This xkcd Comic Hit Home With Me: "Teaching Physics"

xkcd is a comic that tends to be a bit on the academic side but I think their warning disclaimer tells you better what this comic series about than I can:

"Warning: this comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors)."

Of course, this warning is tongue-in-cheek but it does give you a flavor of what the comic series contains.

My husband forwarded this comic from this a few days ago called "Teaching Physics" (click on it to see the full size image on xkcd.com):

Now, I have talked at length on this blog about doing education outreach at LIGO.  In that process, I interact with many students, teachers and people from the public and I use the 'rubber sheet' analogy often when describing that gravity it really an effect of the curvature of space-time.  However, this only works if one thinks about a real rubber sheet that they could interact with on Earth, i.e. there is still gravity around to pull masses down on the sheet.  Most people have no problem overlooking the fact that we are using gravity to describe the curvature of space-time but there are the few who bring up the paradox to me.

This is where I disagree with how the instructor in this comic handled the situation.  To me, the correct response is not to sigh and dismiss this useful (if imperfect) analogy.  Instead, I recognize that the observation is a valid one and compliment the person on being insightful (usually including that most people don't see the problem).  I then ask them to take the gravity around them for granted and just use the rubber sheet as a visualization tool.  After all, there are many analogies in physics but if you think about any of them for too long you start finding imperfections in them.  (Like using water waves to describe properties of light [electromagnetic] waves - a few problems with this include that water waves need a medium [water] to propagate and water waves are easily damped when light isn't.)

I'm not criticizing the author of this comic!  After all, I don't think this instructor is doing "outreach" as much as teaching in a formal education setting.  I've had a lot of experience there too and, depending on the student (like are they the kind that try to be difficult at every turn or are they truly being insightful), I very well may have had the same reaction.  And I just love that there is a comic out there that makes me jump up and say, "That's happened to me!"