- 3017 - UNIVERSE - like Swiss Cheese? The mission is to study the nature of Dark Matter for a better understanding of matter, space and time. We are studying the Cosmic Microwave Background radiation with higher resolution and higher sensitivity. Telescopes integrated together with computers, are among projects designed to find the answers. (See Review 3019 - Telescopes - connect them all together?)
------------------------ 3017 - UNIVERSE - like Swiss Cheese?
- In 1925 no astronomers believed the Universe was expanding. The stars and the galaxies were thought to be static in the night sky. Even Einstein thought the Universe was static and he even added fudge factors in his equations to make the Universe balance without expansion or contraction.
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- Einstein later called this his greatest blunder. In 1929 Edwin Hubble at Mount Wilson Observatory provided data that galaxies were receding away from us. By 1934, when my Ford pick up truck came off the assembly line, all astronomers were convinced the Universe was expanding.
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- In 1998, 23 years ago, astronomers discovered that the Universe was not only expanding it was expanding at an accelerating rate. No one was prepared to explain why. What was causing the expansion to go faster and faster?
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- Some unknown source of energy must exist in the space between the galaxies that is repelling them apart. The vacuum of space between the galaxies is itself expanding. All masses feel this energy, just like all masses feel gravity. It is a repelling force, rather than an attracting force.
- We do not know what it is so we will call it “Dark Energy”. In the Universe as a whole Dark Energy has overcome gravity. In our local Milky Way Galaxy stars are not expanding apart because gravity is holding everything together.
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- The same is true of our Local Group of Galaxies. The group contains enough mass that gravity is still king and overcomes the repelling force that would expand the space between them. However, other galaxies further away are being repelled away from us.
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- In the vast areas of open space Dark Energy is stronger than gravity. In the bigger Universe billions of galaxies are all moving apart from each other because gravity is too weak to stop the expansion.
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- Astronomers measure the receding velocity of distant galaxies by their “ redshift” of light. The wavelength of the light from these speeding galaxies gets stretched into a longer wavelength, or a lower frequency, or a redder color.
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- This is the same way as the sound of a race car gets a lower roar when it passes your ears and is speeding away from you. The Universe is getting cooler as it expands. It is
- 270C, according to the Cosmic Microwave Background (CMB) measurements, (+2.73 Kelvin).
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- The observed brightness of any galaxy also tells astronomers its distance. If a galaxy with a given redshift looks dimmer than calculated then the galaxy must be further away. Its light has taken longer to reach us and the Universe must have taken longer to grow to its current size.
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- The expansion rate of the Universe must have been slower in the past that previously expected. Consequently the Universe expansion must be faster today, it must be “accelerating” its expansion at a more rapid rate.
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- This accelerating expansion conclusion came as a big surprise to astronomers. Up until this conclusion astronomers thought the force of gravity was gradually slowing down the expansion of the Universe since the Big Bang occurred. The fact that it is speeding up was totally unexpected. And, still not understood as to how or why. Dark Energy is just a name for something we can not explain.
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- Sonme unknown force that exists in the vacuum of space is one explanation. But, puzzled astronomers have come up with another explanation that does not require Dark Energy. This is the idea that we happen to be living in a part of the Universe that is a giant void.
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- Suppose the Universe is not expanding evenly in all directions. The balloon of expansion is not growing as a perfect sphere, but, warped and bulged differently depending on the direction of expansion. In the bigger scheme the total Universe might be decelerating its expansion with the matter pulling spacetime, slowing the expansion down.
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- Suppose in our part of the Universe we just happen to live in a giant void with all the greater mass surrounding us outside the void. Suppose the average density of the matter in our part of the Universe is only 30% of the density elsewhere.
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- Then, the local expansion rate in our part would be faster inside the void than it is everywhere else. The expansion rate would be fastest at the very center of the void and diminish toward the edge, where the higher density exterior starts to take over.
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- The scenario would explain the redshift we observe. Light traveling a given distance would be redshifted by less than it would be if the whole Universe was expanding at our local rate. Light has to travel a greater distance than it would in a uniformly expanding Universe. Galaxies would appear farther away and therefore appear dimmer.
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- For this scenario to work the void we are in the middle of would have to be enormous, about the size of our “Observable Universe”. This seems unlikely that we are so special.
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- But, so does energy out of the vacuum of space. Is it Dark Energy or is it the Void? How can we tell? Does the bigger Universe look like Swiss cheese? Astronomers need better measurements and more data if they are going to tell which scenario is more likely the reality.
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- The mission is to study the nature of Dark Matter for a better understanding of matter, space and time. Studying the CMB with higher resolution and higher sensitivity willl help. Telescopes integrated together with computers, are among other projects designed to find the answers. Stay tuned. Cosmology has more mysteries to solve.
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February 3, 2021 UNIVERSE - likeswiss cheese? 1047/8 3017
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--------------------- --- Thursday, February 4, 2021 ---------------------------
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