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This, and the fact that the pulsations are weakly nonlinear, allows a description of the system in terms of amplitude equations [21] [22] and a construction of the bifurcation diagram (see also bifurcation theory) of the possible types of pulsation (or limit cycles), such fundamental mode pulsation, first or second overtone pulsation, or more ...
A cyclic model (or oscillating model) is any of several cosmological models in which the universe follows infinite, or indefinite, self-sustaining cycles. For example, the oscillating universe theory briefly considered by Albert Einstein in 1930 theorized a universe following an eternal series of oscillations, each beginning with a Big Bang and ending with a Big Crunch; in the interim, the ...
He explained how all mass energy is positive and all gravitational energy is negative and they cancel each other out, leading to a universe of zero energy. [16] His investigation of the oscillatory universe hypothesis, which Alexander Friedmann had proposed in 1922, drew attention to difficulties as regards entropy and resulted in its demise ...
RS Puppis, one of the brightest known Cepheid variable stars in the Milky Way galaxy (Hubble Space Telescope)A Cepheid variable (/ ˈ s ɛ f i. ɪ d, ˈ s iː f i-/) is a type of variable star that pulsates radially, varying in both diameter and temperature.
Einstein's theory of general relativity predicts that this system should emit strong gravitational radiation, causing the orbit to continually contract as it loses orbital energy. Observations of the pulsar soon confirmed this prediction, providing the first ever evidence of the existence of gravitational waves.
The concept of universal wavefunction was introduced by Hugh Everett in his 1956 PhD thesis draft The Theory of the Universal Wave Function. [8] It later received investigation from James Hartle and Stephen Hawking [9] who derived the Hartle–Hawking solution to the Wheeler–deWitt equation to explain the initial conditions of the Big Bang ...
In this book Krauss demonstrates how the dark matter problem is now connected with two widely discussed areas in the modern cosmology: the ultimate fate of the universe and the cosmological constant. He also discusses an antigravity force that may explain recent observations of a permanently expanding universe.
The universe is believed to still be homogeneous enough that the theory is a good approximation on the largest scales, but on smaller scales more involved techniques, such as N-body simulations, must be used. When deciding whether to use general relativity for perturbation theory, note that Newtonian physics is only applicable in some cases ...