All right – what if you had a space-car that could go at the speed of light?
Now we’re talking. The speed of light is about 670 million mph, so a car that fast could do about 6 thousand billion miles (or 6 trillion miles) if it kept driving, non-stop, for a whole year. We call this distance a light year, and it’s much more useful for measuring the huge distances – between stars and across galaxies – that we’ve been talking about.
For example, the Milky Way is about 100,000 light years across, so it’d take 100,000 years for our souped-up, superfast, light-speed car to cross it. Still way too long to manage, but easier to imagine, maybe.
Go on, then – how long to get across the whole universe?
Well, we can only measure the universe as far as we can see it. With the best telescopes we have, that’s about 15 billion light years (or 90 billion trillion miles – I won’t even bother trying to write that out with zeros) in every direction. So at the speed of light, it’d take at least 30 billion years to cross it. That’s about 2 billion years longer than the age of the universe itself.