If you dig a tunnel straight through the center of the Earth - how long would it take you to reach the other side?
For decades the answer to that was about 42 minutes. But Alexander Klotz, a graduate student at McGill University in Canada, came up with new calculations that estimate it would actually take around 38 minutes. The 240 second difference is credited to density.
The original calculations assumed that the Earth has the same density throughout - and the gravitational force changes as you approach the center, much like the weight of a spring that bounces up and down.
But in reality, the planet's layers become more dense as you travel from the crust to the core.
As the density increases, the gravitational force increases meaning you'll fly through the tunnel even faster. At least until you pass through the center.
We can imagine what it's like to fall through the Earth, but you still don't want to fall into a black hole. The good news? They're pretty to look at.
Check out some supermassive black holes in the gallery below:
Supermassive Black Hole Finder
How long it really takes to fall through the Earth
SPACE - UNDATED: A Computer Simulated Image released by the NASA shows the gas from a star that is ripped apart by tidal forces as it falls into a black hole in Space. Some of the gas also is being ejected at high speeds into space. Using observations from telescopes in space and on the ground, astronomers gathered the most direct evidence yet for this violent process: a supermassive black hole shredding a star that wandered too close. NASA's orbiting Galaxy Evolution Explorer (GALEX) and the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii were used to help to identify the stellar remains. A flare in ultraviolet and optical light revealed gas falling into the black hole as well as helium-rich gas that was expelled from the system. When the star is torn apart, some of the material falls into the black hole, while the rest is ejected at high speeds. The flare and its properties provide a signature of this scenario and give unprecedented details about the stellar victim. To completely rule out the possibility of an active nucleus flaring up in the galaxy instead of a star being torn apart, the team used NASA's Chandra X-ray Observatory to study the hot gas. Chandra showed that the characteristics of the gas didn't match those from an active galactic nucleus. The galaxy where the supermassive black hole ripped apart the passing star in known as PS1-10jh and is located about 2.7 billion light years from Earth. Astronomers estimate the black hole in PS1-10jh has a mass of several million suns, which is comparable to the supermassive black hole in our own Milky Way galaxy. PHOTOGRAPH BY NASA / Barcroft Media /Barcoft Media via Getty Images
This artist's conception illustrates one of the most primitive supermassive black holes known (central black dot) at the core of a young, star-rich galaxy. (Photo by: Universal History Archive/UIG via Getty Images)
The Herschel Space Observatory has shown that galaxies with the most powerful, active, supermassive black holes at their cores produce fewer stars than galaxies with less active black holes. (Photo by: Universal History Archive/UIG via Getty Images)