There are two arguments against objective knowledge: the difficulties in comprehending the entire universe, and our individual subjective experience.
It is very difficult to begin a discussion about what it means to be human without first discussing what it means to have ideas and knowledge. And there is a very strong argument against beginning a discussion at the formulation of ideas. That is the two pronged attack of incomplete knowledge; and Godel’s incompleteness theorem, the Turing machine and the applied post-structural notion of cultural self-justification.
Without complete knowledge of everything, we can always be potentially wrong. This is evident in Karl Poppers falsifiablilty hypothesis, where no truth can be proven correct, only proven wrong. It is possible to create a far larger number of hypotheses than is physically possible for humanity to disprove. Therefore our inability to disprove god, fairies, string theory, relativity leads us to the unenviable position to entertain the notion that these phenomena may actually exist.
The answer to this problem is Bertrand Russel’s argument of the astrophysical teapot. It is impossible to disprove that a teapot is not orbiting the sun. However it is highly implausible. Therefore we are all technically teapot agnostics, we don’t know the teapot is there but we can’t disprove it. However for the sake of forwarding our own arguments, we act as if we are teapot atheists.
This however leads to the further problem of the criteria which is used to select which ideas to be agnositc / atheistic about and which to pursue for further enquiry. Godel attacked logical positivism, which asserts that all ideas and problems can be solved mathematically, by disproving that any mathematical proof was self contained, that each proof would require an infinite number of other proofs to provide the basis for the proceeding proof. In theory it could be possible after a certain number of proofs to have incidentally described the entire Universe. However Alan Turing’s conceptual Turing machine used for calculating problems has the issue of never being able to determine when the problem will actually be solved. Waiting for a calculating machine for near to infinity with no indication of an end point is not a viable solution for proving/disproving problems. The post-structuralist and deconstructive attacks on language and argument also state that any culture or discourse is reliant on the power structures that advocate it and the temporal cultural state of the people participating in it. Thus the structures will often be based on either self-referential justifications such as freedom, liberty and happiness as fundamental Truths equivalent to gravity, or false premises that hoodwink the masses into believing things that have no basis other than historical mass delusion – religion as the opiate of the masses.
At this point having used logic to disprove itself we are led to the only possible logical conclusion: logic is relative and because everything can be theoretically possible the Universe (if there is one) must be entirely subjective. The Universe is fundamentally thus based on such principles as chaos, emergence and quantum uncertainty which are entirely indeterminate beyond experiencing the phenomena in action, if indeed we are witnessing what we think we are. Or in the case of quantum uncertainty, the act of witnessing changes the state of being. Whatever it is that is driving or not driving the Universe it is completely out of our grasp to conceptualise or hypothesise.
There are two problems with absolute relativism. To live with relativist principles we need to change our normal way of thinking. We should either suspend entirely all logical enquiry in discovering new ideas or truths, or change the way we discover ideas from logic to one of unverifiable belief. These sorts of beliefs cannot be transferred in their entirety from one organism to another because they have no ultimately reducible signified – introspection is ultimately accessible only to the individual. The second problem is that superficially to our senses there appears to be some level of consistency in experience and continuity in the Universe. Whilst it is possible to create ad infinitum explanations that might explain this illusion of consistency and continuity, another possible explanation is that there is an objective reality but we have incomplete knowledge of it and it is so complex that there is a computational impasse in trying to decipher it.
An objective reality would explain the perception we have of consistency and continuity, it would follow some Universal basic principles which by existing would be discoverable through a process of reduction and logic. These principles may include an element of uncertainty but this does mean that the Universe is therefore uncertain at all levels. The Universe is also vast, and as highlighted by the earlier discussion of the Turing machine it is impossible to predict when or if we will ever discover the underlying principles. Just because we as a human species do not have the computational ability to discover something does not mean that it is therefore non-computable.
This last rebuttal and justification is therefore the post-structuralist argument of self-justifying ideas. An often used argument for God is ‘just because humans may not know the nature of God, does not mean that it does not exist’. This is equivalent to the statement regarding computational impasse. The difference between the two arguments is that if God exists the only way that God can be proven is if God chose to prove itself to us. In the case of computational impasse we are the ones in control of reaching the proof. With computational impasse humanities quest for absolute Truth is like the Turing machine. We may stumble upon it one day, which unlike God proving itself is entirely within our own capacity.
This argument is therefore based on my need to be in control of myself, or to understand the factors that influence me. I refuse to relinquish my belief and ideology to something that is incomprehensible. As Isiah Berlin posits, if I ask a person who worships trees why and they say because it is a tree I cannot understand that. If they explain how the tree relates to them, that I can understand.