jadero

I get it now. I was taking exception to your characterization of 3 and 5 being equally inaccurate in the sense of how close they are to the actual true value, which, of course, can never be known, except in every more accurate approximations.

In that case, I guess we still have a difference of opinion. I think that using approximations that are closer to their true value are more useful in teaching, despite (and maybe because of) the greater difficulty. If the student is not yet ready for that level of difficulty, then perhaps a different problem should be presented.

To that end, I actually think that there are several things to teach. That PI is not 3 or 3.14 or any other decimal expansion. That 3 is close enough for most casual encounters outside school. That 3.14 is close enough for most engineering work. That 3.1416 is close enough for most scientific work. That 15 decimal places is close enough for rocket scientists. That 37 decimal places are enough to calculate the circumference of the universe to within the diameter of a hydrogen atom. (https://www.jpl.nasa.gov/edu/news/2016/3/16/how-many-decimals-of-pi-do-we-really-need/ is my reference for the last two items. The others are just wild-ass guesses.)

I would draw your attention to the difference between mathematics and reality. Although mathematics is extremely useful in modeling reality, it's important to remember that while all models are wrong, some are nonetheless useful.

Thus, a household gardener or storage tank owner or a builder of small boats can choose the appropriate diameter of hose, tank, or pontoon very effectively by rounding PI to 3 but cannot do so when "rounding" to 1 or 5. In these cases, it literally doesn't matter how many decimal points you use, because the difference between 3 and any arbitrary decimal expansion of PI will be too small to have concrete meaning in actual use.

Under the philosophy you are promoting, it would be impossible to act in the physical world whenever it throws an irrational number at us.

I don't know, but I suspect that there is a whole branch of mathematics, engineering, or philosophy that describes what kinds of simplifications and rounding are acceptable when choosing to act in the physical world.

The real world in which we act has a fuzziness about it. I think it's better to embrace it and find ways to work with that than to argue problems that literally have no numerical solution, at least when those arguments would have the effect of making it impossible to act.

Not necessarily. Calculating the flotation of a cylindrical pontoon using pi=5 will leave you with a boat that sinks!

Just an ordinary person doing ordinary things :)

Especially given that using π=3 is accurate enough for most daily use by ordinary people for ordinary things.

As long as nobody is using drinking water for irrigation, the output does pretty closely match the input.

But my point was that we can treat that water for use and reuse. That way, the desalination is kept to a minimum.

It's not quite that simple. After extracting water, matching salinity would require extracting salt or adding water. It's not that there aren't sources of water that can be used for salinity matching, including the output of sewage treatment, the reality is that it probably makes more sense to treat that water than to desalinate in the first place.

Extracting the salts might be a source of valuable minerals and metals, but there is still no free lunch.

As far as I know, we still would be putting stuff back that doesn't make a good match for what we took. That means depending on the natural environment for dilution and "treatment". That has been an ongoing problem for humanity. We're very good at exceeding the capacity of the environment to cope with our wastes.

I completely understand the comment about perpetual motion machines, but tend to think that it's more of a scale management problem than a strict prohibition.

The impossibility of perpetual motion is not a reason to shut down research into methods of making power production and power consumption more efficient.

Are you saying that dealing with the waste brine is impossible in any way, shape, or form and that this is a reason to not pursue desalination research?

I used to be municipal water treatment plant operator (Level 2). I'm well aware that treatment waste is something that must be dealt with in any plant that does more than just disinfection.

I already admitted to not being up on the state of the art, but I was under the impression that there are potentially viable methods of dealing with waste brine in environmentally sustainable ways. Perhaps not at a scale that allows literally every human to use desalination for all needs, but that there are cases where desalination is a good solution.

My curiosity has been piqued. I will, of course, start looking for resources on waste brine management, but any pointers you have will be much appreciated.

One of the challenging issues with a complex problem is that the problem is not solved until the whole thing is solved.

One of the nice things about a complex problem is that you don't have to solve the whole thing at once in order to make progress toward a complete solution.

I don't know the state of the art on dealing with waste brine. If that is already deemed insoluble above a certain scale, then we better not invest in anything that exceeds that scale. On the other hand, if research into handling waste brine in sustainable ways is ongoing and making progress, then why not continue attacking the extraction problem?