- 2866 - BIG BANG - creations. - When I was first in school science believed that the universe has always existed and always will. Few people challenged this or even suspected it might not be true. That started to change in 1910 with the publication of Albert Einstein’s general theory of relativity. This review discusses the discoveries this all started.
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- The first models developed from Einstein’s equations showed that the universe does not have to be static and unchanging, but it can evolve. The equations themselves were unstable and produced infinities in either direction.
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- In the 1920s, Belgian priest and astronomer Georges Lemaître developed the concept of the Big Bang. Coupled with Edwin Hubble’s observations of an expanding universe, astronomers were coming around to the idea that the universe had a beginning and could have an end.
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- It wasn’t until the 1960s that strong observational evidence supported the Big Bang and I first started to read about it. The breakthroughs were the discovery of the cosmic microwave background radiation and the realization that active galaxies existed preferentially in the distant universe, which meant they existed when the cosmos was much younger than it is today, and so the universe has been evolving.
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- By the 1980s, most astronomers were convinced that the universe began with a Bang, but they had little clue how it would end. There were basically three scenarios, all based on how much matter the universe contained.
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-------------------- If the cosmos had less than a certain critical density, the universe was “open” and would expand forever;
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-------------------- If the density were above the critical value, the universe was “closed” and the expansion ultimately would stop and then reverse, leading to a “Big Crunch”;
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------------------- If the universe were at the critical density, it was “flat” and expansion would continue forever, but the rate would eventually slow to zero.
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- Observations seemed to favor an open universe, with astronomers finding only about 1 percent of the matter needed to halt expansion. But scientists knew that a lot of ‘dark matter“, non-luminous material that nevertheless has gravitational pull, existed. Would it be enough to stop the expansion?
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- In the 1980s Alan Guth proposed his inflation hypothesis. This says a brief period of hyper expansion in the universe’s first second made the universe flat. Astronomers eagerly accepted inflation because it solved some of the problems with the Big Bang model and also was philosophically pleasing.
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- But the most remarkable development came in the late 1990s. Astronomers using the Hubble Space Telescope and several large ground-based instruments were examining dozens of distant type 1a supernovae.
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- This variety of exploding star arises when a white dwarf in a binary system pulls enough matter from its companion star to push it above 1.4 solar masses. At that stage, the white dwarf can no longer support itself, which triggers a runaway nuclear chain reaction that causes the star to explode.
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- Because all these exploding white dwarfs have the same mass, they all have the same approximate peak luminosity. Simply measure how bright the type 1a supernova appears, and you can calculate its distance.
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- Astronomers found the most distant supernovae were fainter than their distances would imply. The only way this makes sense is if the expansion of the universe is speeding up. Gravity works to slow down the expansion, and did so successfully for billions of years. But it now appears we have entered an era where gravity is no match for the mysterious force causing the expansion to accelerate.
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- The force may take the form of “dark energy“, “quintessence“, the “cosmological constant“, or some other strange name with a different effect. But the results of this energy, which makes up 68 percent of the mass-energy content of the cosmos, likely will lead to unending expansion.
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- Researchers think that a newly identified subatomic particle may have formed the universe's “dark matter” right after the Big Bang, approximately 13.8 billion years ago.
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- While scientists have determined that up to 27% of the matter in the universe could be dark matter, our understanding of what the mysterious substance might be is still lacking, as no one has ever directly observed it. Now, in a new study, nuclear physicists have suggested that dark matter could be made from a newly identified particle: the “d-star hex quark“.
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- Matter can be broken down into molecules, which can be broken down further into atoms and even further into the subatomic particles protons and neutrons. Then, when you break those down, you get quarks. So, everything we've ever seen, touched or tasted has ultimately been made up of quarks.
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- While neutrons and protons are each made up of three quarks, hexaquarks are made up of six quarks. Their existence was predicted for decades, and in 2014, researchers were able to confirm the existence of hexaquarks.
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- Though these exotic particles are made up of more quarks than protons are, hexaquarks are actually much smaller than the more familiar particles. Hexaquarks also decay much faster than other subatomic particles.
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- Hexaquarks are also a type of boson particle, meaning that multiple d-star hexaquarks can combine in ways different from how protons and neutrons combine. Are hexaquarks be the key to understanding dark matter?
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- During the early period of the universe, d-star hexaquarks could have cooled and expanded into what is known as a Bose-Einstein condensate (BEC). This is a fifth state of matter that forms when a cloud of atoms or subatomic particles cools to temperatures approaching absolute zero, or 0 Kelvin (minus 459.67 degrees Fahrenheit).
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- At these extreme temperatures, the particles ,or atoms, clump together into a single entity that can be described by a wave function. In other words, the particles coalesce and behave like a single particle.
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- While hexaquarks decay quickly in a lab, they are much more stable and long-lasting within a neutron star and, the researchers think, possibly also in a BEC, which is dark matter.
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- Researchers will perform experiments to study the properties of hexaquarks, like their size and how they interact with both other hexaquarks and normal, or nuclear matter (protons and neutrons inside a nucleus).
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- That could be dark matter but what could e dark energy? As far as cosmologists can tell, the mysterious force behind the accelerated expansion of the universe, a force that we call dark energy, remains constant.
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- It's entirely possible that dark energy changed in the past and those changes may have flooded the universe with the particles of our everyday lives. Something strange is happening to the cosmos. It's expanding, but it's also full of matter. The gravitational attraction of all that stuff ought to be slowing down that expansion of the universe as time goes on.
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- And yet, the expansion isn't slowing down. It's not even staying at the same rate. It's getting faster. Every day that goes by, our universe gets bigger and bigger, faster and faster. Cosmologists call this accelerated expansion "dark energy," in part because we basically have no idea what's causing it, where it came from or what it will do in the future.
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- All we know is that starting about 5 billion years ago, dark energy turned on and stayed on. We also know that during those 5 billion years, dark energy’s “strength” (as measured by its density) has stayed constant. It doesn't appear to be getting weaker or stronger with time, making it a cosmological “constant“.
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- While we barely understand the nature or cause of dark energy, we do know that it can't do much more than accelerate the expansion of the universe. That's because the universe is old, cold and mostly dead.
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- This big-picture means that there isn't a lot of energy to go around. If dark energy did something now, like change over time, it wouldn't have a big effect, because dark energy is already incredibly feeble.
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- Yes, it’s accelerating the expansion of the universe, but only mildly, which is why it took us so long to identify its effects in the first place. This weakness limits both what dark energy can do today and what we can learn about it; there just aren't a lot of effects for cosmologists to measure. But the early universe was much hotter, denser, more compact and, most especially, more energetic.
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- While dark energy emerged onto the cosmic scene about 5 billion years ago, that wasn't necessarily its first appearance. Dark energy could have been alive and kicking in the young cosmos, doing all sorts of interesting things before temporarily subsiding into the background.
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- Researchers have found that a brief fluctuation in dark energy could have flooded the early universe with exotic particles like quarks, gluons and leptons that would eventually congeal into the atoms we know today. According to these researchers, this flood must have happened after inflation, when the very early universe grew incredibly large in a very short amount of time.
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- After this inflation, the universe was altogether empty; all of the pre-inflation was simply blown away like dust in the wind. Something had to come after that to "reheat" the cosmos, bringing in a fresh round of particles to the universe in what we commonly think of as "the Big Bang."
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- Most theorists think that whatever caused inflation itself must have also generated the reheating, but this new work suggests that early dark energy could have created the flood of particles by losing its own energy.
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- Of all the questions humanity has ever pondered, perhaps the most profound is, “where did all of this come from?” For generations, we told one another tales of our own invention, and chose the narrative that sounded best to us.
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- The 20th century brought us General Relativity, quantum physics, and the Big Bang, all accompanied by spectacular observational and experimental successes. These frameworks enabled us to make these theoretical predictions.
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- This led to a series of remarkable predictions, including that:
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------------------ More distant galaxies should be smaller, more numerous, lower in mass, and richer in hot, blue stars than their modern-day counterparts,
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------------------ There should be fewer and fewer heavy elements as we look backwards in time,
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------------------ There should come a time when the Universe was too hot to form neutral atoms and a leftover bath of now-cold radiation that exists from that time,
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------------------ There should even come a time where atomic nuclei were blasted apart by the ultra-energetic radiation leaving a relic mix of hydrogen and helium isotopes.
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- All four of these predictions have been observationally confirmed, with that leftover bath of radiation, originally known as the “primeval fireball” and now called the cosmic microwave background, discovered in the mid-1960s often referred to as the smoking gun of the Big Bang.
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- Does this mean that we can extrapolate the Big Bang all the way back, arbitrarily far into the past, until all the matter and energy in the Universe is concentrated into a single point. The Universe would reach infinitely high temperatures and densities, creating a physical condition known as a “singularity“ where the laws of physics as we know them give predictions that no longer make sense and cannot be valid anymore.
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- The physics of the expanding Universe, it was “a day without yesterday.” Only, there were a number of unresolved puzzles that the Big Bang posed, but presented no answers for.
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-------------------------- Why did regions that were causally disconnected had no time to exchange information, even at the speed of light and have the same temperatures as one another?
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------------------------- Why were the initial expansion rate of the Universe and the total amount of energy in the Universe which gravitates and fights the expansion perfectly balanced early on: to more than 50 decimal places?
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------------------------- Why, if we reached these ultra-high temperatures and densities early on, are there no leftover relic remnants from those times in our Universe today?
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- In 1979, a young theorist named Alan Guth had a spectacular realization that changed history. His new theory, known as “cosmic inflation“, postulated that perhaps the idea of the Big Bang was only a good extrapolation back to a certain point in time, where it was preceded by this inflationary state. Instead of reaching arbitrary high temperatures, densities, and energies, inflation states that:
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-------------------- The Universe was no longer filled with matter and radiation,
but instead possessed a large amount of energy intrinsic to the fabric of space itself,
which caused the Universe to expand exponentially where the expansion rate doesn’t change over time,
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------------------- Which drives the Universe to a flat, empty, uniform state,
until inflation ends.
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------------------ When it ends, the energy that was inherent to space itself, the energy that’s the same everywhere, except for the quantum fluctuations imprinted atop it, gets converted into matter and energy, resulting in a hot Big Bang.
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- Theoretically, this was a brilliant leap, because it offered a plausible physical explanation for the observed properties the Big Bang alone could not account for.
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--------------------- Causally disconnected regions have the same temperature because they all arose from the same inflationary “patch” of space.
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-------------------- The expansion rate and the energy density were perfectly balanced because inflation gave that same expansion rate and energy density to the Universe prior to the Big Bang.
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------------------- There were no left over, high-energy remnants because the Universe only reached a finite temperature after inflation ended.
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- In fact, inflation also made a series of novel predictions that differed from that of the non-inflationary Big Bang, meaning we could go out and test this idea. As of today, in 2020, we’ve collected data that puts four of those predictions to the test:
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------------------- The Universe should have a maximum, non-infinite upper limit to the temperatures reached during the hot Big Bang.
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------------------- Inflation should possess quantum fluctuations that become density imperfections in the Universe that are 100% adiabatic, that is with constant entropy
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------------------- Some fluctuations should be on super-horizon scales: fluctuations on scales larger than light could have traveled since the hot Big Bang. Those fluctuations should be almost, but not perfectly, scale-invariant, with slightly greater magnitudes on large scales than small ones.
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- The fluctuations from inflation get stretched across the Universe, creating over densities.
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- This means that the Big Bang wasn’t the very beginning of everything; it was only the beginning of the Universe as we’re familiar with it. Prior to the hot Big Bang, there was a state known as “cosmic inflation“, that eventually ended and gave rise to the hot Big Bang, and we can observe the imprints of cosmic inflation on the Universe today.
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- Inflation lasted for only a tiny, minuscule fraction of a second. Only for the final 10^-33 seconds of it can we observe the imprints that inflation left on our Universe. It’s possible that inflation lasted for only that duration, or for far longer.
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- It’s possible that the inflationary state was eternal, or that it was transient, arising from something else. It’s possible that the Universe did begin with a singularity, or arose as part of a cycle, or has always existed. But that information doesn’t exist in our Universe. Inflation, by its very nature, erases whatever existed in the pre-inflationary Universe.
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- Inflation is like pressing the cosmic “reset” button. Whatever existed prior to the inflationary state, if anything, gets expanded away so rapidly and thoroughly that all we’re left with is empty, uniform space with the quantum fluctuations that inflation creates superimposed atop it.
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- When inflation ends, only a tiny volume of that space. somewhere between the size of a soccer ball and a city block, will become our observable Universe. Everything else, including any of the information that would enable us to reconstruct what happened earlier in our Universe’s past, now lies forever beyond our reach.
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- It’s one of the most remarkable achievements of science of all: that we can go back billions of years in time and understand when and how our Universe, as we know it, came to be this way.
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- Revealing those answers has only raised more questions. The puzzles that have arisen this time, however, may truly never be solved.
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- If that information is no longer present in our Universe, it will take a revolution to solve the greatest puzzle of all: where did all this come from?
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- What I learn, is like I pickup like pebbles on the beach while a whole ocean of unknown is ahead of me.
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- October 17, 2020 2866
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--------------------- --- Monday, October 19, 2020 ---------------------------
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