Cosmic Origins: a Story Written in Light

Fedor here, production assistant and researcher at MOBProd. I have always been obsessed with science ever since I was a little kid, running around Caltech campus where my dad was a grad student. I wanted to be a scientist, but realized in college that I am better at talking about the science than doing it. I love telling human stories through a scientific lens, and vice versa, as well as trying to wrap my head around tough-to-understand science concepts. In my blog posts, I will mostly focus on science history and the surprising connections between science and culture. This first one, an intro to an upcoming MOBProd web video series, is about the fascinating subject of light. Hope you enjoy!

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Light is an amazing thing: it has no mass yet it comes in discrete packets. These packets, called photons, behave like waves and like particles. Perhaps it is this paradoxical nature of light that makes it such a rich source of study for scientists--much of what we know about the universe is because of the wealth of information that light can carry.

Hot things, like a glowing fire poker or the Sun, emit energy in the form of light. This light carries fingerprints of the atoms that emitted it, which is how we know what stars and other celestial shiners are made of.

Light from two exploding stars, Eta Car A and B, showing telltale patterns of helium, argon, iron, and nickel. Credit: NASA, ESA, and the Hubble SM4 ERO Team

Light from two exploding stars, Eta Car A and B, showing telltale patterns of helium, argon, iron, and nickel. Credit: NASA, ESA, and the Hubble SM4 ERO Team

Light can even pick up the signatures of atoms and molecules it encounters. In fact, that's why we see leaves as green, because a molecule in the leaves called chlorophyll absorbs certain wavelengths of light (primarily red and blue) and reflects others (primarily green). So even with your eyes you can make an educated guess as to the composition of a substance by the light it emits or reflects.

Of course, astrophysicists don't just eyeball it, they have very specific tools and databases that can classify the light they see coming from outer space. Light is effectively the only thing that astrophysicists, cosmologists, and anyone else studying the universe at large can rely on--it's a little difficult to retrieve a sample of stellar material... But, as we are starting to see, we can learn so many things from light. Let's keep going.

Light sets the ground rules for much of physics. The speed of light is 3.0x10^8 m/s... otherwise known as Very Fast. It's the fastest thing we know of--it imparts a "cosmic speed limit", as astrophysicists and high school science classroom posters love to joke.

Light from this screen only takes about a nanosecond to get to your eyes--much too fast for you to notice anything bizarre going on. If you turn off your screen (though why would you!), you would perceive the screen turning off instantaneously.

But light from the Sun takes about 8 minutes to get to us. If that light missed the Earth and kept going, it would take more than 5 hours to get to Pluto. So, if suddenly the Sun went dark, Earthlings would know only after 8 minutes. Our Plutonian friends would get the news only after another 5 hours.

Although we do not experience this light/time/space relationship on a daily basis, astronomers are all too familiar with this phenomenon. Since space is Very Big, the light we get from those faraway stars at night is Very Old. We're looking back into time when we stare into the stars--some of them may have exploded but we won't see the flash for years to come.

Light has also become a yardstick for astronomers--that's why they measure distances in lightyears, the distance light traverses in a year. If you were wondering, one light year is about 5.8 trillion miles aka Very Far. To put our past discussions into this parlance, we are 8 light minutes away from the Sun, while Pluto's orbit is about 5.5 light hours away.

To help picture this mind-boggling concept and the vastness of space, people sometimes use the example of how far our first radio broadcasts have traveled through the Milky Way (spoiler: it's not that far). But I would like to propose a different, perhaps more visual analogy.

This is the galaxy NGC 4639, photographed by the Hubble Space Telescope in 2015:

Hubble photos never cease to amaze. Credit: ESA/Hubble & NASA

Hubble photos never cease to amaze. Credit: ESA/Hubble & NASA

NGC 4639 is a galaxy roughly 70 million light years away yet, from the looks of it, it is similar to our own--milky, spirally, with something of a bar through the middle. Perhaps that will make it easier to postulate that aliens live there, which is what I am going to ask you to do.

Now imagine that these aliens have a huge telescope with fantastical zooming abilities, pointed in our direction. What do they see? Well, since they are 70 million light years away, they see Earth as it was 70 million years ago. If they look closely, the aliens could even see a T. rex chomping away at some unfortunate prey.

If you happened to be 70 million light years away from Earth and looked back, you would see more than just the bones of this T. rex... Credit: ScottRobertAnselmo

If you happened to be 70 million light years away from Earth and looked back, you would see more than just the bones of this T. rex... Credit: ScottRobertAnselmo

Pretty cool, huh? So, not only can light carry information about the materials it interacts with, it can also serve as a recording device. And as scientists have managed to gaze deeper into space, they have seen the past unspooling before them.

With this knowledge of how light works, questions inevitably follow. Big questions, such as: how far back can we see? What does that earliest light tell us about the infant universe? What can it tell us about the Big Bang? Why is our universe the way it is?

I find these questions fascinating, but it's hard to find good answers to them. That's why I enlisted the help of Dr. Adrienne L. Erickcek, a theoretical cosmologist and Assistant Professor at the University of North Carolina at Chapel Hill. She looks at the oldest light from the depths of the universe in the hopes of answering these questions. She will be our expert guide in this journey.

Next up for Cosmic Origins: the Big Bang. Seems a good a place to start as any.