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Freezing Speed of Hot Versus Cold Water
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Siwastaja:

--- Quote from: IanB on February 23, 2022, 06:53:58 pm ---Why would you say conclusive proof requires an explanation of a mechanism?

--- End quote ---

It is absolutely nececessary to rule out coincidental unexpected correlations; if you have just measurement results and no explanation for them, you are not proving any theory, just replicating the experiment and it's well possible it demonstrates something completely different yet you have no idea.

I think it's quite revealing you don't understand such basic requirement of scientific research.

So yes, you need both. Only then it is valid science.
bdunham7:

--- Quote from: Siwastaja on February 23, 2022, 07:33:36 pm ---It is absolutely nececessary to rule out coincidental unexpected correlations; if you have just measurement results and no explanation for them, you are not proving any theory, just replicating the experiment and it's well possible it demonstrates something completely different yet you have no idea.

--- End quote ---

The causation/correlation issue only arises when you don't directly control the causation part.  If I take 1000 cuts of meat from 100 different animals and hang them over fire by a stick, I can safely conclude that the fire causes them to cook without understanding how or why.  It's true that not understanding 'why' might cause a mistaken conclusion to be made that does not allow me to predict the result in a slightly different experiment-- for example is the cooking due to the heat or the light?  I take the philosophical position that we never actually completely know "why" or "how" anything happens, we just have models that are good enough to allow us to make predictions with a certain amount of reliability.

If I can control various aspects of water in an experiment--how it is heated/cooled/handled and so forth, I can see if and when the Mpemba effect occurs and then make a catalogue of the various conditions where it does and doesn't seem to manifest itself, such as the water sample temperatures, the container characteristics, the freezer temperature, etc etc.  This catalogue might show me, for example, that the Mpemba effect is observed as long as the hot water is at least 80C, the container is metal but not wood or clay and only if the freezer temperature is between -5 and -15C.  That list of conditions where the effect does and does not occur would constitute scientific knowledge without ANY model or knowledge of the underlying processes, or even the atomic or molecular nature of water itself.  This is how science worked for thousands of years--there weren't many models and they were all completely wrong anyhow for the most part, except perhaps for simple mechanical devices.  Nowadays some think we have all that figured out, but I'm not so sure.
IanB:

--- Quote from: Siwastaja on February 23, 2022, 07:33:36 pm ---
--- Quote from: IanB on February 23, 2022, 06:53:58 pm ---Why would you say conclusive proof requires an explanation of a mechanism?

--- End quote ---

It is absolutely nececessary to rule out coincidental unexpected correlations; if you have just measurement results and no explanation for them, you are not proving any theory, just replicating the experiment and it's well possible it demonstrates something completely different yet you have no idea.

I think it's quite revealing you don't understand such basic requirement of scientific research.

So yes, you need both. Only then it is valid science.

--- End quote ---

I think you are introducing something new here (the need for a scientific theory) that is not part of the original question. The question at hand is: "Can such an effect be observed by anyone, anywhere, in a reproducible manner?" In other words, is there even a phenomenon that needs explanation?

In this case I contend that no such phenomenon has been conclusively demonstrated in a laboratory, so there is not even a reason to seek a mechanism.

On the other hand, if someone hypothesizes a mechanism, then it should be testable by experiment. But I contend there is no more than anecdotal evidence or hearsay at the moment, with no reproducible, experimental procedure to demonstrate it.

Surely, if there was an experimental procedure that reliably produced the effect, then it would be documented somewhere? You or I could read the experimental method, and given an adequate laboratory we could reproduce it for ourselves. It would be in high-school science classes. There would be YouTube videos by the likes of NileRed or Veritasium showing it. Where are they?
PlainName:

--- Quote ---but the ultimate question for me is whether I should use hot or cold water in my ice cube tray.
--- End quote ---

It's useful to remind us of the original proposition, but then why do you arbitrarily say:


--- Quote ---f you observe the Mpemba effect, then at the end after they are cooled to say -20C
--- End quote ---

Why -20? Isn't the question merely which freezes faster? Otherwise you could pick -127C, and microwaved super-heated water to start, and all of a sudden the conditions for your 'ultimate question' are just as much rubbish as you complain his (alleged!) edge cases are.
bdunham7:

--- Quote from: dunkemhigh on February 25, 2022, 12:48:26 am ---Why -20? Isn't the question merely which freezes faster? Otherwise you could pick -127C, and microwaved super-heated water to start, and all of a sudden the conditions for your 'ultimate question' are just as much rubbish as you complain his (alleged!) edge cases are.

--- End quote ---

Because that is approximately how cold my freezer is?

You can pick any numbers you like, and as I said elsewhere, it would be appropriate to try different combinations.  But -20C isn't what is important, it is the entire dataset as the cooling and freezing occurs, time and temperature.  The point is simply that you need to observe that long enough and far enough down that you can be sure that the phase change is complete.  Then you can go back and look at the data to see when you deem the sample 'frozen'.  If that point is clear and indisputable, great.  If not, you have more questions.
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