Do Physics First
A personal view by Karl Kruszelnicki
Suppose that you have a degree in Physics, and that you are being interviewed for your first paying job. To get the interview going, the interviewer will ask, "So, you have a degree in Physics?" The best answer is, "No, I have a degree in How To Solve Problems".
There are two main reasons why it is essential to make physics a big part of your first degree.
First, physics teaches you how to be a good scientist. You learn how to work out what the problem is, and then, how to solve it. You will learn how to do experiments. You will learn how to design experiments, how to make measurements, and how to analyse your results.
Note one very important thing. You are learning how to be any type of Scientist, not just a Physicist.
Once you know Physics, you need only a very small amount of Local Knowledge to do science into diabetes, the fatigue of metals, the different states of water (still a very poorly understood liquid), or why a tail is more efficient than a propeller (and maybe put the "fish" back into efficiency for ships). You need only a few weeks of solid reading to get started in any other field. You will pick up the rest of the knowledge that you need as you go along.
The second important thing that Physics teaches you is the essential "mental toolbox" to be any kind of good scientist. It doesn't matter whether you are trying to make a sick pancreas "morph" into a healthy pancreas while it's still in the body of a diabetic, or whether you are trying to save fuel by designing a better plane wing.
Every thing that we can measure is in some way dependent on the Four Forces that run the Universe.
They are the Gravity Force (that keeps the planets in their orbits), the Electromagnetic Force (radio, TV, etc), the Weak Nuclear Force (certain types of radioactivity), and the Strong Nuclear Force (holds the protons in the nucleus together). No matter what you are trying to investigate, it will be mediated by one, or more, of these forces. Knowing this makes your job as a scientist so much easier!