My parents and I were talking about the Internet, and I got on the question of what would happen if the Internet, for whatever reason, just stopped existing. I know it’s impossible, short of destroying every ISP in the world, but what would happen if it did? The whole Internet, from yahoo to eBay to goatse.cx. Would there be just inconvience, or would the world economy go down the porcelain equalizer?
Well, the world did just fine before the Internet existed, and I suspect it will be fine if it stopped existing. Though, yes, it would be, in many cases, a monumental inconvenience. We’ve come to rely quite heavily on it, as we have with every other modern technological conveniuence, such as the cell phone, microwave ovens, and computers.
People would go back to picking up women the old fashioned way, parents would have an easier time telling their kids to stay away from strangers and Q.E.D. would never reach 10k posts by 2004 :~(
Geez, the Internet isn’t that old, and not really that essential to modern life (not yet, anyway). I still remember the days before the World Wide Web became popular, and I remember long years spent happily ignorant of what DARPA and that guy from CERN had cooked up, even though I’m only 21. Actually, I even remember what it was like before my house had a telephone, but that has more to do with where I grew up (the Philippines) than with any time-travelling machines in my basement.
I can gladly give up computers, tv, telephones, the Internet, electricity, and even running water without too, too much bloodshed. You will, however, have my flushing toilet only after stepping over my cooling corpse.
If we had warning, then yes, I’m sure that we could adapt back to an off-line society. But were it sudden, it would be very jarring.
Banks would suddenly be isolated from each other. You might not be able to cash a check at any bank other than the issuer. For that matter, you might not even be able to do that: I’m not sure where banks store account information, but if a branch doesn’t have access to that information, they’re pretty much paralyzed.
Research of all sorts would grind to a halt. In addition to the Internet’s value for collaborations (I can send an e-mail to a physicist anywhere in the world, and get a reply within a day), most journal subscriptions anymore are electronic. Without the Internet, I wouldn’t have access to any of the papers I’d like to use.
I’m not sure of the exact extent, but military and intelligence operations probably rely heavily on the Internet.
And most tragically of all, there would be no SDMB.
One of the reasons I was able to move to this island in Maine after I retired was having access to the internet for items I can’t get here, like books, birthday presents for my family, a travel agency, a drugstore with the exotic supplements I take, etc. Two people on the island make their living on E-bay. I love it here but I’m not the hermit type; I want quiet and peace but not at the price of no contact with the world. I have to have my Drudge and AP breaking news.
Message boards like this one would really slow down. Imagine if every time I wanted to post a message or a reply, I had to travel all the way to Chicago and pin my replies to the message board, then read other replies and head back to Houston to compose my replies. Oh sure, I could hang out in Chicago for a bit, but since it would probably take weeks for any replies to my messages to appear, I might as well head home.
The mods would likely all go broke attending to their duties, but most of whatever trolls get out of doing what they do would be gone.
We might never hear from Sublight or Miss Magic8ball again.
And Dopefests would have to start organizing a couple of years in advance.
But hey! No more spam!
We’d all have to go down in our basements and find those 5 1/4" floppies that have our copy of WWIV, get our local dialup BBS’s running, and subscribe to FIdonet 
All this kind of electronic communication existed before the internet. I worked at companies that had such communications between offices, using IBM’s SNA communications protocol. Fairly common among larger companies.
I imagine without the Internet we’d just go back to that.
Of course, if the OP’s idea was that all digital electronic communications were gone, then we’d be stuck. Of course, the whole question is just silly anyway.
Why wouldn’t there be a SD? It would just become a regular ol’ BBS, although hopefully not run on WWIV like Lumpys says…
*WWIV = Watch While I Vomit
um…a great number of people would have to search through the yellow pages to find a library?
Our SD forum would consist of nothing but letters to the editor of the Chicago Reader.
I do a lot of dog adoptions to people who heard about my rescue through the internet. So I guess for me a if I lost the internet it would mean a lot more dogs in shelters would not find homes 
The porn business would take a serious demand side hit.
There are many companies that rely on the Internet for business. Harware manufacturers like Cisco, Sun and IBM, for starters. And of course the various portal sites (like Yahoo), online services (publications, subscription services like personals and porn) and mail order companies like Amazon. The economic effects would be enormous.
I might get some proper work done for a change
shudders
thats not funny - don’t even joke about that.
[sub]real work?! oh the horror…[/sub]
Magayuk, do you have more dogs adopted now than before the Internet?
Making the Internet cease to exist would require destroying the entire worldwide telecommuncations infrastructure. If the Internet ceased to exist, so would almost all telephone service (they use the same communication channels) as well as a lot of other services. Obviously the impact on business and culture would be dramatic.
That said, even if you destroyed all the existing communication channels, we’d have the Internet back up and running in a matter of hours, on amateur radio AX.25 packet networks, if nothing else. It’d be slower, but it’d be up.
Ah, but the opportunities for reopening old-fashioned storefront pornshops would be great for the enterprising! 
Wasn’t part of the net’s genesis the idea of making it resistant to destruction?
Were we to lose only the WWW, reverting net access to the statu quo ante 1992, a lot of the economic/academic heavy lifting of online data would still be able to go on; but in any case, the hit on the mass-market end-consumer side would be so brutal – even if we resurrect it thru a back door as indicated by KellyM, it would throw us into a serious recession.