Rachel Keranen - The Big Bang Theory and Light Spectra

Supernovas emit different types of light, including visible light, X-rays, and gamma rays.

Introduction: A Vast Expansion of Time and Space

The evolution of the world can be compared to a display of fireworks that has just ended: some few red wisps, ashes, and smoke. Standing on a cooled cinder, we see the slow fading of the suns, and we try to recall the vanished brilliance of the origin of the worlds.
Georges Lematre

I t is human nature to wonder where we come from and how the universe came to be. In the scientific world, that question has fallen largely to the physicists, astrophysicists, and astronomers who use the properties of light and spacetime to study the universe in its earliest days.

The oldest stories of the universe, however, are mythologies based in superstition and supernatural events. Many of these myths describe gods as creative powers who shaped Earth and the universe. Over time this form of creation narrative began to change.

Ancient Greek scientists began to create more scientific theories in which they tried to describe the motion and elemental composition of the celestial bodies. The models were beautiful, but ultimately they did not match actual observation.

More than a millennium later, Nicolaus Copernicus began a scientific revolution with his assertion that Earth revolved around the sun. Over the next few hundred years, a new focus on observation-based hypotheses and advancements in optics and telescopes propelled the scientific world through discovery after discovery. It became possible to study not just the movement of the stars through the sky, but also the movement of stars and galaxies toward or away from Earth by studying their absorption of light. Our knowledge of light itself expanded as scientists discovered portions of the electromagnetic spectrum invisible to the naked eye, including longer wavelength infrared radiation and shorter wavelength ultraviolet light.

Still, many scientists, including the great physicist Albert Einstein, believed that the universe was infinite in size and time, with no beginning to speak of. For some scientists, to talk of a beginning suggested a return to the nonscientific creation mythologies.

Others worked through the equations in Einsteins general theory of relativity and said that the universe must be either contracting or expanding. Two such scientists, Alexander Friedmann and Georges Lematre, both argued that the universe was expanding and in the past had likely been compressed in one very small, very dense region. Lematre suggested that the small, dense region was a primeval atom that decayed into the matter that composes the universe. Einstein dismissed both Friedmann and Lematre as scientists with accurate mathematics but terrible physics.

In 1929, American astronomer Edwin Hubble forever changed the conversation with his discovery that the galaxies in our universe are moving away from us at rate that corresponds directly to their distance from us. The universe is expanding, his observations showed, directly contradicting the beliefs of Einstein and other physicists who preferred a static model of the universe over time and space.

Friedmann had been largely ignored when he published his data, and he died young, but Lematres theories got a fresh breath of air after Hubbles analysis was published. Einstein admitted his mistake and praised Lematres work, and a new era of cosmology was born.

Physicist George Gamow, one of the only nuclear physicists in America not pulled into the Manhattan Project due to his Soviet roots, picked up the mantle and developed what would become known as the big bang theory. Gamow and his graduate student Ralph Alpher proposed a model in which the early universe consisted of highly compressed gas that expanded rapidly and gave birth to hydrogen and helium, which fused into heavier elements and produced the universe we know today.