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

Anders Sandberg anders at aleph.se
Tue May 24 17:02:20 UTC 2016

On 2016-05-24 01:33, John Clark wrote:
> On Mon, May 23, 2016 at 2:57 PM, Anders Sandberg <anders at aleph.se 
> <mailto:anders at aleph.se>> wrote:
>     O
>     ​ ​
>     n 2016-05-23 19:19, John Clark wrote:
>         ​>> ​
>         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.
>     ​> ​
>     Huh? Can you unfold how the nucleosynthesis data doesn't fit dark
>     matter? Last time I checked the literature (fall last year) there
>     was a fairly decent parameter window of the nuclei/DM parameter
>     space, where lithium abundance was used as a sensitive constraint
>     on the properties of DM.
>> The present
>> lithium
> ​and Helium ​
> abundance
>> gives a tight constraint on the amount of normal baryonic matter 
> (matter made from electrons neutrons and protons) that
> ​could have ​
> existed at the time of  nucleosynthesis
> ​, and there is not nearly enough of it to account for
> Dark Matter. So whatever Dark Matter is it can not be normal ​
> baryonic matter
> ​,​
> ​ and it can't be made of Stellar Black Holes

So how does this rule out WIMPs? In fact, if I understand the models 
right, WIMPs are much better at explaining halo shapes than MACHOs. 
While it might be annoying to posit some new weakly interacting 
particle, there is ample precedent for them existing (neutrinos) and 
they sometimes show up because of other theories (axinos and Susy). It 
seems a bit premature to immediately latch on to black holes.

Although it does indeed nicely explain that early black hole. Of course, 
we should be able to figure out a frequency distribution of early too 
large holes from this theory and check it.

Dr Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University

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