Taking out a loan to pursue a degree in theoretical physics in the EU. Bad idea? How common is it for students to take a loan to pursue a theoretical physics degree in Europe, as a non-EU foreigner.
Theoretical physics and mathematics students are advised not to take a loan as there are very few jobs in both the fields. I was admitted to a Masters Theoretical Physics (Quantum fields and Strings) program at Uppsala. So far I am still looking for a scholarship.
Is taking out a loan to pursue a degree as non-EU citizen in one of these two fields always a bad idea?
There are three things the cost of tuition means here, and they give you information about whether or not taking out the loan for a theoretical Master's degree a good idea.


It is expensive to train someone in this work, and someone has to pay for the training. The way that academia has developed, it is usually the sponsors of later research who pay (government, universities, private foundations). (In contrast, professional degrees are often paid for by individuals themselves, although it varies by country and profession.)
Financially, unless you are independently wealthy, you need to check how easily you can pay back this money after you graduate. 


I'd suggest researching the pay levels of various careers that you can pursue with that Masters degree. If you want to immediately work in an industry that pays well (e.g. designing infrastructure for the advent of quantum computing??? at a government laboratory???), and grads from that program have a reasonable shot, then it is not unreasonable to take a loan.
However, if most related jobs do not pay well or require a Ph.D., then you are unlikely to get your money back (soon) by working in the field. You might then be forced to work in, say, software to pay the bills, if your programming skills are transferable enough.
This recent question seems to find it is rare for academic positions to be offered to Masters graduates in theoretical physics.

The cost of the program to you (that is, the absence of a scholarship) may be a signal about where you would rank. 


Funding is certainly a signal for doctoral programs, in my (U.S.) experience. I had several doctoral acceptances where I was told I wouldn't be funded in my first year, but that I could probably find a teaching position; I was one of the more borderline candidates they decided to accept, apparently, and when funding is limited schools tend to invest in the strongest students first, to attract them to the school and make sure that they have the best chance of success. This also told me I might have trouble getting professors' help at those schools, because their time is a limited resource, as well.
If this is true in your case (i.e. others have funding for the same program, and thus you have information about how you compare), then use the information to further inform your actions. It might mean you must be at the very top of your Masters program to have a strong shot at becoming a Ph.D. student. It might also mean that you should in some way improve your application to be more competitive for scholarships or funded programs in the future.