Dark matter and dark energy
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Universe Composition: Dark Matter and Dark Energy Overview
Current research shows that ordinary matter—atoms and molecules—makes up only about 5% of the universe. The remaining 95% consists of two mysterious components: dark matter (about 25%) and dark energy (about 70%) Cottrell2019Wu2023Turner1998+1 MORE. These substances are invisible and interact with the universe in ways that are not yet fully understood Cottrell2019Wu2023Arun2017+1 MORE.
Dark Matter: Evidence, Candidates, and Challenges
Observational Evidence and Role
Dark matter is needed to explain why galaxies and galaxy clusters do not fly apart, given their observed rotation speeds and gravitational effects Sarkar2007Cottrell2019Wu2023+3 MORE. Its presence is inferred from phenomena such as galaxy rotation curves, gravitational lensing, and the cosmic microwave background Sarkar2007Arun2017Turner1998+1 MORE.
Possible Candidates
The leading candidates for dark matter include non-baryonic particles like axions, neutralinos, sterile neutrinos, and primordial black holes Arun2017Oks2021Trugenberger2020. Some models also consider self-interacting dark matter, dibaryons, and even exotic compact objects Arun2017Oks2021. Despite many experiments, direct detection of dark matter remains elusive Wu2023Arun2017Oks2021.
Alternative Theories
Some researchers propose alternatives to dark matter, such as Modified Newtonian Dynamics (MOND) and modifications to general relativity, to explain the observed effects without invoking unseen matter Sarkar2007Arun2017Oks2021.
Dark Energy: Accelerating Universe and Theoretical Models
Observational Evidence and Effects
Dark energy is proposed to explain the observed accelerated expansion of the universe, as seen in the redshift of distant supernovae and the large-scale structure of the cosmos Sarkar2007Cottrell2019Wu2023+4 MORE. It acts as a kind of "antigravity," pushing galaxies apart Cottrell2019Wu2023Arun2017.
The Cosmological Constant and Competing Models
The simplest explanation for dark energy is the cosmological constant (vacuum energy), but its predicted value from quantum theory is vastly larger than what is observed, leading to the "cosmological constant problem" Sarkar2007Nadar2024Trugenberger2020. Other models include dynamical dark energy (quintessence), braneworld scenarios, Chaplygin gas, and phantom energy, each with different implications for the universe's fate Sarkar2007Arun2017Trugenberger2020.
Alternative Explanations
Some recent studies question whether dark energy is needed at all, suggesting that alternative explanations for supernova observations or new forms of matter with unusual properties could account for the data Stetsenko2020Oks2021. There are also unified models that attempt to explain both dark matter and dark energy as different aspects of a single phenomenon, such as in certain quantum gravity frameworks Arun2017Žulj2024.
Ongoing Mysteries and Future Directions
Despite significant progress, the true nature of dark matter and dark energy remains unknown. Many theoretical models and experimental searches are ongoing, and some results challenge the need for these concepts altogether Stetsenko2020Arun2017Oks2021+1 MORE. The search for direct detection of dark matter and a deeper understanding of dark energy's properties continues to be a major focus in cosmology and physics Wu2023Arun2017Oks2021+1 MORE.
Conclusion
Dark matter and dark energy are central to our understanding of the universe, accounting for most of its mass-energy content. While their existence is supported by strong observational evidence, their true nature is still a mystery. Multiple models and alternative theories are being explored, and future discoveries may reshape our understanding of the cosmos Sarkar2007Cottrell2019Wu2023+6 MORE.
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