Limitations of scientific knowledge
Science does not claim to provide truths but rather approximations to truths. Any scientific theory or even any scientific statement has at some point an arbitrary level of acceptance. Sometimes this level is called the postulates of the theory. The theory makes no attempt to justify these postulates but accepts them as stated. This is like what we accept as truths in forming our concepts except that in science these are explicitly acknowledged not as truths but as approximations to truths. Experiment and evidence can then test the predictions and will decide whether and when the theory needs rethinking.
In classical physics, starting with Newton, a number of assumptions were made within the descriptions. These were simply accepted as facts needing no explanation. An example is the absolute and constant flow of time in Newtonian Mechanics. With the development of the theory of relativity it was shown to be quite wrong. This meant that a previously accepted ‘truth’ had been questioned and shown to be only an approximation to the truth. The whole of classical physics, with its accepted descriptions of reality, has received many body blows by the development of Quantum Mechanics, which comprehensively challenged the basic accepted concepts and proved to be a much more useful theory in describing reality.
Scientific understanding can only grow in areas where there is a good opportunity for gathering experimental data. The best theories are numerically very accurate such as in Quantum-Electro-Dynamics where 1 in 1000 000 000 000 accuracy is relatively easily demonstrated. The worst theories are very approximate such as in cosmology where the ultimate fate of the universe is unknown. It could be in an accelerating expansion forever, slow its expansion to reach a constant size eventually or it could collapse after expanding. So, these approximations are sometimes wide of the mark of truth. [After many years of study on this the theory has been shown to be basically flawed in a recent experiment which looked at Supernovae - the Universe is apparently expanding at an accelerating pace!]
Where we are only concerned with the quantity of something we can easily experiment with, we can rely on science to provide ever more accurate measures. These quantities, however, become increasingly inaccurate for possible experiences that are far from easy to experiment with. So, we can determine factual statements of relative quantity as true such as ‘the moon has less mass than the earth which has less mass than the sun’. We can also be very accurate in saying how much more or less mass one has relative to the other. However, what is being described in terms of quality is not an area in which we can rely on physics. The difficulty in this example is explaining exactly what mass is. We can apply the concept well in areas of common experience such as understanding the motion of planets and snooker balls etc., but to explain definitively what mass is, is not achieved in science. Attempts to explain the postulates of various theories go on into greater and greater depths and the true nature of reality is something that remains elusive. It is possibly something science can never find. It may be that the true nature of reality lies in an area inaccessible to experiment.
Because of this no understanding of any part of reality can really be considered as known. It is only an approximate description, which, though numerically good, may be a totally inaccurate description of the true nature of that part of reality.
Since asserting that such understanding is true or known is not acceptable, then to assert that all reality fits our understanding is to be quite wrong. The most we can do is to see if we can apply our approximate descriptions to the rest of what we perceive of reality and, if it is still numerically good, include this new larger part of reality in our theory. It seems that all perceived reality, or more accurately that part of existence we are able to discover through our repeatable observations, obeys the same physical laws. However, that it does so may be a condition for our perceiving it in the first place. To assert that reality ends where our perceptions end is completely unjustified. If we cannot see or otherwise perceive something it doesn’t mean that it doesn’t exist.