According to Johns Hopkins University professor of astronomy and physics Adam Riess, the universe’s actual expansion rate is producing a significant discrepancy when compared with predictions from the early universe, creating what scientists call the Hubble tension. Speaking on Quanta Magazine’s The Joy of Why podcast with co-host Steven Strogatz, Riess noted that the two main methods for estimating the universe’s present-day expansion rate are producing significantly different answers.
Measuring Cosmic Expansion with Supernovae
To understand how fast the universe expands, researchers rely on celestial objects known as Type IA supernovae. According to Riess, these exploding stars serve as standard candles or lighthouses because they are very homogeneous and uniform. When a white dwarf star exceeds the Chandrasekhar limit of 1.4 times the mass of the sun, it triggers a runaway thermonuclear explosion.
By measuring both the redshift of the light and the distance to these supernovae, astronomers can track the expansion history of the cosmos.
The Discovery of Accelerating Expansion
Astronomers have known since the 1930s that the universe is expanding, but in the 1990s, the discovery that this expansion is accelerating rather than slowing down came as a huge shock to the field. According to Riess, the data showed that the universe’s expansion is actually accelerating rather than decelerating. This acceleration is driven by dark energy.
Unraveling the Hubble Tension
A major conflict has emerged regarding the exact expansion rate, or Hubble constant. As a result, how fast the universe is really expanding has become a matter of considerable debate — with no small amount of angst — and the discrepancy has become known as the Hubble tension.
Did you know? One Type IA supernova explosion can be equivalent in brightness to about a billion stars shining normally like our sun.
Future Observatories and the Quest for Answers
Resolving the Hubble tension will require advanced instrumentation and rigorous independent verification. As Janna Levin noted during the podcast, it is a really interesting moment in cosmology.
Frequently Asked Questions
What is the Hubble tension?
According to Adam Riess, the Hubble tension is the significant discrepancy between the two main methods for estimating the universe’s present-day expansion rate.
Why are Type IA supernovae important in cosmology?
Type IA supernovae act as standard candles because they are very uniform, allowing astronomers to measure distances and track the expansion history of the universe.
What is dark energy?
Dark energy was proposed as the cause of the accelerating expansion of the universe.
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