Mirror image

One of the hallmarks of science is its falsifiability.  Models should generate predictions that are testable, allowing you to see if they conform to what we observe and measure of the real universe.  It's why science works as well as it does; ultimately, nature has the last word.

The problem is that there are certain realms of science that don't lend themselves all that well to experiment.  Paleontology, for example -- we're dependent on the fossils that happen to have survived and that we happen to find, and the genetic evidence from the descendants of those long-gone species, to piece together what the ancient world was like.  It's a little difficult to run an experiment on a triceratops.

An even more difficult one is cosmology -- the study of the origins and evolution of the universe as a whole.  After all, we only have the one universe to study, and are limited to the bits of it we can observe from here.  Not only that, but the farther out in space we look, the less clear it becomes,  By the time light gets here from a source ten billion light years away, it's attenuated by the inverse-square law and dramatically red-shifted by all the expanding space it traveled through to get here, which is why it takes the light-collecting capacity of the world's most powerful telescopes even to see it.

None of this is meant as a criticism of cosmology, nor of cosmologists.  But the fact remains that they're trying to piece together the whole universe from a data set that makes what the paleontologists have look like an embarrassment of riches.

The result is that we're left with some massive mysteries, one of the most vexing of which is dark energy.  This is a placeholder name for the root cause of the runaway expansion of the universe, which (according to current models) accounts for 68% of the mass/energy content of the universe.  (Baryonic, or ordinary, matter is a mere 5%.)  And presently, we have no idea what it is.  Attempts either to detect dark energy directly, or to create a model that will account for observations without invoking its existence have, by and large, been unsuccessful. 

But that hasn't stopped the theorists from trying.  And the latest attempt to solve the puzzle is a curious one; that dark energy isn't necessary if you assume our universe has a partner universe that is a reflection of our own.  In that universe, three properties would all be mirror images of the corresponding properties in ours; positive and negative charges would flip, spatial "handedness" (what physicists call parity) would be reversed, and time would run backwards.

Couldn't help but think of this, of course.

The idea is intriguing.  Naman Kumar, who authored the paper on the model, is enthusiastic about its potential for explaining the expansion of the universe.  "The results indicate that accelerated expansion is natural for a universe created in pairs," Kumar writes.  "Moreover, studying causal horizons can deepen our understanding of the universe.  The beauty of this idea lies in its simplicity and naturalness, setting it apart from existing explanations."

Which may well be true.  The difficulty, however, is that the partner universe isn't reachable (or even directly detectable) from our own, Lost in Space notwithstanding.  It makes me wonder how this will ever be more than just an interesting possibility -- an idea that, in Wolfgang Pauli's often-quoted words, "isn't even wrong" because there's no way to test whether it accounts for the data any better than the other, less "natural" models do.

In any case, that's the latest from the cosmologists.  Mirror-image universes created in pairs may obviate the need for dark energy.  We'll see what smarter people than myself have to say about whether the claim holds water; or, maybe, just wait for Evil Major West With A Beard to show up and settle the matter once and for all.

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