Well, define "Interchangeable"
I can say a lot of thing in this world is "Interchangeable" but with different meaning. For example, can we interchange the concept of "Male" and "Female"? On a glance, you cannot, because male mean male, female mean female. However, what if I am talking about the gender of human? You still can't because there can only be either male and female in human gender, but how about something "Asexual"?
On the other hand, Einstein is one of the major proponent of Quantum Physics in 20th Century, and if you are talking about Contemporary Physics, you need to include quantum physics as one of its core topics. Basic we all knew from the development of Electronic Microscope, Atomic Behaviour is very much different than elemental behaviour which we understand before, so to say "Contemporary Physics does not cover Quantum Physics is simply wrong"
And idioms or not, if I say I have been in this world for 38 years and still can't find a job, does that mean I started finding a job at age 0? This is not a idioms, this is how people say things.
I don't know about you, but I don't think my Physics is bad enough not to be able to discuss with other people. Again, unless you have specific topics you have in mind that you think I am wrong, I am more than happy to discuss it. Even if I am not really up to the par in physics, that does not mean I cannot discuss matter about Physics, we are all here to learn right?
If you have to be creditable expert in the field before you can comment on something, then I guess this forum should have been blank, because as far as I see, none of youse are creditable in defence related matter.