But I bow to your decision after all I found the Cardassian numbers on the internet and am not sure how official/known they are.
I've never heard of any officially established Cardassian number words. I looked it up, and what you're referring to is apparently
this, which was created by fans on a Usenet newsgroup.
Great, and here I was thinking that you wouldn't look kindly on my attempts to undermine your research.
As a rule, we can't make much progress in life if we're unwilling to be corrected. Certainly in science, published research is expected to be challenged, tested, and refined, and that's part of the process of writing hard science fiction too. Heck, Larry Niven got a whole book,
The Ringworld Engineers, out of a fan correction of an error in his calculations in the original
Ringworld. The fans pointed out that the Ringworld would be unstable since its center of mass was within its primary star rather than orbiting it, and so he wrote a sequel to explain how that instability was dealt with.
I have universe A with alternative timelines A1 and A2 (A2 branched from A1) and universe B.
A person from B visits A1 returns to B and then visits A2 - or first visits A2 and then A1. Do the A timelines converge?
Well, generally a "universe" really is an alternate timeline, if it has an Earth and humanity and familiar individuals. But I did make a distinction between alternate timelines created by time travel (e.g. the one where Edith Keeler lived and Hitler won) and those that diverged spontaneously (e.g. the Mirror or Myriad Universes). The convergence only happens between the timeline where the time travel in question occurs and the timeline that was created by the time travel, because it's the time travel itself that creates the entanglement between them. It was necessary that it not happen between spontaneously generated alternates, or else the Mirror Universe couldn't have endured. I worried a bit about "In a Mirror, Darkly" and the
Defiant traveling through time to affect the history of the MU, but the rule (which I admit is a fudge and I don't have a very solid rationale for) is that it only happens if the time travel
creates the timeline in the first place, thereby "imprinting" it with a phase signature of the original timelinee.
Is entropy measurable? If yes, couldn't it be used to pinpoint when and where time travel occurred and from what time period?
Entropy isn't a universal constant. It's a property of a particular closed system. You can measure the entropy increase of a particular mechanism doing work, but that won't be the same as the entropy somewhere else.
Enterprise gave us the idea of "quantum dating" to determine the year of origin of an object and whether it was in the past or future. Which is nonsense, but we're stuck with it.
And lastly what is your take on whether the Time Planet is safe from time tempering? Or if it forces timeline jumping, if I got the theory right? It seams to be in the City episode (Kirk and co are unchanged, but Enterprise disappeared) while in Yesteryear also the researchers and McCoy are affected. The novel Imzadi followed the City principle... Also if it is protected could it be used to store information before a shielded database is developed? Or does it only work if the Guardian is used for time travel and not a different tool, like the slingshot?
I address the Guardian more fully in
DTI: Forgotten History.