6.5. A COSMIC CALENDAR 97
is figure, and many others like it, uses a rather whimsical time scale to go horizontally
left-to-right from the beginning of the Big Bang to the present. e scale is neither linear nor
strictly logarithmic. A linear scale does not work for reasons already discussed; events near the
beginning of the big bang, occurring within a fraction of a second, would be indistinguishable
set in context with events that occurred billions of years later.
But a logarithmic scale, such as shown in Figure 4.2 depicting the same sequence of events,
has its own disadvantages. Such a logarithmic scale hides the fact that much of importance
happened right at the beginning, within a fraction of a second. is illustration, on the other
hand, attempts to capture the spirit of the timing of the events in the history of the universe,
even as it sacrifices numerical accuracy.
6.5 A COSMIC CALENDAR
Instead of putting events in the history of the universe on a long paper tape, we can appeal to our
knowledge of the annual calendar. We all know from experience how long a year is; but we also
experience directly, and so have an intuitive feel for, tiny fractions of that year—namely months,
weeks, days, hours, minutes, and seconds. And so we can, using an ordinary linear scale, put our
history of the universe onto a single calendar year, with the beginning of the Big Bang starting
the instant after midnight on January 1, and the present just before midnight one year later, on
December 31.
Since we use 365 days to represent our 13.8 billion years since the beginning of the Big
Bang, then one day represents 13:8=365 D 0:0378 billion, or 37.8 million, years. Similarly, an
hour represents 1.57 million years, a minute 26,300 years, and a second 438 years.
Since we have already calculated a time line to represent the history of the universe in a
space of 100 m (Chapter 4, Section 4.1), to put these same events on a 365-day calendar we need
simply multiply the numbers in the third column of Table 4.1 by 3.65.
Looking at Table 6.3 emphasizes again that for the history of e Universe, much of the
action was at the very beginning, when the universe was only a tiny fraction of a second old. But
I have also thrown in some more recent events. e Cosmic Calendar has the important feature
of putting ourselves in context; the universe was a done deal, by the time we came along, at only
eight minutes before midnight. Even the dinosaurs had to wait until Christmas to have their
day.
An excellent review of different uses of historical time lines and variations on the idea of
the cosmic calendar can be found at en.wikipedia.org/wiki/Cosmic_Calendar.
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