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--------------------- 2476 - UNIVERSE - Age of the Universe?
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- The age question with how old is the Earth. Science once tried to figure that out by calculating how long it would take the oceans to get salty. They new how fast rock salts dissolved and the estimated how much water was in the oceans, but their calculations were not very accurate.
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- Another attempt was to assume the Sun was hard coal and calculate how long it would burn. At the time there was no knowledge of atoms or nuclear fusion, or even what the Sun was made of.
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- The real breakthrough came with radioactive dating. Once science learned in the laboratories how fast a particular radioactive material would undergo radioactive decay and turn into another element they could calculate how long the material had been decaying, that is its age.
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- They could do this with rocks in the Earth or meteorites that landed from outer space. Measure the percentage of the element that was radioactive, the percentage that had decayed into a new element through fission versus how much material was there to start with. ( See Reviews # 871 and #872 on Carbon-14 and Potassium-40 dating).
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- These calculations performed many times on different rocks determined the Earth to be 4,500,000,000 years old and the Solar System to be 5,000,000,000 years old.
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- To get how old the Universe was we had to look to the stars that were older than our Sun. How long a star lives depends on its size. The bigger the star the shorter its lifetime.
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- When stars die they explode into supernovae or into planetary nebulae and leave behind a carbon star called a White Dwarf. White Dwarfs have no fuel left to burn so they simply cool down at the natural rate from thermal radiation. By studying the White Dwarfs in the Universe astronomers came up with an age of 10 to 20 billion years old. Quite a wide error allowance.
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- Another method was to use Globular Clusters of stars. These clusters of stars were assumed to be all formed at about the same time and would all be about the same age. But, as we pointed out big stars die faster that smaller stars. Our Sun is mid-sized and will live about 10 billion years.
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- So, astronomers could count the sizes of the stars in the cluster. What were the sizes of most of the stars that are gone, are now White Dwarfs, Neutron Stars, or Black Holes, but no longer stars on the Main Sequence of burning hydrogen. Knowing the point on the Main Sequence diagonal on an HR Diagram told them how old the remaining stars were in the cluster. Still, calculations were not too precise at 10 to 15 billion years old.
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- Another method arrived at the turn of the century when we discovered that nebulae in the night sky were actually galaxies. After studying many galaxies it was determined that most were moving away from us. In other words the Universe was expanding. By using Doppler technology to learn velocity, and Cepheid variables to learn how far these galaxies were away from us astronomers could calculate the rate of expansion.
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- Again, the accuracy was not perfect putting the expansion rate at 50 to 100 kilometers/second per mega parsec. The most recent calculations put it at 73.5 km/sec/mps. This equates to 47,000 miles per hour per million lightyears distance. In other words a galaxy that is 1 million lightyears further away will be receding away from us 47,000 miles per hour faster.
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- It turns out that the reciprocal of the expansion rate is the age of the Universe, if you assume the expansion rate is a constant. The reciprocal is distance / velocity which is time. These calculations got us to 10 to 17 billion years old for the Universe started its expansion with the Big Bang.
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- This all depended on the expansion rate being constant. But, what affect did gravity have in slowing up the expansion rate? What effect did Dark Energy have in speeding up the expansion rate? And, what shape was the Universe? Can we assume it was a straight line back to the Big Bang or was it on a spherical curve, or a convex saddle shape?
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- None of these answers were available to us until we discovered the Cosmic Microwave Background radiation. Microwave satellites could take a high resolution snapshot of the microwave background that was released when light first left the plasma created with the Big Bang. This light was released when the Universe was 380,000 years old.
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- The radiation was at a temperature of 3,000 Kelvin and was Gamma Rays. Today it is Microwaves and only 2.73 Kelvin. The temperature has cooled be a factor of 1000 and the Universe has expanded be a factor of 1000 since CMB was released.
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- Quantum fluctuations in the early Universe created granularity in the radiation. It was not perfectly smooth. The variations were small, only one part in 100,000 in temperature. But they were the same across the entire sky which told astronomers that the Universe was nearly flat.
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- They were also about 1 arc second in size which corresponds to the granularity in the beginning expanding to what it is today. The granules correspond to the density of galaxies and voids across the cosmos. Gravity caused the denser regions to become stars, blackholes, and galaxies. The rarified regions became voids in the bubbles of galaxies and galaxy strings that we see today.
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- From the CMB calculations the Universe is 13.7 billion years old. Astronomers determined that about half the time of expansion gravity dominated and was slowing the rate of expansion. However, in the last half of the expansion Dark Energy is dominate and the acceleration rate is speeding up.
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- Will it speed up forever? Will the Universe die a cold void totally dispersed throughout space? Or, will Dark Energy reverse itself and the Universe collapse into another Big Bang to repeat things all over again?
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- We don’t know, but we are learning.
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- November 7, 2019. 1012 2476
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--------------------- Thursday, November 7, 2019 -------------------------
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