Raw materials and energy need to be expensive or we will over-use them. That puts limits on how large the rest of the economy can be by comparison. On the other side, intangible things like music and entertainment are much easier to make cheaper or even free. If we can reduce the price to near zero then that limits how large a part of the economy they can be. For more about this:<p><a href="http:&#x2F;&#x2F;physics.ucsd.edu&#x2F;do-the-math&#x2F;2011&#x2F;07&#x2F;can-economic-growth-last&#x2F;" rel="nofollow">http:&#x2F;&#x2F;physics.ucsd.edu&#x2F;do-the-math&#x2F;2011&#x2F;07&#x2F;can-economic-gro...</a>