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-------------------- 2478 - UNIVERSE - what is its shape?
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- Astronomers can't agree about how fast the universe is expanding or what shape it is expanding into? Ever since our universe emerged from an explosion of a tiny speck of infinite density and gravity, it has been ballooning, and the expansion of the universe keeps getting faster.
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- How quickly it's expanding has been an astronomical question. Measurements of this expansion rate from nearby sources seem to be in conflict with the same measurement taken from distant sources.
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- One possible explanation is that there is a brand-new particle that has emerged and is altering the future destiny of our entire cosmos.
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- This "closed universe." doesn't fit with existing theories of how the universe works. It has been largely rejected in favor of a "flat universe" that extends without boundary in every direction and doesn't loop around on itself.
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- However, an anomaly in data from the best-ever measurement of the CMB offers evidence that the universe is closed after all. The difference between a closed and open universe is a bit like the difference between a stretched flat sheet and an inflated balloon.
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- In either case, the whole thing is expanding. When the sheet expands, every point moves away from every other point in a straight line. When the balloon is inflated, every point on its surface gets farther away from every other point, but the balloon's curvature makes the geometry of that movement more complicated.
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- In an open, flat universe, the photons, left undisturbed, would travel along their parallel courses without ever interacting.
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- The conventional model of the universe's inflation suggests that the universe should be flat. Rewind the expansion of space all the way to the beginning, to the first 0.000,000,000,000,000,000,000,0001 seconds after the Big Bang and you will see a moment of incredible, exponential expansion as space grew out of that infinitesimal point in which it began.
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- However, there is an anomaly in the CMB. The CMB is the oldest thing we see in the universe, made of ambient microwave light that fills all of space when you block out the stars and galaxies and other interference.
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- It's one of the most important sources of data on the universe's history and behavior, because it's so old and so spread throughout space. There is significantly more "gravitational lensing" of the CMB than expected. Gravity seems to be bending the microwaves of the CMB more than existing physics can explain.
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- If the universe were curved, it would raise a number of problems contradicting those other data sets from the early universe and making discrepancies in the universe's observed rate of expansion much worse.
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- Astronomers have devised multiple clever ways of measuring what they call the Hubble constant. This number represents the expansion rate of the universe today, The expansion rate is thought to be 49,300 miles per hour per every million lightyears distance.
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- One way to measure this expansion rate is to look at nearby supernovae, the explosion of gas and dust launched from the universe's largest stars upon their death. There's a particular kind of supernova that has a very specific brightness, so we can compare how bright they look to how bright we know they're supposed to be and calculate the distance.
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- By looking at the light from the supernova's host galaxy, astrophysicists can also calculate how fast they are moving away from us. By putting all these pieces together, we then can calculate the universe's expansion rate.
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- There is more to the universe than exploding stars. There's also something called the cosmic microwave background, which is the leftover light from just after the Big Bang, when our universe was a mere baby, only 380,000 years old. With missions like the Planck satellite tasked with mapping this remnant radiation, scientists have incredibly precise maps of this background, which can be used to get a very accurate picture of the contents of the universe.
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- We can take those ingredients and run the clock forward with computer models and be able to say what the expansion rate should be today, assuming that the fundamental ingredients of the universe haven’t changed since then.
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- Since one measurement comes from the very early universe, and another comes from more relatively recent time, the thinking is that maybe some new ingredient in the cosmos is altering the expansion rate of the universe in a way that we didn’t already capture in our models.
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- The theory is that what is dominating the expansion of the universe today is a mysterious phenomenon that we call “dark energy“. From the young universe to the present-day universe, physicists assume that dark energy is constant. But, maybe dark energy is changing.
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- We think dark energy has something to do with the energy that's locked into the vacuum of space-time itself. This energy comes from all of the “quantum fields” that permeate the universe.
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- In modern quantum physics, every single kind of particle is tied to its own particular field. These fields wash through all of space-time, and sometimes bits of the fields get really excited in places, becoming the particles like electrons and quarks and neutrinos.
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- All the electrons belong to the electron field, all the neutrinos belong to the neutrino field, and so on. The interaction of these fields form the fundamental basis for our understanding of the “quantum world“. These quantum fields have a fundamental amount of energy associated with them, even in the bare empty vacuum itself.
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- However, using the exotic quantum energy of the vacuum of space-time to explain dark energy, we immediately run into problems. When we perform some very simple calculations of how much energy there is in the vacuum due to all the quantum fields, we end up with a number that is about 120 orders of magnitude stronger than what we observe dark energy to be.
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- When we try some “more sophisticated calculations“, we end up with a number that is zero. Which also disagrees with the measured amount of dark energy.
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- If these measurements of the expansion rate are accurate and dark energy really is changing, then this might give us a clue into the nature of those quantum fields. The amount of change in the quantum fields needed to account for the change in dark energy is calculated.
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- The calculation requires a certain kind of particle mass, which turns out to be roughly the same mass of a new kind of particle that's already been predicted, named the “axion“. Physicists invented this theoretical particle to solve some problems with our quantum understanding of the strong nuclear force.
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- This particle presumably appeared in the very early universe, but has been "lurking" in the background while other forces and particles controlled the direction of the universe.
- We have never detected an axion, but if these calculations are correct, then that means that the axion is out there, filling up the universe and its quantum field. Also, this hypothetical axion is already making itself noticeable by changing the amount of dark energy in the cosmos.
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- It could be that even though we've never seen this particle in the laboratory, it's already altering our universe at the very largest of scales. Stay tuned, there is more to learn. Stay in school.
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- November 9, 2019 2478
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--------------------- Sunday, November 10, 2019 --------------------
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