Archons does bother me, but it may have been the first time they threw aliens in Earth clothes at us with no parallel Earth justification. So I figure: alright, I'll buy that happening ONCE. It's like: I'll buy Earth clothes on a planet that's never heard of Earth ONCE in Dr Who, meaning the first one like that, Genesis of the Daleks. Maybe it could happen by pure coincidence once. But then in newWho, they threw a cavalcade of aliens in Earth clothes at us all the time. Apparently no one cares but me. Most people just assume their own clothes are so natural and normal to them, that aliens will naturally all want to look like that too.
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Hey wait, this thread is about Alt Factor. Discussion of this one always involves complaints about, I don't know, about fifteen different factors, "obvious" flaws, most of which never occurred to me as problems over 50 years of viewing. Many just are not problems, and are only made so because of unnecessary assumptions on the part of the complainer.
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I'll only answer regarding the immortality... What was always clear to me from my first viewing in 1967 onward, was that being in the interdimensional zone was not in anyway like life or existence as we know it. It never once occurred to me to interpret Kirk as spouting hyperbole about the Lazuruses fighting "forever". This was not a mild show. It has immense scale to it. Forever means forever. Just the bizarre, extreme nature of the gateway made it natural to expect a suspension of physical laws, including mundane physical survival needs. We may not be told exactly why, but it would be absurd to expect mundane normality.
Not magic. It only seems magical because we don't get the SF justification. They are rushing through a totally new situation so fast that they just don't have time to figure out and explain all the elements. Just to show that the immortality aspect is not something that has to be magic, consider Scotty's transporter trick to survive decades without supplies, in Next Gen's "Relics". Now, if one sees the transporter as magic, s/he's pretty much dismissed Trek entirely. We at least accept it as future tech. Well, why do we accept that Scotty's trick worked? Because existence is not quite existence in a transported state. Time does not pass for you, because you do not quite exist. Your existence is suspended.
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Same here in AF. The kind of reality of both universes does not exist there. That's why it can come into contact with both universes. Just by being in it, you no longer quite exist. You're there, but you're something... else. Not + or -.
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As long as YOU are suspended, so is your aging. So are your stomach and bowels.