* Compare the views of Hubble and Friedman about the expansion of the universe:
Edwin Hubble’s observation
In 1929, Edwin Hubble announced that his observations of galaxies outside our own Milky Way showed that they were systematically moving away from us with a speed that was proportional to their distance from us. The more distant the galaxy, the faster it was receding from us. The universe was expanding after all, just as General Relativity originally predicted! Hubble observed that the light from a given galaxy was shifted further toward the red end of the light spectrum the further that galaxy was from our galaxy.
The specific form of Hubble's expansion law is important: the speed of recession is proportional to distance. Hubble expressed this idea in an equation - distance/time per megaparcec. A megaparcec is a really big distance (3.26 million light-years).
Alexander Friedman’s theory
In the early 1920’s Friedman for told a theory were universe begins with a Big Bang and continues expanding for untold billions of years (that’s the stage we’re in now.) But after a long enough period of time, the mutual gravitational attraction of all the matter slows the expansion to a stop.” The universe will eventually start to contract in a big crunch.
Friedman embraced the idea that the equation in Einstein’s theory of relativity shows a universe that is in motion, and not constant.
* A flow chart to show and describe the transformation of radiation into matter which followed the “big bang”:
* Einstein’s view of the connection between matter and energy:
Association between mass (m) and energy (E) in Albert Einstein’s theory of relativity, complete by the formula E= mc2, where c equals 300,000 km (186,000 miles) per second i.e. the speed of light.
In physical theories prior to that of special relativity, mass and energy were seen as distinct entities. The energy of a body at rest could be assigned an arbitrary value. In special relativity, the energy of a body at rest is determined to be mc2. There for, each body of rest mass m possesses mc2 of “rest energy,” which potentially is available for conversion to other forms of energy. The mass-energy relation implies that if energy is released from the body as a result of such a conversion, then the rest mass of the body will decrease. Such a switch of rest energy to other forms of energy occurs in ordinary chemical reactions, but much larger conversions occur in nuclear reactions. This is particularly true in the case of nuclear-fusion reactions that transform hydrogen to helium, in which 0.7 % of the original rest energy of the hydrogen is converted to other forms of energy.
Although the atomic bomb proved that vast amounts of energy could be liberated from the atom, it did not demonstrate the precision of Einstein’s equation.
* Accretion of galaxies and stars
After a few hundred thousand years after the Big Bang, the Universe was cooled down and atoms were formed. As the Universe was further expanding and cooling, the atom particles lost kinetic energy and gravity began to attract them together forming regions of high mass density. The regions of high mass density began to attract nearby material and gain mass. This process is known as accretion.
At some time or another, all matter in the universe formed discrete gas clouds known as protogalaxies. As further accretion occurred, galaxies were formed. Accretion also occurred inside galaxies, forming stars. As the average temperature of matter in the universe, then as the universe expands there is less hot matter such as stars and colder dark space/matter between it, so when you average things out, you get a lower temperature. * Relationship between the temperature of a star to the wavelength and color emitted from that star.
Stars appear to be exclusively white at first glance. If we look carefully, we can see that there are a range of colors blue, white, red etc. stars are small...
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