There’s a difference between:
knowing how to make a bomb (simply possessing the knowledge with no intention of putting that knowledge into practice)
knowing how to make a bomb and intending to put that knowledge into practice in order to blow it up in an empty field just because you like pretty explosions
knowing how to make a bomb and intending to use that knowledge to make a weapon for use against other people or property
actually making a bomb with no intention to use it
actually making a bomb and blowing it up in an empty field
actually making a bomb and using it as a weapon
There’s no need for vague paranoia when you can be legally accurate. Numbers 1,2,4 and 5 are not illegal (far as I’m aware, although I’m sure someone will be along to correct me if I’m wrong). Numbers 3 and 6 are.
Obviously, if the police stormed your house one day and found a ready-made bomb you would have a hard time proving that it was just for scientific purposes (you’re interested in pyrotechnics) but the point is assuming that you could prove you made the bomb for innocent purposes then you wouldn’t have done anything wrong.
As regards googling for information on bomb-making. Can your ISP track what websites you visit? Even if they can, they would probably only be doing this if the police were already interested in you for other reasons.
And in any case, merely googling for information is not illegal in itself - although it may possibly be used as evidence against you if you were prosecuted for some other offence.
Personally, one of the first things I did when I got net access was look for all the “dodgy” websites I’d heard so much about. One thing I discovered is that there are people out there who genuinely do make bombs just for purely innocent reasons (coz they are pyromaniacs).
I have read various SAS type novels where they always make bombs out of ordinary ingredients lying around in your kitchen so I was interested in how this is done. You never know when you may need it. I’ve never tried it mainly because it is extremely dangerous, not because I’m worried about the legal implications.
But the reason I was interested in it is purely because it’s an interesting subject and I’m interested in ALL interesting subjects from an academic standpoint. eg you can make a functional bomb out of flour and water apparently, which is why flour mills can be quite dangerous places to work.
Nitroglycerin, on the other hand, is incredibly unstable and you would have to be an idiot to go anywhere near the stuff. Adding sawdust stabilises it somewhat. Nitroglycerin and sawdust is basically what dynamite is. The history of dynamite is quite interesting - I think a lot of people got blown up before they figured out that you need to add sawdust.
I wouldn’t worry about terrorists. I’m sure Osama already knows all this stuff. And home-grown terrorists will find out what they need to know anyway - they won’t come here for their information.