Physics becomes inconsistent and everything explodes. Or the Matrix finally errors out and detaches everyone. You'll wake up and find yourself in some dystopian nursery, embedded in slime.

It would not immediately be obvious but would have catastrophic knock on effects.

For day to day living the first thing people would notice is their home WiFi stops working and their mobile phone doesn't work at all (calls, mobile data, WiFi). And - as most countries still do it - terrestrial TV broadcasts would suddenly stop (possibly affects rural areas more, many homes in urban centres use cable but obviously this depends on your country). Radio would stop working obviously.

Military-wise it would probably mean immediately going to a state of high alert as a simultaneous loss of communication to many places would be interpreted as an attack that needs immediately investigating. While the military network is resilient and has non-radio ways of communicating it's not expecting to switch to this in an instant and there would be great paranoia about what's actually going on.

All planes would cease being able to communicate with ATC which would effectively ground the entire civilian air space. Instrument landing systems (runway radio beacons) would stop working so all landings would be manual, if the weather was bad pilots would have to divert without being able to check availability with anyone. Clearing the air without radio is a mammoth task and there would almost certainly be accidents as multiple planes try to approach the same run ways, or land on ones that are occupied, or run out of fuel seeing congested runways below and nowhere to go.

Urban rail transit would grind to a halt with drivers losing comms with signal switch stations. Some have non radio alternatives but with every walkie talkie ceasing to work this may not be enough. The network (like the tube and the metro) would halt and slowly manage an evacuation.

There would be general chaos trying to get to work (inc hospitals and other key workers) as RFID security passes stop working and everyone has to be validated manually.

Overall, apart from with airlines, I think the first day it would be inconvenient but not lethal. But then what would follow would be a lot of urban society being unable to function safely. Delivery via air would grind to a halt. Any location requiring security would lock down as security staff would have no way of communicating out of sight unless the place still had wired phones. Governments would immediately be assessing how long their national stockpiles would last without air freight. Possibly highways would get nationalised under emergency government control to prioritise road freight.

China would possibly invade Taiwan. It would be disastrous attempting an invasion without radio but they would probably have calculated that it affect the Americans worse.

What do you even mean with "part of the spectrum"? It is all used for radio (except the part that's nearly unusable).

Would you only regard air, or all dielectric materials? Then 'cable' and other networks are down as well.

The most people live in the southern hemisphere, India and China. August is winter here.

Radio waves are the same as light, so if radio stopped working the way you envisage, light would too.

Electricity, electronics and electrons are deeply connected with radio waves, so anything electronic would likely cease to function.

Any flying plane with fly by wire would likely crash, traditional linkage type planes would need to land because their engines would cease to operate.

Helicopters would probably auto rotate to an immediate landing.

People would likely starve pretty rapidly, since society is built around electricity.

The phenomenon most like what you describe is called an EMP, Electro Magnetic Pulse.

Radio waves are a pretty big part of the EM spectrum. Do you mean like sudden intense jamming from outer space, or like physics just stops suddenly?

If its the former, its going to depend on what parts of the spectrum are being jammed, but most modern militaries are actually pretty prepared for radio jamming and have alternate systems for most critical applications. The scenario is fairly similar to the EMP saturated environment expected in a nuclear war. The military has spent a lot of time and money preparing to moderate the worst of those effects. Civilian systems would not handle things very well at all. Expect lots of catastrophic cascading failures and instances of permanent damage.

If its the later, all bets are off any time physics breaks.

Edit: thinking about it a little more, I think the biggest risk would be that a nuclear submarine might in interpret sudden intense jamming as evidence that a nuclear war had in fact occurred and decide to fire its missiles when it was unable to contact anyone on any frequency.

You don't think a microwave is radio? This post is nonsense