Can you explain what you mean by 'bolt-on extras to GR'?

On Sun, Dec 1, 2013 at 7:18 PM, LizR <[email protected]> wrote:

> Thanks, that's an impressive list. I'd be rather surprised if "bolt-on
> extras to GR" can explain all those.
>
>
> On 2 December 2013 12:43, Richard Ruquist <[email protected]> wrote:
>
>> Liz,
>>
>> There are 7 other repeatable observations explained by dark matter. From
>> wiki-dark matter
>>
>>
>>    - 3.1 Galaxy rotation 
>> curves<http://en.wikipedia.org/wiki/Dark_matter#Galaxy_rotation_curves>
>>    - 3.2 Velocity dispersions of 
>> galaxies<http://en.wikipedia.org/wiki/Dark_matter#Velocity_dispersions_of_galaxies>
>>    - 3.3 Galaxy clusters and gravitational 
>> lensing<http://en.wikipedia.org/wiki/Dark_matter#Galaxy_clusters_and_gravitational_lensing>
>>    - 3.4 Cosmic microwave 
>> background<http://en.wikipedia.org/wiki/Dark_matter#Cosmic_microwave_background>
>>    - 3.5 Sky surveys and baryon acoustic 
>> oscillations<http://en.wikipedia.org/wiki/Dark_matter#Sky_surveys_and_baryon_acoustic_oscillations>
>>    - 3.6 Type Ia supernovae distance 
>> measurements<http://en.wikipedia.org/wiki/Dark_matter#Type_Ia_supernovae_distance_measurements>
>>    - 3.7 Lyman-alpha 
>> forest<http://en.wikipedia.org/wiki/Dark_matter#Lyman-alpha_forest>
>>    - 3.8 Structure 
>> formation<http://en.wikipedia.org/wiki/Dark_matter#Structure_formation>
>>
>>
>>
>> On Sun, Dec 1, 2013 at 4:58 PM, LizR <[email protected]> wrote:
>>
>>> On 30 November 2013 12:04, Telmo Menezes <[email protected]> wrote:
>>>
>>>>
>>>> Thanks for the explanations. Ok, I think I now understand why dark
>>>> matter is the best hypothesis.
>>>>
>>>> It is, to date. Neverthless, you would have been quite correct had it
>>> been the anomaly in the orbit of Mercury that you were trying to explain,
>>> rather than the anomalous rotation of galaxies observed in 1933 by Fritz
>>> Zwicky. Pre-Einstein, various theories were advanced to explain the
>>> anomalous perihelion advance of Mercury (relative to what Newtonian
>>> gravitation predicted it should have been) including "hidden matter" - an
>>> undetected planet (called Vulcan, as Trekkies and Dr Who fans will
>>> appreciate) and an odd mass distribution inside the Sun.
>>>
>>> But in that case, it turned out that the best answer WAS to modify
>>> gravity.
>>>
>>> So far DM has remained the top explanation even as more phenomena
>>> involving it have been discovered (garvitational lensing for example). Some
>>> of its characteristics are now fairly well measured; its nature remains
>>> unexplained... which makes life interesting for particle physicists and
>>> cosmologists.
>>>
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>>
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