# Can I ask silly Fermi questions?

Can I ask a Fermi question on Physics Stack Exchange and looking for creative and plausible answers? Even that may sound silly? Such as: How much sea level will it rise if you pee at the sea?

• Closely related: meta.physics.stackexchange.com/q/6020/50583 – ACuriousMind Aug 22 '15 at 15:21
• "How much sea level will it rise if you pee at the sea?" Lol!!! There are variable factors in here, which your question doesn't specify, and hence it should be put on hold since you need to add these extra details. e.g. please specify how long you haven't peed before relieving yourself in the sea! – 299792458 Aug 22 '15 at 15:32
• @TheDarkSide Making plausible assumptions about all the factors you mentioned is exactly the fun part of a fermi question (if not the most fun part) :) – Shing Aug 22 '15 at 15:34
• Well, the safest answer, even without those assumptions, which will most likely stand the test of explicit calculations, is to go the Dirac way. Q - "How much sea level will it rise if you pee at the sea?". One word answer - "infinitesimal"! End of conversation! – 299792458 Aug 22 '15 at 15:38
• In the case of your example, Wolfram Alpha can answer that for you with an answer on the order of 5x10<sup>-18</sup>m. It is both too simple and too silly. Keep it interesting. – Floris Aug 23 '15 at 19:10
• @Floris Of course I want interesting Fermi question too, the topic "silly Fermi question" is really something that I want to make sure if Fermi questions are allowed, then where the boarder is drawn? – Shing Aug 24 '15 at 13:29
• btw, I have done that question on my own, and I was quite amazed that how much the sea level will raise to an atom is almost as same as an atom to a person. An answer of "infinitesimal" sort does not give you any interesting information. – Shing Aug 24 '15 at 13:30
• @Shing - I don't think it is easy to draw a clear border - although as I said above, if a simple Wolfram Alpha query can answer it, it's probably "too silly". Let's not encourage "exploring where the line should be drawn" - but trust the community to moderate. If too many high-rep people don't think it belongs, it will get closed. – Floris Aug 24 '15 at 13:31
• @TheDarkSide 1) Without the detail, you could still take the maximum volume an average adult bladder can hold (about 600mL). And 2) It won't even rise an infinitesimal amount because of how much water evaporates, flows into, and is rained on the oceans continuously. That 600mL is orders of magnitude below the per second variations in sea level that already exist and it's entirely possible that more water evaporates during the 21 seconds it takes you to relieve yourself than you put in. – Jim Aug 24 '15 at 16:48
• btw, 21 seconds is the average time it takes all mammals to empty a full bladder. Since, for a mammal of mass $m$, the time it takes is proportional to $m^{1/5}$, it's reasonable to say that almost regardless of size, it takes humans/mammals about 21 seconds to relieve a full bladder – Jim Aug 24 '15 at 16:50
• @Jim - OH MY GOD !!! – 299792458 Aug 24 '15 at 17:53
• @TheDarkSide I know, that's the most interesting thing you ever heard, right? – Jim Aug 24 '15 at 17:58
• @Jim That's a very specific equation for a rather scattered data set. My rabbit has an incredible capacity to contain and eject pee. A rabbit and a cat may have similar mass, but the rabbit holds 3x the pee. – Blackbody Blacklight Sep 11 '15 at 13:15
• @BlackbodyBlacklight I think the results of the study presented an average rule. There are bound to be some outliers found amongst all the species of mammal. – Jim Sep 14 '15 at 14:02

There are two problems with Fermi problems here.

First, this site isn't meant to have open-ended questions, or challenge questions. Answerers aren't meant to be competing against one another for the most interesting solution. Rather, we answer questions in order to build up a knowledge base and help disseminate facts and results in physics. Many Fermi problems have multiple acceptable answers depending on what assumptions are made, and this platform simply isn't designed to handle such cases. Remember, there can exist insightful/entertaining/good things in life that are nonetheless off-topic for this site, and there is nothing that needs fixing with this state of affairs.

Second, and more subtly, many Fermi problems simply aren't physics. The classic "how many piano tuners are in Chicago?" is a prime example of this. The solution is to make educated guesses for some input parameters, and then perform simple stoichiometry to convert units. This might demonstrate rational thinking, and it might require a decent background in everyday life, but it really isn't physics.

If a Fermi question is objectively answerable, is not posed as a quiz for the site's userbase, and is actually about a physics concept, then it is okay. The question must stand on its own; taking the form of idle musing purportedly had by some long-dead physicist is not sufficient to make a post on-topic.

• decent background in everyday life hah – Ryan Unger Sep 1 '15 at 16:59

I'm inclined to say no. This probably falls under the part in the help center where it talks about asking practical, answerable questions based on actual problems that you face; now, that's not meant to be interpreted too literally, but the reason it says that is to discourage precisely these sorts of just-for-fun puzzle-type questions.

• The approach that more experience members take to Fermi-like problems may at times be instructive; but I agree we probably don't want to flood the site with "silly" examples. It would cause the level of the site to drop by more than an infinitesimal amount. – Floris Aug 23 '15 at 19:06