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-------------------------- 2432 - UNIVERSE - expanding space
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- See Review 2413 about the COSMIC LADDER, how astronomers measure the distances to the stars. This Review explores further about our expanding Universe. We can not see it or feel it but it is out there and in control of our destiny. The appendix lists more reviews about the Universe.
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- Our Universe is a vast, enormous place, full of stars, galaxies, clusters of galaxies, and vast cosmic voids in between them. As time goes on, gravitation will continue to pull these large concentrations of matter towards one another. At the same time the expansion of the vacuum of space throughout the Universe between the galaxy clusters works to drive them apart.
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- 20 years ago, we discovered the ultimate fate to be controlled by dark energy that will defeat gravitation and continue this expansion. Our Universe will never turn around and recollapse.
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- The current estimate for the diameter of the universe is 93 billion light years.
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- The Universe is full of galaxies that are clumped and clustered together. The farther away we look, distance-wise, the farther back in time we’re looking as well. Within our own galaxy, a star that’s 10 light years away is being seen as it was 10 years ago: it takes 10 years for light, moving at the speed of light, to traverse that distance.
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- At extremely large distances, the expansion of the Universe plays a bigger role. A galaxy whose light is arriving after a 10 billion year journey will be farther away than 10 billion light years today; it will be more like 16 billion light years distant.
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- Light gets emitted, travels through space, but the expanding space pushes all the unbound objects apart. This includes practically every distant galaxy outside of the local group of galaxies that are still controlled by their mutual gravitational attraction.
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- It isn’t simply that galaxies are moving away from us that causes a redshift, but rather that the space between ourselves and the galaxy redshifts the light on its journey from that distant point to our eyes. As the Universe continues to expand, objects that emitted the light wind up farther away than even the number of years the light traveled for when it arrives.
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- Under the framework of General Relativity and the laws of physics we can determine how the Universe expanded over its history and how it will expand infinitely far into the future. That part of the Universe that’s accessible to us today, 13.8 billion years after the Big Bang, is now 46 billion light years in radius.
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- The observable Universe might be 46 billion light years in all directions from our point of view, but there is more, unobservable Universe, perhaps even an infinite amount, just like ours beyond that. There is likely much more Universe, in all directions.
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- We can only observe the parts of the Universe where light has had enough time to reach us since the Big Bang. Based on the observed expansion rate, and the fact that we know our Universe is made of:
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------------------------- 68% dark energy, which acts like a cosmological constant of expansion.
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------------------------- 27% dark matter, which dilutes with volume as the Universe expands.
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------------------------- 4.9% normal matter, which acts like dark matter but also collides with itself.
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------------------------- 0.1% neutrinos, which acts like matter today but like radiation when it moves close to the speed of light.
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------------------------- 0.01% photons, which dilute with volume and also have their wavelengths stretch-and-cool as the Universe expands.
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- Dark energy has come to dominate. As we move forward into the future, it will be the sole determining factor in the Universe’s expansion rate. As the Universe continues to expand, the matter density continues to drop, but the density of dark energy will remain constant.
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- Because the expansion rate (squared) is proportional to the energy density of the Universe, the constant density that dark energy gives means the expansion rate remains a constant.
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- Based on the current expansion rate as observed by the Planck satellite, 67 km/s/Mpc, that means two big things for the future: the expansion rate will be 55 km/s/Mpc, when only dark energy is important, and this expansion rate will cause distant objects to recede in an accelerating fashion, and the Universe will continually expand exponentially.
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- (Note that km/s = kilometers per second velocity and an Mpc is a megaparsec, an astronomical unit of distance that equates to about 3.26 million light years.)
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- A constant expansion rate means that distant objects accelerate, and that the Universe expands exponentially.
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- Imagine a galaxy 10 Mpc away. If the expansion rate is 55 km/s/Mpc, then it appears to move away from us at 550 km/s due to the Universe’s expansion. Over time, it moves farther and farther away.
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--------------------------- When it’s 10 Mpc away, it recedes at 550 km/s.
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--------------------------- When it’s 20 Mpc away, it recedes at 1100 km/s.
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--------------------------- When it’s 40 Mpc away, it recedes at 2200 km/s.
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--------------------------- When it’s 80 Mpc away, it recedes at 4400 km/s.
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- The more time goes by and the farther away the galaxy is, the faster it recedes from view. Our observable Universe, as we know it right now, is 92 billion light years in diameter. At 13.8 billion years of age that is how far the expansion has taken us.. Anyone living in our Universe, at any location, would see almost exactly the same thing from their vantage point.
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- When will the Universe reach 100 billion light years in diameter? When it’s 14.9 billion years old, just 1.1 billion years from now. At that point, the Universe will be 73% dark energy and the expansion rate will have dropped to 65 km/s/Mpc.
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- By time the Universe is 24.5 billion years old, a little more than 10 billion years in the future, it will be 94% dark energy, the expansion rate will be 57 km/s/Mpc, but the observable Universe will be 200 billion light years in diameter.
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- At an age of 37.6 billion years, the Universe will be 99.4% dark energy, the expansion rate will be 55.4 km/s/Mpc, and now the Universe will be 400 billion light years in diameter.
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- Every 12.2 billion years after that, the size of the Universe will double, with the expansion rate leveling off at 55.4 km/s/Mpc. This means the Universe will hit 1 trillion light years in diameter when it’s 54 billion years old; 10 trillion light years at 86 billion years; 100 trillion light years at 118 billion years; and a quadrillion light years in diameter at 149 billion years. By time the Universe is ten times its current age, it will be nearly ten thousand times its current size. That is the power of exponential expansion.
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- (The same thing happens in compound interest in your savings account. That is the power of compound interest and exponential growth.)
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- The observable Universe contains somewhere around 2 trillion galaxies. As we move ahead into the very distant future, all of that matter that isn’t a part of our local group of galaxies will recede from us towards these distant horizons of the Universe.
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- What is now contained within a sphere that’s 93 billion light years in diameter will be stretched out over larger and larger volumes, leading to a Universe where the average density eventually drops to zero.
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- If you were born when the Universe was ten times its current age, our local group of galaxies will merge into one and it would be the only galaxy you could see in the Universe for trillions of light years.
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- Enjoy our Universe the way it is while you are here, because it is expanding away from all of us at this exponential rate with every moment that passes. May you live in interesting times.
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- Other Reviews available:
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- 2419 - and - 2393 - Age of the Universe
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- 2412 - Comprehending the expanding Universe.
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- 2394 - Wrap your mind around the Universe.
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- 2348 - The Universe from start to finish. 13 pages.
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- 2347 - The Island Universe
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- 2335 - The Universe almost did not happen.
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- 2334 - How is it expanding?
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- 2262 - How fast is it expanding? List 21 more reviews about the Universe.
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- August 11, 2019
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----- 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” -----------
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--------------------- Sunday, August 11, 2019 --------------------
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