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Watch an Early Silent Film About Relativity

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Albert Einstein first published his theory of special relativity in 1905; his work on general relativity followed in 1915. By 1923, Premier Productions made this silent film to explain the most salient bits. Although it's entirely silent (and of course quite dated), it's a thoroughly lucid way to understand Einstein's most important work.

My favorite stunt is around 1:45 when the filmmakers strap two pistols to a wheel, set it spinning madly, then fire the pistols simultaneously. What could possibly go wrong? Incidentally, the filmmakers used animation rather than real slow-motion photography to show the relative speeds of light and bullets in this bit. Again, 1923. The other excellent part concerns the relativity test conducted during the eclipse of 1919. Enjoy!

Note: you can download this film from the Internet Archive (part of the Prelinger Archives).

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Big Questions
How Many Dimensions Are There?
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Ask someone to name every dimension they know of and they'll likely list the following: length, width, and depth. They might also add time if they’re thinking outside the three-dimensional box. But asking a string theorist, “How many dimensions are there?” would elicit a very different response. According to this branch of theoretical physics, there are at least 10 dimensions of space, most of which are impossible for humans to perceive.

Dimensions are the metrics that physicists use to describe reality. Sounds broad, right? Let's start with the three dimensions most people learn in grade school. The spatial dimensions—width, height, and depth—are the easiest to visualize. A horizontal line exists in one dimension because it only has length; a square is two-dimensional because it has length and width. Add depth and we get a cube, or a three-dimensional shape.

These three coordinates are used to pinpoint an object's location in space. But space isn’t the only plane we exist on; we also exist in time, which is where the fourth dimension comes in. Once we know a dot's altitude, longitude, latitude, and position in time, we have the tools needed to plot its existence in the universe as we know it.

But some physicists who subscribe to string theory argue there’s more to reality than the observable universe. String theory, also known as "superstring theory," aims to unify two main theories describing how the universe works: general relativity (which applies to very large objects) and quantum mechanics (which applies to very small ones). In a four-dimensional universe, this theory wouldn’t be possible, but once scientists tweaked the math to include 10 dimensions—11 including time—their equations worked.

After coming up with a theory that hinges on the existence of 10 space dimensions, string theorists then had the job of explaining where those new dimensions were hiding. Their answer: They are just as real as the "big" dimensions we can see, but the extra dimensions are curled up so tightly that they're too small for us to notice directly.

Our basic understanding of physics makes this hard to process, but string theorist Brian Greene does a great job of framing the concept in terms most people can understand. In his 2005 TED Talk, Greene compares these invisible dimensions to the cables connected to telephone poles: From a window, a wire looks like a one-dimensional line. But if we were to study it up close we'd see that the cord is actually round, making it three-dimensional. No analogy comparing unobservable dimensions to objects in the observable world can ever be perfect, but this illustrates how something so fundamental to reality could be hiding in plain sight.

String theory states there must be at least 10 dimensions of space plus one dimension for time, but there are physicists who argue that there are more. Some posit a universe composed of 11 space dimensions. But to really blow someone's mind when they ask how many dimensions there are, say 26: That's the magic number according to Bosonic string theory, and it's as high as mainstream physicists are willing to go for the time being.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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science
Is Teleportation Actually Possible?
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The idea of teleportation—typically depicted in movies, books, and TV shows as vanishing in one place only to reappear fully formed in another—is a science fiction staple. Humans likely won’t be able to beam across space and time anytime soon, but experts say that the futuristic concept is actually rooted in real-life quantum physics.

In the TED-Ed video below, Sajan Saini, the education director at MIT's AIM Photonics Academy, explains the science of teleportation and addresses the question of whether we’ll ever be able to harness it to transmit objects across the universe.

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