100k Stars - Hackdot

Re:100k Stars by grandchild on Wednesday October 07, 2020 @07:51AM (#24707269)

So I quickly did a back-of-envelope calculation using [0] for source of mass and diameter of the universe.

Then I used the formula given in [1]: r = (2 G M) / (c^2).

    You have: (2 * G * 1.5 * 10^56 grams ) / (c^2)
    You want: lightyears
            * 2.3548373e+10

So about 23,548,373,000 ly of SR, while the radius of the observable universe is given as ~46,500,000,000 ly. So the ordinary-matter ratio is about half the density of a black hole. Not quite there, but still _much_ closer than I would have thought!

If we account for not just ordinary matter but dark matter (a ratio of 4.9% to 26.8%) the picture is different:

    You have: (2 * G * (1.5 * 10^56 grams + (1.5/4.9*26.8) * 10^56 grams) ) / (c^2)
    You want: lightyears
            * 1.5234355e+11

So the SR then would be about 5 times larger. But I have no idea whether dark matter would count towards the black hole mass and SR, and I don't know if anyone does.

[0] https://en.wikipedia.org/wiki/Observable_universe

[1] https://en.wikipedia.org/wiki/Schwarzschild_radius

(The scientific calculator I used, which is awesome every day is "units" btw: https://linux.die.net/man/1/units)

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Re:100k Stars by gnramires on Wednesday October 07, 2020 @10:55AM (#24708903)

Yes, dark matter has mass, this is its defining characteristic: it seems to be a detectable mass, just doesn't interact electromagnetically.

In any case, it's important to note the Schwarzchild model is a spherically symmetrical ball. Mass in our Universe seems more or less uniformly dispersed (with some anisotropy). Without a center for mass to collapse, I suspect the black hole dynamics don't apply.

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