The Speed of Light Is SO Slow

We often marvel at how light travels at (3 \times 10^8) meters per second, zipping around Earth seven times in a single heartbeat. It only takes about two seconds to reach the Moon, eight and a half minutes to get from the Sun to us, and a few hours to touch Neptune. But zoom out to interstellar or intergalactic scales, and suddenly, that lightning-fast speed starts to feel painfully slow.

Interstellar Delays

Our nearest star (beyond the Sun) is around four to five light years away. That means even the simplest “hello—how are you?” radio message would take about five years to get there and another five to get a response—ten years total. And you wouldn’t even know if they received the initial message until you got that reply (assuming they reply at all).

The Milky Way Gap

Now consider the other side of our own galaxy: distances can span 100,000 light years. The signals we send could take 100 millennia to arrive—and another 100 millennia for a response. Whatever conversation we’re trying to have would be out of date by about 200,000 years by the time we got a “Fine, thanks, and you?”

Galaxy to Galaxy

And that’s just our galaxy. Across intergalactic space, we measure distances in millions or even billions of light years. Any back-and-forth communication at these scales becomes effectively impossible—a cosmic snail mail so slow that entire civilizations might rise and fall before a single message completes its round trip.

Universe in Time, Not Miles

Because of these vast distances, astronomers often talk about the universe in terms of time rather than raw miles. When we see light from a galaxy two billion light years away, we’re looking two billion years into the past. Meanwhile, the universe keeps expanding, making the gaps even larger.

If the speed of the universe—a better name for the “speed of light”—were somehow faster, our universe would seem “smaller.” More of it would be accessible to us within a human lifespan. But in our reality, the speed limit is set, and it shapes what (and who) we can reach. It’s a sobering reminder that, on a cosmic scale, even the fastest thing we know can feel frustratingly slow.