Talk:2643: Cosmologist Gift

Explain xkcd: It's 'cause you're dumb.
Revision as of 18:51, 11 July 2022 by 162.158.166.235 (talk) (compare)
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- The explanation mentions “Eight zeptograms” although Randall’s box says “4 zeptograms of dark matter.”

- The 4,800 daltons in the explanation is roughly the size of a small protein; for example, insulin is about 5,800 daltons.

- Randall’s box says it contains 4 zeptograms of dark matter. Could someone explain this? My incomplete (biologist’s) understanding of dark matter is that astrophysicists do not yet know what it is. So how could Randall claim the box contains 4 zeptograms of it?

Thanks!

Fixed; thank you. 172.70.210.125 01:18, 9 July 2022 (UTC)

Here's a more recent PBH DM source than those already cited which could comport with Randall's 0.4% DM particles implication, but doesn't do so explicitly. 172.70.206.213 02:35, 9 July 2022 (UTC)

With the math corrected per 162.158.134.89 below, the figure is 34% ubiquitous particles. 172.70.211.36 09:44, 9 July 2022 (UTC)

And this comic was the perfect birthday gift for me. 108.162.245.203 02:42, 9 July 2022 (UTC)

  • How was the 23,000 neutrinos/m³ figure obtained? A flux of 7e10/(s·cm²), or 7e14/(s·m²), at a speed of close to 3e8 m/s, gives 2.3e6/m³. That would correspond to a box size of about 0.013 m³, or a bit larger than a typical shoe box. 162.158.134.89 07:19, 9 July 2022 (UTC)
Corrected. 172.70.211.52 09:40, 9 July 2022 (UTC)

To note {and I've summarised in an edit) that photons from the Sun can have been travelling for 100,000 years from its core to space, before their 8ish minute trip to the box (assuming you let them in, e.g. leave the lid off, or filter out all but the hard X-rays/etc), whilst neutrinos hardly notice so are 8 or 9 minutes old (before being adjusted for time dilation) regardless. And you can still put as much lead-lined wrapping paper on your present as you want, to keep it a surprise! 172.69.79.211 14:45, 9 July 2022 (UTC)

I saw your very interesting source was from 1997 and mostly about neutrino cycles -- which surprisingly match the menstrual cycle better than the orbit of the moon does -- but not mostly about energy migration out of the sun. It looks like the sun actually has multiple layers that engage in different forms of energy transformation. I added a link to the radiative zone (where gamma rays spend 171 thousand years colliding with matter, getting longer wavelength at each collision, until they leave) but somebody should probably learn about all the different zones at some point and make sure the text is correct. I never knew the sun was so complex! I partly imagine high-energy ancient civilizations somewhere deep inside, having their own forms of night and day and seasons. 162.158.62.23 14:44, 10 July 2022 (UTC)
I took the 28 day neutrino cycles link out, because it really doesn't help explain anything in the comic, and was out of place and confusing where it appeared. 162.158.166.41 17:20, 11 July 2022 (UTC)

I don't see how the box containing dark matter is at all consistent with the premise of dark matter being primordial black holes. PBHs wouldn't be ubiquitously distributed through space such that any given volume contains a constant tiny number of them, would they? Black holes that are that tiny would have evaporated long ago by Hawking radiation, by my understanding. BunsenH (talk) 17:26, 11 July 2022 (UTC)

If dark matter was 100% particles, then a volume on Earth containing 30,000 solar neutrinos would have 12 zeptograms of dark matter, not 4. Since the box is labeled with only a third as much dark matter, the implication is that Randall might think some is clustered in MACHOs. In the past decade the only MACHO DM theory with more than a handful of papers per year is PBHs, which skyrocketed in popularity after LIGO/VIRGO, but are still less popular among mainstream cosmologists as 100% WIMPs. 162.158.166.235 18:48, 11 July 2022 (UTC)