"Being without becoming [is] an ontological absurdity" says the Doctor in 'The Time Monster'.
He's talking about time, about the fact that time is - by definition - a process of change. Time is what entropy looks like to those of us in the midst of it. Entropy increases, thus time's arrow goes forward. 'Becoming' is just a way of saying 'change'. Everything is always in the process of becoming something else. Every apple is in the process of becoming a rotten apple, or an eaten apple, or seeds resown. 'Ontology' is the fancy name used by philosophers to mean the study of what it means for things to exist, to be real. The Doctor is saying: "the idea of things being frozen in time is inherently absurd because things that don't change effectively don't exist".
Though, of course, in 'The Time Monster', things and people do get frozen in time. The story shows us something happening which has already been established as impossible. It's almost as if we are being explicitly invited to read the story metaphorically.
This is something that doesn't quite happen in 'The Three Doctors'. As Phil Sandifer has said, the story should be set in the Land of Fiction. The moments when Omega materialises an ornate chair from nowhere, and when the Doctors make a normal door appear amidst all the bubbly orangely madness, are moments when we see how Omega's realm should have been done - as an openly metaphorical realm of familiar imagery surreally employed. We have a similar problem in 'The Trial of a Time Lord'. Clearly the entire trial should have occured in the Matrix, in the realm of metaphor, in the nest of sinister and surreal Victoriana, instead of in a bog-standard courtroom with some spangly bits stuck on because it's in space. Omega's realm should have been such a place. It should have been like the Land of Fiction, or Goth's Matrix, or the Valeyard's Matrix, or Heaven in A Matter of Life and Death. We are, after all, clearly engaged in a life and death metaphor here, with things disappearing from our world and being stranded in another, and then hauntingly returning to attack our world. However, as I say, 'The Three Doctors' attempts to foreclose on such readings by stubbornly insisting upon sciency-sounding jargon. Black holes, anti-matter, etc. The metaphorical possibilities of being transported from one realm of reality to another of unreality are shut-down (the attempt is at least made) by the technobabble about matter being processed so it can exist in a world of anti-matter.
Thing is, it never quite takes. Anti-matter is rarely used to mean anything scientific in sci-fi. The name itself is metaphor, expressing a scientific concept that is very hard to grasp in literal terms, especially for the layman. In sci-fi, 'anti-matter' is usually metaphorical. In 'Planet of Evil', anti-matter is straightforwardly hauntological! It is evil matter. Ghostly matter. Gothic matter. Hammer matter. It can infect our world, bringing ghosts with it, making jungles into haunted spaces, turning a sci-fi boffin from a Dr Jekyll into a shambling, simian Mr Hyde. In 'The Three Doctors', despite the attempt to shut down the metaphorical reading, anti-matter refers to the realm of ideas, and more particularly to the way of thinking about the world that sees ideas as primary, as more fundamentally real than material things.
As Engels pointed out, all philosophy can be divided into idealism and materialism. Idealism, in this context, refers to the notion that ideas are in some way more fundamental or more primary or more influential than matter, and that material things exist in some way 'after' ideas. Materialism, in this context, refers to the notion that material reality is more fundamental, more primary or more influential, and that ideas stem from matter rather than the other way round. In many ways, materialism has won this argument. Modern science is pretty unambiguous in its findings: ideas are products of brains, which are products of material processes. The material world existed long before anybody had any ideas about it, and would continue to exist if there were no ideas. However, it's interesting how many scientists harbour idealist conceptions in other areas. Take Richard Dawkins, for instance. In many ways, a classic example. His scientific viewpoint is decidely materialist. We don't even need to get into the old debate about whether his genes-eye-view of evolution is reductionist and determinist. We can take his own account of things at face value and declare, undoubtedly with his agreement, that his worldview is materialist rather than idealist. There is no mystical component. In the beginning there was not the word. However, in spite of himself, his ideas about memes are highly idealist. He tries to ground his view of culture in a hard-headedly materialist understanding modelled on his view of genetics, but his account flies off into the realm of idealism. Memes are themselves entirely notional units which exist only in poor-defined and fuzzy metaphorical accounts. Dawkins sees society and culture as made of such notional units (their size, complexity and nature fluctuates with the needs of his storytelling) which interact almost without human agency. They occupy human heads like germs in bodies. They replicate like bacteria in the gut. They spread like diseases. They self-organise and use people as hosts. And this dance of these selfish memes, these impersonal little idea-creatures, forms the basis of changes in human society and, ultimately, human history. They get transmitted in novels and films, etc, until they occupy enough heads to make sufficient numbers of people act in ways that change the "moral zeitgeist". It really is like computer viruses causing widespread changes in how computers work by replicating and transmitting across networks. It's an account that is as essentially mystical as it is incoherent, even as it models itself on a materialist account of biological evolution - a delicious irony coming from such a crusty so-called atheist and sceptic. Ironies pile on top of each other when Dawkins tries to use the memetic view of culture to explain the otherwise inexplicable (to him) popularity of supposedly irrational ideas... and falls directly into the most embarassingly vulgar and irrational kinds of idealist reductionism. The really interesting thing here is that Dawkins arrives at this thoroughly idealist view of society, culture and history via the route of vulgar materialism, the kind of vulgar materialism which insists upon a reductionist genes'-eye-view of evolution coupled with a reductionist view of brains as being like machines which run software. And this is where we can draw a distinction between vulgar materialism and dialectical materialism.
Dawkins' materialism is vulgarly positivist because it is based upon treating reductionism as though it is more than a tool, as though it represents something true about how the world works. Reductionism is fine as a method - it has done some wonderful heavy-lifting in the history of science. It is, essentially, the procedure of studying things by taking them apart (either literally or metaphorically) into bits and pieces and then studying the pieces in isolation to see how they work on their own. And that's fine. You can learn a lot about rivers by studying water molecules. The great mistake made by so many people is the idea - which is impliclty held often by people who would explicitly reject it if it were offered to them - that you can understand everything you need to know about rivers from the study of water molecules because rivers are essentially nothing more than aggregations of lots of water molecules. A more dialectical view of materialism would see an interrelation of material at various levels, from the molecular to the social. It would remember that rivers are also things that people use socially.