Theoretically, if there are no economic setbacks, the extremely rich (the 86 richest people in the world who now have a wealth of about 2,000 billion dollars) will double their wealth every 7 years if they have a revenue of about 10 % a year which has been the case during the last decades.
Maths is not economy, but theoretically if those people double their wealth every 7 years, in 2023 they will have 4,000 billion dollars, in 2030 8,000 billion, in 2037 16.000 billion, in 2044 32,000 billion, in 2051 64,000 billion, in 2058 128,000 billion and so on.
Oxfam made headlines at Davos last year with a study showing that the 85 richest people on the planet have the same wealth as the poorest 50% (3.5 billion people).
As these people have almost nothing you can only guess how long time it takes for them to double their wealth if they have any.
The total wealth in the world in 2016 will be about 300,000 billion dollars. The richest half will own about 150,000 billion dollars in 2016.
Thomas Piketty says something like this: For democracy to regain control over global financial capital it must invent new tools, including a progressive global tax on capital plus a high level of transparency. He suggests 0.5% on wealth between €200,000 and €1m, 1% between €1m and €5m, 2% above €5m and 10% above €1bn. It should be levied on real estate, financial and business assets, art treasures and vintage cars – no exceptions. http://www.theguardian.com/society/2015/jan/20/lessons-on-inequality-from-piketty-to-pharaoh
If you are interested you will find more on http://economics.uwo.ca/people/davies_docs/credit-suisse-global-wealth-report-2014.pdf