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B Is mpemba effect resolved?

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  1. Sep 25, 2016 #1
  2. jcsd
  3. Sep 25, 2016 #2

    Nugatory

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    That depends on exactly what you consider the "Mpemba effect" to be; there is no unambiguous and generally accepted definition of what it is. The wikipedia article on the Mpemba effect, along with its talk page (it is always wise to look at the talk page!) explains some of the issues here.

    The original paper is here: http://arxiv.org/abs/1310.6514, and it's interesting in its own right.

    As an aside, the Daily Mail is not in general an acceptable source here, and this article is an example of why. It's not even first-hand reporting; it's digesting without understanding (no competent science journalist could write a sentence that starts "The Mpemba Effect is the theory that....") a blog that in turn is trying to summarize the paper for a lay audience.
     
  4. Sep 26, 2016 #3
    So according to the paper you gave reference to, is the paradox resolved? Is the explanation accepted by scientists ?
     
  5. Sep 26, 2016 #4

    jbriggs444

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    Did you read the first two words in Nugatory's response?
     
  6. Sep 26, 2016 #5

    russ_watters

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    Since there is no general agreement on if the effect even exists or if so, what it is, the closest you can get to a scientific community consensus is that when it occurs, it is probably an experimental artefact. In other word, it is something that shouldn't happen if starting temperature is the only difference, so when it happens it is because starting temperature isn't the only difference.
     
    Last edited: Sep 26, 2016
  7. Sep 26, 2016 #6
    This concept has never made sense to me.
    The water which is originally hotter must at some stage cool to be at the same temperature as the originally cooler water.
    From that point it would then continue to cool in the same manner as the originally cooler water had done.
    So given that all other conditions are the same, the time taken for the hotter water to cool to some given temperature cannot possibly be less than the cooler water.
    It can only be longer because it first has to cool to the temperature that the originally cooler water started at.
     
  8. Sep 26, 2016 #7

    russ_watters

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    Right. The link in the OP shows a temperature/time graph that clearly shows the cold water sub-cooling, which delays and slows the freezing. In order for the cold water to experience sub-cooling and the heated water not, something else must be different. For example, maybe heating the water drives off dissolved gases that interfere with the crystallization. In either case, if both are treated the same, ie, boiled first, and then stuck in the freezer at different temperatures, the effect would not occur.

    But that is just one example of a certain scenario (others don't heat the water to a boil first, for example).
     
  9. Sep 27, 2016 #8
    Thank you, that was very helpful
     
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