Without getting overly philosophical about it, we can say that absolute logical proof for the existence of God and the authenticity of Torah is, under normal circumstances, unachievable. But then, considering the kinds of knots professional philosophers enjoy tying themselves into, absolute logical proof for just about anything is unachievable. So let's take that off the table.
It is, however, perfectly reasonable to expect to find compelling evidence for God and Torah. How else could God expect a skeptic to find his way home?
Before we go any further, though, let me ask another question: is the search for compelling evidence necessary? Could a sincere and fair minded individual simply say "I'm comfortable with the strong, living relationship that I already enjoy with God and mitzvos [perhaps based on the kind of ideas we found here] and I don't feel the need for the power boost that evidence might offer."? For reasons I'm unsure are relevant to this discussion, I suspect that such an approach is not unreasonable. If you are such a person, you might want to stop reading this page now.
Good. Now that he's gone, the rest of us can continue (did you also feel it was getting a little stuffy in here?).
What kind of compelling evidence are we looking for? I will remind you of a resource that I've mentioned previously that has quite a lot of useful material. However, we're going to focus on a different class of evidence...the class that I believe is specifically recommended by the Torah itself:
"Ask about the early days that were before you: from the day that God created man on the earth and from (one) edge of the heavens to the (other) edge has there ever been anything as great as this or has anything like it been heard?
"Has a nation ever heard the voice of God speaking from the midst of the fire as you heard and lived?
"Or has God ever proven Himself by coming to take for Himself a nation from the midst of a nation with feats and signs and wonders and battle and with a strong hand and an outstretched arm and great fear as the Lord your God did to you before your eyes in Egypt?
"You have seen (in order) to know that the Lord is God, there is no other besides Him.
"From the heavens He allowed you to hear His voice to discipline you, and on the land He showed you His great fire, and His words you heard from within the fire...
"And you know today and will return it to your heart that the Lord is God in the heavens above and on the earth below, there is no other."
I believe that this is at least part of what Rabbi S.R. Hirsch had in mind, i.e., that we Jews don't need "faith" in God, because we know Him directly from our national experience. But what form does this "knowledge" take for those of us not old enough to remember Mt. Sinai personally?
Rabbi Dovid Gottlieb, in his freely-available online book, offers four classes of evidence supporting the authenticity of Torah. None of the classes, on its own, is an absolute empirical proof, but all of them together can, at the very least, be reasonably characterized as compelling.
Because some readers might find this useful, I will briefly summarize each of Rabbi Gottlieb's four classes. Please bear in mind that I am certainly not doing the original book true justice and that you will be far better served by reading the real thing.
The Problem of Jewish Survival
There would seem to be no natural explanation for the cultural survival and success of the Jewish people. If the continued existence of the Torah nation fits none of academia's accepted historical models - if, in fact, each of these models predicts our early assimilation or demise - then, barring the discovery of a better model, the most reasonable conclusion is that our religious survival is supernatural. Since the Torah itself explicitly predicts Jewish survival (and eventual redemption, see Deut. 30:1-5), its God is therefore the miracle's most likely source.
Rabbi Gottlieb explains how...
But not only did Judaism survive against all rational odds, it proved to be arguably the very greatest cultural influence; successfully introducing the fundamental principles of monotheism, justice and morality to the civilized world.
- despite extensive cultural contact, the beliefs (monotheism, exclusivity, spirituality, morality and the absolute power of God) held by a solid core of loyal Jews remained entirely distinct from any other culture of the ancient world.
- despite suffering a uniquely bitter, centuries-long exile, core Jewish belief's have never reflected the influence of their dominant - and often hostile - host cultures (in the ways that Christians and Muslim communities have borrowed from many of the cultures with which they've had contact). Even if internal loyalty to classical Jewish beliefs may not be perfect, there is no substantial argument as to what they are.
- despite facing serious and regular threats from both hostile neighbors and from renegade Jewish movements, our physical existence persevered.
While the current state of academic archeology might not passionately support the authenticity of the Torah's historical narrative, neither does it negate it:
The absence of corroborating documentary evidence should be expected: even if they witnessed it, why should ancient civilizations have recorded events like the exodus from Egypt (remember, recording history for its own sake is a very modern goal)? Who says that their conflicting accounts are more accurate than ours? Is it reasonable to conclude that the absence of ancient physical evidence is remarkable? Why should it have both survived the ravages of time and happen to be just where modern archaeologists search for it?
The claim that ancient Jewish history is a product of myth development lacks credibility due to an ever-growing body of discoveries refuting supposed Biblical anachronisms.
Rabbi Gottlieb focuses specifically on the set of predictions concerning national destruction and exile found in Deuteronomy 28-30. These are particularly useful because the individual predictions are interdependent, meaning that if any one of them would fail to occur just as predicted, the entire set would prove false. Therefore, the odds against all of them occurring (which is the same as saying "the odds against someone living 3400 years ago successfully predicting" them) is the product of the odds against each one by itself.
Here are Rabbi Gottlieb's choices:
"In Deuteronomy 28-30 there is a prediction of what will happen to the Jewish people if they don't live up to the standards of the Torah. It predicts conquest accompanied by wanton slaughter of the population: men, woman, children, old, young, and so on. It predicts an exile resulting in world-wide scatter, and that during this period of world-wide scatter, Jews will have no independent government. One result of the exile is that some Jews will be brought back by boat to Egypt to be sold as slaves, and they will not be purchased. Nevertheless, the Jewish people will survive, will never completely be destroyed, and will ultimately return to the land of Israel. It also predicts that the conqueror will speak a language that the Jewish people don't understand."
Multiplying the resulting numbers together generates a likelihood of one chance out of many thousands that a human author of the Bible could have guessed what was coming. The God described by the Bible, on the other hand, would obviously enjoy inside information...
The Kuzari Argument
Acknowledging the complexity of this argument, Rabbi Gottlieb himself encourages readers to consider some introductory ideas before jumping into the thick of things. Take a few moments to read his introduction and a useful dialogue.
The first step is to state the Torah's claim (what, according to the Torah itself, was supposed to have actually happened). We can then consider how believable it is. Or, to put it another way, had it not happened, how likely it would be for a faker to have successfully fooled his unsuspecting audience and passed it off as the historical truth.
We find in the text (Shmos 19:9): "And God said to Moshe, behold I will come to you in the thickness of a cloud so that the people will hear when I talk with you and also believe in you forever..."
Thereafter (ibid, verse 19): "And the voice of the shofar continued and (become) very strong and Moses spoke and God answered him with a voice."
There's the claim: That God spoke to Moses, clearly choosing him as His prophet; not in a dream or in his private tent, but in front of and in full view of the entire nation. This is the authority that underlies every single statement that would later be made by Moshe. If it didn't happen, everything falls apart. Years later (shortly before his death) Moses publicly reminds the people of what they had seen (Devarim. 5:4-5): "Face to face God spoke with you at the mountain from the midst of the fire; I stood between God and you at that time to tell you the word of God..."
Now the fact that, throughout recorded history, there has always been a strong and literate core of observant Jews who accepted the authenticity of the accounts of the Torah means that the absurd claims (three million people survived for forty years by eating mannah every day...?) made sense to them.
How do we know this? Because if the book was made up and only published after the fact, why should any large group of intelligent people accept what would have been obvious lies? For example, they could have reacted with: "Really! If this book is true, and it says (Devarim. 31:24-26) 'and it was when Moses finished writing the words of this Torah in a book until its end; and Moses commanded the Levites, the bearers of the Ark of the covenant of God, saying: Take this book of the Torah and place it...' - then why haven't I ever heard about it until now? Where has it been all these years? Why didn't my father tell me about it?"
So the fact that Jews accepted and still accept the Torah as it is with all its outrageous claims tells us that all the claims were believable. Or, in other words, that they were true.