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- We have only known about an accelerating universe for the last 15 years. We assumed the expansion was slowing down over time. We thought that gravity, that universal attractive force, would eventually slow down the massive galaxies that were moving away from each other.
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- When astronomy witnessed a supernova explosion they dated it to have happen 8,000,000,000 years ago. That is how long it took for the light to reach us.
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- When astronomers were able to measure the brightness of supernovae they concluded that the light took 12,000,000,000 years reach us. The supernovae were dimmer then a decelerating, or even a constant cosmic expansion ,could explain. For the light to take that much longer to reach us the universe expansion must be accelerating. Something is needed to drive the acceleration. A body in motion tends to stay in motion with a constant velocity. A force is needed to speed it up, slow it down, or, changes its direction. Something must be providing the force that causes the expansion to be speeding up. We call this something “Dark Energy“.
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- We know about the something that would be holding back expansion of the universe. That is matter and gravity. Gravity is only an attractive force.
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- We do not know about something that is a repulsive force. An anti-gravity, that is pushing expansion faster and faster.
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- Astronomers assume that universe of the largest scales is homogeneous, it looks the same at any moment in time from all points in all directions.
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- But, how would our conclusions change if the universe was not homogeneous? What if different parts of space were expanding at different rates? What if we happen to be residing in a giant void in space? Our local expansion would be accelerating faster within the void than it would be elsewhere.
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- If the universe is full of lumps and voids on the grandest scales than dimmer supernovae, and longer light travel , can be explained without a hypothetical dark energy accelerating expansion.
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- This idea is counter intuitive. It is not what we observed in the Cosmic Microwave Background radiation that is homogeneous to 1 part in 100,000. It is not what we observe in the uniform distribution of galaxies. However if we live in a big enough void these observations could still be the same.
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- The largest observable structures in the universe are galaxy clusters 200,000,000 light-years across. Beyond that scale the universe appears to be uniform.
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- Astronomers still like the idea that the galaxies, filaments, and voids we observe originated in the microscopic quantum oscillations at the start of universe and uniformly grew to the proportions we see today.
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- What we need is more data.
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- The more supernovae we observe the more accurately we can reconstruct the expansion history of the universe. Comparing apparent acceleration rates with the red shift of wavelengths and the brightness of the light source with enough sources we could settle this issue.
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- Another avenue for this research lies in the precise analysis of distortions in the Cosmic Microwave Background.
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- We calculate the Cosmic expansion by counting of how much matter is in a region of space divided by the volume of that space. That gives us an average density of matter. We put that into the theory of relativity equations for gravity and get an average expansion rate.
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- Applying these equations for volumes a space approximating the entire universe becomes impossibly difficult.
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- What we need is for data.
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- We still need to discover the geometry of universe. Is it flat, spherically shaped, or saddle shaped? We need to discover the composition of dark matter? We need to discover the source of antigravity if the acceleration of expansion is real? We need to be able to measure the gravity waves? We need to detect primordial neutrinos? Is the universe really expanding. Maybe the universe is not homogeneous? Maybe we just happen to live in a giant void in space? Outside higher density regions may be causing a temporary expansion justi for us? An announcement will be made shortly stay tuned
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RSVP, with comments, suggestions and corrections. An index of all reviews is available. Some reviews are at: -------------------- http://jdetrick.blogspot.com -------
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or: ---- https://plus.google.com/u/0/ ,or, “Jim Detrick” ------- www.facebook.com ,
------ www.twitter.com, or, 707-536-3272 ------ Thursday, January 2, 2014
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