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The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. [1] It is an intrinsic expansion, so it does not mean that the universe expands "into" anything or that space exists "outside" it.
The International Astronomical Union uses the term "age of the universe" to mean the duration of the Lambda-CDM expansion, [13] or equivalently, the time elapsed within the currently observable universe since the Big Bang. The expansion rate at any time is called the Hubble parameter ˙, which is modeled as ˙ = + + + (), where are density ...
The thinning of matter over time reduces the ability of the matter to gravitationally decelerate the expansion of the universe; in contrast, dark energy is a constant factor tending to accelerate the expansion of the universe. The universe's expansion passed an inflection point about five or six billion years ago when the universe entered the ...
In 1931, Lemaître went further and suggested that the evident expansion of the universe, if projected back in time, meant that the further in the past the smaller the universe was, until at some finite time in the past all the mass of the universe was concentrated into a single point, a "primeval atom" where and when the fabric of time and ...
The observations stretch back to about 12.3 billion years ago, when the universe was roughly a tenth Ferocious black holes reveal 'time dilation' in early universe Skip to main content
Perhaps unsurprisingly, our universe has just the right mass–energy density, equivalent to about 5 protons per cubic meter, which has allowed it to expand for the last 13.8 billion years, giving time to form the universe as observed today. [65] [66] There are dynamical forces acting on the particles in the universe which affect the expansion ...
If, however, the universe contains dark energy, then the resulting repulsive force may be sufficient to cause the expansion of the universe to continue forever—even if >. [10] This is the case in the currently accepted Lambda-CDM model , where dark energy is found through observations to account for roughly 68% of the total energy content of ...
However, it may still be possible to determine the expansion of the universe through the study of hypervelocity stars. [131] 1.05×10 12 (1.05 trillion) The estimated time by which the universe will have expanded by a factor of more than 10 26, reducing the average particle density to less than one particle per cosmological horizon volume ...