Physically speaking, our Universe seems uncannily perfect. It stands to reason that if it wasn't, life as we know it – and planets, atoms, everything else really – wouldn't exist.
Now, three physicists from the US, France, and Korea have put forward a new explanation for why life, the Universe, and everything in it has had such a prime opportunity to exist at all.
For some reason, the amount of energy – or more precisely, the mass it equates – and the Universe's accelerating expansion are so neatly balanced, there's been ample opportunity for a few interesting things to unfold over the past 13 billion years or so.
A few magnitudes either way, and the overwhelming gravity would have glued the expansion of spacetime together better than a mouthful of taffy... or been so weak, the rapidly expanding Universe would have left little of interest in its wake.
Such an apparent near-perfect balance might be a consequence of something called fine-tuning, a process in physics where the features of a system necessarily match or cancel out with such precision. If it didn't, the system just wouldn't look the way it does.
For example, our Universe happens to be neutrally charged. For some reason, there happens to be a near-identical number of protons to cancel out each electron's charge; add a few more electrons and it would be negative, forcing clumps of matter to push itself apart.
On the other hand, it could be a consequence of what's referred to as 'naturalness'. The Moon's near-perfect occlusion of the Sun during a solar eclipse, for example, isn't ordained by hard laws of astronomy. The size of the Moon, the Sun, and our perspective of both don't need any further explanations to make sense.
Physicists generally don't like appealing to vague coincidences when they observe the Universe. If two features of a system seem incredibly well matched, there's a strong desire to dig through the rulebook for a deeper explanation.
For electrons and protons, the solution could come with explanations of why there's an imbalance of matter over antimatter.
In the case of the Universe's incredible reflection of energy and expansion, there's no shortage of clever and creative ideas to chew on. Most tend to fall into two categories, however.
One centers on something called the anthropic principle, which says only a universe capable of generating thinking brains like ours can ask philosophical questions such as 'why am I here?'
This might imply there are other universes, though. Maybe an infinite number, most either collapsing the moment they're born or exploding in puffs of endless boredom. Ours just happens to be one of the good ones! Although fun to think about, without any way of establishing the existence of multiverses it isn't a proposition that could bear scientific fruit.
As for the second category, there is the possibility that we're missing some crucial piece of the physics puzzle, such as new fields or symmetries that could fail under specific conditions.
The fact that the resting mass of the Higgs boson – the particle representing a field that gives many fundamental particles their mass – turned out to be unexpectedly light might suggest there's a gap in our understanding of forces and particles.
It itself is the result of another fine-tuning conundrum, being the result of strangely-exact cancellations of other physics. For example, there seems to be some sort of mysterious fine-tuning between the mass of a Higgs boson and the cosmological constant – the density of energy in the vacuum of space.
This latest suggestion mashes together the idea of unknown physics behind the Higgs boson's shockingly itty-bitty mass with a kind of quantum multiverse effect, one that this time could feasibly be tested.
Their model puts the Higgs particle at the center of the fine-tuning explanation. By coupling the boson with other particles in such a way that its low mass would effectively 'trigger' events in physics we observe, it provides a link between forces and mass.
From there, the authors show how weakly interacting variables in a field might affect different kinds of empty space, specifically patches of nothingness with varying degrees of expansion. This potentially demonstrates the link between Higgs bosons and the cosmological constant.
It's a multiverse in a way, given the triggers occurring in different patches of infinite expanding space could plausibly give rise to a seemingly well balanced Universe like ours.
Their math suggests these triggers would be limited to a few possibilities, and even has room for explanations of dark matter. Better still, it also predicts the existence of multiple Higgs particles of varying masses, all smaller than the one we've already observed. That gives the hypothesis something that can be tested, at least.
Until then, it'll remain one of many neat ideas that could one day explain the eerily well-matched tug-of-war that has permitted a complex cosmos to unfold. A place we've come to love as our Universe.
This research was published in Physical Review D.
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