Light years away.

... in the spirit of rambling.

The first time I really paid any attention to what a light-year was was while reading Project Hail Mary. I even made a couple of notes about it in my notes app.

I love books like that. Books that make you pause mid-sentence to check the meaning of a word, google a term you would have otherwise overlooked, or stop everything just to text a friend, "You really should read this one."

I had always thought a light-year was a measure of time. Turns out it is a measure of distance — the distance that light travels in one year.

Light travels at a speed of roughly 300,000 kilometers per second, making a light-year approximately 9.46 trillion kilometers. (Inserts cricket sounds.)

The closest neighboring star to Earth, Proxima Centauri, is about 39.9 trillion kilometers away (4.2 light-years).

Now, let's do a little maths.

At roughly the top speed achieved by the Apollo missions (39,400 km/h), it would still take around 27,000 years to travel a single light-year.

So it would take about 108,000 earth years to get to Proxima Centauri.

(More cricket sounds.)

Naturally, my next question was: would we ever be able to travel at the speed of light?

Unfortunately, no.

Why?

Mass.

According to our current understanding of physics, anything with mass would require more and more energy as it accelerates closer to the speed of light. To actually reach the speed of light would require an infinite amount of energy, which is the universe's way of saying, "Absolutely not."

This brought me to another concept: time delay.

At its core, the idea is pretty simple. Light travels at a finite speed, which means information cannot reach us instantaneously. It takes a measurable amount of time for light to travel from an object to our eyes, cameras, or telescopes.

Because nothing travels faster than light, distance is directly tied to time.

So when astronomers observe a star that is 10 light-years away, they see the star exactly as it was ten years ago.

In essence, looking into deep space is like looking backwards in time.

When we look at the Sun, we see it as it was eight minutes ago. If the Sun were to suddenly vanish (don't panic, it won't), we wouldn't know for another eight minutes.

Proxima Centauri appears to us as it was over four years ago.

The Andromeda Galaxy appears as it was 2.5 million years ago. The light reaching our eyes tonight left Andromeda before humans had developed written language.

Which is absolutely ridiculous when you stop and think about it.

Every star in the night sky is an old photograph.

Every telescope is a time machine.

And because of this time delay, we never actually see the universe as it is. We only ever see it as it was.

The night sky isn't a snapshot of the present.

It's a museum of the past.

Today's rambling was in response to Salvin Sawyerr's comment that I ramble about “science stuff.” I am no science nerd but I did try my best. To read more science related stuff, check out his newsletter.

P.S.: if there's any topic you'd love to read me ramble on about, let me know in the comments.