At T+1 Second to 300,000 Years Old

The beginning of the cosmos intrigues people. It’s sometimes tough to wrap our minds around the concept of how this universe we inhabit came to into existence and how it has continued to expand space and time for 13.7 billion years. Recently, at the end of one of my shipboard presentations, an audience member asked me how big the universe was when it was one second old.

The birth and expansion of the universe is a fascinating story.  I’m not sure why my audience member focused on the T+1 second point—but, it was an interesting time. Just as the earliest life on Earth formed when conditions were right, more than 3.8 billion years ago, from a soupy mix of nucleic acids and other strings of organic material that combined in just the right chemical way, so the cosmos at T+1 second was an important way point in the evolution of the universe we know today. It was a time when things were cool enough to begin the next stage of evolution in the cosmos.

The guy’s question was a good one.  The simple answer is that the universe had expanded to be about a thousand times the size of the solar system by the time it was a second old. It was a hot place—about 10 billion degrees hot—and consisted of a soupy mix of neutrons and protons. Only a few seconds later, that mix began to hatch the first atomic nuclei: deuterium (a form of hydrogen) and helium. (For a more detailed timeline of the Big Bang and the early universe, go here.)

As this baby universe continued to expand, its “stuff”—while cooling down—was still hot enough that electrons were wandering about, trapping photons of light. Trapped light means darkness, and thus the earliest epochs were dark. Cosmologists call them the “cosmic dark ages”.  Eventually, things cooled enough that the rapidly expanding cosmos turned transparent (as opposed to the opaque darkness).  Still no stars, no galaxies, but the cool transparent universe gave off a glow that we detect today as the Cosmic Background Radiation.  The stage was set for the first stars, and their radiation lit up the still-young universe.  At that point the cosmos was about a thousand times smaller than it is today.

I admit, I’m fascinated by the period from the Big Bang to the formation of the first stars.  When I was first studying astronomy, that 300,000-year period of time was just beginning to be understood. For example, we didn’t know much about the first stars and exactly when they formed.  Also at that time (in the late 1970s) The satellites that studied the first hints of light from the early universe (COBE, WMAP and others) were on the drawing boards. Today, we have the capability of detecting minute variations in the microwave background that is the remnant radiation from the Big Bang.  Those tiny slivers of temperature changes tell an amazing story of the earliest cosmic times and how the matter that existed then was already clumping together and would become the first stars and galaxies. Future missions (such as the James Webb Space Telescope, if it isn’t killed by its own budgetary woes and the “hate science because we don’t understand it” crowd) will help scientists delve more deeply into those primordial moments in time. There are many more fascinating moments to be explored before and beyond the T+1 second mark in our cosmic history.