|Jet, flying over my house|
I have long been interested in cosmology, origin-of-the-universe matters. Within this field I read about "multiverse theory."
I don't believe in a vast ensemble of universes.
This morning I read a just-published article by theoretical physicist Sabine Hossenfelder - "Scientific Theory and the Multiverse Madness." Hossenfelder doesn't believe in a multiverse, either. She writes:
- "Before you pack your bags and search for a universe more to your liking, let me add there's no way to cross over into another universe or even interact with one. This only works in science fiction. Indeed, to my taste, the multiverse itself is already too close to fiction."
- "For a theory to be scientific its predictions must also have a reasonable chance to accurately describe reality. Construing up one of an infinite number of multiverse variants has no reasonable chance. Theoreticians justify their multiverse research by claiming that it continues the noble quest for simplicity. But as we have seen, this argument is wrong because it neglects the need to introduce a probability distribution on the multiverse. The multiverse replaces a simple explanation with a more complicated one. Such a move is only justified if the added complication explains additional data, but for the multiverse that isn't so."
- "To our best knowledge, assuming the existence of any universe besides our own is unnecessary to explain anything we have ever observed. In the best case, then, the multiverse is an interpretation. You can believe that the seeming arbitrariness of the constants of nature is due to an infinite number of other universes. You can believe that, but you don't have to. Science cannot confirm that the other universes exist, but it also cannot rule them out. Just like science cannot rule out the gods and angels."
See the entire article for explanation.
Here Princeton physicist Paul Steinhardt writes:
"A pervasive idea in fundamental physics and cosmology that should be retired: the notion that we live in a multiverse in which the laws of physics and the properties of the cosmos vary randomly from one patch of space to another. According to this view, the laws and properties within our observable universe cannot be explained or predicted because they are set by chance. Different regions of space too distant to ever be observed have different laws and properties, according to this picture. Over the entire multiverse, there are infinitely many distinct patches. Among these patches, in the words of Alan Guth, "anything that can happen will happen—and it will happen infinitely many times." Hence, I refer to this concept as a Theory of Anything." (Steinhardt is one of the originators of inflationary theory and multiverse theory.)
The problem with a Theory of Anything is that "any observation or combination of observations is consistent with a Theory of Anything. No observation or combination of observations can disprove it." (Ib.) This creates a problem for multiverse theory. Steinhardt writes:
"The worth of a scientific theory is gauged by the number of do-or-die experimental tests it passes. A Theory of Anything is useless because it does not rule out any possibility and worthless because it submits to no do-or-die tests. (Many papers discuss potential observable consequences, but these are only possibilities, not certainties, so the Theory is never really put at risk.)"
As far as we know, and in principle we can never know otherwise (see Hossenfelder), ours is the only universe there is.
One very good book to read on this is Worlds Without End: The Many Lives of the Multiverse, by Mary-Jane Ruberstein.