From what I've seen( replacement at molecular scale of human mind's substrate taking place, apparent nature of reality, etc.) it'd seem like one may very well continue to exist irregardless of the destruction of the body. But it's the information, the memories, the personality, that which is dear to one that is lost. One transitions from one state into another without willing it, one does not have the internal control of what awaits one. Given that, I believe Immortality to be the perpetual capacity to choose when and how one'd transition from a particular state of existence into another, a form of freedom if you will, freedom to choose what awaits one.
( 'cause the word always sparks an image of me taking a nuke right in the chest with no effect )
In a world made of concepts, of information. The way to achieve persistence, is to take the nature of the world into account. What can we do to protect information? We can extensively duplicate our data and use top-down, bottom-up error-correction/protective input in order to faithfully preserve it and safeguard it. The information is made more resistant to all forms of attack, this idea has been suggested by many by expousing the creation of copies/up-load. Provided you've proper redundancy, spacing, defensive means nukes cannot destroy this.
Another way would be to develop the information, to scale it up, to make the pattern more elaborate/extensive/distributed. This is my favorite method. The entity ceases to be simple, and its mind grows, it becomes distributed, with the backing of vast substrate, and continues to expand. As it continues to grow, it becomes ever more resistant to all forms of attack. Nuclear attacks are pretty useless against this, after a short while.
As for allowing individuals to enjoy extremely long/nigh indefinite lifespans, my views are quite simple. Man has shown incapable of withstanding the forces of cultural/mental entropy. Wars, genocide, famine, crime, etc, etc, etc are innevitable in a world governed by men. Increasing IQ alone(maybe after a certain very high threshold, but still we know not whether such alone would necessarily guarantee empathy in a human sense) seems not to suffice, given that there seems to exist high IQ individuals engulfed by zealotry, blind faith in ancient books filled with nonsense, and the like.
In order to guarantee human rights, and to ensure a long-term stable form of government, one that is just, and does not fall prey to corruption, active measures seem necessary. In other words in order for us to ensure that life is protected, and that long lifespans are possible we MUST ENSURE THAT an ADEQUATE GOVERNING FORCE IS PRESENT, one not subject to the whims of the corruptible or worse, corrupted. One capable of overseeing all nations, and managing resources as we expand into the stars. One backed by overwhelming force, enough to ensure, to guarantee human rights, to break any barrier that may stand in the way of this. This is, IMHO, of the
UTMOST importance to those who cherish life and believe all should be free to enjoy it.(will elaborate further in subsequent IDEAL world multi-board/forum post, that's coming soon.).
PS A HINT at where I'm going, what I mean... We've seen throughout fantasy literature, though folklore, etc. People that are fair, people that are just, and graceful. Often have we not wandered? these people should they not be ruling these lands?!? In these worlds, countless presented to us, should it not be those who're wise, those who're intelligent, those who're caring that should be the voters and the constituents of the highest form of government.
Well, irregardless of local/internal gov.s of individual nations, which can be left for the citizens of such nations, a new nation can be created, an ideal one, backed by absolute military might, to oversee and to manage, to be what the U.N should have been. One that would take decisions above the nations of men.
We KNOW what the bounds of causality are, environmental and genetic influence. Thus we can bring about an IDEAL PEOPLE by giving them the right modifications/attributes... highly EMPATHIC, highly INTELLIGENT, HIGHLY INFORMED, people who're passive and caring by nature, who're not blinded by rage/fear, nigh immune to these, who are benevolent, who're graceful, who're beautiful, fey in nature. Individuals from any nation could join and become members of this ideal universal overseeing nation, simply by taking the necessary behavioral, informational, genetic, etc modifications. This nation would posses a TRUE DEMOCRACY, and individuals within would vote and would compose the final government above all others.
Outside of the ideal nation, other nations would be internally governed as they saw fit, provided they did not try and violate human rights. Colonies/territories could be assigned to groups with certain ideologies or certain modifications that may be persecuted or attacked by opposing parties in other nations, military protection given and their rights of free expression and life protected from fundamentalists/deathlists/terrorists/etc.
This is a general overview of the concept for an IDEAL world at present, subject to modification, and open to suggestions. For the world calls for change, and a new form of government is needed to ensure the rights of all.