Let's say God really wanted to give us convincing proof that he exists. How would he do it?
In the following passage, philosopher Robert Nozick explores the characteristics of the proof that would be required.
"The history of thought is littered with attempts to prove the existence of God. Since it is not at all easy to imagine how God could provide a permanently convincing proof to us of his existence, the failure of people to do so is not surprising. Any particular signal announcing God’s existence - writing in the sky, or a big booming voice saying he exists, or more sophisticated tricks even - could have been produced by the technology of advanced beings from another star or galaxy, and later generations would doubt it happened anyway. More promising is a permanent signal, one so embedded in the basic structure of the universe that it could not have been produced by any of its inhabitants, however advanced.
What then would an effective signal be like? Understanding the message should not depend upon complicated and convoluted reasoning which is easily mistaken or faulty. Either people wouldn’t figure it out, or they would not trust it if they did. To cope with the fact that anything can be interpreted in various ways, the signal would have to show its meaning naturally and powerfully, without depending on the conventions or artificialities of any language. The signal would have to carry a message unmistakably about God, if about anything; its meaning should shine forth. So the signal itself would have to be analogous to God; it would have to exhibit analogues of at least some of the properties it speaks of and itself instancing part of its message, the signal would be a symbol of God.
As an object symbolizing God, it would have to command respect - no people traipsing all over it, cutting and analyzing it in their laboratories, or coming to dominate it; best might be for it to be unapproachable. For people who don’t yet have the concept of God, it would help if the symbol also gave people the idea, so they could know what the symbol was a symbol of.
A perfect symbol should be spectacularly present, impossible to miss. It should capture the attention and be available by various sense modalities; no one should have to take another’s word for it. It should endure permanently or at least as long as people do, yet not constantly be before them, so that they will notice it freshly.
No one should have to be an historian to know the message had come. The signal should be a powerful object, playing a central role in people’s lives. To match God’s being the source of creation or standing in some crucially important relation to it, all life on earth should depend on the signal and center about it.
If there were some object which was the energy source of all life on earth, one which dominated the sky with its brilliance, whose existence people could not doubt, which couldn’t be poked at or treated condescendingly, an object about which people’s existence revolved, which poured out a tremendous quantity of energy, only a small fraction of which reached people, an object which people constantly worked under and whose enormous power they sensed, one they even were unable to look at directly yet which did not oppress them but showed how they could coexist with an immensely dazzling power, an object overwhelmingly powerful, warming them and lighting their way, one their daily bodily rhythms depended upon, if this object supplied energy for all life processes upon earth and for the beginning of life as well, if it were dazzlingly spectacular and beautiful, if it served to give the very idea of God to some cultures that lacked the concept, if it were immense and also similar to billions of others scattered throughout the universe so that it couldn’t have been created by more advanced beings from another galaxy or by any being lesser than the creator of the universe, then that would be a suitable message announcing God’s existence."
- Robert Nozick, The Examined Life, Philosophical Meditations, 1989. pp 49-51