- 3754 - UNIVERSE - what is the shape of the universe? The universe may be vast, but researchers have multiple points of evidence that reveal its shape. The universe may seem shapeless because it is so vast, but it does have a form that astronomers can observe. Then there is dark energy constantly expanding the universe.
--------------------- 3754 - UNIVERSE - what is the shape of the universe?
- Physicists think the universe is flat. Several lines of evidence point to this flat universe:
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---------------------- light left over from the Big Bang,
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--------------------- the rate of expansion of the universe at different locations,
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--------------------- the way the universe "looks" from different angles.
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- In a 2003 study published in The Astrophysical Journal, astronomers measured irregularities in the cosmic microwave background (CMB), light left over from the Big Bang. The CMB was observed by NASA's Wilkinson Microwave Anisotropy Probe (WMAP) and later by the European Space Agency's Planck spacecraft.
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- The amounts of positive and negative energy in a flat universe are exactly the same, and therefore cancel each other out. If the universe had a curvature, one would be higher than the other. A flat universe corresponds to a universe with zero energy.
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- The WMAP measurements of CMB fluctuations suggested the universe was both infinite and flat. These measurements were compared with those made by the European Space Agency's Planck spacecraft, which further constrained the possible shapes the universe could take.
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- Another reason astronomers are positive the universe is flat is its rapid expansion, which is captured by the Hubble constant. Because the universe went from coming into existence as a compact ball of matter to expanding outward at remarkable speeds, all that stretching rendered it flat.
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- Evidence for the flatness of the universe also shows up in what's known as the “critical density“. At the critical density, a hypothetical universe would be flat and would eventually stop expanding, but only after an infinite time.
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- If a hypothetical universe were denser than this, it would be curved like a sphere and eventually collapse in on itself due to its gravity, the "Big Crunch."
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- But all measurements of our real universe suggest it is just below the critical density, meaning the universe is both flat and will expand indefinitely.
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- Another line of evidence also suggests the universe is flat: It is “isotropic“, meaning it looks the same from every angle. The data on oscillations in regular, or "baryonic," matter, as well as models of how atomic nuclei heavier than hydrogen were created soon after the Big Bang revealed the curvature of the universe.
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- In different geometries, matter and light evolve differently, which allows adtroomers to extract the three-dimensional shape of the universe from observation data.
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- This research found that to within a 0.2% margin of accuracy, the universe was flat. The data gathered indicate that the spatial curvature is consistent with zero. It implies that our universe within statistical uncertainty is infinite.
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- There are giant voids of nothingness may be flinging the universe apart. Dark energy could be caused by pressure from these giant voids of nothingness.
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- Gigantic deserts of almost complete nothingness that make up most of the universe may be causing the expansion of the universe to speed up. That means these vast tracts of nothingness could explain dark energy, the mysterious force that seems to be flinging the universe apart.
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- Zoom all the way out from the solar system and the Milky Way galaxy, and an interesting pattern emerges: the cosmic web, the largest pattern found in nature. At these scales, where entire galaxies appear as little dots of lights, astronomers observe long, thin ropes of galaxies called filaments, dense clumps called clusters, and between them all vast regions of almost total emptiness.
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- These barren regions are the great cosmic voids, the smallest of which are 20 million light-years across, while the largest can be more than 160 million light-years across.
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- Like the gaps in a spider web, the voids make up the vast majority of the volume of the universe, despite hosting almost none of the matter. Aside from the cosmic web itself, which stretches from one end of the observable universe to the other, the cosmic voids are the single largest things in the universe.
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- Astronomers first detected cosmic voids in the late 1970s, but since then, they've largely been ignored. Astronomers and cosmologists have instead focused on the brightly lit structures of the universe, such as galaxies and clusters. Through those studies, astronomers detected a surprise in the 1990s: It was dark energy.
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- Dark energy is the name given to the observed accelerated expansion of the universe. This means that not only is the universe expanding every day; it's expanding ever faster with every passing moment.
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- Astronomers have no clue what's powering this period of accelerated expansion, which appears to have started about 5 billion years ago. Hence the term dark energy. It's a massive cosmological conundrum.
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- What do the voids have to do with dark energy? For one thing, the effects of accelerated expansion aren't felt inside of star systems or galaxies; there, the gravitational attraction of matter is more than strong enough to completely overwhelm it.
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- Neither our own solar system nor the Milky Way is getting bigger because of dark energy. But because the voids are almost completely empty, they feel the effects of dark energy far more readily.
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- Dark energy isn't just found in the voids, but is caused by them. How can these gigantic regions of emptiness cause accelerated expansion? The answer isn't to look at only the existence of cosmic voids but also their dynamics.
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- Cosmic voids don't simply exist. Like all other large structures in the universe, they grew from humble beginnings into their present enormous stature. Billions of years ago, all the matter in the universe was spread out pretty evenly; there were no big density differences from place to place.
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- But over time, any place that had a little more matter than average started to attract more matter onto it. With more matter, that region had even more attraction, which fueled even more growth. Over billions of years, matter accumulated to form galaxies, groups and clusters.
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- As those structures grew, the voids emptied and enlarged. But instead of seeing it as a passive process, we can view the growth of voids as exerting pressure on the structures around them. As voids grow, the walls of galaxies between them steadily thin out and eventually dissolve, allowing voids to merge. In the next few billion years, the voids will end up dissolving the cosmic web, forcing all matter into isolated clumps separated by hundreds of millions of light-years of emptiness.
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- This pressure distorts space-time around the voids, just like any other source of matter or energy in the universe. The space-time distortion means that as the voids expand, they push on the galaxies at their borders, causing them to separate despite the gravitational attraction between them.
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- The cumulative effects of all the large voids in the universe working together to dissolve the cosmic web leads to an accelerated expansion. The strength of this void-driven accelerated expansion matches the current estimates of dark energy.
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- Astronomers need more measurements of voids to get a better calculation of their combined pressure. Also, we need more information about dark energy itself, especially whether its strength has changed in the past few billion years.
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- Maybe dark energy isn't caused by some exotic force or process in the universe but is simply a byproduct of the normal evolution of “emptiness“. You will empty your brain trying to wrap your mind around this.
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November 23, 2022 UNIVERSE - what is the shape of the universe? 3754
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