Saturday, June 9, 2018

Hubble Constant and Quantum Gravity



-  2098  -  Scientists still cannot explain gravity.  We can explain how it works rather well.  But, not the true nature of gravity.  Einstein's Theory of Relativity is the best explanation we have.  But, we cannot reconcile that theory with the theory of quantum mechanics.  Understanding gravity in the framework of quantum mechanics is one of the great challenges in modern physics today.  Is gravity even a quantum entity?
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-----------------  2098 -  Hubble Constant and Quantum Gravity
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-  The expansion of the Universe was calculated over 100 years ago.  Recently it is being measured more precisely using the Hubble Telescope.   Results confirm that the universe is expanding faster now than expected following the trajectory of the Big Bang that was previously calculated.
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-  Astronomers are using Cepheid variable stars to measure accurate distances near to and far from Earth.  These measurements over the past six years are used to calculate how fast the Universe is expanding over time. 
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-  Previous measurements using the Cosmic Microwave Background measurements put the expansion rate at 67 kilometers per second faster for every 3.3 million light years distance.  The Hubble measurements have the value at 73 kilometers per second per megaparsec.  (the 3.3 million lightyears is equal to one megaparsec.)  The new result shows a 9% faster expansion than previously determined.
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-  The discrepancy may underlie some new physics to be discovered.
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-  One explanation involves Dark Energy having an acceleration factor that changes over time. 
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-  A second explanation is that the Universe contains a new subatomic particle called a "sterile neutrino".  This new, yet to be discovered particle, travels near the speed of light but is only affected by gravity, not by the electromagnetic forces.
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-  A third possibility is that Dark Matter interacts more strongly with normal matter or electromagnetic radiation than currently expected. 
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-  Any of these scenarios would change the contents of the early Universe leading to inconsistencies in our theoretical models.
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-  Scientists still cannot explain gravity.  We can explain how it works rather well.  But, not the true nature of gravity.  Einstein's Theory of Relativity is the best explanation we have.  But, we cannot reconcile that theory with the theory of quantum mechanics.  Some think we need to discover a new particle, the graviton, but, it could be that it is too weak to be nearly impossible to measure its force.  
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-  Quantum effects in the gravitational field are exceptionally small.  This is because the gravitational coupling constant is 43 orders of magnitude smaller than the fine structure constant that governs the electromagnetic fields.  
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-  Understanding gravity in the framework of quantum mechanics is one of the great challenges in modern physics today.  Is gravity even a quantum entity?
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 -------------------------   Saturday, June 9, 2018   --------------------------------
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