Unsolved Problems in Physics

Introduction

• Humans create voluntary problems (children, taxes), but some issues require large-scale tools (particle accelerators, telescopes).
• Lecture explores unsolved problems in physics ranked by fundamentality.

The Arrow of Time

• Time moves forward with no formula requiring it; laws of physics work equally in reverse.
• Irreversibility due to entropy, where the universe progresses to greater disorder.
• Microscopic laws don’t distinguish time direction, yet macroscopic universe shows clear time direction.

Ultra-High-Energy Cosmic Rays

• Detected rays seem to violate the GZK limit, a theoretical energy threshold.
• "Oh My God" particle detected, carrying energy beyond the limit.

Magnetic Monopoles

• Predicted by grand unified theories and string theory, but never detected in nature.
• Theories suggest possible production via powerful particle accelerators or cosmic strings.

Matter-Antimatter Asymmetry

• Universe started with equal matter and antimatter; matter prevailed.
• Possible explanations include CP violation and hypothetical baryon production processes.

Neutron Lifetime Discrepancy

• Different results from beam and bottle methods for measuring neutron lifetime.
• Discrepancy may stem from experimental errors or dark matter interactions.

Proton Decay

• Uncertainty whether protons decay; current experiments set lower bounds on half-life.
• If protons decay, it affects the stability of matter over long timescales.

Supersymmetry (SUSY)

• Proposes correspondence between bosons and fermions via superpartners.
• SUSY particles have not been detected, suggesting higher masses or broken symmetry.

Strong CP Problem

• Strong force doesn’t exhibit CP violation unlike weak force.
• Proposed solutions include new particles like the axion, potential dark matter candidates.

Neutrino Oscillations

• Neutrinos can change "flavors" suggesting they have mass.
• Anomalies like the reactor antineutrino anomaly hint at new physics.

Black Hole Singularity

• Unable to reconcile quantum physics and general relativity for singularities.
• Naked singularities and cosmic censorship hypothesis explored.

Information Paradox

• Information seemingly lost in black holes contradicts quantum mechanics principle of unitarity.
• Proposed solutions include fuzzballs and alternative black hole models.

Vacuum Catastrophe

• Discrepancy between observed and predicted vacuum energy density.
• Issue known as the cosmological constant problem, suggesting need for new physics.

Quantum Measurement Problem

• Superposition collapse in quantum mechanics lacks consensus explanation.
• Two main interpretations: Copenhagen interpretation and Many Worlds Interpretation.

Fine-Tuning Problem

• Certain fundamental constants appear finely-tuned for life.
• Raises questions about the existence of a fundamental principle or the anthropic principle.

Dark Matter and Dark Energy

• Effects observed, but nature remains mysterious.
• Dark energy drives universe expansion; dark matter provides gravitational effects.

Theory of Everything

• Seeks to unify all fundamental forces and reconcile general relativity with quantum mechanics.
• String theory and loop quantum gravity are current attempts.

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These notes provide an overview of current unsolved physics problems, offering insights into where future discoveries might arise.