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--------------------- 2454 - BIG BANG - how do we know what happened?
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- It all starts at the Big Bang, which "is a moment in time, not a point in space“. Specifically, it's the moment when time itself began, the instant from which all subsequent instants have been counted. The Big Bang wasn't really an explosion but rather a period when the universe was extremely hot and dense and space began to expand outward in all directions at once.
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- The Big Bang model states that the universe was an infinitely small point of infinite density. Mathematical infinities don't make sense in physics equations, so the Big Bang is really the point at which our current understanding of the universe breaks down.
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- Within a very short time, the first 0.000,000,000,000,000,000,000,000,000,0001 (that’s a decimal point with 30 zeros before the 1) seconds after the Big Bang, the cosmos could have expanded exponentially in size, driving apart areas of the universe that had previously been in close contact.
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- This era, known as “inflation“, remains hypothetical, but cosmologists like the idea because it explains why far-flung regions of space appear so similar to one another, despite being separated by vast distances.
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- A few milliseconds after the beginning of time, the early universe was really hot, between 7 trillion and 10 trillion degrees Fahrenheit hot. At such temperatures, elementary particles called quarks, which are normally bound tightly inside of protons and neutrons, wandered around freely.
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- Gluons, which carry a fundamental force known as the strong force, were mixed in with these quarks in a soupy primordial fluid that permeated the cosmos. Researchers have managed to create similar conditions in particle accelerators on Earth. But the difficult-to-achieve state only ever lasted a few fractions of a second, in terrestrial atom smashers as well as in the early universe.
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- Within a few thousandths of a second after the Big Bang the cosmos expanded, it cooled, and soon conditions were cool enough for quarks to come together into protons and neutrons. One second after the Big Bang, the universe's density dropped enough that neutrinos, the lightest and least-interacting fundamental particle , could fly forward without hitting anything, creating what's known as the cosmic neutrino background, which scientists have yet to detect.
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- For the first 3 minutes of the universe's life, protons and neutrons fused together, forming an isotope of hydrogen called deuterium as well as helium and a tiny amount of the next-lightest element, lithium.
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- But once the temperature fell, this process stopped. Finally, 380,000 years after the Big Bang, things were cool enough so that hydrogen and helium could combine with free electrons, creating the first neutral atoms.
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- Photons, which had previously run into the electrons, could now move without interference, creating the cosmic microwave background (CMB), a relic from this era that was first detected in 1965.
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- For a very long time, nothing in the universe gave off light. This period, which lasted around 100 million years, is known as the Cosmic Dark Ages. This epoch remains extremely difficult to study because astronomers' knowledge of the universe comes almost entirely from starlight. Without any stars, it's difficult to know what went on.
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- By around 180 million years after the Big Bang, hydrogen and helium began to collapse into large spheres, generating infernal temperatures in their cores that lit up into the first stars. The universe entered a period known as Cosmic Dawn, or reionization, because the hot photons radiated by early stars and galaxies broke neutral hydrogen atoms in interstellar space into protons and electrons, a process known as ionization.
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- Just how long reionization lasted is difficult to say. Because it occurred so early, its signals are obscured by later gas and dust, so the best scientists can say is that it was over by around 500 million years after the Big Bang.
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- Small early galaxies began to merge together into larger galaxies and, around 1 billion years after the Big Bang, supermassive blackholes formed in their centers. Bright quasars, which produce intense beacons of light that can be seen from 12 billion light-years away, turned on.
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- The universe continued to evolve over the next several billion years. Spots of higher density from the primordial universe gravitationally attracted matter to themselves. These slowly grew into galactic clusters and long strands of gas and dust, producing a beautiful filamentary cosmic web that can be seen today.
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- About 4.5 billion years ago, in one particular galaxy, a cloud of gas collapsed down into yellow star with a system of rings around it. These rings coalesced into eight planets, plus various comets, asteroids, dwarf planets, and moons, forming a familiar stellar system. The planet third from the central star managed to either retain water after this process, or else comets later delivered a deluge of ice and water.
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- On that third, watery world, between 3.8 and 3.5 billion years ago tiny, simple microbes winked into existence. These life-forms emerged and evolved into wondrous sea monsters and gigantic, leaf-eating dinosaurs. Eventually, about 200,000 years ago, along came upright creatures capable of marveling at our mysterious universe and discovering how the whole thing came to be.
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- Of course, that isn't the end of things. Physicists still don't quite know what's in store for the universe. That depends on the details of dark energy, a still-mysterious force driving apart the cosmos and whose properties have not been well measured.
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- In one possible future, the universe will continue to expand forever, long enough that all the stars in all the galaxies will have run out of fuel, and even black holes will evaporate into nothing, leaving behind a dead cosmos permeated by inert energy.
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- Or another possible future, gravity will eventually overcome dark energy's expansionary force, pulling all matter back together in a sort of reverse Big Bang known as the Big Crunch. Alternatively, dark energy could accelerate everything apart farther and farther from everything else, creating what's known as the Big Rip, in which the cosmos literally tears itself apart.
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- At the time of the Big Bang, the observable universe (including the materials for at least 2 trillion galaxies), fit into a space less than a centimeter across. Now, the observable universe is 93 billion light-years across and still expanding.
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- There are many questions about the Big Bang, particularly about what came before it ,if anything. Here is a chronology of our discoveries:
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- Edwin Hubble discovered something very important about the universe in 1929. The whole thing is expanding. He made his discovery by measuring something called redshift, which is the shift toward longer, red wavelengths of light seen in very distant galaxies. (The farther away the object, the more pronounced the redshift.) Hubble found that redshift increased linearly with distance in far-off galaxies, indicating that the universe isn't stationary. It's expanding, everywhere, all at once.
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- Hubble was able to calculate the rate of this expansion, a figure known as the Hubble Constant. It was this discovery that allowed scientists to extrapolate back and theorize that the universe was once packed into a tiny point. They called the first moment of its expansion the Big Bang.
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- In 1964, Arno Penzias and Robert Wilson, researchers at Bell Telephone Laboratories, were working on building a new radio receiver in New Jersey. Their antenna kept picking up a strange buzzing that seemed to come from everywhere, all the time. They thought it might be pigeons in the equipment, but removing the nests did nothing. Neither did their other attempts to reduce interference. Finally, they realized they were picking up something real.
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- What they'd detected, it turned out, was the first light of the universe: cosmic microwave background radiation. This radiation dates back to about 380,000 years after the Big Bang, when the universe finally cooled enough for photons (the wave-like particles that make up light) to travel freely.
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- The discovery lent support to the Big Bang theory and to the notion that the universe expanded faster than the speed of light in its first instant. That's because the cosmic background is quite uniform, suggesting a smooth expansion of everything at once from a small point.
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- In 1989, NASA launched a satellite called the Cosmic Background Explorer (COBE), which measured tiny variations in the background radiation. The result was a "baby picture" of the universe which shows some of the first density variations in the expanding universe. These miniscule variations probably gave rise to the pattern of galaxies and empty space, known as the cosmic web of galaxies, that we see in the universe today.
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- The cosmic microwave background also enabled researchers to find the "smoking gun" for inflation, that massive, faster-than-light expansion that occurred at the Big Bang.
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- In 2016, physicists announced that they had detected a particular kind of polarization, or directionality, in some of the cosmic microwave background. This polarization is known as "B-modes." The B-mode polarization was the first-ever direct evidence of gravitational waves from the Big Bang.
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- Gravitational waves are created when massive objects in space speed up or slow down The first gravitational waves that were ever discovered came from the collision of two black holes. The B-modes provide a new way to directly probe the early universe's expansion.
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- One of the strangest discoveries in physics is that the universe is not only expanding, it's expanding at an accelerating rate. This discovery dates back to 1998, when physicists announced the results of several long-running projects that measured particularly heavy supernovas called Type Ia supernovas.
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- The results revealed weaker-than-expected light from the most distant of these supernovas. This weak light showed that space itself is expanding: Everything in the universe is gradually getting farther away from everything else.
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- Scientists call the driver of this expansion "dark energy," a mysterious engine that could make up about 68% of the energy in the universe. This dark energy seems to be crucial to making theories of the beginning of the universe fit observations that are being conducted now.
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- Results from the Hubble Telescope, in April 2019, have deepened the puzzle of the expanding universe. The measurements from the space telescope show that the universe's expansion is 9% faster than expected from previous observations. For galaxies, every 3.3 million light-years' distance from Earth translates to an additional 46 miles per second faster than earlier calculations predicted.
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- The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), is measuring the faint light from galaxies as far away as 11 billion light-years, which will allow astronomers to see any changes in the universe's acceleration over time. They'll also be studying the echoes of disturbances in the 400,000-year-old universe, created in the dense soup of particles that made up everything right after the Big Bang.
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- They hope his will reveal the mysteries of expansion and explain the dark energy that drove it. Wow, how did you figure all this stuff out?
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- October 19, 2019.
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--------------------- Sunday, October 20, 2019 -------------------------
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