I probably have made the above concept clear enough on the website as a whole, but then again dealing with it separately in the objections section may be a good idea. In case anyone hasn’t read the explanations on ageing and rejuvenation first and jumps directly to the answers to objections, they might not get the full picture and think we’re just trying to make people live longer without curing them of the ill health of old age.
The concern of more life in a sicker body is well illustrated by the greek myth of Tithonus. In short, Tithonus was a mortal who was in love with Eos, the titan of the dawn. She fancied him back, but they had a problem: As a deity, she was immortal, but Tithonus was not. One day he’d give up the ghost and their idilly would be broken. Thus, Eos pleaded with Zeus to make Tithonus immortal as well. Problem solved, right? Yeah, not really.
Eos may have got the looks, but unfortunately for Tithonus, not the smarties. She asked Zeus to make Tithonus immortal, but she didn’t think to ask for eternal youth as well. Result: Tithonus never died alright, but he got biologically older and older, and consequently sicker and sicker. When he eventually became such a wreck that he couldn’t even lift a finger, Eos locked him up for his own safety, and eventually did what any loving companion would do in the same situation: She turned him into a grasshopper and sent him back to Earth. We don’t know how long it took before any of the many grasshopper predators around managed to eat him, but given it was an old and sick grasshopper, it probably didn’t take too long.
Now, you may think that Zeus was an arsehole for not pointing out the small print, and you’d be right, but you may also think that Eos must’ve been quite the dodohead not to realise such an obvious catch—and you’d be wrong. It was unjust of me to say she got no smarties.
We can’t blame Eos for not realising that Tithonus would live forever but grow sicker and sicker, because in real life this is a physical impossibility. (Well, gods are such for a reason, I guess.) The ancient Greek didn’t know this, but biological ageing is a constant, progressive, chronic accumulation of damage that builds up throughout life. For a long time, this damage doesn’t really affect you, because your body is set up to tolerate a certain amount of it. However, eventually the damage will reach a threshold beyond which your body’s self-repair biological machinery is unable to compensate, and you’ll start gradually falling apart. The later stages of this process are what we call the diseases of old age; the final state is death, i.e. the point when the body is too damaged to function.
The reason I say what happened to Tithonus is a physical impossibility is that he could not keep on living and ageing biologically forever without hitting the death threshold. He hit the threshold of pathology and he kept worsening for centuries, but that can’t be. That would imply that the death threshold is infinitely far away, and that his body could essentially reach a state of infinite entropy and still somehow function. (Now that’s a sure-fire way to piss off all physicists past, present, and future.) The oldest humans have lived to maybe 130, and they’re quite the exception. Barring radical interventions, keeping you alive ‘forever’ (or even just much longer than our current lifespans) is impossible. Those who object to rejuvenation by saying that quality is more important than quantity may be reassured: Quality is what we are going for; quantity is only an obvious consequence of quality. There’s no chance to get to significant extra quantity without first getting significant quality.
That’s why we’re not trying to keep you alive forever in a decrepit body. Not only would it suck, but it is also not possible. What rejuvenation is all about is periodically repairing the accumulation of damage in your body, so that the pathology threshold is never reached. No matter how old you may be, rejuvenation would restore your health back to that of a typical 25-year-old or so. As consequence, the death threshold is never reached either. You may well happen to die because of an accident, or of an infectious disease that we don’t know how to cure, but you wouldn’t die of age-related pathologies because you would never get any. That’s why the average lifespan of a person in a post-rejuvenation world may well be centuries long.
I’m sure you understand now why the concern of a longer/infinite lifespan in a decrepit body is commonly known in the field as the Tithonus error.
Objections to rejuvenation
Objections to living ‘forever’
All answers in short