I say that we cannot. Impossible. The Earth quantum tunnelling to Andromeda tomorrow at noon is more likely.
Generally, the simpler things are, the more probable they are. I'm not talking about Occam's razor, I'm talking that adding more fixed variables makes things mathematically less likely (it's exponentially more likely to randomly meet three persons dressed in red, green, and blue, than six persons dressed in red, green, blue, cyan, magenta and yellow). It is therefore not only reasonable to look for the simplest wholesale model of the universe that explains everything in it, but adding unnecessary things to that model makes your explanation less and less likely – add a whole universe worth of somethings, and the improbably of the universe is squared. (In multi-universe terms, there would be a gazillion more universes where we are having the same conversation, but those somethings
aren't present. Chances we are in the one where they are present? One in a gazillion.)
Now, to fully explain the universe and avoid the circular arguments, you
do need to invoke other universes in the argument in at least some fashion, probably go all in on it. As an example, we may or may not discover that space-faring civilizations like ours develop in only one out of a million universes. Without other universes, not only in the sentence itself is nonsensical, the totally reasonable possibility appears impossible – you would be forever looking for the reasons why we're lucky to hit such an incredible chance to be here. We are actually making the flawed argument that they have to be here, because we are – assuming other universes as part of the equation gives us the ability to look at real possibilities without ours. And that's without considering every parameter of the universe that had to be right for development of life to be possible at all. Considering our universe special would always leave unanswered questions, more than can be simply handwaved, and makes go along with wrong assumptions; but considering it non-special along all possible ones seems like a simple resolution, that leads to less problems.
Except if you imply we're connected to the others and
can actually travel there. Then we go off the rails. Now they are no longer simply a tool for setting up your argument and exploring the range of possibilites, they become an active part of
our reality that we are trying to explain. If we can travel there, the universes can interact; if they can interact, they did interact naturally once; if they did, they are more than extensions of our own that also need to be now explained together with a larger metaverse, which would require
other metaverses to explain its existence, until it's metaⁿverses all the way down.
More than that, suggesting travel is possible, implies the universes are close to one another in some fashion (what fashion?), and they thus share a common
dependent development, that now needs to be explained in a common package.
Let's assume our development occurred completely independently of other universes, i.e. you don't have to explain an interaction that drastically altered our history at the dawn of time, or include the whole of some other unrelated universe in our ancestry. And yet we have that one that universe is “near”* us, and we can travel there. Since the development is independent, we're not locked to a particular one, hence this can be an arbitrary** compatible one. This means that in another universe where we are having the exact same conversation, they can travel to... an absolutely different one, which makes ours and theirs development diverge completely. Hence the universes are no longer independent. So travel implies dependence, but the actual problem is that any moment of our existence after we travelled to that other universe is a gazillion times less probable, because nothing suggested we should have travelled to that
exact one, yet all of its features now shape our future development; and our hypothetical identicals from mirror Earths would have travelled to a completely different one. (Quantum non-determinism has the same effect, but it occurs gradually, not at once)
* I mean, there is no mechanism for travel suggested, there is no known magnitude by which they could be “near” (other than similarity, but that would involve travelling to them by running a computer simulation, not doing space magic) – it's on those suggesting such craziness to be a possiblility to suggest how that happens – but I'm assuming there was.
** Fixing more things decreases probability, so some randomness is inevitable.
