Monday, November 12, 2007

Mars and Science Move Backward

Ptolemy's cosmology compared to Copernicus. Complicated, isn't it?

This week Mars is only 102 million kilometres away, the closest it will be for a some time. The bright red planet can currently be found in the constellation Gemini. On the night of November 15 Mars will appear to halt and then reverse course in the sky. From this week until January 30 the planet will show retrograde motion. Anyone observing the sky for a length of time will witness this backward flight.

For a long time humans thought that Earth was centre of the Universe and the planets circled around us. To explain retrograde motion, astronomers conjured up epicycles, spheres within spheres. By the time of Copernicus, some cosmologies had 60-100 epicycles. The mathematics were quite complicated, which kept science restricted to an elite few. Only in the 16th century did Copernicus' cosmology challenge the epicycles.

Big Bang theory states that the Universe expanded from a tiny volume. Anyone observing the sky will see that it is roughly uniform in any direction. The cosmic microwave background is uniform to one part in 10,000. Large portions of the sky appear to have reached thermal equilibrium, indicating that the Universe expanded faster than today's speed of light.

To explain the uniform sky, scientists starting in the 1970's conjured up inflation. According to this idea, when the Universe was just 10^{-33} seconds old it expanded at warp speed, many times faster than light. Inflation would violate Relativity's principle that nothing can travel faster than light. It would also violate the First Law of Thermodynamics about conservation of energy. Since nothing like inflation has ever been observed in nature, scientists imagine "inflations" and scalar fields.

Inflation shares the convenient quality of being unprovable. We cannot time travel to the first 10^{-33} seconds and observe inflation in action. The temperatures and energies of the Big Bang are also too great for any human experiment to reproduce. The mathematics are quite complicated, which keeps science restricted to an elite few.

Observations of distant Type Ia supernovae indicate that the Hubble ratio v/c appears to accelerate, evidence that the speed of light c is slowing. To explain this, scientists conjured up "dark energy." According to this idea, another repulsive force is causing velocity v to accelerate. This would also violate Relativity and the First Law of Thermodynamics. Since nothing like "dark energy" has ever been observed in nature, scientists have imagined all sorts of diverging ideas. The mathematics are quite complicated, which keeps science restricted to an elite few.

Ptolemy's cosmology of epicycles survived for 1500 years. It prevented humans from figuring out the obvious, that Earth circles the Sun. Today's mainstream cosmology is composed of inflation and "dark energy," which share many qualities with epicycles. Like invisible spheres, repulsive energies can never be observed in nature. Mars appears to travel backward in the sky, but will soon reverse again and travel forward. Will human science show this much intelligence?

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Blogger Zeynel said...

Great post and video. But there is something I don't understand. As this page says, it is

a common misconception that the Copernican model did away with the need for epicycles. This is not true, because Copernicus was able to rid himself of the long-held notion that the Earth was the center of the Solar system, but he did not question the assumption of uniform circular motion. Thus, in the Copernican model the Sun was at the center, but the planets still executed uniform circular motion about it. As we shall see later, the orbits of the planets are not circles, they are actually ellipses. As a consequence, the Copernican model, with it assumption of uniform circular motion, still could not explain all the details of planetary motion on the celestial sphere without epicycles. The difference was that the Copernican system required many fewer epicycles than the Ptolemaic system because it moved the Sun to the center.

In fact, Copernicus used more epicycles, not fewer.

So I wonder why the Copernican video looks so neat and clean?

But regardless of the number of epicycles I agree with your thesis that because of the dominance of the priestly class humanity could not figure out the motion of the earth for such a long time.

7:03 PM  
Blogger L. Riofrio said...

Only in the 16th century did Copernicus' cosmology challenge the epicycles. The revolution needed Kepler's elliptical orbits and Newton's gravity to be complete. Latter part of the animation shows Copernican cosmology with Keplerian ellipses.

Copernicus was himself a member of the priestly class, as were Giordano Bruno and Georges Lemaitre. (Kepler completed theological studies but was not ordained.) The Catholic church has seen the light and in 1951 endorsed Big Bang cosmology. Those who hold back science today are not required to believe in God.

9:47 AM  

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