Friday, March 30, 2018

Friday Science: Hawking 3 (Expansion of Universe)

I started Friday reviews of Stephen Hawking's A Brief History of Time.
Chapter 1
Chapter 2

Chapter 3: The Expanding Universe
1. I'm trying to figure out why I found this book so hard to read back in the nineties. My brain is a strange thing. Sometimes nothing will go in and then at other times a mess of complicated stuff goes right through. My breakthrough book was The Perfect Theory.

So chapter 1 talks about the earth at the center of the universe. We hear about Copernicus and Newton. He mentions relativity and quantum mechanics. Chapter 2 then gives Einstein's special and general theories of relativity. Chapter 3 is about the Big Bang.

2. This chapter makes it clear that Hawking sees how the Big Bang theory could play into belief in God but of course he rejects that. I'm always a little puzzled by Christians who have a really negative view of a big bang, because it seems to serve in strong support of the cosmological argument for the existence of God.

It must be the fact that most scientists think it took place a little less than 14 billion years ago. But that's not the same as evolution. John Piper, for example, is very open to an old earth even though he does not believe in evolution.

3. He talks a little about the process of discovering that we are inside a galaxy of stars and that there are millions of other galaxies of stars. Edwin Hubble in 1924 was the first to discover other galaxies. The two factors in the brightness of a star are its luminosity and its distance from us. Hubble's logic went like this:
  • If we know the luminosity of what we're observing, we can figure the distance from us.
  • We know the distance of some stars near us using geometry. Since we know the distance, we can determine the luminosity of various type of stars.
  • [We can type them by analysis of the light they emit, their spectra.]
  • Now, knowing the luminosity of these types, we can figure out the distances of distant ones.
4. Hubble discovered that the spectra of all the stars everywhere was shifted to the red end of the spectrum. That is to say, using the Doppler effect, they were moving away from us. In short, every point, everywhere in the universe, is moving away from every other part of the universe. The universe is expanding.

Indeed, the farther away a galaxy is, the faster it is moving away! The speed of expansion suggests whether 1) it will eventually slow down and pull back in on itself (cosmic crunch), 2) it will continue at a steady speed, or 3) it will expand faster and faster until there is a cosmic rip. The third seems to be the case. Alexander Friedmann in 1922, four years before Hubble, had predicted the expansion.

Einstein hated the idea of cosmic expansion, actually introduced a "cosmological constant" into his formulas to make it stop. :-) Ironically, he was right about the constant, but wrong about expansion.

5. In 1965, two men working for Bell Labs picked up a background radiation that was theoretically explained by a big bang. If the universe was infinitely old, it would have already dissipated. The universe must have been fantastically hot to begin with, but it has been cooling down ever since. If we extrapolate back, the universe would have begun as something like a "singularity," a single point.

"Dark matter" has also been proposed to explain why galaxies swirl as they do. The outer rims of the galaxies swirl at the same basic speed as other parts.

A lot of people didn't like the idea of an expanding universe. It played too easily into an argument for God. Fred Hoyle in England was a very charismatic propagator of a "steady state" theory, where matter is constantly being created. He's a study in how people believe as much because of the person selling stuff as on the basis of truth. He was wrong. Go away, charmer.

6. The chapter ends with Roger Penrose's discovery of the probability of black holes, and of course Hawking's work built off of him. Together they proposed that the universe had begun with such a singularity that then expanded in a big bang. Again, this idea faced a lot of resistance but, in the end, the math was the math.

The problem--still unsolved--is that general relativity and quantum mechanics don't fit together. This is no problem today because the cosmos is really big and the atom is really small. But before the big bang, the universe was immensely dense and immensely small. This is the biggest problem in modern physics.

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