[ExI] Has the mystery of Dark Matter been solved?

Norman Jacobs wincat at swbell.net
Wed May 25 20:51:30 UTC 2016

I would like to discuss with you please, if you have a moment or two


Norman L. Jacobs

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Email: wincat at swbell.net


From: extropy-chat [mailto:extropy-chat-bounces at lists.extropy.org] On Behalf
Of Anders
Sent: May 25, 2016 3:33 AM
To: extropy-chat at lists.extropy.org
Subject: Re: [ExI] Has the mystery of Dark Matter been solved?


Likely just to annoy John, there is a recent paper (
http://arxiv.org/abs/1603.08522 ) 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.

On 2016-05-23 20:30, Robin D Hanson wrote:

Yes, this seems a very reasonable guess to me as well. 


On May 23, 2016, at 1:19 PM, John Clark <johnkclark at gmail.com> wrote:


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.

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.


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

 John K Clark



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Robin Hanson rhanson at gmu.edu 
Future of Humanity Inst., Oxford University
Assoc. Prof. Economics, George Mason University
See my new book: http://ageofem.com


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