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## Exact number of seconds per year affects the CÐ value??

If one uses the number of seconds in a Sidereal year as defined [1] on Wikipedia, and 13.72 billion years since the Big Bang, then then number of seconds since the big bang is: (365 d 6 h 9 min 9.7676 s) = 31558186.176 seconds, * 13.73e09 = 4.3329389619648e17 seconds. log(4.3329389619648e17) =~ 17.6368. This is different from 17.6355 in the article. Perhaps a value for year other than Sidereal was used? Please help me understand what I am missing. Also, I am unfamiliar with the notation 13.73(12) used in the article. \$tephen T. Crye (talk) 05:12, 9 August 2009 (UTC)

I believe that notation refers to the error in the least significant place; in this case, 13.73(12) means 13.73±0.12. -- pne (talk) 07:19, 15 May 2014 (UTC)
Ah yes, see here: Uncertainty#Measurements. -- pne (talk) 07:21, 15 May 2014 (UTC)

## Lasts vs. Begins at

I am confused about something. I assume "CÐ 100" and the "100th cosmological decade" are equivalent. I also assume that each decade is discrete, that is, the 99th decade ends when the 100th decade begins. Currently, the articles says that the 100th decade both 1) lasts 10100 seconds, and 2) lasts from 10100 to 10101 seconds after the Big Bang. If the 100th cosmological decade begins at 10100 and ends at 10101, then to be precise, it lasts 9*10100 seconds. Similarly, using the log years per decade convention, the 100th cosmological decade begins at 10100 and lasts for 9*10100 years. Unless anyone knows better, I'll try to fix this soon.

On a related note, I've heard it described that "each cosmological decade is ten times the length of all the previous time put together" (paraphrased from The Universe, episode 18). This is also incorrect, as it inflates the length of each decade by 11%. (Or worse if you compound the error, which is kind of hard since you have to go back an infinite number of decades to start compounding). Each cosmological decade is only ten times the length of the previous decade. --Spiffy sperry (talk) 04:38, 13 May 2008 (UTC)

Of course all these statements make sense if you drop your requirement that these "decades" don't overlap. This is not a notation used by working cosmologists, by the way, so possibly the precise meaning is still up for grabs. That funny-looking symbol certainly needs a reference. PaddyLeahy (talk) 18:11, 18 May 2008 (UTC)

## Conversion formula

To convert the cosmological decade as expressed in log years per decade, the article says "simply divide by seconds per year; in logarithmic terms, simply subtract 7.3230203 from the values listed above." I know that the length of the year hasn't remained constant throughout history, but I note that this value for seconds per year is precisely 2/3 of what it is today. In the sidereal year, there are 31,558,153 seconds, so log(31,558,153) = 7.4991116 (a number also used in the article), but log(31,558,153*2/3) = 7.3230203. What's the significance of using the smaller number for the conversion? --Spiffy sperry (talk) 04:19, 15 May 2008 (UTC)

This edit shows the original entry, where both instances based on seconds per year use 2/3 of the actual value. Then in this edit, the first instance is corrected, but the second isn't. I've removed the first instance (it was in the context of 365.2564 days since the Big Bang, which isn't meaningful). I'll correct the second. --Spiffy sperry (talk) 13:17, 31 May 2008 (UTC)