If we are ever to become a Type III civilization ourselves (if we want to stick around in the very long run), we will certainly end up looking quite different than we do today, not just in terms of details (Jetson's hovercrafts versus modern cars versus earlier horse-carts) but in the very basics. Certainly humans qua homo sapiens sapiens aren't likely to be around; gene therapy, nanotech and bioengineering are on the immediate horizon and will change us drastically even if evolution doesn't. But indeed, we may end up giving up bodies altogether, maybe giving up individuality, giving up physical mobility, maybe giving up just about everything we unconsciously associate with civilization and society and humanity. Life - whatever shape it might take (perhaps not biological in the sense we think of today, but biotechnological) - will certainly look very different, and the technology used is hard to imagine.

Our typical ideas on communication with ETI revolve around the assumptions that our civilization will be confined to one chunk of space-time (whether a single planet or a whole system) such that interstellar travel - especially of the relativistic, time-dilating sort - around the galaxy (or between galaxies!) would be just a colonization sort of thing. However, if we are willing to give up the attachment to the paradigm of a "home system" (and thus a home reference-frame, and corresponding time), then instead we could look forward to a move away from any sort of star-system-based home to a nomad civilization where home goes with the civilization as they move through the galaxy (and experience time-dilation, if relativistic speeds are used).

My favorite example of a possible Type III civilization technology is Matrioshka Brains (see very cool article explaining them here). Matrioshka Brains (or something even harder to imagine that a Type III civilization might turn out to be/use) have lifetimes much longer than our own sun's, and could be extended almost indefinitely by being migrated (or migrating themselves, if they are conscious and in control of the process) to new stars for new fuel. In essence, this technology functions on the time scale of the universe (where a few hundred thousand years is a blink), its raw thinking power limited only by the laws of physics, and its physical location not connected to any particular place permanently but using stars only as energy sources (rather than homes). In essence, a Type III civilization using or made up of these technological marvels would exist in a way almost unimaginable to us Type 0 (approaching Type I) civilizations.

Certainly, existence as a nomad super-civilization is nothing like our current existence; but chances are we will not be able to maintain anything like our current existence if we hope to live long enough to reach Type III development, so even if a person is optimistic about the future of our civilization, they need to come to terms with the fact that what will live on won't be anything like us, won't be us but some other thing, some other civilization. And that is a sobering thought: even if we can achieve civilization immortality, we can't really achieve civilization immortality. By extension, there is no reason to think that our individual existence will be kept around for indefinite extension since our form of existence will not be kept around. So again, even if immortality is physically possible, it won't be personal immortality of who we are here and now, of human beings qua Shakespeare and Hitler.

So perhaps the lesson here is one of depersonalization and focusing on the larger side of things: do our individual lives matter on the cosmic scale? Not really, they don't. The universe does not care whether you or I live on; neither will a Type III civilization arising out of our current civilization in the future. But something, some sort of existence, life, conscious thought will likely go on, can go on perhaps forever (perhaps into new dimensions or forms of existence unimagined by our current understanding of physics and reality), and that is a damn cool thing if you are willing to detach a little from the need for personal immortality.

When you think about it, who we are - our identity - changes over time. I may have the same name (and other qualities) as the twelve year old my parents were raising ten years ago, but is that person me? Well, not really, or not entirely. Who I am has been shaped and molded by my experiences and my memories and my thoughts and emotions; I think and feel and experience in a different way than that person did. I exist now, he does not.

Yet should that twelve year old (could he understand the question) really bemoan his lack of existence today? I do not see why, any more than I should bemoan the fact that tomorrow I will wake up a slightly changed person having been shaped by today's experiences. When seen in this light, an individual identity's destruction is not necessarily a bad or fearful thing - it is natural and even potentially wonderful. And given this, we can perhaps come to terms with the fact that we as individuals will not live on indefinitely, even if our civilization somehow masters the Type III (or IV or V...) technology needed to live indefinitely.

And once we come to terms with that, then perhaps we can fully appreciate the utter coolness that resides in possibilities like Matrioshka Brains, and other possible futures we cannot even imagine yet.