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----------------- 1749 - Dark Energy Expanding the Universe
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- A hundred years ago astronomers discovered the Universe was expanding. Two decades ago astronomers discovered that the expansion was accelerating faster and faster. The expansion will eventually be faster than the speed of light.
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- In 2006 studies of the Cosmic Microwave Background produced more evidence that the Universe experienced an early phase of hyper-expansion, called, “ Cosmic Inflation”.
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- All of the distant galaxies are moving away from us at an accelerating rate. Doesn’t that put us at the center of the expansion? No, there is no center. No matter where you go in the Universe your field of reference has everything expanding away from you.
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- Light traveling through expanding space gets stretched out to wider wavelengths. As wavelengths increase light energy decreases. Gamma Rays released 380,000 years after the Big Bang have been stretched out to Microwave wavelengths today. All individual photons get redder ( longer wavelengths) and loose energy in an expanding space.
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- Expanding space implies another principle. There is not a preferred frame of reference for “physical interactions”. The Universe is self-contained. It is expanding without expanding into anything.
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- General Relativity principle tells us that matter and energy in a gravitational field move the way curved space-time dictates. Gravity bends light by curving space-time.
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- When the visible Universe was half its current size the density of matter was 8 times higher and the radiation was twice as hot. The earlier the Universe the denser and hotter it was. Back to the beginning it was the creating of matter out of energy and time itself created.
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- What was there before matter, energy and time were created? God only knows.
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- How long will the Universe last? In to infinity? God only knows.
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- Hyper-expansion in the theory of Cosmic Inflation requires the actual Universe to be bigger than our Observable Universe. What we call the Observable Universe appears to be 13,700,000,000 years old. What we see as 13.7 billion years ago has expanded to 46.5 billion lightyears distance today because the expansion was occurring during the whole time that light was traveling to reach us.
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- So the diameter of the Universe must be 93 billion light years across, not counting that part that expanded faster that the speed of light during Cosmic Inflation. God only knows how big it is today?
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- The Observable Universe has a horizon bounded by the finite speed of light, 186,000 miles per second. But, if space is expanding faster than the speed of light than the Universe is moving beyond what is even Observable today.
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- 70% of the Universe is made of something we don’t understand. We call it Dark Energy. Energy is simply diluted mass , since mass is concentrated energy, according to E=mc^2.
-------------- Energy = mass * ( 90,000,000,000,000,000 )
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- Dark Energy is the energy that is expanding the Universe at an ever accelerating rate. Right now the rate is:
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------------------- 49,000 miles per hour for every million lightyears of space.
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- Dark Energy is “vacuum energy“, a property of space itself.
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- Dark Energy will eventually turn the entire Universe into a “ vacuum” if it keeps accelerating and diluting everything into space.
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- Dark Energy is the biggest mystery in astronomy today.
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- Dark Energy might even be space itself. We don’t know?
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- Dark Energy is an anti-gravity force causing all the galaxies to be moving away from each other. Except those local galaxies that are closely coupled by the gravitational force.
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- Astronomers long thought that gravity would eventually stop the expansion of the Universe. But, these discoveries since 1998 are telling them the opposite is true. The Universe keeps getting older, colder, and diluted to become a vacuum, a very expansive vacuum.
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- What do astronomers think this energy could be?
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- It could be an intrinsic, uniform property of space itself. It could be an undiscovered energy field that fills all of space like a fog. It could be the same energy field responsible for Cosmic Inflation. Somehow it just slowed down.
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- It could be that our observations to date are an illusion? Maybe our physics is wrong? Maybe gravity is not a constant? Maybe gravity simply weakens over distances greater than distance squared.
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- Astronomers reached the expanding conclusion by measure supernovae luminosity (brightness) and Redshift ( Doppler shift, or wavelength stretching due to receding velocities , or expanding space) These calculations depended on a “standard candle” of brightness. A certain type of supernovae that explodes at exactly 1.4 Solar Mass. This is a situation where a star is accreting mass from some other star and it reaches “critical mass” of 40% greater that the Sun’s mass, and, it explodes in a supernova.
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- Because the mass is known accurately the luminosity of the explosion can be calculated accurately. Using the brightness to calculate distance:
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------------------ Apparent Brightness = Luminosity / 4*pi*(distance)^2
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- And, using Redshift to calculate distances:
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----------------- Receding Velocity = Speed of light * Redshift
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--------------- Receding Velocity = Hubble’s Constant * Distance
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- Hubble’s Constant is the expansion rate of the Universe at 22 kilometers per second per million lightyears distance.
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------------ Ho = 49,000 miles per hour per million lightyears of space.
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- The conclusion from these calculations is that the further galaxies are away the faster they are receding away. And, this faster rate is accelerating with time.
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- Besides Brightness and Redshift calculations astronomers are using another approach. There may exist acoustic waves ( oscillations) in the expansion that spaces all the galaxies in a distinct physical scale ( called Baryonic Acoustic Oscillations). These acoustic waves measured in lightyears distances may constitute a “ standard ruler” that can be used to measure Universe expansion.
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- Astronomers need more data and more precision . The goal is to gather data on 300,000,000 galaxies and merge all the measurement techniques together. It is a big puzzle for astronomy. Stay tuned, there is much more to learn.
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- Other reviews available upon request:
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- #1290 = The Universe mass is 4.1 *10^105 galaxies.
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- #1047, #1083, #1084 - Redshifts can not distinguish from an expansion in space or a variation of time
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- #822, etc. and nine other reviews on the mysteries of Dark Energy
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