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How Did the Universe Begin, How Will It End, and How Do We Know?
November 1, 2013
Category: Science and Technology > Physical Sciences
Where did the universe come from? Disregard your creation myths — Judeo-Christian or other. Physics offers the following explanation, observationally verified. Truth is stranger than fiction.
The universe began as a random fluctuation of the quantum vacuum — a cosmic burp, the Big Bang,13.82 billion years ago. Something from nothing. No creator. No design. No purpose. Just physics. Sorry.
The expanding universe cooled, with pure radiation producing the lightest elements ― hydrogen, helium, lithium ― aggregating into the first stars, where thermonuclear fusion created the heavier elements, ultimately released in supernovae explosions to aggregate into 400 billion galaxies, averaging 200 billion stars, each hosting several planets, including ours, formed 4.5 billion years ago. Single-cell life evolved 3.6 billion years ago, and Homo sapiens 200,000 years ago. Now, briefly, there's you and me.
That's the story so far. Whither? Our sun will consume its nuclear fuel and expand as a red giant, engulfing the earth in several billion years. But we won't see that fiery end, no doubt having suffered an asteroid-caused mass extinction similar to the dinosaurs. The earth has had multiple mass extinctions. We go next, most likely.
That's how we will end. But how will the universe end? Actually, it won't. It will expand faster and faster, ultimately faster than light speed (allowed by Einstein's theory), at which time (in 100 billion years) all galaxies other than our own will disappear from view. Subsequent civilizations will think their galaxy is alone in the universe, just as 19th-century scientists did. Ironic.
This narrative is trustworthy because theoretical predictions agree in astonishing detail with cosmological observations, of which the most important are:
- The expansion of the universe
- Hubble discovered that all galaxies are moving away from us, with the farthest galaxies receding fastest. Go backwards in time and you infer the Big Bang.
- The cosmic microwave background (CMB)
- Bell Labs discovered the CMB, the afterglow of the Big Bang. All-sky analyses of the CMB reveal the slight density variations 13.82 billion years ago which led to the formation of the stars and galaxies we see today. Startling agreement between the density spectra of the CMB and of today's universe provides detailed confirmation of the universe's evolution.
- The abundances of the elements
- The famous graph below shows the element abundances, reflecting creation of hydrogen, helium, and lithium in the first 3 minutes after the Big Bang, followed by creation of the heavier elements in stars formed 200 million years later. In one of the greatest triumphs of 20th-century science, the features of this graph match theoretical predictions almost perfectly, even though the abundances span a factor of 1000 billion. For example, we know precisely why iron is common and gold is 10 million times rarer.
That's the story of the universe, in a nutshell. It's not as comforting as religious myth. But reality doesn't owe us comfort. The universe is the way it is, like it or not.
I kind of like it. It's all we have.