#Cosmology
Revised theory of gravity doesn’t predict a Big Bang

Taking as a starting point what is a very old idea of the beginning of the Universe as an alternative for General Relativity and the Big Bang theory, Astrophysicists Máximo Bañados from Universidad Católica de Chile and Pedro Ferreira from University of Oxford have resurrected a theory from the early 20th century that has a very interesting property of not having singularities.

They have reconsidered the theory of gravity proposed by Arthur Eddington who in 1924 proposed a “gravitational action” — the mechanism that describes how gravity can emerge from space-time being curved by matter and energy — which could serve as an alternative starting point to general relativity. However, it only worked for empty space and didn’t include any source of energy such as matter, making it an incomplete theory.

Ever since scientists have attempted various ways of including matter into the theory unsuccesfully. In this study, Banados and Ferreira have tried a new way to extend the theory to include matter by using a gravitational action called the Born-Infeld action.

They found that a key characteristic of Eddington’s theory is that it reproduces Einstein gravity precisely in the vacuum conditions, but it produces new effects when matter is added, bringing implications especially for high-density regions, such as in the very early Universe or within a black hole.

More intriguingly, the theory could lead to an entirely new view of the Universe that doesn’t include a singularity such as a ‘Big Bang’ in early times, meaning that it was once infinitely small. Eddington’s revised theory requires a minimum length of space-time at early times, which means that the Universe could not have been a singularity.

The theory predicts that the Universe may have loitered for a long time at a relatively small size before growing large enough to be controlled by standard cosmological evolution. Another possibility is that the Universe could have undergone a bounce, resulting from the collapse of a previous Universe. Any kind of singularity-free Universe would solve the singularity problem that has bothered scientists about general relativity, since a singularity cannot be mathematically defined.

In the future, the researchers hope to perform a more detailed analysis of the gravitational Born-Infeld action. The theory is still in the early conceptual stages, and has a long way to go before they know how accurate it is.

Source: PhysOrg.com | The paper is available via Physical Review Letters and arXiv.org

Revised theory of gravity doesn’t predict a Big Bang

Taking as a starting point what is a very old idea of the beginning of the Universe as an alternative for General Relativity and the Big Bang theory, Astrophysicists Máximo Bañados from Universidad Católica de Chile and Pedro Ferreira from University of Oxford have resurrected a theory from the early 20th century that has a very interesting property of not having singularities.

They have reconsidered the theory of gravity proposed by Arthur Eddington who in 1924 proposed a “gravitational action” — the mechanism that describes how gravity can emerge from space-time being curved by matter and energy — which could serve as an alternative starting point to general relativity. However, it only worked for empty space and didn’t include any source of energy such as matter, making it an incomplete theory.

Ever since scientists have attempted various ways of including matter into the theory unsuccesfully. In this study, Banados and Ferreira have tried a new way to extend the theory to include matter by using a gravitational action called the Born-Infeld action.

They found that a key characteristic of Eddington’s theory is that it reproduces Einstein gravity precisely in the vacuum conditions, but it produces new effects when matter is added, bringing implications especially for high-density regions, such as in the very early Universe or within a black hole.

More intriguingly, the theory could lead to an entirely new view of the Universe that doesn’t include a singularity such as a ‘Big Bang’ in early times, meaning that it was once infinitely small. Eddington’s revised theory requires a minimum length of space-time at early times, which means that the Universe could not have been a singularity.

The theory predicts that the Universe may have loitered for a long time at a relatively small size before growing large enough to be controlled by standard cosmological evolution. Another possibility is that the Universe could have undergone a bounce, resulting from the collapse of a previous Universe. Any kind of singularity-free Universe would solve the singularity problem that has bothered scientists about general relativity, since a singularity cannot be mathematically defined.

In the future, the researchers hope to perform a more detailed analysis of the gravitational Born-Infeld action. The theory is still in the early conceptual stages, and has a long way to go before they know how accurate it is.

Source: PhysOrg.com | The paper is available via Physical Review Letters and arXiv.org

The Universe’s First Fireworks

The right panel is an image from NASA’s Spitzer Space Telescope of stars and galaxies in the Ursa Major constellation. This infrared image covers a region of space so large that light would take up to 100 million years to travel across it. The image was captured with the Infrared Array Camera (IRAC) with an exposure time from May 19 to May 26, 2004 for a total of 24 hours per pixel.

The left panel is the same image after stars, galaxies and other sources were masked out. The remaining background light is from a period of time when the universe was less than one billion years old, and most likely originated from the universe’s very first groups of objects — either huge stars or voracious black holes. Darker shades in the image on the left correspond to dimmer parts of the background glow, while yellow and white show the brightest light.

Source: NASA Spitzer Space Telescope

The Universe’s First Fireworks

The right panel is an image from NASA’s Spitzer Space Telescope of stars and galaxies in the Ursa Major constellation. This infrared image covers a region of space so large that light would take up to 100 million years to travel across it. The image was captured with the Infrared Array Camera (IRAC) with an exposure time from May 19 to May 26, 2004 for a total of 24 hours per pixel.

The left panel is the same image after stars, galaxies and other sources were masked out. The remaining background light is from a period of time when the universe was less than one billion years old, and most likely originated from the universe’s very first groups of objects — either huge stars or voracious black holes. Darker shades in the image on the left correspond to dimmer parts of the background glow, while yellow and white show the brightest light.

Source: NASA Spitzer Space Telescope

Researchers Shed Light on Birth of the First Stars

In the beginning, there were hydrogen and helium. Created in the first three minutes after the Big Bang, these elements gave rise to all other elements in the universe. The factories that made this possible were stars. Through nuclear fusion, stars generated elements such as carbon, oxygen, magnesium, silicon and the other raw materials necessary for making planets and ultimately life.

But how did the first stars come to be? New research from Columbia University shows that it all boils down to this simple reaction:
H- + H → H2 + electron

The research details a key chemical reaction that took place in the universe about a million years after the Big Bang. That reaction, called associative detachment, allowed clouds in the universe to cool, condense and form the first stars.

In order to understand how the first stars formed, we need to know how the clouds that gave birth to them cooled. Molecular hydrogen (H2) radiated the heat out of the clouds, so we need to know how much H2 was in the cloud. This in turn requires understanding the chemical process by which the H2 formed.

H2 is formed when two hydrogen atoms come together and bind to one another to make a molecule. The team measured this probability, with results showing that the likelihood for this is higher than previous theoretical calculations and experiments have shown. 

The previous uncertainty in this reaction limited the ability to predict if a cloud of gas would form a star or not, and if it did, then what the mass of that star would be. That’s an important thing to quantify, because the mass of a star determines the elements it will synthesize.

The predicted masses for the first stars depend on the initial conditions of the primordial clouds from which they formed, which are highly uncertain and still an active area of research. By comparing model predictions to observations of the universe astronomers can approximate what these initial conditions must have been.

But the accuracy of these estimates depends critically on the understanding of the underlying chemical reactions. With the new data in hand, cosmologists will be better able to determine what the initial conditions were in the early universe leading to the formation of the first stars.

Image: A computer-generated model showing what the first star looked like. [+]

Source: Columbia University

Researchers Shed Light on Birth of the First Stars

In the beginning, there were hydrogen and helium. Created in the first three minutes after the Big Bang, these elements gave rise to all other elements in the universe. The factories that made this possible were stars. Through nuclear fusion, stars generated elements such as carbon, oxygen, magnesium, silicon and the other raw materials necessary for making planets and ultimately life.

But how did the first stars come to be? New research from Columbia University shows that it all boils down to this simple reaction:

H- + H → H2 + electron

The research details a key chemical reaction that took place in the universe about a million years after the Big Bang. That reaction, called associative detachment, allowed clouds in the universe to cool, condense and form the first stars.

In order to understand how the first stars formed, we need to know how the clouds that gave birth to them cooled. Molecular hydrogen (H2) radiated the heat out of the clouds, so we need to know how much H2 was in the cloud. This in turn requires understanding the chemical process by which the H2 formed.

H2 is formed when two hydrogen atoms come together and bind to one another to make a molecule. The team measured this probability, with results showing that the likelihood for this is higher than previous theoretical calculations and experiments have shown.

The previous uncertainty in this reaction limited the ability to predict if a cloud of gas would form a star or not, and if it did, then what the mass of that star would be. That’s an important thing to quantify, because the mass of a star determines the elements it will synthesize.

The predicted masses for the first stars depend on the initial conditions of the primordial clouds from which they formed, which are highly uncertain and still an active area of research. By comparing model predictions to observations of the universe astronomers can approximate what these initial conditions must have been.

But the accuracy of these estimates depends critically on the understanding of the underlying chemical reactions. With the new data in hand, cosmologists will be better able to determine what the initial conditions were in the early universe leading to the formation of the first stars.

Image: A computer-generated model showing what the first star looked like. [+]

Source: Columbia University

"Galactic archaeologists" find origin of Milky Way’s ancient stars

Many of the Milky Way’s ancient stars are remnants of other smaller galaxies torn apart by violent galactic collisions around 5 billion years ago, according to a new research by scientists at Durham’s Institute for Computational Cosmology and their collaborators at the Max Planck Institute for Astrophysics, in Germany, and Groningen University, in Holland, who ran huge computer simulations to re-create the beginnings of our galaxy.

The simulations revealed that the ancient stars, found in a stellar halo of debris surrounding the Milky Way, had been ripped from smaller galaxies by the gravitational forces generated by colliding galaxies. Cosmologists predict that the early universe was full of small galaxies that led short and violent lives. These galaxies collided with each other, leaving behind debris that eventually settled into more familiar looking galaxies like the Milky Way.

The researchers said their finding supports the theory that many of the Milky Way’s ancient stars had once belonged to other galaxies instead of being the earliest stars born inside when it began to form about 10 billion years ago. The simulations show how these ancient stars, are related to events in the distant past. The stellar halo preserves a record of a dramatic primeval period in the life of the Milky Way which ended long before the Sun was born.

The computer simulations started from shortly after the Big Bang, around 13 billion years ago, and used the universal laws of physics to simulate the evolution of dark matter and the stars. These simulations are the most realistic to date, capable of zooming into the very fine detail of the stellar halo structure, including star “streams” — which are stars being pulled from the smaller galaxies by the gravity of the dark matter.

One in 100 stars in the Milky Way belongs to the stellar halo, which is much larger than the galaxy’s familiar spiral disk. These stars are almost as old as the universe.

Image: Simulation showing a Milky Way-like galaxy around 5 billion years ago when most satellite galaxy collisions were happening.

Source: Astronomy.com

"Galactic archaeologists" find origin of Milky Way’s ancient stars

Many of the Milky Way’s ancient stars are remnants of other smaller galaxies torn apart by violent galactic collisions around 5 billion years ago, according to a new research by scientists at Durham’s Institute for Computational Cosmology and their collaborators at the Max Planck Institute for Astrophysics, in Germany, and Groningen University, in Holland, who ran huge computer simulations to re-create the beginnings of our galaxy.

The simulations revealed that the ancient stars, found in a stellar halo of debris surrounding the Milky Way, had been ripped from smaller galaxies by the gravitational forces generated by colliding galaxies. Cosmologists predict that the early universe was full of small galaxies that led short and violent lives. These galaxies collided with each other, leaving behind debris that eventually settled into more familiar looking galaxies like the Milky Way.

The researchers said their finding supports the theory that many of the Milky Way’s ancient stars had once belonged to other galaxies instead of being the earliest stars born inside when it began to form about 10 billion years ago. The simulations show how these ancient stars, are related to events in the distant past. The stellar halo preserves a record of a dramatic primeval period in the life of the Milky Way which ended long before the Sun was born.

The computer simulations started from shortly after the Big Bang, around 13 billion years ago, and used the universal laws of physics to simulate the evolution of dark matter and the stars. These simulations are the most realistic to date, capable of zooming into the very fine detail of the stellar halo structure, including star “streams” — which are stars being pulled from the smaller galaxies by the gravity of the dark matter.

One in 100 stars in the Milky Way belongs to the stellar halo, which is much larger than the galaxy’s familiar spiral disk. These stars are almost as old as the universe.

Image: Simulation showing a Milky Way-like galaxy around 5 billion years ago when most satellite galaxy collisions were happening.

Source: Astronomy.com

Dark Energy and Dark Matter Might Not Exist, Astronomers Allege

New research by astronomers in the Physics Department at Durham University suggests that the conventional wisdom about the content of the Universe may be wrong. They looked at observations from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite to study the remnant heat from the Big Bang. They found evidence that the errors in its data may be much larger than previously thought, which in turn makes the standard model of the Universe open to question.

Launched in 2001, WMAP measures differences in the Cosmic Microwave Background (CMB) radiation, the residual heat of the Big Bang that fills the Universe and appears over the whole of the sky. The angular size of the ripples in the CMB is thought to be connected to the composition of the Universe. With these results, scientists concluded that the cosmos is made up of 4% normal matter, 22% dark matter and 74% dark energy.

Astronomers used objects that appear as unresolved points in radio telescopes to test the way the WMAP telescope smoothes out its maps. They find that the smoothing is much larger than previously believed, suggesting that its measurement of the size of the CMBR ripples is not as accurate as was thought. If true this could mean that the ripples are significantly smaller, which could imply that dark matter and dark energy are not present after all.

If dark energy does exist, then it ultimately causes the expansion of the Universe to accelerate. On their journey from the CMB to the telescopes like WMAP, photons travel through giant superclusters of galaxies. Normally a CMB photon is first blueshifted when it enters the supercluster and then redshifted as it leaves, so that the two effects cancel.

But if the supercluster galaxies are accelerating away from each other because of dark energy, the cancellation is not exact, so photons stay slightly blueshifted after their passage. Slightly higher temperatures should appear in the CMB where the photons have passed through superclusters. However, the new results, based on the Sloan Digital Sky Survey which surveyed 1 million luminous red galaxies, suggest that no such effect is seen, again threatening the standard model of the Universe.

If the Universe really has no ‘dark side’, it will come as a relief to some theoretical physicists. Having a model dependent on as yet undetected exotic particles that make up dark matter and the completely mysterious dark energy leaves many scientists feeling uncomfortable. It also throws up problems for the birth of stars in galaxies, with as much ‘feedback’ energy needed to prevent their creation as gravity provides to help them form.

Image: A map of the cosmic microwave background radiation (CMB) made by the Wilkinson Microwave Anisotropy Probe (WMAP). [+]

Source: RAS, SPACE.com

Dark Energy and Dark Matter Might Not Exist, Astronomers Allege

New research by astronomers in the Physics Department at Durham University suggests that the conventional wisdom about the content of the Universe may be wrong. They looked at observations from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite to study the remnant heat from the Big Bang. They found evidence that the errors in its data may be much larger than previously thought, which in turn makes the standard model of the Universe open to question.

Launched in 2001, WMAP measures differences in the Cosmic Microwave Background (CMB) radiation, the residual heat of the Big Bang that fills the Universe and appears over the whole of the sky. The angular size of the ripples in the CMB is thought to be connected to the composition of the Universe. With these results, scientists concluded that the cosmos is made up of 4% normal matter, 22% dark matter and 74% dark energy.

Astronomers used objects that appear as unresolved points in radio telescopes to test the way the WMAP telescope smoothes out its maps. They find that the smoothing is much larger than previously believed, suggesting that its measurement of the size of the CMBR ripples is not as accurate as was thought. If true this could mean that the ripples are significantly smaller, which could imply that dark matter and dark energy are not present after all.

If dark energy does exist, then it ultimately causes the expansion of the Universe to accelerate. On their journey from the CMB to the telescopes like WMAP, photons travel through giant superclusters of galaxies. Normally a CMB photon is first blueshifted when it enters the supercluster and then redshifted as it leaves, so that the two effects cancel.

But if the supercluster galaxies are accelerating away from each other because of dark energy, the cancellation is not exact, so photons stay slightly blueshifted after their passage. Slightly higher temperatures should appear in the CMB where the photons have passed through superclusters. However, the new results, based on the Sloan Digital Sky Survey which surveyed 1 million luminous red galaxies, suggest that no such effect is seen, again threatening the standard model of the Universe.

If the Universe really has no ‘dark side’, it will come as a relief to some theoretical physicists. Having a model dependent on as yet undetected exotic particles that make up dark matter and the completely mysterious dark energy leaves many scientists feeling uncomfortable. It also throws up problems for the birth of stars in galaxies, with as much ‘feedback’ energy needed to prevent their creation as gravity provides to help them form.

Image: A map of the cosmic microwave background radiation (CMB) made by the Wilkinson Microwave Anisotropy Probe (WMAP). [+]

Source: RAS, SPACE.com

And interesting article about the expanding universe written by Dave Goldberg. Read the full story at io9 »

Our universe at home within a larger universe?

Could our universe be located within the interior of a wormhole which itself is part of a black hole that lies within a much larger universe? Such a scenario in which the universe is born from inside a wormhole is suggested by theoretical physicist Nikodem Poplawski from Indiana University.

Poplawski takes advantage of the Euclidean-based coordinate system called isotropic coordinates to describe the gravitational field of a black hole and to model the radial geodesic motion of a massive particle through the event horizon of Schwarzschild and Einstein-Rosen black holes.

Because Einstein’s general theory of relativity does not choose a time orientation, if a black hole can form from the gravitational collapse of matter through an event horizon in the future then the reverse process is also possible. Such a process would describe an exploding white hole: matter emerging from an event horizon in the past, like the expanding universe.

A white hole is connected to a black hole by an Einstein-Rosen bridge (wormhole) and is hypothetically the time reversal of a black hole. Poplawski’s paper suggests that all astrophysical black holes, may have Einstein-Rosen bridges, each with a new universe inside that formed simultaneously with the black hole.

From that it follows that our universe could have itself formed from inside a black hole existing inside another universe.

Image: Einstein-Rosen bridges have never been observed in nature, but they provide theoretical physicists and cosmologists with solutions in general relativity by combining models of black holes and white holes.

Source: Indiana University
Our universe at home within a larger universe?

Could our universe be located within the interior of a wormhole which itself is part of a black hole that lies within a much larger universe? Such a scenario in which the universe is born from inside a wormhole is suggested by theoretical physicist Nikodem Poplawski from Indiana University.

Poplawski takes advantage of the Euclidean-based coordinate system called isotropic coordinates to describe the gravitational field of a black hole and to model the radial geodesic motion of a massive particle through the event horizon of Schwarzschild and Einstein-Rosen black holes.

Because Einstein’s general theory of relativity does not choose a time orientation, if a black hole can form from the gravitational collapse of matter through an event horizon in the future then the reverse process is also possible. Such a process would describe an exploding white hole: matter emerging from an event horizon in the past, like the expanding universe.

A white hole is connected to a black hole by an Einstein-Rosen bridge (wormhole) and is hypothetically the time reversal of a black hole. Poplawski’s paper suggests that all astrophysical black holes, may have Einstein-Rosen bridges, each with a new universe inside that formed simultaneously with the black hole.

From that it follows that our universe could have itself formed from inside a black hole existing inside another universe.

Image: Einstein-Rosen bridges have never been observed in nature, but they provide theoretical physicists and cosmologists with solutions in general relativity by combining models of black holes and white holes.

Source: Indiana University
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