Science1 publisher2 min readPublished
Early-universe simulations show decoherence suppressing false-vacuum tunnelling
Physicists at Syracuse, Portsmouth and ENS in France argue in a paper accepted by JCAP that decoherence can strongly suppress false-vacuum tunnelling. The tools come from quantum computing, where scientists study the same effect to protect fragile information.
The Scientist · Science desk
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What happened
- Syracuse postdoc Gregory Kaplanek, of Jason Pollack's lab, wrote the paper with Robson Christie, Jaewoo Joo and David Wands of Portsmouth and Vincent Vennin of France's Ecole Normale Superieure.
- Some calculations indicate the Higgs field, which helps give particles their mass, may itself rest in a false vacuum; a tunnel to a deeper state could change particles and forces everywhere.
- In the model, early expansion largely decides which of two energy states a field favours, with heavier fields settling toward the lowest, before decoherence locks that outcome in.
- The authors caution that the work neither proves the universe's present state will last forever nor determines the odds that the Higgs field eventually decays.
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Why it matters
- capability Vacuum-decay calculations can now borrow open-quantum-systems tools from quantum-computer research to include a field's environment in the tunnelling problem.
- decision A tunnelling estimate that treats an early-universe field as isolated would miss the suppression this team found, so modellers who leave the environment out now need a reason to.
- constraint Estimates of how long a possible Higgs false vacuum survives are unchanged by this paper, on its authors' own account, until gravity and a varying expansion rate are added.
The physics turns on information. As the field interacts with its surroundings, the interactions carry information about it outward [6]. Once that information is effectively lost track of, interference between the two possible outcomes fades [6]. That fading is decoherence. In the regime the team studied, it also suppresses the field's ability to tunnel at all [6]. The authors describe this as a variation of the quantum Zeno effect, in which persistent monitoring of a system inhibits its transitions [12]. To get there they paired open-quantum-systems techniques with numerical simulations of a quantum field evolving in an expanding universe [5].
The order of the two stages limits what the effect can do. Decoherence arrives second, and it locks in whatever outcome the expansion has already produced [7]. Lighter fields can come out of the first stage more evenly split between the two energy states [7]. For such a field, lockdown would preserve the split. It holds a field where it is, in the higher-energy state as readily as in the lower one [13]. The team describes the field as trapped in whatever state it has already settled into [4].
The first thing I want from any suppression result is its size. The release describes the suppression as strong and the transition as far less likely, but it does not state a numerical factor or the range of field masses where the effect holds [11].
The thing this doesn't tell you is whether the Higgs field is any safer today. To answer that, the authors say, a calculation would have to account for a changing cosmic expansion rate and for the field's own influence on gravity [9]. They list both as additional factors, so the present model does not include them [14].
The paper's title, "Cosmic Lockdown: When Decoherence Saves the Universe from Tunneling", makes the larger claim [1]. I think the defensible claim is narrower and still interesting. In an expanding universe, whether a field can tunnel out of a false vacuum depends on what the field is coupled to, and tools developed for quantum computers can calculate the difference [4][10]. The team presents the work as a bridge between quantum information science and cosmology [10].
What to watch
- The figures in the published JCAP paper: how large the suppression is, and for which field masses and couplings it holds.
- Follow-up calculations that add a changing expansion rate and the field's own effect on gravity, the ingredients the authors say a Higgs stability claim requires.