What will be the 10 most populous countries by 2050?:
The next 5 will also surprise you. In most trend projections I've seen, by 2060 world population is declining. Western European populations decline much sooner than that. Developing countries are getting richer, despite what western countries have done to retard their economies. Population growth is hugely inversely proportional to wealth.
Take a look at all the western European countries; Germany, Italy, France, Britain, etc., as well as Japan. That is the simple reason they are structurally bankrupt, since their social net is based on a tax based Ponzi scheme as opposed to your life insurance which returns your payments based on investments.
And while China's population will decline, India's projection may be too aggressive since their development is astounding, and significantly based on internal consumption while China still relies on exports. China relied on laws, forced abortion and sterilization to limit its population, while India will rely on her growing wealth.