Concept
Void (astronomy)
Overview
Cosmic voids are vast spaces between filaments (the largest-scale structures in the universe), which contain very few or no galaxies. In spite of their size, most galaxies are not located in voids but are gravitationally bound together, creating huge cosmic structures known as galaxy filaments. The cosmological evolution of the void regions differs drastically from the evolution of the universe as a whole: there is a long stage when the curvature term dominates, which prevents the formation of galaxy clusters and massive galaxies. Hence, although even the emptiest regions of voids contain more than ~15% of the average matter density of the universe, the voids look almost empty to an observer.
Voids typically have a diameter of 10 to 100 megaparsecs (30 to 300 million light-years); particularly large voids, defined by the absence of rich superclusters, are sometimes called supervoids. They were first discovered in 1978 in a pioneering study by Stephen Gregory and Laird A. Thompson at the Kitt Peak National Observatory.
Voids are formed through gravitational instability - starting from initially small anisotropies from quantum fluctuations in the early universe, the anisotropies grew larger in scale over time. Regions of higher density collapsed more rapidly under gravity, eventually resulting in the large-scale, foam-like structure or "cosmic web" of voids and galaxy filaments seen today. Voids located in high-density environments are smaller than voids situated in low-density spaces of the universe.
Voids appear to correlate with the observed temperature of the cosmic microwave background (CMB) because of the Sachs–Wolfe effect. Colder regions correlate with voids, and hotter regions correlate with filaments because of gravitational redshifting. As the Sachs–Wolfe effect is only significant if the universe is dominated by radiation or dark energy, the existence of voids is significant in providing physical evidence for dark energy.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
In the original texts
Passages from public-domain books where Void (astronomy) is discussed.
And then, if haply any think this comes, When bodies spring apart, because the air Somehow condenses, wander they from truth: For then a void is formed, where none before; And, too, a void is filled which was before. Nor can air be condensed in such a wise; Nor, granting it could, without a void, I hold, It still could not contract upon itself And draw its parts together into one.
Titus Lucretius Carus, On the Nature of Things
names the idea; a chapter is titled for it; states what it is
So one who denies His existence there goes against his own ideas. He is existent, has a body, is not existent without a body. They cannot say that beyond the universe is a void. For the impossibility of a void has been made quite certain in the philosophical sciences. For that upon which the name void is commonly applied, are nothing but dimensions (_Abad_), in which there are no bodies. For when these dimensions…
Averroës, The Philosophy and Theology of Averroes
names the idea; states what it is
But admit that an absolute void is possible: it is not of that void that I am thinking when I say that the object, once annihilated, leaves its place unoccupied; for by the hypothesis it is a _place_, that is a void limited by precise outlines, or, in other words, a kind of _thing_. The void of which I speak, therefore, is, at bottom, only the absence of some definite object, which was here at first, is now…
Henri Bergson, Creative Evolution
names the idea; states what it is
“Aristotle decides that there is no void on such arguments as this. In a void there could be no difference of up and down; for as in nothing there are no differences, so there are none in a privation or negation; but a void is merely a privation or negation of matter; therefore, in a void, bodies could not move up and down, which it is in their nature to do. It is easily seen” (Dr.
John Stuart Mill, A System of Logic, Ratiocinative and Inductive
names the idea; states what it is
Void, as we have seen, of all title to credence, is the story of Paul's commission from Jesus:--void may it be seen to be, even if taken by itself, and without need of resort to any counter-evidence. Who could have expected to have found it, moreover, disproved by the most irresistible counter-evidence--by the evidence of the Apostles themselves?
Jeremy Bentham, Not Paul, but Jesus
names the idea; opens on it
Related ideas
Place in the tradition
Part of Universe.