4598 - SUPERNOVAE - new and unusual?

 

-  4598 -   SUPERNOVAE  -  new and unusual?  -     In 1181, Japanese and Chinese astronomers saw a bright light appear in the constellation Cassiopeia. It shone for six months, and those ancient observers couldn’t have known it was an exploding star. To them, it looked like some type of temporary star that shone for 185 days

----------------------------------   4598  -  SUPERNOVAE  -  new and unusual?

-   In the modern astronomical age, we’ve learned a lot more about this object. It was a supernova called “SN 1181 AD”, and we know that it left behind a remnant “zombie” star. New research examines the supernova’s aftermath and the strange filaments of gas it left behind.

-

-    Though it was seen almost 850 years ago, only modern astronomers have been able to explain SN 1181. For a long time, it was an orphan. While astronomers were able to identify the modern remnants of many other historical supernovae, SN 1181 was stubborn.

-

-    Finally, in 2013, amateur astronomer Dana Patchick discovered a nebula with a central star and named it “Pa 30”. Research in 2021 showed that Pa 30 is the remnant of SN 1181. The SN exploded when two white dwarfs merged and created a Type 1ax supernova.

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-    SN 1181 is unusual. When supernovae explode, there’s usually only a black hole or a neutron star left as a remnant. But SN 1181 left part of a white dwarf behind, an intriguing object astronomers like to call a zombie star. Strange filaments resembling dandelion petals extend from this strange star, adding to the object’s mystery.

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-   Researchers have gotten a new, close-up look at Pa 30.    Their research is titled “Expansion Properties of the Young Supernova Type Iax Remnant Pa 30 Revealed.  This recently discovered Pa 30 nebula, the putative type Iax supernova remnant associated with the historical supernova of 1181 AD, shows puzzling characteristics that make it unique among known supernova remnants, including a “unique radial and filamentary structure.

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-    The hot stellar remnant at Pa 30’s center is also unique. Its presence, as well as the lack of hydrogen and helium in its filaments, indicates that it’s the result of a rare Type1ax supernova. Since hydrogen and helium make up 90% of the chemicals in the Universe, objects without either of them are immediately interesting.

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-   The astronomers used the Keck Cosmic Imager Spectrograph (KCIS) to examine the 3D structure and the velocities of the filaments. The KCIS was built to observe the cosmic web, the intricate arrangement of gas, dust, and dark matter that makes up the large-scale structure of the Universe. The gas and dust are extremely dim, and the KCIS was made to perform spectroscopy on these types of low surface brightness phenomena.

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-   KCIS is a powerful spectrograph that can capture spectral information for each pixel in an image. It can also measure the redshift and blueshift of objects it observes, meaning it can determine their velocity and direction of movement. The researchers were able to show that material in the filaments travelled ballistically at approximately 1,000 kilometres per second.

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-   This means that the ejected material has not been slowed down, or sped up, since the explosion.   Thus, from the measured velocities, looking back in time allowed us to pinpoint the explosion to almost exactly the year 1181.

-

-    “Pa 30” has some unusual features. It’s unusually asymmetrical, while most SN remnants are more spherical. Its filamentary structure displays significant variation in ejecta distribution along the line of sight. Some filaments are more prominent than others and extend further, creating an irregular and lopsided appearance.

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-     Some parts of the nebula are travelling at different speeds and in different directions. Elements in the nebula are also distributed unevenly. Iron is far more concentrated in some regions than others. All of these features suggest that the initial explosion mechanism was asymmetric and that the ejecta in the filaments stem from the initial explosion observed in 1181.   “Pa 30” also has a very sharp inner edge with an inner gap that surrounds the zombie star.

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-    Many of Pa 30’s features suggest an asymmetric explosion as the cause.  The ejecta show a strong asymmetry in flux along the line of sight, which may hint at an asymmetric explosion. The researchers found that the total flux from redshifted filaments is 40% higher than from blueshifted filaments.

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-   An asymmetric supernova explosion suggests that the underlying physics are complex. Rotation, complex magnetic fields, and the presence of a stellar companion can all contribute to asymmetry. Coupled with the unusually hot white dwarf left behind and its high-velocity stellar wind, the evidence suggests that it was a “Type 1ax supernova”.

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-    That means the “zombie star” is likely the remnant of a failed thermonuclear explosion in a white dwarf. The white dwarf could have been just below the Chandrasekhar mass and not exploded completely.

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-    Or, it could’ve been one of the theoretically possible but elusive super-Chandrasekhar mass white dwarfs. These objects are of great interest because they could be the cause of unusually bright supernovae. If Pa 30’s progenitor was a super-Chandrasekhar mass white dwarf, it could explain some of the remnant’s unusual characteristics.

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-    3D characterization of the velocity and spatial structure of a supernova remnant tells us a lot about a unique cosmic event that our ancestors observed centuries ago. But it also raises new questions and sets new challenges for astronomers to tackle next.

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-    Further IFU spectroscopic observations with wider coverage of the nebula will confirm if there exists a global asymmetry in the nebula ejecta.

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November 4, 2024           SUPERNOVAE  -  new and unusual?                4598

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--------------------- ---  Tuesday, November 5, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4597 - EXOPLANETS - planets outside our solar system?

    

-  4597 -   EXOPLANETS  -  planets outside our solar system?  -   By watching the Sun, astronomers are learning more about Exoplanets?   We can detect the wobble of a star from the gravity of planets in orbit. Local variations in the stars can add noise to the data but researchers have been studying the Sun to help next-generation telescopes detect more Earth-like planets.

---------------------   4597  -   EXOPLANETS  -  planets outside our solar system?

-

-   To date 5,288 exoplanets have been discovered in orbit around other star systems.   Before 1992 we had no evidence of other planetary systems around other stars. Since then, and using various methods astronomers have detected more and more of the alien worlds.

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-    Techniques to detect the exoplanets range from monitoring starlight for tiny dips in brightness to studying the spectra of stars. Just over 1,000 exoplanets have been discovered using the radial technique making it one of the most successful methods.

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-   The local variations in the properties of stars has made it difficult to find smaller planets using the radial technique but a team of astronomers led by Eric B. Ford from the Department of Astronomy and Astrophysics at the Penn State University has just published a report of their findings following observations of the Sun. Observations of the Sun between January 2021 and June 2024 using the NEID Solar spectrograph at the WIYN Observatory have been used in their study.

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-   The planet, named “TOI-3757 b”, is the fluffiest gas giant planet ever discovered around this type of star.    Across the 3 years and 5 months of observations, the team identified 117,600 features which are not likely to have been caused by the weather, hardware or calibration issues so they could be used for their study. Given that the distance between the Sun and Earth is precisely known the team can use this to analyse solar observations and measure other solar variability.

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-   Impressively the team have been able to show that the NEID instrumentation is able to measure radial velocity of the Sun accurate to 0.489 meters per second. Using this data the team conclude that Scalpels algorithm (a technique developed for medicine that uses machine learning to analyse and extract data from images) performs particularly well. It can reduce the root mean square (used to analyse signal amplitude) of solar radial velocity from over 2 m/s-1 down to 0.277 m/s-1!

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-   The results are significantly better than previous studies at removing solar variability from its radial velocity observations. This suggests that the next generation of exoplanet radial velocity instruments are capable, at least technically at detecting Earth-massed planets orbiting a star like the Sun. This does require sufficient observing time which the team estimate would be about 103 nights of observations.

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November 3, 2024            EXOPLANETS  -  planets outside our solar system?          4597

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--------------------- ---  Tuesday, November 5, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4596 - NEIL ARMSTRONG - first man on the moon.

 

-  4596 -  NEIL  ARMSTRONG  -  first man on the moon.  -  On July 20, 1969, the American astronaut Neil Armstrong put his left foot on the lunar surface and famously declared, “That’s one small step for man, one giant leap for mankind.”

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   4596  -  NEIL  ARMSTRONG  -  first man on the moon. 

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-    In the 50 years since then, according to Armstrong biographer James R. Hansen, author of First Man: The Life of Neil A. Armstrong, which inspired the 2018 film First Man, some think Neil Armstrong’s famous quote is a riff on a line from J.R.R. Tolkien’s The Hobbit, in which the author describes protagonist Bilbo Baggins becoming invisible and jumping over the villain Gollum, “not a great leap for a man, but a leap in the dark.”

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-    And there is, in fact, an Armstrong-Tolkien connection. After leaving NASA, Armstrong and his family moved to a farm in Lebanon, Ohio, that he dubbed Rivendell, which is also the name of a valley and the home of the half-elf, half-human Elrond, in Lord of the Rings.    Armstrong also had Tolkien-themed email address in the ’90s.

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-   However, when Hansen asked Armstrong to set the record straight on that theory, the    Apollo 11 astronaut said he didn’t read Tolkien’s books until after the Apollo 11 mission.

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-   Was the famous quote taken from a NASA memo?   Others have said Armstrong may have been influenced by a April 19, 1969, memo he had seen from Willis Shapley, an associate deputy administrator at NASA headquarters. “The intended overall impression of the symbolic activities and of the manner in which they are presented to the world should be to signalize the first lunar landing as an historic step forward for all mankind that has been accomplished by the United States of America,” he wrote. “The ‘forward step for all mankind’ aspect of the landing should be symbolized primarily by a suitable inscription to be left on the Moon and by statements made on Earth, and also perhaps by leaving on the Moon miniature flags of all nations.”

 

-   Armstrong, however, claimed he had no recollection of the memo.  The astronaut told Hansen the line had no complicated origin story, and simply came to him in the lead-up to the historic moment: “What can you say when you step off of something? Well, something about a step. It just sort of evolved during the period that I was doing the procedures of the practice takeoff and the EVA [extravehicular activity] prep and all the other activities that were on our flight schedule at that time.”

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-   Commander Neil Armstrong climbing down the ladder of the Lunar Module (LM) the 'Eagle,' to become the first man to set foot on the Moon on July 20, 1969.   Armstrong died on Aug. 25, 2012, at the age of 82

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November 3, 2024         NEIL  ARMSTRONG  -  first man on the moon.           4596

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--------------------- ---  Tuesday, November 5, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4595 - WATER - in the early universe?

 

-  4595 -  WATER  -  in the early universe?  -    The search for life elsewhere in the universe can be reduced to the search for water. We haven't yet found lifeforms that detach this substance from our conception of "life" itself, so we have no choice but to accept the water trail as our north star in the quest to find worlds that mirror our own.

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-----------------------------------------   4595  -  WATER  -  in the early universe?

-

-    A planet outside the solar system may have a temperate water ocean about half the size of the Atlantic.   Of all currently known temperate exoplanets, “LHS 1140 b” could well be our best bet to one day indirectly confirm liquid water on the surface of an alien world beyond our solar system.

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-    “LHS 1140 b”, the exoplanet orbits a red dwarf star about a fifth the size of the sun and sits 48 light-years away from Earth in the constellation Cetus which, as luck would have it, translates to "the whale."

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-    “LHS 1140 b”  lives in its star's habitable zone, known as its "Goldilocks zone." As that nickname would suggest, this is the area around a star where it's neither too hot nor too cold for a world to host liquid water, but rather fits the standard by which the fairy tale character Goldilocks lives.

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-   Scientists couldn't quite confirm whether the exoplanet is a mini-Neptune — a planet less massive than our original Neptune, but one that still has Neptunian characteristics — or a super Earth. A super Earth is a world that's larger than Earth, but still either rocky or water-rich. 

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-    They also confirmed the world may have a nitrogen-laced atmosphere like Earth does. While it is still only a tentative result, the presence of a nitrogen-rich atmosphere would suggest the planet has retained a substantial atmosphere, creating conditions that might support liquid water.

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-     There are also a variety of other habitable-zone exoplanets scientists are drawn to. The most obvious are probably the seven worlds of the TRAPPIST-1 system, a planetary lineup that looks almost disturbingly similar to our solar system's structure.   Some of them are in the habitable zone like Earth is.

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-    The star “LHS 1140” appears to be calmer and less active making it significantly less challenging to disentangle LHS 1140 b's atmosphere.    The JWST data further suggests the exoplanet's mass might be made of between 10 percent and 20 percent liquid water.    It paints a fantastical picture of what the planet might look like in simple terms. It could look like a snowball, essentially, that orbits its star while rotating in such a way that one side always faces that star.

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-    It's like the moon's orbit around Earth; we can't ever see the far side of the moon because the moon rotates at the same rate it revolves around Earth. One side never faces us, and the other always does.

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-   Similarly, this would mean that, if the JWST's illustration of the LHS 1140 b scene is correct, the side of the planet always facing its sun would be exposed to lots of heat. This would be the part of the snowball that's "melted" into a liquid ocean.

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-   Current models indicate that if LHS 1140 b has an Earth-like atmosphere, it would be a snowball planet with a bull's-eye ocean about 2,485 miles in diameter.   The surface temperature of the ocean may very well even be a  "comfortable" 68 degrees Fahrenheit.

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-   Far more work must be done, especially with the JWST, in observing the nuances of         “LHS 1140 b”.

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November 2, 2024           WATER  -  in the early universe?                  4595

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

--------------------- ---  Sunday, November 3, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4594 - CARBON - abundant in early universe?

 

-  4594 -  CARBON  -  abundant in early universe?     The James Webb Space Telescope (JWST) has once again found evidence that the early universe was a far more complex place than we thought. This time, it has detected the signature of carbon atoms present in a galaxy that formed just 350 million years after the Big Bang.  This is one of the earliest galaxies ever observed.

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----------------------------------   4594  -  CARBON  -  abundant in early universe?

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-    Earlier research suggested that carbon started to form in large quantities relatively late, about one billion years after the Big Bang.   ‘Metal’ is the name astronomers give to any element heavier than hydrogen or helium, and seeing metals like carbon so early is a surprise.

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-    Carbon is one of the building blocks of life on Earth, but it also plays a role in galaxy and solar system formation. It is one of the materials that can accumulate in the protoplanetary disks around stars, snowballing to become planets, moons, and asteroids.

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-    But astronomers weren’t expecting to see that process happening so early.   When the first stars (called population-III stars) were born, in an era of the universe known as “Cosmic Dawn”, the only plentiful elements around were hydrogen and helium. All heavier elements didn’t yet exist. They were only able to form later, inside the cores of stars, therefore wouldn’t be detectable until well after the deaths of the first stars.

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-   Dying population-III stars that explode as supernovas throw their heavier elements out into the universe, allowing future populations of stars to develop rocky planets with more chemistry.

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-     The galaxy in question, named “GS-z12”, is thought to contain largely second generation stars, built from the remains of those first supernovas.  We were surprised to see carbon so early in the universe, since it was thought that the earliest stars produced much more oxygen than carbon-

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-    We had thought that carbon was enriched much later, through entirely different processes, but the fact that it appears so early tells us that the very first stars may have operated very differently.

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-    JWST’s Near Infrared Spectrograph allowed astronomers to break down the light coming from the distant galaxy into its constituent parts, revealing all the different wavelengths present. Every element and chemical compound has its own signature when viewed via spectroscopy, and the signal for carbon was very strong. There was also a fainter signal for neon and oxygen, though those remain tentative detections.

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-    How carbon emerged before oxygen is an open question, but one hypothesis proposes that scientists now need to revisit their models of population-III star supernovas. If these supernovas occurred with less energy than previously thought, then they would scatter carbon from the stars’ outer shells, while most of the oxygen present would be captured within the event horizon as the stars collapsed into black holes.

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-    Regardless of how it happened, there is now a strong case for heavy elements early in the universe.   JWST is revealing unexpected details about the first galaxies that will ultimately make scientists’ predictions about the evolution of the universe.

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-   Because carbon is fundamental to life as we know it, it’s not necessarily true that life must have evolved much later in the universe. Perhaps life emerged much earlier.  Although if there’s life elsewhere in the universe, it might have evolved very differently than it did here on Earth.

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October 31, 2024             CARBON  -  abundent in early universe?                     4594

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--------------------- ---  Sunday, November 3, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4592 - JAMES WEBB - finds Brown Dwarfs?

 

-  4592 -   JAMES  WEBB  - finds Brown Dwarfs?  -  James Webb telescope finds 1st possible 'failed stars' beyond the Milky Way.  It may have found dozens of elusive brown dwarfs tht are strange objects larger than planets but smaller than stars beyond the Milky Way for the first time ever.

----------------------------------------   4592  -   JAMES  WEBB  - finds Brown Dwarfs?

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-    While the astronomers were zooming in on the young star cluster NGC 602 in the nearby Small Magellanic Cloud (SMC), they spotted what may be the first evidence of brown dwarfs ever seen outside the Milky Way. Brown dwarfs, or "failed stars," are peculiar objects that are bigger than the largest planets but not massive enough to sustain nuclear fusion like the stars do.

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-    Brown dwarfs seem to form in the same way as stars, they just don't capture enough mass to become a fully fledged star.   “NGC 602” is a roughly 3 million-year-old star-forming cluster on the outskirts of the SMC, a satellite galaxy of the Milky Way that contains roughly 3 billion stars. (Our galaxy, in comparison, contains an estimated 100 billion to 400 billion stars.)

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-    Orbiting about 200,000 light-years from Earth, the SMC is one of the Milky Way's closest intergalactic neighbors and a frequent target for astronomical studies.   Previous observations of NGC 602 taken with the Hubble Space Telescope revealed that the cluster hosts a population of young, low-mass stars.

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-     Now, thanks to JWST's incredible sensitivity to infrared light, astronomers have found stellar newborns that reveal how much mass they have accumulated in their short lives.

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-    The results suggest that 64 stellar objects within the cluster have masses ranging between 50 and 84 times that of Jupiter. Brown dwarfs typically weigh between 13 and 75 Jupiter masses.  This makes many of these objects prime candidates to be the first brown dwarfs spotted beyond our galaxy.

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-    These failed stars appear to have formed in much the same way as stars like the sun through the collapse of massive clouds of gas and dust. However, for a collapsed cloud to become a star, it must continue accumulating mass until it reaches an internal temperature and pressure high enough to trigger hydrogen fusion at its core.  It begins combining hydrogen atoms into helium and releasing energy as light and heat in the process.

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-   Brown dwarfs never acquire enough mass to sustain permanent fusion, leaving them larger than a planet but smaller and dimmer than a star. This failure to ignite may be a common outcome in the universe.   Astronomers have discovered about 3,000 brown dwarfs in the Milky Way but estimate that there may be as many as 100 billion in our galaxy alone, potentially making them as common as stars themselves.

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-   Studying this group of extragalactic failed stars further could help clarify why so many stars seemingly fail to ignite.  These objects could also reveal new insights about the early universe. NGC 602 is a young cluster containing low abundances of elements heavier than hydrogen and helium, so its composition is thought to be very similar to that of the ancient universe, before later generations with the elements we see near Earth.

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-    By studying the young metal-poor brown dwarfs newly discovered in NGC 602, we are getting closer to unlocking the secrets of how stars and planets formed in the harsh conditions of the early Universe.

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October 30, 2024                  JAMES  WEBB  - finds Brown Dwarfs?              4592

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--------------------- ---  Sunday, November 3, 2024  ---------------------------------

 

 

 

 

 

           

 

 

4593 - BIG BANG THEORY - that started everything?

 

-  4593 -  BIG  BANG  THEORY  -  that started everything?   This explosion is really a period of explosive expansion, which we call “cosmic inflation”. What happens before inflation, though? Is it a “spacetime singularity”, is it spacetime foam? The answer is largely unknown

-------------------------------   4593  -  BIG  BANG  THEORY  -  that started everything?

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-    How did everything begin? It's a question that humans have pondered for thousands of years. Over the last century or so, science has homed in on an answer: the Big Bang.

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-   The Big Bang describes how the universe was born in a cataclysmic explosion almost 14 billion years ago. In a tiny fraction of a second, the observable universe grew by the equivalent of a bacterium expanding to the size of the Milky Way. The early universe was extraordinarily hot and extremely dense. But how do we know this happened?

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-   Let's look first at the evidence. In 1929, the American astronomer Edwin Hubble discovered that distant galaxies are moving away from each other, leading to the realization that the universe is expanding. If we were to wind the clock back to the birth of the universe, the expansion would reverse and the galaxies would fall on top of each other 14 billion years ago.

-

-   The English astronomer Fred Hoyle sarcastically dismissed the hypothesis as a "Big Bang" during an interview with BBC radio on March 28, 1949.  Then, in 1964, Arno Penzias and Robert Wilson detected a particular type of radiation that fills all of space. This became known as the “cosmic microwave background” (CMB) radiation. It is a kind of afterglow of the Big Bang explosion, released when the cosmos was a mere 380,000 years old.

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-    The CMB provides a window into the hot, dense conditions at the beginning of the universe. Penzias and Wilson were awarded the 1978 Nobel Prize in Physics for their discovery.

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-   More recently, experiments at particle accelerators like the Large Hadron Collider (LHC) have shed light on conditions even closer to the time of the Big Bang. Our understanding of physics at these high energies suggests that, in the very first moments after the Big Bang, the four fundamental forces of physics that exist today were initially combined in a single force.

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-   The present day four forces are gravity, electromagnetism, the strong nuclear force and the weak nuclear force. As the universe expanded and cooled down, a series of dramatic changes, called phase transitions (like the boiling or freezing of water), separated these forces.

-

-    Experiments at particle accelerators suggest that a few billionths of a second after the Big Bang, the latest of these phase transitions took place. This was the breakdown of electroweak unification, when electromagnetism and the weak nuclear force ceased to be combined. This is when all the matter in the universe assumed its mass.

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-    Moving on further in time, the universe is filled with a strange substance called quark-gluon plasma.   This "primordial soup" was made up of quarks and gluons. These are sub-atomic particles that are responsible for the strong nuclear force. Quark-gluon plasma was artificially generated in 2010 at the Brookhaven National Laboratory and in 2015 at the LHC.

-

-    Quarks and gluons have a strong attraction for one another and today are bound together as protons and neutrons, which in turn are the building blocks of atoms. However, in the hot and dense conditions of the early universe, they existed independently.

-

-    The quark-gluon plasma didn't last long. Just a few millionths of a second after the Big Bang, as the universe expanded and cooled, quarks and gluons clumped together as protons and neutrons, the situation that persists today. This event is called “quark confinement”.

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-   As the universe expanded and cooled still further, there were fewer high energy photons (particles of light) in the universe than there had previously been. This is a trigger for the process called “Big Bang nucleosynthesis” (BBN). This is when the first atomic nuclei—the dense lumps of matter made of protons and neutrons and found at the centers of atoms—formed through nuclear fusion reactions, like those that power the sun.

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-   Back when there were more high energy photons in the universe, any atomic nuclei that formed would have been quickly destroyed by them (a process called photodisintegration). BBN ceased just a few minutes after the Big Bang, but its consequences are observable today.

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-   Observations by astronomers have provided us with evidence for the primordial abundances of elements produced in these fusion reactions. The results closely agree with the theory of BBN. If we continued on, over nearly 14 billion years of time, we would reach the situation that exists today.

-

-    Scientists have no direct evidence for what came before the breakdown of “electroweak unification” (when electromagnetism and the weak nuclear force ceased to be combined). At such high energies and early times, we can only stare at the mystery of the Big Bang.

-

-   When we go backwards in time through the history of the universe, the distances and volumes shrink, while the average energy density grows. At the Big Bang, distances and volumes drop to zero, all parts of the universe fall on top of each other and the energy density of the universe becomes infinite. Our mathematical equations, which describe the evolution of space and the expansion of the cosmos, become infested by zeros and infinities and stop making sense.

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-    We call this a “singularity”.  Albert Einstein's theory of general relativity describes how spacetime is shaped. Spacetime is a way of describing the three-dimensional geometry of the universe, blended with time. A curvature in spacetime gives rise to gravity.

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-   But mathematics suggests there are places in the universe where the curvature of spacetime becomes unlimited. These locations are known as “singularities”. One such example can be found at the center of a black hole. At these places, the theory of general relativity breaks down.

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-   From 1965 to 1966, the British theoretical physicists Stephen Hawking and Roger Penrose presented a number of mathematical theorems demonstrating that the spacetime of an expanding universe must end at a singularity in the past: the “Big Bang singularity”.

-

-   Space and time appear at the Big Bang singularity, so questions of what happens "before" the Big Bang are not well defined. As far as science can tell, there is “no before”; the Big Bang is the “onset of time”.

-

-    However, nature is not accurately described by general relativity alone, even though the latter has been around for more than 100 years and has not been disproven. “General relativity” cannot describe atoms, nuclear fusion or radioactivity. These phenomena are instead addressed by “quantum theory”.

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-    Theories from "classical" physics, such as relativity, are deterministic. This means that certain initial conditions have a definite outcome and are therefore absolutely predictive. Quantum theory, on the other hand, is probabilistic. This means that certain initial conditions in the universe can have multiple outcomes.

-

-   Quantum theory is somewhat predictive, but in a probabilistic way. Outcomes are assigned a probability of existing. If the mathematical distribution of probabilities is sharply peaked at a certain outcome, then the situation is well described by a "classical" theory such as general relativity. But not all systems are like this. In some systems, for example atoms, the probability distribution is spread out and a classical description does not apply.

-

-    What about gravity? In the vast majority of cases, gravity is well described by classical physics. Classical spacetime is smooth. However, when curvature becomes extreme, near a singularity, then the quantum nature of gravity cannot be ignored. Here, spacetime is no longer smooth, but gnarly, similar to a carpet which looks smooth from afar but up-close is full of fibers and threads.

-

-    Thus, near the Big Bang singularity, the structure of spacetime ceases to be smooth. Mathematical theorems suggest that spacetime becomes overwhelmed by "gnarly" features: hooks, loops and bubbles. This rapidly fluctuating situation is called “spacetime foam”.

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-    In “spacetime foam”, causality does not apply, because there are closed loops in spacetime where the future of an event is also its past (so its outcome can also be its cause). The probabilistic nature of quantum theory suggests that, when the probability distribution is evenly spread out, all outcomes are equally possible and the comfortable notion of causality we associate with a classical understanding of physics is lost.

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-    Therefore, if we go back in time, just before we encounter the Big Bang singularity, we find ourselves entering an epoch where the quantum effects of gravity are dominant and causality does not apply. This is called the “Planck epoch”.

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-   Time ceases to be linear, going from the past to the future, and instead becomes wrapped, chaotic and random. This means the question "why did the Big Bang occur?" has no meaning, because outside causality, events do not need a cause to take place.

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-    In order to understand how physics works at a singularity like the Big Bang, we need a theory for how gravity behaves according to quantum theory. Unfortunately, we do not have one. There are a number of efforts on this front like “loop quantum gravity” and “string theory”, with its various incarnations.

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-    However, these efforts are at best incomplete, because the problem is notoriously difficult. This means that spacetime foam has a powerful mystique.   So how did our expanding and largely classical universe ever escape from spacetime foam? This brings us to “cosmic inflation”.

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-    Inflation  is defined as a period of accelerated expansion in the early universe. It was first introduced by the Russian theoretical physicist Alexei Starobinsky in 1980 and in parallel, that same year, by the American physicist Alan Guth, who coined the name.

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-    Inflation makes the universe large and uniform, according to observations. It also forces the universe to be spatially flat, which is an otherwise unstable situation, but which has also been confirmed by observations. Moreover, inflation provides a natural mechanism to generate the primordial irregularities in the density of the universe that are essential for structures such as galaxies and galaxy clusters to form.

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-    Precision observations of the “cosmic microwave background” in recent decades have spectacularly confirmed the predictions of inflation. We also know that the universe can indeed undergo accelerated expansion, because in the last few billion years it started doing it again.

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-    What does this have to do with spacetime foam?   If the conditions for inflation arise (by chance) in a patch of fluctuating spacetime, as can occur with spacetime foam, then this region inflates and starts conforming to classical physics.

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-   According to an idea first proposed by the Russian-American physicist Andrei Linde, inflation is a natural—and perhaps inevitable—consequence of chaotic initial conditions in the early universe.

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-    The point is that our classical universe could have emerged from chaotic conditions, like those in spacetime foam, by experiencing an initial boost of inflation. This would have set off the expansion of the universe. In fact, the observations by astronomers of the CMB suggest that the initial boost is explosive, since the expansion is exponential during inflation.

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-   In March 20 of 2014, Alan Guth explained it succinctly: "I usually describe inflation as a theory of the 'bang' of the Big Bang: It describes the propulsion mechanism that we call the Big Bang."

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-    From our point of view, cosmic inflation is the Big Bang, the explosion that started it all.

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October 31, 2024          BIG  BANG  THEORY  -  that started everything?             4593

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