What is dark matter?We are much more certain what dark matter is not than we are what it is. What is dark energy? It is responsible for the cosmic speeding, and international teams of astronomers are working to refine measurements of that acceleration.

In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. Since this discovery measurements have improved and other cosmological phenomena, also sensitive to the rate of expansion, have been used to confirm these results.
Specifically, astronomers measure the redshifted spectra of, and luminosity distances to, stellar explosions called type 1a supernovae. In a nutshell, current theory cannot explain the acceleration. Dark matter makes up about 25%. The time required for light from a supernova to reach our telescopes is encoded in the distance (the relation is slightly more complicated than distance = rate x time, due to the cosmic expansion), while the change in the size of the universe from explosion to observation stretches the wavelength of the emitted light, as characterized by the redshift. Dark matter pulls and dark energy pushes. At stake is judgment on Einstein's greatest blunder (the cosmological constant), possible insight into the fundamental theory of nature (quantum gravity and the quantum state of the universe), and the fate of the universe (a Big Chill or a Big Rip?). No one expected this, no one knew how to explain it.

First, it is dark, meaning that it is not in the form of stars and planets that we see. If we can figure out what it really is, it is certain we will find a more illuminating name.With the establishment of the big bang cosmological model, it had widely been expected that since the birth of the universe some 13.7 billion years ago, the cosmic expansion had been slowing down. The luminous mass is determined by adding up all the light and converting that number to a mass based on our understanding of how stars shine. Understanding the evolution of the universe requires knowledge of its starting conditions and its composition. Dark matter must be the basic building block of the largest structures in the universe: galaxies and clusters. Dark energy is important because it is the force that may explain why the universe continues to expand. Theoretically, the simplest models for a new form of energy to the Universe happen in increments for w of ⅓; the fact that dark energy is very close to … So the expansion of the universe has not been slowing due to gravity, as everyone thought, it has been accelerating. Maybe there is something wrong with Einstein's theory of gravity and a new theory could include some kind of field that creates this cosmic acceleration. There are candidate theories, but none are compelling.
The first observational evidence for its existence came from supernovae measurements, which showed that the universe does not expand at a constant rate; rather, the expansion of the universe is accelerating. High concentrations of matter bend light passing near them from objects further away, but we do not see enough lensing events to suggest that such objects to make up the required 25% dark matter contribution.This image shows the distribution of dark matter, galaxies, and hot gas in the core of the merging galaxy cluster Abell 520.

So the mystery continues.A last possibility is that Einstein's theory of gravity is not correct.

But two independent research teams found in 1998 that the expansion was speeding up. These and other results agree with the theoretical predictions of the primordial abundances of the light elements as a result of the nuclear processes that took place in the first three minutes of the universe--also known as big bang nucleosynthesis. So, the question arises about why is it so important. That is, dark matter is invoked to explain greater-than-expected gravitational attraction. Dark energy and dark matter describe proposed solutions to as yet unresolved gravitational phenomena.

Prior to these observations, the only forms of matter-energy kn… Granted, the slowing had not been observed, but, theoretically, the universe had to slow. Then came 1998 and the Hubble Space Telescope (HST) observations of very distant supernovae that showed that, a long time ago, the universe was actually expanding more slowly than it is today. That would not only affect the expansion of the universe, but it would also affect the way that normal matter in galaxies and clusters of galaxies behaved. It is called "dark" because it must necessarily be very weakly interacting with regular matter--much like dark matter--and it is referred to as energy because one of the few things we are certain of is that it contributes nearly 70 percent of the total energy of the universe. Roughly 70% of the Universe is made of dark energy. The result could present a challenge to basic theories of dark matter.How do Earth, the planets, and the heliosphere respond?Weather and Atmospheric Dynamics Focus Area Publications and Research HighlightsCarbon Cycle and Ecosystems Focus Area Publications and Research HighlightsIndia overtakes China as top emitter of sulfur dioxideLocal land subsidence increases flood risk in San Francisco BaySea surface salinity could provide new insight into severe stormsSeeing the connection between neighboring volcanoes at depthWarm ocean waters off Greenland put glaciers at more riskDevelopmental, Reproductive & Evolutionary Biology ProgramExperiments - Developmental, Reproductive & Evolutionary Biology ProgramHardware - Developmental, Reproductive & Evolutionary Biology ProgramPublications - Developmental, Reproductive & Evolutionary Biology ProgramWhat We Study - Developmental, Reproductive & Evolutionary Biology Program


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