There are many extremes on Earth. From the coldest place to the highest place and beyond, as humans, we are always curious about such extremes.
Recently a new extreme was confirmed by scientists, the longest straight line path you can take across the ocean. In the true spirit of citizen scientists, this path was first discovered by a Reddit user 5 years ago and was just recently confirmed by computational models.
You might think that it shouldn't take too long for a computer to find such a route, and in fact, once the programming was done it took the computer about 10 minutes to find the solution -it took much longer, however, to find a way to write the program.
Straight line journeys on our Earth are actually not straight lines, but great circles. These great circles have to go along the larges circle possible, always cutting Earth in half. With the current geographic resolution of Earth (about 1.8 square kilometers), there are more than 230 million possible great circles to take a look at.
Not only do you have to look at the great circle but you would then need to find all sea level, water bound paths along that circle, then find the longest one on that great circle, and then compare it to the other 230 million plus paths from each other circle.
It was more than 5 trillion points to look at.
While the Reddit user used a globe and string to find the longest ocean path on Earth, scientists had to go back to the drawing board to write a program to verify that result. 5 trillion points are just too much for our computers to handle. Instead, scientists turned to another type of programming called branch and bound. In this technique, you are looking for the largest number (or solution) possible.
All of these options can be thought of as a tree with a root system, where large branches of the tree are estimations or bounds on all of the smaller twigs. If a branch as a whole is tested and seen to be less than another solution already in hand you can throw out the entire branch. Instead of checking each and every single twig on the tree you end up cutting branches off until you find the one optimal solution.
By using this method scientists were able to get the solution in just 10 minutes of computational time and were able to verify the path found.
The longest oceanic voyage comes in at nearly 20,000 miles - for reference, Earth's circumference is just over 24,000 miles.
Why does it look like a curved line on a flat map? Because Earth isn't flat. A straight line on a curved surface will look curved when projected onto a flat surface! Don't believe us, check out the video below.
Try it yourself. Using string, a ruler, and a globe can you find the longest oceanic voyage on Earth? What about the longest drive over land with no major lakes? You can check your answers here!