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Likely just to annoy John, there is a recent paper (
<a class="moz-txt-link-freetext" href="http://arxiv.org/abs/1603.08522">http://arxiv.org/abs/1603.08522</a> ) arguing the early supermassive
holes could be due to direct collapse of gas clouds. I cannot judge
the likelihood of this, but it will be interesting to see how it
turns out.<br>
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<div class="moz-cite-prefix">On 2016-05-23 20:30, Robin D Hanson
wrote:<br>
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Yes, this seems a very reasonable guess to me as well.
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<div class="">On May 23, 2016, at 1:19 PM, John Clark <<a
moz-do-not-send="true"
href="mailto:johnkclark@gmail.com" class=""><a class="moz-txt-link-abbreviated" href="mailto:johnkclark@gmail.com">johnkclark@gmail.com</a></a>>
wrote:</div>
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<p class=""><font class="" size="4">I would give 50%
odds that the mystery of Dark Matter has been
solved and it will turn out not to be some new
particle but will consist of Primordial Black
Holes. We know from the percentage of the
elements Hydrogen, Deuterium, Helium and Lithium
how much regular matter was around one minute
after the Big Bang when nucleosynthesis cooked up
these elements, and there is no room for Dark
Matter. So the Black Holes that form the bulk of
the Dark Matter can't have come from the corpses
of dead stars made of regular matter; but maybe
Black Holes formed long before nucleosynthesis
occurred when the universe was much less than one
minute old and things were too hot for even
protons to exist much less elements.</font></p>
<font class="" size="4">Stephen Hawking proposed this
explanation for Dark Matter some years ago but the
idea had fallen out of favor because it was largely
(but not entirely) ruled out by the data. We know
that to account for all the Dark Matter the Black
Holes can't be larger than 100 solar masses because
there would be more gravitational microlensing than
we observe. And we know that to account for all the
Dark Matter the Black Holes can't be smaller than 10
solar masses because we'd see Black Hole explosions
/evaporations (if they were REALLY small) and the
orbits of widely spaced binary stars would be
disrupted, but we don't see any of that.</font></div>
<div class="gmail_default"><br class="">
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<div class="gmail_default"><font class="" size="4">There
is still a window for Primordial Black Holes being
Dark Matter that the data hasn't excluded and it's
between 10 and 100 solar masses, and during its
short engineering run that's just what LIGO
discovered. It found a 29 solar mass Black Hole
merging with a 36 solar mass Black Hole in a fifth
of a second producing a 62 solar mass black hole and
3 solar masses of energy in the form of
Gravitational Waves. Everybody was amazed they
found something that good so quickly when the
instrument hadn't even reached its design
sensitivity yet, everybody thought it would take
years of observing to detect a thing like that.
Maybe they just got extraordinarily lucky, or maybe
Black Holes are far far more common than had been
previously thought. Maybe 85% of all the matter in
the universe is in the form of Primordial Black
Holes. The two LIGO detectors will get back online
in September and with greatly improved sensitivity
and will be joined by a third detector, VIRGO near
Pisa in Italy. So we should know pretty soon if Dark
Matter and Black Holes are the same thing, if they
are then the second greatest mystery in physics will
have been solved, but we'll still have the mystery
of Dark Energy.<br class="">
<br class="">
John K Clark<br class="">
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<br class="">
<div class="">Robin Hanson <a moz-do-not-send="true"
href="mailto:rhanson@gmu.edu" class="">rhanson@gmu.edu</a> <br
class="">
Future of Humanity Inst., Oxford University<br class="">
Assoc. Prof. Economics, George Mason University<br class="">
See my new book: <a moz-do-not-send="true"
href="http://ageofem.com" class="">http://ageofem.com</a><br
class="">
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