Tim Cullen turns his attention to String Theory – and he is not exactly being friendly (see https://malagabay.wordpress.com/2015/06/24/string-theory/ .. and begins his blast with the words, 'string theory is a theory of quantum gravity' and goes on to say it 'is a problem that is stuck at the bottom of a very deep rabbit hole'. One feature of string theories is that they require extra dimensions of spacetiome for their mathematical consistency, and 'while groping around at the bottom of the rabbit warren physicists are often guided by intuition and conjecture' (quoting Wikipedia). These conjectures are later proved by mathematicians and in this way string theory serves as a source of new ideas in pure mathematics.
There are of course, lots of other critics of string theory and multi dimensions in space. He provides two book titles – Peter Waite, 'Not Even Wrong: the failure of string theory and the search for unity in physical law' Basic Books:2006, and Lee Smolin, 'The Trouble with Physics: the rise of string theory, the fall of a science, and what comes next' Mariner Books:2006. Lee Smolin is a mathematical physicist himself and he points out that none of these elaborate new theories have been tested experimentally – and string theory cannot actually be tested (so its open house).