This is fascinating - and frustrating. I guess all will become clear one
day...


On 7 November 2013 17:22, meekerdb <meeke...@verizon.net> wrote:

>  On 11/6/2013 7:52 PM, LizR wrote:
>
>  On 7 November 2013 16:33, meekerdb <meeke...@verizon.net> wrote:
>
>>     OK, but that doesn't alleviate the confusion. If anything it makes
>> it worse. What exactly can we deduce from the entropy of the observable
>> universe being approximately maximal when measured by other means, given
>> that the BB apparently places a bound on the entropy that can exist inside
>> a given volume? Assuming the universe to be, say, 250 times larger than the
>> hubble sphere (for the sake of argument) the BB would say that the maximum
>> entropy it can contain is 62,500 times the entropy of the hubble sphere.
>>
>>
>>  No it doesn't say that.  The BB applies to an event horizon, not just
>> any spherical volume.  In an expanding universe there is only one specific
>> radius where the boundary is moving away at c, and that's an event horizon.
>>
>
>  I could have sworn that JB's article in Scientific American said this
> applied to *any* sphere.
>
>
> The inequality S<BB may be said to apply to any sphere we can investigate
> - because equality is only reached when the sphere is so big that it is
> receding at c.
>
>
>   The impression I got was that If the sphere isn't an event horizon,
> it's because the information within it is less than the BB.
>
>
> That's right.
>
>
>   Once you pile enouigh stuff into it to exceed the BB you get a black
> hole. Or did I misunderstand what he was saying?
>
>
> No, that's right.  But that's applying the BB to a BH.  The application to
> cosmology and the Hubble sphere doesn't lend itself to same cause->effect
> relationship, since the Hubble sphere is expanding and taking stuff in.
> But it's analogous.  That's why it's so suggestive that it seems satisfy
> the BB equality.
>
>
>
>  I had a look on the fount of all knowledge and it doesn't mention that
> the BB only applies to event horizons ...
> http://en.wikipedia.org/wiki/Bekenstein_bound
>
>  In fact I think it implies that an event horizon forms when the
> information content of the enclosed volume reaches the BB....I think....!
>
>  So my question stands.
>
>>
>> As to what we can deduce from it...that's a good question.
>>
>>
> It would seem to have interesting cosmological implications. (I'm not sure
> what they are, though!) Maybe that the hubble sphere is an event horizon -
> which I guess it is, from our viewpoint.
>
>
> Yes, it's *defined* as our even horizon.  But it's not clear what that
> implies.
>
> Brent
>
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