I've been wondering why there is so little activity on physics stack exchange compared with math stack exchange. It occurred to me that a contribution to the difference is that we may be closing too many questions as "duplicates".
Using a liberal definition of "duplicate" means that there will be fewer questions available to answer and this reduces the likelihood that someone searching for an answer will be able to locate it.
Let us review official Stack Exchange policy on duplicates. From the blog, my emphasis:
Jeff Atwood, Nov 15, 2010 Dr. Strangedupe: Or, How I Learned to Stop Worrying And Love Duplication
One thing I want to be clear about, though, is that duplication is not necessarily bad. Quite the contrary — some duplication is desirable. There’s often benefit to having multiple subtle variants of a question around, as people tend to ask and search using completely different words, and the better our coverage, the better odds people can find the answer they’re looking for. And isn’t that, really, the whole point of this exercise?
Joel Spolsky, Jan 5, 2011, The Wikipedia of Long Tail Programming Questions
If you’re going to close a user’s question as a duplicate, it has to be a real duplicate. For example, if a user asks, “What does the IP address 22.214.171.124/24 mean?” it’s OK to close that as a duplicate of a more general question like “What do IP addresses of the form a.b.c.d/e mean?” But it’s not OK to close it as a duplicate of a twenty-seven page guide to netmasks. That’s the moral equivalent of saying “RTFM.” Stack Overflow is not meant to be a library of reference manuals. It’s supposed to contain the same information as a library of reference manuals, in the form of millions of questions and answers. Combined with Google, that gives us the magical power of a library of reference manuals you never have to read! It’s like, you got to the library, and there’s a wizard there at the door, and you ask your question, and, instead of being told to read a book, you just got (are you sitting down?) the actual answer!
That’s why we actually don’t mind having several versions of every question, where there are variations in wording or circumstances. The more chance that someone types a question into Google and finds their exact question already answered, the better a job we’ve done.
Now that we've reviewed official SE policy on duplicate, let's take a look at a question I posted that, as I write, has 3 votes to close based on "duplicate":
Here's the question:
Does throwing a watch into the air cause it to gain or lose time?
Suppose I'm on a non rotating planet. I have two identical, perfect watches. I synchronize them. Then I throw one of them into the air and catch it. Does the one I throw into the air gain or lose time with respect to the one I was holding?
And here's the question proposed as its duplicate:
Maximum time difference between clocks in a gravity field
You blast off in a rocket which has a clock on board, and there's a clock on the ground. The idea is that you have to be back when the clock on the ground says one hour has passed. Now you want it so that when you come back, your clock is as far ahead as possible. According to Einstein, if you go very high, your clock will go faster, because the higher something is in a gravitational field, the faster its clock goes. But if you try to go too high, since you've only got an hour, you have to go so fast to get there that the speed slows your clock down. So you can't go too high. The question is, exactly what program of speed and height should you make so that you get the maximum time on your clock?
This assistant of Einstein worked on it for quite a bit before he realized that the answer is the real motion of matter. If you shoot something up in a normal way, so that the time it takes the shell to go up and come down is an hour, that's the correct motion. It's the fundamental principle of Einstein's gravity--that is, what's called the "proper time" is at a maximum for the actual curve.
The two questions are similar in that they begin on a planet and involve a time piece. But in the first posted the question is "exactly what program of speed and height should you make so that you get the maximum time on your clock?" In the other, the question is: "Does the one I throw into the air gain or lose time with respect to the one I was holding?"
I submit that (under the policy of Stack Exchange) it should be clear and obvious to all that these are not the same question. The first has to do with maximizing a time difference over a path that is not a geodesic (i.e. the rocket ship) as compared to a path that is on a planet's surface (and hence is not a geodesic). The second has to do with the relationship between two paths, one stationary on the planet's surface, the other a geodesic near the planet's surface.
First, it's unfair to expect that a reader not already possessing an understanding of general relativity will see any relationship between these problems. Second, it's unlikely that they will locate the original post in searching for the problem. Third, it's unlikely that they will be able to work out the answer to the problem based on the answers given in the original post.
Finally, I'd like to point out that voting to close a question as duplicate has a tendency to suppress answers to the question. Why bother to write up an answer to a question that is going to be closed as a duplicate? For the question at hand, neither of the two answers give directly tell which watch gains and loses time. The best answer so far provided is: "The "stationary" watch, which is actually accelerated, is following some other path and so must experience a shorter proper time." To someone seeking to understand general relativity this will be confusing at best.