Hubble expansion of universe
Pro Research Analysisby 
Searched over 200M research papers
Hubble Expansion of the Universe
Introduction to Hubble's Law and Cosmic Expansion
Edwin Hubble's groundbreaking discovery in 1929 revealed that the universe is expanding. This was based on the observation that a galaxy's distance is proportional to its redshift, a relationship now known as Hubble's Law2 3. This discovery fundamentally changed our understanding of the cosmos, leading to the development of the field of observational cosmology, which studies the universe's expansion and evolution over billions of years3.
Measuring the Hubble Constant
Early and Late Universe Measurements
The Hubble constant (H0) quantifies the current rate of the universe's expansion. It can be estimated using measurements from both the early and late universe. However, these two estimates have shown a significant discrepancy. Measurements from the early universe, based on the cosmic microwave background (CMB) and the standard cosmological model, differ from those obtained from the late universe, which use various methods and data1. This discrepancy has become more pronounced with improved measurement techniques, reducing the uncertainty in late universe measurements to less than 2% by 20191.
Methods of Measurement
Several methods have been developed to measure the Hubble constant. These include observations of Type Ia supernovae, gravitational lensing systems, and the use of Cepheid variables. Each method has its own set of challenges and potential systematic errors, which contribute to the differing results5 7. For instance, gravitational lensing provides a way to measure distances that are less sensitive to cosmological assumptions, but more observations are needed to improve precision5.
The Discrepancy in Hubble Constant Measurements
Potential Explanations
The inconsistency between early and late universe measurements of the Hubble constant has led to various hypotheses. Some suggest new physics beyond the standard cosmological model (ΛCDM) might be required to explain the discrepancy. Others propose that systematic errors in measurement techniques could be the cause6. One potential solution involves increasing the expansion rate just before recombination, but this is tightly constrained by other cosmological observations6.
Impact on Cosmology
This discrepancy has significant implications for our understanding of the universe. It challenges the current cosmological model and suggests that there might be unknown factors influencing the universe's expansion. Resolving this issue is crucial for accurately determining the universe's age, size, and overall structure4.
Conclusion
The Hubble expansion of the universe remains a central topic in cosmology. While Edwin Hubble's initial discovery set the stage for modern cosmology, ongoing research continues to refine our understanding of the universe's expansion rate. The current discrepancy between early and late universe measurements of the Hubble constant highlights the need for further investigation and potentially new physics to fully explain the universe's behavior.
Sources and full results
Most relevant research papers on this topic
The expansion of the Universe is faster than expected
The Hubble constant is faster than expected, with multiple independent measurements in 2019 proving a discrepancy with early Universe predictions.
Highly CitedHubble's diagram and cosmic expansion
Edwin Hubble's classic article on the expanding universe in 1929 introduced the concept of a galaxy's distance being proportional to its redshift, leading to modern investigations of the expanding, evolving, and accelerating universe.
Highly CitedHubble’s Law and the expanding universe
The Hubble Law, a key discovery in cosmology, reveals that the universe has been expanding for 14 billion years, with dark matter, dark energy, and billions of galaxies.
The Hubble constant and the expansion age of the Universe
Recent progress in measuring the Hubble constant suggests the Universe has a kinematic age of less than 142 billion years, favoring a low-matter-density universe and either an open or flat universe with a non-zero cosmological constant.
A measurement of the Hubble constant from angular diameter distances to two gravitational lenses
The Hubble constant, H0, is 82.48.3+8.4 kilometers per second per megaparsec, using angular diameter distances to strong gravitational lenses as a calibrator.
Hubble constant hunter’s guide
The most likely solution to reconcile the Hubble constant and cosmic microwave background data is to increase the expansion rate in the decade before recombination.
Highly Cited