Just because you’re growing faster than a straight line doesn’t mean you’re growing exponentially.
Exponential growth means that you are growing at a rate of cx, where c is a constant greater than 1 and x is a period of time. If c = 2 and x = 1 month, then you are doubling every month. If c = 2 and x = 1 billion years, then you are still growing exponentially but you are doubling every 1 billion years! Or if c = 1.00000000000001 and x = 1 day you are still growing exponentially but you are doubling every 1 trillion years!
I’m no expert on Viral Marketing Optimization (VMO), but the experts who tune their systems achieve exponential growth when c > 1 (with a reasonable x I assume).
Note: Thanks to Paul Bucheit for creating quick blogging.
Nor does the value of a network seem to even be geometric, let alone exponential.
These guys argue that Metcalfe was wrong: http://www.spectrum.ieee.org/jul06/4109
but there has been rebuttals, as summarized on the wikipedia article: http://en.wikipedia.org/wiki/Metcalfe’s_law
j e r r y
Nivi,
“Exponential growth” has become sort of synonymous with fast and good and you’re right to call that out. But it’s not the case that exponentials are the exception; almost everything is an exponential in the real world. On the flipside, exponential growth doesn’t mean your user base will grow fast (relative to your burn rate, or whatever).
Things grow or shrink over time because of the differences between multiple opposing processes, which are themselves exponential. One pushes up and the other pushes down. You get user growth from viral invitations. You get user decay as a Poisson process. Or whatever. But the difference between exponentials is still an exponential. So most things in the real world are fundamentally exponential in nature.
This is true for user growth through invite-a-friend, atmosphere density, popularity of Facebook applications through a rich-getting-richer effect; basically everything. Linear growth is hard to get (it requires opposing forces to be exactly balanced)!
People get confused and think they have a linear process because all exponentials look linear at the beginning! Remember Taylor expansions, C^x is approximately x when x