The discussion centers on the distinction between the expansion of space and the relative motion of galaxies, specifically addressing how redshift measurements indicate that galaxies are receding from us at velocities exceeding the speed of light, such as 3c. Participants assert that the metric expansion of space, as described in the ΛCDM Big Bang model, provides a more comprehensive explanation for observed phenomena, including the cosmic microwave background (CMB) and Hubble's Law. The conversation emphasizes that redshift does not solely indicate motion through space but rather reflects the dynamic nature of space itself. The consensus is that the expansion of space is a fundamental aspect of our universe's structure.
PREREQUISITESAstronomers, astrophysicists, cosmologists, and anyone interested in understanding the dynamics of the universe and the nature of cosmic expansion.
phinds said: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.
No-where-man said: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 said: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 said: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?
No-where-man said: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?
Drakkith said:This cannot be true since gravity is the result of curved 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.
phinds said: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.
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.
No-where-man said:I thought it's the opposite, that gravity affects spacetime, that the gravity is directly responsible for creating curves of spacetime?
Drakkith said: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.
Mordred said: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