Einstein's gravity versus Big Bang

[bluescience]

So, in einstein's theory, gravity is simply a geometric distortion between dimension. So if it so not a force, then howcome there are still theories about the force expanding the universe vs the force of gravity pulling it back one day?

 

Do these theories just ignore relativity?

[ajb]

All modern cosmologies will be based on general relativity or something every close to it, such as an F[R]-gravity.

 

It may just be a minor language issue here rather than anything deep. Do you have specific examples in mind here?

[bluescience]

All modern cosmologies will be based on general relativity or something every close to it, such as an F[R]-gravity.

 

It may just be a minor language issue here rather than anything deep. Do you have specific examples in mind here?

Yeah, i am reading a couple books and i believe the one called,"a really short history of nearly everything" is the one that confused me. It talks about GR and SR, but then it also talks about how the Big Bang expanded with just the right amount of gravitational force so that the universe wouldn't collapse in a short amount of time or continually expand faster than it does now, making matter so spread apart that interactions would be very rare and limited. Bill Bryson(the author) also states that Maybe our universe expanded with the slightest extra gravitational force above the perfect needed amount, so eventually that grav force will take over and the universe will come collapsing down.

 

 

What confuses me is: Can gravity still be treated as a 'force' even after Einstein's theory or relativity?

Edited April 20, 2016 by bluescience

[ajb]

What confuses me is: Can gravity still be treated as a 'force' even after Einstein's theory or relativity?

The short answer is that you can treat gravity as a force.

 

The slightly more technical answer is that gravity is a pseudo-force that really comes from the impossibility of finding inertial frames of reference.

 

I know you are just starting out so I do not want to confuse you with technical stuff. But still, have a look at pseudo-forces.

[Mordred]

More complexity though I wouldn't worry too much about this aspect in your studies yet.

 

How the Universe expands or contracts is definable in GR by the Einstein field equations. Of which the FLRW metric is a simplified variation. (Not that it is less accurate)

 

Expansion requires two relations potential energy (gravity) and kinetic energy. To put loosely.

 

In your other thread Mathius Blau link I provided covers these details in the later chapters roughly page 850 if I recall correctly

Edited April 21, 2016 by Mordred