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I know that there exist nonnuclear EMP weapons, but these do not influence the entire world. Could someone build a device that creates an EMP that is powerful enough to make all mobile phones on the entire world stop working? How expensive would such a device be?

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    $\begingroup$ It depends on the meaning of the phrase "make all mobile phones on the entire world stop working". If you mean "brick them", then I'm afraid there is no way to brick all mobile phones by means of a humongous EMP while not killing their owners. $\endgroup$
    – AlexP
    Jun 25, 2023 at 11:26
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    $\begingroup$ Only "mobile phones"? What you need are viruses more likely. $\endgroup$
    – BMF
    Jun 25, 2023 at 12:05
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    $\begingroup$ @camelccc: The Plain Old Telephone System (POTS) used looooong cables to connect the terminals to the exchanges. Long cables couple very well with EMPs. Mobile phones have very short wires in them and are most usually not connected to any cable. In fact, the user holding the phone is a two-meter-long conductor which will couple with the EMP about a hundred times better than the diminutive phone. This is why I asked what exactly is the goal, because, while bricking the phones is hard, simply disrupting communications by frying the transponders in the cell towers is a little easier. $\endgroup$
    – AlexP
    Jun 25, 2023 at 13:34
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    $\begingroup$ An EMP that could disable all cell phones even in a 200 mile radius area would bring down the electrical grid and probably blow up propane distribution due to EM coupling onto long pipes not sufficiently grounded. It's kinda hard to justify taking out cell phones without taking a lot of the supporting infrastructure with them. $\endgroup$
    – JBH
    Jun 25, 2023 at 19:33
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    $\begingroup$ @camelccc Sure, a powerful EMP attack on the world would only kill those trusting their lives to electronics (say, everyone in a jetliner) and probably a few freak incidents involving long wires, but if you blow the electronics it won't be long before almost everyone is dead anyway. It's a civilization-ending event. $\endgroup$ Jun 26, 2023 at 3:38

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To take out all the mobile phones in the world, you would need multiple EMP explosions. The range of a single explosion is limited to the line of sight as the operative parts of the EMP are the gamma rays that strip electrons from the air molecules. (https://en.wikipedia.org/wiki/Nuclear_electromagnetic_pulse)

Secondly, the main way to take out mobile phones is to take out the base stations. These are far more vulnerable as they have antennas and a lot of wiring that can pick up the electrical pulse. They are also connected into the rest of the telco systems which are likely to stop working with an EMP. Without the base stations, you can't do anything with a mobile phone.

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    $\begingroup$ Except that the base stations only serve to make the mobile phones work as telephones, which is by very far a minority of their uses. Most usually they are used as small computer terminals, navigation systems, media players etc. $\endgroup$
    – AlexP
    Jun 25, 2023 at 15:35
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    $\begingroup$ @AlexP True, but they still need the base stations in order to transmit data. The GPS is often augmented by cell tower data. $\endgroup$
    – David R
    Jun 25, 2023 at 20:54
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    $\begingroup$ @AlexP - For that matter, most "computer terminal" uses will require internet access. Media playing has largely moved to online streaming services. You might be able to receive a GPS signal, but besides any use of cell tower/wifi station signals for better triangulation, in almost all cases maps are downloaded dynamically. $\endgroup$ Jun 25, 2023 at 22:50
  • $\begingroup$ While many cellphones can connect to a wired ethernet if connected to a suitable USB-C dock, this still makes them less mobile and assumes a still-working wired infrastructure (however, a lot of that is fibre optic based these days, so not as vulnerable as one might assume). $\endgroup$ Jun 25, 2023 at 23:37
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    $\begingroup$ Also fun fact, if you have adequate warning of an incoming EMP, take your mobile phone and other devices, turn them off, put them into your microwave oven, close the door (DO NOT TURN THE MICROWAVE ON) and leave them there until the EMP burst happens. Microwaves use a portion of the EM spectrum (called a microwave) to heat water in food and cook the food. To keep the user from being cooked as well, the interior of the microwave has a faraday cage to prevents the microwaves from getting out... but it also prevents EMPs from damaging electronics inside the microwave. + $\endgroup$
    – hszmv
    Jun 26, 2023 at 18:08

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