- 2170 - Gravitational waves are the next way to measure the expansion rate of the universe. The two other methods being used to measure expansion are Supernovae Type1a and Acoustic waves in the cosmic microwave background. Their answers differ by 9%. This is not even close enough for government work, let alone astronomy.
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------------------ 2170 - Gravitational Waves
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- Gravitational waves are created when very large masses move at very fast speeds. Gravity is very weak compared to the other natural forces, electromagnet and forces inside the atom. So, it is extreme astronomy that creates these events. When two neutron stars or blackholes orbit each other at tremendous velocities before they merge, for example, that is when gravity waves are strong enough to be “seen”.
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- Could these waves be new yardsticks to measure the size of the Universe?
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- Measurements need standards , something to measure against. If we know a light bulb is exactly 100 watts we can measure its distance away from us by how bright it appears. If we know a stick is exactly one meter long we can compare its length in our field of view and calculate how far away it is.
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- To date Supernovae Type 1a have been the “standard candle” light bulbs used to measure astronomical distances. The other standard ruler, or stick, has become measurements of baryonic acoustic oscillations. The distances that separate the galaxies in the Universe are wavelength multiples of these acoustic oscillations.
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- The expansion of the Universe has gone through different phases since the Big Bang. At first gravity was the dominate force slowing the expansion of the universe. The distance between galaxies was still increasing but slowing down.
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- But, when the galaxies got too spread out the tug of gravity became too weak and acceleration created by Dark Energy became the dominate force. This switch over occurred about 5 billion years ago. Dark Energy expanding the Universe is still the dominate force today, 5 billion years later.
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- Here is the dilemma for astronomers today: When we measure the Universe expansion using the brightness of supernovae explosions that gives us one answer. However, using the acoustic oscillations in the cosmic microwave background gives us a different answer. They both cannot be right?
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- How to learn which is right? Gravitational waves may be a third measurement that may tell us the best answer for how fast the Universe is expanding.
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- So far astronomers have only calculated one major event of colliding neutron stars. A single calculation is not enough. Many more blackhole and neutron star collisions need to be measured carefully to have a definitive answer. This is estimated to take another 5 years of gravity research. Here are the two different answers we are trying to reconcile:
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- Type1a Supernovae and the local distance ladder give us an expansion rate of
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-------------------------- 73.24 (+ 1.74 or - 1.74).
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- The cosmic microwave background measurements give us an expansion rate of
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-------------------------- 66.93 (+0.62 to -0.62).
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------------------------------------------------------------------------- Other reviews available:
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- 2175 - Why is gravity so small?
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- 2174 - Gravity - what is it really?
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- 2127 - Einstein’s ring. If the curvature of space-time near the closer galaxy is great enough then multiple images of the background galaxy will form on either side of the lens galaxy.
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- 2089 - The gravity of the details. Maybe it is time to discover some new physics to define gravity?
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- 2014 Gravity - a property of space and time. Also lists 12 more reviews on the subject gravity.
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- November 23, 2018
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-------------------------- Friday, November 23, 2018 --------------------------
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