What’s outside the universe? What’s smaller than the smallest thing in the universe? What was before the universe started, and what will come after? Here’s a possibility…

The fundamental particles in our universe could themselves be whole universes, and our universe could be one of the smallest things in another universe one level up. That could go on forever in both directions.

It’s compelling because…

• it tells what’s outside our universe, so we feel better about that, and
• it has nice symmetry going upscale and downscale, and allows an infinite number (and presumably variety) of universes to exist all at once, and
• it tells that our universe’s mass and other bulk properties (spin? anti-/matter ratio?) are determined by what fundamental particles exist in the next universe up. (Contrariwise there might not be a fixed set of fundamental particles at the next level up.)

It’s problematic because…

• we don’t feel the need to explain what’s inside fundamental particles, so it’s unnecessary in that respect, and
• it means that the lifetime and mode of death of our universe are determined from the outside – we’re just some fundamental particle waiting to be transformed in a reaction – yet we believe the lifetime and mode of death of our universe are determined by events within our universe.
• It implies that for universes one level below, they’re constrained to have a limited combination of bulk properties (mass, spin, etc), and yet part of the attraction of the weak anthropic principle is that many different kinds of universes could exist, more or less exploring all types of possible universes. Sure we’re proposing infinite layers above and below, but it’s worrisome if such constraints exist here (though it could just be in this layer below, it’s our only data point for that), for our idea that many possible kinds of universes exist. Though maybe there are only a limited number of possible types of universes. But I want evolution to work that out – unstable universe types last short times and are recycled into the following universe, with more-or-less random properties, and the stable ones exist for a long time, and the interesting one give rise to life.