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May 9, 2018 · Lisa Randall. Lisa Randall is Frank B. Baird, Jr., Professor of Science at Harvard University. She serves on Scientific American’s board of advisers.Among her many books is Dark Matter and the ...
- What Is Spacetime
George Musser. George Musser is a contributing editor for...
- What Is Consciousness
Illustration by Chris Gash. Consciousness is everything you...
- What Is Spacetime
- Tweaking Gravity
- Comparing The Theories
- Unusual Galaxies
- More Problems
- Moving Forward
- A Collision Offers Clues
First put forward by Israeli physicist Mordehai Milgrom in 1983, modified gravity changes the mathematical rules that govern how the force of gravity arises from mass. In most cases (that is, in nonextreme situations where Newtonian gravity is a good approximation), we describe this force by the inverse square law: the strength of gravity between t...
In the absence of any signs of new particles, we should ask how well the theories of dark matter and modified gravity, respectively, explain the evidence we do have from nature. For the most part, the hypothesis that the universe contains about five times as much dark matter as normal matter works well to explain the cosmos around us. Although dark...
There are other problems with the dark matter hypothesis—for instance, “low-surface-brightness galaxies.” In these dim galaxies, visible matter is spread more thinly than in galaxies similar to the Milky Way. The dark matter hypothesis originally led us to expect that galaxies with low surface brightness—that is, low amounts of visible matter—shoul...
The issue with low-surface-brightness galaxies is far from the only shortcoming of particle dark matter. The theory predicts, for instance, a highly peaked density of matter in the cores of galaxies, in contrast with what we measure. It predicts many more small dwarf galaxies than we observe and fails to predict the way that galaxies and their sate...
At this point, both particle dark matter and modified gravity have advantages and shortcomings. Some recent theoretical developments suggest that maybe the truth is in between: a type of particle dark matter that can masquerade as modified gravity. In 2015 Justin Khoury of the University of Pennsylvania and his colleagues found that some types of p...
The Bullet Cluster is a pair of galaxy clusters that crashed together long ago. It is a rare instance of a high-speed head-on collision. Images taken in visible and x-ray light (red), along with measurements of how gravity is bending light (gravitational lensing) (blue), reveal that in each cluster the center of the total mass and gravity is mispla...
Apr 11, 2023 · about 27% dark matter - so far unseen directly and defying description; around 68% dark energy - the mysterious component accelerating cosmic expansion
Oct 3, 2018 · There is a growing sense of ‘crisis’ in the dark-matter particle community, which arises from the absence of evidence for the most popular candidates for dark-matter particles—such as weakly ...
- Gianfranco Bertone, Tim M. P. Tait, Tim M. P. Tait
- 2018
3 days ago · dark matter, a component of the universe whose presence is discerned from its gravitational attraction rather than its luminosity. Dark matter makes up 30.1 percent of the matter-energy composition of the universe; the rest is dark energy (69.4 percent) and “ordinary” visible matter (0.5 percent).
- Adam Riess
- What is dark matter?Dark matter is a component of the universe whose presence is discerned from its gravitational attraction rather than its luminosity.
- What percentage of the matter-energy composition of the universe is made of dark matter?Dark matter makes up 30.1 percent of the matter-energy composition of the universe. The rest is dark energy (69.4 percent) and “ordinary” visible m...
- Who first inferred the existence of dark matter?Dark matter’s existence was first inferred by Swiss American astronomer Fritz Zwicky, who in 1933 discovered that the mass of all the stars in the...
- What are the types of dark matter?Two varieties of dark matter have been found to exist. The first variety is about 4.5 percent of the universe and made of the familiar baryons (i.e...
Aug 21, 2015 · Only about 5% of the universe consists of ordinary matter such as protons and electrons, with the rest being filled with mysterious substances known as dark matter and dark energy. So far ...
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Jun 1, 2018 · Chris Gash. June 2018 Issue. Space & Physics. Physicists and astronomers have determined that most of the material in the universe is “dark matter”—whose existence we infer from its gravitational...
