A lot of the questions that I hear most often from non-Buddhists, new Buddhists and/or skeptical westerners is about rebirth and how it happens. To begin this post I'd like to talk about my personal beliefs toward rebirth. I believe in rebirth because even from just a scientific perspective one can see that there is an order, structure and meaning behind the Universe and the patterns of life. On a more subtle level science has proved that nothing disappears but rather it simply changes form. The same applies to energy; Energy cannot be created or destroyed, only converted from one form to another.
A radio in a car is run by the energy produced by the engine, which is run by the energy of gasoline, which came from the energy of pressure and heat converting decomposing organic matter into oil. The organic matter (mostly plants and animals including dinosaurs) was fueled by the radiation from the sun (plants) and other organic matter (plants being eaten by animals and dinosaurs). Before that the potential organic energy in plants formed as a result of carbon dioxide energy released by other plants and animals, which transformed into chlorophyll that fed the plants via photosynthesis. Photosynthesis is a process fueled by the transformation of the sun's energy into sunlight. The sun's energy and mass was likely the result of a dying star, which created a supernovae (stellar explosion). This expelled massive amounts of energy and matter, which was reborn as our Sun. So our Sun is nothing more than the rebirth of a star.
Ultimately the energy of all super bodies in the Universe resulted from the powerful, trans-formative energy produced by the Big Bang itself, which is my view was the result of collapsing/dying Universe that existed before the current incarnation of our Universe. This would have been achieved through something called the, "cyclic model" which is basically a model where the Universe goes through an infinite number of self-sustaining cycles or Big Bangs and Big Crunches or collapses.
It's not unlike the energy created as an accordion expands and contracts in the form of sound waves. The power, which fuels our galactic accordion is said to be that of a substance known as "dark energy" which would solve the entropy build up problem and be in keeping with the second law of thermodynamics. I could get even more in-depth with the "cyclic theory" but I'm worried I'll lose you. Thus, if you're interested in reading about it further I'd suggest reading this page and the book mentioned within. So finally, there you have the massive cycle of an infinite number of deaths and rebirths of energy and matter occurring upon our Earth and within our Universe. So seeing how we are literally made from the guts of stars exploding their matter and energy; why would we humans be exempt from that paradigm of cycles, which even the giant, celestial bodies must adhere to?
The same is true of the seasons, which was the first cycle I contemplated that led me toward believing the birth, life, death and rebirth theory. Spring (birth), Summer (mid-life), fall (old age and sickness), Winter (death) and it would seem to end there if rebirth wasn't real or possible. However, it doesn't stop there as we know Spring is reborn anew and the cycle continues until the cycle of Earth's life ends. Then when Earth is absorbed one day by our dying sun before it explodes via new supernovae to expel the seeds and energy needed to be reborn anew as another planet or star somewhere else in our vast Universe. The cycle continues. So again, why would the rebirth of our energy into a new form of being not be possible? The potential energy of the body is absorbed into the earth, air, water and fire of our planet to be reborn as a flower, a tree or a mushroom, which would be eaten by a living being.
However, what of the energy left over in the mind upon the death of the body? In my view, that energy of our mind is nothing less than our karma but how does that karmic energy released find it's way into a new form? This often baffles many western, science based Buddhists. At this point I'd like to borrow an explanation of this from the Venerable S. Dhammika at Buddhanet:
Think of it being like radio waves. The radio waves, which are not made up of words and music but energy at different frequencies, are transmitted, travel through space, are attracted to and picked up by the receiver from where they are broadcast as words and music. It is the same with the mind. At death, mental energy travels through space, is attracted to and picked up by the fertilized egg [or receiver]. As the embryo grows, it centers itself in the brain from where it later "broadcasts" itself as the new personality.James: The question then arises, "Why does that karmic energy get picked up by a particular egg/embryo?" To answer that I'd refer back to our example of our Solar System.
According to the nebula hypothesis, the Solar System began as a nebula, an area in the Milky Way Galaxy that was a swirling concentration of cold gas and dust. Due to some perturbation, possibly from a nearby supernova, this cloud of gas and dust began to condense, or pull together under the force of its own gravity. Condensation was slow at first, but increased in speed as more material was drawn toward the center of the nebula. This made gravity strong, making condensation faster.As we saw earlier, supernovae are the expulsion of energy from a dying star. So imagine the supernovae as being the karmic energy of the mind being dispersed upon the death of the body. In our example the swirling spiral arms of the galaxy where all this takes place is the womb (called star nurseries). The dust particles within these nursery clouds are the tiny, unfertilized eggs while the gas is the sperm. This swirling, growing star cloud (now an embryo) is then charged with blasts of superheated energy (karma) from the supernovae (dying mind) thus infusing it with the energy (karma) of the former star (deceased body/mind). The energy released by a supernova is trapped by the gravitational pull of these star clouds (embryos) and converted into new stars (new birth). In this "new life" example the gravitational pull is similar to that from the karmic pull of the parents of our next life. They say that like energy attracts similar energy. So given that understanding it's no wonder that the Great Buddhist Masters teach us that our next rebirth will depend in part upon the karmic energy of our future parents. We will be attracted to the karmic energy that mirrors what our karmic energy demands.
Another possible explanation is electromagnetism. Electromagnetism pervades everything and everyone. It's not unlike an uncountable number of intersecting energy grids of infinite sizes, which permeates and connects all things to the power station (our sun) and to each other's homes (minds). It's possible that our karma travels from old body to whatever new birth occurs via the electromagnetic field that acts like a true Indra's net. The brain is charged with electromagnetic neurotransmitters, which act as pathways for the energy created to reach every cell in our body. Our brains are basically organic batteries and could very easily be emitting energy waves that can be received by a new life form or other type of entity when the death of the body occurs via the electromagnetic field/grid. We certainly know that our brains are good conductors of traditional electricity!!
I'll end with something to keep in mind about rebirth. There are many things like electricity and radio waves, which we can not see but we accept that they are real because we see their effects. Just because we can not see the exact details of rebirth doesn't mean that it we don't see it's effects and thus its reality. Why are some of us born with traits and characteristics that don't seem traceable to the genes or behavior of immediate family members? Why are we born with a fear of water for example and our siblings are not? These could very likely be the effects of karma fueled rebirth. My examples might not fully explain the process but I think they come close and at least show that rebirth is very, very likely.
UPDATE: I will admit whole-heartedly that my examples and ideas are by no means definitive. If rebirth is real then there has to be a missing puzzle piece to bring it all together. I welcome new science to help us fill in the blanks a bit. I have faith in the end that this process is true but it's not blind, unflinching faith. I'm not married to it. I could very well just die and that's it. I have no problem with that scenario. I don't fear annihilation of the body and mind though it's hard to square that with the central Buddhist teachings that nothing every really goes away but that (as science explains) it simiply changes for. Perhaps though the most likely change is on a more subtle level of our ashes become apart of a patch of flowers being fueled by the minerals in our ashes. I am open to many interpretations, which I think Buddhism embraces as a whole unlike many religions, which is partly what attracted me to it in the first place.