Adapted from “What If? 2: Additional Serious Scientific Answers to Absurd Hypothetical Questions,” published by Riverhead Books, a member of Penguin Random House LLC.
See you in a quadrillion years or so.
“The edge of the observable universe is about 270,000,000,000,000,000,000,000 miles away.
If you drive at a steady 65 miles per hour, it will take you 480,000,000,000,000,000 — that’s 4.8 × 10¹⁷ — years to get there, or 35 million times the current age of the universe.
This will be a dangerous road trip. I don’t mean because of space stuff — we’re not worrying about all that — but because driving itself is pretty dangerous. In the United States, the average middle-aged driver suffers about one fatal crash per 100 million miles driven. If someone built a highway out of the solar system, most drivers wouldn’t make it past the asteroid belt. Truck drivers, who are used to driving long distances on highways, have a lower per-mile crash rate than other drivers, but they would still be unlikely to reach Jupiter.
Based on national crash rates, the odds of a driver traveling 46 billion light-years without a crash would be about 1 in 10¹⁰^¹⁵. That’s roughly the same as the probability of a monkey with a typewriter typing out the entire Library of Congress, with no typos, 50 times in a row. You’ll want a self-driving car, or at least one with one of those alarms that warns you if you drift out of your lane.
The trip would take a lot of fuel. At 33 miles per gallon, it would take a moon-size sphere of gasoline to reach the edge of the universe. (As of 2021, NASA’s New Horizons spacecraft has traveled about five billion miles on a budget of about $850 million, which works out to 17 cents per mile — pretty similar to the cost of gas and snacks on a road trip.) You’d run through about 30 quintillion oil changes, requiring a container of engine oil the volume of the Arctic Ocean. (An old piece of advice says that you need to change your oil every 3,000 miles, but most car experts agree that’s a myth — modern gasoline engines can comfortably go two or three times that distance between changes.)
It’s going to be a very long drive, and the scenery won’t change much at all. Most of the visible stars will burn out before you even exit the Milky Way galaxy. If you want to try touching a room-temperature star, I suggest planning a route that takes you past Kepler-1606. It’s 2,800 light-years away, so when you drive past it after 30 billion years, it will have cooled to a comfortable room temperature. It currently has a planet, although that will probably have been devoured by the time you get there.
Once the stars have burned out, you’ll have to find a new source of entertainment. Even if you bring every audiobook ever recorded and every episode of every podcast, that won’t even last you to the edge of the solar system.
The British anthropologist Robin Dunbar famously suggested that the average human maintains about 150 social relationships. The total number of humans who have ever lived is somewhere north of 100 billion. A 10¹⁷-year road trip would be long enough to replay the lives of every one of those people in real time — in a sort of unedited documentary — and then rewatch every one of those documentaries 150 times, each time with a different commentary track by the 150 people who knew the subject best.
By the time you had finished watching this complete documentary of human perspective, you’d still be less than 1 percent of the way to the edge of the universe, so you’d have plenty of time to rewatch the whole project — each human life with all 150 commentary tracks — 100 times before you finally arrived.
Once you reached the edge of the observable universe, you could spend another 4.8 × 10¹⁷ years driving back home, but since there won’t be any Earth to return to — only black holes and the frozen husks of stars will remain — you might as well keep going.
As far as we know, the edge of the observable universe isn’t the edge of the actual universe. It’s just the farthest that we’re able to see, because there hasn’t been time for light to reach us from any farther parts of space. There’s no reason to think that space itself ends at that particular point, but we don’t know how much farther it goes. It might just continue forever. The edge of the observable universe isn’t the edge of space, just the edge of the map. There’s no way to be sure what you’ll find when you cross it.
Be sure to pack extra snacks.