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Posts tagged with cosmology


M31 is a globular cluster located 25,100 light years away from Earth. It consists of 300,000 stars and is about 145 light years in diameter.

via intothecontinuum

hi-res




Black Hole Fragmentation
Image Credit: Burkhard Zink, Nikolaos Stergioulas, Ian Hawke, Christian D. Ott, Erik Schnetter, and Ewald Muller

Black Hole Fragmentation

Image Credit: Burkhard Zink, Nikolaos Stergioulas, Ian Hawke, Christian D. Ott, Erik Schnetter, and Ewald Muller


hi-res
















At the local viewing of the transit of Venus, I asked an astronomer named Lisa how people noticed a planet going in front of the Sun in the first place. (Surely they weren’t just staring at the sun all day?)
She told me:
Edmund Halley predicted the transit of Venus. He died before being seen right, which seems sad, but we didn’t discuss that any further. Theory preceded observation. EDIT: Apparently Jeremiah Horrocks first wrote of the transit of Venus.
The first observed transit of Venus killed that last free parameter to allow scientists to figure out the absolute distance from Earth to the Sun. (Previously they’d only known relative distances between planets.)
I asked her the question I had formulated while watching Lawrence Krauss’ talk: how can you know, as in know-know, know know know, whether a star is bright or close?Her answer: astronomers make a lot of assumptions. (Ahhh, satisfaction.) In particular they assume that most stars are normal (Gaussian, not just usual). Well, that makes a lot of sense then.
Nowadays another telescope is being built (thank you, government) that will triple the range within which relevant things can be seen, so we will be able to see to the centre of the Milky Way galaxy (and equal distance in the opposite direction) — and do so very precisely.So precisely that we will be able to measure parallax — the difference in how stars appear in winter versus summer, when we’re on opposite sides of the Sun — and obtain precise knowledge of where many, many stars are. (Tripling length means roughly times 3³ volume, so more like 20-30 times more stars’ positions will be known.)
Now this is the kicker in your Popperian dirtsack. Ancient Greeks had the right theory (heliocentric solar system) but discarded it on the basis of experimental evidence!Never preach to me about progress-in-science when all you’ve heard is a one-liner about Popper and the communal acceptance of general relativity. Especially don’t follow it up by saying that “science" marches toward the Truth whilst "religion" thwarts its progress.According to Astronomer Lisa, it’s not true that the Greeks simply thought they and their Gods were at the centre of the Universe because they were egotistical. They reasoned to the geocentric conclusion based on quantitative evidence. How? They measured parallax. (Difference in stellar appearance from spring to fall, when we’re on opposite sides of the Sun.) EDIT: More by @rmathematicus, suggested by @sc_k. How did heliocentrism eventually triumph in the Renaissance?Given the insensitivity of their measurement tools at the time, the stars didn’t change positions at all when the Earth moved to the other side of the Sun. Based on that, they rejected the heliocentric hypothesis.If the Earth actually did move around the Sun, then the stars would logically have to appear different from one time to another. But they remain ever fixed in the same place in the Heavens, therefore the Earth must be still (geocentric).
I always told this story to myself as the gradual removal of anthropocentrism from the natural order. First we learn we’re not the centre of the Universe, then we’re not the only Galaxy, we’re not the only species that falls in love, we’re evolved by chance like everyone else, and so on. But that story is wrong. It doesn’t fit this bit of the history of ideas and I bet it doesn’t fit other bits of history either. I need a new story.

At the local viewing of the transit of Venus, I asked an astronomer named Lisa how people noticed a planet going in front of the Sun in the first place. (Surely they weren’t just staring at the sun all day?)

She told me:

  1. Edmund Halley predicted the transit of Venus. He died before being seen right, which seems sad, but we didn’t discuss that any further. Theory preceded observation. EDIT: Apparently Jeremiah Horrocks first wrote of the transit of Venus.
  2. The first observed transit of Venus killed that last free parameter to allow scientists to figure out the absolute distance from Earth to the Sun. (Previously they’d only known relative distances between planets.)
  3. I asked her the question I had formulated while watching Lawrence Krauss’ talk: how can you know, as in know-know, know know know, whether a star is bright or close?

    Her answer: astronomers make a lot of assumptions. (Ahhh, satisfaction.) In particular they assume that most stars are normal (Gaussian, not just usual). Well, that makes a lot of sense then.
  4. Nowadays another telescope is being built (thank you, government) that will triple the range within which relevant things can be seen, so we will be able to see to the centre of the Milky Way galaxy (and equal distance in the opposite direction) — and do so very precisely.

    So precisely that we will be able to measure parallax — the difference in how stars appear in winter versus summer, when we’re on opposite sides of the Sun — and obtain precise knowledge of where many, many stars are. (Tripling length means roughly times 3³ volume, so more like 20-30 times more stars’ positions will be known.)
  5. Now this is the kicker in your Popperian dirtsack. Ancient Greeks had the right theory (heliocentric solar system) but discarded it on the basis of experimental evidence!

    Never preach to me about progress-in-science when all you’ve heard is a one-liner about Popper and the communal acceptance of general relativity. Especially don’t follow it up by saying that “science" marches toward the Truth whilst "religion" thwarts its progress.

    According to Astronomer Lisa, it’s not true that the Greeks simply thought they and their Gods were at the centre of the Universe because they were egotistical. They reasoned to the geocentric conclusion based on quantitative evidence. How? They measured parallax. (Difference in stellar appearance from spring to fall, when we’re on opposite sides of the Sun.) EDIT: More by @rmathematicus, suggested by @sc_k. How did heliocentrism eventually triumph in the Renaissance?

    Given the insensitivity of their measurement tools at the time, the stars didn’t change positions at all when the Earth moved to the other side of the Sun. Based on that, they rejected the heliocentric hypothesis.

    If the Earth actually did move around the Sun, then the stars would logically have to appear different from one time to another. But they remain ever fixed in the same place in the Heavens, therefore the Earth must be still (geocentric).

I always told this story to myself as the gradual removal of anthropocentrism from the natural order. First we learn we’re not the centre of the Universe, then we’re not the only Galaxy, we’re not the only species that falls in love, we’re evolved by chance like everyone else, and so on. But that story is wrong. It doesn’t fit this bit of the history of ideas and I bet it doesn’t fit other bits of history either. I need a new story.




Lawrence Krauss, author of A Universe from Nothing lecturing on cosmology.

  • Don’t really agree with or like his monolithic straw-man representation of “religion" versus "science" at minute 6. "Religion pretends to know all the answers" .


    Sub-i, sub-j, larry. There are many religions and many sciences.
  • Minute 14. Edwin Hubble’s original data! straight-line plot through a bunch of dispersed points. “That’s why we know he was a great scientist” — nobody laughed in the tape, but I did — “he knew that he should draw a straight line through a cloud of points”. I also love it when people take the time to go through an old paper, pull things out, and present them anew.
  • I have never understood the business of standard candles. To me it seems like you have two degrees of freedom (distance and brightness), only one of which can be knocked out by the measurement of apparent brightness.

    So say we figure out a “standard candle” — a star with a particular colour signature that tells us “The star is at X phase of its life, is made up of Z, and such stars always shine at a constant brightness of 1 for Q million years.”

    But still — how do we know that our theory is right? How do we know, know, know that  it’s really brightness of 1? It’s not like we can triangulate. And it’s certainly not like we’ve been there and seen it first-hand.
  • I had the same problem in a discussion with a geologist a few months ago. I sometimes get the sense that working scientists are so immersed in the practical fact that, yes, for all intents and purposes we know X to be true, that they’re not willing to step back to an abstract, philosophical level and say: “Well, if you really keep pulling on the threads, there are assumptions at the bottom of everything, so yes, we really don’t absolutely know X to be the case. However, Philosophical Prig, we don’t really know we’re not living in The Matrix either! So hush up and get back to doing something relevant.” But that’s the kind of answer I really want to hear: no, we don’t know know know, but for all practical purposes, yes we know.
  • Minute 15. How old is the universe? So Hubble got the answer wrong in 1929, and it was obviously wrong. “Scientists don’t know what they’re doing”

    But I had the same reaction to people talking about dark matter in the 90’s. “What is this stuff we call dark matter? Or dark energy?” As I understood it at the time, “dark matter” just represented a 90% fudge factor in astronomical measurements. It could be that gravity or quarks or anything else about the laws of physics is simply different in other parts of the universe. And how would we rule out that hypothesis? We just rule it out by assuming that the laws of Nature are the same everywhere, because that’s what we’ve assumed for the last few hundred years and it’s always worked out. Straight-line extrapolation to “That assumption must be true now and everywhere” despite that we’re now talking about multiple galaxies so unimaginably far away.
  • Minute 18:30 "This is a Hubble plot, much better than Hubble’s plot. It was made after the discovery that on a log-log plot, everything is a straight line.” Again, no laughs, but I thought that was hilarious.
  • Calculations that estimate the total energy in all vacuums add up to 10^28 times the observed mass of the universe. Whoops.
  • Dark matter here on Earth? Let’s go down into the mines and measure it. (By the way, where would the physicists be if those evil resource-extraction companies in Lead, South Dakota hadn’t negotiated with the legal entities that be and drilled into the Earth’s crust? Way to play it as it lies, Sandia Labs. #scruples)
  • Flat, closed, or open universe? (also why are these the only three options?) Well, we only observe 30% of the mass thta would be required to make the universe flat.
  • A gigantic, gigantic, um, really gigantic triangle — to measure the curvature of the universe.
  • That’s what those microwave-background radiation detecting balloons in Antarctica have been doing.
  • There’s always something there, even when there’s nothing. (see this video of the quantum fields flickering about in empty space)
  • 90% of the mass of a proton is due to the vacuum. (not delta spikes, more like 1/x or exp(−x) integrals.) Therefore your mass is 90% due to quantum fluctuations around the zero point energy.
  • The universe also has a net total energy of 0. Hence the possibility of “a universe from nothing” (our universe needn’t have a Creator since there is enough mass/energy in the physical vacuum that those virtual fluctuations could have acted as a Prime Mover).
  • 70% + 30% = 100%
  • Making our place in the Universe even less special. “Regular” matter—the stuff we observe—is only a 1% pollution in the uniform dark-energy / dark-matter background of the universe.
  • Deep-future scientists (like in a few billion years) won’t be able to observe other galaxies. Measuring the universe, they will observe (correctly) that their galaxy is the only one around, and that there is nothing but empty, eternal space around them.
  • So they will be “Lonely and ignorant, but dominant. Of course those of us who live in the United States are already used to that.”




If you put your hand up in the night, away from L.A., and look at a dark spot of the sky the size of a dime—with a large enough telescope, you could see 100,000 galaxies there.

Stars explode once every 100 years per galaxy. So in that little region with 100,000 galaxies, on a given night you’ll see ten stars explode.

The universe is huge, and old, and rare things happen all the time.

Lawrence Krauss

minute 17:30 of this lecture

(Source: youtube.com)




Without science, explaining why there is something rather than nothing requires explaining every leaf, rock, beetle and star.

Cosmology and evolutionary theory pare the explanation requirement down … we might have to explain only a physical law or three, and everything else … can follow naturally. … [I]t might be that we don’t have to explain why there is matter and energy, perhaps not even why there is three-dimensional space and time or why physical constants have the values they have.

It is also possible, although harder to conceive, that we could explain everything down to nothing: no physical laws, only logic. Putting that another way, it might be that naive mental pictures of nothing are logically impossible.

Aaron C. Brown, reviewing Why There is Something Rather than Nothing by Lawrence Krauss




Astronomy, cosmology, older & newer scientific theories

  • Lord Kelvin thought the sun was powered by gravity — squeezing itself and generating heat in the process, which was expelled
  • In Darwin’s time the geological evidence made things look older than the cosmological evidence. (Knowledge of nuclear physics was necessary to explain how the sun could last long enough to be as old as rocks on Earth apparently were.)
  • Newton’s incorrect, though seemingly logical, reasoning as to why the universe must be infinite and static.
  • Einstein’s GR+ cosmological constant —> Wilhelm de Sitter —> LeMetre, mathematician & clergyman, and Freeman
  • Theoretical models of solar evolution inform our inference of brightness vis-a-vis distance of stars. Are these models flawed?
  • As much evolution as took place between bacteria and us, will take place before the Sun fries the Earth, in 4b years.




Question. Why do we live in a 3-dimensional universe?

Tentative Answer. Maybe because 3 dimensions is the most interesting number of dimensions? Maybe 3-D is the boundary between “too constrained” and “too free”.

The above link is to some mathematicians discussing other interesting dimensions besides 3 — because they already know 3-D is uniquely suited to complexity.

In other words, lots of “facts” are only facts in ℝᵈ when d=3. So by the anthropic principle…we live in 3-D.





Here’s one fact that’s unique to just the fourth dimension.

Exotic ℝ⁴: There are infinitely many non-diffeomorphic smooth structures on the topological space ℝᵈ if and only if d=4.

Otherwise there is only one diffeomorphism class.

^ pictures of diffeomorphisms

(A diffeomorphism preserves the relationships between neighbouring points.)