If all machines on planet Earth were destroyed (possibly by an extremely powerful electromagnetic pulse from an alien civilization), how large of a percent of the human population would die out?

Clearly, the most important factor in human survival would be food and water, and people in cities would probably die of starvation if they chose not to move somewhere where food is grown (after all the canned food was eaten hooray for canned food...again). In addition, water-purification systems wouldn't work anymore, so the only thing people could rely on would be fresh spring water, melted ice (which would be difficult to transport without machines), etc.

EDIT: Apparently EMP's cannot destroy old machines such as old tractors etc that can be used for harvesting food. So, could you guys focus on water purification instead?

On the other hand, certain civilizations scattered throughout the world are living perfectly fine without machines, so those people would definitely be able to survive.

So, the answer could be that whatever percent of the population does not rely on machines will live. But, is it possible for the percentage to be higher?

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    $\begingroup$ EMP would destroy sensitive electronics, but at worst would bump is back to 1900 level technology. There's be initial disruption and a few deaths, but within 3 years things would settle back to a new normal. Almost everything we do with electronics can be done without electronics, albeit with a loss of efficiency. $\endgroup$ – pojo-guy Dec 16 '17 at 21:59
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    $\begingroup$ Really all machines, including simple machines such as levers, pulleys and screws? EMPs are not magic, and most machines are naturally immune to EMPs; a phone in somebody's pocket, for example, is immune to any kind of EMP which does not also kill its owner. Guns are immune. Old tractors are immune. Steam locomotives are immune; don't tell me the U.S. Army does not keep a stock of steam locomotives... $\endgroup$ – AlexP Dec 16 '17 at 22:21
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    $\begingroup$ Water filters are not electronic, and so are generally immune from EMP. Er, you might want to do a bit more research on what an EMP is the realistic capabilities. Pumps generally suffer no damage. The centralized control of pumps might be vulnerable...in which case humans can usually disconnect those controls and operate the pumps manually, accepting a loss of throughput efficiency. $\endgroup$ – user535733 Dec 16 '17 at 23:55
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    $\begingroup$ @pojo-guy And that's ignoring the apocalypse survival folks who keep powered off laptops inside Faraday cages. survivorlibrary.com $\endgroup$ – Draco18s no longer trusts SE Dec 17 '17 at 0:50
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    $\begingroup$ I think this is 'primarily opinion based'. You will have to define what the EMP destroys for it to be answerable. One single EMP won't affect the entire Earth the same way, not even one originating from the Sun, since part of the Earth will be facing it and part facing away. Since the EMP damage level will vary in different parts of the Earth, the person who answers will have to decide for themselves what stops working. Therefore, this question requires opinion to answer, and should be closed. $\endgroup$ – kingledion Dec 17 '17 at 3:17

I won't discuss plausibility of OP premises, I will just assume all powered machines are gone in a flash, I also assume purely mechanical machines are mostly unaffected.

Actually the percentage can even be lower than that of people not actively relying on machines.

Actual percentages are very difficult to determine, but a series of things need to be factored in:

  • There are very few places in this world which are completely self-sufficient.
  • Most of almost-self-sufficient populations are in remote locations; they are the only ones almost sure to survive.
  • Several populations (e.g.: Amish) do not actively use machines, but are neither self-sufficient nor in a remote location.
  • Self-sufficient communities in any accessible place are likely to be flooded by people from non-self-sufficient neighborhoods.
  • Once population has trimmed-out enough almost all regions can be made self-sufficient.
  • Many (if not all) of current high-yeld crops won't be feasible.
  • Most of currently farmed land is not suitable as-is for reversal to "ancient" plantation style.
  • Most of current farmers have no idea of how to rise their crops without "modern" devices.
  • Most of the crops in this world are not usable for "normal" agriculture as seeds used do not give fertile plants, so seeding crops won't sprout (thanks, Monsanto!).
  • After a sufficient number of people has died a series of second-stage problems will kick-in:
    • Plague or similar disease will spread.
    • Large structures (dams, bridges, skyscrapers, ...) will begin to fail due to lack of maintenance.
    • Organized raider gangs will (try to) take over any self-sustaining community.
    • Many communities will drop below the minimum level needed to keep knowledge running.
    • Many communities will drop below level where biodiversity is enough to ensure healthy survival.
  • Reboot of civilization might be difficult because lots of readily-accessible resources have been depleted. Some materials can be recycled from scavenged sources (e.g.: iron, plastic, asphalt, ...), but others have been fractionated into useless debris (e.g.: quicksilver, wolfram, ...).
  • Much will depend on how fast some "monastic" knowledge-preserving communities can form.

Of course if "an alien civilization" is behind this then everything will depend on their long-term aims.

Update: Some comments pointed out purely mechanical machinery won't be affected by any EMP imaginable.

This is, of course, true.

OTOH in our world we are heavily (and even more so with every year) relying in electronic controllers to do the work previously done by simple mechanical devices. Whoever thinks we can go back is severely misguided; today's electronic controllers do much more than control machinery, they compensate for imperfection.

When controllers were rudimentary (e.g.: spark coils in cars or mechanical teletypes) all mechanics was highest precision because it had to work flawlessly on the given input, nowadays the same things are built in cheap plastic because the "smart controller" can track uneven movement, take it into account and (usually) produce a better result than the previous high precision (and expensive!) counterparts.

Trying to run a modern car engine without electronic control is a difficult exercise, very likely to result in a useless pile of busted junk.

Even the Army is (at least partially) abiding to this trend and relying more and more on "tactical coverage" impossible to get without electronics (e.g.: some tanks have no windows and rely on cameras to "see" outside).

  • $\begingroup$ what about water filtration? $\endgroup$ – NL628 Dec 16 '17 at 22:42
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    $\begingroup$ @NL628: It depends on on what exactly you mean. Ceramic filters used to make drinkable bacteria infected water (like those used in many back-country regions) will, of course, continue to work, even if ability to make new ones may be gone. Also more "state of the art" filters, (e.g.: reverse osmosis filters used to desalinize sea water) will work, but rather complex machinery needed to set pressure differential and control the system may not work anymore. I'll update the Answer to reflect a bit of further thinking sparked from this comment. $\endgroup$ – ZioByte Dec 17 '17 at 0:30
  • $\begingroup$ Oh, okay thank you so much! I understand now. $\endgroup$ – NL628 Dec 17 '17 at 3:20

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