The other day I saw this life-hack:

enter image description here

And I was wondering how true it is. First of all, I always thought(listening to weather forecasts) that low-pressure atmosphere is what correlates with rain; although I never learned the argument behind it.

Anyway, even if low atmospheric pressure correlates with storms and rain; how much(and in what sense) does this affect the bubbles in my morning coffee(if any)? My initial guess is that there should be a threshold pressure that will differentiate whether the bubbles will stick to an edge or suspend in the middle. Since this is an everyday-life question, I should say that experimental answers are welcome as well as rigorous theoretical ones.

Also, I am wondering if we can make a barometer based on the bubbles in a mug of coffee? If so, how sensitive it would be?

  • 2
    $\begingroup$ skeptics.stackexchange.com/q/8602 $\endgroup$ Aug 21, 2013 at 8:18
  • $\begingroup$ @JohnRennie I wasn't aware of that post! Perhaps the true home of that question should be Physics SE. Anyway, the question doesn't have an answer, and as a physicist I am more concerned about the physics; not just an answer. $\endgroup$
    – Ali
    Aug 21, 2013 at 8:24
  • 1
    $\begingroup$ To be honest I think the whole idea is rubbish, though I have no experimental evidence to justify my claim. A quick Google makes claims that increased pressure makes the coffee surface concave or affects bubble formation within the coffee. However the former is clearly wrong and I'd guess bubbles are due to entrained air during stirring. I'd guess the bubble behaviour is dominated by capillary forces, and it's hard to see how these would be affected by pressure. Humidity could affect the wetting propeties of the cup, so I suppose humidity could have some effect. $\endgroup$ Aug 21, 2013 at 8:34
  • $\begingroup$ @JohnRennie Yeah, honestly something inside me agrees with you(the possibility of the idea being rubbish ;-), but I would rather see an explicit answer before judging its truth. I think that's how science should work. $\endgroup$
    – Ali
    Aug 21, 2013 at 9:32

1 Answer 1


This is quite humorous.

In an 1883 offical US military publication, "Weather Proverbs" by 1st Lt. Dunwoody, at page 107 it is stated "When coffee bubbles collect in the centre of the cup expect fair weather. When they adhere to the cup, forming a ring, expect rain." This is the opposite of the lifehack proverb!

In 1997 Dave Thurlow, using a grant from the US National Science Foundation, insisted that the "bubbles in the middle mean sunny" version was supported by theory. http://www.weathernotebook.org/transcripts/1997/01/31.html However, he bases this on the coffee/air interface switching from concave up to convex with change in atmospheric pressure, which is extremely doubtful. Instead, the material of the cup wall and its interaction with the coffee would determine concavity.

The Young-Laplace equation describes the air/liquid interface.

The fact that the proverb and its opposite are both professed should be a strong indication that there is no truth in the proverb, absent some logical reason based upon the Young-Laplace equation.

  • 1
    $\begingroup$ Slight quibble: by "converse" I think you mean "negation" or "opposite" (logical complement). (A theorem and its converse can both be true: converse of $A\Rightarrow B$ is $B\Rightarrow A$). I only mention it because it did throw me for a bit, and so it might do other readers as well. BTW good answer. $\endgroup$ Feb 27, 2014 at 23:20
  • $\begingroup$ you're right, sorry $\endgroup$
    – DavePhD
    Feb 27, 2014 at 23:26
  • $\begingroup$ @DavePhD That's what I call a nice answer! $\endgroup$
    – Ali
    Feb 28, 2014 at 0:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.