Rainbows are exquisite apparitions. Hanging immobile on a canvas of blue, as if an artistic Titan had swung an arc with a hand full of pastel brushes. On an exceptionally clear day, bright and crisp after a heavy rainstorm, one can occasionally observe a magnificent double rainbow, the colors in each arch inverted, nested one on top of the other, suspended cartoon-like high above in the sky. It is a sight to behold.
The old story goes that he who follows the rainbow to the end will find a pot of gold. It is but a legend of course, there is no end to find. Rainbows we now know are an artifact of optics. But metaphorically we can make such a journey. It will be a quest in mind only, fueled by burning curiosity, and it will end in a treasure immeasurable by the dollar or the Pound Sterling. Our guide will be a brilliant rebel, a Rhodes Scholar, turned Lawyer, turned scientist. And what he found, somewhere over the rainbow, was and remains perhaps the greatest single, scientific discovery of all time.
Meet our guide: Edwin Powell Hubble. An accomplished scholar, world class athlete, and veteran of World War 1. By age 30, he had set records in track and field, played college basketball, and gone on to earn a Rhodes Scholarship where he received a degree in Law at Oxford University. After a few years in the legal business, he decided his real love was astronomy, and began working at the powerful telescope housed at the
Mount Wilson Observatory in the 1920s.
Hubble's first discovery was that some of the fuzzy celestial patches astronomers had long called nebula were in fact galaxies in their own right. As large, or larger, than our own Milky Way. He utilized a type of star known as a Cepheid Variable to estimate the distance to several nearby galaxies such as the Great Spiral Nebula in the Constellation of Andromeda. Cepheid Variables, as the name suggests, wax and wane in brightness (Luminosity) over time. Their period of fluctuation is a function of their mass. With the mass known, we can calculate the absolute luminosity. If you know how bright they should be, and you measure how bright they actually appear, you can work out how far away they must be. Because of Hubble's groundbreaking work, the size of the universe went from our single Milky Way Galaxy containing billions of stars, to a universe chock full of billions of galaxies each made up of zillions of stars.
That alone was quite a contribution! But Hubble's most amazing discovery was to come from following a path cobbled in rainbow brick.
As the study of optics progressed in the 17th century, early lensmakers noticed little rainbow like aberrations popping up all over the place as they peered through their early magnifying glasses and telescopes. For the most part, these early astronomers were concerned with getting rid of the pesky distortions, but a few started looking into the phenomena in general. The rainbow patterns produced by refracting sunlight were called Spectra, from the Latin word spectre meaning 'ghost'. Unsurprisingly, the science of studying those rainbow spectra is called Spectroscopy.
Everyone knows that a rainbow doesn't appear unless the sun is out. So obviously a rainbow must be the spectra of sunlight. To study solar spectra more closely, early scientists developed a device called a spectroscope which would project a rainbow of sunlight onto a convenient screen in a lab- as opposed to inconveniently, only during rainstorms, and way up in the sky. A spectroscope is made of two parts: a prism (or a similar device called a diffraction grading) and a lens to make an image out of the rainbow pattern. When early opticians first did this, they were surprised to find that a focused and sharp spectra not only shows the familiar color bands, but a series of fine lines spaced randomly through them! These lines, shown below in a spectra taken of the sun using a spectroscope, were called Fraunhofer Lines, named after the second guy to discover them (The first was a fellow named Wollaton). Pretty cool name: Kinda brings up the thought of a Bavarian Tavern selling kick-ass, thick German beer.
Naturally, as soon as the spectroscope was devised, astronomers were checking out what kind of spectra any light source would produce. Once they started playing with gas lights and burning substances of all kinds, it didn't take very long for astronomer/physicists in the latter half of the 19th century to figure out that each of those lines is produced by a specific substance, always at the exact same location, the same color region within the rainbow pattern. Oxygen has its own set of Fraunhofer Lines, as does carbon, or even whole molecules like water. It turns out that some of the single lines are more prominent than others. This has to do with how much of a particular substance is present in the light emitting source which produces the spectra.
The Balmer Series of Fraunhofer Lines, shown above with the other lines removed for clarity, is produced by the single most common element in the universe, Hydrogen. Since there is so much Hydrogen in the average star, those lines are particularly noticeable in the spectra of galaxies.
Now everyone has probably heard of the Doppler Effect. You stand next to a street or a railroad as a vehicle comes roaring by and the pitch changes as it passes. Waves coming off an object speeding towards you are compressed; if they're sound waves that means they sound higher in pitch. If waves are coming off an object traveling away from you, they're stretched out. If they're sound waves, that means a lower pitch. That's why you get that audible shift in pitch as a train moves past you.
Light waves also exhibit that same shift. Only with light, it's not the sound that gets compressed or stretched out, it's the frequency, i.e., the color. Any light emitting object traveling away from you will be red-shifted. And with good equipment, one can calculate the exact velocity of an object that is moving towards or away from the observer to a high degree of accuracy using that Doppler Shift in light-or radio waves, or sound (Radar guns used by police make use of this same principle only they use radio waves which are below the visible wavelengths).
We can tell if a star, or even a whole galaxy of stars, is moving away from us, and at what velocity by looking at its spectrum. And the first thing we look for is the Balmer Series because that's the most visible landmark in a stars' spectra; Hydrogen being the most common element in most stars, and thus in all galaxies which are of course simply collections of billions of stars.
A galaxy that is moving away from us will show a spectra in which the Balmer Series is red-shifted towards the right hand side...not where it's supposed to be. The faster the galaxy is moving away from us, the more the Balmer Series (And every Fraunhofer line) is shifted into the redder regions of the rainbow pattern. The problem in the early 1900s was that we didn't have the resolution and magnifying power available in our telescopes to obtain a spectra from a faint, distant object, such as a galaxy.
Edwin Hubble, using the powerful telescope at the Mount Wilson Observatory, was able to get a readable spectrum from those distant galaxies which had enough resolution to be able to see the Balmer Lines-barely. And that's where things ground to a screeching halt; the Balmer series weren't where they were supposed to be! Some were shifted a little to the red region, others were way, way, over.
Hubble had the benefit of two new analytic techniques previous astronomers did not have. He had both the distances of several Galaxies from the Cepheid Variable Technique, and he had the redshifts of those same galaxies using the spectrum he obtained form the Wilson Observatory. And, when he correlated those two sets of data, he found that the further away a galaxy was from us, the more it was red-shifted!
The conclusion is pretty easy to visualize. The galaxies were moving away and the velocity with which they were receding was a function of their distance from us: Either our Milky Way Galaxy is the center of the universe and every other galaxy was hauling ass away from it. Or all the galaxies were moving away from each other, ours included. By the 1920s, astronomers had long gotten used to the idea that the earth and the sun weren't the center of the Universe, so the latter view was adopted. But how could everything be moving away from everything else?
Imagine the universe as the surface of a balloon, and the galaxies as dots on that balloon's surface. If you blow the balloon up each dot moves away from all the others. If you happen to be on one dot, from your perspective it appears that all the other dots/galaxies are moving away from yours. And the further away the dot/galaxy is from your point of observation, the faster it's moving away from yours!
In other words, the universe was expanding!
This effect was christened the Hubble Redshift. And then astronomers asked the obvious question: If the universe was getting bigger as we go forward in time, then it must have been smaller in the past. A universe can get big forever, there is no limit on infinity. But run that process backwards, and it can't get smaller forever. Sooner or later it reaches a single point. And there it has to stop.
That single point, our Cosmic Genesis, would have to have been a truly titanic explosion if the galaxies were still flying apart like shrapnel, billions of years later. And so the term Big Bang was coined to describe the initial hypothetical event. The universe, which up until Hubble's momentous discovery was thought to be both infinite and eternal, was instead finite and had a beginning in time!
In recognition of Edwin Hubble, the first space telescope launched into orbit was named in his memory. After the initial problem in the optics was repaired, the Hublle Space Telescope (HST) gazed at the Cosmos, the results take our breath away. Below is just a small sample of what Mr. Hubble's Telescope has revealed.
Cat's Eye Nebula (Enlarge) Super Nova Remnant LMCN49t (Enlarge)
Cartwheel Galaxy (Enlarge) Whirlpool Galaxy (Enlarge)
Then the mighty eye of the HST was turned to what astronomers thought was an empty patch of space. It was left pointed at that tiny region, the size a postage stamp held one-hundred yards away, for ten days, as light slowly tricked in, photon by photon.
Deep Field View ( Enlarge)
You are looking at the first stellar objects to form, at the very edge of the Universe; the beginning of time and space. The Deep Field View is the furthermost we can see in our Cosmos. Each one of those tiny pinpricks of light is a galaxy. Each galaxy contains perhaps as many as a trillion stars. And the view is the same no matter what 'empty' region of space we look at: billions of galaxies, a trillion trillion stars. Our Universe is grand indeed.
And God said, Let there be light: and there was light.
I suppose I can understand why fundamentalists don't care much for evolutionary biology. I can even sympathize with why a Biblical Literalist would feel uncomfortable with an ancient Cosmos. I think both positions are foolish, ill-conceived, and impossible to defend scientifically. But I can understand the conflict between them.
I can't for the life of me wrap my head around Creationists objections to the Big Bang. If ever there was a symphosis of the Abrahamic Creation story and science, that would be it. If ever there was a logical place to posit a Prime Mover, there it is. I'm not religious. But If I were, I can't imagine a better place for God to work His Will than the secret Hubble revealed. Nor can I envision a greater Testament to the Brilliance of any Creator, than one who Created the Universe with a single act, which would in turn initiate countless processes, all unfolding over eons, to produce this glorious, star-studded, breathtakingly beautiful, Universe. I know some of you are religious, so you tell me: Is this not inspirational? Is this not worthy of your God? Does this grandeur not humble you, make your hairs stand on end, and fill you with immense pride and thankfulness for the genius of your Creator?
When Edwin Hubble first began working at Mount Wilson, the universe was thought to be static, on the order of one-hundred thousand light years wide, and consisted of an island single galaxy, our Milky Way. In only a decade, it had grown a thousand fold in size to over a hundred-million light years, with zillions of galaxies as big or bigger than our own, and was expanding at the speed of light. His namesake, the Hubble Space Telescope, now informs us that we live in a universe billions of light years across. Had observational astronomy been on the list of natural sciences which were candidates for the Nobel Prize, Hubble would have been a Laureate many times over.
So the next time a summer shower opens up, and you gaze skyward as the sun comes out to paint a ribbon of pastel violets, blues, greens, yellows, and reds, think of Edwin Hubble, his search for the pot of gold, how amazing science can be, and what can be learned. All by fiddling around with a rainbow.
But, if the Big Bang had really happened, we would expect to see the Bang itself! The further one looks into space, the further one looks back in time. For the speed of light is as finite as our universe. That story, along with other developments, will be covered next time.