Our Universe

31/12/2019

I wish this year comes to a conclusion it also ends all of the issues and attract all of the success and happiness for you and your family.

Happy New Year 2020!

24/11/2019

27/10/2019

{Happy Diwali}

May this festival of lights, with the blessings of Goddess Lakshmi, bring you a lot of joy of success, health, wealth and prosperity and keep the darkness of ignorance and adversities away from your life. We wish you and very Happy & Safe Diwali....

Save Environment, go green , avoid crackers...

31/12/2018

“Wishing you and your family good health, happiness,
success and prosperity in the coming year!
Have a great start to a great year!”

06/08/2017

04/07/2017

Hubble eyes a powerful galaxy with a password name

Not all galaxies have the luxury of possessing a simple moniker or quirky nickname. This impressive galaxy imaged by the NASA/ESA Hubble Space Telescope is one of the unlucky ones, and goes by a name that looks more like a password for a computer: 2XMM J143450.5+033843.

Such a name may seem like a random jumble of numbers and letters, but like all galactic epithets it has a distinct meaning. This galaxy, for example, was detected and observed as part of the second X-ray sky survey performed by ESA's XMM-Newton Observatory. Its celestial coordinates form the rest of the bulky name, following the "J": a right ascension value of 14h (hours) 34m (minutes) 50.5s (seconds). This can be likened to terrestrial longitude. It also has a declination of +03d (degrees) 38m (minutes) 43s (seconds). Declination can be likened to terrestrial latitude. The other fuzzy object in the frame was named in the same way -- it is a bright galaxy named 2XMM J143448.3+033749.

2XMM J143450.5+033843 lies nearly 400 million light-years away from Earth. It is a Seyfert galaxy that is dominated by something known as an Active Galactic Nucleus -- its core is thought to contain a supermassive black hole that is emitting huge amounts of radiation, pouring energetic X-rays out into the Universe.

04/07/2017

Massive dead disk galaxy challenges theories of galaxy evolution

By combining the power of a "natural lens" in space with the capability of NASA's Hubble Space Telescope, astronomers made a surprising discovery -- the first example of a compact yet massive, fast-spinning, disk-shaped galaxy that stopped making stars only a few billion years after the big bang.

Finding such a galaxy early in the history of the universe challenges the current understanding of how massive galaxies form and evolve, say researchers.

When Hubble photographed the galaxy, astronomers expected to see a chaotic ball of stars formed through galaxies merging together. Instead, they saw evidence that the stars were born in a pancake-shaped disk.

This is the first direct observational evidence that at least some of the earliest so-called "dead" galaxies -- where star formation stopped -- somehow evolve from a Milky Way-shaped disk into the giant elliptical galaxies we see today.

This is a surprise because elliptical galaxies contain older stars, while spiral galaxies typically contain younger blue stars. At least some of these early "dead" disk galaxies must have gone through major makeovers. They not only changed their structure, but also the motions of their stars to make a shape of an elliptical galaxy.

"This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies," said study leader Sune Toft of the Dark Cosmology Center at the Niels Bohr Institute, University of Copenhagen, Denmark. "Perhaps we have been blind to the fact that early "dead" galaxies could in fact be disks, simply because we haven't been able to resolve them."

Previous studies of distant dead galaxies have assumed that their structure is similar to the local elliptical galaxies they will evolve into. Confirming this assumption in principle requires more powerful space telescopes than are currently available. However, through the phenomenon known as "gravitational lensing," a massive, foreground cluster of galaxies acts as a natural "zoom lens" in space by magnifying and stretching images of far more distant background galaxies. By joining this natural lens with the resolving power of Hubble, scientists were able to see into the center of the dead galaxy.

The remote galaxy is three times as massive as the Milky Way but only half the size. Rotational velocity measurements made with the European Southern Observatory's Very Large Telescope (VLT) showed that the disk galaxy is spinning more than twice as fast as the Milky Way.

Using archival data from the Cluster Lensing And Supernova survey with Hubble (CLASH), Toft and his team were able to determine the stellar mass, star-formation rate, and the ages of the stars.

Why this galaxy stopped forming stars is still unknown. It may be the result of an active galactic nucleus, where energy is gushing from a supermassive black hole. This energy inhibits star formation by heating the gas or expelling it from the galaxy. Or it may be the result of the cold gas streaming onto the galaxy being rapidly compressed and heated up, preventing it from cooling down into star-forming clouds in the galaxy's center.

But how do these young, massive, compact disks evolve into the elliptical galaxies we see in the present-day universe? "Probably through mergers," Toft said. "If these galaxies grow through merging with minor companions, and these minor companions come in large numbers and from all sorts of different angles onto the galaxy, this would eventually randomize the orbits of stars in the galaxies. You could also imagine major mergers. This would definitely also destroy the ordered motion of the stars."

The findings are published in the June 22 issue of the journal Nature. Toft and his team hope to use NASA's upcoming James Webb Space Telescope to look for a larger sample of such galaxies.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

The Very Large Telescope is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of Northern Chile.

04/07/2017

Topsy-turvy motion creates light switch effect at Uranus
Unlike Earth, this icy planet's magnetosphere opens and closes every day

More than 30 years after Voyager 2 sped past Uranus, Georgia Institute of Technology researchers are using the spacecraft's data to learn more about the icy planet. Their new study suggests that Uranus' magnetosphere, the region defined by the planet's magnetic field and the material trapped inside it, gets flipped on and off like a light switch every day as it rotates along with the planet. It's "open" in one orientation, allowing solar wind to flow into the magnetosphere; it later closes, forming a shield against the solar wind and deflecting it away from the planet.

This is much different from Earth's magnetosphere, which typically only switches between open and closed in response to changes in the solar wind. Earth's magnetic field is nearly aligned with its spin axis, causing the entire magnetosphere to spin like a top along with Earth's rotation. Since the same alignment of Earth's magnetosphere is always facing toward the sun, the magnetic field threaded in the ever-present solar wind must change direction in order to reconfigure Earth's field from closed to open. This frequently occurs with strong solar storms.

But Uranus lies and rotates on its side, and its magnetic field is lopsided -- it's off-centered and tilted 60 degrees from its axis. Those features cause the magnetic field to tumble asymmetrically relative to the solar wind direction as the icy giant completes its 17.24-hour full rotation.

Rather than the solar wind dictating a switch like here on Earth, the researchers say Uranus' rapid rotational change in field strength and orientation lead to a periodic open-close-open-close scenario as it tumbles through the solar wind.

"Uranus is a geometric nightmare," said Carol Paty, the Georgia Tech associate professor who co-authored the study. "The magnetic field tumbles very fast, like a child cartwheeling down a hill head over heels. When the magnetized solar wind meets this tumbling field in the right way, it can reconnect and Uranus' magnetosphere goes from open to closed to open on a daily basis."

Paty says this solar wind reconnection is predicted to occur upstream of Uranus' magnetosphere over a range of latitudes, with magnetic flux closing in various parts of the planet's twisted magnetotail.

Reconnection of magnetic fields is a phenomenon throughout the solar system. It occurs when the direction of the interplanetary magnetic field -- which comes from the sun and is also known as the heliospheric magnetic field -- is opposite a planet's magnetospheric alignment. Magnetic field lines are then spliced together and rearrange the local magnetic topology, allowing a surge of solar energy to enter the system.

Magnetic reconnection is one reason for Earth's auroras. Auroras could be possible at a range of latitudes on Uranus due to its off-kilter magnetic field, but the aurora is difficult to observe because the planet is nearly 2 billion miles from Earth. The Hubble Space Telescope occasionally gets a faint view, but it can't directly measure Uranus' magnetosphere.

The Georgia Tech researchers used numerical models to simulate the planet's global magnetosphere and to predict favorable reconnection locations. They plugged in data collected by Voyager 2 during its five-day flyby in 1986. It's the only time a spacecraft has visited.

The researchers say learning more about Uranus is one key to discovering more about planets beyond our solar system.

"The majority of exoplanets that have been discovered appear to also be ice giants in size," said Xin Cao, the Georgia Tech Ph.D. candidate in earth and atmospheric sciences who led the study. "Perhaps what we see on Uranus and Neptune is the norm for planets: very unique magnetospheres and less-aligned magnetic fields. Understanding how these complex magnetospheres shield exoplanets from stellar radiation is of key importance for studying the habitability of these newly discovered worlds."

04/07/2017

Astronomers detect orbital motion in pair of supermassive black holes
VLBA reveals first-ever black-hole 'visual binary'

Using the supersharp radio "vision" of the National Science Foundation's Very Long Baseline Array (VLBA), astronomers have made the first detection of orbital motion in a pair of supermassive black holes in a galaxy some 750 million light-years from Earth.

The two black holes, with a combined mass 15 billion times that of the Sun, are likely separated by only about 24 light-years, extremely close for such a system.

"This is the first pair of black holes to be seen as separate objects that are moving with respect to each other, and thus makes this the first black-hole 'visual binary,'" said Greg Taylor, of the University of New Mexico (UNM).

Supermassive black holes, with millions or billions of times the mass of the Sun, reside at the cores of most galaxies. The presence of two such monsters at the center of a single galaxy means that the galaxy merged with another some time in the past. In such cases, the two black holes themselves may eventually merge in an event that would produce gravitational waves that ripple across the universe.

"We believe that the two supermassive black holes in this galaxy will merge," said Karishma Bansal, a graduate student at UNM, adding that the merger will come at least millions of years in the future.

The galaxy, an elliptical galaxy called 0402+379, after its location in the sky, was first observed in 1995. It was studied in 2003 and 2005 with the VLBA. Based on finding two cores in the galaxy, instead of one, Taylor and his collaborators concluded in 2006 that it contained a pair of supermassive black holes.

The latest research, which Taylor and his colleagues are reporting in the Astrophysical Journal, incorporates new VLBA observations from 2009 and 2015, along with re-analysis of the earlier VLBA data. This work revealed motion of the two cores, confirming that the two black holes are orbiting each other. The scientists' initial calculations indicate that they complete a single orbit in about 30,000 years.

"We need to continue observing this galaxy to improve our understanding of the orbit, and of the masses of the black holes," Taylor said. "This pair of black holes offers us our first chance to study how such systems interact," he added.

The astronomers also hope to discover other such systems. The galaxy mergers that bring two supermassive black holes close together are considered to be a common process in the universe, so astronomers expect that such binary pairs should be common.

"Now that we've been able to measure orbital motion in one such pair, we're encouraged to seek other, similar pairs. We may find others that are easier to study," Bansal said.

The VLBA, part of the Long Baseline Observatory, is a continent-wide radio telescope system using ten, 240-ton dish antennas distributed from Hawaii to St. Croix in the Caribbean. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. That extraordinary resolving power allows scientists to make extremely fine measurements of objects and motions in the sky, such as those done for the research on 0402+379.

The Long Baseline Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities,

04/07/2017

Tiny 'motors' are driven by light
Researchers demonstrate nanoscale particles that ordinary light sources can set spinning

Science fiction is full of fanciful devices that allow light to interact forcefully with matter, from light sabers to photon-drive rockets. In recent years, science has begun to catch up; some results hint at interesting real-world interactions between light and matter at atomic scales, and researchers have produced devices such as optical tractor beams, tweezers, and vortex beams.

Now, a team at MIT and elsewhere has pushed through another boundary in the quest for such exotic contraptions, by creating in simulations the first system in which particles -- ranging from roughly molecule- to bacteria-sized -- can be manipulated by a beam of ordinary light rather than the expensive specialized light sources required by other systems. The findings are reported today in the journal Science Advances, by MIT postdocs Ognjen Ilic PhD '15, Ido Kaminer, and Bo Zhen; professor of physics Marin Soljacic; and two others.

Most research that attempts to manipulate matter with light, whether by pushing away individual atoms or small particles, attracting them, or spinning them around, involves the use of sophisticated laser beams or other specialized equipment that severely limits the kinds of uses of such systems can be applied to. "Our approach is to look at whether we can get all these interesting mechanical effects, but with very simple light," Ilic says.

The team decided to work on engineering the particles themselves, rather than the light beams, to get them to respond to ordinary light in particular ways. As their initial test, the researchers created simulated asymmetrical particles, called Janus (two-faced) particles, just a micrometer in diameter -- one-hundredth the width of a human hair. These tiny spheres were composed of a silica core coated on side with a thin layer of gold.

When exposed to a beam of light, the two-sided configuration of these particles causes an interaction that shifts their axes of symmetry relative to the orientation of the beam, the researchers found. At the same time, this interaction creates forces that set the particles spinning uniformly. Multiple particles can all be affected at once by the same beam. And the rate of spin can be changed by just changing the color of the light.

The same kind of system, the researchers, say, could be applied to producing different kinds of manipulations, such as moving the positions of the particles. Ultimately, this new principle might be applied to moving particles around inside a body, using light to control their position and activity, for new medical treatments. It might also find uses in optically based nanomachinery.

About the growing number of approaches to controlling interactions between light and material objects, Kaminer says, "I think about this as a new tool in the arsenal, and a very significant one."

Ilic says the study "enables dynamics that may not be achieved by the conventional approach of shaping the beam of light," and could make possible a wide range of applications that are hard to foresee at this point. For example, in many potential applications, such as biological uses, nanoparticles may be moving in an incredibly complex, changing environment that would distort and scatter the beams needed for other kinds of particle manipulation. But these conditions would not matter to the simple light beams needed to activate the team's asymmetric particles.

"Because our approach does not require shaping of the light field, a single beam of light can simultaneously actuate a large number of particles," Ilic says. "Achieving this type of behavior would be of considerable interest to the community of scientists studying optical manipulation of nanoparticles and molecular machines." Kaminer adds, "There's an advantage in controlling large numbers of particles at once. It's a unique opportunity we have here."

Soljacic says this work fits into the area of topological physics, a burgeoning area of research that also led to last year's Nobel Prize in physics. Most such work, though, has been focused on fairly specialized conditions that can exist in certain exotic materials called periodic media. "In contrast, our work investigates topological phenomena in particles," he says.

And this is just the start, the team suggests. This initial set of simulations only addressed the effects with a very simple two-sided particle. "I think the most exciting thing for us," Kaminer says, "is there's an enormous field of opportunities here. With such a simple particle showing such complex dynamics," he says, it's hard to imagine what will be possible "with an enormous range of particles and shapes and structures we can explore."

04/07/2017

Under pressure: Extreme atmosphere stripping may limit exoplanets' habitability

New models of massive stellar eruptions hint at an extra layer of complexity when considering whether an exoplanet may be habitable or not. Models developed for our own Sun have now been applied to cool stars favoured by exoplanet hunters, in research presented by Dr Christina Kay, of the NASA Goddard Flight Center, on Monday 3rd July at the National Astronomy Meeting at the University of Hull.

Coronal mass ejections (CMEs) are huge explosions of plasma and magnetic field that routinely erupt from the Sun and other stars. They are a fundamental factor in so called "space weather," and are already known to potentially disrupt satellites and other electronic equipment on Earth. However, scientists have shown that the effects of space weather may also have a significant impact on the potential habitability of planets around cool, low mass stars -- a popular target in the search for Earth-like exoplanets.

Traditionally an exoplanet is considered "habitable" if its orbit corresponds to a temperature where liquid water can exist. Low mass stars are cooler, and therefore should have habitable zones much closer in to the star than in our own solar system, but their CMEs should be much stronger due to their enhanced magnetic fields.

When a CME impacts a planet, it compresses the planet's magnetosphere, a protective magnetic bubble shielding the planet. Extreme CMEs can exert enough pressure to shrink a magnetosphere so much that it exposes a planet's atmosphere, which can then be swept away from the planet. This could in turn leave the planetary surface and any potential developing lifeforms exposed to harmful X-rays from the nearby host star.

The team built on recent work done at Boston University, taking information about CMEs in our own solar system and applying it to a cool star system.

"We figured that the CMEs would be more powerful and more frequent than solar CMEs, but what was unexpected was where the CMEs ended up" said Christina Kay, who led the research during her PhD work.

The team modelled the trajectory of theoretical CMEs from the cool star V374 Pegasi and found that the strong magnetic fields of the star push most CMEs down to the Astrophysical Current Sheet (ACS), the surface corresponding to the minimum magnetic field strength at each distance, where they remain trapped.

"While these cool stars may be the most abundant, and seem to offer the best prospects for finding life elsewhere, we find that they can be a lot more dangerous to live around due to their CMEs" said Marc Kornbleuth, a graduate student involved in the project.

The results suggest that an exoplanet would need a magnetic field ten to several thousand times that of Earth's to shield their atmosphere from the cool star's CMEs. As many as five impacts a day could occur for planets near the ACS, but the rate decreases to one every other day for planets with an inclined orbit.

Merav Opher, who advised the work, commented, "This work is pioneering in the sense that we are just now starting to explore space weather effects on exoplanets, which will have to be taken into account when discussing the habitability of planets near very active stars."

04/07/2017

Jupiter: Atmosphere and aurora in unprecedented detail

Subaru Telescope images reveal weather in Jupiter's atmosphere in the mid-infrared. High-resolution thermal imaging of Jupiter by the COoled Mid-Infrared Camera and Spectrometer (COMICS) mounted on the Subaru Telescope on Maunakea is providing information that extends and enhances the information that the Juno mission is gathering in its unprecedented mission to probe that planet's interior and deep atmospheric structure together with details of the magnetosphere and its auroral interactions with the planet. "The Subaru observations of Jupiter so far this year have been timed to coordinate with the greatest benefit to Juno mission," said Glenn Orton, PI for the portion of the Keck Telescope exchange time with the Subaru Telescope and coordinator for Earth-based observations supporting the Juno project at JPL.

"During our May 2017 observations that provided real-time support for Juno's sixth perijove, we obtained images and spectra of the Great Red Spot and its surroundings. Our observations showed that the Great Red Spot, the largest known vortex in the solar system, had a cold and cloudy interior increasing toward its center, with a periphery that was warmer and clearer. This implied that winds were upwelling more vigorously toward its center and subsiding on the periphery. A region to its northwest was unusually turbulent and chaotic, with bands that were cold and cloudy, alternating with bands that were warm and clear bands. This region is where air heading east toward the Great Red Spot flows around it to the north, where it encounters a stream of air flowing over it from the east," adds Orton. "This information will allow us to determine the three-dimensional structure of winds that are otherwise only tracked in two dimensions using cloud features in reflected sunlight." "A wide variety of filters installed in COMICS is advantageous in sensing Jupiter's temperatures in its upper troposphere and in its stratosphere," noted co-investigator and Subaru Telescope staff astronomer Takuya Fujiyoshi.

Juno has now made five close-up passes of Jupiter's atmosphere, the first of which was on August 27, 2016 and the latest (the sixth) on May 19 of 2017. Each of these close passes has provided Juno's science team with unexpected surprises, and the Juno science return has benefited from a coordinated campaign of Earth-based support. This campaign includes observations from spacecraft near or orbiting the Earth, covering X-ray through visible wavelengths and ground-based observatories covering near-infrared through radio wavelengths.

Another set of supporting observations that were simultaneous with the Subaru observations were made by the Gemini North telescope's NIRI instrument, which imaged Jupiter in the near-infrared, measuring reflected sunlight from cloud and haze particle in Jupiter's upper troposphere and lower stratosphere -- levels generally higher in Jupiter's atmosphere than most of the Subaru measurements, providing complementary information. "Wide coverage of wavelength available from the telescopes on Maunakea is thus advantageous for the study," Fujiyoshi says.

The NASA Juno spacecraft was launched in August 2011 and began orbiting Jupiter in early July 2016. A primary goal of the mission is to improve our understanding of Jupiter -- from its atmospheric properties, to our understanding of how Jupiter and other planets in the outer Solar System formed. Subaru's mid-infrared imaging and spectroscopy with COMICS are particularly useful to Juno's instrument, by providing information about the temperature field and the distribution of ammonia, a condensate in Jupiter similar to water in the Earth's atmosphere. These serve as boundary conditions for the distribution of ammonia at this level and much deeper in Jupiter's atmosphere.

30/06/2017

Can we ditch dark energy by better understanding general relativity?

Dark energy and dark matter are theoretical inventions that explain observations we cannot otherwise understand.

On the scale of galaxies, gravity appears to be stronger than we can account for using only particles that are able to emit light. So we add dark matter particles as 25% of the mass-energy of the Universe. Such particles have never been directly detected.

On the larger scales on which the Universe is expanding, gravity appears weaker than expected in a universe containing only particles – whether ordinary or dark matter. So we add "dark energy": a weak anti-gravity force that acts independently of matter.

Brief history of "dark energy"

The idea of dark energy is as old as general relativity itself. Albert Einstein included it when he first applied relativity to cosmology exactly 100 years ago.

Einstein mistakenly wanted to exactly balance the self attraction of matter by anti-gravity on the largest scales. He could not imagine that the Universe had a beginning and did not want it to change in time.

Almost nothing was known about the Universe in 1917. The very idea that galaxies were objects at vast distances was debated.

Einstein faced a dilemma. The physical essence of his theory, as summarised decades later in the introduction of a famous textbook is:

Matter tells space how to curve, and space tells matter how to move.

That means space naturally wants to expand or contract, bending together with the matter. It never stands still.

This was realised by Alexander Friedmann who in 1922 kept the same ingredients as Einstein. But he did not try to balance the amount of matter and dark energy. That suggested a model in which universes that could expand or contract.

Further, the expansion would always slow down if only matter was present. But it could speed up if anti-gravitating dark energy was included.

Since the late 1990s many independent observations have seemed to demand such accelerating expansion, in a Universe with 70% dark energy. But this conclusion is based on the old model of expansion that has not changed since the 1920s.

Standard cosmological model

Einstein's equations are fiendishly difficult. And not simply because there are more of them than in Isaac Newton's theory of gravity.

Unfortunately, Einstein left some basic questions unanswered. These include – on what scales does matter tell space how to curve? What is the largest object that moves as an individual particle in response? And what is the correct picture on other scales?

These issues are conveniently avoided by the 100-year old approximation—introduced by Einstein and Friedmann—that, on average, the Universe expands uniformly. Just as if all cosmic structures could be put through a blender to make a featureless soup.

This homogenising approximation was justified early in cosmic history. We know from the cosmic microwave background—the relic radiation of the Big Bang—that variations in matter density were tiny when the Universe was less than a million years old.

But the universe is not homogeneous today. Gravitational instability led to the growth of stars, galaxies, clusters of galaxies, and eventually a vast "cosmic web", dominated in volume by voids surrounded by sheets of galaxies and threaded by wispy filaments.

In standard cosmology, we assume a background expanding as if there were no cosmic structures. We then do computer simulations using only Newton's 330-year old theory. This produces a structure resembling the observed cosmic web in a reasonably compelling fashion. But it requires including dark energy and dark matter as ingredients.

Even after inventing 95% of the energy density of the universe to make things work, the model itself still faces problems that range from tensions to anomalies.

Further, standard cosmology also fixes the curvature of space to be uniform everywhere, and decoupled from matter. But that's at odds with Einstein's basic idea that matter tells space how to curve.

We are not using all of general relativity! The standard model is better summarised as: Friedmann tells space how to curve, and Newton tells matter how to move.

Enter "backreaction"

Since the early 2000s, some cosmologists have been exploring the idea that while Einstein's equations link matter and curvature on small scales, their large-scale average might give rise to backreaction – average expansion that's not exactly homogeneous.

Matter and curvature distributions start out near uniform when the universe is young. But as the cosmic web emerges and becomes more complex, the variations of small-scale curvature grow large and average expansion can differ from that of standard cosmology.

Recent numerical results of a team in Budapest and Hawaii that claim to dispense with dark energy used standard Newtonian simulations. But they evolved their code forward in time by a non-standard method to model the backreaction effect.

Intriguingly, the resulting expansion law fit to Planck satellite data tracks very close to that of a ten-year-old general relativity-based backreaction model, known as the timescape cosmology. It posits that we have to calibrate clocks and rulers differently when considering variations of curvature between galaxies and voids. For one thing, this means that the Universe no longer has a single age.

In the next decade, experiments such as the Euclid satellite and the CODEX experiment, will have the power to test whether cosmic expansion follows the homogeneous law of Friedmann, or an alternative backreaction model.

To be prepared, it's important that we don't put all our eggs in one cosmological basket, as Avi Loeb, Chair of Astronomy at Harvard, has recently warned. In Loeb's words:

To avoid stagnation and nurture a vibrant scientific culture, a research frontier should always maintain at least two ways of interpreting data so that new experiments will aim to select the correct one. A healthy dialogue between different points of view should be fostered through conferences that discuss conceptual issues and not just experimental results and phenomenology, as often is the case currently.

What can general relativity teach us?

While most researchers accept that the backreaction effects exist, the real debate is about whether this can lead to more than a 1% or 2% difference from the mass-energy budget of standard cosmology.

Any backreaction solution that eliminates dark energy must explain why the law of average expansion appears so uniform despite the inhomogeneity of the cosmic web, something standard cosmology assumes without explanation.

Since Einstein's equations can in principle make space expand in extremely complicated ways, some simplifying principle is required for their large-scale average. This is the approach of the timescape cosmology.

Any simplifying principle for cosmological averages is likely to have its origins in the very early Universe, given it was much simpler than the Universe today. For the past 38 years, inflationary universe models have been invoked to explain the simplicity of the early Universe.

While successful in some aspects, many models of inflation are now ruled out by Planck satellite data. Those that survive give tantalising hints of deeper physical principles.

Many physicists still view the Universe as a fixed continuum that comes into existence independently of the matter fields that live in it. But, in the spirit of relativity – that space and time only have meaning when they are relational – we may need to rethink basic ideas.

Since time itself is only measured by particles with a non-zero rest mass, maybe spacetime as we know it only emerges as the first massive particles condense.

Whatever the final theory, it will likely embody the key innovation of general relativity, namely the dynamical coupling of matter and geometry, at the quantum level