Great topic. I wish I had more time to interact with it. Essentially I would start off by saying that you are not going to get "scientific proof" of any God's existence (unless we are talking about little "g" gods, who are physical beings who live in the universe, as opposed to some kind of ultimate being, which is what most of us westerners mean by "GOD").
Rather, you are only going to objectively "prove" God's existence in the arena of philosophy. Anything else will simply be subjective (visionary experiences, private revelations, or whatever... non-transferable ecstatic or mystical experiences).
I don't reject "Science" (most Christians accept mainstream science, including evolution & the big-bang, which incidentally was a theory first developed by a Catholic priest in good standing). But "science" has changed since the time of Aristotle. It no longer can answer such ultimate questions. Philosophy and science have divided and so it remains for philosophy to answer such questions.
So any "proofs" for God will be philosophical proofs. Sure, people continue to attempt scientific proofs of God, but I would say most of us don't rely upon such things. But that's fine, because all truth does not lie in "science." If it did, most of us would not live our lives the way we do (including atheists). All of our morals, ethics, ideals and even the basis of our laws, social structures, etc. are based upon philosophical ideas, not "science." Science itself is founded upon philosophical principles of intelligibility, general reliability of our senses, uniformity of nature, etc.
Now then I wanted to comment on a few things:
Originally Posted by Dark Jedi Han
About the Bible:
What my CHRISTIAN teacher told me is that the first written texts about Jesus came much later than him, like a few hundred years after, if I'm not completely wrong.
Either you or your "Christian teacher" (sadly, simply being a Christian or a teacher doesn't make you an expert) is "completely wrong."
If they had a doctorate degree in Scripture studies or something, I would take their view more seriously, but I'd ask for evidence for why they hold that position. In any case, here is the answer...
The earliest texts we have about Jesus are the letters of Paul (aka Saul of Tarsus), written from about the year 49 through the year 67. As Jesus died in about 30, that's a mere two decades after his death that we have writings preserved by contemporaries. According to Paul, some of Jesus's original disciples (namely "Cephas" aka Simon Peter), James ("the brother of the Lord") and John were still alive and he interacted with them. The four canonical Gospels are thought by most scholars to be the earliest documents with the designation "Gospel" (but recall, they were written after the letters of Paul) and appeared between 65 and 95 CE (most scholars consider Mark to have been the first, then Matthew and Luke-Acts, followed by John). A few scholars put them earlier, a few put them later, but most would say right around 70 CE is when you get a bunch of Gospels about Jesus. the "Gnostic" writings and so forth do appear centuries later, but almost nobody of any academic standing considers them the least bit reliable in comparison. In about the year 90 we have independent testimony of the Jewish historian Josephus to the historical existence of Jesus and his brother James (and while one reference is questionable, most scholars consider it at least partially genuine and another reference which includes the mention of James, is not disputed by modern historians). Tacticus and Suetonius (pagan writers), near contemporaries of Josephus also attest to Jesus and his movement, but within a century or a bit later than Jesus himself. The argument that the Biblical writings cannot be used as sources is a strange one, of course but it is often thrown out by skeptics without justification. All historical writings are fragmentary and biased.
Another objection is that Paul "never met Jesus" but that's not really an issue because he knew Jesus' inner circle, and he fought against Jesus' movement (why would he do that if he didn't at least know who Jesus was or what he stood for?) prior to his conversion. Paul in his letters writings to already existing communities of disciples (including ones he did not found) as if they already know the basic story of Jesus and beliefs about him. He cites what scholars identify as early "hymns" and "creeds" (for instance in Philippians 2:1-11). In short, the argument (made by some) that Paul "invented' the Christian faith is laughable at best. Likewise there is clear indication in the undisputed letters of Paul that other letters of his were written that are now lost to us. This means there was more information out there than just is recorded in the letters (unless I suppose he simply repeated himself). We know that the early apostles did most of their teaching orally, rather than in writing. However there is a robust "Tradition" preserved in for example the early Church Fathers and in the ancient creeds and liturgies of the Church. So one should not think "I can't find it clearly in the bible, therefore it must not have happened." The original audiences had more information than is recorded in these texts. But that doesn't mean we can't figure out what it is they knew, most likely, as any historian could determine.
As an aside: For anyone who argues that Jesus was not a historical figure, I would point you to (agnostic biblical scholar) Bart Ehrman's "Did Jesus Exist?" which provides a thorough summary of the consensus view of modern scholarship on Jesus and demolishes the "Mythicist" position. Not all founders of religions are equally attested in the historical evidence. Of course Ehrman caught lots of "heat" from other (less credentialed) atheists but has responded to them on his blog.
I do get tired of the arguments that the bible has been "translated and re-translated" or "written and re-written" so we "can't know what the texts really said." I also get tired of pointing out to some skeptics that nobody is using the "bible said it, so it must be true" argument in these types of debates. As a Catholic, I don't accept "sola scriptura" anyway (a theory held by a minority of Christians no earlier than the 14th century). I have to normally explain to those same people that the bible is a library, not a single book, and there's no evidence it was created by "illiterate bronze age desert dwellers" or "by the establishment for political power." Yet those kinds of things keep getting thrown around. There is nothing unbelievable about a preacher and faith-healer who was crucified, that some of his followers considered the Messiah and somehow divine. There is also nothing unbelievable about such a man viewing himself as the Son of God in a divine sense. Such people exist today, and such people existed 2,000 years ago. Unfortunately many of the skeptics one hears are still dealing with their own emotional issues against a fundamentalist Christian upbringing and are unaware of the studies out there beyond popular apologetics and counter apologetics.
It's true, a bunch of people dying for their beliefs is not proof (by itself) those beliefs are true. It does however indicate that the people were sincere. Who would willingly die for a lie?
That is, the common argument that Christianity began as some kind of plot or ploy to control the masses with an invented lie doesn't really pan out. It would have to be a vast conspiracy (we can't assume a conspiracy without evidence of that conspiracy). You could argue that all the disciples and early followers were deluded, but that's different than claiming it was a deliberate lie.
One can't compare followers of Muhammad 1300 years later dying in suicide attacks to the early followers of Jesus. Another difference there is that these guys were terrorists (or guerrilla fighters waging a "war") vs. those who had nothing to gain (in earthly terms) by their deaths. Muhammad and Jesus are very different characters.
The idea that Christianity was invented for political power doesn't really fly since the religion didn't have political power for the first three centuries of its existence (and it wasn't Constantine who made it the state religion, that was Theodosius, fifty years later in about 381 CE).
In any case, Thomas Aquinas would argue that one could reason their way to the existence of a creator God, and admit the possibility that that God could reveal Himself to His creation if He so chose. But to accept the truth of the Christian faith, one still would have to accept the claims of divine revelations themselves.
A skeptic could still say Jesus and his followers were sincere, but deluded, and provide a naturalistic explanation for everything and say either God doesn't exist, or God didn't reveal himself through this religion.
When Jesus (peace upon him) was crucified, he spoke to God, saying: "Lahi" or "Eli (= God), did you leave me?" (it may be wrong, but I remember well that there were two contradictions in the different Gospels)
Another thing: Jesus asks for water.
Jesus quotes Psalm 22 in his native Aramaic. The Quran tells stories of Jesus that were apparently unknown to the early Christians, in the 7th century, a much longer space of time since Jesus' earthly life than the canonical Gospels.
In one Gospel, a Roman centurion puts a sponge on his spear, drips it in water and tends it to Jesus. In another one, it was completely different.
This is just to say that many versions exist, but we will never know which one is true.
The early Christians considered all of them true and preserved them for that reason. Modern people want one version of the story. Information was simply preserved differently back then. The Torah also contains multiple versions of the same story, often side by side (just not seperated out into different "books" as in the New Testament). There are also variations of the Quran, though this is an emerging field, because Islam has long resisted this since the Uthmanic "reform."
And by the way: I'm a muslim, and recognize Jesus as a Messenger of God, but not as His son. Of course, that is for another thread.
Some would argue that we have more reliable evidence for the existence of Jesus than for Muhammad as historical figures. Of course I accept the existence of both and I am even willing to grant that both were sincere in their beliefs. However from the point of view of "which one is true" one could come at it from many different angles, but the general Muslim position is that Christianity is a corruption that Muhammad and the Quran came to restore. The trouble is much the same for Muslims as for Mormons. Where is the evidence of this corruption? Presumably in the Muslim view there was an "original faith" that more closely adhered to Islam than to Christianity. So surely there should be evidence of this. If we say all evidence was destroyed, how do we know the claim to restoration is correct? That doesn't even begin to answer the question of whether God exists of course (and doesn't even answer which religion is true, only which is closer to the "earlier faith" they both claim lineage from).
Of course the claim of Muslims is that they have the same God as Jews and Christians. So if our God doesn't exist, then neither does theirs (I would not say different understandings of the same God equal different Gods).
The Trinity doctrine is a key difference between Christian and Jewish or Muslim understanding of God, but I would just say for now that it has its roots not only in the revelation of Christ, but in ancient Jewish theology of the personification of "Wisdom," the "Angel of the Lord" and so forth, out of the Old Testament (remember that the Jewish TaNaKh and the Protestant "old testament" is smaller than the book of Scriptures used by most Jews in the first century). It is not, as some have alledged, some kind of "borrowing" from pagan mythology. Trinitarianism is a form of monotheism, not polytheism. This sadly is a big misunderstanding by many critics of Christianity.
It's simply reasonable to believe in the Christian God. You could say it's also reasonable not to. But one can't simply dismiss it, especially with the excuse "I don't understand" or "it sounds silly to me," or "I never really studied it." But without some kind of personal investment through an experience or act of faith, one could freely doubt it or accept it but not allow it to have any kind of impact on one's life. Most Christians live the way they do because they think it's the right thing to do, and it gives them joy (not happiness per se, as that's a fickle emotion). It's the best thing going, so they accept it.
[Edit: fixed tags]