I should say a million times, that Advaita is not physics. Especially after the publication of such books as "The Tao of Physics" and the endless Deepak Chopra stuff there is a great danger that what I have to say here will be misunderstood.
Superstring Theory says that everything in the universe and the space-time within which everything in the universe exists is a manifestation of superstrings.
In this sense, string theory is a monistic theory.
The only reason to mention string theory is to remind people that they are familiar with monism, even if they didn't know it.
Advaita is a monistic philosophy. It however takes consciousness to be the root of everything, not strings. In a physical theory like string theory, consciousness is a side-product of sufficiently complex agglomerations of matter, like our brains and accompanying bodies. In Advaita, space, time, matter are side-products of consciousness.
Advaita cannot be a theory of physics, nor be mathematical.
The last thing to mention is that as per Advaita, this insight into the nature of things is available directly to the awareness. It does not require mathematics, or particle colliders to confirm this, as per Advaita, it takes a prepared mind.
A whole system of ethics and an entire culture flow from the (Hindu) accretions around this core idea. However, Hinduism is much more than Advaita and includes denials of the core idea as well.
Note that just as one could have and does have several religions around the transcendent personal god of Judaism/Christianity/Islam, one could have several religions about this absolute monism. The "religious" component of Advaita comes from the specific practices and traditions that it has bound to itself from Hinduism.
So is my current understanding. It is of course, subject to revision, upon greater understanding.
Is Advaita true? Fortunately, it doesn't matter. Yes, I know I have made an extremely provocative statement. The point is that there is no value in belief or non-belief in Advaita, what matters is what you do. Following the golden rule ("do unto others as you would have done unto you") is an excellent starting point, for instance. There are many "derivations" of the golden rule in different cultures. In Advaita, the derivation is that the others **are** you. You have to see this directly, and making a habit of the rule helps, supposedly.