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dark energy

Comparing astronomical observations with the predictions of the big bang models (which link the properties of matter and the speed of the universe’s expansion), it turns out that more than 70 percent of the density of the universe is supplied by what is called dark energy, a type of energy that is associated with empty space itself. Ordinary matter or energy are conserved when the universe expands: If I have 10 hydrogen atoms in a certain region of space, and if that region now expands to twice its initial volume, it will still contain no more than the initial 10 hydrogen atoms, now spread over the larger volume. On the other hand, the amount of dark energy in that region of space doubles in the process, just as the volume, the “amount of space” is twice as large than it was in the beginning.

There’s another crucial difference between ordinary energy and dark energy. The gravitational influence of ordinary masses and ordinary energy is attractive – it is aimed at pulling all the contents of the universe closer together. Dark energy, on the other hand, acts to accelerate the universe’s expansion. In that way, it is equivalent to a certain type of what is called a cosmological constant.

As yet, nobody knows how (and if) dark energy fits somewhere into our current picture of the fundamental constitutents of the universe, for instance: into the standard model of particle physics or some extension of that model. This makes dark energy one of the greatest mysteries of modern physics.

Definitioner

space

In a strict sense: Space as we know it from everyday life: the totality of all locations in which objects can sit, with three dimensions. In a more general sense used by mathematicians, all kinds of sets of points are spaces - a line for instance, which has but a single dimension, or a two-dimensional surface, but also higher-dimensional spaces. Also, in such more general spaces, geometry can be different from the standard Euclidean geometry taught in high schools - such spaces can be curved.

matter

In general relativity: All contents of spacetime that contribute to its curvature: particles, dust, gases, fluids, electromagnetic and other fields. In particle physics: All elementary particles with half-integer spin, such as electrons and quarks, as well as their composites such as protons and neutrons, in contrast with force particles.

hydrogen

The lightest (and, in our universe, the most abundant) chemical element. The atomic nucleus of an ordinary hydrogen atom is a single proton. If the atomic nucleus contains an additional neutron, the atom is called heavy hydrogen or deuterium.

energy

Physical quantity with the special property that, in physical processes, energy is neither destroyed nor created, simply transformed from one form of energy to another. Some of the different forms of energy that are defined separately are kinetic energy, thermal energy and the energy carried by electromagnetic radiation. Processes that transform one form of energy into another take place in all machines we use in everyday life, from the engine of a subway train (electrical energy into kinetic energy of the train) to an electric blanket (electrical energy into thermal energy). One important consequence of special relativity is that energy and mass are completely equivalent - two different ways to define what is, on closer inspection, one and the same physical quantity. See the keyword equivalence between mass and energy.

dark energy

Comparing astronomical observations with the predictions of the big bang models (which link the properties of matter and the speed of the universe's expansion), it turns out that more than 70 percent of the density of the universe is supplied by what is called dark energy, a type of energy that is associated with empty space itself. Ordinary matter or energy are conserved when the universe expands: If I have 10 hydrogen atoms in a certain region of space, and if that region now expands to twice its initial volume, it will still contain no more than the initial 10 hydrogen atoms, now spread over the larger volume. On the other hand, the amount of dark energy in that region of space doubles in the process, just as the volume, the "amount of space" is twice as large than it was in the beginning. There's another crucial difference between ordinary energy and dark energy. The gravitational influence of ordinary masses and ordinary energy is attractive - it is aimed at pulling all the contents of the universe closer together. Dark energy, on the other hand, acts to accelerate the universe's expansion. In that way, it is equivalent to a certain type of what is called a cosmological constant. As yet, nobody knows how (and if) dark energy fits somewhere into our current picture of the fundamental constitutents of the universe, for instance: into the standard model of particle physics or some extension of that model. This makes dark energy one of the greatest mysteries of modern physics.

current

Matter in coordinated, flowing motion - think of water flowing in a pipe. An important example is the electric current associated with moving electric charges. Electric currents are the sources of magnetic fields.

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dark energy

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