re: Aliens come and take away every man-made object. Humans maintain their current knowledge..

We will all be walking there buck naked through the woods and fields because there aren’t any roads.

Comb our hair with a rock. Brush teeth with a broken twig. Leave our family under the tree we slept under. All naked and hungry while I go to an imaginary job under another tree because there aren’t any buildings to work in.

And the clothing thing is just to point out that we don’t have any basic necessities. All the way down to personal items like clothing.

Look around your house. All that would be gone. No stove, pots, pans. No Tupperware, knives, canned goods. No furniture, plumbing. No running water.

It would be unsurvivable for almost our entire population.

Humanity survived exactly that already. In worse climate conditions.

I may overestimate humans, but we have historical evidence that you severely underestimate us.

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Survivalist go on Alone and barely survive 6 weeks. Thats couples as well.

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Humans are tribal, we survive better in large numbers.

You need some people to be chipping flint, some to be stripping bark, some to be gathering fiber plants.

Heat, Shelter, Food.

On a good note all pollution would be gone.

Lots of people would die and quickly.

I say 90 percent of the world's population (in western civilization) is dead within 2 years.

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But that other 800,000,000 people would probably get us back on track.

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The vast majority of those people are from the least educated areas on the planet. They aren't bringing much knowledge with them.

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Well we went from no computers in the 1950s to 70 years later everyone has one in there hand and it calls people and take pictures. So 70 years

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If they took every human artifact off planet and we had to relearn/reproduce it from scratch it would take many thousands of years to get back to the computer age.

We do not have the memory on how to turn ore into metal without modern tools, much less refine materials finely or precisely enough for computer chips

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There would be no economic system left. The few pockets of survivors would be hunter-gatherers for generations, maybe some would manage to salvage limited agriculture, but who knows.

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not generations, no. As I said, in another post, it would take most of a year for the human population to crash down to a level the earth can sustain.

Immediately after that, people would be mining cold for energy and or for metal. The industrial revolution would happen in just a half dozen years or so. Technology would absolutely explode after that. So with the population.

My guess is 50 years, and we would be back to where we are now technologically.

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We do not have the memory on how to turn ore into metal without modern tools, much less refine materials finely or precisely enough for computer chips

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I think we do

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Well we went from no computers in the 1950s to 70 years later everyone has one in there hand and it calls people and take pictures. So 70 years

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You missed the most crucial part of the OP