Conclusive Evidence

The fifteen years, from 1951 to about 1965, brought a number of developments that gradually weighed in favor of the Big Bang Theory.  Among these was the confirmation that radio galaxies exist.  Radio galaxies are sources of radio waves.  Astronomers had been aware of a far-away source of radio waves for some years but the debate over whether the source was a star or a galaxy was relevant to the Steady State or Big Bang Theory debate.  The theory was that radio galaxies were assumed to be young galaxies.  Under the Big Bang Theory, young galaxies should be very far away but under the Steady State Theory, young galaxies should be distributed more or less evenly throughout the universe.  Therefore, if the distribution of radio galaxies could be determined, that would provide evidence for one theory or another.

By 1961 over 5,000 radio galaxies had been discovered and their distances determined, some by direct observation and some by statistical methods.  The result clearly favored the Big Bang Theory: radio galaxies tended to be very far from the Milky Way.  Still, there had been no knockout punch one way or the other.  That changed in 1965.

Arno Penzias and Robert Wilson were working together at Bell Laboratories in 1963 in a new field called radio astronomy.  They both had an interest in radio sources in the universe and convinced Bell to let them use the radio telescope during down time.  In order to understand what the telescope was “seeing,” Penzias and Wilson had to filter out background noise.  This noise is exactly what you hear between stations on a radio dial.  It is electromagnetic radiation that comes from any number of sources: overhead power lines, a power plant, a competing and nearer radio station, for example.  To study distant radio sources, Penzias and Wilson pointed their telescope at an area of the sky where there should be little interference.  To their surprise, there was a persistent background noise.  The two tried everything to account for this but couldn’t.  Most astronomers would have ignored it because, though annoying, it wasn’t very significant.

I took the picture at a conference where Arno ...

I took the picture at a conference where Arno Penzias was a member of the panel. (Photo credit: Wikipedia)

Recall that in the 1940s Gamow, Alpher and Herman had predicted cosmic microwave background (CMB) radiation as a left-over signal from the Big Bang.  Because at that time there was no way to detect CMB, their theory had languished and now, 20 years later, was all but forgotten.  Certainly Penzias and Wilson weren’t aware of it at the time.  Toward the end of 1964 Penzias attended a conference in Montreal, Canada, where he casually mentioned this phenomenon to Bernard Burke of Massachusetts Institute of Technology.  A couple of months later Burke excitedly contacted Penzias to tell him that two theoreticians at Princeton, Robert Dicke and James Peebles, had presented a paper in which they predicted CMB (they, too, were unaware of Gamow’s, Alpher’s and Herman’s work two decades earlier).

Suddenly everything fell into place for Penzias and Wilson.  The background noise had nothing to do with extraneous power sources or even “white dielectric material” (pigeon droppings) left on the horn of the telescope as they had once supposed.  Instead, they had quite unwittingly and unintentionally proved the Big Bang Theory.  Not only did the Big Bang Theory account for CMB but the Steady State Theory had no place for it to exist.  Over the next 13 years a number of astronomers verified CMB, measured it and compared it to the predictions of the Big Bang Theory.  Everything matched.  In 1978 Penzias and Wilson received the Nobel Prize in physics for their discovery.  This firmly cemented the Big Bang Theory as the explanation for how the universe came to be.  That conclusion, however, only raised another question: what caused the Big Bang?  As Carl Sagan said: “Ten or twenty billion years ago, something happened — the big bang, the event that began our universe.  Why it happened is the greatest mystery we know.  That it happened is reasonably clear.”

WMAP image of the (extremely tiny) anisotropie...

WMAP image of the (extremely tiny) anisotropies in the cosmic background radiation (Photo credit: Wikipedia)

Religion Weighs In

Most scientific debates take place in coffee houses and scientific conferences.  But with something as fundamental as how the universe began the public got involved.  George Gamow was in large part responsible for the publicity by writing articles for popular magazines.  Eventually even the Catholic Church got involved.  In 1951 Pope Pius XII gave an address in which he praised the Big Bang Theory as proof  of the existence of a creator:

“Thus everything seems to indicate that the material universe had a mighty beginning in time, endowed as it was with vast reserves of energy, in virtue of which, at first rapidly and then ever more slowly, it evolved into its present state. . . . In fact it would seem that present-day science, with one sweeping step back across millions of centuries, has succeeded in bearing witness to that primordial Fiat lux uttered at the moment when, along with matter, there burst forth from nothing a sea of light and radiation, while the particles of chemical elements split and formed into millions of galaxies. . . . Therefore there is a Creator.  Therefore God exists!”

image of pope Pius xii

image of pope Pius xii (Photo credit: Wikipedia)

The atheist and jokester Gamow seized on this and mischievously quoted the Pope in a research paper he published in 1952, knowing it would annoy many of his colleagues who were anxious to avoid any overlap between science and religion.  The large majority of physicists believed that the validity of the Big Bang Theory had nothing to do with God and that the Pope’s endorsement of it should not be used in a serious debate.  Supporters of the Steady State Theory began to use the Pope’s address as a way of mocking the Big Bang Theory.  British physicist William Bonner suggested that the Big Bang Theory was part of a religious conspiracy to shore up Christianity.  “The underlying motive,” he said, “is of course to bring in God as a creator.  It seems like the opportunity Christian theology has been waiting for ever since science began to depose religion from the minds of rational men in the seventeenth century.”

Bonner was clearly referring to Galileo’s experience.  Since that unfortunate encounter between religion and science, science had portrayed a religious person as someone who checked his intellect at the door of the church when he entered.  This wariness toward religion sometimes bordered on paranoia.  English Nobel laureate George Thomson observed: “Probably every physicist would believe in creation if the Bible had not unfortunately said something about it many years ago and made it seem old-fashioned.”

English: George Gamow (1904—1968) — Russian-bo...

English: George Gamow (1904—1968) — Russian-born theoretical physicist and cosmologist. Русский: Георгий Гамов (1904—1968) — советский и американский физик-теоретик, астрофизик и популяризатор науки. (Photo credit: Wikipedia)

By the end of the decade of the 1950s, scientists were fairly equally divided between the two theories.  Both models had established themselves as serious contenders but neither had proven conclusive.  Both were based on observations that were made at the limits of science’s technology, so the “facts” deduced from those observations had to be taken not lightly but with critical examination.  Furthermore there were a number of highly intricate connections between the facts that were necessary in order to arrive at the final version of each theory.

The State of the Universe Mid-Century

By the time Fred Hoyle inadvertently created the term “Big Bang,” this was the state of the universe debate.

Gamow and Herman made a specific prediction based on their calculations.  They predicted the light left over from the Big Bang would have been in the 10-3 millimeter length 300,000 years after the Big Bang.  Because the universe had been expanding, the light would have been stretched, or red-shifted, so that is was now about one millimeter in length.  This is longer than visible light.  One millimeter is in the microwave wavelength.  Gamow and Herman called this cosmic microwave background radiation, or CMB radiation.  This was a bold prediction, in the same league with Babe Ruth calling his shot in Game 3 of the 1932 World Series or Joe Namath predicting a Jets’ win over the heavily favored Baltimore Colts in Super Bowl III.

Unfortunately no one had taken up Gamow’s and Herman’s cause.  There are many reasons for this.  First, the Big Bang theory was still the minority view of most scientists.  No one wanted to look for CMB radiation that might be there based on a theory that most people didn’t accept.  Secondly, Gamow had a reputation as a bit of a jokester and wasn’t taken altogether seriously.  For instance, he once said that heaven was 9.5 light years from earth.  He based this on the fact that in 1904, at the outbreak of the Russo-Japanese War, many in Russia were praying for the destruction of Japan.  It wasn’t until 1923 that a severe earthquake hit Japan.  Gamow said, tongue in cheek, that prayers were limited by the speed of light and since it took 19 years for them to get to heaven and the response to get back, it must be 9.5 light years from Earth to heaven.  A third reason that Gamow’s and Herman’s theory wasn’t worked on was it required a unique skill set.  Their theory was based on the intersection of astronomy, nuclear physics and microwave detection.  Almost no one had those skills and even if they did the technology to detect CMB radiation was in its infancy.

This intersection of astronomy and nuclear physics comes as a result of running the expanding universe predicted by Friedmann and Lemaitre and demonstrated by Hubble backwards to its logical end.  As the universe contracts back on itself it becomes more and more compact.  Its curvature becomes greater and greater until, at the instant of the Big Bang, it has infinite curvature.  Mathematics abhors infinity.  It simply can’t deal with it.  It’s like trying to divide by zero; it can’t be done.  General relativity breaks down when the curvature becomes infinite.  Physicists had to turn to other models to predict what happened.  Those other models are in the realm of nuclear physics, or particle physics as it has come to be called.  To fully understand the birth of the universe, one had to understand not only the cosmos as it is today, which is the realm of general relativity, but also what went on from those first crucial nanoseconds after the explosion, when temperatures were in the millions of degrees and no matter existed; the universe was composed completely of energy, to about five minutes after the explosion when atomic nuclei began to form.  And then, after the first 300,000 years, for the next ten million years or so, how did the lighter elements like hydrogen and helium

The Hubble Ultra Deep Field, is an image of a ...

The Hubble Ultra Deep Field, is an image of a small region of space in the constellation Fornax, composited from Hubble Space Telescope data accumulated over a period from September 3, 2003 through January 16, 2004. The patch of sky in which the galaxies reside was chosen because it had a low density of bright stars in the near-field. (Photo credit: Wikipedia)

combine to form heavier elements?

You can begin to see why many physicists still clung to the eternal universe theory.  The implications of the Big Bang are staggering.  Besides the question “how did it happen” there is the question, “how did we get from the plasma soup to stars, galaxies and planets.”  It’s much easier simply to say that the universe has always looked like it does and always will.  It was never created and it will never end.  It just is.  With the new life breathed into the Steady State view by Hoyle, Bondi and Gold the debate took on some aspects of trench warfare during World War I with both sides staring at each other across a no-man’s land.

According to Hoyle

Gamow and Herman, faced with overwhelming apathy over their notion of CMB radiation proving the Big Bang theory, withdrew from the fight in the 1953.  The Big Bang Theory had two strikes against it: the fact that it predicted the age of the universe to be less than the age of the stars it contained; and, while it adequately explained the formation of lighter elements such as hydrogen and helium, it couldn’t explain the existence of heavier elements.  The theory could be salvaged if only someone could detect the existence of CMB radiation but years of trying to gin up any interest in attempting that had failed.

Fred Hoyle

Fred Hoyle (Photo credit: Wikipedia)

Meanwhile, Fred Hoyle had built a reputation as the foremost critic of the Big Bang theory.  Trained in England he earned a PhD from Cambridge, working alongside some of the most famous physicists of the era, Paul Dirac, Max Born and Hoyle’s hero, Arthur Eddington.  In 1942, while assisting the war effort, he met Thomas Gold and Hermann Bondi.  The three formed an alliance based  on their interest in cosmology.  In 1946 they made a breakthrough in reviving the eternal universe model.  That  model failed to explain the red shift observed by Hubble.  Hoyle, Bondi and Gold theorized a revised model whereby the universe was expanding but eternal.

The inspiration for this theory seems to have been a low-budget horror film called Dead of Night.  The film was written in such a way that the story evolved, characters were introduced and their stories told, yet it ended exactly where it began.  It could have gone on forever without a resolution.  In that sense it seems a lot like the comedy series Seinfeld, characters getting in and out of situations but never really accomplishing anything.  As the story goes, after the film Gold asked “what if the universe was like that?”  From that came the revised steady state theory.  The universe does indeed expand but as it does new matter is continually created. This modification overcame the prediction of the Big Bang theory, that the universe was becoming less dense as the matter within it expanded.  Instead, though the universe did expand, the newly created matter filled in the gaps, making it eternally the same.  It was much like a river that flows in its course, decade after decade, century after century, apparently unchanging but never containing the same water.

The immediate question leveled against the Steady State Theory was, where was all this new matter coming from?  Hoyle replied that this shouldn’t be a concern.  The creation of one atom in a space the size of the Empire State Building every century was enough to account for the new matter.  While Hoyle acknowledged that the Steady State Theory had flaws, so did the Big Bang Theory, as we have already noted.  What Hoyle did was give cosmologists a clear choice:  Big Bang, which implies a beginning of time and space, a moment of creation (with all the implications attendant to that notion), and an unknown future; or Steady State, which offers an eternal existence, constant creation of matter, and a predictable future.

The other thing Hoyle did, ironically, was to coin the term Big Bang.  Prior to 1950 the term Big Bang as a description of that theory had not been used.  In that year Hoyle appeared as a guest on a BBC radio program to discuss the competing theories of the universe.  Hoyle said, in part, “On scientific grounds this Big Bang assumption is much the less palatable of the two.  For it is an irrational process that cannot be described in scientific terms. . . . On philosophical grounds, too, I cannot see any good reason for preferring the Big Bang idea.”  As Hoyle spoke, his voice took on a derisive tone when he used the words “big bang,” apparently trying to convey his disdain for the theory by dismissing it as nothing more than a firecracker explosion.  To his chagrin the term caught on and the theory was thenceforth and forever to be known as the Big Bang Theory.

What Did the Big Bang Look Like?

As I wrote in an early post, many people are familiar with the basic Big Bang Theory: that the universe was born in a violent explosion.  Beyond that popular conception is hazy, with a lot of people thinking the planets, stars, galaxies, asteroids and everything else popped into being fully formed.

If you had been present at the explosion there wouldn’t have been much to see.  Unimaginable amounts of energy were released.  It was pure chaos, with temperatures far too high to allow the energy to convert to matter (Einstein’s famous E = mc2 , where E stands for energy, m for mass and c for the speed of light shows that energy and matter are interchangeable).  However, within about 300 seconds of the Big Bang the temperature had dropped to where lighter elements like hydrogen and helium could form.  During the next critical minutes nuclei were formed.  Once the universe cooled to about one million degrees C, nuclear fusion stopped.  Matter existed in a state known as plasma.  Most people are familiar with the first three phases, solid, liquid and gas.  Hotter than gas, plasma is a state of matter in which the temperature is so high that atomic nuclei cannot hold onto electrons.  This condition existed until the temperature dropped to about 3,000 C, which took about 300,000 years.  At that point nuclei could hold onto electrons and elements began to form.

One other thing was present at the Big Bang: enormous amounts of light.  Had you been there you wouldn’t have seen anything because light is scattered by plasma, just as it is scattered by water droplets in the air, which creates fog.  Just as you can’t see in a car at night in fog because the fog scatters the light from your headlights, so would the light from the Big Bang have been scattered.  For 300,000 years or so the universe was the proverbial pea soup.

After 300,000 or so years the temperature was low enough to form elements, which are electrically neutral.  Light doesn’t interact with neutral elements so it could pass unhindered through the universe for the first time.

Two scientists, George Gamow and Robert Herman, had been working on proving the Big Bang Theory.  They suddenly realized that if the Big Bang Theory was correct and the theory about plasma cooling to allow formation of atoms, which in turn allowed light to pass unimpeded through the universe, the remnants of that light should still be visible today.  If it could be detected it would further prove then validity of the Big Bang Theory.  In fact, detection of this luminoues echo of the Big Bang would be almost conclusive proof of the Theory.  Conversely, if the light wasn’t found the Big Bang couldn’t have happened.

Into What is the Universe Expanding?

If the universe is expanding, where is it expanding to?  After all, the universe contains everything there is, both matter and empty space.  Into what is the universe expanding?

This was the next big question, along with the discrepancy between the age of the earth and the age of the universe, to face the Big Bang proponents.  The prevailing theory among Big Bang backers in the late 1920s was that space itself is expanding.  Imagine a deflated balloon.  Take a marker and cover the balloon with dots.  Now inflate the balloon.  Each dot remains in the same place on the surface of the balloon but as the size of the balloon increases the dots move apart from each other.  The dots represent galaxies and the surface of the balloon is the universe.  Just as the balloon expands so does space itself.

Friedmann did not live to see his theory vindicated but Lemaitre was still alive to revel in his new-found acceptance.  To recap, both Friedmann and Lemaitre predicted that, at a time in the distant past, everything was squeezed into a tiny point.  Lemaitre called this the primeval atom while Friedmann said it wasn’t even that big at the beginning.  Friedmann developed his theory by ignoring general relativity while Lemaitre accepted general relativity but rejected the cosmological constant.  Either way, Hubble’s observations supported a moment of creation, or, as Lemaitre put it, “a day without a yesterday.”

Einstein had lost interest in cosmology in the 1920s but with Hubble’s discovery his interest was rekindled.  In January, 1931, he admitted that he was wrong about a steady state universe and accepted Lemaitre’s theory.  He called the cosmological constant, which was necessary to overcome the effect of gravity that would eventually cause the universe to reverse its expansion and collapse on itself, the greatest mistake of his career.  Not all scientists were so happy to abandon the cosmological constant, though.  The Big Bang proponents found a use for it because by tweaking it they could change the rate of expansion of the universe.

Einstein’s endorsement of Lemaitre’s theory catapulted Lemaitre into celebrity status.  Because Lemaitre was both a physicist and a priest he had dual status as a celebrity.  Lemaitre was careful to keep religion out of science, saying “A lot of people believe the Bible actually pretends to teach science.  This is a good deal like saying that there must be authentic religious dogma in the binomial theorem.”  Nevertheless, Big Bang critics jumped on Lemaitre’s religious training by arguing that his theory was nothing more than a pseudo-scientific attempt to justify the Book of Genesis.  The “primeval atom,” they argued was simply a prop for a master creator.  To bolster their argument against the Big Bang theory they pointed to a defect we’ve already noted: the Big Bang theory predicted a universe that is younger than the Earth.  To them, the universe was eternal and unchanging.  Yet the eternal universe group knew they couldn’t just throw rocks at the Big Bang Theory.  They had some explaining of their own to do, such as how does Hubble’s Law fit into their model?  If the universe is static and unchanging how do you explain the red shift of virtually all the galaxies racing away from each other?

English: This illustration shows abstracted &q...

English: This illustration shows abstracted “slices” of space at different points in time. It is simplified as it shows only two of three spatial dimensions, to allow for the time axis to be displayed conveniently. (Photo credit: Wikipedia)

Hubble the Hero

The 100 inch (2.5 m) Hooker telescope at Mount...

The 100 inch (2.5 m) Hooker telescope at Mount Wilson Observatory near Los Angeles, California. This is the telescope that Edwin Hubble used to measure galaxy redshifts and discover the general expansion of the universe. At the time of this photograph, the Hooker telescope had been mothballed, although in 1992 it was refitted with adaptive optics and is once again in use. Keywords: 100 inch Hooker, telescope, Mount Wilson Observatory, Edwin Hubble (Photo credit: Wikipedia)

Edwin Hubble was already famous by 1924 but that year he became a celebrity.  A few years earlier he had met Grace Burke, daughter of a California millionaire.  Grace was already married when Hubble fell in love with her but in 1921 she was widowed when her husband, a geologist, fell down a vertical mineshaft to his death.  Grace and Edwin renewed their relationship and were married in 1924.  Hubble was working at the Mt. Wilson observatory about 15 miles from Los Angeles at the time.  With his marriage into money he gained entry to parties where movie stars and politicians mingled.  Hubble was gregarious and outgoing and soon the likes of Douglas Fairbanks and Cole Porter visited the Mt. Wilson observatory where Hubble regaled them with stories.

Hubble had heard of Slipher’s and others’ discoveries that the majority of galaxies are moving away from us.  He took it as his duty as the world’s foremost astronomer to solve this problem.  The 100-inch Mt. Wilson telescope was 17 times more powerful than Slipher’s.  Hubble spent countless hours staring through it at the night sky.  With his assistant Milton Humason he set about measuring the speed of the receding galaxies.

What they discovered was the first observational evidence to support Lemaitre’s and Friedmann’s theory that the universe is not static but is expanding.  Hubble plotted the distance of dozens of galaxies against their speed and discovered a linear relation.  In other words, if a galaxy was twice as far from earth as another, the first was moving twice as fast.  Instead of traveling at random speeds and in random directions, virtually all galaxies were traveling at speeds proportional to their distance and moving away from the Milky Way.

By running the movie in reverse, so to speak, Hubble showed that last year all galaxies were closer to us than now, a hundred years ago they were closer still.  Moreover, and this was the incredible part, since the velocity was in proportion to the distance, the more distant galaxies would arrive at the beginning point at the same time as the nearer ones.  A galaxy three times as far away moved three times as fast, so, assuming that the relative speeds were constant, there was a time in the distant past when all galaxies were gathered together in one region of the universe.

Hubble’s findings weren’t conclusive proof of the Big Bang (it still had not been so named) and Einstein and others still favored a steady state view of the universe.  But it did give ammunition to the expanding universe proponents and put the burden on the steady-staters to reconcile their view with this indisputable evidence of galactic movement.

Hubble’s discovery gave rise to what is known as Hubble’s Law.  This isn’t an exact law like gravity but is more of a rule of thumb.  What it does is allow the distance of a galaxy to be calculated by knowing its speed, or its speed to be calculated if the distance is known.  The most profound implication of Hubble’s Law is that the age of the universe can be calculated.  Using Hubble’s Law and the speed of various galaxies led to a conclusion that the universe is 1.8 billion years old.

The only problem with this age is that geologists have calculated the age of the Earth at around 4 billion years.  How can the Earth be older than the universe that contains it?  While Hubble’s discovery gave credence to a time of beginning or creation of the universe, it posed internal inconsistencies.

Nevertheless, Hubble had a showman’s sense of when to leave the stage.  Rather than stay around after his prime, he stepped down at the top of his game.  He did not get involved in the next Great Debate

over the steady-state vs. expanding universe.  He luxuriated in his celebrity status as the man who had expanded the universe from the Milky Way to a perhaps infinite number of galaxies, who had shown that all these galaxies are racing away from us and who, though he might not acknowledge it himself, had nurtured the seed of the notion that the universe began at a finite time in the past, thus giving some objective evidence that Genesis’ statement “let there be light” is more than just a poetic description.

The Doppler Effect

Everyone is familiar with the Doppler Effect; they just might not know the name.  We hear it every time we hear a police or fire truck siren.  You will note that the siren raises in pitch as the car is coming toward you and lowers as it travels away.  Sound waves are like light and water waves.  They have a wavelength, the distance from one crest to the next.  The closer the crests are to each other, or the shorter the wavelength, the higher the sound the wave makes.  Conversely, the longer the wavelength the lower the sound.

Doppler effect

Doppler effect (Photo credit: Wikipedia)

When the source of the sound is moving, such as when a siren is attached to a fire truck, as the truck comes toward us each wave that comes from the siren is slightly closer than the previous wave.  This has the effect of shortening the wavelength, raising the pitch of the siren.  Of course, the siren is emitting a steady pitch; we only perceive it to be higher or lower based on the movement of the fire truck relative to us.  As the truck moves away, each wave that is emitted is slightly farther away than the previous wave, so the wavelength is longer and the pitch drops.

The Doppler Effect is highly accurate and is the science behind radar guns.  A radar gun doesn’t actually emit radio waves (“radar” stands for RAdio Detection And Ranging) because the radio waves are too long to be reflected accurately by cars.  Radar guns actually use microwaves.  By measuring the change in frequency of the reflected microwave off a moving car, the gun calculates the speed of the car.

By the beginning of the 20th Century, the trifecta of spectroscopy, the Doppler Effect and more powerful telescopes allowed astronomers to make unparalleled strides in analyzing stars.  Their velocities could be measured accurately and by 1912 it was determined that  some stars were moving along at a few kilometers per second and some were zipping through the cosmos at over 50 km/sec.  To put this in perspective if a jet plane could travel 50 km/sec it would cross the Atlantic ocean in a couple of minutes.

In 1912 an amateur astronomer, Vesto Slipher, became the first person to measure the velocity of a nebula (recall that at this time the Great Debate over nebula vs. galaxy had not been resolved).  He discovered that the Andromeda Nebula was blue-shifted (meaning it is moving toward the Milky Way) to such an extent as to have a velocity of 300 km/sec.  Doubting his measurements he trained his telescope on the Sombrero Nebula (now galaxy) and discovered a red shift (meaning the Sombrero Galaxy is moving away from the Milky Way) that yielded a speed of 1,ooo km/sec., nearly 1% of the speed of light.  A plane traveling this fast would go from New York to London in about six seconds.

As more astronomers looked at the Doppler Effect on galaxies they discovered a very weird and unexpected result.  The vast majority of galaxies are moving away from the Milky Way.  Scientists expected some galaxies to be moving toward us while others moved away, but almost all were racing away as if the Milky Way had measles.

Various theories about why this is so were advanced but no consensus emerged.  Eventually Edwin Hubble, already famous for settling the Great Debate, would make another monumental discovery that would further support the Big Bang Theory.

Light: The DNA of the Universe

If you follow the various crime dramas on TV, you know that once the villain’s DNA is found the crime scene analysts can tell everything about him:  sex, age, height, weight, race, what he had for dinner last night and probably where he lives.  Whether that is real science or not, light tells just about everything there is to know about a star.

In 1842 French philosopher Auguste Comte tried to categorize certain things that would forever remain unknown.  Among those was “the chemical and mineralogical” makeup of stars.  He would be proven wrong within two years of his death.

Light is a form of energy.  Physicists think of light as being a wave, much like waves in water.  The wavelength of light is measured by the distance from the crest of one wave to the crest of the next.  The shorter the wavelength of light, the more energy it has and vice versa.  Humans tend to think of light only in terms of those wavelengths that the eye can detect, which range from the longest wavelengths of red to the shortest of violet.  Wavelengths longer than red are called infrared, while wavelengths shorter than violet are called ultraviolet.  Scientists, however, often lump all electromagnetic radiation under the heading of “light.”  Other forms of electromagnetic radiation are radio waves, which have wavelengths in the hundreds of meters (a meter is roughly a yard), to microwaves, exactly what are used in microwave ovens and are what the police really use in radar guns, and are still much longer than infrared light, to gamma and x-rays, which have very short wavelengths and thus high energy, which allows x-rays to penetrate solids.  The higher energy of the shorter wavelength light, such as x-rays and gamma rays, can cause damage to humans.   Gamma rays are one of the deadly emissions from a nuclear explosion.

Complete spectrum of electromagnetic radiation...

Complete spectrum of electromagnetic radiation with the visible portion highlighted (Photo credit: Wikipedia)

Since light is a form of energy scientists can use light to determine the temperature of a star.  An object heated to about 500 degrees Celsius (900 degrees Fahrenheit) begins to glow red, literally red-hot.  At 3,000 C (5,400 F), it begins to emit white light. So by analyzing the spectrum of light given off by a star, science can determine its temperature.

In 1752 Scottish physicist Thomas Melvill noticed that different substances emitted different colors when burned.  By carefully categorizing the colors emitted by the burning of various elements and comparing those to the light given off by a star the star’s composition can be deduced.  Melvill wasn’t expecting this nor was he looking for it.  His discovery illustrates the adage that most scientific discoveries are accompanied not by a cry of “Eureka!” but by a murmured “that’s funny.”

Each element has a distinctive color, which acts as its DNA, allowing it to be identified just by looking at it.  This combination of light, color and atoms is called spectroscopy.  The science of studying light emitted by objects is called spectroscopic emission.  The opposite phenomenon, absorption of certain light wavelengths by a substance, also exists and that is called spectroscopic absorption.  Spectroscopic absorption allowed scientists to determine the composition of the sun.  By noting which wavelengths were absorbed and therefore not visible in the light emitted from the sun, scientists could determine what elements were present in the sun that absorbs those wavelengths.

In addition to determining the composition and temperature of stars from starlight, the star’s velocity can also be found.  This stunning discovery was made by Thomas Huggins and his wife, Margaret, herself an accomplished astronomer and 24 years his junior.  When Thomas, at 84, was too feeble to clamber around a telescope, his young wife, only 60, was able to take over.

Science had long known that stars appear to change position in the sky relative to Earth and to other stars.  This movement across the sky is called proper motion.  However, proper motion is incremental and even with advanced technology is difficult to detect.  In addition, proper motion only tracks movement of a star laterally in the sky, as if all the stars were in the same plane.  Proper motion can tell nothing about the movement of a star either toward or away from the earth.

Mr. and Mrs. Huggins were able to combine spectroscopy with a piece of physics known as the Doppler Effect, after Christian Doppler, the Austrian physicist who discovered it, to determine the velocity of stars.  The Doppler Effect would become key in proving the Big Bang Theory.