On 11/6/2013 7:52 PM, LizR wrote:
On 7 November 2013 16:33, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>>
OK, but that doesn't alleviate the confusion. If anything it makes it
exactly can we deduce from the entropy of the observable universe being
approximately maximal when measured by other means, given that the BB
places a bound on the entropy that can exist inside a given volume?
universe to be, say, 250 times larger than the hubble sphere (for the sake
argument) the BB would say that the maximum entropy it can contain is
the entropy of the hubble sphere.
No it doesn't say that. The BB applies to an event horizon, not just any
volume. In an expanding universe there is only one specific radius where
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/
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.
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.
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