# In what physical world would you be able to unstir milk from coffee? Time travel is not allowed. **URL:** \ **Category:** Factual Questions\ **Created:** [November 16, 2012, 8:38pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236 "2012-11-16T20:38:56Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 17, 2012, 6:48am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/21 "2012-11-17T06:48:12Z")
> [@moriah](#): > > First, the two video links show a thick viscous liquid stretching and unstretching… not the same as mixing and unmixing. It is, and it isn’t - sure, the video shows laminar stretching, but I think a case could be argued that stirring coffee does the same, only faster and less neatly. If the crank in the video was rated clockwise for an hour, the experiment would not.‘unwind’, because homogenous mixing would have occurred. However, if one were able to apply force in delicate and controlled enough fashion, one would be able to unstir coffee - it just rakes more effort. Maxwell’s Demon _can_ exist; he’s just costly to run. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [November 17, 2012, 7:12am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/22 "2012-11-17T07:12:56Z")
> [@njtt](#): > > …Maybe one could conceive of a world where matter was not particulate, but there, how would you stir your coffee at all? Our world is particulate, lock, stock, and barrel? I’m not sure what that means. Also, since you’ve entertained the notion, what would such a “non-particulate” universe entail? ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [November 17, 2012, 7:16am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/23 "2012-11-17T07:16:02Z")
> [@pseudotriton\_ruber\_ruber](#): > > hate to add so obvious a note, but I can never tell with the Mods sometimes. I am kidding. Post #13 is a joke. I’m not actually calling anyone a cheapskate. That’s OK. Although I’m actually quite profligate, to the point that psychological caution is required. ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [November 17, 2012, 7:21am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/24 "2012-11-17T07:21:07Z")
> [@njtt](#): > > I think the OP is actually asking is what laws of physics would have to be different in order for the “unstirring” to be possible by relatively simple physical means (comparable in difficulty to regular stirring). As others have been saying, you would have to repeal the second law of thermodynamics, and, as I previously said, _that_ would entail repealing the atomic/molecular theory of matter. With that gone, it does not seem to me that you would have a universe in which stirring and mixing was possible in the first place. Oh, okay. It’s unusual physics we’re looking for. Well, how about the many worlds hypothesis? Just go to the one where Strom Thurmond won the 1948 Presidential election. In that world it would be illegal to mix coffee and milk. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 17, 2012, 7:25am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/25 "2012-11-17T07:25:49Z")
How about quantum unstirring)? Make coffee add milk stir then stir again destroy all universes where the coffee and milk do not separate voila! Unstirred coffee! ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [November 17, 2012, 10:17am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/26 "2012-11-17T10:17:33Z")
What happens if you let stirred coffee and milk just sit for a while? Do they seperate? I have no idea because I wouldn’t ever come near enough to a cup of coffee to smell it. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [November 17, 2012, 10:25am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/27 "2012-11-17T10:25:29Z")
You can do it in our universe – it just takes a very, very, _very_ long time, but there was no timescale constraint in the OP… > [@Leo\_Bloom](#): > > Our world is particulate, lock, stock, and barrel? > > I’m not sure what that means. > > Also, since you’ve entertained the notion, what would such a “non-particulate” universe entail? I don’t think that whether the universe is particulate is really germane to the question (a lot of people would also argue that quantum field theory is incompatible with a particle ontology). The key point is really that the second law of thermodynamics necessarily applies to every system as long as it has a certain number of different states to be in, where the ‘ordered’ states are a smaller set than the ‘disordered’ ones. In this case, drawing a state at random gives you a disordered one with a higher probability, and thus, any small change done to the system is more likely to leave it in a less ordered state. Since any system like the coffee+milk one obeys these requirements – lots of ways to be stirred vs. comparatively small amount of ways to be separated: that’s the reason the stirring itself works, after all --, there’s really no way to find a consistent set of rules that allows some form of ‘efficient’ unstirring, simply by virtue of the laws of probability. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [November 17, 2012, 1:47pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/28 "2012-11-17T13:47:39Z")
Believe it or not, based on my conception of what I’ve read, I did wonder about field theory as a challenge to atomic/molecular/“particulate” theory, but was too embarrassed too say it. Whether field theory is a theory or an ontology of quantum physics strikes me in itself as an interesting question. It’s a big subject, I suppose. Finally, thank you for your simple explanation of entropy as a matter of more or fewer disordered states and probability. But, as you say, with infinite time you get a get-out-of-jail card with constraints of probability.\* \*I just thought of a thread query… ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 17, 2012, 3:40pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/29 "2012-11-17T15:40:49Z")
> [@TriPolar](#): > > What happens if you let stirred coffee and milk just sit for a while? Do they seperate? Not really. If left long enough (days, weeks) the mixture will spoil and curdle - and will separate into various fluids and clotted solids, but none of them will be fit to be described as either ‘milk’ or ‘coffee’ any more. Furthermore, milk isn’t just one thing, neither is coffee, for that matter - they’re both mixtures themselves - so even if the components of milky coffee were prone to rapid settling or splitting, it wouldn’t be likely that they would split back to milk and coffee. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 17, 2012, 3:47pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/30 "2012-11-17T15:47:33Z")
Thermodynamics even permits a cup of coffee to be unmixed - people have been saying that entropy can’t be reversed - but it can. Local entropy (i.e. inside a cup) can be reversed by the application of energy (increasing the entropy outside the cup). A the entropy of a closed system consisting entirely of milky coffee can’t be reversed, but the local entropy of a cupful (an open system) can. ---
**Author:** ![leadarrows](https://avatars.discourse-cdn.com/v4/letter/l/2acd7d/32.png) [@leadarrows](https://boards.straightdope.com/u/leadarrows)\ **Post date:** [November 17, 2012, 3:47pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/31 "2012-11-17T15:47:37Z")
Allowing they are of a different density a Centrifuge might do the trick. ---
**Author:** ![Aquadementia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aquadementia/32/555_2.png) [@Aquadementia](https://boards.straightdope.com/u/Aquadementia)\ **Post date:** [November 17, 2012, 4:21pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/32 "2012-11-17T16:21:51Z")
Again I find myself vexed for not having a centrifuge in my home! Some chromatography may also be useful. Has anyone ever tried lemon in their coffee? I expect that could remove the milk in an awful way. ---
**Author:** ![drastic\_quench](https://avatars.discourse-cdn.com/v4/letter/d/e36b37/32.png) [@drastic\_quench](https://boards.straightdope.com/u/drastic_quench)\ **Post date:** [November 17, 2012, 5:31pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/33 "2012-11-17T17:31:23Z")
“Waiter needs to know NOW”? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 17, 2012, 7:09pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/34 "2012-11-17T19:09:38Z")
> [@Aquadementia](#): > > Has anyone ever tried lemon in their coffee? > I expect that could remove the milk in an awful way. I’ve not tried it, but I intend to now you have mentioned it. Without the milk though - lemon in tea is always without the milk so the same should at least be observed for coffee. Lemon in milky coffee, yes. Is going to make coffee flavoured cheese curds. Probably not nice. … Although mature cheese + honey + a sprinkling of ground coffee is nice ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [November 17, 2012, 7:12pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/35 "2012-11-17T19:12:14Z")
> [@Mangetout](#): > > Thermodynamics even permits a cup of coffee to be unmixed - people have been saying that entropy can’t be reversed - but it can. Local entropy (i.e. inside a cup) can be reversed by the application of energy (increasing the entropy outside the cup). > > A the entropy of a closed system consisting entirely of milky coffee can’t be reversed, but the local entropy of a cupful (an open system) can. What does this mean? And you say in such a case–a theoretical one, only?–it can be done, “for real?” ---
**Author:** ![hkepotat](https://avatars.discourse-cdn.com/v4/letter/h/edb3f5/32.png) [@hkepotat](https://boards.straightdope.com/u/hkepotat)\ **Post date:** [November 18, 2012, 12:27am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/36 "2012-11-18T00:27:16Z")
> [@Leo\_Bloom](#): > > See subject. A very dry world. Mix 8 fl oz of instant coffee with 2 fl oz of powdered creamer, stir. Pour onto a table, rub a balloon on your hair, and pass it over the mixture, and watch as it comes unmixed. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [November 18, 2012, 2:02am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/37 "2012-11-18T02:02:22Z")
:)! ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [November 18, 2012, 2:24am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/38 "2012-11-18T02:24:29Z")
Get Merlin to unstir it; he lives backwards in time so he should be able to unmix things. AKA get a wizard to do it. ---
**Author:** ![Alka\_Seltzer](https://avatars.discourse-cdn.com/v4/letter/a/c89c15/32.png) [@Alka\_Seltzer](https://boards.straightdope.com/u/Alka_Seltzer)\ **Post date:** [November 18, 2012, 11:06am UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/39 "2012-11-18T11:06:07Z")
> [@Chief\_Pedant](#): > > [Here’s a popular video](http://www.youtube.com/watch?v=UpJ-kGII074) that is probably the closest we’ll get in this world. Nice video, but when I make coffee it isn’t normally that gloopy. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 18, 2012, 2:49pm UTC](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236/40 "2012-11-18T14:49:50Z")
> [@Leo\_Bloom](#): > > What does this mean? And you say in such a case–a theoretical one, only?–it can be done, “for real?” Theoretical. It means the laws of physics don’t fobid it. Doesn’t mean we can actually do it, yet at least. [Previous page](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236.md?page=1) [Next page](https://boards.straightdope.com/t/in-what-physical-world-would-you-be-able-to-unstir-milk-from-coffee-time-travel-is-not-allowed/641236.md?page=3)