Home » Posts tagged 'expanding universe'
Tag Archives: expanding universe
Search the Site
Login
AskPhysics Videos
Subscribe to Blog via Email
Top Posts & Pages
 IMPORTANT DERIVATIONS FROM OPTICS FOR CBSE STUDENTS CLASS XII AISSCE
 Questions normally not answered by Students in Viva
 Previous years Board Questions from Optics
 BOARD QUESTIONS FROM WAVE OPTICS (CBSE/AISSCE)
 ASK A QUESTION
 Why dispersion does not occur in a glass slab?
 Download CBSE Physics AISSCE 2012 Board Question papers and solution
 Variation in acceleration due to gravity (g) with depth
 CLASS 11  HALF YEARLY EXAMINATION SAMPLE PAPER 1
 Deduce an expression for velocity of em waves in vacuum
Our Social Presence
Archives
Tags
Is the universe expanding or are we getting smaller?
Is the universe expanding or are we getting smaller?
Asked Dany Burton
The Question is left for the readers to answer
Related articles
Cosmological Constant and its Significance
Abdul Najeeb asked via Facebook:
Would you plz explain me what is a cosmological constant? When Einstein snubbed it as the "biggest blunder" in his life, what else is the real importance of the constant? Also what is cosmological acceleration and its’ effect on the constant…plz…but in simple words…plzzzz:)))))
Ans:
The cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe.
Einstein abandoned the concept after the observation of the Hubble redshift indicated that the universe might not be stationary, as he had based his theory on the idea that the universe is unchanging.However, the discovery of cosmic acceleration in the 1990s has renewed interest in a cosmological constant.
{courtesy : Wikipedia}
More details will be added soon
Importance of Cosmological Constant
Understanding the unnaturally small size of the cosmological constant poses one of severest challenges for a theory of gravity. At late times and for large distances, the apparent size of the cosmological constant is constrained to be extremely small in terms of the natural scale for gravity, the Planck mass. In contrast, no observations bound the value of the cosmological constant during the earliest stages of the universe, when corrections to the EinsteinHilbert action were nonnegligible, and its presence can lead to a richer family
of metrics. Among the solutions for a more general gravitational action, the presence of a positive cosmological constant does not inevitably lead to a de Sitter expansion. Such solutions must still yield or evolve into a low energy theory in which the effective cosmological constant is small to be phenomenologically acceptable. If the characteristic scales on which these metrics vary are of extremely high energy or short distance, then it may be possible to integrate out such features to arrive at a slowly varying e®ective theory.
To determine whether an action for gravity, generalized beyond an EinsteinHilbert term, admits these features  natural coefficients for the terms in the action and a rapid variation  we must ¯rst solve the highly nonlinear field equations. This task is difficult even when only the next curvature corrections are added. In 3 + 1 dimensions, Horowitzand Wald and later Starobinsky [3] discovered oscillating solutions for actions that
included quadratic curvature terms but no cosmological constant. Numerical solutions were found in 4 + 1 dimensions in the presence of a cosmological constant and a scalar field, along with the quadratic curvature terms. In this latter scenario, metrics exist that depend periodically on the extra spatial coordinate so that choosing the size of the extra dimension to be the period produces a compact extra dimension without any finetunings or singularities. The parameters in the action ¯x the size of the extra dimension uniquely.
However, without an analytical approach it becomes di±cult to generalize these solutions to include an evolution in time. Without this freedom, it is di±cult to understand how a universe starting from a more general state can find itself in one of these configurations.
Ask a Doubt
Post your Physics Doubts here
Latest Posts

Optics question

Maxwell’s equations for electromagnetic waves

A Physicist Driver confusing Police

Would an underground nuclear explosion generate an Electromagnetic pulse?

The indigenous Cryogenic Engine of India

Siphons and fluid dynamics

Why do we take differential element “dx” from the origin at a distance “x” only?
AskPhysics Q&A
 what is a laser?
 How Quantum Field Theory explains triboelectricity?
 Important topics to study for NEET Physics
 What are the most important topics in JAM Physics?
 If the size of the unit decreases by 20% the% change in the numerical value is
 Why is easier to hammer a sharp nail into wood than a blunt one?
 Can we dissociate aluminium using infrared multi photon dissociation method?
 Vector A + Vector B = vector C and A +2B is perpendicular to A then find relation between vector B and C.
 Why a ray when moves to normal from rarer to denser medium
 What is the major term involved in refraction
askphysics@Twitter
Ask Physics
@askphysics
 Post Edited: Optics question https://t.co/oTo10JWQBd
about 2 weeks ago