without any of its colors missing.

Typically the shorter wavelengths (the blues) get scattered out but the longer wavelengths (the reds) are able to overcome obstacles their smaller brethren couldn’t pass.

This effect gets worse the farther away we observe (M71 is a mere 13,000 light years away), but not due solely to dust.

The accelerating expansion of the universe causes many galaxies to also have their light shifted to the red spectrum in color.

Because of this, they will start turning invisible to us and the sky will go black.

Since 1990, the Hubble Space Telescope has broadened our species’ collective understanding of the universe. For the past 24 years, this massive telescope has been regarded as one of the greatest scientific instruments we as humans have ever constructed. Hubble has contributed to our understanding of the universe in various ways, upending several key theories about the cosmos. Specifically, the Hubble Space Telescope proved vital with regards to the realization that the expansion of the universe is accelerating – not slowing down as was widely believed.

While Hubble continues to unveil the universe to us, plans for its successor are already underway. NASA has developed infrared-sensitive telescopes and instruments, such as the Wide Field Camera on Hubble which was fitted in 2009. This relatively new addition of infrared viewing capability is a small sample of what is on the horizon for astronomical study. The James Webb Space Telescope – set to launch in 2018 – will expand upon this technology and has a mission objective that includes observing the most distant objects in the universe. This task simply isn’t possible using standard cameras, as astronomers will have to rely upon infrared technology accordingly.

As part of Hubble’s 24th anniversary of being in service, we at Penny4NASA want to plug David Gaynes’ documentary, “Saving Hubble.”



What is the strongest force in the Universe?

“On the largest scales, the fundamental, tiny amount of energy inherent to space itself — less than one Joule of energy per cubic kilometer of space — is enough to overcome even the gravitational attraction between the most massive galaxies and clusters in the Universe. The result? An accelerated expansion, as the most distant galaxies and clusters move farther and farther away from one another at ever faster rates as time goes on. On the largest cosmic scales, even gravity doesn’t get its way.”

But what does it truly mean to be strong? We have four fundamental forces in the Universe: the strong, electromagnetic, weak and gravitational forces. You might think that, by virtue of its name, the strong force is the strongest one. And you’d be right, from a particular point of view: at the smallest distance scales, 10^-16 meters and below, no other force can overpower it.
But under the right circumstances, each of the forces can shine. Up until recently, on the largest scales, we thought that gravitation – by and large the weakest of the forces – was the only force that mattered. And yet, when we look on the very largest scales, many billions of light years in size, even gravitation doesn’t win the day.
There are four possible answers depending on how you look at the question. Come find out who’s the strongest of them all!

Gravity May Have Saved Universe After Big Bang

New research by a team of European physicists could explain why the universe did not collapse immediately after the Big Bang.

Studies of the Higgs particle – discovered at CERN in 2012 and responsible for giving mass to all particles – have suggested that the production of Higgs particles during the accelerating expansion of the very early universe (inflation) should have led to instability and collapse.

Scientists have been trying to find out why this didn’t happen, leading to theories that there must be some new physics that will help explain the origins of the universe that has not yet been discovered. Physicists from Imperial College London, and the Universities of Copenhagen and Helsinki, however, believe there is a simpler explanation.

In a new study in Physical Review Letters, the team describe how the spacetime curvature – in effect, gravity – provided the stability needed for the universe to survive expansion in that early period. The team investigated the interaction between the Higgs particles and gravity, taking into account how it would vary with energy.

They show that even a small interaction would have been enough to stabilise the universe against decay.

“The Standard Model of particle physics, which scientists use to explain elementary particles and their interactions, has so far not provided an answer to why the universe did not collapse following the Big Bang,” explains Professor Arttu Rajantie, from the Department of Physics at Imperial College London.

“Our research investigates the last unknown parameter in the Standard Model – the interaction between the Higgs particle and gravity. This parameter cannot be measured in particle accelerator experiments, but it has a big effect on the Higgs instability during inflation. Even a relatively small value is enough to explain the survival of the universe without any new physics!”

The team plan to continue their research using cosmological observations to look at this interaction in more detail and explain what effect it would have had on the development of the early universe. In particular, they will use data from current and future European Space Agency missions measuring cosmic microwave background radiation and gravitational waves.

“Our aim is to measure the interaction between gravity and the Higgs field using cosmological data,” says Professor Rajantie. “If we are able to do that, we will have supplied the last unknown number in the Standard Model of particle physics and be closer to answering fundamental questions about how we are all here.”