What theory says that human lifespan has no limits with technology assistance? Anything involving replacing biological systems with artificial ones is not really extending human lifespan, it’s replacing human life with something else.
But who says that's the endgame? Presumably an advanced enough medical technology could remove the internal byproducts of aging, and get your cells to stop dying / running out of steam / going cancerous. Obviously we have no idea how to do that, and maybe we never will, but it seems plausible.
The best possible outcome would be watching your digital copy having digital life, while you yourself wither away regardless. More akin to having a child than oneself preservation. Not really something special, having physical children still beats this.
I wouldn't personally do that unless I was already dying. But, I see no reason believe it wouldn't preserve the soul. Your organic brain is already doing it all the time on a small scale.
We also know germ line cells can give rise to new organisms which can give rise to germ line cells in an unbroken chain effectively forever.
This is quite far from making a human immortal but it shows that there appears to be nothing in physical law or intrinsic to biology that prohibits it. Therefore it is possible.
Star travel and terraforming Mars are also possible. Possible does not imply anything about difficulty. We don’t really know if radical life extension or borderline immortality are fusion hard, quantum computing hard, or starship hard.
Not in any sense that's applicable to humans.
The often-cited animal examples, like greenland sharks, tortoises, and lobsters, are slow-moving ectotherms with "cold" metabolisms. Adjusting for watts per unit mass of biochemistry, they might "live" less in all their centuries than you do in a single decade [0-3].
In that sense they're only "long-lived" in the same way a tree is long-lived. Yeah, it might not die. But it's also not doing much that produces wear and tear, misfolded proteins, scar tissue, plaque buildup, etc.
Microorganisms and cnidarians, which can be truly immortal, are even more divergent. For example a common form of "immortality" involves periodically regenerating body parts by reverting to stem cells. IIRC regeneration is ancestral to all animals, but mostly lost in mammals.
Humans can actually already regenerate to a limited extent [4]. But how are you going to regenerate an entire primate nervous system (which "immortal" animals don't have), without losing everything you are?
In fact, the use of regeneration to achieve "immortality", and even that only rarely and in very simple animals, suggests it may not be possible at all for living organisms to live indefinitely in the same body. Otherwise, why would evolution waste calories rebuilding a whole body?
I suspect some systems-theoretic effect like the Red Queen hypothesis [5], but on a micro scale. Change is the only constant, and immortality implies trying to stay the same when the only thermodynamically favorable options are to grow or decay.
0: https://www.nature.com/articles/s41598-020-76371-0
1: # Greenland shark metabolism over entire lifespan
sh -c "units '((30mg/oxygen)*(mol/g))/hour/(1000/1000^0.84*kg) * (434kJ/mol) * 200year' MJ/kg"
2: # Greenland shark lifespan metabolism, alternate estimation
sh -c "units '192kcal/day*200year/126kg' MJ/kg"
3: # Human metabolism over 1 decade
sh -c "units '150W/100kg*10years' MJ/kg"
4: https://en.wikipedia.org/wiki/Regeneration_in_humans
5: https://en.wikipedia.org/wiki/Red_Queen_hypothesisBut really the your argument is already shifting to "there is no life ver similar to humans that do it, so it must be impossible" which imo is a much larger stretch then assuming it's possible.
The OP is also massively underestimating plant complexity. We aren’t much more complex than a tree either.
We are higher metabolism than both though, and with that the OP has a point. We are already long lived for a high metabolism animal. Our metabolic rate makes it harder for our repair mechanisms to stay ahead of oxidative and radiation damage. That will make extreme life extension hard for us, harder than if we were reptilians or arthropods.
The fact we haven't seen an organism live forever is strong evidence that that's the case. You're the one making the case without any evidence!
This is not at all guaranteed until we actually manage to do it. And that's exactly what we're discussing, you can't just say "but it must be possible". There's no rule of the universe that says it should, and given life has been around for 4 billion years and there's no single species (specially animals which is what we really should consider here if we're talking about human lifespan) that manages to live for more than a few hundred years, I think that's strong evidence that life is approaching a fundamental limit here. Someone else said "maybe that's enough" - well, why?? Maybe 100 years is already quite enough then??
Reproduction does result in new matrix/scaffolding being built but the cells build that (and can rebuild it if so directed).
Of course some things "we" care about exist exclusively in the matrix (configurations of neurons, learned behaviors, memories, etc) so that could well be a limit for those parts of the body where we care primarily about preserving the matrix.
Anyway my point is that "reproduction" doesn't create whole new life, it's just a continuation.
Then you're just arguing that we're already immortal, after all we reproduce, but I don't think that's what we're talking about when we talk about longevity. Longevity is the continued existence of a particular being, not its continuation through descendants.
That’s not forever and it required a very specific environment, but biological degradation on that timescale can be effectively zero.
Also, some few (fairly primitive) animals are "biologically immortal," for example, lobsters (which are motile and vaguely resemble us more than, say, sponges and jellyfish) don't experience senescence.
That being said, I think we have a long way to go if we want to make any progress at all, and I doubt I will live to see it.
There is no "full understanding" of a complex system.