How is the big bang related to the general theory of relativity?

[JJHK]

hi guys, I've read a few articles that say that einstein's general relativity paved the way for the big bang theory. Can anyone explain how they are connected?

 

[balaonspace]

galaxies are massive bodies whose motions are governed by general relativity. there is sufficient evidence to point that galaxies are receding from each other but gravity is an attractive force. if we solve the GR equations backwards in time then space will contract and galaxies/matter will converge to a point from which they expanded. that singularity in field equations is coined big bang.

 

[GeorgeDishman]

hi guys, I've read a few articles that say that einstein's general relativity paved the way for the big bang theory. Can anyone explain how they are connected?

The basic maths that describes the evolution of the universe as a whole are the Friedmann Equations:

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

Friedmann derived them in 1922 as a solution to Einstein's equations of General Relativity.

 

[Fredrik]

GR is built up around an equation (Einstein's equation) that describes the relationship between the properties of spacetime itself, and the properties of the fields and particles that "live" in spacetime. Astronomical observations tell us that on very large scales (larger than clusters of galaxies), matter is distributed evenly across the universe. On those scales, space is both homogeneous ("looks the same at every location") and isotropic ("looks the same in every direction"). So it's natural to look for solutions of Einstein's equations that describe spacetimes that are homogeneous and isotropic. It turns out that all of those solutions have the property that's now called "the big bang": The distance in space between any two curves in spacetime that describe the motion of massive particles in free fall, goes to zero as the time coordinate goes to zero, if we use the coordinate system in which the matter distribution is homogeneous and isotropic. (In that coordinate system, the time coordinate t is only defined for t>0). So all the solutions that approximately describe the large-scale behavior of the universe are telling us that matter was closer together in the past.

Note that the big bang isn't an event in spacetime. (There's no event in spacetime with time coordinate 0). The big bang is the property of spacetime that I described above. The original big bang theory is the claim that the large-scale behavior of matter in our universe is approximately described by one of those solutions. Since then, other theories have been developed, theories in which some entirely different thing is called "the big bang". Unfortunately, I don't know those theories well enough to explain them.

 

[sardar]

The big bang theory and the general theory of relativity are closely related in the sense that they both attempt to explain the origins and behavior of the universe. The big bang theory proposes that the universe began as a singularity, an infinitely small and dense point, and has been expanding ever since. On the other hand, the general theory of relativity, developed by Albert Einstein, describes how gravity works and how it affects the fabric of space and time.

The connection between these two theories lies in the fact that the big bang theory is based on the principles of general relativity. In fact, the equations of general relativity were used by scientists like Alexander Friedmann and Georges Lemaître to develop the big bang theory. These equations describe the expansion of the universe and how it has changed over time.

Furthermore, the big bang theory also supports one of the key predictions of general relativity - the theory of cosmic inflation. According to this theory, the universe underwent a rapid period of expansion in its early stages, which is supported by observations of the cosmic microwave background radiation. This expansion is also consistent with the predictions of general relativity.

In summary, the big bang theory and the general theory of relativity are closely connected as the former is based on the principles of the latter. Both theories have greatly contributed to our understanding of the universe and continue to be tested and refined through ongoing research and observations.