Universe: Tracing the Beginning and Calculating its Age

  • The age of the universe is precisely 13.8 billion years old, according to our best scientific methods.

  • But how do we learn the age of the universe when there’s no trace left of its beginnings?

  • We see the same constellations on the night sky as our astronomer ancestors and assume the universe above is fixed and unchanging, but the universe changes and had a beginning.

  • Our knowledge that the universe even had a beginning is relatively recent, and it corresponds to our discovery that there even is a universe outside the Milky Way galaxy.

  • Astronomers were arguing about the nature of spiral nebulae in the 1920s, but it all changed when Vesto Slipher found that they were moving away from us at incredible speeds and Edwin Hubble figured out their distances by locating a star type called a Cepheid variable.

  • We learned that essentially, galaxies are racing away from us, and the further the galaxy, the faster it seems to be retreating.

  • Until then, science had provided no reason to imagine that the universe was anything but static and had always looked pretty much the way it looks now, but the new picture was far more dynamic.

  • The recession of the galaxies makes perfect sense in the context of Einstein’s then-new general theory of relativity, and the Belgian physicist and Jesuit priest Georges Lemaître suggested that Slipher’s observed redshifts could be a sign of the universe’s expansion.

  • Lemaître put forward the idea that the world began in a state that he referred to as a “primeval atom.”

  • The big bang model of the universe suggests that the universe must have once been in an extremely hot, dense state and expanded from there.

  • The name “big bang” was coined by the astronomer Fred Hoyle during a 1950 BBC radio broadcast, not to popularize the idea, but rather to mock it.

  • This idea that the universe has a beginning brings to mind the creation stories of various mythic or religious traditions, but Lemaître himself disagreed, stating that the theory remains entirely outside any metaphysical or religious question.

  • To accurately calculate the age of the universe, we need to account for a few more things, such as the fact that galaxies aren’t only moving away from us due to the expansion of the universe, but they also have random motion as they’re tugged by the gravitational fields of nearby galaxies and clusters.

  • We also need to account for the fact that the universe’s expansion rate is not constant, but has changed over time.

  • By observing the cosmic microwave background radiation, we can get a snapshot of the universe as it was only a few hundred thousand years after the big bang.

  • The cosmic microwave background radiation also tells us that the universe is flat, and by combining all of these factors, we arrive at a precise age for the universe: 13.8 billion years old.

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