Where did the freidman equation come from?

[keepit]

where did the freidman equation come from?

 

[bapowell]

It comes from the Einstein Equations under the assumptions of spatial homogeneity and isotropy with a perfect fluid source.

 

[keepit]

Thanks Bapowell. Would the Freidman equation become far wrong if Einsteins equations were ever significantly changed?

 

[yenchin]

Thanks Bapowell. Would the Freidman equation become far wrong if Einsteins equations were ever significantly changed?

Depending on how you change the Einstein Equations, of course the Friedmann equation [note the spelling] would look different. People have been looking at many theories of gravity that modifies Einstein's equations in different ways, for example, you should google f(R) gravity and see how the Friedmann equation changes in that model.
Why do you ask?

 

[Chalnoth]

Thanks Bapowell. Would the Freidman equation become far wrong if Einsteins equations were ever significantly changed?

Doubtful. The first Friedmann equation can also be derived from Newtonian gravity, provided you are working with normal matter and, potentially, a cosmological constant. To get a significant change you need to vary gravity at large distance scales, which is generally considered to be a bit unlikely.

 

[keepit]

Yenchin,
Thanks for your reply. sorry about the spelling.
I was just trying to better understand the validity of the relationship between the flatness of space and the presence of matter and the expansion of space. Would the extra space go back where it came from if more matter was interjected where space has expanded?

 

[Polyrhythmic]

You want to know what would happen if for some reason matter appeared out of nowhere? It's hard to say, since the driving force of cosmic expansion, dark energy, is not understood so far.

 

[Chalnoth]

You want to know what would happen if for some reason matter appeared out of nowhere? It's hard to say, since the driving force of cosmic expansion, dark energy, is not understood so far.

Dark energy was utterly negligible in the early universe, when matter was produced. To understand the production of matter in the early universe, we have to understand inflation, specifically how it ended.