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05.20.2018: One Chapter of Nonfiction

Today's soundtrack is Fiona Apple: Tidal.

This morning, I'm reading chapter 3 of Stephen Hawking's A Brief History of Time, "The Expanding Universe."

Stars that are nearer to us appear to move in the sky; stars that are further away appear static. William Herschel catalogued the "positions and distances of vast numbers of stars" (p. 46) and confirmed that the Milky Way is a spiral galaxy. Edwin Hubble proved that there are many galaxies in the universe by measuring their luminosity and accounting for both actual brightness and distance from the observer. He was able to find the "distances to nine different galaxies" (p. 48).

We can tell a star's type by the colour of light that it emits. Certain chemicals absorb specific kinds of light, so we can determine the chemicals of a star's atmosphere by what light it displays. We can also note that due to difference in light wavelength, "stars moving away from us will have their spectra shifted toward the red end of the spectrum (red-shifted) and those moving toward us will have their spectra blue-shifted" (p. 50). This is directly related to the Doppler effect. Interestingly, when we look at the stars around us, "nearly all [are] moving away from us" (p. 52) - because the universe is expanding all around us. Though everyone else tried to find ways to explain away an expanding universe, Alexander Friedmann instead tried to understand and explain it. Friedmann said that no matter what direction you look, and no matter your location in the universe, it looks approximately the same in every direction. This idea was proven through use of a microwave detector by Arno Penzias and Robert Wilson, who found that no matter which direction they pointed their detector, they were able to pick up approximately the same signal.

Though we don't have evidence for or against this theory, scientists believe we are not in the centre of the universe. They believe the expanding universe is like a spotted balloon being blown up. The bigger it gets, the further the spots appear from each other, though no one spot is in the centre.

There are three models of the universe that address its expansion and possible collapse. In the first, the universe experienced a big bang that made it expand, and eventually it will slow down due to gravity, collapsing back in on itself. In the second model, the big bang cause fast enough expansion that gravity will never stop the universe's expansion, but it will eventually slow down. In the third model, the universe experienced a short acceleration, but the expansion slowed dramatically, and someday will reach nearly zero, a point of almost-collapse, but since the galaxies will be so far apart, they will be nearly static, since their gravitational pulls won't affect each other.

There are two ways, really, of predicting what the universe will do in the long-term scope of things. In an open universe, the galaxies will drift farther and farther away from each other until the stars run out of fuel and die. In a closed galaxy, gravity eventually wins out over the universe's expansion, pulling the galaxies together, and eventually results in a "big crunch" (p. 59) where the universe collapses into one point. Which do we think will happen? There isn't yet enough evidence to say for sure, but currently the evidence points to the likelihood of an open universe.

A theory that was brought up as an alternative to the Big Bang theory of the creation of the universe was the Steady State theory, which proposed that new galaxies were slowly formed in the space left empty by galaxies as the expansion of the universe pulled them apart. That theory has since been abandoned because of evidence contradicting it.

Hawking wrote his thesis paper with the intent of proving that the universe started with a singularity, the Big Bang. He later changed his mind and was convinced that the effects of quantum mechanics negated the need to have the universe begin with a singularity; instead, he believed that the partial theory of general relativity could be combined with the partial theory of quantum mechanics to create the "quantum theory of gravity" (p. 67).


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