Turns Out There Is No Actual Looking Up

Is there an up out there? New research says no. Out there in the universe, one direction is much like another. Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger

Direction is something we humans are pretty accustomed to. Living in our friendly terrestrial environment, we are used to seeing things in term of up and down, left and right, forwards or backwards. And to us, our frame of reference is fixed and doesn’t change, unless we move or are in the process of moving. But when it comes to cosmology, things get a little more complicated.

For a long time now, cosmologists have held the belief that the universe is homogeneous and isotropic – i.e. fundamentally the same in all directions. In this sense, there is no such thing as “up” or “down” when it comes to space, only points of reference that are entirely relative. And thanks to a new study by researchers from the University College London, that view has been shown to be correct.

For the sake of their study, titled “How isotropic is the Universe?“, the research team used survey data of the Cosmic Microwave Background (CMB) – the thermal radiation left over from the Big Bang. This data was obtained by the ESA’s Planck spacecraft between 2009 and 2013.

The team then analyzed it using a supercomputer to determine if there were any polarization patterns that would indicate if space has a “preferred direction” of expansion. The purpose of this test was to see if one of the basic assumptions that underlies the most widely-accepted cosmological model is in fact correct.

The first of these assumptions is that the Universe was created by the Big Bang, which is based on the discovery that the Universe is in a state of expansion, and the discovery of the Cosmic Microwave Background. The second assumption is that space is homogenous and istropic, meaning that there are no major differences in the distribution of matter over large scales.

This belief, which is also known as the Cosmological Principle, is based partly on the Copernican Principle (which states that Earth has no special place in the Universe) and Einstein’s Theory of Relativity – which demonstrated that the measurement of inertia in any system is relative to the observer.

This theory has always had its limitations, as matter is clearly not evenly distributed at smaller scales (i.e. star systems, galaxies, galaxy clusters, etc.). However, cosmologists have argued around this by saying that fluctuation on the small scale are due to quantum fluctuations that occurred in the early Universe, and that the large-scale structure is one of homogeneity.

By looking for fluctuations in the oldest light in the Universe, scientists have been attempting to determine if this is in fact correct. In the past thirty years, these kinds of measurements have been performed by multiple missions, such as the Cosmic Background Explorer (COBE) mission, the Wilkinson Microwave Anisotropy Probe (WMAP), and the Planck spacecraft.

For the sake of their study, the UCL research team – led by Daniela Saadeh and Stephen Feeney – looked at things a little differently. Instead of searching for imbalances in the microwave background, they looked for signs that space could have a preferred direction of expansion, and how these might imprint themselves on the CMB.

As Daniela Saadeh – a PhD student at UCL and the lead author on the paper – told Universe Today via email:

“We analyzed the temperature and polarization 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.”

Basically, their results showed that there is only a 1 in 121 000 chance that the Universe is anisotropic. In other words, the evidence indicates that the Universe has been expanding in all directions uniformly, thus removing any doubts about their being any actual sense of direction on the large-scale.

And in a way, this is a bit disappointing, since a Universe that is not homogenous and the same in all directions would lead to a set of solutions to Einstein’s field equations. By themselves, these equations do not impose any symmetries on space time, but the Standard Model (of which they are part) does accept homogeneity as a sort of given.

These solutions are known as the Bianchi models, which were proposed by Italian mathematician Luigi Bianchi in the late 19th century. These algebraic theories, which can be applied to three-dimensional spacetime, are obtained by being less restrictive, and thus allow for a Universe that is anisotropic.

On the other hand, the study performed by Saadeh, Feeney, and their colleagues has shown that one of the main assumptions that our current cosmological models rest on is indeed correct. In so doing, they have also provided a much-needed sense of closer to a long-term debate.

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

So the next time you find yourself looking up at the night sky, remember… that’s a luxury you have only while you’re standing on Earth. Out there, its a whole ‘nother ballgame! So enjoy this thing we call “direction” when and where  you can.

And be sure to check out this animation produced by the UCL team, which illustrates the Planck mission’s CMB data:

[embed]https://zenodo.org/record/48654/files/SVTT_movie.mp4[/embed]

Further Reading: arXiv, Science

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The Dutch Are Going To The Moon With The Chinese

Radio image of the night sky. Credit: Max Planck Institute for Radio Astronomy, generated by Glyn Haslam.

One of the defining characteristics of the New Space era is partnerships. Whether it is between the private and public sector, different space agencies, or different institutions across the world, collaboration has a become the cornerstone to success. Consider the recent agreement between the Netherlands Space Office (NSO) and the Chinese National Space Agency (CNSA) that was announced earlier this week.

In an agreement made possible by the Memorandum of Understanding (MoU) signed in 2015 between the Netherlands and China, a Dutch-built radio antenna will travel to the Moon aboard the Chinese Chang’e 4 satellite, which is scheduled to launch in 2018. Once the lunar exploration mission reaches the Moon, it will deposit the radio antenna on the far side, where it will begin to provide scientists with fascinating new views of the Universe.

The radio antenna itself is also the result of collaboration, between scientists from Radboud University, the Netherlands Institute for Radio Astronomy (ASTRON) and the small satellite company Innovative Solutions in Space (ISIS). After years of research and development, these three organizations have produced an instrument which they hope will usher in a new era of radio astronomy.

Essentially, radio astronomy involves the study of celestial objects – ranging from stars and galaxies to pulsars, quasars, masers and the Cosmic Microwave Background (CMB) – at radio frequencies. Using radio antennas, radio telescopes, and radio interferometers, this method allows for the study of objects that might otherwise be invisible or hidden in other parts of the electromagnetic spectrum.

One drawback of radio astronomy is the potential for interference. Since only certain wavelengths can pass through the Earth’s atmosphere, and local radio wave sources can throw off readings, radio antennas are usually located in remote areas of the world. A good example of this is the Very-Long Baseline Array (VLBA) located across the US, and the Square Kilometer Array (SKA) under construction in Australia and South Africa.

One other solution is to place radio antennas in space, where they will not be subject to interference or local radio sources. The antenna being produced by Radbound, ASTRON and ISIS is being delivered to the far side of the Moon for just this reason. As the latest space-based radio antenna to be deployed, it will be able to search the cosmos in ways Earth-based arrays cannot, looking for vital clues to the origins of the universe.

As Heino Falke – a professor of Astroparticle Physics and Radio Astronomy at Radboud – explained in a University press release, the deployment of this radio antenna on the far side of the Moon will be an historic achievement:

“Radio astronomers study the universe using radio waves, light coming from stars and planets, for example, which is not visible with the naked eye. We can receive almost all celestial radio wave frequencies here on Earth. We cannot detect radio waves below 30 MHz, however, as these are blocked by our atmosphere. It is these frequencies in particular that contain information about the early universe, which is why we want to measure them.”

As it stands, very little is known about this part of the electromagnetic spectrum. As a result, the Dutch radio antenna could be the first to provide information on the development on the earliest structures in the Universe. It is the also the first instrument to sent into space as part of a Chinese space mission.

Alongside Heino Falcke, Marc Klein Wolt – the director of the Radboud Radio Lab – is one of the scientific advisors for the project. For years, he and Falcke have been working towards the deployment of this radio antenna, and have high hopes for the project. As Professor Wolt said about the scientific package he is helping to create:

“The instrument we are developing will be a precursor to a future radio telescope in space. We will ultimately need such a facility to map the early universe and to provide information on the development of the earliest structures in it, like stars and galaxies.”

Together with engineers from ASTRON and ISIS, the Dutch team has accumulated a great deal of expertise from their years working on other radio astronomy projects, which includes experience working on the Low Frequency Array (LOFAR) and the development of the Square Kilometre Array, all of which is being put to work on this new project.

Other tasks that this antenna will perform include monitoring space for solar storms, which are known to have a significant impact on telecommunications here on Earth. With a radio antenna on the far side of the Moon, astronomers will be able to better predict such events and prepare for them in advance.

Another benefit will be the ability to measure strong radio pulses from gas giants like Jupiter and Saturn, which will help us to learn more about their rotational speed. Combined with the recent ESO efforts to map Jupiter at IR frequencies, and the data that is already arriving from the Juno mission, this data is likely to lead to a some major breakthroughs in our understanding of this mysterious planet.

Last, but certainly not least, the Dutch team wants to create the first map of the early Universe using low-frequency radio data. This map is expected to take shape after two years, once the Moon has completed a few full rotations around the Earth and computer analysis can be completed.

It is also expected that such a map will provide scientists with additional evidence that confirms the Standard Model of Big Bang cosmology (aka. the Lambda CDM model). As with other projects currently in the works, the results are likely to be exciting and groundbreaking!

Further Reading: Radbound University

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Beyond WIMPs: Exploring Alternative Theories Of Dark Matter

Image from Dark Universe, showing the distribution of dark matter in the universe. Credit: AMNH

The standard model of cosmology tells us that only 4.9% of the Universe is composed of ordinary matter (i.e. that which we can see), while the remainder consists of 26.8% dark matter and 68.3% dark energy. As the names would suggest, we cannot see them, so their existence has had to be inferred based on theoretical models, observations of the large-scale structure of the Universe, and its apparent gravitational effects on visible matter.

Since it was first proposed, there have been no shortages of suggestions as to what Dark Matter particles look like. Not long ago, many scientists proposed that Dark Matter consists of Weakly-Interacting Massive Particles (WIMPs), which are about 100 times the mass of a proton but interact like neutrinos. However, all attempts to find WIMPs using colliders experiments have come up empty. As such, scientists have been exploring the idea lately that dark matter may be composed of something else entirely.

Current cosmological models tend to assume that the mass of dark matter is around 100 Gev (Giga-electrovolts), which corresponds to the mass scale of a lot of the other particles that interact via weak nuclear force. The existence of such a particle would be consistent with supersymmetric extensions of the Standard Model of particle physics. It is further believed that such particles would have been produced in the hot, dense, early Universe, with an a matter mass-density that has remained consistent to this day.

However, ongoing experimental efforts to detect WIMPs have failed to produce any concrete evidence of these particles. These have including searching for the products of WIMP annihilation (i.e. gamma rays, neutrinos and cosmic rays) in nearby galaxies and clusters, as well as direct detection experiments using supercolliders, like the CERN Large Hardon Collider (LHC) in Switzerland.

Because of this, many researcher teams have begun to consider looking beyond the WIMPs paradigm to find Dark Matter. One such team consists of a group of cosmologists from CERN and CP3-Origins in Denmark, who recently released a study indicating that Dark Matter could be much heavier and much less interacting than previously thought.

As Dr. McMullen Sandora, one of the research team members from CP-3 Origins, told Universe Today via email:

“We can’t rule out the WIMP scenario yet, but with each passing year it’s getting more and more suspect that we haven’t seen anything. In addition, the usual weak scale physics suffers from the hierarchy problem. That is, why all the particles we know about are so light, especially with respect to the natural scale of gravity, the Planck scale, which is about 1019 GeV. So, if dark matter were closer to the Planck scale, it wouldn’t be afflicted by the hierarchy problem, and this would also explain why we haven’t seen the signatures associated with WIMPs.”

Using a new model they call Planckian Interacting Dark Matter (PIDM), the team has been exploring the upper limit of mass of dark matter. Whereas WIMPs place the mass of dark matter at the upper limit of the electroweak scale, the Danish research team of Marthias Garny, McCullen Sandora and Martin S. Sloth proposed a particle with a mass near another natural scale entirely – the Planck Scale.

On the Planck Scale, a single unit of mass is equivalent to 2.17645 × 10-8 kg – roughly a microgram, or 1019 times greater than the mass of a proton. At this mass, every PIDM is essentially as heavy as a particle can be before it becomes a miniature black hole. The team also theorizes that these PIDM particles interact with ordinary matter only through gravitation and that large numbers of them formed in the very early Universe during the “reheating” epoch –  a period that occurred at the end the Inflationary Epoch, some 10-36 t0 10-33 or 10-32 seconds after the Big Bang.

This is epoch is so-named because, during Inflation, cosmic temperatures are believed to have dropped by a factor of 100,000 or so. When the inflation ended, the temperatures returned to their pre-inflationary temperature (an estimated 1027 K). At this point, the large potential energy of the inflation field decayed into Standard Model particles that filled the Universe, which would have included Dark Matter.

Naturally, this new theory comes with its share of implications for cosmologists. For example, for this model to work, the temperature of the reheating epoch would have to have been higher than is currently assumed. What’s more, a hotter reheating period would also result in the creation of more primordial gravitational waves, which would be visible in the Cosmic Microwave Background (CMB).

“Having such a high temperature tells us two interesting things about inflation,” says Sandora. “If dark matter turns out to be a PIDM: the first is that inflation happened at a very high energy, which in turn means that it was able to produce not just fluctuations in the temperature of the early universe, but also in spacetime itself, in the form of gravitational waves. Second, it tells us that the energy of inflation had to decay into matter extremely rapidly, because if it had taken too long the universe would have cooled to the point where it would not have been able to produce any PIDMs at all.”

The existence of these gravitational waves could be confirmed or ruled out by future studies involving Cosmic Microwave Background (CMB). This is exciting news, since the recent discovery of gravitational waves is expected to lead to renewed attempts to detect primordial waves that date back to the very creation of the Universe.

As Sandora explained, this presents a win-win scenario for scientists, as its means that this latest candidate for Dark Matter will be able to proven or disproven in the near future.

“[O]ur scenario makes a concrete prediction: we will see gravitational waves in the next generation of cosmic microwave background experiments.  Therefore, it’s a no-lose scenario: if we see them, that’s great, and if we don’t see them, we’ll know dark matter is not a PIDM, which will mean that we know it has to have some additional interactions with ordinary matter. And all this will happen within the next decade or so, which gives us plenty to look forward to.”

Ever since Jacobus Kapteyn first proposed the existence of Dark Matter in 1922, scientists have been searching for some direct evidence of its existence. And one by one, candidate particles – ranging from gravitinos and MACHOS to axions – have been proposed, weighed, and found wanting. If nothing else, it is good to know that this latest candidate particle’s existence can be proven or ruled out in the near future.

And if proven to be correct, we will have resolved one of the greatest cosmological mysteries of all time! A step closer to truly understanding the Universe and how its mysterious forces interact. Theory of Everything, here we come (or not)!

Further Reading: Physical Review Letters

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Cosmologist Thinks a Strange Signal May Be Evidence of a Parallel Universe

In the beginning, there was chaos. Hot, dense, and packed with energetic particles, the early Universe was a turbulent, bustling place. It wasn’t until about 300,000 years after the Big Bang that the nascent cosmic soup had cooled enough for atoms to form and light to travel freely. This landmark event, known as recombination, gave rise […]