Re: Interested in thoughts on this excerpt from Martin Rees

From: Russell Standish <>
Date: Fri, 28 Jul 2006 00:07:37 +1000

Thanks for giving a digested explanation of the argument. This paper
was discussed briefly on A-Void a few weeks ago, but I must admit to
not following the argument too well, nor RTFA.

My comment on the observer moment issue, is that in a Multiverse, the
measure of older observer moments is less that younger ones. After a
certain point in time, the measure probably decreases exponentially or
faster, so there will be a mean observer moment age.

So contra all these old OMs dominating the calculation, and giving
rise to an expected value of Lambda close to zero, we should expect
only a finite contribution, leading to an expected finite value of

We don't know what the mean age for an observer moment should be, but
presumably one could argue anthropically that is around 10^{10}
years. What does this give for an expected value of Lambda?

Of course their argument does sound plausible for a single universe -
is this observational evidence in favour of a Multiverse?


On Thu, Jul 27, 2006 at 11:08:04AM -0700, "Hal Finney" wrote:
> This is actually a very interesting paper, by Starkman and Trotta. I had
> seen some mention of it but hadn't tracked it down. Here is the abstract:
> The paper basically shows that observers (or civilizations) can last
> longer in universes with smaller CC's. The CC eventually puts an end
> to the observations that can be made, because the expansion gets too
> fast and there is no longer enough energy density. The higher the CC,
> the sooner this happens. With CC's as high as what we observe, the
> theoretical lifetime of civilization is much shorter than in universes
> with smaller CC's.
> The authors choose to use as their measure, the number of times the
> CC can be measured in a given universe. This makes low-CC universes
> have a much higher measure, because the window for CC observations is
> longer in those. Hence they conclude that the highest probability is
> for a CC much smaller than we observe, and so our own CC value cannot
> be explained anthropically.

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Received on Thu Jul 27 2006 - 21:00:00 PDT

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