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Encyclopedia
A cosmological decade is a division of the lifetime of the cosmos. The divisions are logarithmic in size
Logarithmic scale
A logarithmic scale is a scale of measurement using the logarithm of a physical quantity instead of the quantity itself.A simple example is a chart whose vertical axis increments are labeled 1, 10, 100, 1000, instead of 1, 2, 3, 4...

, on base 10. Each successive cosmological decade represents a ten-fold increase in the total age of the universe
Age of the universe
The age of the universe is the time elapsed since the Big Bang posited by the most widely accepted scientific model of cosmology. The best current estimate of the age of the universe is 13.75 ± 0.13 billion years within the Lambda-CDM concordance model...

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## As expressed in log (seconds per Ðecade)

When CÐ is measured in log( seconds/Ð ),  1 begins at 10 second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

s and lasts 90 seconds (until 100 seconds after Time Zero).  100, the 100th cosmological decade, lasts from 10100 to 10101 seconds after Time Zero. CÐ  is Time Zero.

The epoch
Epoch (astronomy)
In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as celestial coordinates, or elliptical orbital elements of a celestial body, where these are subject to perturbations and vary with time...

−43.2683 was 10(−43.2683) seconds, which represents the Planck time
Planck time
In physics, the Planck time, , is the unit of time in the system of natural units known as Planck units. It is the time required for light to travel, in a vacuum, a distance of 1 Planck length...

since the big bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

(Time Zero). There were an infinite number of cosmological decades between the Big Bang and the Planck epoch (or any other point in time). The current epoch,  17.6355, is 10(17.6355) seconds, or 13.73(12) billion years, since the Big Bang. There have been 60.9 cosmological decades between the Planck epoch, CÐ −43.2683, and the current epoch, CÐ 17.6355.

## As expressed in log (years per Ðecade)

Fred Adams and Greg Laughlin, in The Five Ages of the Universe
The Five Ages of the Universe
The Five Ages Of The Universe is a popular science book written by Professor Fred Adams and Gregory Laughlin first published in 1999.- Book contents :...

, first defined the cosmological decade as expressed in log years per decade. In this definition, in the 100th cosmological decade, lasts from 10100 years to 10101 years after Time Zero. To convert to this format, simply divide by seconds per year; or in logarithmic terms, subtract 7.4991116 from the values listed above. Thus when CÐ is expressed in log( years/Ð ), the Planck time could also be expressed as 10(−43.2683 − 7.4991116) years = 10(−50.7674) years.

In this definition, the current epoch is CÐ (17.6355 − 7.4991116), or CÐ 10.1364. As before, there have been 60.9 cosmological decades between the Planck epoch and the current epoch.

In their view, the history of the universe can be segmented into five Ages:
 Age Ðecades Process Primordial −50 to +5 from the Planck time until universe becomes transparent to radiationTimeline of the Big BangThis timeline of the Big Bang describes the history of the universe according to the prevailing scientific theory of how the universe came into being, using the cosmological time parameter of comoving coordinates... Stelliferous 6 to 14 stars shine brightly (our current epoch is +10.1364) Degenerate 15 to 37 stars degenerate, get dimmer Black Hole 38 to 99 stars evaporate, galactic black holes evaporate Dark Era 100 onward lone protons and other particles get even farther and farther apart from each other