Tldr it's still definitely bad, but it's not the irreversible one-shot to a continent and the climate that it was made out to be.
Electrical and communications systems are built to tolerate natural phenomenon that have marked similarities to EMP, so while the EMP would definitely knock out power in the most impacted areas and to a great extent in more outlying areas, major components would be able to be brought back online in a timely fashion, and backup systems would remain available for key portions of infrastructure, such as battery and diesel generators to keep emergency communication systems online.

Communication infrastructure is particularly sensitive to EMP, but as a result it's been insulated due to practical necessity against environmental sources, as well as as a deliberate defense against EMP, since we've known about the risks for decades.

EMP does damage proportional to the size of the conductor it's attached to, since it causes current to flow, and the more there is, the more current flows. That's why power lines generate massive currents, and small things don't.
A cell phone has a very small antenna, so while it's fragile it's not getting hit as hard and can potentially just be disrupted but not physically damaged.
Computers are sensitive to single digit voltage fluctuations, but their parts aren't big enough to generate enough current to burn anything, and the source of the biggest current, the power grid, is already insulated from the sensitive parts because the grid regularly has fluctuations that could cause disruptions, and can be reasonably predicted to have potentially damaging fluctuations often enough to warrant components that burn out in a controlled fashion to protect expensive things.

Damage would be severe, widespread, and variously protracted. Not a quick trip back to the 1800s though. More like the great blackout of 2003, but with a bit more fire.

[–] groet 7 points 1 day ago (2 children)

If I remember correctly, EMP doesn't really work on very small devices. You need a "antenna" that is long enough to induce a strong enough current to fry your electronics. So anything connected to a long wire. The power grid is itself a huge antenna and will be completely destroyed but a small battery powered device will be unharmed.

[–] superkret 8 points 1 day ago* (last edited 1 day ago) (1 children)

When the power grid is down now, phones are down, the internet is down, mobile networks are down, payment systems and ATMs are down, gas stations are down, refrigeration is down, etc. etc.
Basically, 3 days later civilization is down, irreversably.

[–] ricecake@sh.itjust.works 5 points 1 day ago

We actually have extensive electrical backups for almost all of those things. The landline phone system was built in an era where people were significantly more concerned with nuclear war than we are now, so it would fare pretty well.
Home Internet would be down, but the actual data centers all have multiple backups for power.
The cell system would kick most people off, but it also has a lot of backup power built into it because it's viewed as an important part of disaster response in the modern world. Part of the reason it sheds load is to keep capacity available for emergency response.

Don't get me wrong, it would be super bad, more disruptive than a typical or even atypical power outage, and last a long time, but it wouldn't irreversibly take out civilization.

[–] hydroptic@sopuli.xyz 2 points 1 day ago* (last edited 1 day ago) (1 children)

Lots of our battery powered devices have a bunch of literal antennas, though. I actually don't know the frequency ranges on which an EMP can be expected to "pump out" significant amounts of energy, but if there's enough in the bands where WiFi, Bluetooth, GPS etc operate that's going to fry devices that don't have some sort of protection built in. I also have no clue how common it is for radio modules used in consumer stuff to protect against voltage surges on their antennas, but somehow I'd imagine it's not very common.

[–] ricecake@sh.itjust.works 3 points 1 day ago

EMP works a little different. It doesn't emit energy in a frequency in the sense that WiFi uses a frequency.
A changing electric field creates a magnetic field, and a changing magnetic field creates an electrical field. An electrical field makes charged particles move, and electrons move very easily in metal wire, so we get measurable current flow. This is ultimately the principle behind how generators work.

What an EMP does is basically turn any conductive material it hits into part of a very short lived generator. The bigger the conductor, the bigger the current. If something is big enough, it can generate enough current to damage itself, depending on how big or fragile it is.

A lot of small electronics have antenna, but they're very small, so they don't generate much current. If that current would be enough to overcome the voltage protection the devices have to protect against the voltage surge from nearby lightning or the like is beyond me.