On 9/27/2011 8:07 PM, nihil0 wrote:

On 9/27/2011 4:18 PM, nihil0 wrote:## Advertising

1) There is an infinite number of Hubble volumes in our universe, which are all casually disconnected (as the theory of inflation implies). 2) There is a limit on how much matter and energy can exist within a region of space of a given size, such as a Hubble volume. 3) There is only a finite number of possible configurations of matter, due to the Uncertainty Principle. I can explain any of these ingredients in more depth if you'd like me to, but I hope you see that they lead to the conclusion that all quantum-physical possibilities in our universe are realized infinitely many times.On Sep 27, 7:47 pm, meekerdb<meeke...@verizon.net> wrote:No they don't. There's an implicit assumption that what happens in these other universes has the same or similar probability distribution as we observe in ours. A reasonable assumption, but not a logically necessary one. I think it's what Bruno means by "homogeneous". It's logically possible that all but a finite number of these universes are just exact copies of the same completely empty universe, for example. BrentYou imply that it's logically possible that there is only a finite number of universes that are filled with matter, and you seem to think few will resemble ours.

`I don't think that. I just noted it's logically possible, contrary to assertions that our`

`universe must be duplicated infinitely many times.`

However, according to Vilenkin, Greene, and Tegmark, a generic prediction of the theory of inflation is that there is an *infinite* number of Hubble volumes (what you are calling universes). Let's call the hypothesis that all quantum-physical possibilities are realized infinitely many times "the hypothesis of Cosmic Repetition". Brian Greene argues for this hypothesis quite persuasively. He says, "In an infinitely big universe, there are infinitely many patches [i.e., Hubble volumes]; so, with only finitely many different particles arrangements, the arrangements of particles within patches must be duplicated an infinite number of times." (The Hidden Reality, pg. 33)

`It's plausible - but not logically required. Suppose all the infinite universes are`

`number 1, 2, ... Number 1 is ours. Number 2 something different. Numbers 3,4, ...inf`

`are exact copies of number 2. So there are only two arrangements of particles; in spite`

`of there being infinitely many universes.`

As for the probability distribution of matter and/or outcomes, I'll let Tegmark do the explaining: "Observers living in parallel universes at Level I observe the exact same laws of physics as we do, but with different initial conditions than those in our Hubble volume.

`This is questionable. Most theories of the universe starting from a quantum fluctuation`

`or tunneling from a prior universe assume that the universe must start very small - no`

`more than a few Planck volumes. This limits the amount of information that can possibly`

`be provided as initial conditions. So where does all the information come from? QM`

`allows negative information (hidden correlations) so that one possibility is that the net`

`information is zero or very small and the apparent information is created by the existence`

`of the hubble horizon.`

The currently favored theory is that the initial conditions (the densities and motions of different types of matter early on) were created by quantum fluctuations during the inflation epoch (see section 3). This quantum mechanism generates initial conditions that are for all practical purposes random, producing density fluctuations described by what mathematicians call an ergodic random field. Ergodic means that if you imagine generating an ensemble of universes, each with its own random initial conditions, then the probability distribution of outcomes in a given volume is identical to the distribution that you get by sampling different volumes in a single universe. In other words, it means that everything that could in principle have happened here did in fact happen somewhere else. Inflation in fact generates all possible initial conditions with non-zero probability, the most likely ones being almost uniform with fluctuations at the 10^5 level that are amplified by gravitational clustering to form galaxies, stars, planets and other structures. This means both that pretty much all imaginable matter configurations occur in some Hubble volume far away, and also that we should expect our own Hubble volume to be a fairly typical one — at least typical among those that contain observers. A crude estimate suggests that the closest identical copy of you is about ∼ 10^(10^29)m away. . ." (The Multiverse Hierarchy, section 1B, http://arxiv.org/abs/0905.1283) Do you still disagree with the hypothesis of Cosmic Repetition? Which parts of the argument do you accept or deny?

See above. Brent

Best regards, Jon

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