Views on immortality
The Greeks took for granted that the Olympian gods were immortal but disagreed on whether humans possessed immortal souls. As a matter of philosophy, Plato claimed they did. He based his argument largely on his concept of ideal forms. Plato believed that everything has an ideal, what we might today call an archetype. Since people seem to have inborn knowledge of these abstract forms, he argued, it follows that we must come from and return to that realm of the ideal.
Scholar Tad Brennan elaborates on Plato's view:
"Forms and particulars differ systematically: Forms are invisible, unchanging, uniform and eternal, where particulars are visible, changeable, composite and perishable. The human soul is invisible too, and it investigates Forms without the aid of bodily senses. By ruling a particular body it resembles the divine which rules and leads. … Its uniformity and partlessness exempt it from the decomposition that destroys compounded bodies; for all these reasons we may conclude that it is immortal." ("Immortality in ancient philosophy." In E. Craig, Ed., Routledge Encyclopedia of Philosophy. London: Routledge, 2002)
Aristotle took a different view. He generally seems to have disbelieved in the immortality of the soul. In particular, he ruled out any sensation or emotional experience outside the body. However, he left room for the thinking mind to persist, perhaps as part of a grand eternal mind.
The Jewish View
Opinion seems to differ within Jewish religious communities about whether Judaism accepts personal immortality or not. Philosophically, most recognize Maimonides (1135-1204) as the most influential Jewish philosopher. He reorganized Talmudic thought and synthesized it with Aristotelian philosophy. The curious result is that Maimonides fostered a Jewish belief in immortality. In the words of philosopher Garth Kemerling, "Balancing the philosophical and prophetic traditions, Maimonides himself provided Aristotelian arguments for the existence of god, Biblical evidence for the creation of the universe, and a carefully-crafted synthesis of reasons for the possibility of a divinely-produced immortality for embodied human beings."
The Islamic View
The Quran is generally seen to describe Allah's creation of immortal souls. Life after death is widely accepted by Muslims. However, challenges have arisen within the Islamic tradition of philosophy. Muslim scholars translated and studied Plato and Aristotle for centuries before they were rediscovered by the West. During the 11th and 12th centuries, Muslim philosophers published new interpretations of Islam in light of ancient Greek philosophy. Among these was Ibn Rushd, who was greatly taken with Aristotle. In light of Aristotle's views, Ibn Rushd argued that immortality could only be understood as the absorption of the individual mind into the greater whole of the universal intellect, according to Kemerling.
The Christian View
It goes without saying that in the standard view of Christianity humans possess immortal souls. However, there is more to it than that. Thomas Aquinas, the great 13th century theologian, adapted Aristotelian thinking to Christianity by arguing that God intervenes in the creation of each human to add an immortal soul to the ordinary stuff of which we're made. This remains, I believe, the Catholic view today, and is shared by many other Christians. So to is belief in the Resurrection of Jesus Christ, and the promise of a physical resurrection of the dead at some future date.
Not all Christians take these beliefs literally. Anglican Archbishop A. Michael Ramsey in a 1945 book wrote, "a bodiless immortality is inconceivable because it seems to make the future life maimed and meaningless." More recently, Episcopal Bishop John Spong has rejected the traditional ideas of theism, miracles and immortality in favor of a more philosophical Christianity. In his book A New Christianity for a New World, he declares, "I have walked beyond theism, but not beyond God" (p. 239).
Rene DesCartes complicated matters in the 17th century with a brilliant consideration of the relation between body and mind (or soul). DesCartes reasoned that the mind is all that can be known for sure, and that therefore it is distinct and different from the body. He argued (wrongly, it seems) that the mind interacts with the body through the pineal gland in the brain. (See the Contemporary Philosophy section for more.)
The Buddhist View
Buddhism, along with some other Eastern religions, embraces the idea of reincarnation. The "soul" continually re-emerges in various organic forms, including human, until it achieves release from the cycle of life, suffering and death in nirvana.
Contemporary Philosophy
Contemporary philosophers do not speak with one voice, but by and large they reject immortality on the grounds that it requires a discredited dualism. This means, in brief, that the immortality relies on the immaterial soul being in charge of the body, and the soul is a concept that scientifically inclined philosophers have tended to discard, because it runs into the interaction problem. How, philosophers ask, can an immaterial entity "cause" anything to happen in the physical world? This problem has become truly intractable since Einstein. If energy and mass are equivalent (and the atom bomb proves they are), then anything that causes something to happen via energy is, by definition, a material entity. If you argues for special "nonmaterial soul energy," you run straight into the law of conservation of energy, which seems to be an immutable feature of our universe. Of course, philosophy departments around the nation would have to shut their doors if a "final answer" on any dispute were ever reached, and to be sure there are some contemporary philosophers who uphold the dualist banner. Among their arguments is an attack on the scientific understanding of causation at its most fundamental level.
Immortality of Life
The idea that we can live forever in our bodies has gained wide popularity with the rise of the Human Genome Project. Many web sites are dedicated to this cause. However, many knowledgeable scientists scoff at the notion. Fifty-one of them joined to publish a statement in Scientific American in 2002. It reads, in part, "Eliminating all the aging-related causes of death presently written on death certificates would still not make humans immortal. Accidents, homicides, suicide and the biological processes of aging would continue to take their toll. The prospect of humans living forever is as unlikely today as it has always been, and discussions of such an impossible scenario have no place in a scientific discourse." But Ray Kurzweil, inventor and AI entrepreneur, disagrees. Of immortality, he writes, "Humans may achieve this through a variety of technological advances within this century." But for whom? Kurzweil has also written a book forecasting the rise of "spiritual machines" in the near future.