Was Jesus really resurrected?
One of the central tenets of Christianity is that Jesus was crucified for the sins of humanity and then rose from the dead three days later. Rising from the dead is a pretty spectacular stunt. In fact, many Christian apologetics site hold this up as the singular reason for believing Christianity is true. So what makes people believe that a Jewish Rabbi pulled it off 2000 years ago?
The short answer is the Gospels. The Gospels of Matthew, Mark, Luke & John tell the story of the life of Jesus. They weren't written by eyewitnesses to the events, but were dedicated to the apostles. The gospel of Mark was written (at the very earliest) 40-50 years after the crucifixion, Matthew & Luke more than 50-60 years after (and with a copy of Mark in hand), and Luke at least 60-70 years after (with copies of the other three in hand). (Bear in mind the average life expectancy was 30 and most people probably wouldn't have made it much past 50).
(Paul was converted to Christianity by seeing Jesus, but even Christian scholars believe that he saw Jesus in a vision, not in the flesh.)
So, what do the Gospels say about the resurrection?
According to Mark; two Marys and Salome found the tomb empty and one young man in white there said that Jesus would be seen at Galilee. It doesn't say whether he will be seen in body or in spirit. A little bit more was added a couple of hundred years later, but the original version of Mark stops at this.
According to Matthew; two Marys found an angel that blazed like lightning, paralyzed two guards, rolled back the stone and said that Jesus would be seen at Galilee. The two Marys rush off to tell the apostles, and see Jesus on the way home. They grovel at his feet, hinting he is physically present.
According to Luke; two Marys and Joanna (and perhaps others) found two young men in white. Peter also checks out the empty tomb. They meet Jesus who tells them explicitly he is physically resurrected, and eats a fish to prove it.
According to John; Mary, Peter and one other disciple find the tomb empty. Peter and the disciple leave and Mary sees two angels_ _in white, then sees Jesus, which she announces to the other disciples. He appears to them and proves he is physically resurrected by showing off his wounds and even letting Thomas put his fingers into his wounds.
Chinese whispers anyone? 70 years is a long time for rumours to grow. How accurately do we know events that happened within the last 50 years? Look at all the competing theories around things like Elvis's death (or is he really still alive?), Marilyn Monroe's suicide (or did the Kennedys kill her?), Apollo (was it staged in a Hollywood back lot?) or even really recent things like 9/11 (were the twin towers actually dynamited from inside?). Who is to say that one of these won't end up being the generally accepted theory in a thousand years time?
Remember that the Jews at the time weren't convinced there was anything special about Jesus. And the small Christian sect itself had other branches who didn't believe in his divinity or in a physical resurrection. The dominant branch eventually had those other branches declared heretics and put them to death if they didn't renounce their beliefs. It's that dominant branch that became the Chrisitanity we have today - the victors get to write history.
So, in the Gospels we have four successively embellished versions of a story written down at least 40 years after it happened, by people who didn't witness it and at a time when there probably weren't many people around who did (and who probably wouldn't bother to correct the recruitment propaganda of a small fringe Jewish sect anyway).
Clearly on their own, the Gospels don't cut it as evidence that the events they narrated really happened. Do we have _any _corroborating evidence outside the Bible that this happened?
Well, no, actually. The best most Bible apologists can come up with is casual mentions of Christians from around 115AD onwards. Clearly there were a sect of people who believed Jesus was the messiah and rose from the dead. They most likely got their information from the Gospels. The existence of _Christians _does nothing to prove the truth of the resurrection. There is almost no evidence that Jesus even existed at all, never mind that he performed miracles, was crucified and then was resurrected.
The writings from the period chronicle all sorts of events, but are largely silent about Jesus. The historian Josephus (who was born around the time Jesus died) wrote about the period in which Jesus was supposed to have lived, however the only mention of Jesus is one paragraph which even many Christian scholars (and most secular scholars) believe was added later by a scribe.
So basically, we have zero evidence for the resurrection. The evidence for Jesus's existence and crucifixion isn't much better actually, but let's assume we believe at least that Jesus really existed and was crucified. How could the resurrection story have gotten started?
Jesus was proclaimed to be the messiah. He was supposed to lead the Jews into battle to throw off the Roman oppression, to restore Israel, destroy the wicked and judge everyone. The one thing he was mostly certainly not supposed to do was get killed. His followers were pretty much screwed when that happened. They'd been following him for years trying to establish their own Jewish sect. After his death they continued his teachings, and some of them saw him in dreams and visions. Over the following decades the story evolved from a few apostles seeing visions of their dead teacher to become a full bodily resurrection and ascension.
This is just one explanation, one which assumes fairly pure motives on the part of everyone involved. There are many other possible explanations as well, all of which are plausible and which can be explained in terms of natural events and human motivations. A walking dead guy seems to be the least likely explanation.
There is simply no evidence that Jesus actually rose from the dead.