It's one of the coolest moments in the trailer for Justice League, and a scene that journalists from all over were raving about after their set visit last month: The Flash, Barry Allen, meets Bruce Wayne, Batman. With some great banter both before and after the action, Bruce makes his intentions clear: he needs other superheroes. But when Barry protests, Bruce does the Batman thing, and throws a sharpened Batarang right at Barry's head.
Luckily, he was right about Mr. Allen, and he was in fact the speedster called The Flash. After Barry effortlessly dodges and catches the flying Batarang, Bruce says, "So you're fast." But how fast is he (no, this isn't the setup to a terrible joke, promise)? Well, TheScienceOf.org wanted to know, too - so they figured it out, using things like "tested science" and "math" that we were told wouldn't be on the test.
Using peak human throwing speed and knife rotation to figure out distance (about 15 feet), and speed (about 44 feet/second), they figured out that the time it took the batarang to go from Bruce's hand to be in Barry's was just about .34 second - 340 milliseconds. As they wrote, "an average human eye blink lasts 300-400 milliseconds," so in Bruce's perspective it was a literal and time-perfect "blink of an eye."
For The Flash, however, he moved into "at speed" mode - something established since Barry Allen's first DC Comics appearance in 1956. According to the way the trailer was presented, the batarang's travel from hand to hand took about 21 seconds from Barry's perspective. That means that The Flash is moving and processing information at a factor of about 62; "1 second in our world equals roughly 62 in his. One minute for us, a shade over an hour for him, if he's 'at speed' the whole time."
The Science Of also noted that this isn't necessarily a speed limit for The Flash, but rather how he moved in this moment. Seeing as it was a fairly instinctual moment, this is almost a measurement merely of reflexive speed than of how hard he can actually push himself. Read more at the link above to see how his speed would work for everyday tasks.