- 3422 - UNIVERSE - what shape and what causes this expansion? Astronomers around the world can't seem to agree about how fast the universe is expanding. Ever since our universe emerged from an explosion of a tiny speck of infinite density and gravity, it has been ballooning, and not at a steady rate, either the expansion of the universe keeps getting faster.
------- 3422 - UNIVERSE - what shape and what causes this expansion?
- Measurements of this expansion rate from nearby sources seem to be in conflict with the same measurement taken from distant sources. One possible explanation is that something is changing the expansion rate. What is that something?
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- Theorist have proposed that a brand-new particle has emerged and is altering the future destiny of our entire cosmos. Everything we think we know about the shape of the universe could be wrong. Instead of being flat like a bed sheet, our universe may be curved, like a massive, inflated balloon.
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- Data from the “cosmic microwave background” (CMB), the faint echo of the Big Bang, released in 2018, contradict conventional wisdom. Who are we to believe? It is the fate of the universe we are dealing with here. This is no minor issue.
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- If the universe is curved, it curves gently. That slow bending isn't important for moving around our lives, or solar system, or even our galaxy. But travel beyond all of that, outside our galactic neighborhood, far into the deep blackness, and eventually, moving in a straight line, you'll loop around and end up right back where you started.
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- It is a "closed universe." This idea has been around for a while, but this idea has been largely rejected in favor of a "flat universe" that extends without boundary in every direction and doesn't loop around on itself. Closed or flat that is the question!
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- Now, an anomaly in data from the best-ever measurement of the CMB offers solid, but not conclusive, 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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- This means that in a closed universe if you have two photons and they travel in parallel in a closed universe, they will eventually meet. 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, according to that model, and you'll see a moment of incredible, exponential expansion as space grew out of that infinitesimal point in which it began.
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- The physics of that superfast expansion point leads to a flat universe. That's the first reason to believe the universe is flat. If the universe isn't flat, you have to "fine-tune" the physics of that primordial mechanism to make it all fit together, and redo countless other calculations in the process. But, that might end up being hard but necessary.
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- There's an anomaly in the Cosmic Microwave Background. The CMB is the oldest thing we see in the universe, made of ambient microwave light that suffuses all of space when you block out the stars and galaxies and other interference.
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- The CMB is the most important source of data on the universe's history and behavior, because it's so old and so spread throughout space. There's significantly more "gravitational lensing" of the CMB than expected, meaning that gravity seems to be bending the microwaves of the CMB more than existing physics can explain.
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- The data comes from a 2018 release from the Planck experiment, a European Space Agency (ESA) experiment to map the CMB in more detail than ever before.
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- To explain that extra lensing, the Planck Collaboration has just tacked on an extra variable, which the scientists are calling "A_lens," to the group's model of the universe's formation, trying to explain what they see. There's no connection with physics. Meaning there's no A_lens parameter in Einstein's theory of relativity. They can explain A_lens with a positively curved universe, which is a much more physical interpretation that you can explain with general relativity.
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- The Planck data point to a closed universe with a standard deviation of 3.5 sigma (a statistical measurement that means about 99.8% confidence that the result isn't due to random chance). That's well short of the “5 sigma” standard physicists usually look for before calling an idea confirmed.
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- The closed-universe model would raise a number of problems for physics.
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- Astronomers have devised multiple clever ways of measuring what they call the Hubble parameter, or Hubble constant ( H0). This number represents the expansion rate of the universe today.
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- One way to measure the expansion rate today is to look at nearby supernovas, 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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- Then, 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 the pieces together, we then can calculate the universe's expansion rate. Simple as one, two, three.
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- But there's 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 380,000 years old.
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- 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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- From there, 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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- These two estimates disagree by enough to make astronomers worried that we're missing something. Perhaps, one or both measurements are incorrect or incomplete.
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- But if we assume that both measurements are accurate, then we need something else to explain the different measurements. 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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- What is dominating the expansion of the universe today is a mysterious phenomenon that we call “dark energy“. It's an awesome name for something we basically don't understand. All we know is that the expansion rate of the universe today is accelerating, and we call the force driving this acceleration "dark energy."
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- In our comparisons from the young universe to the present-day universe, physicists assume that dark energy, whatever it is, is constant. But, maybe dark energy is changing.
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- Scientists believe that 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.
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- No matter where you go in the universe, you can’t escape these quantum fields. Even when they’re not vibrating enough in a particular location to make a particle, they’re still there, wiggling and vibrating and doing their normal “quantum thing“. So these quantum fields have a fundamental amount of energy associated with them, even in the bare “empty” vacuum itself.
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- If we want to use this 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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- On the other hand, 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. The answer must be somewhere in between!
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- Trying to understand dark energy through the language of the vacuum energy of space-time, that energy created by those quantum fields, is difficult. 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. Specifically, if dark energy is changing, that means that the quantum fields themselves have changed.
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- Physicists have calculated the amount of change in the quantum fields needed to account for the change in dark energy. If there is a new quantum field that's responsible for the change in dark energy, that means there is a “new particle” out there in the universe.
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- The amount of change in dark energy that was calculated 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: the “axion“. Physicists invented this theoretical particle to solve some problems with our quantum understanding of the strong nuclear force at the center of every atom.
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- This axion 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.
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- However, we've 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.
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- This hypothetical axion is already making itself noticeable by changing the amount of dark energy in the cosmos. So 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.
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- You just don’t know what is out there yet to be discovered. Curious mind are in pursuit. If you read this whole thing you must be one of those curious minds.
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January 21, 2022 UNIVERSE - what shape and what causes this expansion? 3422
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