- 3205 - DARK ENERGY - mysteries getting stranger? Phantom dark energy and phantom dark gravity, or dark matter, are keeping astronomers busy. Could understanding the dark universe help us to further understand space and time?
-------------------- 3205 - DARK ENERGY - mysteries getting stranger?
- What makes the universe behave the way it does? It's a question scientists have been striving to answer for hundreds of years. From Einstein's theory of general relativity to dark matter and dark energy, our understanding of the universe has massively expanded.
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- As our knowledge expands, these explanations increasingly struggle to be consistent with what we are observing, and so scientists are now looking at new ideas to explain what we see, "dark radiation" and "phantom energy." Can theories match new observations?
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- Studying the Universe has brought the gradual realization that everything we can see in the universe, every dust cloud, asteroid field, planet, star, nebula and galaxy cluster, simply doesn't have sufficient mass to ensure that the universe behaves in the way it clearly does.
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- A potential solution to this problem was first suggested as far back as the early 1930s with “dark matter“, so-called because it must consist of a material that neither emits nor reacts with visible light, or indeed any part of the electromagnetic spectrum.
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- Dark matter must make up around 23% of the total mass in the universe. Once dark matter theory is added to Einstein's theory, it fits everything from star formation to the fact that galaxies don't simply fly apart due to their rate of spin.
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- In 1929 another observation was made by Edwin Hubble revealing that the universe appeared to be expanding. Most galaxies were moving away from us, and those that were furthest away were accelerating the fastest.
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- The correlation between the distance and speed at which the universe is expanding was soon dubbed the “Hubble constant“, however it is neither constant nor unchanging as the universe expands. The Hubble “constant” is accelerating faster and faster.
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- When it came to what was causing this expansion, astronomers eventually opted for the idea of “dark energy” as a solution. Dark energy must be an unknown form of energy permeating all space that ensures matter increasingly repulses matter.
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- Again, for Einstein's theory to work, this dark energy needs to account for more than about 73% of the energy in the universe.
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- When astronomers compare distance measurements and their relation to the redshift in the light detected from the objects the universe appears to have expanded more in the latter half of its life.
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- Dark energy may well explain why, going by measurements taken of the direction patterns in the cosmic microwave background (CMB), it appears the universe is close to being flat, which would only be possible if some form of unknown energy existed to balance its overall density against an otherwise insufficient amount of mass, that is matter and dark matter combined, in the universe.
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- In the year 2021 cosmologists are increasingly talking about “dark radiation” and a specific form of dark energy that's been called “phantom energy“. There is also talk of "dark" or "modified" gravity, a somewhat more drastic approach that suggests we simply don't fully understand the fundamental nature of the universe and that gravity, at huge cosmological scales, doesn't actually follow the rules in Einstein's theory of general relativity.
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- Dark energy and dark gravity are both proposals to explain the significantly accelerating cosmic expansion, which can't be explained otherwise. Some people have suggested that maybe gravity has a different description on cosmological scales, so that goes under the name of “modified gravity” or “dark gravity“. Basically there is a gap between the 'allowed' amount of radiation in the early universe and the amount we can account for.
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- Based on the most accurate 2020 calculations of the distances between Earth and 19 different galaxies, relying on the "yardsticks" of more than 2,000 variable Cepheid stars and Type 1a supernovae, the revised speed of the expansion of the universe is 45.5 miles per second for every 3.26 million light-years.
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- That is, every 3.26 million light-years further away we look, we find the universe is expanding 45.5 miles per second faster. At this rate, distances between cosmic objects are likely to double in another 9.8 billion years. That is 49,300 miles per hour per million lightyears distance.
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- The challenge that this measurement poses is that it doesn't fit the expansion rate predicted from wider measurements made of the afterglow from the Big Bang, That is the “cosmic microwave background“.
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- The universe is currently expanding 9% faster than it should be. We either add in something new or we really have to figure out what we think about dark matter and dark energy and what they are.
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- This surprising finding may be an important clue to understanding those mysterious parts of the universe that make up 95% of everything and don't emit light, such as dark energy, dark matter and dark radiation.
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- An international survey looking at the “gravitational lensing” caused by galaxies, published in the December 2016 found that their equations could explain the observations without the need for dark matter.
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- There is an understandable reluctance to totally let go of both Einstein's theory of gravity and the well-established data on the CMB. The former may be found to be incomplete, but, that's not the same as it being wrong.
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- With dark energy already assumed causing the universe to expand, it's not a huge step to suggest ways in which it may actually be pushing galaxies away from each other with even greater, or increasing, strength than originally expected.
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- However, another idea with growing support is that this greater-than-expected expansion of the universe is down to previously undiscovered subatomic particles that, in their early history, traveled close to the speed of light. Collectively these are termed dark radiation, and include a proposed "fourth flavor of neutrino," known as “sterile neutrinos“.
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- What is needed is evidence. At the moment the rate of expansion of the universe is the only significant, indirect, sign of dark energy, and specifically phantom energy. Putting together a really good measurement of the rate of expansion of he Universe is the primary way that something like dark energy or phantom energy is being tested.
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- In many of the theories phenomena like “gravitational lensing” should look different in a universe described by dark gravity rather than general relativity. Scientists are looking for ways to use “weak lensing experiments“, where instead of the lens being the sun and the source of light being a star in the galaxy, as happened in 1919, which proved Einstein's theory correct, the lens is not the Sun but a cluster of galaxies and the light is much bigger.
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- Most astronomers are committed to the idea of there being these dark aspects to the universe. If some aspect of dark gravity proves that Einstein simply got it wrong? "If we discover a new gravitational phenomena, then we will realize that Einstein's theory has a similar role to Newton's theory.
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- It's a beautiful theory that leads to testable predictions with high accuracy, but it's only valid in a certain domain, a certain range of validity, at which point it gives out to yet another new theory.------------------------- Other reviews available:
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- 3116 - DARK ENERGY - a mystery for science? Dark energy is one of the greatest mysteries in science today. We know very little about it, other than it is invisible, yet it fills the whole universe, and it pushes galaxies away from each other. The result of this force is that it is making our cosmos expand at an accelerated rate.
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- 3095 - DARK ENERGY - into WIMPs and MACHOs? The more we learn the more we know the less we know. That is certaintly true with astronomy. We have come to the most recent conclusion that 95% of the Universe is “dark”. We call it Dark Energy and Dark Matter. Of course Matter is Energy too, according to energy = mass*c^2 .
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- 3086 - DARK ENERGY - What is the Universe Made of? Dark Energy was not known until 1998 so we have only 30 years to think about it. The most likely answer is vacuum energy. A vacuum is not really a vacuum but a see of virtual particles and anti-particles going into and out of existence in such a short time they do not defy the laws of physics and cannot be detected using the laws of physics.
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- 3079 - DARK ENERGY - Could the Astronomer’s Math be Wrong? - Therefore, the Universe is not expanding at a constant rate, it is accelerating in its expansion. Astronomers do not know what could cause this so they call it “Dark Energy” and their calculations are that Dark Energy composes 73% of all the mass-energy in the Universe
- 2972 - DARK ENERGY - with Nancy Grace? A new NASA space observatory could push planet-hunting forward at warp speed by gathering data up to 500 times faster than the venerable Hubble Space Telescope does. The “Nancy Grace Roman Space Telescope” (formerly known as the Wide-Field Infrared Survey Telescope or WFIRST) passed a key ground-system design review this month, according to NASA.
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- 2793 - DARK ENERGY - a mystery for science? Dark energy is one of the greatest mysteries in science today. We know very little about it, other than it is invisible, yet it fills the whole universe, and it pushes galaxies away from each other. The result of this force is that it is making our cosmos expand at an accelerated rate.
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- 2758 - DARK ENERGY - a mystery? Dark Energy is a mystery used to explain an ever accelerating , expanding Universe. Galaxies and groups of galaxies not held together by gravity are separating apart from each other. There is a tough of war between the pull of gravity and the push of dark energy.
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- 2632 - DARK ENERGY - some form of anti-gravity? - Is dark energy the “cosmological constant“. The fact that we see the Universe expanding as it does means that there must be some new form of energy causing these distant galaxies to recede from us faster and faster as time goes on. This Review 2632 lists 20 more reviews about Dark Energy:
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- 2428 - COSMLOGICAL CONSTANT - - The Cosmological Constant was invented by Albert Einstein. When he was thinking about gravity and the birth of the Universe, he could not see how , if gravity were the only force working over long distances, the Universe would not stop expanding and begin contracting into a “ Big Crunch”.
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- July 1, 2021 DARK ENERGY - mysteries getting stranger? 3205
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--------------------- --- Friday, July 2, 2021 ---------------------------
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