Human history has seen accelerating growth, via a sequence of faster growth modes. First humans grew faster than other primates, then farmers grew faster than foragers, and recently industry has grown faster than farming. Most likely, another even faster growth mode lies ahead. But it is worth remembering that this need not happen. For a very concrete historical analogue, the Cambrian Explosion of multi-cellular life seems to have resulted from an accelerating series of key transitions. But then around 520 million years ago, after life had explored most multi-cellular variations, change slowed way down:
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1. We know that even current growth rates are not sustainable in the long run (maybe a few thousand years). So, we know growth is going to basically 0.
I don't know that. I think the growth in per-capita gross world product will continue to accelerate, barring global thermonuclear war or takeover by Terminators. This will continue until money is basically meaningless. (If everyone in the world has the wealth of Bill Gates, I don't see any meaning to money.)
"2. The Fermi paradox. One plausible candidate for the great filter is just that the universe doesn't cooperate with sci-fi scenarios and we are closer to the end of innovation than the beginning."
The "universe" stopping global economic growth seems like a mystical proposition to me.
"3. The fact that growth rates have noticeably slowed for developed economies also argues for deceleration rather than acceleration."The trillion dollar questions are why this has happened, and whether its likely to continue. My personal guesses are that: 1) population growth has slowed in these countries (they've aged), and 2) this is not likely to continue, because computer brains will replace (and vastly exceed) human brains.
The underlying mechanism is formed by breakthrough technologies: fire, complicated language, domestication of anmials, boats, agriculture, pottery, metal working, writing, mathematics, aquaducts/irrigation, the steam engine, hygiene, electricity, radio, the transistor, etc... and we know there are more to come (advanced bioengineering, clean energy sources, artificial intelligence).
Robin, how evidentially significant should we regard a trend of the sort you describe in the absence of an obvious underlying mechanism? What is the track-record of extrapolations from such trends? Are there other considerations that we can rely upon to estimate more precisely the degree to which that trend supports your predictions?
If not statistics, what kind of reasoning?
I'm not sure you can apply statistics to this, not until somebody offers a clear definition of a "mode switch" (right now we could interpret the term so that there were more than three mode switches).
And how strong a prediction is provided by a short string of prior (as far as we know, unrelated) transformations?
How, pray tell, do you compare the predictive power of these opposed (very weak) clues?
The fact that in the very long run growth must slow gives only a very weak prediction about how the next mode compares to the current mode. The more total modes there were and will be, the weaker this indication is.
Re 2 - If the "perfect storm" idea is right re the Cambrian explosion, that seems a pretty good explanation of the Fermi paradox.
Re 3 - That's just a catch up effect. It's easier to catch up than to break new ground. Doesn't have much effect on the global long-term growth rate.
I can think of a few contrary indications.
1. We know that even current growth rates are not sustainable in the long run (maybe a few thousand years). So, we know growth is going to basically 0. Why not draw a line from where we are at now to there? That's a lot simpler than predicting a large jump in growth rate followed quickly by a massive deceleration to below where we are now.
2. The Fermi paradox. One plausible candidate for the great filter is just that the universe doesn't cooperate with sci-fi scenarios and we are closer to the end of innovation than the beginning.
3. The fact that growth rates have noticeably slowed for developed economies also argues for deceleration rather than acceleration.
"So it remains possible that growth will slow down now, or after the next transition"
Uhm, yeah, but we already knew that. Natural resources are limited and at some point we will have exhausted all the low hanging and even most of the high technological-breakthrough fruit...
One can probably find many contrary indications: for example, regression toward the mean comes to mind as a logical argument as to why the rate of change will slow.
[As empirical evidence, the unidirectionality of three mode shifts doesn't even reach the .1 significance level.]
The data is that the three most recent mode switches along this path were to much faster modes. No switches to much slower modes. That seems sufficient to suggest "more likely than not", in the absence of substantial contrary indications.
>Most likely, another even faster growth mode lies ahead.
You like to speculate about a faster growth mode lying ahead but "most likely" seems like a stretch. Is there any reasonable way to put a probability on it?
This seems like a case where the outside view is very weak compared to the inside view. It'd be like trying to figure out the prognosis of a patient with pneumonia and, instead of looking at a meta-analysis or randomized controlled trial, we looked at a case study of a patient with lung cancer, a case study of a patient with asthma, and a case study of a patient with the common cold. (Not saying the inside view is much better.)