Proof of Universe Expansion

[bchui]

Where can we find the prove of universe expansion from the equations of General Relativity?

 

[pervect]

Where can we find the prove of universe expansion from the equations of General Relativity?

First you need to make some assumptions - that the universe is homogeneous and isotropic.

Then the solution of Einstein's equations is a FRW metric, see for instance http://en.wikipedia.org/wiki/Friedmann-Lemaître-Robertson-Walker_metric

The expansion or contraction is governed by Friedman's equations

http://en.wikipedia.org/wiki/Friedmann_equations


If you add a cosmological constant to these equations, there is a static solution (the Einstein static universe), but it is unstable, and also requires some very special parameter values.

So you can't quite "prove" that the universe must be expanding or contracting (as there is the static Einstein solution), but it would require a lot of coincidences to have this happen if GR is correct.

Of course, observation strongly suggests that the universe is expanding.

 

[Entropia]

The proof of universe expansion can be found in the equations of General Relativity through observations of the cosmic microwave background radiation (CMB) and the redshift of distant galaxies.

The CMB is a faint glow of radiation that permeates the entire universe and is believed to be leftover from the Big Bang. By studying the characteristics of the CMB, such as its temperature and distribution, scientists have been able to confirm the expansion of the universe.

Additionally, the redshift of distant galaxies is another key piece of evidence for universe expansion. This phenomenon occurs when light from an object is stretched as it travels through expanding space, causing it to appear more redshifted. By measuring the redshift of distant galaxies, scientists have been able to calculate the rate of expansion of the universe.

Furthermore, the equations of General Relativity, specifically the Friedmann equations, provide a mathematical framework for understanding the expansion of the universe. These equations describe the evolution of the universe over time, including its expansion.

In summary, the proof of universe expansion can be found in the observations of the CMB and the redshift of distant galaxies, as well as in the equations of General Relativity. Together, these pieces of evidence provide strong support for the concept of an expanding universe.