A new rocket that seemingly can create thrust without using fuel to push backwards has just been published. My thoughts in news.com.au were not entirely positive. Simply put this would break Newton's 3rd law, and also translation invariance (or the idea that the laws of physics don't change in one spot to another). If this rocket really doesn't need fuel to create thrust than that would be the end of physics as we know it. Instead my guess is that this is likely just thermal expansion as the microwaves (inside the EM drive) are turned on and heat it.