I have enjoyed the debate on the existence of God in your columns, and have hesitated to join in because I do not feel I have any right to try to impose my own views in this matter on anyone else.

However, I am surprised that no-one has referred to the "parable" which I first came across in a fascinating book - the Anthropic Cosmological Principle, written by three professors of mathematics (John Wheeler at Princeton, John Barrow at Oxford and Frank Tipler at Tulane University, New Orleans) - and which develops a mathematical proof for immortality.(Read the book; it is truly fascinating.) The parable describes the theologian looking for the existence of God and the scientist seeking to understand the workings of the universe as mountaineers climbing through clouds. It proposes that when they get to the summit, they will meet, having reached the same goal by different routes.

It is a modern parable which I find fascinating and helpful, because we are all entitled to hold our own beliefs - but how many of us can actually claim to know?

Patrick McNally, Kennoch House, St Quivox, Ayr.

Andrew Morton's vitriolic attack on me (Letters, September 4) has given me the best laugh I've had for ages. He is clearly being "seculaphobic". If he bothered to read the objectives of the National Secular Society, he would learn that we want a society where all are free to practise their chosen religion, change it or not have one at all, each according to his conscience.

What we object to is that belief in any one religion can be used to secure special privileges over those of other faiths or none. We also work to protect vulnerable groups from being the victims when the religious exercise what Mr Morton would call the right to freely express their religion. It is religious groups of all kinds, not secularlists, that have sought exemption from equality legislation to enable them to vilify some groups in society.

It is religious groups, too, not secularists, that have sought to curb freedom of expression by demanding an extension to blasphemy laws and incitement to religious hatred laws.

Those democratically elected to govern us, whether they are religious believers or not, are there to represent the interests of all their constituents, not just those who believe in a particular god or gods, and not to advance their personal religious agendas. Not so in Mr Morton's world, where the religious are apparently allowed to do just that.

David Cameron said recently that he was a Christian, but his politics were not faith-led, and quite right, too. Would that Bush and Blair had had the same approach.

Alistair McBay, National Secular Society, 5 Atholl Crescent, Edinburgh.

Chris Parton is wrong to say that I am "very sure what happened before the Big Bang". Before the Big Bang there was no space, no time and no matter. As I have already said, this is incomprehensible. If this is so, then neither I nor any other human being can know or understand this. Which is precisely the point I was making.

Brian Quail, 2 Hyndland Avenue, Glasgow.

Andrew Morton either misses or chooses to ignore the point (September 4). The existence of God can neither be conclusively or non- conclusively proved, and we decide to believe or not believe on the basis of a balance of probability.

It is not the right to hold or express these views that Alistair McBay is questioning. Rather, it is the right not to be constantly bombarded with them.

Would Mr Morton be as tolerant of atheists interrupting his dinner to tell him about The Bad News, or watch atheist choirs on Sunday prime-time television singing about the non-existence of God and the afterlife? Restricting this irritating evangelism to places of worship is no more an infringement of freedom of speech than asking BT to block unsolicited sales calls.

George Savage, Technology Transfer Executive, SUIP Ltd, Scion House, Stirling University Innovation Park.

It is bizarre that "scientists" can ridicule "faith" in the existence of God when no concrete evidence can be produced to prove his/her existence; they seem to be happy enough with the theoretical existence of "dark matter". All explanations of how the universe works crumble without its postulated presence yet it cannot be proven to exist. Sounds pretty much like an act of faith to me.

David J Crawford, 131 Shuna Street, Glasgow.

There is surely only one reason for all forms of life on earth (Even the most respected figures still pose questions about the meaning of life, September 4) and that is an attempt to ensure the continuation of the survival of the species.

Human beings are credited with being the most intelligent form of animal life but we appear to be doing our best to prove otherwise.

Ian F M Saint-Yves Dunvegan, School Brae, Whiting Bay, Arran.