Physics answers how we exist, while metaphysics asks why we exist
In the general culture the difference between the terms physics and metaphysics is often confused. These are two very different branches of thought, and even metaphysics is used to describe to different topics.
Physics and metaphysics were once deeply entwined. The ancient Greeks began to systematically study the world around them and developed a field of study we now refer to as natural philosophy. It was an initial attempt to rigorously study and understand the natural world. However, the ancient Greeks (and other ancient cultures that also embarked on their own versions of natural philosophy) lacked the tools and insight to develop their study beyond asking the questions that we still ask today. During the Renaissance (literally the rebirth) much of their conclusions about the natural world had to be discarded to great social tumult as these ideas (such as the Earth being flat, or there being only four elements) had been held as absolute truth for centuries. The Greeks were only able to construct a foundation of inquiry that later became physics and metaphysics.
Physics
Physics is the study, understanding, and knowledge of the physical, measurable universe around us. This encompasses a lot; it is essentially everything but our society and culture. Physics asks why things are the way they are, but finds answers to how they are the way they are. These are the detailed question and answers of existence. What is matter? What is energy? What is the arrow of time? How many dimensions are there in the universe? How many universes are in the multiverse?
Metaphysics
Metaphysics, in it's academic sense, is the study of theology and ontology. Theology is the study of the western God as well as religion and spirituality. Ontology is the study of beingness and the nature of reality. These are the larger questions of existence. Why do we exist? Why does the universe exist? Is there a God, or gods? Is there a purpose or design to the universe? Why do I exist? Do I have a purpose?
Metaphysics is also more commonly referred to as the study of mythology and the occult - which some also classify as theology (it's a matter of spiritual or religious perspective). Even in this sense, metaphysics questions the nature of existence, although it's methods for seeking answers, such as astrology, were long ago replaced by the more concrete methods of physics and science.
The Ultimate Question
It can be argued that the ultimate question, is "Why does anything exist?" or just "Why?" Both physics and metaphysics are deeply concerned with this question - it really is what fuels anyone concerned with finding answers through either discipline. So, physics and metaphysics aren't cleanly separate, they are still somewhat entwined and complementary.
In the book "The Hitchhiker's Guide to the Galaxy", late author Douglas Adams poses the ultimate question through his characters. In essence they ask, "What is the answer? To life, the universe and everything?" Unfortunately for the characters, they didn't properly ask a question, and got back (from a supercomputer designed to answer this question), the enigmatic "42". The point that Adams made is that it is possible that there is no answer to the ultimate question, and that there may always be another question lurking around the corner. The universe is richer for it.
