In All Life is Problem Solving, Popper sought to explain the apparent progress of scientific knowledge – that is, how it is that our understanding of the universe seems to improve over time. This problem arises from his position that the truth content of our theories, even the best of them, cannot be verified by scientific testing, but can only be falsified. Again, in this context the word "falsified" does not refer to something being "fake"; rather, that something can be (i.e., is capable of being) shown to be false by observation or experiment. Some things simply do not lend themselves to being shown to be false, and therefore, are not falsifiable. If so, then how is it that the growth of science appears to result in a growth in knowledge? In Popper's view, the advance of scientific knowledge is an evolutionary process characterised by his formula: