The best way to comprehend the universe time scale is to refer everything to
the galactic year. Our galaxy, the Milky Way (MW), completes a rotation every
240 million years (MY). We can round this up to 1/4 billion years and use it as
the typical time scale of cosmic events. One can refer to this as God's year
or, as we will, the cosmic year. The best available information
suggests 13.7 billion years for the age of the universe. That is, the
universe is about 55 cosmic years (55 CY) old. The solar system was formed
18 CY ago. The evolution of land animals started 25 cosmic months ago. The
dinosaurs appeared about 1 CY ago and disappeared 3 cosmic month ago.
At that time the mammals started their ascendancy.
Primate evolution started about 1 cosmic month ago. The homo line separated from
the rest of the primates, by parting ways with our nearest cousins the
Chimps, only 9 days ago. The modern humans emerged from the homo group 70 hours
ago. Agricultural civilizations started to appear probably only 21 minutes ago
and finally our explosive science & technology driven civilization has been
around a mere 38 seconds. On this scale a typical human life lasts no more
than 9 cosmic seconds!
Similarly we can more intuitively grasp the physical dimension of the universe
by using the 100,000 LY diameter of the Milky Way (MW), our home Galaxy, as
the yardstick of universe's distances.
We can call it either God's mile or the cosmic mile (CM). The radius of the
universe (greater than 13.7 billion light years) is thus greater than 137,000
CM. A cosmic foot corresponds
to 19.2 light years and a cosmic inch corresponds to 1.6 light years. Therefore
the Sun and its nearest neighbor Proxima Centauri are about 2.5 cosmic inches
apart. The distance between the MW and its nearest twin, the Andromeda galaxy,
is about 20 cosmic miles. To get yardsticks for solar and sub-solar system
distances it is best to use metric notation. A cosmic centimeter
corresponds to .64 light year or 233 light days. A cosmic millimeter is
thus the equivalent of 23 light days, incidentally humanity's furthest probe
has traveled, so far, only a distance of 13 light days, that is a little over
half a cosmic millimeter! A cosmic micrometer would then be a little over
a half light hour. A cosmic nanometer would correspond to about 2 light seconds.
Since light takes 8 seconds to get from the Sun to us, the distance of Earth
from the sun is about 4 cosmic nanometers (The actual distance is 93 million miles).
This means that, on this scale, the Earth, and for that matter, the entire
solar system, would be invisible in God's eye!!!
The Scale of the Universe
Time
Space