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The Last of the Universe’s Ordinary Matter Has Been Found
- gmailsyncer 8y agoThere must be regions of the universe where this "not very dense" gas is dense enough to use a ramscoop
- stephengillie 8y agoProbably 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?
- sandworm101 8y agoCounterintuitively, the energy costs are basically the same. Whether you dive in to pick it up, or run into it out in space, you will still have to accelerate the gas to orbital velocities before you can cram it into a tank. Some of the gas in space may already be moving very fast, may even be in an orbit, but it is probably not aligned with the orbit of your tank. Either way, the energy required to maintain operations anywhere near Jupiter means you probably want to find your hydrogen somewhere else.
- gmailsyncer 8y agoAssuming 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
- zaarn 8y agoLikely only around jupiter-like planets, if any large region of gas was that dense it would quickly collapse into either a gas giant or star or even multiple stars.
- gcbw2 8y agoThe 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 fully described in the paper (i might have missed, just glanced at them for now, and i am an amateur that just like to fiddle with similar data).
- simsla 8y agoYou'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 https://www.nature.com/articles/s41586-018-0204-1
- macintux 8y agoThere's more confidence in the result because two teams using very different methods have arrived at the same conclusion.
- gcbw2 8y agoThe three papers used the same 'filtering' methodology, to keep the simplification analogy.
- nfc 8y agoI'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 because the signal grows roughly with N (N being the number of images) and the noise grows with sqrt(N). So by stacking enough images you'll get the signal to noise necessary to say you've detected sth.
- TomMckenny 8y agoSlightly 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?
- Firerouge 8y agoI'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.
- privong 8y ago> 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. It's an observation, so it sets some level of constraints on the rate. Though it's true that an estimate of that rate would have large uncertainties.
- coldtea 8y ago>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"?
- Baeocystin 8y agoPractically instantaneous on the lengthy time scales the universe operates in, don't you think? And our observations have far from complete coverage of the sky.
- azernik 8y agoThat's a pretty small volume and a pretty short timespan, all things considered.
- yalogin 8y agoI 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.
- akvadrako 8y agoThe universe is not infinite by definition and anyway they are only talking about the visible universe.
- jnordwick 8y agoI really dislike when they say "universe" and really mean "visible universe" or when they say infinite but don't really mean it. I'm not really good at physics at this level so it throws me off. It makes it very difficult to really understand what they are talking about. You would think physicists would be very precise with their language, by I guess they mostly write for people who are know what they are talking about.
- wahern 8y agoThe problem is that there's no generic way to describe the universe without contextualizing the characteristic you're interested in. But as a layman (not an astronomer, not a physicist, not a topologist), I'd argue that it's fair to say that the universe is infinite. I say that not only because of where the evidence regarding expansion and geometry of the universe points, but because even in a discussion of the visible universe you have to address the fact that the visible universe is shrinking as objects at the edge disappear due to expansion. Those objects don't cease to exist (at least not unless you make some highly contentious metaphysical arguments), which means there's no avoiding the inference that there can be (and likely are) an infinite number of objects which exist but which are not visible.
- ubershmekel 8y agoObjects becoming invisible does not infer infinite objects. When you observe shopping carts leaving the store do you assume there are infinite shopping carts outside of the store?
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- analog31 8y agoMy Park Tool 4-5-6 Allen wrench has not been found. ;-)