Re: FarmingFisicistsFumble

Thus spake Oz <Oz@xxxxxxxxxxxxxxxxxxxx>
>Charles Francis <charles@xxxxxxxxxxxxxxxx> writes
>>Thus spake Oz <Oz@xxxxxxxxxxxxxxxxxxxx>
>>>
>>>===============
>>>Phillip Helbig says;
>>>
>>>Consider that one can see galaxies which are very far away, at the
>>>distances you mentioned. Often, there is not an intervening galaxy.
>>>While space is big, really big, one shouldn't forget that the matter is
>>>distributed thinly, really thinly. Consider that the mass of the entire
>>>observable universe, if it could be contained in a ball with the density
>>>of an atomic nucleus, would be in a ball with a radius only a little
>>>larger than the orbit of Mars.
>>>=============
>>>
>>><poleaxed! gobsmacked!>
>>>
>>We shall have to wait and see. Moments before the final collapse it
>>should happen, before swallowing itself up. Where shall we wait?
>
>Hmm, could be tricky.
>
>Now let me see....
>
>The surface area of a BH is proportional to the mass.

The constant of proportionality being zero, you think?
>
>So mass is proportional to (external) radius^2

If you mean the event horizon,

r = 2GM/c^2
>
>But for a neutron star mass is proportional to radius^3.
>
>Ah, so I was right when I said to alison that I thought that at some
>point a BH would be larger than an equivalent sized neutron star
>(IYSWIM).
>
>So herr Helbig is being a bit economical with the truth in that an
>observable-universe-sized BH is probably bigger (probably LOTS bigger)
>than an equivalent mass neutron star.
>
You could work out the radius at equality if you like, and tell him. But
make sure you talk about the Schwarzschild radius (with an s in the
middle) and not the radius of the hole, or you will need your asbestos
armour.


Regards

--
Charles Francis
Please reply by name
.

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