(Part one in a series on Light)
Richard Feynman once claimed that "understanding light is a prerequisite to understanding the universe."
I'd say that's pretty fair. Light is the only signal we have from the space beyond our solar system-- the one clue we can trace. Everything else is inferred...from light.
Light one of the only "givens". If there is matter and if there is gravity, then there is energy, and if there is energy, there is light.
How could there not have been light at the beginning of everything as we know it, if indeed there was a beginning at all? Every narrative we have which claims there was a definitive origin of the universe features light coming forth from a dark void-- "Let there be light," spoken by a Voice moving over the water, or an eruption of everything in one monumental "big bang". Even our "quaint" little earth was born in a protoplasmic pool of lava, heat, and energy, and came forth dripping in light.
Light, this ancient and omnipresent force, the ultimate "blinding speed," is crashing noiselessly all about us, all the time.
Yet for all it does, light rarely calls attention to itself. So let's shed some, and see what we can see. :)
By far, the oldest thing we'll ever be able to see is the light from distant galaxies. Not the galaxies themselves-- just the light. The farther the galaxy, the older the light, but younger the image we see. Old light essentially allows us to look back in time and see things as they were, not as they are. We can really only make educated guesses about what distant objects look like now (and what is time, anyway, since Einstein discovered relativity?)
The "present moment" on earth isn't so hard to understand, because light travels almost instantaneously from point to point, even across continents and via satellites. Because we have successfully learned how to harness light, we can find out about events happening halfway across the world minutes after they occur. Time and light make sense on earth-- they're constant.
In comparison, the light from the moon takes about a second to reach earth's surface-- not a big deal. A stone's throw for light, one huge step (and several rocket launchers) for mankind.
Light from the sun takes ~8 minutes to reach earth-- a mere 93 million miles (it would take 177 years to get to the sun driving in a car at 60 mph without stopping).
Then everything starts getting trippy... like road trippy.
Proxima Centauri, our closest neighbor star system, is 4.3 light-years away from us. If your aunt somehow lived in Proxima Centauri and you sent her a text message, there is no possible way she could get it sooner than 4.3 years from now. Just think about that. [And if you want to understand the how relativity could theoretically affect the relationships you have with the people you love, go see Interstellar:)].
As if four years of traveling at 186,282 miles per second through empty space to get to our next closest neighbor wasn't enough to blow your mind, consider that it takes millions and billions of years for light to reach us from most of the other stars and galaxies in our universe.
13 billion light-years. That's about how far away the oldest objects in our galaxy are, (give or take a few million years). We don't yet have a definitive winner for "most distant." It's kind of hard for scientists to pinpoint it, since the contestants are basically no bigger than pinpoints themselves. In images of deep space, they appear as little red smudges, barely visible. Still, that dot was created by a piece of light that traveled over 13 billion years to reach us. 13 BILLION YEARS at nearly 200,000 miles per SECOND, you guys.
13. Billion. Years.