Tag Archives: Planck

The Universe expands equally in all directions — and this is bad news for Einstein’s equations

Researchers analyzed the background radiation left over from the Big Bang to put an end to a long standing debate: Is our Universe expanding the same in all directions, or does this vary depending on where you look?

The microwave sky as seen by Planck.

Finding out if our Universe is a homogeneous body or not is a really important topic in physics. A lot of really heavy-duty math hinges on us knowing this bit of information — mathematical systems such as Einstein’s field equations (EFE,) a set of 10 equations in his theory of relativity that explain the behavior of gravitation as space-time gets distorted by energy or matter.

A team from the University College London analyzed the cosmic microwave background (CMB,) the left-over radiation from the Big Bang, to find out just that. They found that there isn’t any preferential direction of expansion and the Universe just pushes out evenly all over. This goes along nicely with our current cosmological models — but throws a wrench into the mathematical systems behind EFE.

Homogeneous space

There’s basically two ways our Universe can behave. Either it is homogeneous and isotropic, meaning that its properties are the same no matter which directions you measure them in, or anisotropic, when these properties vary with the direction you measure them in.

Let’s start from a small scale example. On an molecular level, graphite is made up of layers of carbon atoms one on top of the other — kind of like a sandwich. If you apply an electrical current parallel to these layers — along the slices of bread — it’s a really good conductor, because there’s nothing to stop electrons from flowing freely. But if you run the current perpendicular to the layers — through the slices — it’s roughly 20 times more resistant. So its resistivity to electrical current is dependent on which direction you measure it — this is anisotropy.

Certain observations lend weight to the theory that the Universe might be anisotropic — matter, for instance, isn’t evenly distributed throughout it. Star systems, galaxies, and galaxy clusters are clumps of matter seemingly randomly thrown about the Universe, and some researchers have suggested that this caused by some kind of force or directional flow has pushing them into position.

“This, they assume, arises because the Universe was born as a homogeneous soup of subatomic particles in the Big Bang,” explains Adrian Cho for Science magazine. “As the Universe underwent an exponential growth spurt called inflation, tiny quantum fluctuations in that soup expanded to gargantuan sizes, providing density variations that would seed the galaxies.”

Our cosmological models are build from the assumption that these variations only matter on the very small scale (when you’re talking about a whole Universe, “tiny” means clusters of galaxies) but even out as you look at the big picture. But in the early 2000s, NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) mapped ‘bumps’ in the CMB that the homogeneity/isotropy theory couldn’t explain. There’s one region in our Universe so baffling scientists have actually called it the Axis of Evil, which also flies in the face of homogeneity. But an anisotropic Universe could quite comfortably explain both.

Microwaveable answers

To settle the debate once and for all, the University College London team tuned in on the CMB, residual radiation left over from the birth of the Universe. They modeled what an anisotropic Universe would look like, then compared real recordings to their model. As team member Daniela Saadeh told Universe Today:

“We analysed the temperature and polarisation of the cosmic microwave background (CMB), a relic radiation from the Big Bang, using data from the Planck mission. We compared the real CMB against our predictions for what it would look like in an anisotropic universe. After this search, we concluded that there is no evidence for these patterns and that the assumption that the Universe is isotropic on large scales is a good one.”

CMB patterns measured by the Planck mission — top.
CMB patterns modeled for an anisotropic Universe — bottom.
They don’t really fit.
Image credits (top) ESA and the Planck Collaboration, (bottom) D. Saadeh et. al.

They calculated that there’s a 1-in-121,000 chance that the Universe has a preferred direction of expansion, which are pretty good odds in favor of the isotropy theory,

“For the first time, we really exclude anisotropy,” Saadeh told Cho at Science. “Before, it was only that it hadn’t been probed.”

So our cosmological models are safe for now. But as Universe Today points out, EFE can only really be solved in an anisotropic Universe. Solutions to these equations were proposed by Italian mathematician Luigi Bianchi in the late 19th century and allow for an anisotropic Universe. However, if that assumption is proved wrong, the solutions are left up in the air.

On the other hand, proving that the Universe is isotropic means we don’t have to re-think everything we know about cosmology, which is pretty convenient.

“In the last 10 years there has been considerable discussion around whether there were signs of large-scale anisotropy lurking in the CMB,” Saadeh said.

“If the Universe were anisotropic, we would need to revise many of our calculations about its history and content. Planck high-quality data came with a golden opportunity to perform this health check on the standard model of cosmology and the good news is that it is safe.”

The results have been accepted for publication in an upcoming edition of Physical Review Letters under the title “How isotropic is the Universe?”. Until then, you can access the pre-print version at arXiv.org.:

The Universe expands much faster than we thought, and current models can’t explain why

Scientists have completed the most precise measurement of the Universe’s rate of expansion to date,  but the result just isn’t compatible with speed calculations from residual Big Bang radiation. Should the former results be confirmed by independent techniques, we might very well have to rewrite the laws of cosmology.

Data from galaxies such as M101, seen here, allow scientists to gauge the speed at which the universe is expanding.
Image credits X-ray: NASA/CXC/SAO; Optical: Detlef Hartmann; Infrared: NASA/JPL-Caltech

“I think that there is something in the standard cosmological model that we don’t understand,” says astrophysicist Adam Riess, a physicist at Johns Hopkins University in Baltimore, Maryland, who co-discovered dark energy in 1998 and led the latest study.

This discrepancy might even mean that dark energy — thought to be responsible for observed acceleration in the expansion of the Universe — has steadily been gaining in strength since the dawn of time. Should the results be confirmed, they have the potential of “becoming transformational in cosmology” said Kevork Abazajian, cosmologist at the University of California, Irvine.

In our current cosmological model, the Universe is the product of a tug of war of sorts between dark matter and dark energy. Dark matter uses its gravitational pull to slow down expansion, while dark energy is pushing everything apart, making it accelerate. Riess and others suggest that dark energy’s strength has been constant throughout the history of the Universe.

Most of what we know about dark matter-dark energy interaction and how each of them affects the Universe comes from studying remanent Big Bang radiation, known as the cosmic microwave background. The most exhaustive study on this subject was done by the European Space Agency’s Planck observatory. Those measurements essentially give researchers a picture of the Universe when it was really young — 400.000 years of age. Based on them, they can determine how the Universe evolved up to now, including the rate of expansion at any point in its history. Knowing where it was and where it is now, they can also predict those two parameters in the future.

But here’s the thing: they don’t add up to the observed rate of expansion. These predictions are invalidated by direct measurements of the current rate of cosmic expansion — also known as the Hubble constant. This constant is calculated by observing how rapidly nearby galaxies move away from the Milky Way using stars of known intrinsic brightness called ‘standard candles’. Until now the errors were small enough that the disagreement could be ignored, but Riess and his team warn that the discrepancy is too great to ignore any longer.

Riess’s team studied two types of standard candles in 18 galaxies using hundreds of hours of observing time on the Hubble Space Telescope.

“We’ve been going gangbusters with this,” says Riess.

They managed to measure constant with an uncertainty of 2.4%, down from a previous best result of 3.3%. Based on this value, they found that the actual rate of expansion is about 8% faster than what the Planck data predicts, Riess reports.

If both the new Hubble constant and the earlier Planck team measurements are accurate, then there’s a problem with our current model. Either we misunderstood dark energy, or we got it right but it just got stronger as time progressed. Planck researcher François Bouchet of the Institute of Astrophysics in Paris says he doubts that the problem is in his team’s measurement, but that the new findings are “exciting” regardless of what the solution turns out to be.

However, when working on such (forgive the pun) astronomical scales, a lot of things can go wrong. One last possibility is that standard candles aren’t that reliable when it comes to precision measurements, says Wendy Freedman, astronomer at the University of Chicago in Illinois. In 2001 she led the first precision measurement of the Hubble constant. She and her team are working on an alternative method based on a different class of stars. We’ll just have to wait and see.

The full paper, titled “A 2.4% Determination of the Local Value of the Hubble Constant” has been published on the arXiv online repository on and can be read here.

Scientists claim incredibly small stars emerge from black holes

Via Universe Today.

Black holes have fascinated both researchers and laymen for decades. Without a doubt, they are the point of maximum interest in terms of astrophysical research – objects with an incredibly large mass – so large that even light itself can’t escape it… what secrets do these objects still hold?

According to Carlo Rovelli at the University of Toulon in France, and Francesca Vidotto at Radboud University in the Netherlands, one of those secrets is the fact that every black hole still holds the ghastly remnants of its former star (black holes are formed when object’s internal pressure is insufficient to resist the object’s own gravity – which typically means it was a large star). According to their work, these quantum stars can later emerge as the black hole evaporates.

What do you mean ‘as the black hole evaporates’?

Stephen Hawking showed (though there is still some doubt among other physicists) that black holes all emit black-body radiation – a type of electromagnetic radiation emitted by a black body (an opaque and non-reflective body) held at constant, uniform temperature. When particles escape, the black hole loses a small amount of its energy and therefore some of its mass.

Rovelli and Vidotto believe that as a black hole evaporates, the star remains can pop up, in what they call “Planck stars” – which they claim can solve some of the most important questions in astrophysics.

Among the biggest mysteries of the Universe, the so ‘information paradox’ is definitely up with the best. Basically, black holes suck things; they have an incredibly large mass and they attract things – that’s what they do, we know that. But if a black hole slowly evaporates, then what happens to its information? From a physics stand point, the information that describes an object must fully determine its future and be fully derivable from its past, at least in principle. In other words, you can’t really destroy information. But if black holes disappear, what happens to this information? This is the information paradox, and there isn’t any good solution for it; or at least, there wasn’t.

Rethinking the Big Crunch

To get around this problem, they reanalyzed what we know about the theoretical end of the Universe – the big crunch, the reverse of the big bang, in which everything collapses to a infinitesimal dot of infinite mass; pretty hard to wrap your mind around that one, but what they came up with was even more challenging. They believe that quantum gravitational effects prevent the universe from collapsing to infinite density. Instead, the universe ”bounces” when the energy density of matter reaches the Planck scale, the smallest possible size in physics.

“The bounce does not happen when the universe is of planckian size, as was previously expected; it happens when the matter energy density reaches the Planck density,” they say. In other words, quantum gravity could become relevant when the volume of the universe is some 75 orders of magnitude larger than the Planck volume.

They explain that if this is indeed the case, then the same would happen to a black hole – of forming a singularity, the collapse of a star is eventually stopped by the same quantum pressure, a similar force to the one which prevents electrons from crashing on the nucleus of atoms.

“We call a star in this phase a “Planck star”,” they say.

Planck stars would be incredibly small – some smaller than a millimeter. They would exist for a very short time, but due to the fact that time becomes dilated at very high densities, to an outside observer, they would appear to carry on for much longer. For such an observer , a Planck star would last just as long as its parent black hole. This also solves the information paradox.

As the black hole shrinks more and more, it would eventually reach the size of its core star.

“At this point there is no horizon any more and all information trapped inside can escape,” they say.

Information isn’t lost, and it is sent back to the Universe; and they believe that this theory can be tested fairly easily. Due to its very small size, such a Planck star would emit radiation with a very small wavelength – in other words, gamma radiation. The universe is filled with a foggy background of gamma rays that astrophysicists have already observed in considerable detail with orbiting telescopes – could it be that they are in fact observing the gamma signals emitted by the Planck stars? I’m pretty sure time will tell.

Scientific Reference.

Cosmic microwave background seen by Planck

Map of the earliest recorded light paints broad picture of the ancient Universe

Cosmic microwave background seen by Planck

Cosmic microwave background seen by Planck. (c) ESA

Using the incredible  Planck cosmology probe astronomers at the European Space Agency have assembled a map of the “oldest light” in the sky – the cosmic microwave background (CMB) that was thrown into space in all directions just a few hundred thousand years after the Big Bang and which is still picked up here on Earth today.

What’s exciting about the map is that it confirms the current fundamental “cosmological inception” theory – the Big Bang theory. However there are some features and ideas that need to be refined and rethought as a result of the findings. For instance, according tot the new Planck all-sky map, the Universe is  13.82 billion years or 50 million years older than previous estimates. Also, there seems to be more matter (31.7%) and slightly less “dark energy” (68.3%) – the mysterious force that drives the Universe apart and causes an accelerated expansion.

The trace the map, cosmologists studied the CMB – light that was allowed to escape after the early Universe cooled down to allow the formation of hydrogen atoms some 380,000 years ago. By studying temperature fluctuations of the CMB –  seen as mottling in the map – scientists can better assess their current theoretical models with actual data on anomalies, since these fluctuations are thought to actually  reflect the differences in the density of matter when the light first escaped. These ripples are thought to have given rise to today’s vast cosmic web of galaxy clusters and dark matter.

anomaliesWhile some statistical analysis isn’t on par with data provided by the Planck map, cosmologists should rejoice as the news that their fundamental theories reflect reality. Especially those relating to the birth of the Universe, which is thought to have started as hot, dense state in an incredibly small space, and then expanded and cooled.

A cosmic baby picture

Other projects like the Cosmic Background Explorer and the Wilkinson Microwave Anisotropy Probe have provided earlier drafts of the “baby Universe”, however the map obtained from data gathered by the $900 million (€700 million) Planck probe launched in 2009 is the most detailed yet.

“The extraordinary quality of Planck’s portrait of the infant Universe allows us to peel back its layers to the very foundations, revealing that our blueprint of the cosmos is far from complete. Such discoveries were made possible by the unique technologies developed for that purpose by European industry,” says Jean-Jacques Dordain, ESA’s Director General.

“Since the release of Planck’s first all-sky image in 2010, we have been carefully extracting and analysing all of the foreground emissions that lie between us and the Universe’s first light, revealing the cosmic microwave background in the greatest detail yet,” adds George Efstathiou of the University of Cambridge, UK.

What also came as a surprise was a rather discrepant anomaly. Apparently, there’s an asymmetry in average temperature distribution across the Universe, as the southern sky hemisphere is slightly warmer than the north. Another significant anomaly is a cold spot in the map, centred on the constellation Eridanus, which is much bigger than would be predicted.

Nevertheless, cosmologists which have been dreaming about such a map for decades will now have their work cut out for them. Armed with this map, they now have the necessary resources or at least another tool at hand to prove or disprove some of the most controversial theories in cosmology today, like those discussing the rapid and far-reaching inflation of the Universe in its first moments from inception or the claim that there are six or seven spatial dimensions in addition to the three we perceive.

source: ESA