Sunday, May 7, 2023

3989 - UNIVERSE - how big is it?

 

-   3989  -  UNIVERSE  -  how big is it?   Planck’s satellite findings were published in 2015. By carefully examining the microwave background radiation, astronomers have pinned down the universe’s age to 13.8 billion years, accurate to better than 1 percent.  And that is how big it is too, in lightyears.


     

        --------------------------  3989  - UNIVERSE  -  how big is it?

-  With a long enough lever and a place to stand, Archimedes knew he could move the Earth. Where could he stand to weigh the Universe?  When it comes to imagining such colossal masses, the human mind is completely out of its depth.

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-   But first, a note about weight and mass—intimately related but technically distinct qualities. Officially, “weight” describes the gravitational force acting on an object, so an a galaxy “weighs” nothing while floating in empty space.

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-  What researchers are really after is mass, the unvarying amount of stuff in an object, or equivalently, how much force it takes to get the mass moving.  “Weighing” an object  comes down to measuring the gravitational force between it and a massive partner.

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-  Early attempts to weigh the Earth went the route of guessing the planet’s size and density and calculating its mass from there. By the 1600s, estimates of Earth’s diameter, and therefore its volume , were made . But no one was sure of the density, whether the planet was made of mostly water or rock. Everyone was wrong at the time because the planet is actually made up mostly of metal, which is denser than both.

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-  To figure out that density and therefore the mass of the Earth, British scientist Henry Cavendish measured the overall strength of gravity in 1798. Isaac Newton had shown in the 1600s that all objects pull on all other objects, and those with more mass pull harder.

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-  Cavendish hung small metal balls from a wire, placed heavier spheres nearby, and watched the wire twist as the spheres attracted each other. In this horizontal twisting he was able to determine the intensity of the gravitational force between the weights and in general.

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- Knowing how hard the Earth’s mass tugged downward on his spheres (that is, their weights), he could use Newton’s equations to peg the Earth’s composition at a suspiciously metal-like 5.42 times the density of water. Modern physicists have found that he was off by just seven-tenths of one percent.

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-  The Sun pulls on the Earth just hard enough to swing it around once every 365 days, implying a certain force, and therefore a certain mass. Similarly, by considering the Sun as the prime partner of various heavenly body pairings, researchers could calculate the mass of the rest of the planets based on the length of their years.

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-  Watching how moons orbited planets provided another check, as well as a way to weigh the moons. However, asteroid mass estimation remains something of a dark art based on guessing plausible densities and sizes.

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-  Just as researchers can infer the mass of the Earth by watching how hard it drags down objects on or near its surface, or the mass of the Sun by watching how quickly planets orbit around it, they can read the “galaxy’s mass” in the motion of the objects that circle it.

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-  It was the trajectories of orbiting stars that first flagged the presence of dark matter in the 1970s.

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-  In our solar system, Mercury zips around nearly nine times faster than Neptune does because it lies much closer to the source of the vast majority of our solar system’s mass, the Sun.

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-   Researchers expected that a similar pattern should play out in other galaxies, far-out stars tracing slower orbits than close-in ones.  This relationship holds close to the center of most galaxies, but then stops. After a point, no matter how far out they looked, astronomers discovered that stars orbited at surprisingly similar speeds.   Their constant motions imply that a second, invisible source of mass is also pulling on them.

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- The Universe, inconveniently, lacks visible orbiting partners. Here, the standard gravitational scale breaks down.  The absolute size of the universe is unknown, and is constantly expanding, so its mass is similarly undefined. Astronomers can define the volume of the observable universe, however, based on the distance light has been able to travel between the Big Bang and present day.

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-  But the density, averaged out over all of the cosmos’s planets, stars, galaxies, and voids, has proved challenging to measure. One estimate came from the Wilkinson Microwave Anisotropy Probe (WMAP), a satellite that measured warm spots and cool spots in the universe’s earliest light from 2001 to 2010.

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- These warm patches are the remnants of a power struggle from when a dense soup of matter and light filled the young universe. Gravity drew particles together while light pushed them apart, creating sloshing ripples that grew with the expanding universe until WMAP picked them up.

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-  From the patterns in these variations, cosmologists can calculate the age and composition of the universe, including its overall density.  Density works out to be about six protons worth of stuff per cubic meter.  That number technically represents an energy density (since matter and energy can be converted using Einstein’s famous equation), so it includes visible matter, dark matter, and the unknown dark energy driving the expansion of the universe.

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-  WMAP and its successor, the Planck satellite, estimated that by this metric the universe is about 5 percent visible matter, 27 percent dark matter, and 68 percent dark energy.

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-  The volume and density  estimates for the universe’s overall mass as something like 100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 kilograms. That’s roughly 100 billion Milky Way galaxies.

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-   Our deepest astrophotos show ultra-distant quasars and galaxies whose redshifts indicate their light has traveled for nearly 13 billion years. Thus, they are 13 billion light-years away? And, that must define the edge of the visible universe, right?

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-  Ever since a given galaxy emitted the light we’re now seeing, it’s been zooming away from us due to expanding space. Today that same galaxy is 46 billion light-years distant.

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-  How could anything reach a distance of 46 billion light-years in the mere 13 billion years since it emitted the light we now see? That would mean it’s currently receding faster than light. Or that space is so warped we’re not viewing it directly.

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-  Actually, both are true. Faster-than-light recession doesn’t violate relativity in this case because the galaxy’s mass was never accelerated. It’s merely the intervening empty space between galaxies that has been inflating, which makes the real radius of the observable universe very nearly 46 billion light-years.

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-   Light from objects any farther away will never get here because space’s expansion will stretch out, hopelessly weaken, and out-race their rays. So, it’s a real boundary beyond which there is eternal blankness. We use the term visible universe for everything nearer, which is everything we can ever possibly know about.

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-  Given the average density of space, five atoms per cubic yard (1 cubic meter), the visible universe must contain 10^56 tons of matter. And 10^84 photons of light.

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-  What about the universe beyond the part we can see? The real universe? How big is the whole thing?

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-  One theory, using the most plausible figures for when the era of inflation began just after the Big Bang, concludes that the overall universe is 300 billion trillion times larger than the visible universe.

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-  Let’s try another avenue to calculate the size of the Universe?  The “fine structure constant” seems annoyingly inconstant at the outer fringes of the unvierse , it occurs in only one direction that we look.  The ‘fine structure constant’ is a measure of electromagnetism, one of the four fundamental forces in nature (the others are gravity, weak nuclear force and strong nuclear force).

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-  The fine structure constant is the quantity that physicists use as a measure of the strength of the electromagnetic force

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----------------------------  Find Structure Constant  =  e^2  /  h  *  c

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----------------------------  Find Structure Constant  =    1  /  137

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-  It's a dimensionless number and it involves the speed of light, “c”, something called Planck's constant, “h”,  and the electron charge , “e“, and it's a ratio of those things. And it's the number that physicists use to measure the strength of the electromagnetic force.

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-  The electromagnetic force keeps electrons whizzing around a nucleus in every atom of the universe, without it, all matter would fly apart. It is believed to be an unchanging force throughout time and space.

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-   The most distant quasars that we know of are about 12 to 13 billion light years from us.

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-   If you can study the light in detail from distant quasars, you're studying the properties of the universe as it was when it was in its infancy, only a billion years old.

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-  The universe then was very, very different. No galaxies existed, the early stars had formed but there was certainly not the same population of stars that we see today. And there were no planets.

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-  The universe may not be isotropic in its laws of physics—one that is the same, statistically, in all directions. But in fact, there could be some direction or preferred direction in the universe where the laws of physics change, but not in the perpendicular direction. In other words, the universe in some sense, has a dipole structure to it.

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-  In one particular direction, we can look back 12 billion light years and measure electromagnetism when the universe was very young. Putting all the data together, electromagnetism seems to gradually increase the further we look, while towards the opposite direction, it gradually decreases.

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-  In other directions in the cosmos, the fine structure constant remains just that—constant. These new very distant measurements have pushed our observations further than has ever been reached before.

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-  In other words, in what was thought to be an arbitrarily random spread of galaxies, quasars, black holes, stars, gas clouds and planets, with life flourishing in at least one tiny niche of it, the universe suddenly appears to have the equivalent of a north and a south.

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-  For a long time, it has been thought that the laws of nature appear perfectly tuned to set the conditions for life to flourish. The strength of the it may be the oldest question in astronomy: How big is the universe?

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-   Faster-than-light recession doesn’t violate relativity in this case because the galaxy’s mass was never accelerated. It’s merely the intervening empty space between galaxies that has been wildly inflating, which makes the real radius of the observable universe very nearly 46 billion light-years.

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-  Light from objects any farther away will never get here because space’s expansion will stretch out,  weaken, and out-race their rays. So, it’s a real boundary beyond which there is eternal blankness. We use the term visible universe for everything nearer, which is everything we can ever possibly know about.

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-  There’s no sign that galaxy clusters get any sparser as we approach the edge of the observable universe.  One theory, using the most plausible figures for when the era of inflation began just after the Big Bang, concludes that the “overall universe” is 300 billion trillion times larger than the “visible universe“. 

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-  Where the fundamental physical quantities like the fine structure constant are 'just right' to favor our existence, apply throughout the entire universe?

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-   Our standard model of cosmology is based on an isotropic universe, one that is the same, statistically, in all directions. When astronomers consider the universe at the largest scales, they assume that it's homogeneous, and isotropic.

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-   “Homogeneous“ means that observers in any part of the universe will see roughly the same view as observers in any other part.

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-  “Isotropic means” that the universe looks the same in every direction. If you were floating alone in the cosmic void, you could look left, right, up, down out to the edge of the observable universe and see galaxies, galaxy clusters and eventually the cosmic microwave background radiation in all directions. Every direction looks the same.

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-  This is know as the “cosmological principle“, and it's one of the foundations of astronomy, because it means that we have a chance at understanding the physical laws of the universe.

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-  If the universe wasn't homogeneous and isotropic, then it would mean that the physical laws as we understand them are impossible to comprehend. Just over the cosmological horizon, the force of gravity might act in reverse, the speed of light might be slower than walking speed, and unicorns could be real.

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-  While we don't live in a special place in the universe, we do live in a special time in the universe. In the distant future, billions or even trillions of years from now, galaxies will be flying away from us so quickly that their light will never reach us. The cosmic background microwave radiation will be redshifted so far that it is completely undetectable.

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-  Future astronomers will have no idea that there was ever a greater cosmology beyond the Milky Way itself. The evidence of the Big Bang and the ongoing expansion of the universe will be lost forever.  If we didn't happen to live when we do now, within only billions of years of the beginning of the universe, we'd never know the truth.

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- Using today’s most powerful telescopes, astronomers see galaxies located over 13 billion light-years from Earth.   (A light-year equals about 6 trillion miles.) Since they see these distant galaxies in all directions, the current “horizon” of visibility is at least 26 billion light-years in diameter.

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-  But the universe is probably much larger than the portion we can see. This will be the case in the highly likely event that the inflation hypothesis, put forth in 1980 by MIT’s Alan Guth, proves correct. This idea suggests that the extremely young universe experienced a brief period of hypergrowth so severe that it ballooned from the size of a subatomic particle to the size of a softball almost instantly.

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-  If inflation occurred, then the universe is much larger than we might expect based on current observations.  For now, it’s wondrous enough to know we live in a universe that’s at least 550 billion trillion miles across, and it may be much bigger than that

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-   The launch of NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) in 2001 and the European Space Agency’s Planck satellite in 2009 changed all that.   Before WMAP and Planck, the best approach for determining the universe’s age relied on the much-debated Hubble constant, a figure that describes the rate at which the universe is expanding.

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-  To find the Hubble constant, astronomers observe distant galaxies and measure their distances (by using Cepheid variable stars or other objects of known intrinsic brightness) as well as how fast they recede from Earth. They then determine the Hubble constant by dividing the galaxy’s speed of recession by its distance.

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- Once they decide on a value for the Hubble constant, they can estimate the maximum age of the universe by calculating the constant’s reciprocal.

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-  But there was a problem. The values astronomers got for the Hubble constant depended on various assumptions about the universe’s density and composition and the method used to determine distances. So astronomers of different mindsets got different values for the constant.

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-  They generally divided into two camps, one in the range of 50 kilometers per second per megaparsec and the other up at 80 km/sec/Mpc. (A megaparsec equals 3.26 million light-years, or about 20 billion billion miles.)

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-  Therefore, the two groups estimated a range for the age of the universe of about 10 to 16 billion years. (Higher values of the Hubble constant produce younger age values for the universe.)  Let’s settle on 76 km/sec/Mpc.

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-  Researchers announced Planck’s findings in 2015. By carefully examining the microwave background radiation, astronomers have pinned down the universe’s age to 13.8 billion years, accurate to better than 1 percent.  And that is how big it is too, in lightyears.  So, now you know.

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 May 7, 2023         UNIVERSE  -  how big is it?               2813    3989                                                                                                                        ---------------------------------------------------------------------------------------------  Comments appreciated and Pass it on to whomever is interested. ------   Some reviews are at:  --------------     http://jdetrick.blogspot.com -----  --  email feedback, corrections, request for copies or Index of all reviews ---  to:  ------    jamesdetrick@comcast.net  ------  “Jim Detrick”  --------------------------------

--------------------------- ---  Sunday, May 7, 2023  ---------------------------

 

 

 

 

         

 

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