You are saying we can know nothing about anything outside our universe (setting aside your definition of universe as everything that exists). The various multiverse theories, hypotheses, interpretations, etc. suggest otherwise. In other threads, you place a high value on what scientists have to say. Are you now suggesting that you know more than them?
I think you're hijacking sntjohnny's thread, but that's OK. All threads evolve. :)
First, on what grounds do you set aside my definition that the universe is "everything that exists anywhere"? Again, in physics it is pretty well established belief that the universe extends in all directions infinitely.
Second, if you believe that any one of the various multiverse hypotheses suggest that we can know something about a reality which may exist outside this universe, then you haven't read those theories except perhaps as they've been expounded inside a science fiction novel.
You know the difference between a hypothesis and a theory as those terms are used in science and you know that they are not even roughly synonymous. The many-worlds interpretation of quantum mechanics, just to pick one multiverse hypothesis, is not established science. The theory of the modern synthesis is.
"Are you saying that some people believe that we can observe other particular things outside the universe?"
Did I say that?
Yes, you implied it. How else can we "know" something about a reality outside the universe if we cannot observe it in a scientific sense?
We can only know that about reality which we can experience.
I was thinking more along the lines of M-Theory, but there are quite a few others. link
From your link: A multiverse (or meta-universe) is the
hypothetical set of multiple possible universes (including our universe) that together comprise all of physical reality.
Hypothetical??? That sentence expresses my points concisely: One, no multiverse hypothesis is an established part of science. Two, "all of reality" is what I call the universe.
We're not talking absolutist religion here, Doc. To further its quest to know more about reality, science hypothesizes and theorizes (in the speculative sense) all the time. This doesn't mean that every one of those hypotheses will become an established scientific theory along the lines of evolution or relativity, though. Most of them do not.
"I, unlike most Christian sources, can certainly accept the possibility that other universes exist. I only deny that we can know anything about them."
Here you go assuming again, Cog. You must have spent a great deal of time studying Christianity. I'm a Christian and I don't see any problem with having multiple universes.
Saying that you are a Christian and that you believe p, does nothing to negate the claim that MOST Christians do not believe p. It can only negate the claim that ALL Christians believe p -- and of course that was not my claim.
It's interesting that you now say current theory says nothing about the universe before the Big Bang. I'm going to so a quick search, but I seem to recall you saying that we could know about the initial conditions of the universe.
Wow. A search! And I thought I had a lot of time on my hands. Be sure and report your findings back here when you return.
Anyone who says that the initial conditions of the universe are known misspeaks. What he or she intends to say is that the conditions of the universe shortly after the Big Bang are known. Trust me on this. I know.
What I meant, Cog, is the universe eternal?
I believe that it's extremely unlikely (perhaps impossible) that we can know that.
If you find 'ex nihilo, nihil fit' convincing then you probably believe that the universe is eternal. Personally, since 'ex nihilo. . . ' is not a logical truth, I can't see how it applies to a speculative realm that lies on the other side of the Big Bang. This is why, to me, such a question's answer is unknowable.