Hints of Fine-Tuning Amidst Uncertainty about Breakthroughs
Headline-making discoveries sometimes resemble dramas where a plot can turn at any moment. Thus, some skepticism surfaces when breakthroughs such as two recent ones hit the news. One finding showed that the universe really did undergo inflation––the hypothesized extremely rapid, very early expansion that affirms big bang theory. Another announced the discovery of the long-sought Higgs boson, which fills out the standard model for how the physics of the universe operates.
Here is part of the drama.
Scientists finally found the gravity waves associated with big bang inflation…or did they? Is there only one Higgs…or many? Does the mass of the Higgs mean our universe is unstable or not? Is anything established within all this uncertainty? Well, yes and no!
First, based on a wealth of data, scientists had already thought an epoch of inflation occurred in the earliest moments of the universe. The detection of gravity waves reported by the BICEP-2 (a second generation of the Background Imaging of Cosmic Extragalactic Polarization astronomy instrument located at the south pole), if confirmed by future experiments would basically rule out any other option. That would mean inflation happened and the big bang is vindicated. Second, the data from the Large Hadron Collider (LHC)––the world’s largest and most powerful particle accelerator––points to a single Higgs boson, but planned upgrades should provide a more definitive answer. Third, if the BICEP-2 results hold and a single Higgs exists, the calculations point to an even more fine-tuned universe that is necessary to support life.
Assuming inflation produced gravitational waves (actually the polarization of the cosmic microwave background [CMB]) detected by BICEP-2, the energy density (the stored energy per volume of space) scale during this extremely brief period in the universe’s history resides around the grand unification theory (GUT) scale of 1016 GeV (for reference, the energy density today is 28 orders of magnitude smaller at 10-3 eV). These extreme energies mean the Higgs field experiences significant quantum fluctuations during periods of inflation, pushing it into an unstable region. In this unstable region, the Higgs field will eventually fall to a minimum value, resulting in a universe unsuitable for life and the collapse of the cosmos within a second.1 That false start could have––some would say should have––marked our universe’s history. A top quark mass less than 172 GeV seems to restore stability by precluding the rapid collapse of the universe—a value marginally consistent with scientists’ current best measurements.2
In contrast, some argue that a stable universe introduces other problems because of its long-lived state (much longer than the universe’s age). Eventually, such a universe produces copious Boltzmann brains. With an appropriately fine-tuned value for the top quark mass and Higgs boson mass, the universe decays on a timescale similar to the current lifetime of 13.8 billion years. Such a “short” lifetime eliminates the production of Boltzmann brains.
Assuming the drama is over and we have a complete theory describing all the relevant physics (including the Higgs field, the top quark mass, and inflation), these results point to a fine-tuned universe. A top quark mass too large causes the universe to decay too quickly (meaning we shouldn’t be here now). Too small of a mass means Boltzmann brains exist—a possibility in which we are far more likely to be Boltzmann brains than ordinary beings.
These discoveries once again buttress the scientifically uncontroversial claim that our universe appears designed to support life. Even so, one should remember the tentative nature of these results; they lie at the cutting edge of scientific inquiry. It would not surprise me if science reveals a plot twist ahead and future research will show new physics that might “explain” fine-tuning. But an explanation for fine-tuning does not remove the fact that if our universe were any other way, we would not be here as observers. It’s like watching a creation drama and it simply helps us understand the mechanism God used to fashion a life-sustaining habitat for humanity.
- Malcolm Fairbairn and Robert Hogan, “Electroweak Vacuum Stability in Light of BICEP2,” Physical Review Letters 112 (May 23, 2014): 201801.
- CMS Collaboration, “Determination of the Top-Quark Pole Mass and Strong Coupling Constant from the ttbar Production Cross Section in pp Collisions at √s = 7 TeV,” Physical Review B 728 (January 20, 2014): 496–517.