@Lancelot Thorsbane (lol, wow)
When scientists talk about "parallel universes" they're talking about estensions of the known universe which can be inferred under the laws of science. For instance, one theory of quantum mechanics states that a range of probabilities (Or some concept mathematically equivalent to probability) occurs simultaneously. So for for instance, if my probability distribution allows for a certain probability of me typing this post on my keyboard, and another probability of me getting up to use the bathroom, then both sequences of events will occur at the same time, but I will only percieve one because it's a different version of myself that's using the bathroom. However, the mathematics of quantum mechanics imply discrepancies in our understanding of physical reality, which could be explained by a parallel "universe" in which I'm using the bathroom instead.
There are multiple definitions of the term "multiverse". Contrary to what the author of the article says, scientiests do not invariable define the word "universe" as "all that exists". Sometimes, what is meant by "universe", in a sceintific context, is the observable universe, or, the part of the universe we can see with our telescopes. Beyond that, the current inflationary theories of the Big Bang imply that the universe as a whole is vastly larger than just the part we can see. First of all, there are parts of the universe which are so far away that the light from those regions will never reach us due to the expansion of space between us and those regions. This divides up the universe into "Hubble Bubbles", which consist of all things which are close enough to each other that they can exchange light-signals. Beyond that, there are also bubbles of false vacuum, which themselves consist of regions of the universe which have a specific vacuum energy. Different bubbles of false vacuum will have different values for physical constants than our part of the multiverse, so they are very different from anything we are familiar with.
Then there is the Many Worlds Interpretation of Quantum Mechanics, which is essentially as you describe it here. However, this interpretation is not considered standard, and has never been shown to be able to do all the things that the Copenhagen Interpretation can do.
Another example would be higher dimensions. For instance, if string theory is true then there's eleven dimensions instead of just the three that we're used to. So there could be another three dimensional space that exists next to the one we live in. And while we would only be able to percieve our own three-dimensional space, the other three-dimensional must exist in order to be consistent with reality, assuming that string theory is accurate.
How would these theories contradict Objectivist metaphysics?
They don't. The author is presenting a silly argument from definitions. Nothing more than a word game.
Objectivist metaphysics would say that probability pertains not to the real world but to our lack of knowledge about the real world.
Objectivism has no official position on probability. This is because it isn't really a matter of philosophy, but rather about what tool is right for what job.
Subjectivist and frequentist interpretations of probability differ in that the subjectivist interpretation uses probabilities to model beliefs about the world, while the frequentist interpretation uses probabilities as a part of models about the world. Under frequentism, metaphorically speaking, a car is for going places, but under subjectivism a car is also a place where someone might sometimes want to go. Neither "interpretation" of cars is more correct than the other.
To better illustrate the difference between the two, a subjectivist probability interpreter, when talking about Newtonian physics might say that "There is an x% chance that the path of the orbiting planet will correspond to the path predicted by Newton.", whereas a frequentist probability interpreter would say that "Newton's theory predicts that there is a 0% chance that the path of the orbiting planet will not be an ellipse."
It gets kind of confusing because the frequentist interpretation sees probabilities as something that is only a part of a model of the real world, whereas the subjectivist interpretation is itself a model of the real world which seeks to capture how a rational agent might process his beliefs.
This is important because physicists never use the subjectivist interpretation of probability. If a physicists says that there is a 50% chance of a flipped coin landing on heads, then he does not mean that he does not know on which side the coin will land on (since what he does or does not personally know or believe is irrelevant scientifically, only the model and data are important). What he is saying is that, while the laws of mechanics governing the coin are completely deterministic (and that, in principle at least, with enough information and computing power you could predict exactly how the coin will land each time), it is best to simply assume that the coin will land on heads 50% of the time, since modeling all of the motions of the coin would be too complicated to make any calculations feasible.
In science, probabilities are merely a method used to simplify extremely complex phenomena. They are simply a tool, and have no deeper epistemological or metaphysical significance.
For example, if I flip a coin into the air, the probability that it will land heads is 50/50, but in reality it can only land one way, given its nature and the nature of the causal forces acting upon it. Therefore, any theory which says that probabilities apply to reality itself instead of simply to our lack of knowledge about reality would contradict the meaning of probability, which is an epistemological, not a metaphysical concept. Insofar as quantum mechanics says that probabilities are part of the real world, it is per force inconsistent with Objectivist metaphysics.
According to Objectivism, the properties of an entity exist independently of our knowledge of them, yet quantum theory says that by observing subatomic particles one literally brings their identities into existence. In other words, consciousness -- observation -- creates what it observes simply by observing it. Quantum mechanics says that a measurement does not tell us about the pre-existing state of a particle; instead, it creates that state. This is subjectivist metaphysics with a Kantian legacy. Furthermore, QM does not explain just how a measurement could transform nothing in particular into something with definite properties. It is not, as you referred to it, a "law of science." It is mysticism masquerading as science.
Luckily, none of this is actually true. When I began studying QM at uni, I was very much relieved to find out that the underlying reality it describes makes perfect sense and is really quite mundane when you understand it.
There is an excellent video series in youtube which provides a detailed description of quantum theory:
QM says that a particle is actually a cloud of stuff that extends throughout the entire universe and is "denser" in some places (its "density" is actually descibed by a complex number, so it also has a phase and the whole story is a bit more complicated). This cloud has a very specific nature and obeys the laws of physics entirely deterministically. However, since it is an extended entity, it obviously has no unique position or momentum, etc.
The part where probability comes in is when that cloud interacts with other clouds. More specifically, when it interacts with high-energy macroscopic objects like people or rocks. When that happens, we have to use statistical mechanics and combine it with the cloud description of the particle to figure out what will actually happen. The mathematics of QM transform the cloud (the actual description of the particle) into a wave of probabilities with respect to its positon or momentum or whatever. And, of course, statistical mechanics uses (frequentist) probabilities, so really, QM is not fundamentally different than Newtonian mechanics.
In fact, the first two videos of the series I linked to above describe exactly how Max Planck started QM by using statistical mechanics and an assumption that the enrergy of particles comes in discrete packets or "quanta" to resolve the UV-catastrophe.
Also, if you don't have the time to watch the entire series above, just skip to this video to see how an electron acts as a cloud rather than a little hard ball:
Here's also a cool simulation of the double-slit experiment:
String theory is no better, proclaiming that there are eleven dimensions instead of just three. What is that supposed to mean? How does such a theory refer to anything in the real world that can be confirmed by observation? It doesn't. It is pure rationalism -- abstract theory divorced from an empirical foundation. Again, this is not science; it is the abdication of the scientific method, and it flies in the face of common sense. Scientific theory should make difficult-to-understand events intelligible. String theory does the opposite; it makes them less intelligible.
Nothing could be further from the truth.
Consider the state of modern physics. We have two extremely well supported theories of how the universe works, General Relativity and Quantum Mechanics (none of their competitors come even close), and yet, they disagree with each other.
GR says that matter affects things only locally. That is, an infinitesimal piece of matter at any point in spacetime affects only the shape of spacetime at that single point. It is impossible for it to affect things at other points, because at other points, there are other pieces of matter, and between any two points there are more points each with their own piece of matter.
QM, on the other hand, says that it is nonsensical to talk about matter at a single point in spacetime. Since it describes things in terms of waves and wave properties such as frequencies, it takes on a global view of matter, because only the wave as a whole can have a frequency.
In other words, each theory says that the other is insane. So how do we resolve these contradictions? The same way contradictions in physics have always been resolved. By abstracting the underlying mathematics until tthe contradiction disappears and things start making sense.
Einstein discovered special and general relativity by abstracting the geometry of spacetime until the contradicitons between Newton's mechanics and Maxwell's electrodynamics disappeared. The famous mathematician, Riemann, discoverd that Euclidean, Hyperbolic, and Elliptic geometries could be unified by taking each point of the plane and assigning to it an abstract quantity called a "tensor" which is like a little machine which will give you the squared length of a vector at that point (this particular tensor is called a "metric tensor"). The resulting structure is called a "manifold",and depending on how you configured these "little machines", a specific geometry would result and its rules could be figured out entirely by looking at what the little machines do.
This is essentially how GR works. At every point in spacetime, there are two machines. One of them, called the "stress-energy tensor", describes properties of matter if you send a "test particle" through the point (properties such as energy, momentum, pressure and sheer-stress). The other, called the "Einstein tensor", describes the shape of spacetime at that point. Einstein's equation says that the output of this machine is simply 8*pi times the output of the matter machine. The Einstein tensor itself is made up of a collection of metric tensors (and other pieces), and by reverse engineering the Einstein tensor (that is, solving Einstein's equations), we can figure out how its metric tensor is configured, and from that we can figure out the geometry of spacetime generated by matter. We then use our knowledge of spacetime geometry to figure out how matter will move through it, which will in turn change the shape of spacetime again, and so on.
Similarly Paul Dirac was able to derive the properties of an electron by abstracting over Hamiltonian mechanics (a modern theory of Newtonian mechanics that focuses on energy). He saw that a mathematical structure in HM, called a Poisson bracket, which appears in Hamiton's equations of motion (which describe how energy changes across positions and momenta of a particle), followed the same algebraic rules as another abstract algebraic structure called a commutator. He simply wrote out Hamilton's equations and replaced the Poisson brackets with commutators. However, Poisson brackets act on functions (which are rules that assign a single number to each point in spacetime), whereas commutators act on operators (which themselves are rules that describe how a function changes). So Dirac, instead of treating position and momentum as numbers, changed them into operators. The functions that the positon and momentum operators act on are called wave functions, and lo and behold these are the functions that describe matter at the most fundamental level in QM.
Note that an individual wave function is a specific rule that assigns a single complex number to each point in spacetime. So if you could examine a wave function point by point and looked at a wave function at two different points, then the complex numbers at the two points are both part of the same wave funciton even if they have different values.
Contrast this with a tensor, which is defined completely only at a single point, and if you look at two different points, then, even if their tensors have the exact same values, they are in fact two completely different tensors.
It is important to realize that a number is also a kind of tensor. Indeed, early naive attempts at the unification of GR and QM tried to treat wave functions as a collection of tensors (or, a tensor field), or they tried to treat tensor fields as if they were wave functions, but this resulted in nonsense.
In order to resolve these contradictions at the basis of our very understanding of reality, it is necessary to invoke the theory of fiber bundles.
At some point, mathematicians realized that they did not have to restrict themselves to assigning just numbers, vectors, and tensors to points in a manifold. Really, one could assign any sort of mathematical structure, even other manifolds.
This is where the extra dimensions of string theory come from. By assigning a six or seven-dimensional complex manifold to each point of spacetime, one can derive all of QM and GR (with a few additional assumptions because the theory is incomplete).
Now, we could say that string theory is actually about a Newtonian universe made up of points which themselves are extremely complicated abstract machines in order to account for relativistic and quantum mechanical deviations from newtonian physics. Or we could make things much simpler and say that spacetime is simply folded up in a weird way.
Similarly, you could say that the Earth is actually flat, and that it simply has a metric tensor at every point of its surface which produces the illusion of a spherical geometry. But why would you, really? It's much easier to just say that the Earth is round.