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Personally, I like the home-experiment topic very much. For me they are even more relevant to physics than any theoretical/mathematical stuff. I'm pretty sure that the roots of the "not even wrong" attitude to theoretical physics are in exactly this "experimental nihilism".

One can argue that "this is a popular science", so what? What are the reasons to close such questions?

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    $\begingroup$ Do you mind being a little bit more concrete (i.e. listing the home-experiment questions that have been closed)? In general, I don't think there is any problem with such questions, as long as they satisfy other rules of the site. By the way, your rant against theoretical/mathematical physics isn't really helping anyone ;-) $\endgroup$ – Marek Dec 15 '10 at 16:08
  • $\begingroup$ How about asking "Should home experiment questions be on the site?" rather than "Why shouldn't they be on the site?" The way you have it phrased now makes it harder for someone to express the opinion that they're totally fine. $\endgroup$ – David Z Dec 15 '10 at 18:22
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    $\begingroup$ I think home-experiment-questions should be allowed on this site. $\endgroup$ – student Dec 15 '10 at 20:18
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    $\begingroup$ @Marek: The closed question : physics.stackexchange.com/questions/1845 . Or at least, one which I think should be reopened. $\endgroup$ – Frédéric Grosshans Dec 16 '10 at 11:22
  • $\begingroup$ Generally I think closing a question should be the last resort. I think the first thing to do is to write a good description how to ask, in particular on this site (e.g. like mathoverflow.net/howtoask on mathoverflow). Secondly there sould be an elementary tag and if there is a question which seems to be too elementary to a moderator or to many users they should encourage the questioner to tag it as elementary. Thirdly, if the question is not formulated precise enough, one should encourage the questioner to reformulate it (that's why there is an 'edit' functionality in stackexchange)... $\endgroup$ – student Dec 17 '10 at 19:43
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I think there's a difference between "I tried to use PV = nRT to solve my homework and it didn't work!" and "How can I effectively demonstrate the ideal gas law at home?" For me, the difference is very clear - only one of these questions is interesting.

Having received an undergraduate physics education, I can answer questions on adiabatic expansion easily. I am not sure, though, how close the air in this room is to being an ideal gas. I'm not sure of a good way to build my own barometer or thermometer. I have a basic idea of what these things are and how they could be constructed, but I think it's likely I could learn a great deal if knowledgable people were to answer the question about this simple experiment.

I don't mean only that I would learn the sorts of things I'm supposed to learn in a shop class. I mean I would learn actual physics.

For example, there was one question a while back about how one can measure Avogadro's number at home. I already knew the answer about Brownian motion, but didn't know the one about creating a monolayer of oil on top of a body of water. That answer was physically interesting to me because it led me to wonder why the oil would 1)spread out to a single layer and 2)stay contiguous once it had become a single layer.

The process of thinking about, devising, and executing such simple home experiments is likely to be engaging and educational, even on the level of people who do have significant physics education, and is not equivalent to entry-level theoretical questions.

Also, for people who, unlike I, are already very skilled at experiment, I can guess it would be an interesting challenge to discover simple home experiments that demonstrate physical effects people are interested in observing.

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    $\begingroup$ +1 I think you make a very valid point that questions about home experiments are not necessarily uninteresting to professional/research-level physicists. $\endgroup$ – David Z Dec 16 '10 at 21:29
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    $\begingroup$ +1, I definitely agree. It's great that you were able to put into concrete words my vague ideas that those questions should be sophisticated, undergraduate-level, etc. I think every meta-question as to the nature of what questions we want to allow eventually boils down to: a) it should contain some physics, b) it should be clever/insightful/etc so that everyone learns something new by asking/answering the question. As long as these conditions are satisfied, I don't care what is the question about, it should belong here. $\endgroup$ – Marek Dec 16 '10 at 22:32
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    $\begingroup$ @David: I'm an active researcher. I like thinking about, designing, and trying demos because they illuminate the underling physics, the limits of the physics, and art of isolating particular effects in one neat package. Besides, I'm always on the lookout for another in-class demo... $\endgroup$ – dmckee Dec 18 '10 at 18:28
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Based on some of the information in the other answers, I have an idea. (It might even be a good idea but I don't want to jinx it :-P) Suppose we allow home experiment questions, but only if they meet particular guidelines:

  • Format: A good home experiment question should invite answers that include a specific procedure and a specific method of data analysis. For instance, I like this answer to the question that prompted this discussion, because it reads like a (very short) lab manual, describing the steps to take to perform the experiment, the data that will be collected, and the method by which you can interpret the results to demonstrate the relevant phenomenon. I don't like this one or this one.

  • Specificity: Questions should ask about a specific quantity that can be measured, or a specific physical principle that can be demonstrated (although the latter type may be at slightly higher risk of being closed as too vague). For instance, "How can I measure the resistance of the human body at home?" would be okay (assuming it meets the other guidelines of course). Similarly, "How can I demonstrate interference of light waves?" should be fine. But something like "What interesting demos can I do with a hair dryer?" would be too unfocused.

  • Materials: Questions cannot be restricted to "common household materials" because if you limit yourself to the things that most people happen to have lying around the house, there's not that much you can do. It would be better to allow (and even encourage) answers describing experiments which use materials that can be purchased at a reasonable cost from, say, a hardware store or electronic supply store. Someone who is really interested in physics wouldn't mind spending a little bit of money to further their knowledge.

  • Level: Questions should invite answers describing experiments that would be interesting to a college undergrad majoring in physics, or someone at a higher level (grad student, professor). This doesn't always mean that the experiments should require a college-level physics education to pull off; in fact, a good description of an experiment will often (but not always) be clear enough for someone without any specialized training to follow it. But the experiment should be based on physics that is more substantial than introductory level, and ideally should allow someone with a physics education to figure out new and interesting ways to analyze the data.

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  • $\begingroup$ @Specificity: My question physics.stackexchange.com/questions/1845/… is a bit like your example about the hair dryer, however a bit more focused (since I wanted only electromagnetic phenomena). The point in restricting things to WLAN or mobiles was the idea that this are devices are relatively new and have an enourmous influence on the everyday life of students. So I found it interesting from a motivational perspective to ask for experiments demonstrating em-phenomena using exactly those devices. $\endgroup$ – student Dec 17 '10 at 19:54
  • $\begingroup$ @student: agreed, that was my impression as well. I'd like to see your question focus more on what you would like to see demonstrated (for instance, the interference of EM waves) and not so much on restricting what materials could be used to demonstrate it. You could offer cell phones and wireless devices as examples of good materials to use. Also we are looking for an undergraduate level of sophistication at a minimum; this is not the site for high-school-level experiments. If your question were different in those two ways, I think I would be more amenable to seeing it reopened. $\endgroup$ – David Z Dec 17 '10 at 20:36
  • $\begingroup$ I changed my question regarding the level and the 'other' tools. However I don't want to narrow the focus for this question and I want to have mobiles or WLAN antennas as the main tools. (Perhaps a "list" or "big-list" tag would be a nice idea (as in mathoverflow) $\endgroup$ – student Dec 17 '10 at 22:12
  • $\begingroup$ @student: note that this isn't any sort of official policy yet. I'm still hoping to get feedback from more people about whether this would be a good set of guidelines. If it does become an official policy, then in the interest of consistent enforcement, your question and a couple of the other [home-experiment] questions would have to be closed. (Of course a closed question can always be edited to make it suitable for reopening.) If you think we should be using a different set of guidelines, I'd be interested to hear your objections and reasons. $\endgroup$ – David Z Dec 18 '10 at 22:36
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Well, I guess that (once again) this has to do with what level the site is aiming at. Because at some point of sophistication, you can no longer really run experiments at home (you certainly can't run LHC at home, but also lots of other much simpler experiments).

Now, I personally think that the site should be aimed at least at the undergraduate level. So this means that it should be fine to allow experiments such as the ones that are being done in standard university courses. In other words, experiments with at least some degree of sophistication.

But for experiments that anyone with no experience in physics can do at home, I don't believe that such questions belong here. There is a proposal of Popular Natural Science which would be an ideal place for such questions. So if you want home-experiment go support that proposal!

Someone could suggest that we should leave such questions here at least until the PNS reaches beta but I think this would lower site's level and so I am reluctant to allowing that. Also, perhaps it would be useful to go over the older questions and close them as well. I know some people won't be happy, but I believe this site should have boundary. We don't do biology here. We don't do mathematics here. And we are definitely not doing elementary school physics here... The question is are we doing home-experiments here?

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    $\begingroup$ I've been thinking, home experiments don't necessarily have to be the kind of things that someone with no physics education can perform and analyze at home. Those sorts of simple experiments (which sometimes aren't experiments at all) are certainly better on PNS. But that doesn't mean there aren't home experiments we can talk about here. (They would be "home" merely in the sense that they don't require specialized lab equipment) $\endgroup$ – David Z Dec 17 '10 at 6:24
  • $\begingroup$ @David: right, thanks for pointing that out. $\endgroup$ – Marek Dec 17 '10 at 9:02
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As @Marek said, I think it really depends on what you think the site is for. Let me see if I can summarize some of the reasons for avoiding these types of things that he left out:

First of all, the people who will use this site the most (by far) are research level physicists. I would say at least graduate school level, and most of the people answering questions are probably postdoc or beyond. (I myself am a graduate student, and I'll be the first to admit I don't have the breadth of knowledge to answer most of the good questions on this site). The problem is that the percentage of total internet users that are actually research level physicists is very, very small. So statistically, even if a very small percentage of that internet using public visits this site and an even smaller percentage ask questions that are mostly relevant to non-physicists, we would still be inundated with questions that are not that interesting for academic, research-level physicists. I believe there's a post by the StackOverflow team that calls this the "Yahoo answers effect" (though you may disagree with me on the interpretation of this blog post; feel free to that's the purpose of the meta site). It may seem rude, mean, or unfair to say so, but to be honest, this site really does a lot more good as a place for people to ask and answer questions pertaining to their jobs rather than their hobbies, and it definitely does everyone a lot more good as a place to ask and answer high level questions rather giving out Physics 101 homework answers for free (I know that's not exactly the same thing that this question is about, but it falls into the same category in my mind).

Hope I didn't step on too many toes; if I did, I apologize in advance, particularly if they are the toes of any of the nice people who have taken the time to answer my questions.

Also, don't get me wrong, I'm all for promoting physics education to the wider public; I just think that a popular science site or something like that would be a much better place for it.

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    $\begingroup$ I think research-level physicists have already concluded that this site is too low-level for them, hence the theoretical physics proposal (and several of the earlier questions on this meta site). $\endgroup$ – David Z Dec 16 '10 at 21:27
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    $\begingroup$ ...although, I would be very happy if we could get enough high-level questions here to change their minds and bring them back. (Probably not practical, but I can wish :-P) $\endgroup$ – David Z Dec 16 '10 at 22:37
  • $\begingroup$ By the way, as a graduate student you should know enough to answer many questions on the site. So please, do not restrain yourself needlessly (just because there will always be someone better) and provide answers. Sure, they won't be the best but I think everyone will gain something by your posting them. I know I learned a huge deal in the past few weeks just by trying to answer what I thought were quite simple questions. $\endgroup$ – Marek Dec 17 '10 at 0:10
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I think if you ask a home-experiment question on this site, there is no restriction on the sophistication of the answer, one can propose very suggest experiments which answer the question, one can argue theoretically or mathematically why the proposed home experiment would work etc.

However if you pose the same question on a basic level side, I think there should (and will) be (almost) also basic answers.

Analogously for other "basic" questions. The point is, that it sould be possible to ask such questions without restrictions on the sophistication level of the answers.

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    $\begingroup$ This raises an interesting point, that questions about home experiments can still benefit from the insight of an advanced physicist sometimes. But they have to have a certain level of sophistication (at least in terms of the analysis you can do on them) to do so. In other words, I don't think we should be discussing simple things that just happen to demonstrate some physical principle, but rather more involved experiments that actually take some thought to interpret while showing something interesting in the end. $\endgroup$ – David Z Dec 17 '10 at 6:21

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