From light to light

I am always thinking about something. I have this constant sense of urgency that keeps telling me that every moment that I am not thinking, I am wasting time. That’s just who I am.

The other day I was driving to the supermarket. As I turned on the signal light at a corner, I thought about how the light in the car’s dashboard got there. That blinking light got me into thinking about the story of that small amount of energy, in the form of a few photons, that were detected by my retina, processed in my brain’s visual cortex and perceived as light by my consciousness (What is consciousness anyway?).

The beginning of the story of this tiny amount of light could go all the way to the Big Bang itself, simply because the story of our Universe started right there. Before the Big Bang, we have very little idea of what was going on. In fact, there are many good reasons to think that it makes no sense to talk about a time “before” the Big Bang, since time itself seems to have been created at the very same moment when our universe was born, 14 billion years ago, give or take a couple of million years.

Anyway, to speed things up I will start this story with two hydrogen atoms within our sun, say, about 300-400 millions of years ago.

Stars generate their energy through a process called nuclear fusion. In younger stars, the main players are hydrogen atoms, which are the most abundant type of atoms in our universe. The physical environment at the center of stars is brutal to say the least. The temperatures and pressures there provide the conditions that make atoms collide with each other with a lot of energy, oftentimes with such force that it allows them to overcome the natural repulsive forces that keep them separate.

When this happens between two hydrogen atoms, they fuse with each other, initiating a series of events that end up forming a different kind of atom, helium. This is when things start to get interesting. In these series of steps initiated by fusing two hydrogens (through something called quantum tunneling, never mind what that is…), the intermediate physical entities leading to the final product, helium, possess slightly less mass than the sum of the masses of their precursors. In other words, there is some mass missing; where does it go? It is converted to energy. Here’s why.

The main reason why is this small amount of remaining mass is so important is because in our physical universe, matter is a form of energy; you may have heard this stated in another way, E=mc2. This fact was firstly realized and formulated by no other than arguably the best-known scientist ever, Albert Einstein. Based on this relationship, even a small amount of mass (m), when multiplied by the (squared) speed of light in a vacuum (c) which is 300,000 km/second, results in a big amount of energy (E). So you see, even such a small amount of missing mass equals to A LOT of energy, and this happens gazillions of times in all the stars in our universe. This is essentially why stars shine. And this process does not stop with helium. All the heavier atoms found in nature are also formed in a similar way, yes even carbon, the element of life itself.

Quite literally, we are stardust.


There is order in this universe of ours, as we can describe it with generalizations (we call them laws) that explain its fundamental properties. The first of these laws states that energy cannot be created nor destroyed. This is the so-called First Law of Thermodynamics. By the way, the Second Law of Thermodynamics basically states that it is way more difficult to build something up than to destroy it (in my mind, this law applies to everything, from molecule formation to personal relationships, but I digress…).

Let’s follow that energy that is released in our original example from a long time ago, with that little remaining mass left from hydrogen fusion.

After about 100 to 200 thousand years after this fusion event (yes, that long; look it up, it is a fascinating story in its own right) that energy, which originated near the center of the sun, reached the surface and was emitted as radiant energy (light). After about 8 minutes after being emitted, the light that happened to travel in the direction of the earth, arrived here. At that time, life had already invented the process of photosynthesis. Some of that energy was captured by specialized structures within plant cells, these structures are called chloroplasts, which in turn contain molecules capable of capturing light and convert it into chemical energy, ready to be used by life in various ways, including the synthesis of macromolecules such as proteins, nucleic acids, etc.

Did you happen to notice that we started with matter, which was converted to energy and now that energy was converted to matter again?


Over time, the plant that captured the energy and used it to generate nourishing chemicals was eaten by an animal that, upon dying, went through the process which forms what we call today “fossil fuels”, the main source of energy that we use in our society. Some of that fossil fuel was used to make gasoline, which I put in my car. When I drive the car, a part of that gas burns in a controlled way; a very small part of that matter is converted to kinetic energy (movement), and yet a smaller part of that kinetic energy is used to partially charge the car’s battery, which in turn feeds the electrical system of the car. So, when I turned the signal light on, some of the photons that left the sun all those millions of years ago, were converted into photons again, which I perceived as the blinking light in my dashboard, going full circle.

So, you see, I am always thinking about something; it is fascinating how a simple observation can initiate a train of though that can lead to so many interesting concepts! It works for me; it may work for you too. You will never know where you may end. Read, think and be merry!

Credit: NASA

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