Today some theorists speculate that there are many other universes in addition to our own. The multiverse is the name used for some hypothetical set of a vast number of universes. But the idea of some other realm outside of our universe (or “parallel” to our universe) was advanced way before anyone started using the term “multiverse.” For over 150 years it has been maintained that there exists some realm of existence we can't see with our eyes, a plane of existence where souls go to after death. Such a realm of existence is often called the Other Side.
An interesting question to consider is: which of these ideas is more scientific – the Other Side or the multiverse?
Some would argue that we should judge whether an idea is scientific based on how much attention it gets among mainstream scientists. But such reasoning is not valid. Reviewing definitions of “scientific,” I see none that say anything like “popular among scientists.” I do see some definitions that say, “based on or characterized by the methods and principles of science.”
Science is based on the idea of empirical verification through observations and experiments. So perhaps we should judge whether an idea is scientific based on whether we can hope to empirically verify the idea, or at least gather empirical evidence that substantially supports the idea, making us think it is likely. Let's compare the multiverse and the Other Side based on their prospects of empirical verification.
Looking at the multiverse idea, we see a concept that has no real prospects of empirical verification. We cannot imagine any observations we might make that would lead us to say that we had substantial evidence of another physical universe. The main reason why is that we can only observe things in our universe.
Multiverse enthusiasts have suggested otherwise, but their arguments are unpersuasive. It is sometimes argued that if the cosmic inflation theory was verified, that would give evidence for a multiverse. But this idea is not correct. The cosmic inflation theory (at least in some of its many forms) involves both the idea that the universe underwent an exponential phase of expansion during its first second, and the idea that our universe is only one of many “bubble universes.” The only one of these claims that we could hope to verify is the first of these claims. Verifying the first of these claims would not verify the second claim, the idea that our universe is only one of many “bubble universes.” If a theory involves an assertion of X and Y, you do not prove Y merely by proving X.
Verifying something about the first second of our universe would only tell us something about our universe, and would not tell us anything about the existence of any other universes.
Multiverse enthusiasts have also suggested that we might find evidence for some other universe by studying the cosmic background radiation, and seeing some unusual spot, bump, or ring indicating a “collision with another universe” early in time. Such an idea is fallacious. For one thing, the cosmic background radiation has already been exhaustively analyzed to an extreme degree, and no such thing has been found. Secondly, even if some unusual spot, bump, or ring was found in the cosmic background radiation, there would always be many ways to plausibly explain it without the extravagant assumption of another universe.
We also do not provide evidence for a multiverse by providing evidence that our universe seems to be fine-tuned or exquisitely well balanced. Evidence that some particular thing looks like a designed thing can never be properly argued as evidence for other universes. For example, it would be quite absurd to argue along these lines:
Walking in the country, I passed an arrangement of flowers that consisted of a grid of 30 evenly spaced rows and 30 evenly spaced columns. Realizing that the plants were most unlikely to achieve this arrangement by chance, I recognized that this was evidence there must be many universes, because under such a hypothesis we would expect such an arrangement to occur by chance at least once.
It seems, therefore, that the multiverse is on extremely weak ground in regard to empirical verification. Not only is there no evidence for such a concept, but the prospects of ever getting evidence are incredibly slim. It is hard to imagine any plausible set of future observations that we might have that would justify someone saying, “Aha, now there is good evidence for another universe.”
Let's compare this situation in regard to the idea of the Other Side. There we find a very different situation. Many people think that there is very substantial evidence for the Other Side, which has been steadily accumulating for more than 150 years.
One of the main items of evidence comes from mediums, people who claim to have contacted souls on the Other Side. Some mediums have been exposed as frauds, but some have had remarkably successful careers, and have stood up well to scientific investigations. Three of the most famous examples are Daniel Dunglas Home, Leonora Piper, and Gladys Osborne Leonard. In more recent times scientists such as Gary Schwartz PhD and Julie Beischel PhD have done controlled scientific studies of mediums in which they scored far better than non-mediums when trying to gather information about the deceased relatives of unidentified individuals.
Another line of evidence for the Other Side comes from near-death experiences. Those who have such experiences frequently report briefly entering some kind of mysterious other realm where they encounter deceased relatives.
So there is a substantial body of observational evidence supporting the idea of the Other Side. We may contrast this with the evidence situation in regard to the multiverse. There are simply no corresponding observations – real or alleged – in which people claim to have observed or experienced any other universe that is part of a multiverse.
There is, to the best of my knowledge, simply no one out there who is making any claims such as the following:
I had this weird experience. Suddenly I found myself drifting out to some strange place where the laws of physics were very different from ours. All the matter was arranged in some totally weird way unlike anything I have ever seen. It must have been one of the alternate universes of the multiverse.
To the best of my knowledge, there is no one claiming to have experienced some other physical universe of the multiverse, nor is there anyone claiming to have made contact with some other inhabitants of another physical universe of the multiverse. In terms of evidence, the idea of the multiverse is on ridiculously weak empirical ground. But the idea of the Other Side seems to have substantial observations to support it.
So which idea is more scientific, the Other Side or the multiverse? If we judge the question based on what is more fashionable in the halls of scientific academia, the answer might be the multiverse. But if we judge the matter based on the basis of which idea has more evidentiary support, it seems we would conclude that the Other Side is more scientific than the multiverse.