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Dark energy may not be a constant that would lead to a revolution in physics




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The farthest X-ray of the Universe from the Quasar GB 1428 helps to illustrate how bright these fantastic objects are to measure quasars in order to measure the expansion of the universe we understand the nature of dark energy as never before. X-ray: NASA / CXC / NRC / C.Cheung et al., optical: NASA / STScI; Radio: NSF / NRAO / VLA

For the past generation, we have recognized Sure, it's full of stars, galaxies, and a series of light-emitting phenomena wherever we look. The known processes that produce light are based on the particles of the Standard Model: the normal matter in our world Universe: All normal matter ̵

1; protons, neutron electrons, neutrinos, etc. – accounts for only 5% of the total.

The other 95% is a dark puzzle, but it can not be any of the particles As we know, 27% of the universe is a kind of dark matter that in no known way interacts with light or normal matter. And the remaining 68% are dark energy that appears as an energy form inherent in the space itself. A new set of observations challenges what we currently think about dark energy. If it stops, everything we know will change.

Without dark energy, the universe would not accelerate. But to explain the distant supernovae, dark energy (or something that exactly mimics it) appears to be necessary, among other things. NASA & ESA, Possible Models of the Expanding Universe

The best technique we have to understand what the universe is made of is not to go out and count everything that's out there directly , If this were the only way, we would literally miss 95% of the universe because it is not directly measurable. What we can do about it is a torment of General Theory of Relativity: the fact that all different forms of matter and energy affect the tissue of space-time itself and how it changes over time.

In particular through measurement The rate of expansion is today and just as the rate of expansion has changed throughout our cosmic history. We can use these known relationships to reconstruct what the universe must be made of. From the complete collection of available data, including information from supernovae, the large-scale structure of the universe, and the cosmic background radiation of the microwaves, we were able to construct the concordance image: 5% normal matter, 27% dark matter. and 68% dark energy.

Limitations to the dark energy of three independent sources: supernovae, the cosmic microwave background (CMB), and the baryonacoustic oscillations (BAO) found in the large-scale structure of the universe. Note that we need dark energy even without supernovae. More recent versions of this chart are available, but the results remain largely unchanged. Supernova Cosmology Project, Amanullah et al., Ap. (2010)

To the best of our knowledge, dark matter behaves just like normal matter from the point of view of gravity. The total mass of dark matter is fixed. So, as the universe expands and the volume increases, the density of dark matter decreases as it does with normal matter.

However, it is believed that dark energy is different. Instead of being a kind of particle, it seems to behave as if it were a kind of energy inherent in the space itself. As space expands, the dark energy density remains constant rather than decreasing or increasing. After the universe has expanded long enough, dark energy dominates the energy budget of the universe. Over time, it becomes more dominant over the other components and leads to the accelerated expansion observed today.

While matter (both normal and dark) and radiation decrease as the universe expands due to its increasing volume, dark energy is an energy form inherent in outer space itself. When new space is created in the expanding universe, the dark energy density remains constant. E. Siegel / Beyond The Galaxy

Traditionally, methods of measuring the expansion of the universe have relied on one of two observable indicators.

  1. Standard Candles : where the intrinsic behavior of a light source is known, and we can measure the observed brightness and complete its removal. By measuring the distance and redshift for a large number of sources, we can reconstruct how the universe has expanded.
  2. Standard Rulers : where an intrinsic magnitude scale of an object or phenomenon is known and we can measure the apparent angular size of that object or phenomenon. By transforming the angular size into the physical quantity and measuring the redshift, we can reconstruct in a similar way how the universe has expanded.

The difficulty of these two techniques – the way that astronomers spend the night – is the fear our beliefs are that intrinsic behavior can be wrong and influence our conclusions.

Two of the most successful methods for measuring large cosmic distances are based on either their apparent brightness (L) or their apparent angular size (R), both directly observable. If we can understand the intrinsic physical properties of these objects, we can use them either as standard candles (L) or as standard rulers (R) to determine how the universe has spread over its cosmic history. NASA / JPL-Caltech

To this day our best standard candles in the history of the universe have brought us very far: the light that was emitted when the universe was about 4 billion years old. Considering that today we are nearly 14 billion years old, we have been able to look back extremely far, with Type Ia supernovae being the most reliable and robust distance indicator for studying dark energy.

Recently, however, a team of scientists has begun to use X-ray emitting quasars, which are much brighter and therefore visible even earlier: when the universe was only one billion years old. In an interesting new article, researchers Guido Risaliti and Elisabeta Lusso use quasars as standard candles to go back further than ever to measure the nature of dark energy. What they found is still tentative, but still amazing.

A new study using the data from Chandra, XMM-Newton and Sloan Digital Sky Survey (SDSS) suggests that the dark energy could vary over the course of cosmic time. The illustration by this artist helps explain how astronomers tracked the effects of dark energy about a billion years after the Big Bang by specifying the distances to nearly 1,600 quasars, fast-growing black holes that glow extremely brightly. Two of the most distant quasars are depicted in Chandra images in the Insets. Image: NASA / CXC / M.Weiss; X-ray: NASA / CXC / Univ. of Florence / G.Risaliti & E.Lusso

With data from about 1,600 quasars and a new method of determining distances to them, they found strong agreement with the supernova results for quasars from the past 10 billion years: dark energy is real, about two-thirds of the energy in the universe, and seems to be a cosmological constant in nature.

However, they also found more distant quasars that showed something unexpected: at the greatest distances, there is a deviation from "constant" behavior. Risaliti has written a blog post detailing the implications of his work, including this gem:

Our last Hubble chart gave us completely unexpected results: while our measurement of the expansion of the universe coincided with the supernovae at the usual distance (from an age of 4.3 billion years to date), the inclusion of more distant quasars shows a strong deviation from the expectations of the cosmological standard model! If we explain this deviation by a dark energy component, we find that their density must increase with time.

The relationship between the distance module (y-axis, a measure of distance) and redshift (x-axis) and the quasi-data in yellow and blue with Supernove data in cyan. The red dots are averages of the yellow quasar points that have bunched together. While the supernova and quasi data agree with each other, if both are present (up to a redshift of about 1.5), the quasi data goes much further, indicating a deviation from the constant (solid) interpretation. G. Risaliti and E. Lusso, arXiv: 1811.02590

This is a notoriously difficult measurement, mind you, and the first thing you could think about is that the quasars we measured could be unreliable as a standard candle.

If that was your thought: Congratulations! This is something that once happened when people tried to use gamma-ray bursts as a distance indicator to go beyond what the supernova could teach us. As we learn more about these outbreaks, we've found that they are not up to standard. We also uncovered our own prejudices about the kinds of outbreaks we might discover. At least one of these two types of bias is likely to play a role here, and this is generally considered to be the most likely explanation for this outcome.

Although it is discovered why this will be a pedagogical undertaking and a challenge It is unlikely that many are convinced that the dark energy is not a constant.

The expected fate of the universe is that of eternal, accelerating expansion, corresponding to w, the set on the y-axis, the -1 corresponding exactly. If w is more negative than -1, as some of the data support, our fate will instead be a big rip. C. Hikage et al., ArXiv: 1809.09148

But what if this new study is correct? What if dark energy is not a constant? What if, as other observations have suggested in the last two decades, it actually changes over time?

The graph above shows results from a few different datasets, but I want you to see the value of w on the y-axis. What we call w is the equation of state for dark energy, where w = -1 is the value we would get for dark energy as a cosmological constant: an unchangeable form of energy to space itself inherent. If w differs from -1, however, this could change everything.

The various ways in which dark energy can go into the future. Staying constant or gaining strength (in a big rip) could possibly rejuvenate the universe, while reversing the character could lead to a big-crunch. NASA / CXC / M.Weiss

Our standard fate, w = -1, causes the universe to expand forever, with structures that are not driven by the action of dark energy today , are separated from each other. However, when w changes over time or is not equal to -1, it all changes.

  • If w is less negative than -1 (eg -0.9 or -0.75), dark energy weakens over time and eventually becomes unimportant. If w grows and becomes more and more positive over time, it can cause the universe to collapse in a major crisis.
  • However, if this new result is true, w is more negative than -1 (eg -1.2 or -1.5 or worse), the dark energy only gets stronger over time, whereby the space fabric expands at an ever faster rate. Tied structures such as galaxies, solar systems, planets and even atoms themselves are torn apart after some time. The universe will end in a catastrophe known as the "big rip."

The "Big Rip" scenario will occur as the dark energy increases, while remaining negative over time. Jeremy Teaford / Vanderbilt University [19659002] The quest to understand the ultimate fate of the universe has fascinated mankind since the beginning of time. With the emergence of general relativity and modern astrophysics, it has suddenly become possible to answer this question from a scientific point of view. Will the universe expand forever? Relapse? Oscillate? Or are you being torn apart by the physics that underlies our reality?

The answer can be determined by looking at the objects in the universe itself. However, the key to unlocking our ultimate cosmic fate depends on understanding what we are looking at and making sure that our answers are not influenced by the assumptions we make about the objects we measure and observe. The dark energy may not always be a constant, and only by looking at the universe itself will we know for sure.

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The farthest X-ray of the Universe, from the Quasar GB 1428. illustrates how bright these fantastic objects are. If we can figure out how to measure the extent of the universe with quasars, we can use nature understand the dark energy like never before. X-ray: NASA / CXC / NRC / C. Cheung et al; Optical: NASA / STScI; Radio: NSF / NRAO / VLA

For the last generation we realized that Of course, it is full of stars, galaxies, and a series of light-emitting phenomena everywhere we look, but every one of the known processes that produce light is based on the particles of the Standard Model: the normal matter in The normal matter is everything – protons, neutrons, electrons, neutrinos, etc. – represents only 5% of the total.

The other 95% is a dark mystery but it can not de be particles that we know. According to our best measurements, 27% of the universe is a kind of dark matter that does not interact with light or normal matter in any known way. And the remaining 68% are dark energy that appears as an energy form inherent in the space itself. A new set of observations challenges what we currently think about dark energy. If it stops, everything we know will change.

Without dark energy, the universe would not accelerate. To explain the distant supernovae, we see, among other things, dark energy (or something that exactly mimics it). NASA & ESA, Possible Models of the Expanding Universe

The best technique we have for understanding what the universe is made of is not to go out and directly count all that is out there. If this were the only way, we would literally miss 95% of the universe because it is not directly measurable. What we can do about it is a torment of General Theory of Relativity: the fact that all different forms of matter and energy affect the tissue of space-time itself and how it changes over time.

In particular through measurement The rate of expansion is today and just as the rate of expansion has changed throughout our cosmic history. We can use these known relationships to reconstruct what the universe must be made of. From the complete collection of available data, including information from supernovae, the large-scale structure of the universe, and the cosmic background radiation of the microwaves, we were able to construct the concordance image: 5% normal matter, 27% dark matter. and 68% dark energy.

Limitations of dark energy from three independent sources: supernovae, the cosmic microwave background (CMB), and the baryonacoustic oscillations (BAO) found in the large-scale structure of the universe. Note that we need dark energy even without supernovae. More recent versions of this chart are available, but the results remain largely unchanged. Supernova Cosmology Project, Amanullah et al., Ap. (2010)

To the best of our knowledge, dark matter behaves just like normal matter from the point of view of gravity. The total mass of dark matter is fixed. So, as the universe expands and the volume increases, the density of dark matter decreases as it does with normal matter.

However, it is believed that dark energy is different. Instead of being a kind of particle, it seems to behave as if it were a kind of energy inherent in the space itself. As space expands, the dark energy density remains constant rather than decreasing or increasing. After the universe has expanded long enough, dark energy dominates the energy budget of the universe. Over time, it becomes more dominant over the other components and leads to the accelerated expansion observed today.

While matter (both normal and dark) and radiation decrease as the universe expands due to its increasing volume, dark energy is an energy form inherent in outer space itself. When new space is created in the expanding universe, the dark energy density remains constant. E. Siegel / Beyond The Galaxy

Traditionally, methods of measuring the expansion of the universe have relied on one of two observable indicators.

  1. Standard Candles : where the intrinsic behavior of a light source is known, and we can measure the observed brightness and complete its removal. By measuring the distance and redshift for a large number of sources, we can reconstruct how the universe has expanded.
  2. Standard Rulers : where an intrinsic magnitude scale of an object or phenomenon is known and we can measure the apparent angular size of that object or phenomenon. By transforming the angular size into the physical quantity and measuring the redshift, we can reconstruct in a similar way how the universe has expanded.

The difficulty of these two techniques – the way that astronomers spend the night – is the fear our assumptions fear. Intrinsic behavior can be wrong and influence our conclusions.

Two of the most successful methods for measuring large cosmic distances are based on either their apparent brightness (L) or their apparent angular size (R), both directly observable. If we can understand the intrinsic physical properties of these objects, we can use them either as standard candles (L) or as standard rulers (R) to determine how the universe has spread over its cosmic history. NASA / JPL-Caltech

To this day our best standard candles in the history of the universe have brought us very far: the light that was emitted when the universe was about 4 billion years old. Considering that today we are nearly 14 billion years old, we have been able to look back extremely far, with Type Ia supernovae being the most reliable and robust distance indicator for studying dark energy.

Recently, however, a team of scientists has begun to use X-ray emitting quasars, which are much brighter and therefore visible even earlier: when the universe was only one billion years old. In an interesting new article, researchers Guido Risaliti and Elisabeta Lusso use quasars as standard candles to go back further than ever to measure the nature of dark energy. What they found is still tentative, but still amazing.

A recent study using data from Chandra, XMM-Newton, and Sloan Digital Sky Survey (SDSS) suggests that dark energy may have changed over the course of cosmic time. The illustration by this artist helps explain how astronomers tracked the effects of dark energy about a billion years after the Big Bang by specifying the distances to nearly 1,600 quasars, fast-growing black holes that glow extremely brightly. Two of the most distant quasars are depicted in Chandra images in the Insets. Image: NASA / CXC / M.Weiss; X-ray: NASA / CXC / Univ. of Florence / G.Risaliti & E.Lusso

With data from about 1,600 quasars and a new method of determining distances to them, they found strong agreement with the supernova results for quasars from the past 10 billion years: dark energy is real, about two-thirds of the energy in the universe, and seems to be a cosmological constant in nature.

However, they also found more distant quasars that showed something unexpected: at the greatest distances, there is a deviation from "constant" behavior. Risaliti has written a blog post detailing the implications of his work, including this gem:

Our last Hubble chart gave us completely unexpected results: while our measurement of the expansion of the universe coincided with the supernovae at the usual distance (from an age of 4.3 billion years to date), the inclusion of more distant quasars shows a strong deviation from the expectations of the cosmological standard model! If we explain this deviation by a dark energy component, we find that their density must increase with time.

The relationship between the distance module (y-axis, a measure of distance) and redshift (x-axis) and the quasi-data in yellow and blue with Supernove data in cyan. The red dots are averages of the yellow quasar points that have bunched together. While the supernova and quasi data agree with each other, if both are present (up to a redshift of about 1.5), the quasi data goes much further, indicating a deviation from the constant (solid) interpretation. G. Risaliti and E. Lusso, arXiv: 1811.02590

This is a notoriously difficult measurement, mind you, and the first thing you could think about is that the quasars we measured could be unreliable as a standard candle.

If that was your thought: Congratulations! This is something that once happened when people tried to use gamma-ray bursts as a distance indicator to go beyond what the supernova could teach us. As we learn more about these outbreaks, we've found that they are not up to standard. In addition, we have uncovered our own prejudices about the types of outbreaks we might discover. At least one of these two types of bias is likely to play a role here, and this is generally considered to be the most likely explanation for this outcome.

Although it is discovered why this will be a pedagogical undertaking and a challenge It is unlikely that many are convinced that the dark energy is not a constant.

The expected fate of the universe is that of eternal, accelerating expansion, corresponding to w, the set on the y-axis, the -1 corresponds exactly. If w is more negative than -1, as some of the data support, our fate will instead be a big rip. C. Hikage et al., ArXiv: 1809.09148

But what if this new study is correct? What if dark energy is not a constant? What if, as other observations have suggested in the last two decades, it actually changes over time?

The graph above shows results from a few different datasets, but I want you to see the value of w on the y-axis. What we call w is the equation of state for dark energy, where w = -1 is the value we would get for dark energy as a cosmological constant: an unchangeable form of energy to space itself inherent. If w differs from -1, however, this could change everything.

The various ways in which dark energy could go into the future. Staying constant or gaining strength (in a big rip) could possibly rejuvenate the universe, while reversing the character could lead to a big-crunch. NASA / CXC / M.Weiss

Our standard fate, w = -1, causes the universe to expand forever, with structures that are not driven by the action of dark energy today , are separated from each other. However, when w changes over time or is not equal to -1, it all changes.

  • If w is less negative than -1 (eg -0.9 or -0.75), dark energy weakens over time and eventually becomes unimportant. If w grows and becomes more and more positive over time, it can cause the universe to collapse in a major crisis.
  • However, if this new result is true, w is more negative than -1 (eg -1.2 or -1.5 or worse), the dark energy only gets stronger over time, whereby the space fabric expands at an ever faster rate. Tied structures such as galaxies, solar systems, planets and even atoms themselves are torn apart after some time. The universe will end in a catastrophe known as the Big Rip.

The "Big Rip" scenario will occur as the dark energy increases, while remaining negative over time. Jeremy Teaford / Vanderbilt University [19659002] The quest to understand the ultimate fate of the universe has fascinated mankind since the beginning of time. With the emergence of general relativity and modern astrophysics, it has suddenly become possible to answer this question from a scientific point of view. Will the universe expand forever? Relapse? Oscillate? Or are you being torn apart by the physics that underlies our reality?

The answer can be determined by looking at the objects in the universe itself. However, the key to unlocking our ultimate cosmic fate depends on understanding what we are looking at and making sure that our answers are not influenced by the assumptions we make about the objects we measure and observe. The dark energy may not be a constant, and only when we look at the universe itself will we always know for sure.


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