Science is about the study of physical objects and nature.
No, science is the scientific method. If anything happens within the physical universe, it is possible for science to speak of the matter. Scientifically, economics has done a lot, and the fact that you just disavow it for some philosophical reasons doesn't mean that the methods employed are not scientific. There have been scientific studies which look at those things I mentioned, and they're the reason why those things are treated the way they are in economics courses.
How can that question be addressed using only empirical evidence? Is it not a question of philosophy? T
Because the science of economics isn't giving a value to an object, it's describing the human interaction, which is objective, surrounding the value of those objects. Yes, if you want to start talking about why a certain objective is given some value, that is philosophical. If you want to start talking about how people interact with those objects, how they trade those objects, and how the sum of all those interactions mash up, then you're talking scientific theory.
Basically, you guys are looking at the issue on a micro level. It would be like saying we don't know where a baseball is going to be because we don't know where each individual atom is going to be. But we DO know where the baseball is going to be, even though we don't know where the individual atoms that make up that baseball are going to be, or hell, IF they're going to "be." Macroeconomics is a field which deals with, well, these macro issues.
For instance, the concept of aggregate demand, and it's effect on an economy, is not value laden. There is no "object" by which we are questioning it's value. It's a phenomenon, from which we can question it's cause's and effects. Through analysis, we've learned that when there isn't sufficient demand in a market place, then the market place suffers. This has nothing to do with value, it is an object occurrence which we can objectively examine. Keynesianism came to be accepted because it was able to describe the market that people were seeing, and produce effects that it promised to bring; this theory is reproducible, and looks at objective facts.
No one is saying science can objectively ascribe value to an object; we're saying science can objectively examine the market, and the effects of human interaction. Psychology uses the scientific method, but it deals with something which is very unquantifiable, and subjective, but that does not mean that psychology is unscientific.
*edit*
EDIT: All the things you listed are concepts or ideas. Concepts and ideas are human constructions. Science is about the study of physical objects and nature. Philosophy is the study of concepts and ideas. Thus, economics falls under philosophy, not science.
Everything we can imagine is a concept or idea. Atoms are concepts or idea's. Protons are concepts and idea's. If science can't deal with concepts and idea's, then science can't study anything, which is so clearly false that it's not worth arguing against.