4407 - MOON - how old is the moon?

 

-    4407  -   MOON   -  how old is the moon?   -    Moon is 40 million years older than we thought, tiny crystals from Apollo mission confirm.  A new analysis of zircon crystals from the Apollo 17 mission has revealed that the moon formed around 40 million years earlier than past geological evidence suggested. However, our cosmic companion may be even older than that.

-------------------------  4407    -  MOON   -  how old is the moon?

-    The moon is at least 40 million years older than we once thought.  Now we think it is             4.42 million years old.  Scientists confirmed our cosmic companion's new minimum age after reanalyzing tiny impact crystals from lunar samples taken by NASA's Apollo 17 mission in 1972.

-

-    In a 2021 study, researchers first analyzed the lunar gems, known as zircon crystals.  These are microscopic rocks created under intense heat and pressure that, on Earth, are used to date objects such as impact craters. The lunar grains were left behind when the moon formed following a colossal collision between Earth and a Mars-size planet, named Thea.

-

-    The analysis, which involved measuring the decay rate of different versions, or isotopes, of uranium and lead in the crystals' outer layers, revealed that the samples could be up to

4.46 billion years old.

-

-   However, the 2021 study authors noted that there was a large amount of uncertainty in their dating method. As

a result, the oldest confirmed lunar zircon crystals remained a group that was part of a separate Apollo 17 sample that was analyzed in a 2009 study, which put the moon's earliest possible birth date at around 4.42 billion years ago.

-

-   This new study, Oct. 23, 2023, reanalyzed the crystals from the 2021 study, paying close attention to how the lead atoms clustered within the crystals. This confirmed that the crystals are indeed around 4.46 billion years old.

-

-    These crystals are the oldest known solids that formed after the giant impact.   And, because we know how old these crystals are, they serve as an anchor for the lunar chronology.

-

-  Earth is approximately 4.54 billion years old. So based on the newest study, the zircon crystals were formed around 80 million years after our planet formed. However, the collision that birthed the moon could have actually happened even earlier. 

-

-   After the Earth-Thea crash, the infant moon's surface would have been covered by a magma ocean due to the intense energy of the collision. Therefore, the lunar zircon crystals could only have properly solidified into their current state once the magma ocean had cooled down.

-

-   In a 2017 study, researchers created a computer model based on data from multiple lunar zircon samples to predict how long the magma cooling process may have taken and, as a result, when the collision actually took place. This revealed that the moon could be up to 4.51 billion years ago.

-

-    Our understanding of the moon's history and geological evolution is constantly changing with new discoveries.

-

-   In July, 2021,  researchers revealed that the "man in the moon" is 200 million years older than previously thought. And in November 2022, lunar samples collected by China's now-defunct Chang'e 5 rover revealed that volcanic eruptions occurred on the moon as recently as 2 billion years ago, which is around 1 billion years later than we realized.

-

-   Therefore, there is every chance that the moon's official birth date will be revised again at a later date.  I have enough trouble remember my own birthday.

-

-

March 23, 2023              MOON   -  how old is the moon?                  4401

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--------------------- ---  Wednesday, March 27, 2024  ---------------------------------

 

 

 

 

 

           

 

 

- 4406 - UNIVERSE - expanding at different rates?

 

-    4406  -  UNIVERSE  -  expanding at different rates?  -   James Webb telescope confirms there is something seriously wrong with our understanding of the universe.  Depending on where we look, the universe is expanding at different rates. Now, scientists using space telescopes have confirmed that the observation is not down to a measurement error.

-------------------------  4406 -  UNIVERSE  -  expanding at different rates?

-    Astronomers have used the James Webb and Hubble space telescopes to confirm one of the most troubling conundrums in all of physics that the universe appears to be expanding at bafflingly different speeds depending on where we look.

-

-   This problem is known as the “Hubble Tension”  It has the potential to alter or even upend cosmology altogether. In 2019, measurements by the Hubble Space Telescope confirmed the puzzle was real; in 2023, even more precise measurements from the James Webb Space Telescope (JWST) confirmed the discrepancy.

-

-   Now, a triple-check by both telescopes working together appears to have put the possibility of any measurement error to bed for good. The study, published February 6, 2024 suggests that there may be something seriously wrong with our understanding of the universe.

-

-    With measurement errors negated, what remains is the real and exciting possibility we have misunderstood the universe.  In 1998 there was the discovery of “dark energy”, the mysterious force behind the universe's accelerating expansion.

-

-   Currently, there are two "gold-standard" methods for figuring out the “Hubble constant” for the universe expansion rate. The first involves poring over tiny fluctuations in the cosmic microwave background (CMB). an ancient relic of the universe's first light produced just 380,000 years after the Big Bang.

-

-    Between 2009 and 2013, astronomers mapped out this microwave fuzz using the European Space Agency's Planck satellite to infer a Hubble constant of  “46,200 mph per million light-years, or 67 kilometers per second per megaparsec (km/s/Mpc).

-

-   The second method uses pulsating stars called “Cepheid variables”. Cepheid stars are dying, and their outer layers of helium gas grow and shrink as they absorb and release the star's radiation, making them periodically flicker like distant signal lamps.

-

-    As Cepheids get brighter, they pulsate more slowly, giving astronomers a means to measure their absolute brightness. By comparing this brightness to their observed brightness, astronomers can chain Cepheids into a "cosmic distance ladder" to peer ever deeper into the universe's past. With this ladder in place, astronomers can find a precise number for its expansion from how the Cepheids' light has been stretched out, or red-shifted.

-

-    But this is where the mystery begins. According to Cepheid variable measurements the universe's expansion rate is around 74 km/s/Mpc: an impossibly high value when compared to Planck's measurements of 67 km/s/Mpc.  Cosmology had been hurled into uncharted territory.

-

-   Initially, some scientists thought that the disparity could be a result of a measurement error caused by the blending of Cepheids with other stars in Hubble's aperture. But in 2023, the researchers used the more accurate JWST to confirm that, for the first few "rungs" of the cosmic ladder, their Hubble measurements were right. Nevertheless, the possibility of crowding further back in the universe's past remained.

-

-    To resolve this issue astronomers built on their previous measurements, observing 1,000 more Cepheid stars in five host galaxies as remote as 130 million light-years from Earth. After comparing their data to Hubble's, the astronomers confirmed their past measurements of the Hubble constant.

-

-    We've now spanned the whole range of what Hubble observed, and we can rule out a measurement error as the cause of the Hubble Tension with very high confidence.  Combining Webb and Hubble gives us the best of both worlds. We find that the Hubble measurements remain reliable as we climb farther along the cosmic distance ladder.

-

-    The tension at the heart of cosmology is here to stay.

-

-

March 25, 2023        UNIVERSE  -  expanding at different rates?          4406

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--------------------- ---  Wednesday, March 27, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4405 - PLANETS - how do atmospheres vary?

 

-    4405  -  PLANETS  -  how do atmospheres vary?   -   What can they teach us about finding life beyond Earth?   Why study impact craters, planetary surfaces, exoplanets, astrobiology, solar physics, and comets, and what these fantastic scientific fields can teach researchers and space fans regarding the search for life beyond Earth?

-------------------------  4405 -  PLANETS  -  how do atmospheres vary?

-   Planetary atmospheres play a key role in better understanding our own solar system. It can teach us about finding life beyond Earth.  We think the sun was much dimmer in the early history of the solar system, yet Earth and Mars each were as warm or warmer than now. How is this possible?

-

-    Venus and Mars have carbon dioxide dominated atmospheres with more CO2 in the vertical column than Earth. Yet one is colder than Earth and the other warmer. Even though Venus is closer to the sun its clouds reflect so much light that it effectively has less sunlight than Earth, yet its surface is warm enough to melt lead. How is this possible?

-

-    We need to understand other atmospheres to understand the past and future of Earth.  Aside from Earth, Venus, and Mars, the other planetary bodies in our solar system that possess atmospheres include Jupiter, Saturn, Uranus, Neptune, dwarf planet Pluto, and Saturn’s largest moon, Titan, which is the only solar system moon with a dense atmosphere.

-

-    The formation and evolution of these atmospheres are what scientists are attempting to better understand via computer models that are often combined with data obtained by ground- or space-based telescopes. Through this, scientists have learned, and continue to learn, a great deal about the atmospheres of these intriguing and mysterious worlds that inhabit our solar system. But even with all the instruments and technological advancements, what are some of the benefits and challenges of studying planetary atmospheres?

-

-    The same climate models used for Earth are now used for other planets, such as Mars. When the models fail on Earth it is tempting to force them to match Earth data rather than fixing the physics and chemistry in the models. Having the examples from other planets force us to look for errors in Earth models or in our understanding of how Earth climate models work.

-

-    Planetary atmospheres within our own solar system range from sulfuric acid and carbon dioxide (Venus) to carbon dioxide (Mars) to hydrogen and helium (Jupiter, Saturn, Uranus, and Neptune) to nitrogen and methane (Titan and Pluto).

-

-    Despite the sulfuric acid within Venus’ atmosphere, past studies have postulated the possibility of Venus’ higher altitudes potentially having the ingredients to support life as we know it. These unique worlds could offer a glimpse of what scientists could find beyond our solar system, known as exoplanets.

-

-     What can studying planetary atmospheres within our own solar system teach us about exoplanet atmospheres?  We expect a wide range of exoplanetary atmospheres, some are so hot that they likely are raining metals. Even in the solar system there are planets raining condensed natural gas. So, the solar system planets are analogs for exoplanets, but there are definitely exoplanets very different from solar system planets.

-

-    Since the distance to exoplanets ranges from a few light-years to hundreds of light-years, it takes extremely powerful instruments to study their atmospheres. James Webb Space Telescope (JWST) has examined the atmospheres of several exoplanets, including “WASP-39 b”, which is located just under 700 light-years from Earth.

-

-     With its powerful infrared instruments, JWST successfully identified water, carbon dioxide, and potassium on this Jupiter-sized world. As demonstrated on Earth, water is essential for life as we know it. Therefore, finding water on an exoplanet could indicate its likelihood for life, as well.

-

-    Out of the almost 5,600 confirmed exoplanets to date only 69 are deemed potentially habitable. This is primarily due to their orbit residing within their star’s habitable zone (HZ), meaning they orbit at the correct distance from their star for liquid water to potentially exist on its surface, assuming the exoplanet is terrestrial (rocky) like Earth. But finding water within an exoplanet’s atmosphere could also pose the prospect for finding life, as well.

-

-   What can studying planetary atmospheres teach us about finding life beyond Earth?  The Earth’s atmosphere is out of chemical balance due to emissions of various gases by life.   The oxygen in Earth’s atmosphere is not compatible with the methane in the atmosphere. The methane is largely a waste product of life. So, trying to detect life elsewhere is most likely going to start with looking at the chemistry of exoplanet atmospheres for signs of chemical imbalance.

-

-   The scientific discipline responsible for studying planetary atmospheres is known as atmospheric science and encompasses several sub-disciplines, including computer science, astronomy, physics, and meteorology, just to name a few. It is through constant collaboration and innovation of these sub-disciplines that allows scientists to study planetary atmospheres both within and beyond our solar system.

-

-   The most interesting is Mars, because there is a lot of data for Mars, and Mars once had a climate more like Earth’s than the barren desert it is now. Titan, a moon of Saturn is also interesting because it has methane rain, and lakes and seas of hydrocarbons. It also is shrouded in a haze composed of complex organic material.

-

-    How will planetary atmospheres help us better understand our place in the universe in the coming years and decades? Only time will tell, and this is why we science!

-

-

March 25, 2023       PLANETS  -  how do atmospheres vary?                4405

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---   Some reviews are at:  --------------     http://jdetrick.blogspot.com ----- 

--  email feedback, corrections, request for copies or Index of all reviews

---  to:  ------    jamesdetrick@comcast.net  ------  “Jim Detrick”  -----------

--------------------- ---  Wednesday, March 27, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4404 - PLANETS - why is solar system flat?

 

-    4404  -   PLANETS  -  why is solar system flat?  -    Have all 8 planets in our solar system ever aligned?    All eight planets will never truly be in a straight line, but they can get close to it.  The Sun, followed by Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune & Pluto.

----------------------------  4404 -  PLANETS  -  why is solar system flat?

-    The last time the eight planets were grouped within 30 degrees of each other was January 1, 1665.   As the solar system's planets rove around the sun, sometimes a few will appear to line up in the sky.

-

-    It depends on how generous you are with the definition of "align" for the solar system's planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.   To start with, the orbits of the planets are all tilted to different degrees with respect to the sun's equator. This means that, when planets appear to line up in the sky, in reality they are likely not positioned in a straight line in 3D space.

-

-    The concept of planetary alignment is more about the visual appearance from our perspective on Earth rather than any significant physical alignment in space.

-

-    A planetary conjunction is when two or more planets appear close together from our perspective on Earth. It's important to note that the planets are never actually close together. Even when two planets appear lined up to a person on Earth, they are still extremely far apart in space.

-

-    The definition of how close the planets can appear to be considered aligned is not well defined.   If you measured the distance around the circle of the entire horizon, that would equal 360 degrees. To give an idea of the horizon's enormity, the full moon appears only half a degree across, the diameter of the full Moon.

-

-   Astronomer have calculated that the three innermost planets — Mercury, Venus and Earth — "line up within 3.6 degrees on average every 39.6 years" .

-

-    Lining up more planets takes time.   All eight planets will line up within 3.6 degrees every 396 billion years.   Which means it has never occurred and will not occur, since the sun will transform into a white dwarf in roughly 6 billion years from now. During this process, the sun will become a red giant and expand in size to swallow both Mercury and Venus, and probably the Earth as well. Thus, only five planets will remain in our solar system.

-

-   The chances are worse for all eight planets aligning within 1 degree of sky.    This will occur, on average, every 13.4 trillion years. In comparison, the universe is about 13.8 billion years old.

-

-    If you consider the eight planets aligned if they are in the same 180-degree-wide patch of sky, the next time that will happen is May 6, 2492. The last time the eight planets were grouped within 30 degrees was Jan. 1, 1665, and the next time will be March 20, 2673.

 

-    Planetary alignments have virtually no significant physical effects on Earth.  The only impact to life on Earth during an alignment is the wonderful display visible in the sky.  There is no danger of enhanced earthquakes or anything like that. The change in the gravitational force that the Earth will experience due to any planetary alignment is negligible.

-

-   Why do the planets in the solar system even orbit on the same plane?   A  model of the solar system usually shows that the sun, planets, moons and asteroids sit roughly on the same plane.

-

-   About 4.5 billion years ago the solar system was just a massive, spinning cloud of dust and gas.   That massive cloud measured 12,000 astronomical units (AU) across; 1 AU is the average distance between Earth and the sun, or about 93 million miles. That cloud became so big, that even though it was just filled with dust and gas molecules, the cloud itself started to collapse and shrink under its own mass.

-

-   As the spinning cloud of dust and gas started to collapse, it also flattened. Imagine a pizza maker throwing a spinning slab of dough into the air. As it spins, the dough expands but becomes increasingly thin and flat. That's what happened to the very early solar system.

-

-    Meanwhile, in the center of this ever-flattening cloud, all those gas molecules got squeezed together so much, they heated up. Under the immense heat and pressure, hydrogen and helium atoms fused and kick-started a billions-of-years-long nuclear reaction in the form of a baby star: the sun.

-

-    Over the next 50 million years, the sun continued to grow, collecting gas and dust from its surroundings and burping out waves of intense heat and radiation. Slowly, the growing sun cleared out a doughnut of empty space around it.

-

-   As the sun grew, the cloud continued to collapse, forming "a disk around the star that becomes flatter and flatter and expands and expands with the sun at the center.

-

-    Eventually, the cloud became a flat structure called a protoplanetary disk, orbiting the young star. The disk stretched hundreds of AU across and was just one-tenth of that distance thick.

-

-   For tens of millions of years thereafter, the dust particles in the protoplanetary disk gently swirled around, occasionally knocking into each other. Some even stuck together. And over those millions of years, those particles became millimeter-long grains, and those grains became centimeter-long pebbles, and the pebbles continued to collide and stick together.

-

-    Eventually, most of the material in the protoplanetary disk stuck together to form huge objects. Some of those objects grew so big that gravity shaped them into spherical planets, dwarf planets and moons. Other objects became irregularly shaped, like asteroids, comets and some small moons.

-

-    Despite these objects' different sizes, they stayed more or less on the same plane, where their building materials originated. That's why, even today, the solar system's eight planets and other celestial bodies orbit on roughly the same level.

-

-

March 26, 2023           PLANETS  -  why is solar system flat?             4404

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---  to:  ------    jamesdetrick@comcast.net  ------  “Jim Detrick”  -----------

--------------------- ---  Tuesday, March 26, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4403 - BRIGHTEST QUASAR

 

-    4403  -  BRIGHTEST  QUASAR -    The brightest quasar ever seen is powered by black hole that eats a 'sun a day'.   This quasar, as bright as 500 trillion suns, has evaded astronomers for over 40 years because of its incredible luminosity. Not only is it the brightest quasar ever seen, but it's also the brightest astronomical object in general ever seen. It's also powered by the hungriest and fastest-growing black hole ever seen.   It consumes the equivalent of over one sun's mass a day.

---------------------------------------------  4403 -  BRIGHTEST  QUASAR

-

-   The quasar, “J0529-4351”, is located so far from Earth that its light has taken 12 billion years to reach us, meaning it is seen as it was when the 13.8 billion-year-old universe was just under 2 billion years old.

-

-    The supermassive black hole at the heart of the quasar is estimated to be between 17 billion and 19 billion times the mass of the sun; each year, it eats, or "accretes" the gas and dust equivalent to 370 solar masses. This makes J0529-4351 so luminous that if it were placed next to the sun, it would be 500 trillion times brighter than our brilliant star.

-

-     J0529-4351 was spotted in data over 4 decades ago but was so bright that astronomers failed to identify it as a quasar.    How did a quasar fooled astronomers for 44 years?

-

-    Quasars are regions at the hearts of galaxies that host supermassive black holes surrounded by the gas and dust these voids feed on. The violent conditions in disks of matter around such active black holes, called accretion disks and generated by the immense gravity of the objects, heat the gas and dust and cause it to glow brightly.

-

-   Any matter in these disks that doesn't get accreted by a black hole is channeled to the poles where it is blasted out as a jet of particles at near the speed of light, also generating powerful light. As a result, quasars in these “Active Galactic Nuclei” (AGN) regions can shine brighter than the combined light of billions of stars in the galaxies around them.

-

-    The light of J0529-4351 comes from the massive accretion disk that feeds the supermassive black hole, which the team estimates has a diameter of around 7 light-years. That means crossing this accretion disk would be equivalent to traveling between Earth and the sun around 45,000 times.

-

-    It is a surprise that it has remained unknown until today when we already know about a million less impressive quasars. It has literally been staring us in the face until now.  The Quasar J0529-4351 was initially spotted in the Schmidt Southern Sky Survey, which dates back to 1980, but it took decades to confirm it was a quasar to begin with. Large astronomical surveys deliver so much data that astronomers need machine-learning models to analyze them and sort quasars from other celestial objects.

-

-    This quasar is so bright that models passed it over believing it to be a star located relatively close to Earth.   This misclassification was spotted in 2023, when astronomers realized J0529-4351 is, in fact, a quasar after having a look at the object's region using the 2.3-meter telescope at the Siding Spring Observatory in Australia.

 

-    The new discovery that this is actually the brightest quasar ever was made when the X-shooter spectrograph instrument on the Very Large Telescope (VLT) in the Atacama Desert region of Northern Chile followed up on J0529-4351. 

-

-    The astronomers thinks the supermassive black hole at the heart of this quasar is feeding near the Eddington limit, or the point at which the radiation it puts out should push away gas and dust, cutting off this black hole's cosmic larder.

-

-   Confirming this theory will require a further detailed investigation. Fortunately, however, the greedy supermassive black hole is the perfect target for an upgraded “GRAVITY + “ instrument at the VLT, which will improve the high-contrast precision on bright objects.  J0529-4351 will also be investigated by the upcoming Extremely Large Telescope (ELT), currently under construction in the Atacama Desert.

-

-   However, it is the thrill of finding something new and exciting that drives the leader of the team behind this record-breaking discovery. 

-

-

March 24, 2023              BRIGHTEST  QUASAR                            4403

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--------------------- ---  Monday, March 25, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4402 - DARK MATTER TESTS -

 

-    4402  - DARK  MATTER  TESTS  -     Most, if not all galaxies are surrounded by halos of this mysterious, unknown, but ubiquitous material.  This stuff also played a role in galaxy formation. The nature of that role is something astronomers are still figuring out. Today, they’re searching the infant Universe, looking for the tiniest, brightest galaxies. That’s because they could help tell the tale of dark matter’s role in galactic creation.

------------------------------------------------  4402 -  DARK  MATTER  TESTS

-

-    Computer models take into account previously neglected interactions between dark matter and the primordial “stuff” of the Universe. That would be hydrogen and helium gas. The result of the simulations mean tiny, bright galaxies that formed more quickly than in computer models that didn’t include those motions. Now astronomers just need to find them, using JWST, in an effort to see if their theories of dark matter hold up.

-

-    “Dark Matter” Interactions with “Supersonic Baryonic” interactions between baryonic matter in the early Universe.    The clouds of gas moved at supersonic speeds past clumps of dark matter. It bounced off the dark matter. Eventually, after millions of years, the gaseous material fell back together to form stars in a blast of star birth.

-

-    The existence of those smaller, brighter, more distant galaxies could confirm the so-called “cold dark matter” model. It suggests that the Universe was in a hot dense state containing only gases after the Big Bang. Over time, it evolved to a lumpy distribution of galaxies and eventually galaxy clusters. Along the way, stars and galaxies formed, but the earliest steps likely depend on gravitational interaction with dark matter.

-

-    JWST has seen some early galaxies during its time in operation. It hasn’t detected the very earliest ones—yet. However, the images it has provided are tantalizing hints at what might exist in earlier epochs and could provide insight into the role of dark matter. So, it makes sense that astronomers want to push its view back in time as far as they can. And, that means looking for bright patches of light that existed a few hundred million years after the Big Bang.

-

-    The discovery of patches of small, bright galaxies in the early universe would confirm that we are on the right track with the cold dark matter model because only the velocity between two kinds of matter can produce the type of galaxy we’re looking for.  If dark matter does not behave like standard cold dark matter and the streaming effect isn’t present, then these bright dwarf galaxies won’t be found and we need to go back to the drawing board.

-

-     JWST will begin to look for galaxies that are much brighter than expected. If they exist, that will likely prove the interactions occurred early in cosmic time. If none can be found, then maybe scientists still might not understand dark matter interactions.

-

-   The standard cosmological model says that the gravitational pull of clumps of dark matter in the early Universe attracted ordinary matter. Eventually, that caused stars to form, followed by galaxies. Dark matter is thought to move more slowly than light. So, astronomers predicted that the star- and galaxy-formation processes happened very gradually.

-

-   But, what if something else was going on more than 13 billion years ago? How would that change things? It was a time before the first galaxies formed. But, it was a time when ordinary matter in the form of large over densities of hydrogen and helium gas streamed through the expanding Universe. It bounced off slower-moving clumps of dark matter and outran its gravitational pull, at least for a time. Then, the baryonic matter massed together again, under the influence of dark matter. That’s when the star birth fireworks began.

-

-    While the streaming suppressed star formation in the smallest galaxies, it also boosted star formation in dwarf galaxies, causing them to outshine the non-streaming patches of the universe.   The accumulated gas began to fall together after millions of years. That led to a huge burst of star formation. Lots of massive hot, young stars began to shine, out-brilliancing the stars in other small galaxies. Ultimately what this means is that since dark matter is impossible to “see”, those brightly shining patches of galaxies could be indirect evidence of its existence.

-

-   The discovery of patches of small, bright galaxies in the early universe would confirm that we are on the right track with the cold dark matter model because only the velocity between two kinds of matter can produce the type of galaxy we’re looking for.

-

-     JWST should be able to peer into regions of the Universe where tiny infant galaxies are brighter than astronomers expect them to be.  That extreme luminosity will help JWST spot them, showing them as they looked at a time when the Universe was only a few hundred million years old. Because dark matter is impossible to study directly, searching for those bright patches of baby galaxies in the early Universe could offer an effective test for theories about dark matter and its role in shaping the first galaxies.

-

- 

March 24, 2023               DARK  MATTER  TESTS                          4402

------------------------------------------------------------------------------------------                                                                                                                       

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--------------------- ---  Monday, March 25, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4401 - EMERGENT GRAVITY - instead of dark matter?

 

-    4401  - EMERGENT  GRAVITY  -  instead of dark matter?  -    In 2009, theoretical physicists proposed a radical reformulation of gravity. In this theory, gravity is not a fundamental force but rather a manifestation of deeper hidden processes. But in the 15 years since then, there hasn't been much experimental support for the idea. So where do we go next?

-------------------------  4401 -  EMERGENT  GRAVITY  -  instead of dark matter?

-    “Emergence” is common throughout physics. The property of temperature, for example, isn't an intrinsic property of gases. Instead, it's the emergent result of countless microscopic collisions. We have the tools to match those microscopic collisions to temperature; indeed, there is an entire branch of physics, known as statistical mechanics, that makes these temperatures connections known.

-

-    In other areas, the connections between microscopic behaviors and emergent properties aren't so clear. For example, while we understand the simple mechanisms behind superconductivity, we do not know how microscopic interactions lead to the emergence of high-temperature superconductors.

-

-    “Verlinde's theory” is based on what Stephen Hawking and Jacob Bekenstein observed in the 1970s: Many properties of black holes can be expressed in terms of the laws of thermo-dynamics. However, the laws of thermodynamics are themselves emergent from microscopic processes. TheVerlinde says there was more than a mere coincidence and indicated that what we perceive as gravity may be emerging from some deeper physical process.

-

-   “Statistical mechanics” can be used for describing these “emergent” properties.   These techniques applied to gravity arrive at an alternate formulation of gravity. And because gravity is also tied to our concepts of motion, inertia, space and time, this means our entire universe is also emergent from those same deeper processes.

-

-   In 2016, Verlinde expanded his theory by discovering that a universe containing dark energy naturally leads to a new emergent property of space, thus allowing it to push inward on itself in regions of low density.

-

-   This discovery led to a flurry of excitement, as it provided an alternative explanation for “dark matter” . Currently, astronomers believe that dark matter is a mysterious, invisible substance that makes up the bulk of all the mass of every galaxy . While that hypothesis has been able to explain a vast wealth of observations, from the rotation rates of stars within galaxies to the evolution of the largest structures in the cosmos, we have yet to identify the mysterious particle.

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-    Dark matter is a form of matter that cannot be detected by telescopes as it emits no radiation. It is thought that cold dark matter first formed after the Big Bang. This matter then collapsed under its own weight to form vast halos which sucked in normal matter to form visible matter, such as galaxies.

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-   In Verlinde's theory of emergent gravity, as soon as you enter low-density regions, basically, anything outside the solar system, gravity behaves differently than we would expect from Einstein's theory of general relativity . At large scales, there is a natural inward pull to space itself, which forces matter to clump up more tightly than it otherwise would.

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-   This idea was exciting because it allowed astronomers to find a way to test this new theory. Observers could take this new theory of gravity and put it in models of galaxy structure and evolution to find differences between it and models of dark matter.

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-    Over the years, however, the experimental results have been mixed. Some early tests favored emergent gravity over dark matter when it came to the rotation rates of stars. But more recent observations haven't found an advantage. And dark matter can also explain much more than galaxy rotation rates; tests within galaxy clusters have found emergent gravity coming up short.

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-    This isn't the end of “emergent gravity”. The idea is still new and requires a lot of assumptions in its calculations to make it work. Without a fully realized theory, it's hard to tell if the predictions it makes for the behavior of galaxies and clusters accurately represent what emergent gravity would tell us. And astronomers are still trying to develop more stringent tests, like using data from the cosmic microwave background .

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-   Emergent gravity remains an intriguing idea. If it's correct, we would have to radically reshape our understanding of the natural world and see gravity and motion, and even more fundamental concepts, like time and space, through a lens of emergence from deeper, more complicated interactions. But for right now, it remains simply an intriguing idea. Only time and extensive observational testing will tell us if we're on the right track.

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March 23, 2023           EMERGENT  GRAVITY  -  instead of dark matter?       4401

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