We’re back to our Edge series of ideas scientists wish more people knew about. Today is John C. Mather and the Big Bang.
Mather isn’t pleased with popular conceptions.
What astronomers actually have observed is that distant galaxies all appear to be receding from us, with a speed roughly proportional to their distance…[W]e can get the approximate age of the universe by dividing the distance by the speed; the current value is around 14 billion years. The second and more striking conclusion is that there is no center of this expansion, even though we seem to be at the center. We can imagine what an astronomer would see living in another distant galaxy, and she would also conclude that the universe appears to be receding from her own location. The upshot is that there is no sign of a center of the universe…A third conclusion is that there is no sign of an edge of the universe, no place where we run out of either matter or space…The actual universe appears to be infinite now, and if so it has probably always been infinite. It’s often said that the whole universe we can now observe was once compressed into a volume the size of a golf ball, but we should imagine that the golf ball is only a tiny piece of a universe that was infinite even then. The unending infinite universe is expanding into itself.
Consider the idea of the multiverse coupled with eternal inflation. Inflation helped propel the “big bang”, that initial golf ball, into the roomy and expanding universe we see around us today. The idea of eternal inflation is that these golf balls are everywhere, popping into existence and swelling into local universes in their own right.
There isn’t any way to do justice to all the views and variations of multiverses in this short post, so I will comment on only one aspect, Max Tegmark’s second Level of multiverses. These are universes which have different parameters, or different physical constants. The first Level of multiverse is the same as ours, run by the same physics, but each has different initial conditions from whatever conditions existed at the start of ours. How these initial conditions are chosen and why ours got the values it did, except by reference to anthropic principles, is never specified—for the very good reason that nobody knows anything about how the initial conditions were caused, except by some hand-waving about quantum mechanics. Nobody hows how any quantum mechanic result is specified. We do not know what causes QM events, so we cannot know why our universe had the initial conditions it did.
The multiverse is another hypothesis to solve the peculiarities of quantum mechanics, or rather move them back one level so they seem to disappear. Eternal inflation comes from the relativity side of things. Now in this universe (the one out your window), there exists certain physical reactions which physicists have described using parameterized equations. The parameters are not known but estimated; they are hypothetical, meaning they might be wrong. That is, it might be that there are no free parameters and what physicists have proposed equations which are mere estimations of the universe’s true forces. It might be, for instance, that the descriptions of motion and change are entirely deducible from first principles (such as the principle of non-contradiction).
But suppose arguendo the parameterized equations are correct. The values of the parameters—as do the equations themselves!—have to come from somewhere. They must be chosen; a causal mechanism must exist which “assigns” the values (and causes the equations). It might appear that it is a solution to quantum ambiguity to say that a different universe is created which takes each possible value of parameters. Since parameters are assumed (there is no first-principles proof) to be continuous, the number of other universes is thus infinite, with the power of the continuum. That’s a lot of universes!
How? How are the parameters decided? Decided as in caused to be?
We earlier critiqued Tipler’s interpretation of Everett’s Many Worlds, which is a kind of multiverse. Readers will recall I did not buy the physical interpretation of Many Worlds which insisted upon infinite upon infinite upon infinite et cetera ad infinitum ad dudem literum (or whatever the Latin is for “Dude: literally”), and instead favored the epistemological, i.e. probabilistic, view. What’s fascinating is that Leonard Susskind and Raphael Bousso claim that, under certain conditions, Everertt’s Many Worlds matches, or is, the multiverse. Or so says somebody at MIT Technology Review
The author of that article says what is often said, “The reason many physicists love the many worlds idea is that it explains away all the strange paradoxes of quantum mechanics.” It does not. Neither Many Worlds or multiverses does away with the peculiarities of QM: they simply push them back one or more level, so that they seem to go away. Re-read the critique of Many Worlds to see why this was so there. Here, in multiverses, there is no solution to QM by saying infinite number of universes are created with different parameterizations, because there is nothing that says which parameterization went where, and how QM knew about all those parameterizations, and how it had the causal power to make the distinctions. It is true that in this universe we can say, “We’re just one of many, so QM is not strange.” But when pictured as a whole, QM is still strange.
About the multiverse-Many Worlds equivalence, the article says:
But Susskind and Bousso say there is a special formulation of the universe in which [experiments about other universes are] possible. This is known as the supersymmetric multiverse with vanishing cosmological constant.
If the universe takes this form, then it is possible to carry out an infinite number of experiments within the causal horizon of each other.
Now here’s the key point: this is exactly what happens in the many worlds interpretation. At each instant in time, an infinite (or very large) number of experiments take place within the causal horizon of each other. As observers, we are capable of seeing the outcome of any of these experiments but we actually follow only one.
Bousso and Susskind argue that since the many worlds interpretation is possible only in their supersymmetric multiverse, they must be equivalent. “We argue that the global multiverse is a representation of the many-worlds in a single geometry,” they say.
They call this new idea the multiverse interpretation of quantum mechanics…
But what this idea lacks is a testable prediction that would help physicists distinguish it experimentally from other theories of the universe. And without this crucial element, the multiverse interpretation of quantum mechanics is little more than philosophy.
That may not worry too many physicists, since few of the other interpretations of quantum mechanics have testable predictions either (that’s why they’re called interpretations).
Again, you’ll have to review, but in Many Worlds the problem of how the splits happen, and how they appear to require infinite power do not disappear. And it is still the case that we can only follow one of Many Worlds at a time: the one we’re in (and recall you cannot split because you are part intellect and will and these are not made of splittable stuff). This is why there aren’t and can’t be any testable predictions.
This makes the duo’s idea not “little more” than philosphy, but precisely philosophy. And given the spiritual nature of our makeup, incomplete or wrong philosophy.