I'd like to take a poll to see how inclined to hands-on calculation we are, collectively, at cosmo forum. Generally speaking what I mean from scratch is from basic numbers most of us know like 71 and 0.73 (estimated current Hubble rate H = 71 km/s per megaparsec and current dark energy density = 0.73 of the critical energy density need for flatness) If you want, try some of the calculations and respond to the poll later. The poll is multiple answer, so you can recall several things you've calculated and check them all off. The abbreviations in the poll are informal and intended to be self-explanatory. That's basically it, but here's some more detailed explanation if desired: ====================================== My idea is we probably all remember at least some quantitative facts about the universe such as The current Hubble rate is 71 km/s per megaparsec The current dark energy density is about 0.73 of crit (or 73% of estimated total) Space is nearly flat. (That's usually enough to remember but in rare cases when you need a numerical handle you could express it by saying the current total density is less than 1.018 crit at 95% confidence.) CMB temp is 2.728 kelvin and its redshift is 1090. What features of the universe do you know how calculate from scratch? From scratch here means mostly from the numbers 71 and 0.73. Plus any other basic stuff you happen to remember, but in the poll concerns mostly what you can get just from those two numbers. And which features have you in fact actually calculated from scratch recently? I'd like to get a reading on how hands-on our group is, calculation wise. If you haven't done much of this recently you might be rusty and you might want to take a few minutes to get fluent again. In other words see what you can do, before you answer the poll. It's a multiple answer poll, so if you calculated several things you can check them all off. The Google calculator is a great help with this kind of cosmo calculation because it takes care of units like "megaparsec" and you can specify what units you want the answer in. It also knows some fundamental constants like G, which can save a lot of bother. Here some explantion of some of the shorthand abbreviation. HUBBLE TIME---the Hubble time is 1/H--so you type "1/(71 km/s per megaparsec) in years" into Google and it gives the time in years HUBBLE RADIUS----the Hubble radius c/H is the current distance of objects receding at speed c----"c/(71 km/s per megaparsec) in light years" RADIUS OF CURVATURE (minimum, 95% conf)---This is the minimum radius of curvature according to the latest WMAP report, at 95% confidence level. It is the radius of the 3-sphere which space would be if it did turn out to have a slight positive curvature and was therefore finite volume. Calculating is easy, just HUB RAD/sqrt(.018). The number 0.018 represents the curvature and the smaller the curvature the bigger the radius of curvature. Zero curvature means flat-out infinite. VOLUME OF SPACE (minimum, 95% conf)---This is the minimum estimated spatial volume corresponding to the minimum estimated radius of curvature---it is the volume of a 3-sphere of the given radius: 2 pi2 (RAD CURVE)3 CRITICAL DENSITY---the usual formula for the total energy density needed for spatial flatness: 3c2H2/(8 pi G) DARK ENERGY DENSITY----The dark energy density is 73% of the critical density: 0.73 CRIT deSITTER RADIUS----This gives a good estimate of the cosmological event horizon: c2/sqrt(G DARKE) COSMIC MICROWAVE BACKGROUND STUFF---self explanatory, anything you calculated from 2.728 kelvin and 1090 OTHER----let us know about other basic cosmo calculations you've done that only need a few basic numbers as input.