One known cataclysm that could make the whole interruption of all the telecommunications but also every electricity network is a Major big Solar storm that hits the earth!
According to Google, cable on sea are mostly safe from big solar storm[1].
I think it would be good if you start it by explaining what damages can Solar Storm cause to earth in more details but let's take significant solar events as an example. As far as I know, even in the events of significant solar storms, the whole world won't lose the electricity and internet fiber optics will be safe (correct me if I'm wrong).
Yes, but as you said, without electricity it worth nothing! Even if is there some protected structures that will exploit fiber optics, there will privilege to use it to serve iportant communications first than the ordinary Internet!
Yep, it can make down electricity networks, burst any electronics... the most past known and reported event is the
Carrington Event https://en.wikipedia.org/wiki/Carrington_Event.. But bigger solar eruptions can occur and were observed, in November 4th 2003 an eruption even too big that saturated the measuring instruments were observed, initially estimated to be X28 class it was after reevaluated to be X45!
And what if some entities wanted to fool the word creating completely artificial blocks and adding them to the blockchain ? How to trust a copy of the blockchain then ? Do all late copies should not-trusted/canceled ??
That entity still have to produce valid block. It means attack they could do is limited[2] (e.g. creating empty block), while requiring lots of ASIC due to high difficulty.
I remembre around 2014 or so a website offering to buy empty used (addresses/wallets) .. If they do it in a limited network, they will not need very big ressources/hardwares ! (or no?)
How to trust a copy of the blockchain then ? Do all late copies should not-trusted/canceled ??
Trust? Full node software automatically verify whether the block is valid or not. And as stated by other member, node eventually will choose chain with most work after telecommunication problem is solved.
And if they are the only actors of the/that network ??
Authentication signature? There's no such thing on Bitcoin protocol.
I didn't say there is, It will need to be added !