Thanks for the referred video. I cannot agree more with l_ruth on the interpretation of what Dreyfus was saying. I post this answer since I do not think l_ruth's response is sufficient to answer the question by Ameet Sharma. The question that needs an answer is this:
According to Heidegger, physics can't explain Dasein. Doesn't that make Heidegger a dualist? Or is he saying that the physical world can be explained in terms of Dasein?
To answer the question, some preliminary is necessary.
- Dasein means (the mode of) human existence, a la Heidegger. Heidegger postulates that we humans are the only entities that can ask the question of our own existence as well as existence itself. Neither dogs nor ants can ask that kind of question. For this reason, Heidegger thinks that knowing about human existence is the only window to know about the existence itself.
- A (Cartesian) dualist holds the view that the world is composed of things that extend and things that think.
- Heidegger famously rejected the Cartesian dualism. To Heidegger, we humans as beings are necessarily situated in the spatio-temporal coordinate (or beings-in-the-world, a la Heidegger). Separating oneself from the world, i.e., the stage for the Cartesian skepticism, is impossible.
- Dreyfus is well known for his anti-AI view, that is, it is impossible for machine intelligence to be equivalent to human intelligence.
Given these, let's answer the question. Dreyfus’ Heidegger argues that science cannot explain the mode of human existence. Indeed Heidegger argued that the human condition is known analytically, by “existential analytic of Dasein” (https://plato.stanford.edu/entries/heidegger/) So Dreyfus' Heidegger rejects physicalism and materialism (views that try to explain mental phenomena by means of science or by res extensa). Rejecting physicalism does not make Heidegger a dualist. Why? Ameet Sharma is in the right direction since Dreyfus' Heidegger thinks that the physical world can be explained only in terms of Dasein. (see 1)
In the video, Dreyfus is forced to answer how scientific realism is possible under the Heideggerian view, or more specifically, under the Husserlian phenomenological method (an alternative way to understand the physical phenomena) which Heidegger adopted. The potential problem raised for Dreyfus is that if scientific realism is true, then the above 3 (beings-in-the-world) cannot be true. I think Dreyfus's answer is brilliant, which we can only observe from a philosopher master (Professor HerbertHubert Dreyfus passed away this year (2017). Ah Time, that completes us all!). Dreyfus says that it is indeed scientists’ job to explain the natural phenomena, but it is thanks to the phenomenology that warrants the doings of scientists.