Think of them as the three laws of spiritual physics when it comes to the demographics of faith. The bottom line is that religious groups thrive when:

* Believers have children.

* Believers pass their faith on to their children, the children retain that faith and some of these children even embrace vocations as clergy or workers with the faith.

* Believers reach out to others and spread the faith in service and evangelism.

As we like to say here at GetReligion: Demographics is destiny, and so is doctrine.

You could certainly see these factors at play in the recent "Global Catholicism: Trends & Forecasts"(.pdf copy here) conducted by the Center for Applied Research in the Apostolate at Georgetown University.

The bottom line: Catholicism is on ice in Europe and on fire in Africa and Asia. You can read some of the details in my "On Religion" column this week, but here's the bottom line: It's hard for a faith to survive, let alone thrive, when it isn't producing children, clergy and new believers. Heed these thoughts from CARA's Mark Gray:

The bottom line, stressed Gray, is that Catholicism is growing, in pews and at altars, in places -- such as Africa and Asia -- where Catholics are having more children.

Europe's current fertility rate is 1.7 -- well below the replacement rate — with much of the growth among immigrants. Meanwhile, the Catholic population in Africa has risen 238 percent since 1980, in part because of a 5.1 fertility rate, in recent estimates, in sub-Saharan Africa. Weekly Mass attendance is 70 percent in Africa and the number of priests in Africa rose 131 percent in the years covered in this CARA report.

Combine several trends and you get this wrap-up quote:

"Africa has priests but needs more churches. America has lots of churches but needs more priests," said Gray. "You can bring priests from Africa and Asia to America, but you probably can't keep doing that forever. And you can't pick up empty churches in Europe and move them to Africa. ... The pope can't point at the map and move churches and priests around to solve these kinds of problems. The church isn't a corporation."

The trends in America are sobering, but things could be worse.

Consider, for example, the piece in The Spectator that ran under the headline, "2067: the end of British Christianity." Here is the overture.

It’s often said that Britain’s church congregations are shrinking, but that doesn’t come close to expressing the scale of the disaster now facing Christianity in this country. Every ten years the census spells out the situation in detail: between 2001 and 2011 the number of Christians born in Britain fell by 5.3 million -- about 10,000 a week. If that rate of decline continues, the mission of St Augustine to the English, together with that of the Irish saints to the Scots, will come to an end in 2067.

That is the year in which the Christians who have inherited the faith of their British ancestors will become statistically invisible. Parish churches everywhere will have been adapted for secular use, demolished or abandoned.

That's just the Church of England, right? Actually, this piece says "no." The statistical trends indicate that the state church will be dead by 2033. The article stresses that these claims are based on statistical trends alone, not the actions of future believers. Thus:

... A projection is not the same thing as a prediction. So feel free to take any apocalyptic vision of religion in Britain in 2067 with a pinch of salt.

But the point stands: Christianity is dying out among the Anglo-Saxon and Celtic inhabitants of Great Britain. The Gospel that Augustine and his 30 monks brought to England when they landed at Ebbsfleet in ad 597 is now being decisively rejected.

Note the stress on ethnicity. While the flow of Muslims into England has created headlines, similar trends exist among Christian believers from other lands -- but the trends are not as strong. Still, African and Asian Christians may evangelize corners of the land that, generations earlier, helped bring them the faith.

That could happen, but The Spectator says the odds do not favor that outcome.

So what is happening?

Why is British Christianity facing such a catastrophe? There is a one-word answer, but it requires a lot of unpacking: secularisation. ...

It can’t be stressed too often that the secularisation that happens inside churches is as important as the sort that happens outside them.

There's much more. Read it all.