By Doug Schwan, found on Quora.com
This is a good description of what life will be like on the Earth after The Harpazo Event. You do not want to be here.
If you took the entire population of Earth and transported everyone back to the stone age, the first thing you would have would be large-scale slaughter and death of a large percentage of the population. The skills that, say, make the Kardashian’s rich in modern times do diddly-squat in the stone age. Modern people, in general, would not have a clue about the survival skills necessary just to stay alive. Starvation, disease, war-like groups banding together for limited resources— remember, no convenient grocery stores anymore. It’s every man for himself!
Once that all got sorted out you might be left with 30% survivors out of that original population who, more or less, form a stable population.
Once that is accomplished you develop agriculture and a division of labor that starts to permit free-time. This free-time can be used to start along the path of re-discovery. Metallurgy, woodworking etc would have to be developed from scratch all over again. The knowledge base is there but the infrastructure has to be developed all over again.
Think of something as simple as a pencil: You need knowledge of woodworking, metallurgy and rubber molding just to get a #2 pencil invented!
The pace of technological progress would be much faster than we originally evolved our civilization because we have the basic knowledge and don’t have to probe in the dark, we already know what works. Still, it may well take a thousand years to progress back to the original point of civilization as opposed to the 10,000 years it originally took.