How Old is the Universe?

The Universe is vast bubble of space and time, expanding in volume. Run the clock backward and you get to a point where everything was compacted into a microscopic singularity of incomprehensible density. In a fraction of a second, it began expanding in volume, and it’s still continuing to do so today.

So how old is the Universe? How long has it been expanding for? How do we know? For a good long while, Astronomers assumed the Earth, and therefore the Universe was timeless. That it had always been here, and always would be.

In the 18th century, geologists started to gather evidence that maybe the Earth hadn’t been around forever. Perhaps it was only millions or billions of years old. Maybe the Sun too, or even… the Universe. Maybe there was a time when there was nothing? Then, suddenly, pop… Universe.

It’s the science of thermodynamics that gave us our first insight. Over vast lengths of time, everything moves towards entropy, or maximum disorder. Just like a hot coffee cools down, all temperatures want to average out. And if the Universe was infinite in age, everything should be the same temperature. There should be no stars, planets, or us.

The brilliant Belgian priest and astronomer, George Lemaitre, proposed that the Universe must be either expanding or contracting. At some point, he theorized, the Universe would have been an infinitesimal point – he called it the primeval atom. And it was Edwin Hubble, in 1929 who observed that distant galaxies are moving away from us in all directions, confirming Lemaitre’s theories. Our Universe is clearly expanding.

Which means that if you run the clock backwards, and it was smaller in the distant past. And if you go back far enough, there’s a moment in time when the Universe began. Which means it has an age. The next challenge… figuring out the Universe’s birthdate.

Time line of the Universe (Credit: NASA/WMAP Science Team)
Time line of the Universe (Credit: NASA/WMAP Science Team)

In 1958, the astronomer Allan Sandage used the expansion rate of the Universe, otherwise known as the Hubble Constant, to calculate how long it had probably been expanding. He came up with a figure of approximately 20 billion years. A more accurate estimation for the age of the Universe came with the discovery of the Cosmic Microwave Background Radiation; the afterglow of the Big Bang that we see in every direction we look.

Approximately 380,000 years after the Big Bang, our Universe had cooled to the point that protons and electrons could come together to form hydrogen atoms. At this point, it was a balmy 3000 Kelvin. Using this and by observing the background radiation, and how far the wavelengths of light have been stretched out by the expansion, astronomers were able to calculate how long it has been expanding for.

Initial estimates put the age of the Universe between 13 and 14 billion years old. But recent missions, like NASA’s WMAP mission and the European Planck Observatory have fine tuned that estimate with incredible accuracy. We now know the Universe is 13.8242 billion years, plus or minus a few million years.

We don’t know where it came from, or what caused it to come into being, but we know exactly how our Universe is. That’s a good start.

Cosmologist Allan Sandage Dies

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Cosmologist Allan R. Sandage, who helped define the fields of observational cosmology and extragalactic astronomy, died November 13, 2010, at his home in San Gabriel, California, of pancreatic cancer. He was Edwin Hubble’s former observing assistant and one of the most prominent astronomers of the last century. Sandage was 84. Below is his biography from the Carnegie Institution for Science:

Allan Sandage became a Carnegie staff member in 1952 after serving as the observing assistant in observational cosmology to Edwin Hubble on both Mount Wilson and Palomar from 1950 to 1953, and Walter Baade’s PhD student in stellar evolution starting in 1949. Upon the death of Hubble in 1953, Sandage became responsible for developing the cosmology program using the 60- and 100-inch telescopes on Mount Wilson and with the newly commissioned Palomar 200-inch reflector. The programs centered on the recalibration of Hubble’s extragalactic distance scale and combining discoveries in stellar evolution with observational cosmology. Much of his research in the past 50 years has been directed toward these goals.

Early discoveries at Palomar showed that Hubble’s distances to galaxies were progressively incorrect, starting with Baade’s finding in 1950 that Hubble’s measured distance to the Andromeda Nebula, M31, was too small by a factor of about two. Sandage, first alone and later with G.A. Tammann professor of astronomy at the University of Basel, have carried the corrections progressively outward. This work indicates that by the time we reach the nearest cluster of galaxies in Virgo, the correction to Hubble’s scale is close to a factor of 10. Since 1988, Sandage and Tammann have led a consortium using the Hubble Space Telescope to determine distances to parent galaxies that have produced type Ia supernovae, shown earlier to be one of the best standard candles in luminosity known. From the results of the calibrations, Sandage, Tammann, and Abijit Saha of the Kitt Peak National Optical Observatory have determined at this writing (2005) the value of the Hubble constant to be 60 km s -1 Mpc -1.

Sandage’s other early research in observational stellar evolution led to a method developed in 1952 with Martin Schwarzschild of age-dating the stars from the luminosity turn-off from the main sequence of evolving stars in the Hertzsprung-Russell diagram. This method, improved over the years from theoretical calculations of stellar structure by many astronomers, remains the principal method of age dating. Sandage recently returned to problems related to the absolute magnitudes of RR Lyrae variable stars in globular clusters, important to the age dating of these most ancient of objects in the Galaxy.

Source: Carnegie Institution for Science