As a means of debating the meaning of life, Twitter isn't great. Sure, it's good for catching up with the latest Olympic news, cat gifs, and so much more, but for the big, profound issues, the 140 character limit is usually too restrictive.

Nevertheless, I find myself engaged in an ongoing Twitter discussion with an atheist. He got in touch to tell me about all the things he though were wrong with a piece I wrote recently about how Christianity actually works.

Over the last few weeks, we have traded tweets and finally come to an almost inevitable point in a debate between a theist and an atheist. It is what Heidegger called "The fundamental question of metaphysics." And I managed to fit it into a tweet.

It's is simply this: Why is there something rather than nothing?

We humans, the land we stand on, the sea we swim in and the air we breathe don't HAVE to exist. The same goes for the billions of stars, planets and other celestial bodies in the universe. They are contingent – in other words, they're are not there because they are 'necessary'. So we are bound to ask why...

Why does anything exist? Why is there a laptop for me to be typing this on and fingers to do the typing? Why is there something, rather than nothing?

The question was first formally asked by the eminent German scientist and philosopher Gottfried Leibnitz. He said, "The first question we can fairly ask is: Why is there something rather than nothing? After all, nothing is simpler and easier than something."

Since he wrote this in the early 18^th Century, philosophers have battled to provide a coherent answer. As each new scientific revelation about the universe has provided them with more data showing what it is that actually exists, there has been no let up in the debate as to why it exists at all.

While philosophers fill whole careers with this question, for the rest of us, thinking about it for more than a fleeting moment may be an alien concept. When there are bills to be paid, kids to be collected from school and Olympic events to get excited about, it seems almost remote. It's beyond even the teenage angst of 'what is my life about?' Yet it's one of the most profound questions we can ask. Why is anything here at all? It's deep enough to induce serious contemplation – maybe that's why William James described it as, "the darkest question in all philosophy."

While contemporary philosophers continue to duke it out, I'm not even going to attempt to offer an answer here. Instead let's focus on what kind of question it is. My Twitter friend is convinced that science is close to answering it. I suggested that in fact, while science is always getting close to telling us 'how', it will never be able to tell us 'why'. "Idiots said it was impossible to travel faster than sound too," he responded. "Brian Cox thinks we are close to answering it already."

I was intrigued that astrophysicist, pop star, TV presenter and borderline national treasure Brian Cox had said this. I'm not sure he has. Cox knows that science isn't supposed to be answering 'why' questions. In a 2014 interview with the Telegraph, speaking about new theories on the beginning of the universe, Cox said, "These things have not been discussed widely; they need novelists and artists and philosophers and theologians and physicists to discuss them."

He's right of course. We all need some humility here. Cox rightly points out that philosophers have spent hundreds of years debating and thinking about the 'why' of existence. Atheists should be cautious before claiming that science will soon be able to tell us why there is something rather than nothing.

Yet, we theists should be cautious too. That there is something rather than nothing doesn't mean it's game, set and match to us either. We're on tricky ground if we claim that just because atheists don't have a knock-down answer to the question, then there is a '30 second argument for God'.

At best, the question should make us all: theist, atheist and agnostic, stop and think. Why is there something rather than nothing is the kind of question that can lead us onto fascinating journeys through philosophy and theology. It's a starting point for many of the biggest questions in life.

Recent years have seen popular-level treatments of the questions arising. They vary from hardline atheists such as Lawrence Krauss (A Universe From Nothing) through to Orthodox Christians such as David Bentley Hart (The Reason For God). While they differ vastly in philosophical aptitude, these and other books are grappling with that question which if we allow it, will hit us square between the eyes next time we walk out of the front door. Why is there something rather than nothing?

Follow Andy Walton on Twitter @waltonandy