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mperklin t1_jdy8ccw wrote

Reply to comment by patman_007 in Estimates suggest population growth rate to peak at 8.6 billion by madrid987

No, because if the population tops out at 8.6 billion people then the growth rate is 0 (which is not the peak/highest value)

The population may peak at 8.6 Billion, though.

…

^”Ackshually”

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ExoticSalamander4 t1_jdyj0u4 wrote

This is directly analogous to physics

Population is displacement

Growth rate is velocity

Growth rate peaking means acceleration is 0

So the article *title says acceleration will have fallen to zero by the time displacement is 8.6 billion

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SrpskaZemlja t1_jdz9k83 wrote

You have it off when you're bringing acceleration into this.

That would be the rate of change of the rate of change of population. Aka the rate at which the growth rate itself changes.

This article, beyond the bungled headline, says population will peak at 8.6 billion people.

When the amount of people stops rising and begins falling, at that moment, the growth rate is zero. The headline is totally screwed up and conflicts with the article.

There's no point anywhere here where a second derivative (acceleration) is brought in.

EDIT: Really, downvotes? You guys aren't even gonna try to tell me my math is wrong?

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quokka70 t1_je3hkp5 wrote

You are right. The article is saying that the population will peak in 2050, although its headline, which is gibberish, mentions the growth rate peaking, which is what u/ExoticSalamander4 was talking about.

Many years ago I heard a TV reporter say that inflation was accelerating at an increasing rate of speed. I'm not sure how many derivatives that is, but almost certainly more than intended.

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SrpskaZemlja t1_je3hvip wrote

Relevant funny Wikipedia excerpt:

"When campaigning for a second term in office, U.S. President Richard Nixon announced that the rate of increase of inflation was decreasing, which has been noted as "the first time a sitting president used the third derivative to advance his case for reelection."[2] Since inflation is itself a derivative—the rate at which the purchasing power of money decreases—then the rate of increase of inflation is the derivative of inflation, opposite in sign to the second time derivative of the purchasing power of money. Stating that a function is decreasing is equivalent to stating that its derivative is negative, so Nixon's statement is that the second derivative of inflation is negative, and so the third derivative of purchasing power is positive.

Nixon's statement allowed for the rate of inflation to increase, however, so his statement was not as indicative of stable prices as it sounds."

https://en.m.wikipedia.org/wiki/Third_derivative

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SometimesaGirl- t1_je078rz wrote

> The population may peak at 8.6 Billion, though.

I doubt it. The population of parts of Africa (Nigeria for example) is set to quadruple over the next decade or so.
The counterbalance is Europe + China declining. Both (largely) regions where religion has little sway over the population and birth control and the command of go forth and multiply are meaningless.
Now... getting back to Africa...
Oh, shit.

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patman_007 t1_jdy8onm wrote

But the growth rate won't immediately decline to 0 or a negative. It will first rise, then peak, then slow then reverse. And that peak will be at roughly 8.6 billion people....

This isn't saying our population will max out at 8.6 billion.

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SrpskaZemlja t1_jdz967u wrote

But the article is saying the population will max out at 8.6 billion. The headline was written wrong, as the article clearly goes on to say that our population will peak at 8.6 billion.

When you reach the peak of the amount of something over time, at that moment your growth rate is zero. That is not only common sense but also basic calculus.

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patman_007 t1_jdzwlm4 wrote

I'm chalking this to the author not understanding what they were writing. Because if you read the article they flip back and forth between stating the growth rate will peak at that population marker, followed by that the population itself will peaked then. And those are two totally seperate peaks, honestly don't think they could predict the highest possible population that would be harder to determine. NOW, looking through some other info it does appear it is the population that peaks around 8.6 billion.

You need to restudy calculus. Because that's exactly what my point is derived from - see what I did there?? The growth peak will not be the same time as the growth rate peak ( a secondary difference). The growth rate will peak, and THEN when the growth rate hits 1 to 1 the population will begin to decline.

What your stating would be true if humans had kids on a 1:1 ratio, but if the population growth rate peaks at 4 children per 2 adults than there will be a period of time when the growth rate declines from 4 children per to 2 children per and that will still see an increase in population, even post peak growth rate.

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