This is a historical post. Bear in mind that I was slowly coming to accept Popper-Deutsch epistemology.
In my last post I started to discuss the differences between Positivism and Scientific Realism. To over simplify it, Positivism (at least as Hawking defines it) cares only about the mathematically model and how good its predictive abilities are. Positivism does not care about whether or not science is getting ever closer to some underlying truth. Scientific Realism takes all scientific theories seriously as approximations of an underlying truth.
Actually, despite what Deutsch says (in my last post), I feel Positivism has value. Though I generally agree with Deutsch, sometimes you just want to predict an outcome and you don’t really care about why it works. (Quantum Mechanics made many advances without taking itself seriously as an explanation, for example.) In fact, I think most people would be shocked to realize that this is how most science and engineering are done. Scientists rarely become philosophical about what their equations mean for reality.
However, Deutsch is right about one thing. Positivism ultimately fails to grasp the value of believing your explanations. It is only through believing your explanations that you can comprehend them. And only by comprehending them can you refine them into something even more useful.
Over at the Eternal Universe (a Mormon themed Physics site), I found the following post that illustrates the power and limitations of Positivism. Here Joseph Smidt, who, I promise, knows a million times more physics than I do, advocates for Positivism in at least one situation. He points out that in the famous quantum double slit experiment  to calculate the correct answer you have to “assume [a single] particle [goes] through both holes together.”
When you add more slits, if you want to get the right answer, you have to assume “the particle, in some sense, travels… in every path possible.”
And finally, if there are no slits at all, then “the math we use suggests the particles take, in some sense, every possible path.”
Joseph then asks:
Now, is this really what is going on, or is this just a model? I’m guessing it is just a model. However, it’s okay since it has significant predictive power.”
Nevertheless, the question is always going to pester me: why do such bizarre models give such amazing answers?!?!
Whether Joseph realized it or not, he was advocating for Positivism over Scientific Realism – at least in this instance. And can you blame him? Are you ready to accept that a particle actually follows all possible paths from point s to point o?
But Deutsch takes this very same point and says, yes, that’s exactly what we should assume. If that is what the theory says, then that is, in some sense, a more accurate explanation of reality than any other existing alternative. If that were not so, then we’d actually have some simpler mathematical theory that gives the same results but doesn’t have to assume something as ridiculous as each particle passing through infinitely many paths simultaneously. Therefore Deutsch (taking his lead from Karl Popper) argues that our scientific theories are not primarily about prediction, but represent an actual verisimilitude of reality. 
I agree with both Physicists in this case, though not simultaneously. If I’m just trying to use a theory to make a prediction and I’m not prepared to try to cosmologically wrap my brain around a mind bending theory, then Positivism is probably for me. But if my goal is to explain and thus comprehend reality, then Scientific Realism is my only option. Therefore I need to take seriously the fact that a particle can be in infinitely many places at once and follow that thought to it’s logical conclusions.
Of course there is always the possibility that some future theory will replace the current one. Perhaps even one that doesn’t require me to think of particles as being in many places at once. But until that new and better explanation exists, this really is our best explanation of reality – no matter how disturbing it is.
Questions for Discussion:
Do you personally identify more with Positivism or Scientific Realism?
If a particle does take every path to get to it’s destination, what does that mean to us personally?
 Double Split Experiment – I’ll do a future post that explains it better, you don’t need to understand it at this point. The short version is that in quantum physics if you send a single ‘particle’ of light through two slits, it somehow goes through both of them simultaneously and then interferes with itself on the other side. Impossible? Guess again.
 Again we see that Popper is the father of both points of view: both Positivism and Scientific Realism. But keep in mind that Popper himself claims he is not a Positivist.