Let’s explore the chain of reasoning behind this claim. One assumption is that whether a particular parallel universe exists falls within the field of astrophysics, not theology nor logic.
Astrophysics’ well-accepted Big Bang theory with eternal inflation implies a multiverse containing an unlimited number of parallel universes obeying the same scientific laws as in our particular universe. These other universes (which the physicist Max Tegmark calls Type 1 universes) are distant parts of physical reality. They are not abstract objects. Some contain flesh and blood beings.
Parallel universes are not parallel to anything. They are very similar to what David Lewis called possible worlds, but they aren’t the same because his possible worlds must be spatiotemporally disconnected from each other.
The claim that Jesus in our universe is identical to Jesus in another universe does conflict with the intuitively plausible metaphysical principle that a physical object is not wholly in two places at once. This principle is useful to accept in our ordinary experience, but it is not accepted in contemporary physics. The Schrödinger equation of quantum field theory describes the extent to which a particle is wholly in many places at once. This is why physicists prefer to say the nucleus of a hydrogen atom is surrounded by an electron cloud rather than by an electron. In the double-slit interference experiment, a single particle goes through two slits at the same time. So, the metaphysical principle should not be used a priori to refute our claim about the transuniverse identity of Jesus.
Our universe is the product of our Big Bang that occurred 13.8 billion years ago. It is approximately that part of physical reality we can observe, which is an expanding sphere with the Earth at the center, having a radius of 13.8 billion light years.
Our universe once was a tiny bit of explosively inflating material. The energy causing the inflation was transformed into a dense gas of expanding hot radiation. This expansion has never stopped. But with expansion came cooling, and this allowed individual material particles to condense from the cooling radiation and eventually to clump into atoms and stars and then into Jesus.
The other Type 1 parallel universes have their own Big Bangs, but they are currently not observable from Earth. However, they are expanding and might eventually penetrate each other. But, they might not. It all depends on whether inflation of dark energy is creating intervening space among the universes faster than the universes can expand toward each other. Scientists don’t have a clear understanding of which is the case.
Why trust the Big Bang theory with eternal inflation? Is it even scientific, or is it mere metaphysical speculation? The crude answer is that the theory has no better competitors, and it is has been indirectly tested successfully. Its testable implications are, for example, that the results of measuring cosmic microwave-background radiation reaching Earth should have certain specific quantitative features. These features have been discovered—some only in the last five years. The theory also implies a multiverse of parallel universes having our known laws of science but perhaps different histories. If we accept a theory for its testable implications, then it would be a philosophical mistake not to accept its other implications.
One other important assumption being made is that the cosmic microwave-background experiments have not detected any overall curvature in our universe because our universe is in fact not curved. Our universe being curved but finite is also consistent with all our observations. Similarly, if you are standing on a very large globe, it can look flat to you. If our 3-D universe is finite but curved like the surface of a 4-D hypersphere, then space would be extremely large with a very small curvature, but there would be only a finite number of parallel universes, and the argument about Jesus would break down. The most common assumption now among astrophysicists is that our universe is in fact infinite, the multiverse is infinite, and matter is approximately uniformly distributed throughout the multiverse. As Max Tegmark has pointed out, twenty years ago there were many astrophysicists opposed to parallel universes. They would say, “The idea is ridiculous, and I hate it.” Now, there are few opponents of parallel universes, and they say, “I hate it.”
Having established that there are infinitely many parallel universes with the same laws but perhaps different histories, let’s return to the issue of whether Jesus died in more than one of them. One implication of the Big Bang theory with eternal inflation is that some universes are exact duplicates of each other. Here is why. If you shuffle a deck of playing cards enough times, then eventually you will have duplicate orderings. The duplicate orderings are the same, not just “David Lewis counterparts.” Similarly, if you have enough finite universes, which are just patterns of elementary particles, and each has a finite number of possible quantum states, then every universe has an infinite number of duplicates.
One controversial assumption used here is the holographic principle: Even if spacetime were continuous, it is effectively discrete or pixilated at the Planck level. This means that it can make no effective difference to anything if an object is at position x meters as opposed to position x + 10 -35 meters.
This completes the analysis of the chain of reasoning for why Jesus died more than once for our sins. Have you noticed any weak links?