Expansion of space vs stuff just moving away

[No-where-man]

Yes that is correct. Google "metric expansion" and/or see the link in my signature

EDIT: by the way, this whole business of "expanding space" vs "everything just gets farther apart" is a big bone of contentious discussion but basically it is most helpful to just consider metric expansion (things just get farther apart) because otherwise you start using metaphors about space "stretching" or "tearing" and you end up in la la land.

Than all the stories where it says that gravity affects space is also wrong?
If space is not tangible and if it's not physical, how does the black hole affect space (and time for that matter)?
Now, I'm a little confused.

 

[phinds]

Than all the stories where it says that gravity affects space is also wrong?
If space is not tangible and if it's not physical, how does the black hole affect space (and time for that matter)?
Now, I'm a little confused.

Your problem here is that you are thinking of space and time as separate things, but in GR in particular, they cannot be separated. Gravity affects spacetime. The extreme gravity of a black hole has an extreme affect of spacetime.

 

[No-where-man]

Your problem here is that you are thinking of space and time as separate things, but in GR in particular, they cannot be separated. Gravity affects spacetime. The extreme gravity of a black hole has an extreme affect of spacetime.

I wonder if enough extreme gravity can truly destroy space-time-i wonder if this is true?

But you also said that space itself is not anything tangible or physical, so what's the difference if you say it affects space-time, and it does not affect space alone?

 

[phinds]

I wonder if enough extreme gravity can truly destroy space-time-i wonder if this is true?

Well, "destroy" might not be the right description, but an infinite mass would likely cause some problems, but not to worry, there is not and never will be any such thing.

But you also said that space itself is not anything tangible or physical, so what's the difference if you say it affects space-time, and it does not affect space alone?

Space is a classical concept. In the context of what you are talking about, it cannot be considered "alone" because it ISN'T "alone", it is the spatial dimension part of what we call spacetime.

You can ask "if the laws of physics don't apply, then what do the laws of physics say about <put in any statement you like>?" and you won't get a meaningful answer.

 

[Drakkith]

I wonder if enough extreme gravity can truly destroy space-time-i wonder if this is true?

This cannot be true since gravity is the result of curved spacetime.

But you also said that space itself is not anything tangible or physical, so what's the difference if you say it affects space-time, and it does not affect space alone?

This really gets bogged down into a discussion over what certain words mean. You're best, most absolute guaranteed way of understanding spacetime as we know it is to study what General Relativity says.

 

[No-where-man]

This cannot be true since gravity is the result of curved spacetime.

I thought it's the opposite, that gravity affects spacetime, that the gravity is directly responsible for creating curves of spacetime?

This really gets bogged down into a discussion over what certain words mean. You're best, most absolute guaranteed way of understanding spacetime as we know it is to study what General Relativity says.

OK.

 

[No-where-man]

Well, "destroy" might not be the right description, but an infinite mass would likely cause some problems, but not to worry, there is not and never will be any such thing.

OK, but I truly hope it's 100% impossible than for gravity to destroy space-time.

Space is a classical concept. In the context of what you are talking about, it cannot be considered "alone" because it ISN'T "alone", it is the spatial dimension part of what we call spacetime.

OK, understood.

You can ask "if the laws of physics don't apply, then what do the laws of physics say about <put in any statement you like>?" and you won't get a meaningful answer.

OK.

 

[Mordred]

Drakkiths comment on learn what GR teaches, is a good solid point. Here is a statement from Einstein that applies.

"According to the general theory of relativity, the geometrical properties of space are not
independent, but they are determined by matter. Thus we can draw conclusions about the
geometrical structure of the universe only if we base our considerations on the state of the
matter as being something that is known."

keep in mind this line was written prior to the cosmological constant. Which is in essence a negative pressure influence, gravity being a positive pressure influence.

However the above statement is still true provided you also consider the cosmological constants added influence on the average densities of matter.

this isn't the best book to study GR and SR even though its written by Einstein, however it is a free for distribution book. As well as a good historic reference article. Much of the explanations in it are easily read so its a good starting point.

http://www.marxists.org/reference/archive/einstein/works/1910s/relative/relativity.pdf

 

[Drakkith]

I thought it's the opposite, that gravity affects spacetime, that the gravity is directly responsible for creating curves of spacetime?

Nope. Gravity is the result of spacetime being curved by the presence of energy (which includes the energy matter has) and stress. Hence the term stress-energy tensor, which is what is used to calculate the curvature of spacetime.

 

[No-where-man]

Nope. Gravity is the result of spacetime being curved by the presence of energy (which includes the energy matter has) and stress. Hence the term stress-energy tensor, which is what is used to calculate the curvature of spacetime.

Ok, big thanks for correcting me in my obviously completely false understanding of gravity and curved space-time, until now.

 

[No-where-man]

Drakkiths comment on learn what GR teaches, is a good solid point. Here is a statement from Einstein that applies.

"According to the general theory of relativity, the geometrical properties of space are not
independent, but they are determined by matter. Thus we can draw conclusions about the
geometrical structure of the universe only if we base our considerations on the state of the
matter as being something that is known."

keep in mind this line was written prior to the cosmological constant. Which is in essence a negative pressure influence, gravity being a positive pressure influence.

However the above statement is still true provided you also consider the cosmological constants added influence on the average densities of matter.

this isn't the best book to study GR and SR even though its written by Einstein, however it is a free for distribution book. As well as a good historic reference article. Much of the explanations in it are easily read so its a good starting point.

http://www.marxists.org/reference/archive/einstein/works/1910s/relative/relativity.pdf

Big thanks for this explanation and for this link, you guys are very helpful in just about every, possible way, I truly don't know what to say.