Assuming a modern urban fantasy setting (thus, the world is "ours" in the present time, with the known continents, cities, technology, and general environment), what would happen if a supernatural EMP-like event were to knock out all electronics around the world at the same time?

For plot purposes, I need an event able to disable or destroy all manmade satellites (and thus a lot of communication), take down the power grid for (preferably) days, and render communication via cell phones and computers virtually impossible for the forseeable future. Other effects optional! Would an EMP-like event be the best way to do this? If so, what would happen to these specific devices:

a) How would cars - from old, non-computerized models up to the Tesla - react? Would they be disabled, and if so, for how long?

b) How would hospitals react? Would an event capable of knocking out power on this scale temporarily or permanently disable their backup generators, or would they be able to switch over with little to no disruption?

c) Would Internet cables and/or landline telephones be affected, and if so, how?

d) If the event acted like an EMP that successfully (and permanently) disabled all manmade satellites, including communications satellites, what would the effect be on cell phones, Internet availability, and general global communications? Would something that behaved like a real-life EMP be able to knock them out for days or weeks at a time, or would the supernatural event need to have a bit more, er, supernatural to get that effect?

d) Are there any other major side effects, either on manmade structures or on the environment?

e) Bonus: Would this be theoretically achievable with an appropriately-sized EMP or solar flare (thus giving the in-world government a plausible explanation to reduce panic)?

  • $\begingroup$ Why would it have to be supernatural? Solar flares can do the same thing. $\endgroup$
    – Frostfyre
    May 26, 2015 at 3:42
  • $\begingroup$ @Frostfyre: Because the premise is urban fantasy and the event is caused by a big supernatural baddie? :) $\endgroup$
    – thatgirldm
    May 26, 2015 at 4:00
  • $\begingroup$ an EMP is not all that reasonable, see below answers. However, if you want to take out cellphones and THE INTERNET there are tricks you could use to take down communications. Computers would still exist, but far less powerful. Consider asking how to justify taking out communications if that will fit your needs. $\endgroup$
    – dsollen
    May 26, 2015 at 14:58
  • $\begingroup$ @dsollen Yeah, I'll probably ask that as a separate question per Michael's advice on one of the answers. $\endgroup$
    – thatgirldm
    May 26, 2015 at 15:19
  • 1
    $\begingroup$ Related question asked here. $\endgroup$
    – thatgirldm
    May 26, 2015 at 19:51

3 Answers 3


I'll answer in point form.


Referring to this document, it seems that most cars are fairly resistant to EMP. Some government testing showed that cars that were switched off suffered no adverse effects, and some switched on cars stalled and required to be restarted by their drivers. Another test suggested that a 'latching' fault developed in several cars. This fault could be reset be disconnecting the battery for a short time and allowing the circuits to de-energise.

That said, there's a bigger problem. Your cars still need fuel. Cars get fuel from bowsers - which are almost always electric, and almost always grid-connected. If a planet-wide EMP disables the electricity grid for an extended period of time (I expect it would), then cars will fall silent because they simply run outta' gas.

The lack of electricity is going to be the biggest problem. Virtually everything reliant on electricity is taking holiday-without-pay. You don't have to destroy telephone/Internet networks. Killing the power will do that for you just fine.


For similar reasons to cars, hospital backup generators should survive unscathed. Possible exception being generators that were running at the time of the EMP. Again, their long-term viability hinges on a reliable fuel supply.


In many cases, they'd be wrecked. Twisted-pair wiring should be resistant to an EMP if the devices on the end are floating(read:not grounded). Grounding gives a current-path and that's will cause damage. Modern cordless phones all have a ground path - they plug into the mains supply to power the 'cordless' component. Older phones may survive.

The exchange at the other end of the phone line will be grounded, and connected to lots of things that are grounded.


Many species of birds and fish will get very confused as they will interpret the magnetic component of the EMP as a sudden, wild, change in the Earth's magnetic field.

Modern phone networks don't rely on satellites for general use. Most of those are covered by the ever expanding cellular network.

However, they will rely on GPS satellites for navigation. Losing those is going to be very inconvenient for everyone. Particularly aircraft and boats.

You'd expect fibre-optic cables to be very resistant to an EMP. This would be true for smaller(read:thinner, not shorter) cables. Larger bundles will also contain metal wire to supply power to remote signal boosters. These are vulnerable to an EMP - they may get hot and degrade/damage the fibres.

Finally, people in the cold need to hope and pray they have gas-heating.


Scientifically, unlikely but possible. An EMP that strong is possibly beyond the Sun's capabilities. However, it's a perfect scapegoat because those that are knowledgeable enough to dispute it... would need the Internet to spread their dissenting views. After an EMP that big, Internet access is going to be difficult for the luckiest few, and impossible for the bulk of the global population.

A secondary question is; how would governments be able to relay news to everyone about the EMP, be it truthful or propaganda?

  • $\begingroup$ Re: how the governments would spread the news, probably old-fashioned means like word of mouth (ve-e-e-e-ery slow) and possibly radio. Assuming radios survived the EMP, I suppose. $\endgroup$
    – thatgirldm
    May 26, 2015 at 4:04
  • $\begingroup$ @thatgirldm, if you disconnected the antenna from the radio prior to the EMP, it'd probably survive. However, I don't know what can be said about the transmitter. Maybe the government will resort to the good ol' Hear Ye! Hear Ye! town crier. $\endgroup$
    – user6511
    May 26, 2015 at 4:13
  • $\begingroup$ Whoa, so even if the radio was turned off at the time of the EMP it'd be fried? Yikes! I guess short-wave walkie-talkies will make a comeback... $\endgroup$
    – thatgirldm
    May 26, 2015 at 4:26
  • $\begingroup$ I'm making the assumption that when the EMP strikes, the antenna is still electrically connected to the sensitive parts of the radio. Any protections that people use against lightning strikes should be effective against EMP, so you'd find that radios owned by professional- and amateur-radio operators survive. $\endgroup$
    – user6511
    May 26, 2015 at 4:51
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    $\begingroup$ Going with this answer because it most directly addresses my questions. Thanks! $\endgroup$
    – thatgirldm
    May 29, 2015 at 0:20

This would be quite the event, wouldn't it be.

Unfortunately, you're going to find the goal of "render cell phones and computers useless for the forseeable future" to be gargantuan.

EMP basically has two major effects. One is that it can kick electrons lose in funny places, leading to "latch up" or basically something everyone swore had to be a 0 turning into a 1. However, this only matters for devices that are turned on. It's relatively easy to latch modern memory because its small and fast. Slower things that keep their information for long periods (like flash memory) tend to be relatively unaffected.

This means you're looking at the second effect. Enough radiation is sufficient to break down oxide layers in mosfets, rendering the chip permanently unususable. This occurs in the 5000 rad region.

To use the newer units, 5000 rad is 50 seiverts. With that in mind, now we can consult our good friend XKCD's radiation table. As it turns out, 8 Sv is lethal, but XKCD gives us a bit more information: 50Sv is equivalent to spending 10 minutes next to the Chernobyl reactor just after it exploded and melted down.

So in short, your people are going to be remarkably unhappy being exposed to that much radiation. Cars would be disabled because nobody would be around to run them. The self driving tesla's might take over the world, assuming the cockroaches don't take them over first. Hospital wait rooms would be quite nice. No more waiting 3 hours to have a doctor see you... then again, no doctors to see you either. There probably would have been some arcing around telephone lines, but with no one to dial 911, it's probably a minor detail. There may be a minor side effect, such as a mass extinction of virtually everything on the planet (I'm rooting for the cockroaches, myself). I'd have to check to see if a a solar flare could do it, but the sun is pretty darn big. We'd only have to see radiation levels roughly a million fold higher than what we see today. That's not all that tough for the sun.

  • $\begingroup$ Hmm... I was thinking "render cell phones and computers useless" would be as much a side effect of the communications satellites (and the power and probably the cable wires) going out as the actual devices being destroyed, but you make a very good point about the radiation effects. $\endgroup$
    – thatgirldm
    May 26, 2015 at 4:51
  • $\begingroup$ @thatgirldm Ahh, there may be an edit needed, in that case. I happen to have a computer sitting next to me that's unplugged for reasons very much unrelated to EMPs. All I'd need to do is find someone with a generator (it'd be hard to break them with an EMP), and I would have a computer that is "useful" by my definitions. It certainly implies that large corporations (who regularly have their data backed up) would be able to stand up new fabs to make new computers in a very short period of time. $\endgroup$
    – Cort Ammon
    May 26, 2015 at 4:56
  • $\begingroup$ Edit made! I'm looking for something that would effectively block any kind of easy communication for up to several weeks afterward, and based on what you're saying it sounds like modeling this event after an EMP may not be the most effective solution. $\endgroup$
    – thatgirldm
    May 26, 2015 at 5:28
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    $\begingroup$ @thatgirldm In that case, it might be a better idea to state your effect requirements and solution constraints, and ask how to get the desired effect while taking those constraints into account. That allows for answers suggesting alternative possibilities, and doesn't focus peoples' attention specifically on the effects of an electromagnetic pulse. I would definitely recommend posting that as a separate question though, so as to not invalidate the answers already given to this one. $\endgroup$
    – user
    May 26, 2015 at 7:30
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    $\begingroup$ @MichaelKjörling: Done! Question is here. $\endgroup$
    – thatgirldm
    May 26, 2015 at 19:52

You might need something like the Carrington super flare of 1859.

At that time all that could be affected by it were telegraphs, but according to some studies it might be a lot worse today.

A similar event was observed during 2012 (that year was quite the apocalyptic one) but luckily it missed earth.

As for side effects, the northern lights shining as south as Cuba were observed, so at least the sky will be pretty.


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