Science has progressed for 400 years by ultimately explaining observed phenomena in terms of fundamental theories that are rigid. Even minor deviations from predicted behavior are not allowed by the theory, so that if such deviations are observed, these provide evidence that the theory must be modified, usually being replaced by a yet more comprehensive theory that fixes a wider range of phenomena.
The ultimate goal of physics, as it is often described, is to have a "theory of everything", in which all the fundamental laws that describe nature can neatly be written down on the front of a T-shirt (even if the T-shirt can only exist in 10 dimensions!). However, with the recognition that the dominant energy in the universe resides in empty space — something that is so peculiar that it appears very difficult to understand within the context of any theoretical ideas we now possess — more physicists have been exploring the idea that perhaps physics is an 'environmental science', that the laws of physics we observe are merely accidents of our circumstances, and that an infinite number of different universe could exist with different laws of physics.
This is true even if there does exist some fundamental candidate mathematical physical theory. For example, as is currently in vogue in an idea related to string theory, perhaps the fundamental theory allows an infinite number of different 'ground state' solutions, each of which describes a different possible universe with a consistent set of physical laws and physical dimensions.
It might be that the only way to understand why the laws of nature we observe in our universe are the way they are is to understand that if they were any different, then life could not have arisen in our universe, and we would thus not be here to measure them today.
This is one version of the infamous "anthropic principle". But it could actually be worse — it is equally likely that many different combinations of laws would allow life to form, and that it is a pure accident that the constants of nature result in the combinations we experience in our universe. Or, it could be that the mathematical formalism is actually so complex so that the ground states of the theory, i.e. the set of possible states that might describe our universe, actually might not be determinable.
In this case, the end of "fundamental" theoretical physics (i.e. the search for fundamental microphysical laws...there will still be lots of work for physicists who try to understand the host of complex phenomena occurring at a variety of larger scales) might occur not via a theory of everything, but rather with the recognition that all so-called fundamental theories that might describe nature would be purely "phenomenological", that is, they would be derivable from observational phenomena, but would not reflect any underlying grand mathematical structure of the universe that would allow a basic understanding of why the universe is the way it is.