The Last of the Universe’s Ordinary Matter Has Been Found • Hacker News Board

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#11

Post by gcbw2 » Mon, Sep 10, 2018, 8:11 PM UTC

macintux wrote: post #7

gcbw2 wrote: post #6

The hypothesis is they should see CMB distortion between galaxies, which is hidden by the distortion caused by the galaxies themselves. The solution was to assume they were removing the distortion caused by the galaxy halo, and what was left was the original distortion they were looking for. sounds like the work to rule out false-positives would be huge. This is putting a lot of weight on a technique that is not full…

There's more confidence in the result because two teams using very different methods have arrived at the same conclusion.

The three papers used the same 'filtering' methodology, to keep the simplification analogy.

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#12

Post by yalogin » Mon, Sep 10, 2018, 8:14 PM UTC

I know and understand nothing about this topic but given the fact that the universe is infinite by definition makes the conclusive/definitive statement very surprising.

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#13

Post by akvadrako » Mon, Sep 10, 2018, 8:36 PM UTC

yalogin wrote: post #12

I know and understand nothing about this topic but given the fact that the universe is infinite by definition makes the conclusive/definitive statement very surprising.

The universe is not infinite by definition and anyway they are only talking about the visible universe.

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#14

Post by simsla » Mon, Sep 10, 2018, 8:45 PM UTC

gcbw2 wrote: post #6

The hypothesis is they should see CMB distortion between galaxies, which is hidden by the distortion caused by the galaxies themselves. The solution was to assume they were removing the distortion caused by the galaxy halo, and what was left was the original distortion they were looking for. sounds like the work to rule out false-positives would be huge. This is putting a lot of weight on a technique that is not full…

You're right about the first two papers (which used the same approach). Ruling out a FP result would be difficult, which is why it wasn't fully embraced by the scientific community.

The third team took a different approach [1], with results that are both more accurate, less prone to FP, and generally agree with the other findings.

> Here we report observations of two absorbers of highly ionized oxygen (O VII) in the high-signal-to-noise-ratio X-ray spectrum of a quasar at a redshift higher than 0.4. These absorbers show no variability over a two-year timescale and have no associated cold absorption, making the assumption that they originate from the quasar’s intrinsic outflow or the host galaxy’s interstellar medium implausible.

[1] https://www.nature.com/articles/s41586-018-0204-1

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#15

Post by sandworm101 » Mon, Sep 10, 2018, 8:46 PM UTC

yalogin wrote: post #12

I know and understand nothing about this topic but given the fact that the universe is infinite by definition makes the conclusive/definitive statement very surprising.

Who is telling you that the universe is infinite? Astronomers/cosmologists generally all agree that our current universe (the matter-containing 4 dimensions bit we live in) had a defined beginning from which is has grown. There is an outer edge,. defined by the rate of expansion starting from the big bang.

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#16

Post by [deleted] » Mon, Sep 10, 2018, 8:59 PM UTC

gcbw2 wrote: post #10

nfc wrote: post #9

Earlier quoted context omitted.

I'm not really sure of what you mean by false positives. After my understanding of the stacking technique as used in other contexts in astrophysics and without going into too much details : The problem they were facing is that the signal to noise of the images of the filaments was too low to say that they had detected anything in any individual images. However by stacking (adding) images they were able to detect it b…

Think like that: there are two bright lights in front of you. There will always be a halo between those two bright lights. Now, my hypothesis is that "between all two bright lights, there is third, dimmer one, hidding". And then i prove it by filtering X from the two bright light halo, and prove that Y is left proving that the third light is there. Now, how can i be sure Y is really a third dimmer light? and not just…

[deleted]

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#17

Post by Firerouge » Mon, Sep 10, 2018, 9:25 PM UTC

TomMckenny wrote: post #8

Slightly related, I wonder if anyone has figured out the density of interstellar comet or asteroid like objects. I notice that Oumuamua happened to pass within some 20 million km of earth within a decade or so of having systems in place to spot it. Wouldn't this imply there are an awful lot of them?

I'm not qualified to answer your question, but the observation of Oumuamua alone doesn't give a large enough sample size to estimate how often large interstellar comets or asteroids pass through our solar system.

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#18

Post by coldtea » Mon, Sep 10, 2018, 9:33 PM UTC

TomMckenny wrote: post #8

Slightly related, I wonder if anyone has figured out the density of interstellar comet or asteroid like objects. I notice that Oumuamua happened to pass within some 20 million km of earth within a decade or so of having systems in place to spot it. Wouldn't this imply there are an awful lot of them?

>I notice that Oumuamua happened to pass within some 20 million km of earth within a decade or so of having systems in place to spot it. Wouldn't this imply there are an awful lot of them?

Finding one in a decade's span within 20 million km would imply there are "an awful lot of them"?

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#19

Post by aikah » Mon, Sep 10, 2018, 9:37 PM UTC

sandworm101 wrote: post #15

yalogin wrote: post #12

I know and understand nothing about this topic but given the fact that the universe is infinite by definition makes the conclusive/definitive statement very surprising.

Who is telling you that the universe is infinite? Astronomers/cosmologists generally all agree that our current universe (the matter-containing 4 dimensions bit we live in) had a defined beginning from which is has grown. There is an outer edge,. defined by the rate of expansion starting from the big bang.

Then what do physicists call what is beyond the edge of the universe?

edit: excuse my french ;)

Re: The Last of the Universe’s Ordinary Matter Has Been Found

#20

Post by gmailsyncer » Mon, Sep 10, 2018, 9:38 PM UTC

stephengillie wrote: post #3

gmailsyncer wrote: post #2

There must be regions of the universe where this "not very dense" gas is dense enough to use a ramscoop

Probably more in high-gravity locations, such as planets and stars. Thinking about the Juno satellite orbit, would it be better/easier/cheaper to hang a mining station in orbit around Jupiter, or have a satellite/ship dip into Jupiter's atmosphere every orbit?

Assuming there really is other intelligent life out there, "where you were born" seems to make a huge difference in what your species can accomplish in its lifetime.

Seems like we are somewhat validating Vernor Vinge's "zones of thought" idea