On 7/31/2012 10:48 AM, Alberto G. Corona wrote:
"The problem is to explain also why the entropy of the early universe was so low. If you just accept that this is the case and also don't bother about the very distant future, there is no problem. But if you assume that time goes on from the infinite distant past and/or to the infinite distant future, you have a problem, because smaller local low entropy states are then more likely than the whole observable universe being in some low entropy state."


That make me think about the people that try to discover the whys of the arrow of time by taking concepts like "beginning of the universe". That presuposses the arrow of time that he is trying to demonstrate how it arises in the first place. this is a circular reasoning.

No, it's not circular.  Beginning is just the low entropy state.

All that he can demonstrate empirically is that it follows entropy, an then, he is puzzled by the fact that entropy was so low at the "beginning"

The interesting question is why there is there uniformity in the different 'arrows of time'. Why does the local increase in thermodynamic entropy match the expansion of the universe? Why does the radiation AoT match the quantum branching of MWI?


but if we take the idea of a block universe shaped as a four dimensional bell with a singularity in the left ( see the figure that I linked), there is no arrow of time here. is our life that goes along very short segments from left to right in the middle of this figure. what we do is to extrapolate this sort segment to the whole figure. But this is not right. first, time is local, according with general relativity. How we extrapolate it? by assuming that time progress in the universe in the direction that we perceive causality, that is, in the direction of entropy increase.

but even so, there is not a single arrow of time where entropy increases. there are infinite lines of entropy increase/arrows of time departin from the singularity, which diverge radially trough the bell and extend to the right in the figure.

If i´m right, the existence of a gradient of entropy and, thus the existence of a singularity with maximum entropy somewhere, at a point which we consider "origin of the universe", is a pre-requisite for natural selection and life. Natural selection (as I said before) select "good correlations" which deal with macroscopical events, to design life and observers. That is why we see this universe with such unavoidable notion of beginning and not other in other ways.

A boltzman brain is just a curiosity, unless the bolzman fluctionation create not a single brain but a local portion of the universe that develop in a way that maintain intellgent beings. In this case, it is indistinguishable if the universe is or not the product of a boltzman fluctuation.

The problem is that statistical mechanical estimates of probabilities favor the random occurrence of the curiosity over the universe.

Brent

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