Talk:Fermi problem

Fermi Category

Is it worthwhile to list links to any such problems that already have wikipedia articles? I figure the Drake equation is one, but I dunno if there are any others famous enough to get their own articles. -- Finlay McWalter 17:18, 18 Dec 2003 (UTC)

Details

Hi guys

I remember reading that Fermi estimated the yield of a nuclear explosion by dropping some pieces of paper from his hand (Fermi himself presumably some safe distance from ground zero). I did some order-of-magnitude analyses of this and came up with some not-quite-to-within-an-order-of-magnitude answers.

Anyone out there got more detailed info on this experiment? How far did his pieces of paper travel?

          2 & 1/2 Meters acording to this. -> http://www.trinityremembered.com/documents/Fermi.html

Piano

Hi: for the record, the Yellow Pages gives 31 piano-tuning businesses in Chicago, and 4 per business is a reasonable estimate. Nice check. Also, Stein's example as linked isn't at all related to Fermi problems... maybe it's another Stein and another example? -[User:acthomas], 13 Feb 2008 —Preceding unsigned comment added by 140.247.243.189 (talk) 22:32, 13 February 2008 (UTC)

As a piano tuner, I can say that estimate is way too high. With 31 Businesses listed, most are owner, operators, rarely do they work with 4 others. There are way more pianos in any city than all the tuners can handle. I often find myself working 12 hour days tuning 6 or more in a day. You forget schools, churches and universities all have 2 to 150 pianos. Nice deduction, but not true. —Preceding unsigned comment added by 216.51.213.95 (talk) 04:04, 26 August 2008 (UTC)

Yeah, the number one unspoken assumption in that calculation is that the market alone determines how many piano tuners there will be. It starts from the number of pianos and works backwards. Reality doesn't work quite like that; there are other factors like whether the profession is attracting enough people or not. The hand of the market may be invisible, but it's not instrumental. (Another obvious omission: people who get their pianos tuned but not regularly. Ask a dentist how many of his patients get regular checkups and how many wait for the pain to remind them.) ~ CZeke (talk) 05:05, 1 June 2011 (UTC)

Still, correct well within a factor 10, which is the purpose. None of the assumptions are correct, but all of them are close enough, which is the point. I agree though, that the market assumption should be clearly stated. — Preceding unsigned comment added by 203.16.41.5 (talk) 00:10, 7 January 2014 (UTC)

there are 3miilion in Chicaog not 9 million! Juror1 (talk) 23:32, 5 August 2017 (UTC)

Uh, no.

A famous example of a Fermi-problem-like estimate is the Drake equation, which seeks to estimate the number of intelligent civilizations in the galaxy.

I have to dispute this. The Drake equation contains seven terms, only two of which are even possible to intelligently guess about. The other five are utterly impossible to evaluate, approximate, or scry with magic, but could be known only through omniscience. That means that it is not a Fermi-like problem, but rather a meaningless-like problem.--70.131.115.43 (talk) 22:18, 20 February 2009 (UTC)

Why do you assume a Fermi problem is always deducable like you claim? Plus, the Drake equation is closely linked to the Fermi paradox, so there's a context link too. Ingolfson (talk) 09:57, 24 January 2010 (UTC)

Issues with the Piano tuning

Did anyone ever follow up whether he was anywhere close? Also, the example would be tailor-made for showing the fallacies of solving the problem that way (i.e. it does not take into account piano tuners from outside of the Chicago area travelling in to work). Of course for either of those additions, refs would be needed, so we can't simply add something (damned rules! ;-) Ingolfson (talk) 09:56, 24 January 2010 (UTC)

Read the preceding sections on this page. As of Nov 2010 there are 35 piano tuning companies listed in the yellow pages for Chicago. As the expert above testified, they typically work alone - so there may well be only 35 piano tuners in the city. However, Fermi made this estimate in the 1950's when pianos were a lot more common in households than they are today - which probably goes a long way towards explaining the difference.

But the whole point of the Fermi problem is not that this is a technique for getting the right answer. The whole idea is that it teaches you to put appropriate error bars on your estimates. In the article, we use the estimate that piano tuners can tune 4 pianos per day - our "expert" says, no, it's more like six. That estimate for the time taken to tune a piano should probably have a +/- 25% error bar on it - 90 minutes to two and a half hours. Similarly the population estimate, the number of people per household, the percentage of households with pianos...all of the these estimates should have error bars. When you multiply out those error estimates - you should (hopefully) come up with an answer that says (maybe) "between 20 and 200" - and not some exact prediction like "135". Had we done that, I'm pretty sure that the correct answer would lie within the error range. Worse still, the equation omits places like schools and concert halls where there may be dozens of pianos - and that might severely skew the results.

A much better example is in the Drake equation article - where we point out that "a Fermi problem which involves the multiplication of several estimated factors, and such calculations (e.g. the number of piano tuners in Chicago) will probably be more accurate than might be first supposed (assuming that there is no consistent bias in the estimated factors). This is because if there is no consistent bias, then there will probably (with a binomial distribution) be some factors that are estimated too high and other factors that are estimated too low, and such errors will partially cancel each other out.". In that article, we point out that when you pick the most optimistic answers, you wind up with 20,000 alien races in our galaxy that are trying to communicate with us...and with the most pessimistic numbers 0.00065 races. SteveBaker (talk) 13:38, 17 November 2010 (UTC)

Sourcing for number of piano tuners

I notice related topics have been discussed before here, but sourcing

The actual number of piano tuners in Chicago is about 290.[3]

using a Wolfram Alpha answer is somewhat dubious. NotYourFathersOldsmobile (talk) 08:03, 2 February 2016 (UTC)

External links modified

Hello fellow Wikipedians,

I have just added archive links to one external link on Fermi problem. Please take a moment to review my edit. If necessary, add {{cbignore}} after the link to keep me from modifying it. Alternatively, you can add {{nobots|deny=InternetArchiveBot}} to keep me off the page altogether. I made the following changes:

• Added archive http://web.archive.org/web/20160106083744/http://www.google.com/base/a/1551686/D2256477437979091778 to http://www.google.com/base/a/1551686/D2256477437979091778

When you have finished reviewing my changes, please set the checked parameter below to true or failed to let others know (documentation at {{Sourcecheck}}).

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 18 January 2022).

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—^{cyberbot II}_{Talk to my owner:Online} 09:15, 28 February 2016 (UTC)

Physicists and engineers: Does anyone actually call these Fermi problems?

Hi all, question as in title. I believe the correct title of this page is Order—of—magnitude approximation, as that is what it is called, in my experience. Even if some people do call them Fermi problems, order of magnitude approximation or a synonym is manifestly more common, as it will be mentioned at least as many times as Fermi problem. Sometimes an older professor will talk about Fermi, but it is rarely called a Fermi problem. I heard this term used in a popular article and had to look it up right away (the article tried to use the term to predict the outcome of the presidential election... apparently the literature available to lay persons is not adequate to explain the concept). Thanks! Footlessmouse (talk) 20:11, 29 October 2020 (UTC)