Most of us normal, rational people only use one space after a period while typing. But there are still some people out there who think using two periods is better. While we all know that's ridiculous, some scientists are trying to prove they're right.
Psychologists at Skidmore College attempted a study to prove that using two spaces after a period was better than one. First, they had 60 students type out a paragraph using their preferred spacing. Then they asked the students to read a sample text, one with one space after the period and one with two spaces, using eye-trackers.
The researchers found that the students spent less time looking at the punctuation while reading in the sample text with two spaces after the period, presumably because it was more clear that the sentence was finished. They also found that the students who typed using two spaces also read faster when given the two-space sample text.
However, the researchers also admitted that there wasn't really any benefit to using two spaces or one. The students who typed using one space read both sample texts at the same speed, even if they focused more on the punctuation in the one-space text. And there was no difference in comprehension in the two sample texts, so the spacing didn't affect how well a person absorbed what they read.
So in short, adding two spaces after a period made no difference, and therefore that practice should probably be banned.
Unless you're writing a minimum eight-page paper in college. Then using two spaces after a sentence is not only allowed, but encouraged.
(h/t Mental Floss)