Is it OK to do an experiment in which there is no control variable?

What I mean to say is that I can never change only 1 variable by itself, so I cannot prove causality. If I intentionally change 1 variable, at least 1 more variable will change by itself. This means the most I can do is provide evidence for a correlation. Would science teachers say this is a complete waste or accept it for what new information it provides?|||Yes, perfectly OK. Its often necessary to do experiments like you are proposing. This is especially true when formulating new theories in physics because one is often unsure which variables are inter-dependent and which are truly independent. In such cases a correlation analysis is most appropriate, and will help in the formulation.





Even in hypothesis testing, it may still be necessary to adopt the same approach, because sometimes it may not be possible (or practical) to separate one or more inter-dependent variables, one of which needs to be the control variable.





So go for it, and good luck!