<p>I majored in Astronomy as an undergraduate but ended up going to medical school and becoming an MD, now in private practice. The problem with getting a PhD in very theoretical areas of Physics like String Theory, Cosmology and some aspects of Quantum Mechanics and General Relativity is that there are not many practical applications in these fields where an employer could expect to make money from the discoveries that you make. It is true that Quantum Physics is what makes semiconductors possible and they have had a profound impact on our economy and society as a whole. However, most of the research done in theoretical Physics is geared towards gaining a better understanding of how the Universe operates rather than developing commercially viable technology.</p>
<p>In good economic times when money is more readily available companies and governments may be willing to fund research where the knowledge gained is for its own sake. In times like these employers are more likely to be looking for researchers, such as PhDs in engineering, who are trained to develop theories that have practical commercial applications as opposed to simply expanding our knowledge and understanding of Nature.</p>