2019 Nobel Prize in Physics(1)
Reason for Award
for theoretical discoveries in physical cosmology
Laureates
United States of America
Explanation
The universe is thought to have begun with a huge explosion called the Big Bang. Dr. Peebles used mathematics to study how the universe grew and how stars and galaxies formed. He focused on the cosmic microwave background, a kind of “fossil light,” to read the amounts of different ingredients in space. His work showed that the matter we can see makes up only a tiny part of everything. The rest is invisible dark matter and dark energy.
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cosmic microwave background
The CMB is light emitted 380,000 years after the Big Bang and stretched into millimetre waves today. Its tiny temperature fluctuations, measured to one-part-in-100,000, are key to determining the universe’s age and composition. The acoustic peak pattern encodes baryon acoustic oscillations, allowing separation of baryon and dark-matter densities. Polarisation modes let scientists look for inflationary gravitational-wave signatures. The CMB is thus the richest data set in modern cosmology.
dark matter
Dark matter is invisible material inferred from galaxy rotation curves and gravitational lensing. It is estimated to make up 26 % of the universe. Peebles proposed the ‘cold’ dark-matter scenario, where heavy, slow particles aid structure formation. Candidate particles such as WIMPs and axions are being sought in underground and accelerator experiments. Revealing dark matter’s nature is a major challenge in both astronomy and particle physics.
dark energy
Dark energy is an unknown component with negative pressure that drives cosmic acceleration. It accounts for about 69 % of the total energy density. Peebles helped revive Einstein’s cosmological constant Λ as a dark-energy candidate. Type-Ia supernova observations confirmed acceleration, cementing the ΛCDM model. Whether dark energy is quantum vacuum energy or a new field remains an open question.
ΛCDM model
The ΛCDM model is the current cosmological standard, describing the universe with Λ (dark energy), cold dark matter, baryons, neutrinos and photons. With only about six parameters it explains CMB data, galaxy clustering and lensing with high accuracy. Peebles’ work shaped the framework’s backbone. Consistency of parameter estimates across observations supports the model. Nonetheless, tensions such as differing Hubble constants highlight open issues.
baryon acoustic oscillations
BAO are frozen sound waves from the early photon–baryon fluid, giving a standard ruler of roughly 100 Mpc. Peaks in galaxy distributions serve as a yardstick for the cosmic expansion history. Peebles’ acoustic-peak theory linked CMB physics with large-scale structure. BAO measurements are vital for constraining dark-energy equations of state. Surveys like DESI and Euclid aim to refine these constraints.