One of the most significant achievements from theoretical computer science was to show that there are non-computable problems, which can-
not be solved through algorithms. Although the formulation of such prob-
lems is mathematical, they often can be interpreted as problems derived
from other elds, like physics or computer science. However no non-
computable problem with economical or financial inspiration has been
presented before.1 Here we study the problem of valuation: given some
adequate data, find the value of an asset. Valuation is modeled mathemat-
ically by the discounted cash
ow operator. We show, using surprisingly
simple arguments, that this operator is not computable. Since, theoreti-
cally, financial markets should trade assets based on their fair value, our
result suggests that unpredictability of such markets may partially stem
from inherent non-computable behavior. A discussion of this result is also
included
