Article Background & Motivation

• Author wrote article for "Ethan's great medium collection called starts with a bang" 2 weeks ago
• Topic: whether black holes can destroy universe (answer: yes)
• Receiving many emails from people worried about LHC creating universe-destroying black holes
• Purpose: explain why this scenario is very unlikely

Vacuum Metastability Fundamentals

• Current vacuum state not permanently stable - only metastable
• Not lowest possible energy state, will eventually decay to lower energy state
• Decay process releases enormous energy, enough to tear apart all matter
• This mechanism causes end of universe
• Analogy: chemical hand warmers with supercooled liquid
  • Metal plate creates nucleation seed
  • Transforms liquid to solid, releases energy as heat

Current Understanding of Vacuum Stability

• Don't actually know vacuum is unstable - based on extrapolation from current measurements
• Vacuum stability determined by potential with parameters extracted from LHC data
• Extrapolation makes assumptions about energy ranges without actual data
• Estimated vacuum decay time: 10^100 years (much longer than universe age)
• At that timescale: all stars dead, life impossible

Black Holes as Vacuum Decay Triggers

• New paper studied how black holes affect vacuum stability (link in captions)
• Black holes act as nucleation seeds for vacuum decay
• Similar to metal plate in chemical hand warmer
• Nucleation effect only noticeable for very small black holes
• Smaller black hole = stronger curvature at horizon
• All observed black holes too large to trigger vacuum decay

Types of Black Holes That Could Trigger Decay

Primordial Black Holes

• Created in early universe at various masses
• Evaporate down over time, could be evaporating now
• Could trigger vacuum decay when in strong curvature regime
• Could happen any time
• Most physicists don't believe they exist
  • Theoretical reasons: hard to find production models without overproduction
  • Overproduction would prevent universe existing as observed

LHC Black Holes

• Require universe with additional curled-up dimensions (very small radius)
• Would make gravity much stronger at short distances than general relativity predicts
• LHC could produce tiny black holes in this scenario
• Zero evidence for additional dimensions so far
• Not entirely ruled out - some physicists still think LHC might produce them

2008 LHC Risk Assessment

• Press coverage about LHC potentially producing planet-eating black holes
• CERN conducted thorough risk assessment
• Conclusion: very unlikely to happen
• Key argument summary:
  • LHC collision energies reached in astrophysical processes
  • If these could produce dangerous black holes eating stellar objects
  • Should occasionally see stars vanish without reason
  • Never observed star vanishing
  • Estimate: very unlikely black holes would be harmful

Vacuum Decay Risk Not Previously Assessed

• CERN risk assessment didn't consider vacuum decay possibility
• Vacuum decay paper published after risk assessment completed
• Cannot directly apply paper results to LHC black holes
• Paper didn't examine black holes in extra dimensions
• Author's speculation: results likely similar for extra-dimensional black holes

Author's Risk Analysis

• Believes LHC black holes actually less risky considering vacuum decay
• Reasoning:
  • Astrophysical black hole eating star might happen occasionally unobserved
  • Creates remaining risk for LHC black holes
  • But astrophysical black hole destroying entire universe wouldn't be missed
  • Therefore LHC very unlikely to produce any black holes at all
• Conclusion: don't worry about LHC black hole risks