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-----------------------------1904 - Studying the speed of light.
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- Ole Romer in 1676 used the moon, Io, of Jupiter whose orbit worked like a clock. One orbit took 1.769 days, or 42,456 hours, or 2,547,36 minutes.
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- Then, he used the orbit of the Earth about the Sun. The distance from the Earth to the Sun is 93,000,000 miles. Therefore, the diameter of a complete orbit is 186,000,000 miles.
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- Using the closest orbit to start the clock, then waiting six months to arrive at the most distant orbit, Ole found that Io crossed the crest of Jupiter 22 minutes later, every year. This meant it took light 22 minutes for light to cross the 186,000,000 mile additional distance.
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--------------------- distance = rate * time
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--------------------- rate = speed of light = distance / time
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-------------------- speed of light = 186 * 10^6 / 22 / 60
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--------------------- speed of light = 507,272,272 miles per hour.
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- Ole’s very first calculation in 1676 was 76% of the best answer we have today.
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--------------------- Speed of light = 676,616,692 mph
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- Christian Huygens and Isaac Newton got their own calculations to come up with:
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---------------------- speed of light = 492,126,000 miles per hour.
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- In the 1850’s scientists arrived at :
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--------------------- speed of light = 704,635,000 mph
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- It was about the time that physics was measuring electromagnetic charges and electrostatic charges , realized they traveled at the same speed, and that light must also be an electromagnetic wave.
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- In Einstein’s 1905 paper he proposed that the speed of light in a vacuum, measured by a non-accelerating observer, is the same, independent of the motion of the source or the observer. He delivered a lecture using 3 symbols for mass, energy and the speed of light and later proved that mass and energy were the same thing. Mass is simply concentrated energy according to :
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-------------------------- E = mc^2
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-------------------------- c = being the speed of light in a vacuum.
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- The speed of light travels at different speeds due to the medium in which it is traveling. It travels between atoms at its constant speed, but it is being absorbed and re-emitted by atoms as it moves through the medium making a “net” slower speed.
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- For example: a light beam traveling through a glass of water:
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------------------------ The speed in air is------------ 186,222 miles per second
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------------------------ The speed through glass --- 124,275 mps
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------------------------ The speed through water --- 140,430 mps
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----------------------- Through glass ----------------- 124.275 mps
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------------------------ Through air ------------------ 186,222 mps
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- Einstein’s claim that the speed of light from a moving source is counterintuitive. He maintained that the speed of light is always the same regardless of the initial reference frame. In other words light speed does not get added to its motion of a source in a medium. Further, a moving body approaching the speed of light would appear to slow down from the frame of the observer. The distance would shrink and the time would slow to keep the speed, the ratio, a constant.
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- It was not until the 20th century that measurements using laser interferometers and cavity resonators would more accurately measure the speed of light. In 1972 the value became:
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--------------------------- c = 299,792,458 meters per second.
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--------------------------- c = 670,616,692 miles per hour.
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- The other consequence of the speed of light being a “ constant” is the unification of “space-time”. In order for that to happen space and time become variables.
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- In the 1920’s the speed of light was used to determine that the Universe was expanding. And, the further away the galaxy was from us the faster it was receding.
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- This receding calculation was 68 kilometers per second per mega parsec distance away. Put in other units:
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------------------------ 47,000 miles per hour per million lightyears distance.
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- In the 1990’s this acceleration was measured to even be increasing over the past 5 billion years. That would mean the most distant galaxies are receding faster than the speed of light.
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- This does not mean that the galaxies are traveling that fast. It simply says the volume of space between us is expanding that fast. This realization has lead us to what is causing the accelerating expansion? We don’t know? We call it “ Dark Energy”. It remains a “Dark Mystery”. A driving force that we just can not explain.
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- In the meantime, we still think the speed of light is a constant:
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------------------------ c = 670,616,692 miles per hour
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------------------------ c = 186,282 miles per second, in the vacuum of space.
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- Other reviews available on this subject:
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- #1845 Why is the sky blue? It took 100 years to get the correct answer.
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- #1795 - Just seeing light uses half your brain. This review lists #940, #934, #726, #648, #550, #36 and a dozen other reviews about light.
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- Light does not know time.
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- The light that can be viewed through a telescope is 12,000,000, 000 years old and still ticking.
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----- 707-536-3272 ---------------- Tuesday, October 4, 2016 -----
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