The central belief of the Christian religion is Jesus of Nazareth was crucified and 3 days later, rose from the dead. Irrespective of your religious leanings, do you believe that once a human being has died, that they can be resurrected?
Like many others, it depends on the definition of death.
Provided the cellular and subcellular structures of a biological organism are still holding together, then it is usually possible for us to use technology to restart intermediate level functions like breathing and heartbeat, and once those have restarted, then other homeostatic systems can restart (temperature, pH, blood sugar and hundreds of others that rely on active oxygen metabolism to operate, and therefore require breath and heartbeat).
Most systems can sustain themselves for short periods of low oxygen conditions by switching to lactic acid metabolism, but that is only possible for relatively short periods at normal temperatures. If the temperature is rapidly lowered (like being immersed in near freezing water) then there are examples of people being restarted after several hours, and in one case I know of 3 days – and such conditions are very rare. For most people, at normal temperatures, about 15 minutes without breathing leads to irreparable damage.
As to death and resurrection of Jesus, that seems highly improbable (even allowing for interpretations like that in the movie “The Man from Earth”). Death and resurrection is a common theme in sun worshipping cults in higher lattitudes, where every year the sun travels (north in the northern hemisphere) to a point on the horizon at Sunrise/sunset, where it pauses for 3 days, before the human eye can distinguish movement back in the other direction.
It seems that the Roman establishment did what it was very good at during the council of Nicea, and incorporated enough of the various traditions into the state religion that most people could live with it. That is not something unique to Christianity, and can be seen in many other cultures.
There are some 13 other death and resurrection stories that predate Christianity that are well documented – all related to sun worship.
The parts of Christianity that I really admire are a willingness to challenge authority, and admonition not to judge other people (let he who is without sin cast the first stone), and the call to look within for god.
I don’t have your belief in god, and I am an observer of history at many levels.
You asked “Someday our sun will burn out and that will be the end of our planet. Then what?” and a response to that seemed appropriate.
In the last 100 years we have gone from computation using slide rules, and our first attempts at powered flight, to devices smaller than a matchbox and using less power than a candle that can do 100 trillion calculations per second, and an ability to send remote sensing devices to all planets in our solar system, and get the information back here.
Best evidence we have is that our sun should remain relatively stable for a couple of billion years.
If our technology has progressed that far in the last 100 years, I strongly suspect that we will be able to travel between stars and galaxies long before our sun becomes unstable.
I suspect that it is entirely probable that some people alive today will be alive in 100 billion years time; and it is my intention to be amongst that number, and I may or may not make it. The next 30 years are likely to be the hardest to survive. The changes in thinking required to go beyond our biological origins in peace are significant.