Can the internet function without undersea cables?

The internet can and sometimes does work without undersea cables, but a physical connection is always faster than wireless in any form. Undersea cables are usually fibre optics so you are communicating millions of connections over very few cables..at the speed of light! if you used satellite or wifi/radio then you are limited by that slower technology that cant reach as far.

The internet will 're-arrange' itself.

Its smart enough to do that.

I'm referring down to the lower level of that OSI model,  so we're looking at the layers 4 and 3 , Transport and Network.

Data is sent back and forth across the internet infrastructure in packets with headers etc that contain info aobut where they came from, where they are meant to be going and what kind of content they hold.

If its lots of data the packets could be broken up into more and re-assembled at the other end of destination or something.

Its been almost 20 years since I graduated with my BSc Honours in Computing & Multimedia degree, and I recall taking an optional module called Networking and Internet.   I wish i'd spent more time concentrating in that module as much of what I want to know today,  was being taught in those lectures!

The internet is just the hardware cables routers repeaters modems servers etc etc

The internet is a connectionless network as there is no dedicated 1 to 1 connection established between sender and recipient,  unlike say FTP wher there is.

Short answer, Yes.

However much of the internet land and sea based is all just that,  its a big mess of under sea cables and masts and what have you.

Its such a mess that to refactor and revise it would be impractical if not impossible.

those data cable though,  if a few get 'cut' there would be reductions in speed and we'd see bottle necks as traffic would need to be re-routed other ways.

like roads closed,  now you have to find a different route to your destination.

Wireless doesn't have the same reach, speed, and reliability.

One of the limiting factors with communications is the speed-of-light delay, which is 300,000 kilometers per second in a vacuum.

It's around 2/3 of that in a cable.An undersea cable follows the surface of the Earth, so generally the shortest practical path; that makes the London - New York distance around 5,600 kilometers so giving a round-trip delay for request and response roughly 1/40th of a second.

To use radio links it need microwave frequencies, to carry fast data. Microwave links are "line of sight" only, so to get a longer distance than antennas on towers can manage (or across oceans), the links have to go via satellite.

The geostationary communications satellites are in orbit 35,700 kilometers up, so the total round-trip distance is roughly 143,000 kilometers.

That makes the delay for each request to response roughly half a second.

Trying to play any online game with that type of delay is pretty much impossible.

Even loading web pages that typically have to make dozens of requests for different data and images would be tedious.

There are low-orbit satellites being launched in vast numbers, with the intention of providing internet services to places that cannot get it any other way. The low orbits mean the extra path length is fairly minimal - but the equipment to connect with the satellites must continually switch and reroute the connections to whichever satellites are overhead at any instant.

It's not an ideal system but better than nothing at all.

Line of sight. The farther away two antennas are from each other, the taller they have to be to communicate. Otherwise, the Earth itself gets in their way. At some point, it simply becomes impractical, and then impossible, to build antennas that can do that.

So race track results can come in faster than satellite transmitted results. Ever watch The sting?