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Physics LibreTexts

1.29 A Scale Model of Time

Another scale model reveals our place in cosmic time. Let's compress time by a factor of 50 thousand trillion or 5 x 1016. This scaling is also not arbitrary; it reduces the 13.8 billion years since the big bang to a calendar year.


An artists conception of the birth of a star. Click here for original source URL.

On New Years Day, all time and space, matter and energy, are created. By late February the Milky Way is forming. Generations of stars are born and die through the spring and summer. The Milky Way devours a series of its smaller companions and rotates once each week. In early September, near the Orion spiral arm, a mid-sized star forms in a busy stellar nursery, its gas cloud nudged into collapse by the violent death of a nearby supergiant. Two days later, nine rocky bodies have formed from dust swirling around the infant Sun. One is our Earth.

Within one or two weeks, the freshly minted planet is alive. Microbes spread across the face of the planet and deep into its oceans. The Sun converts hydrogen into helium and sends a hominids steady stream of warming photons into space. Several times a week, at random intervals, huge rocks slam into the planet and instigate chaos. Many organisms are extinguished but the rest adapt and diversify. In October, life invents a new way to harness solar energy and the atmosphere begins to fill with oxygen.

In mid-December the pace of life begins to pick up. After several months with no organism larger than a fist, new creatures proliferate in the oceans. Some move on to the land and others learn to fly. By Christmas, dinosaurs rule the forests and swamps of the lush planet. Within three hours of the stroke of midnight on New Year's Eve, hominids appear for the first time. They are descendent of mammals, who were the successful survivors of a huge meteor impact several days earlier. By twenty seconds to midnight, the hominids have evolved to be just like us; they invent tools and agriculture and build the first cities. The Copernican Revolution occurs at one second to midnight.

The scale model of time has described our late arrival on the scene as intelligent life forms, able to explore space and understand the cosmos, but consider this: we may not be the first. An Earth-like planet could have formed somewhere else in the universe much earlier. Let's say it's early June. If evolution followed the same pace as of Earth there would be an alien species attaining our level of technology in late September, just as life was first stirring on the Earth. What would that alien species be capable of now, with a four billion year head start on us?

We live on a cusp of exponential change. All the marvels of the modern world computers, TV, space travel, genetics, the Internet are crammed into the last tenth of a second of the cosmic year. The surging rate of technological change makes it impossible to confidently predict the future. Knowing our insignificance in time and space, we are both awed and unnerved by our vast potential as a self-aware species. If we aren't alone in having these capabilities, the universe must be a very, very interesting place.


The newly formed Hadean Earth experienced very high temperatures due to extreme volcanism and frequent collisions with other bodies, but eventually began to cool. Click here for original source URL.