Blaise Pascal was a philosopher and mathematician in the 17th century. Pascal's wager, in a nutshell, is this: No one knows for certain whether God exists. Maybe he does, maybe he doesn't. It's a gamble whether you believe in him or not. So let's treat it like a gamble, says Pascal, and look at the odds.
He described the payoff of this gamble as follows. If you choose to believe in God, and you happen to be right, then the reward is infinity. Eternal bliss in heaven. However, if you are wrong, then you lose nothing at all. On the other hand, if you choose not to believe in God, and you're right, you gain nothing (in either of the previous two cases, you just die and that's the end). But if you are wrong, your payoff is negative infinity. Eternal suffering in hell.
Since the chance of God existing is unknown, but the payoff/punishment scheme is infinitely in favor of believing in God, just on the small chance that he might exist, you had better believe. It seems to be the only wager that makes sense. But wait a minute...
Problems with Pascal's Wager
- In the case where God does not exist, there is a clear advantage to not believing. In other words, the payoff is not zero. For one thing, if you go through life believing a lie, that is a bad thing in itself.
- Besides that, there is more to being a believer than just saying "Okay, I believe now" and getting on with your life. Serious believers spend a lot of their time in church, and contribute a lot of money as well. There's a reason why some towns have very affluent looking buildings for churches, and why large and elaborate cathedrals are possible: they're funded by folks who donate a tenth of their income throughout their lives through tithing. This is surely most foolish if the object of worship isn't real and much of the money is being spent on the building. Fundamentalist Christians can become miserable in other ways as well. See, Why Fundie teenagers are fucking miserable and A spiritual abuse survivor blog by a daughter of the Christian Patriarchy movement If you want to help poor people we suggest that you donate directly to charities that help the poor and don't waste anything on church buildings or misguided missionary word that damages the culture of indigenous people in a effort to save their imaginary souls. Far too often missionaries put the fear of hell into people who were happy without that before.
- What type of a god refuses to give clear proof of its existence but punishes Souls eternally for not believing in it? Can we trust such a god to keep any promise? 
- Even if you buy into Pascal's wager and decide you should believe, that doesn't give any basis for choosing which religion to believe in. Fundamentalists often use the wager to prove that you should be a Fundamentalist, but of course, Pascal was Roman Catholic and was using it to prove you should be a Roman Catholic! This just highlights the whole problem of which religion is the right one. Since many Fundamentalists believe that Roman Catholics are going to go to hell, Pascal's not much better off than an unbeliever. We don't know if the Jews are correct, or if reincarnation is right. More extreme, there may be a perverse God who only lets atheists into heaven! It's not impossible, right? For all we know, maybe God exists but he doesn't care at all whether people believe in him, however likely or unlikely such a god may be.
- If you can accept Pascal's wager as a realistic reason to believe, that leads you to a point where you have no choice but to believe just about everything on the same grounds, even if every religion DOES say that every other belief is wrong. Maybe if you don't register with Wikia.com, you'll go to hell! Why not? You don't know. Maybe you have to send Jason Wales $10 a week for life. Hey, what's a measly ten bucks if it will save you from eternal hellfire? Or maybe God really likes nude mud wrestling and he will punish those who do not partake of his gift. Perhaps god is not jealous as the Bible says but enjoys extreme irony and in fact punishes believers and rewards atheists to satisfy his need for it. But we're just throwing ridiculous speculations out there that we really have no basis for at all since we didn't actually bother researching anything except what we like to hear.
If all of this sounds utterly silly to you, good! That's probably because you know that you should only believe things which have some sort of clear evidence favoring them. You don't believe just any old preposterous claim about UFO's, pyramid shaped get-rich-quick schemes, or magic pixies just because somebody tells you they're true and because there's a chance you might be wrong. You have a brain — use it and go find out if it's true yourself!
References and Notes
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- The Rejection of Pascal's Wager
- Pharyngula on Pascal's Wager
- What if You Atheists Are Wrong? Aren't You Afraid of Hell?