So what is the site about?

Despite the title, this blog has nothing (or at least very little) to do with string theory, and you can put away your looms and knitting needles, too: the “yarns” on this site are of the storytelling variety. Cosmic Yarns is a blog about science fiction, and its author, Robert Scherrer, is an academic scientist who occasionally moonlights as a science-fiction writer. More specifically, in his “day job”, Scherrer is a cosmologist (and chair of the Department of Physics and Astronomy) at Vanderbilt University in the US, and he has published several stories in the magazine Analog Science Fiction and Fact.

Ooh, I like a good science-fiction story.

So do a lot of physicists – although, as Scherrer observed in a post back in April 2015, it’s hardly a universal obsession. In his experience, he writes, roughly a third of physicists and astronomers are “avid science-fiction fans”, a third have always been indifferent and the remaining third loved it when they were kids but lost interest as they grew older. (This last viewpoint, he notes, is also very common in the general population: there is a saying among aficionados that “the Golden Age of science fiction is 12”.) Scherrer’s blog is mostly aimed at people in the “avid fan” group. Many posts discuss specific stories, books or series written by particular authors, and you will probably enjoy it more if you are already familiar with the works in question (or, alternatively, if you are looking for recommendations to add to your reading list). Other entries, however, focus on plot devices that are common to many works of science fiction, and these posts may also interest physicists who lack Scherrer’s familiarity with the genre.

What sort of plot devices?

Oh, you know. Faster-than-light transport. Failed or misunderstood attempts to communicate with alien life forms. Time travel. Mass extinctions. The usual.

Right…can you be a bit more specific?

Sure. In a pair of posts from April and May 2015, Scherrer examines the science behind supersized and undersized creatures, such as the giant radioactive ants in the classic B-movie Them and the ant-sized human in the recent film Ant-Man. As he explains, neither of these extremes is entirely realistic from a physical or biological perspective. Unnaturally large animals fall foul of the “square-cube law”: as they get bigger, their weight and volume increase in proportion to the cube of their length, but their surface area (which affects their ability to respire, digest and shed heat) only goes up with the square of length. Super-sized ants would also struggle to support their huge weight on their spindly little legs. Microscopic humans are somewhat more plausible, but they would, Scherrer observes, find it hard to swim through water in the same way that we do because of their smaller Reynolds number (the ratio of an object’s inertial force to the viscous force it experiences as it moves through a liquid).

Can you give me a sample quote?

From the last in a series of posts about time travel: “[E]ven if time travel were possible, scientists think that the past could not be changed, since physics would make no sense if we allowed things like the grandfather paradox. This is encoded in Igor Novikov’s ‘self-consistency conjecture’, which simply states what I’ve just said: maybe you can go back in time, but you can’t stop the Kennedy assassination or make the Cubs win the 1945 World Series. Even with this assumption, you still run into the possibility of creating something from nothing. Suppose my future self built a time machine and e-mailed this post back in time for me to put on my blog. Then in the future, I’ll just read it, copy it and e-mail it back in time to my past self. So who wrote it?”

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