# Re: OM measure and universe size

 Russel, We are trying to related the expansion of the universe to decreasing measure. You have presented the interesting equation: H = C + S Let's try to assign some numbers. 1) Recently an article appeared in New Scientist stating that we may be living "inside" a black hole, with the event horizon being located at the limit of what we can observe ie the radius of the current observable universe. 2) Stephen Hawking showed that the entropy of a black hole is proportional to its surface area. $S_{BH} = \frac{kA}{4l_{\mathrm{P}}^2}$ where where k is Boltzmann's constant, and $l_{\mathrm{P}}=\sqrt{G\hbar / c^3}$ is the Planck length. Thus we can say that a change in the Universe's radius corresponds to a change in entropy dS. Therefore, dS/dt is proportional to dA/dt and to 8PR(dR/dt)  R being the radius of the Universe and P = Pi. Let's assume that dR/dt = c Therefore dS/dt = (k/4 L^2) 8PRc = 2kPRc/ L^2 Since Hubble constant is 71 ± 4 (km/s)/Mpc which gives a size of the Universe from the Earth to the edge of the visible universe. Thus R = 46.5 billion light-years in any direction; this is the comoving radius of the visible universe. (Not the same as the age of the Universe because of Relativity considerations) Now I have trouble relating these facts to your equation H = C + S or maybe to the differential version dH = dC + dS. What do you  think? Can we push this further? George Russell Standish wrote: On Wed, Oct 31, 2007 at 05:11:01PM -0700, George Levy wrote:  Could we relate the expansion of the universe to the decrease in measure of a given observer? High measure corresponds to a small universe and conversely, low measure to a large one. For the observer the decrease in his measure would be caused by all the possible mode of decay of all the nuclear particles necessary for his consciousness. Corresponding to this decrease, the radius of the observable universe increases to make the universe less likely. This would provide an experimental way to measure absolute measure. I am not a proponent of ASSA, rather I believe in RSSA and in a cosmological principle for measure: that measure is independent of when or where the observer makes an observation. However, I thought that tying cosmic expansion to measure may be an interesting avenue of inquiry. George Levy   There is a relationship, though perhaps not quite what you think. The measure of an OM will be 2^{-C_O}, where C_O is the amount of information about the universe you know at that point in time (measured in bits). The physical complexity C of the universe at a point in time is in some sense the limit of all that is possible to know about the universe, ie C_O <= C. C is related to the size of the universe by the equation H = C + S, where S is the entropy of the universe (measured in bits), and H is the maximum possible entropy that would pertain if the universe were in equilibrium. H is a monotonically increasing function of the size of the universe - something like propertional to the volume (or similar - I forget the details). S is also an increasing function (due to the second law), but doesn't increase as fast as H. Consequently C increases as a function of universe age, and so C_O can be larger now than earlier in the universe, implying smaller OM measures. However, it remains to be seen whether the anthropic reasons for experiencing a universe 10^9 years and of large complexity we currently see is necessary...