I have done some studying on the membrane theory or string theory. I understand why energy can have no mass, because energy is vibrations different from vibrations that define mass relative to us. The vibrations are on membranes that flow through 11 dimensions. However, it occurred to me that the probability value of vibrations, that define energy, coming together to form exact vibrations that we see as mass, is quite large. For energy vibrations to come together randomly in 10 dimensions with time to form a vibration on the string or membrane that defines mass to us seems very unlikely. Therefore, I am wondering if energy (light) has ever been converted back into mass. I see an easy explanation for mass being converted into zero mass energy, but I don't see a way to convert energy back into mass using the string theory to explain the universe. However, I do see an explanation for converting energy back into mass with an understanding of the vibrations that make mass. However, I don't think anyone is this far since the string theory is still theoretical. Anyway, I would really appreciate if someone could help me with the question. Can energy be converted back into mass? I know mass is a from of energy... If there are any experiments done with this, that would be very helpful if you could direct me... Thank-you so much.