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Ch. 5: Dark Matter 
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 Ch. 5: Dark Matter
Astrophysics for People in a Hurry
by Neil deGrasse Tyson

Ch. 5: Dark Matter


Please use this thread to discuss this chapter.



Thu Oct 12, 2017 2:38 pm
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Post Re: Ch. 5: Dark Matter
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Thus, as best we can figure, the dark matter doesn’t simply consist of matter that happens to be dark. Instead, it’s something else altogether. Dark matter exerts gravity according to the same rules that ordinary matter follows, but it does little else that might allow us to detect it. Of course, we are hamstrung in this analysis by not knowing what the dark matter is in the first place. If all mass has gravity, does all gravity have mass? We don’t know. Maybe there’s nothing wrong with the matter, and it’s the gravity we don’t understand.

We're getting into some loopy stuff now! We know very little about the most common substance in the universe.
Quote:
What we know is that the matter we have come to love in the universe—the stuff of stars, planets, and life—is only a light frosting on the cosmic cake, modest buoys afloat in a vast cosmic ocean of something that looks like nothing.

During the first half million years after the big bang, a mere eyeblink in the fourteen-billion-year sweep of cosmic history, matter in the universe had already begun to coalesce into the blobs that would become clusters and superclusters of galaxies. But the cosmos would double in size during its next half million years, and continue growing after that. At odds in the universe were two competing effects: gravity wants to make stuff coagulate, but the expansion wants to dilute it. If you do the math, you rapidly deduce that the gravity from ordinary matter could not win this battle by itself. It needed the help of dark matter, without which we would be living—actually not living—in a universe with no structures: no clusters, no galaxies, no stars, no planets, no people.

How much gravity from dark matter did it need? Six times as much as that provided by ordinary matter itself. Just the amount we measure in the universe. This analysis doesn’t tell us what dark matter is, only that dark matter’s effects are real and that, try as you might, you cannot credit ordinary matter for it.

The counter-forces between coagulation and dilution become even more complicated in the next chapter.



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Post Re: Ch. 5: Dark Matter
Having now read both chapter five (Dark Matter) and six (Dark Energy), I have to recall my quote at the beginning of chapter four (Between the Galaxies). The universe is indeed stranger than we imagine. If the astrophysicists are correct, we can neither see nor measure the vast majority of matter and energy in the universe. And the discussion of a universe in balance? A vacuum spot in space where matter and energy still "trade places"? Maybe Fred Hoyle wasn't so far off with his steady state universe theory after all.


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Post Re: Ch. 5: Dark Matter
This is loopy, and fascinating, all right. Most of the rest of the stuff we can think of as "existing" we know about from observing it. An exception might be the wave function behind electrons and other particles of "matter" which have their own mysterious behaviors.

In the case of Dark Matter and Dark Energy, we infer them from evidence that they have some effect. Yet, as NDG points out, it may be the range of possible mechanisms we understand imperfectly, more than the range of possible entities.



Wed Nov 29, 2017 5:34 am
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Post Re: Ch. 5: Dark Matter
While I know I'll never understand Dark Matter and Dark Energy until some future astrophysicist figures it out and explains it to me in layman's terms, if such a thing be possible, I do think about it sometimes. When that makes my head hurt I think about this:

Congratulations to Drs. S. Haroche and D. Wineland for winning the Nobel Prize in Physics.
These two physicists got the Prize for doing experiments once thought to be impossible, i.e. studying single atoms and single photons (particles of light).
They proved the correctness of the bizarre properties of quantum mechanics, i.e. that electrons can be two places at the same time.


Then I take a pill for my migraine.


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Post Re: Ch. 5: Dark Matter
Litwitlou wrote:
They proved the correctness of the bizarre properties of quantum mechanics, i.e. that electrons can be two places at the same time.
Then I take a pill for my migraine.

That is so cool. Sorry about your head, though.



Sat Dec 09, 2017 4:44 pm
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