Affiche Dark Matter, Dark Energy - The Dark Side of the Universe
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First proposed in the 1930s, the idea that there is missing mass influencing the behavior of galaxies began to look more and more likely from the 1970s on. We know that it is matter because we can detect its gravitational influence on visible matter, but we cannot see it. An inventory of the distribution of dark matter throughout space shows that it constitutes 25% of the energy density of the universe.


Saisons & épisodes Les résumés de tous les épisodes de Dark Matter, Dark Energy - The Dark Side of the Universe

S01E01 Fundamental Building Blocks 00/00/0000 Scientists now have a complete inventory of the universe, which is composed of three basic constituents: Ordinary matter includes every kind of particle ever directly observed; dark matter consists of massive particles known only because of their gravitational effects; and dark energy is a smoothly distributed component that whose density does not change as the universe expands.
S01E02 The Smooth, Expanding Universe 00/00/0000 Imagine looking into a clear night sky with perfect vision. What would you see? This lecture surveys the visible universe—from the stars in our galaxy to the cloudy patches called nebulae that astronomer Edwin Hubble proved are galaxies in their own right—and Hubble's discovery that the universe is expanding.
S01E03 Space, Time, and Gravity 00/00/0000 Einstein taught us that space and time can be combined into spacetime, which has the ability to evolve and grow. Indeed, what we think of as gravity is just a manifestation of the curvature of spacetime. To find things in the universe—including dark matter and dark energy—all we have to do is to map out this curvature.
S01E04 Cosmology in Einstein's Universe 00/00/0000 The expansion of the universe is governed by its spatial curvature and energy density, both of which have specific ways of changing as the universe grows. These features are related to each other by Einstein's general theory of relativity, which can be used to model the past and possible future of the universe.
S01E05 Galaxies and Clusters 00/00/0000 Applying the laws of dynamics to galaxies and galaxy clusters, we find that more matter is required to account for their motions than can be observed. Some of the missing mass is hot gas; however, this is still not enough, and we need to invoke some new kind of particle in galaxies and clusters: dark matter.
S01E06 Gravitational Lensing 00/00/0000 Another way to detect invisible matter is to use light as a probe of the gravitational field. Passing through curved spacetime, the path of a light ray is deflected due to gravitational lensing. Lensing demonstrates the existence of gravitational fields where there is essentially no ordinary matter.
S01E07 Atoms and Particles 00/00/0000 We peer into the atom to discover the constituents of ordinary matter: nuclei and electrons. Nuclei are made of protons and neutrons, which in turn are made of quarks. Electrons and quarks are examples of fermions, or matter particles. There are also bosons, or force-carrying particles, such as photons and gluons.
S01E08 The Standard Model of Particle Physics 00/00/0000 In the 1960s and 1970s, physicists developed a comprehensive theory of known fermions and bosons. Now called the standard model, this theory fits an impressive amount of data, but it leaves two crucial puzzles: the hypothetical Higgs boson and the graviton, the carrier of the gravitational force.
S01E09 Relic Particles from the Big Bang 00/00/0000 Armed with the core principles of particle physics, we know enough about the early universe to predict how many of each type of particle should be left over from the Big Bang. These "relic abundances" are crucial to understanding the origin of dark matter and light elements.
S01E10 Primordial Nucleosynthesis 00/00/0000 The process of nucleosynthesis describes how protons and neutrons were assembled into light elements during the first few minutes after the Big Bang. We can observe these primordial elements today and check on Einsteinian cosmology and a stringent constraint on theories of dark matter.
S01E11 The Cosmic Microwave Background 00/00/0000 About 380,000 years after the Big Bang, the universe had cooled sufficiently for electrons and nuclei to combine into atoms allowing light to travel much more freely. The relic photons from this era are visible to us today as the cosmic microwave background, which holds clues to the composition and structure of the universe.
S01E12 Dark Stars and Black Holes 00/00/0000 Candidates for dark matter include small, dark stars called Massive Compact Halo Objects (MACHOs) and black holes. Such objects are ultimately composed of ordinary matter, of which there just isn't enough to account for the dark matter. We are forced to conclude that the dark matter is a new kind of particle.
S01E13 WIMPs and Supersymmetry 00/00/0000 Weakly interacting massive particles (WIMPs) are ideal candidates for what comprises dark matter. WIMPs may have their origins in supersymmetry, which posits a hidden symmetry between bosons and fermions, and predicts a host of new, as-yet-unobserved particles, including WIMPs.
S01E14 The Accelerating Universe 00/00/0000 In the late 1990s, two groups of astronomers found to their astonishment that the expansion of the universe is speeding up rather than slowing down. Such behavior can't be explained by any kind of matter and suggests the existence of an entirely new component: dark energy.
S01E15 The Geometry of Space 00/00/0000 Precise measurements of the cosmic microwave background let us measure the total energy density of the universe by observing the geometry of space. We find that the energy in matter alone is not enough, confirming the need for dark energy.
S01E16 Smooth Tension and Acceleration 00/00/0000 Dark energy is smoothly distributed throughout the universe and its density is nearly constant, even though the universe is expanding. Unlike gas under pressure in a container, dark energy is a kind of "negative pressure"—or tension—that imparts an accelerated expansion to the universe.
S01E17 Vacuum Energy 00/00/0000 The density and distribution of dark energy remain the same across all of space­time, but what exactly is dark energy? There are many possibilities, the simplest of which is vacuum energy—an constant amount of energy in every cubic centimeter of space itself. Vacuum energy is equivalent to Einstein's idea of the cosmological constant.
S01E18 Quintessence 00/00/0000 Another idea about dark energy is that it results from a new field in nature, analogous to the electromagnetic field but remaining persistent as the universe expands. This field is called quintessence. It would be observationally distinguishable from the cosmological constant.
S01E19 Was Einstein Right? 00/00/0000 We have inferred the existence of dark matter and dark energy from the gravitational fields they cause. In this lecture, we explore proposals that a modified theory of gravity might allow us to dispense with the need for invoking dark stuff. However, this turns out to be very difficult in practice.
S01E20 Inflation 00/00/0000 Before we had observational evidence that the universe is accelerating, cosmologists considered the possibility of a period of rapid acceleration at very early times—a scenario known as inflation.
S01E21 Strings and Extra Dimensions 00/00/0000 We know about the dark sector because of gravity, and string theory is an ambitious attempt to unify gravitation with the other forces of nature into a theory of everything. String theory promises a theory of quantum gravity, but it also predicts extra, unseen spatial dimensions that are difficult to test.
S01E22 Beyond the Observable Universe 00/00/0000 The speed of light and the age of the observable universe are finite. That means we can't see the whole universe because our vision can only stretch so far. The "multi­verse"—a hypothesis of regions where conditions are very different from those we see in our observable universe—may help explain properties of dark energy.
S01E23 Future Experiments 00/00/0000 Astronomers are designing new observatories to probe the acceleration of the universe and other cosmic phenomena. Physicists are also looking forward to new experiments that will dramatically improve our understanding of particles and forces, and how ordinary matter fits in with dark matter and dark energy.
S01E24 The Past and Future of the Dark Side 00/00/0000 The concordance cosmology is an excellent fit to a variety of data, but it presents us with deep puzzles: What are dark matter and dark energy? Why do they have the densities they do? Our own universe seems unnatural to us. That's good news, as it is a clue to the next level of understanding.
S00E01 Professor Bio 00/00/0000

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