Not in mainstream cosmology, no.
For the JWST “impossible early galaxies,” the serious hypotheses being discussed are still within our own universe: unusually efficient or bursty star formation, different feedback, rapid gas inflow, AGN contamination, altered stellar populations/IMF, super-Eddington black-hole growth, or—more radically—modifications to early-universe cosmology such as early dark energy. A 2026 MNRAS paper, for example, explicitly treats the unexpectedly bright and mature high-redshift population as a possible signature of early-universe physics, but still physics of this universe.
There are also more radical proposals that change the cosmic clock itself. Rajendra Gupta, for instance, has proposed a covarying-coupling-constant plus “tired-light” model that effectively gives much more time for galaxies to form. That is far outside the consensus, but again it does not say the galaxies immigrated from another universe.
The reason an “other-universe galaxy” hypothesis is not seriously invoked is observational. When JWST measures z=10,12,14, we interpret the spectrum as light emitted by matter participating in our spacetime’s cosmological expansion. Its hydrogen, oxygen, carbon lines, etc. behave like ordinary atomic physics subjected to a huge cosmological redshift. Nothing in those spectra currently says, “this object’s previous history occurred in a separate spacetime.”
There is an important distinction, though, which connects nicely to the wormhole question we discussed recently.
Suppose there were a wormhole connecting our universe to another universe. In principle, radiation or matter emerging through it could appear in our universe. One could even construct mathematical models in which a black hole or wormhole is connected to another asymptotic region. General relativity permits geometries of this broad sort.
But then we would need some anomalous signature: perhaps an object whose age/chemical composition cannot possibly be reconciled with our cosmic history, peculiar lensing, an unusual gravitational-wave signature, or spacetime geometry incompatible with an ordinary halo.
JWST’s galaxies haven’t reached that level. Indeed, spectroscopy has made the mundane explanation stronger in several cases: some allegedly z\sim16 galaxies turned out to be lower-redshift dusty objects, while others really were confirmed beyond z=11.
So I would arrange the possibilities something like this:
ordinary astrophysics → extreme early-universe astrophysics → modified cosmology → new fundamental physics → wormholes/other universes
We are presently somewhere around the first three, not the fifth.
But your question contains a genuinely interesting inversion. If someday we found a galaxy at, say, cosmic age 300 Myr whose stellar population was unambiguously 2 billion years old, after every possible stellar-model and redshift error had been eliminated, then simply saying “star formation was more efficient” would no longer work. You cannot make two billion years of stellar aging happen in three hundred million years by increasing star-formation efficiency.
At that point physicists would have to entertain something dramatically stranger: incorrect cosmic chronology, nonstandard spacetime topology, bouncing/pre-Big-Bang inheritance—or, conceivably, matter whose worldline did not originate within our observable cosmic history.
And that would be the point where your phrase “comes from another universe” would stop being science fiction and become a legitimate hypothesis.
JWST has not shown us that yet. But it has moved the observational frontier closer to the sort of question where one can at least specify what evidence would force us to ask it.
