In late 2026, it will become the first spacecraft to travel so far that a radio signal from Earth takes 24 hours, or one light day, to reach it.

According to Einstein, the speed of light is as fast as it's possible for anything to go. That may seem arbitrarily restrictive, but at 186,000 miles per second (299,388 km/s), that leaves a lot of leeway unless you're dealing with things at computer speeds where a delay can be aggravating.

Another thing that can be aggravating is that though light is fast, the universe is, as The Hitchhiker's Guide to the Galaxy says, really big. This means that if you have to cover a long enough distance, the speed of light starts to become noticeable in a way that we don't see on Earth.