Can Space Curve Faster Than Light?

[ktx49]

Hi,

We all know everyone's favorite "exception" to the speed of light limit...that space itself can expand faster than C.

My question is whether space can curve faster than C? I understand that gravity travels at the speed of light...but can space itself move faster than this limit in other ways besides expansion?

Thanks

 

[phinds]

Space does NOT "move faster than light". Things get farther apart at a recession rate that is faster than light but that's not the same thing at all.

Since the curvature of space is a function of gravity and gravitational changes propagate at c, the curvature will not happen faster than c.

 

[ktx49]

thanks for response.
i know my question was poorly formulated...but am I incorrect to say that space expanded faster than C in the early stages of inflation after the big bang?

could the curvature of space ever create an effect similar to that of expansion; in which things moved apart at a speed faster than light?

 

[A.T.]

could the curvature of space ever create an effect similar to that of expansion; in which things moved apart at a speed faster than light?

The distance between the things can increase faster than speed of light due to metric expansion. But that is different from moving away faster than light. For example a light signal sent by one thing can still reach the other thing, even if the distance between them increases faster than speed of light due to metric expansion.

 

[phinds]

thanks for response.
i know my question was poorly formulated...but am I incorrect to say that space expanded faster than C in the early stages of inflation after the big bang?

No. Again, things moved farther apart at a rate bigger than c (staggeringly bigger in fact) but again, that is NOT "space expanding". "Space" is just a framework in which things exist. If a person went from 2' tall to 5' all in a matter of several years you would not say that "length itself expanded" you'd just say the kid got taller.

could the curvature of space ever create an effect similar to that of expansion; in which things moved apart at a speed faster than light?

No, the "curvature of space" is an emergent property based on the strength of gravity. Your statement would be equivalent to saying that rulers could make things get taller.

 

[harrylin]

[quote of ktx49: "am I incorrect to say that space expanded [..] .."]

No.[..] "Space" is just a framework in which things exist. If a person went from 2' tall to 5' all in a matter of several years you would not say that "length itself expanded" you'd just say the kid got taller.

I suspect that mainstream thinking is a bit more subtle, see for example: https://en.wikipedia.org/wiki/Metric_expansion_of_space

 

[A.T.]

No. Again, things moved farther apart at a rate bigger than c (staggeringly bigger in fact) but again, that is NOT "space expanding".

https://en.wikipedia.org/wiki/Inflation_(cosmology)

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation is the exponential expansion of space in the early universe.

 

[pervect]

thanks for response.
i know my question was poorly formulated...but am I incorrect to say that space expanded faster than C in the early stages of inflation after the big bang?I

This isn't incorrect, per se, but it is often misinterpreted. IF you want some reading on the topic of expanding space, I'd suggest http://arxiv.org/abs/0707.0380 and http://arxiv.org/abs/astro-ph/0310808

I'm not particularly fond of the idea of expanding space, but it's taught a lot, and if you want to do it (mostly) right, you might try the first paper, i.e. http://arxiv.org/abs/0707.0380, as that's the goal of the paper.

Abstract:
While it remains the staple of virtually all cosmological teaching, the concept of expanding
space in explaining the increasing separation of galaxies has recently come under fire as a dangerous
idea whose application leads to the development of confusion and the establishment of misconceptions.
In this paper, we develop a notion of expanding space that is completely valid as a framework for the
description of the evolution of the universe and whose application allows an intuitive understanding
of the influence of universal expansion. We also demonstrate how arguments against the concept in
general have failed thus far, as they imbue expanding space with physical properties not consistent
with the expectations of general relativity.

Personally, I"m not a fan of expanding space, an so I might not be the best to answer questions on it - but you can read the papers of people who are fans of the idea and see what they have to say about applying it correctly.

My own views are that metrics are a result of a choice of coordinate system. In most circumstances you want to use cosmological coordinates, which do expand. But if you happen to be interested in a local area, you might well want to use Fermi Normal coordinates, in which space doesn't expand. Furthermore, expanding space is taught and perceived in too many cases as if it were something physical, rather than something that ultimately depends on one' choice of coordinates, which is my biggest complaint.

 

[PAllen]

One point about expanding space is that it is dependent on the foliation chosen. While this doesn't mean it has no value, it is worth noting the completely flat Minkowski space can be foliated (Milne foliation) as to show expanding space exactly analogous to Friedman universes.. Yet, it is obviously completely static. To me, this means that what really distinguishes plausible cosmological models from static, flat, spacetime is something other than expanding space.