The Hubble Constant, which describes the velocity-distance relationship for galaxies, is the foundation of modern cosmology. It establishes the time and distance scale of the universe and the dynamic nature of the galaxies since the beginning of time. It is all the more remarkable that the original data Edwin Hubble took was flawed.
Modern cosmology began in 1923, when Edwin Hubble realized he had observed Cepheid variables in M31, Andromeda. This enabled him to estimate the distance to M31.
Just three year prior, the National Academy of Sciences held the “Great Debate” to discuss the size of the universe. Was our galaxy all there was, as Harlow Shapley argued, or were we in just a small island of stars, among a vast ocean of other galaxies, as Herber Curtis argued?
No one was announced the winner of this debate. It remained an open, and hotly debated question until three years later when Edwin Hubble, searching for nova in M31 realized one of his nova was actual a Cepheid. He estimated the distance to M31 as 900,000 light years.
Harlow Shapely, referring to the letter from Hubble announcing his measurement of the distance to the Andromeda Nebula, was said to have remarked, “Here is the letter that has destroyed my universe.”
Over the next six years, Hubble refined his measurement technique, and searched all the local spiral galaxies, looking for Cepheids to determine the galactic distances. He found that more distant galaxies appeared to have a higher redshift, which he interpreted as a higher velocity away from us.
In 1929, he published his now famous velocity-distance relationship, estimating a slope of the line, which we referred to as the Hubble Constant, of 500 km/sec/Mpc.
His startling conclusion was that all galaxies we see seem to be expanding away from us; the father away they are, the faster they are receding. Not only did the size of the known universe dramatically expand with his first discovery in M31, but now he was describing an exploding universe.
Fifty years of observations in the visible, x-ray and far infrared all show the same general behavior, though as the distance scale is re-calibrated, the value of the Hubble constant has evolved.
The latest measurements, based on a combination of type Ia supernova and the cosmic microwave background radiation anisotropy, offers a value of the Hubble Constant of 70.8 +/- 1.6 km/sec/Mpc.
This relationship is the foundation of modern cosmology, establishing the time and distance scale of the universe and its dynamic nature. While Hubble’s first estimate of the expansion constant was high by more than a factor of seven, it represents only a tiny fraction of the observable sky.
His original measurements went out as far as 2 million parsecs. Recent measurements have extended his observations to 700 million parsec. The tiny red square in the plot above is the total range of Hubble’s original 1929 measurements.
In March, 2009. Dr. Steven Beckwith, the former director of the Hubble Space Telescope institute, presented a public lecture as part of the Silicon Valley Astronomy Lecture Series.
He took all the original galaxies Hubble used to show the expansion relationship in 1929 and re-plotted their distances using the most recent corrected data. Every single measurement was off the chart. “It was all garbage,” Beckwith said. “He got completely lucky!”
In the plot above, Hubble’s original graph is corrected for the most recent accepted distances to the same galaxies he plotted. Their distances are actually so far, they are all off the page. The shallow line is the corrected Hubble expansion curve.
How lucky Hubble was that even with poorly calibrated data, he could establish even a rough trend that would provide the basis to remake our view of the universe.
A video version of Dr. Beckwith’s presentation can be found on iTunesU by going to the iTunes store and searching on Beckwith Dawn of Creation.
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