I've been working my way through Max Tegmark's, Our Mathematical Universe. My post on the first two chapters is here. My post on the third chapter is here.
1. Today I want to cover chapters 4 and 5. I can't believe how much has been happening in cosmic science these last few years. It feels like the cutting edge of science is moving faster than most of us could imagine. It feels like you have to be way smarter to be part of it than ever before. Man I feel old.
So chapter 4 includes some interesting claims. According to the latest estimates, only about 3% of the cosmos is ordinary matter. To get the expansion rate correct, about 68% of the universe would need to be "dark energy," where this is energy we cannot observe that does not cluster to form galaxies and such. It is energy that has a repulsive gravitational effect (77). Then 27% of our universe would be "dark matter," matter that we cannot observe that contributes to the mass of the universe that does affect the clustering of ordinary matter into galaxies.
I don't particularly like the concept of dark matter and energy. They sound like things we make up because our theory is wrong. (They remind me of an old notion called phlogiston). But Tegmark assures us that the numbers have been suggested from more than one universe measurement.
The chapter goes through some of the chase that arrived at these numbers. They mostly seem to derive from precision measurements of fluctuations in cosmic background radiation (a chart on p.72). The "cosmic matter budget" is also said to explain how the total cosmic density can be 10 to the 10th power lower than water and how space can be flat.
2. I would need to reread these chapters to put everything together better. The current thinking seems like something that could be radically reconceived if an Einstein came along, but Tegmark certainly gives the impression that the current thinking is pulling together toward the same conclusions from multiple directions. So I'm writing them down in construction pencil, although some of these findings are far enough along that Nobel Prizes have been awarded.
According to the varied measurements, the universe is currently thought to be about 13.7 or 13.8 billion years old. The "big bang" for Tegmark was a point near the very beginning where the universe doubled its size in under a second. It spent the next few minutes fusing about 25% of total hydrogen into helium. Then this hydrogen-helium plasma cooled for about 400,000 "years" (Gamow), after which the clumping and expansion took place that has resulted in the current visible universe with its swirling galaxies and such.
3. In chapter 5, Tegmark pushes back before this cosmic "big bang." I understand now a little better what he meant when he said that the big bang is not exactly the beginning. If I am getting it right, there is about a third of a second before this "big bang" that needs to be explained. (I have a couple other books I really need to read--Hawking's Brief History and a book called The First Three Minutes).
The key players here are Alan Guth and Andrei Linde. Guth addressed a "horizon problem." Why is the universe the same temperature when there are parts of it that one might say have never touched? Another problem is the "flatness problem." I'm not entirely sure what it means to say that the universe is flat, but apparently, it is balanced exactly right like a bike standing up without a kick stand.
Guth's suggested explanation was "inflation." In 10 to the negative 38th power seconds, the mass of the universe doubled 260 times. It borrows the energy to create this mass from gravitation, if I understand correctly. The gravitational waves which were observed last year are a prediction of this model.
At the end of this chapter, Tegmark suggests that this inflation has never stopped. It's just that it stopped in our pocket of the universe. Following Alex Vilenkin, about a third of the inflating substance of the universe "bangs" into galaxies while the rest continues to inflate beyond our sight. So our "Big Bang" was really the end of inflation in our part of space.
Meanwhile, inflation can, according to general relativity, create an infinite volume inside a finite volume. So our universe began "inside" a space smaller than an atom.
4. Well now. I don't know enough even to understand, much less evaluate these strange theories. But I will read on. I was struck by the tenuousness of it all, how the numbers need to be just right to get what we have. The anthropic principle, which seems to fit nicely into an argument from design.
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