The Hubble Revolution

On April 24, 1990, the space shuttle Discovery blasted off from the Kennedy Space Center in Florida. The shuttle’s payload bay contained the Hubble Space Telescope. It was a momentous occasion. Astronomers had long dreamt of having an orbiting telescope which would allow them to survey the skies unimpeded by the distortion of the earth’s atmosphere. The Hubble was soon deployed at an altitude of 332 miles. Frustratingly, the telescope’s initial performance was plagued by a flaw in its primary mirror which resulted in blurry images. It wasn’t until December of 1993 that astronauts were able to deploy a corrective optics system which rectified the problem. Over the last 3 decades, the Hubble Space Telescope has given humanity an unparalleled view of our cosmos.

As we learned last week, a century ago, the vast majority of scientists believed that the universe was eternal. This conviction began to crumble 1915 when Albert Einstein published his general theory of relativity. Einstein quickly realized that his theory came with a catch; the mathematical equations which governed relativity were inconsistent with a static universe. Relativity required a dynamic cosmos which was either expanding or contracting.

By 1931, Belgian priest and astronomer Georges Lamaitre proposed that the universe had begun as a tiny speck of inconceivably high temperature and pressure. This “primeval atom,” as Lamaitre called it, rapidly expanded (or exploded if you will) until it reached the vast proportions we observe today.

In the early 1900s, scientists had a limited understanding of our universe. Our solar system resides within the Milky Way galaxy, an astonishingly large structure measuring over 100,000 light years across. And our sun is but one of 100 billion stars which comprise our galaxy. It should hardly be surprising then, that a century ago, astronomers believed that our galaxy was the universe! But this would soon change.

Before we proceed, we need to pause and learn a little bit about two basic concepts of astronomy: spectroscopy and the Doppler effect.

Astronomers often use a technique called spectroscopy, which uses a prism to separate light into its constituent colors. Elements such as hydrogen or helium produce characteristic color patterns, thereby allowing scientists to determine which elements are present in celestial bodies.

Most folks are familiar with the Doppler effect as it pertains to sound. We’ve all had the experience of listening to the high pitch of an oncoming car. But when the same vehicle passes by and is now traveling away from us the pitch is lower.

The explanation for this phenomenon is quite simple: the pitch of a sound is a function of its frequency. High notes have high frequency (their sound waves are bunched closer together) while low notes have low frequency (their sound waves are spaced further apart). When a car is approaching us, the sound waves it produces are compressed together resulting in a higher pitch. When a car is racing away, its sound waves are stretched apart, lowering the pitch.

Fewer people realize that the Doppler effect applies not just to sound but also to light. When astronomers observe a distant star, they can use spectroscopy to separate the light into its constituent colors. When a star is moving towards us, its light waves become bunched together into a higher frequency correlating with the blue end of the visible light spectrum. Likewise, when a star is moving away from us, its light waves stretch out to lower frequencies toward the red end of the spectrum.

In the early twentieth century, astronomers were limited by telescopes which could only observe stars within our own Milky Way galaxy. These stars were sometimes blue shifted and sometimes red shifted, giving observers the impression that the stars were simply drifting about in space with no particular pattern. But astronomers also found indistinct patches of light which they called “nebulae,” which in Latin means cloud. Nebulae were believed to represent clouds of gas and dust within our own galaxy.

In 1914, a little-known astronomer with the delightful name of Vesto Slipher began to study these nebulae. Using spectroscopy, Slipher was puzzled to find that most nebulae were dramatically red shifted, indicating that they were receding from us at high velocities.

This brings us to the towering figure of Edwin Hubble. Hubble studied astronomy at the University of Chicago. Upon completing his dissertation, he accepted a position at the Mount Wilson Observatory in California where the most powerful telescope in the world had just been completed. Alas, Hubble’s true calling was delayed by World War I. When the United States declared war on Germany in 1917, Hubble enlisted in the Army.

At the close of the war, Hubble took up his post at Mount Wilson. There he used the newly constructed 100-inch Hooker telescope to interrogate nebulae. Hubble patiently photographed these clouds using long exposures lasting several nights. This technique allowed him to discern individual stars within the nebulae. Hubble’s research suggested that the nebulae might themselves be distant galaxies.

Hubble endeavored to determine just how far away nebulae truly are. In order to accomplish this, he used a particular kind of star called a Cepheid variable. The light from these unique stars fluctuates in a regular pattern, allowing astronomers to determine their exact brightness and thereby estimate their distance.

In 1923, Edwin Hubble found Cepheid variables in the Andromeda Nebula. Based on these Cepheids, he calculated that the Andromeda was 900,000 light years away from the earth, far beyond the borders of our Milky Way galaxy. (Modern techniques show that the Andromeda is actually 2.48 million light years away.) Hubble had thus proven that the Andromeda Nebula could not possibly be a cloud of gas and dust within our own galaxy, but was rather the Andromeda Galaxy, a spiral galaxy similar to the Milky Way.

Hubble’s efforts stunned the world of astronomy. He had massively altered mankind’s understanding of the cosmos. No longer was the universe confined to our own galaxy. Hubble had revealed that the Milky Way was just one of many other galaxies in a universe which was immensely larger than what had been previously imagined.

Edwin Hubble was not one to rest on his laurels. He continued to investigate dozens of additional galaxies, refining his measuring techniques so that he could more accurately determine their distances. Building on the work of Vesto Slipher, Hubble verified that the galaxies were redshifted and thus moving rapidly away from the earth.

In 1929, Hubble first published a paper exploring the relationship between distance and redshift. He demonstrated that there is a clear relationship between the two; namely, the further away a galaxy is located, the faster it is moving away from us. Moreover, this relationship is linear, so that a galaxy twice as far away is receding at twice the velocity. This precise relationship became known as the Hubble Law.

Hubble had thus made another astounding discovery. His work had upended the field of cosmology by providing empirical evidence that the universe was expanding. The Hubble Law indicated that at some point in the distant past, the universe had indeed exploded outward from an infinitesimally small point. The theoretical proposal of Georges Lamaitre – the “primeval atom” – had found concrete proof.

Albert Einstein knew he had missed a tremendous opportunity. Although his theory of relativity suggested an expanding universe, he had stubbornly resisted this conclusion. Einstein had instead proposed his infamous “cosmological constant”, a fudge factor added to his equations in the hope of salvaging an eternal, static cosmos. In 1931, Einstein traveled to Mount Wilson so that he could see Hubble’s evidence with his own eyes. When confronted by the facts, Einstein admitted his error and retracted his cosmological constant, calling it “the greatest blunder of my life.”

Thus, Edwin Hubble had helped midwife the birth of Big Bang cosmology. It is altogether fitting that his name was selected for the amazing telescope which continues to orbit our planet and further his work.

The term “Big Bang” wasn’t actually coined until 1949 when it was used by English astrophysicist Fred Hoyle. Ironically, Hoyle was a bitter opponent of the Big Bang who used the term contemptuously. Nonetheless, both the name and the theory stuck.

Over the years, mountains of evidence have accrued in favor of the Big Bang. Some Christians reject the Big Bang. This is unfortunate. It would be difficult to imagine a theory which is more consistent with the Bible. The Big Bang posits that that some 13.7 billion years ago, the entire universe – matter, energy, space and even time itself – suddenly burst into existence. We now know that our cosmos had a very abrupt beginning, which requires a very impressive Beginner.