In more detail, the question is the following. In the process of science, we accumulate knowledge. That's observations, that's applications, that's theories. But this knowledge, does it exist before we have made it our own and it is just up to us to discover it? Or is this knowledge genuinely new, and does only come into existence once we are thinking about and working with it?
Take for example quantum field theory. If you believe that mathematics has an existence independent of human consciousness, you would argue that quantum field theory existed before we knew of it, and we discovered and then used it. If you don't believe that Plato's world of ideas is real, then you'd instead call it an invention of the human mind. Or take some application like for example the LASER (that just celebrated its 50th birthday). Was the construction of such an instrument always a possibility that existed, and it was just discovered by humans? Or is it an invention, a possibility that only came into existence thanks to our ingenuity?
This admittedly philosophical question, that is eventually one about the meaning of creativity, has a correspondence in the arts. In interviews, I've sometimes found painters or writers saying that the "idea" for their work was waiting for them, they were just the ones who brought it to paper or canvas, they are the discoverer and the medium to bring it into our attention, but not the inventor. Some even speak of a mental "place" that they visit to find their ideas, a place they apparently believe is not a creation of their own mind. Others however describe the creative process as entirely self-made, often including trial and error, many studies and improvements, the making of something genuinely novel that has never existed before, an invention.
I, as many physicists I think, believe that reality exists independent from us. It is thus out there for us to discover. Reality doesn't care about the quirks of the human brain or or problems of our societies. So that would put me on the side of the discoverers. However, it is not that simple. Whatever we do, our discoveries are shaded by human perception. Whatever we observe, we observe it with human senses or human instruments. And the theories we write down, they are stories that humans tell which are meant to describe the real world, rather than actually being the real world. To illustrate that, let me recycle an image I used in my earlier post on Models and Theories, see left. You first need to discover. But once you measure it, once you write it down, and make it suitable for human use, you're creating an - necessarily imperfect - image, may that be a collection of data points or a theory. And that's the part of the process which is an invention.
I would argue for example that while we have discovered quantum mechanical effects which exist somewhere in "the real world out there," the theory we have to explain them is a human construct, it's an invention. It uses variables and language that are specific to our species, it carries the history of particle-wave duality, it is suitable to describe the data that we have measured with our devices. An alien civilization might discover the same effects, but they might invent a different story to explain them, a theory that explains their data in possible entirely different ways.
I didn't get the job. I doubt it had anything to do with my inability to explain my reply to this particular question. But still, I wished I had been able to express myself better back then.
Now it's your turn: Discovery or Invention?