Bending space and space time - what is the difference?

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Discussion Overview

The discussion centers on the differences between the concepts of space and spacetime, particularly in the context of general relativity (GR) and how mass influences these dimensions. Participants explore the implications of mass on the curvature of space and spacetime, and the interconnectedness of time and space.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants propose that mass bends space, suggesting that this bending causes other masses to be attracted towards it.
  • Others argue that it is incorrect to say only space is bent; they emphasize that spacetime is the relevant concept in GR, which includes both space and time.
  • A later reply questions whether adding mass increases the force of attraction by bending space further, leading to a discussion about the role of time distortion in gravitational attraction.
  • Some participants note that while space can be curved, the time component is crucial for understanding gravitational effects, and neglecting it can lead to misunderstandings.
  • There are mentions of the relationship between relative motion, mass, and the distortion of both space and time, with references to different types of curvature.
  • One participant highlights that experiences are not solely based on electromagnetic waves, pointing out other sensory experiences that do not involve light.
  • Another participant clarifies that while many phenomena are electromagnetic in nature, the discussion should not overlook the distinct roles of different forces at various scales.

Areas of Agreement / Disagreement

Participants express differing views on whether it is appropriate to discuss bending space without considering time. While some agree on the interconnectedness of space and time, others maintain that the nuances of their relationship are not fully resolved, indicating ongoing disagreement.

Contextual Notes

Some statements rely on specific interpretations of curvature and the mathematical framework of GR, which may not be universally accepted. The discussion also reflects varying levels of understanding and assumptions about the nature of mass, space, and time.

Premanand
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Sorry... This question may be very basic. As a self taught, I understand that the mass will bend the space around it such that any other mass entering the bent space will immediately be pushed towards the center because of the bent space. Higher the mass, higher will be the bent (if that is the right word)... and since speed of light is constant, the 'experience' will also vary accordingly as all our nerves and all other biological activity happens by electromagnetic waves... Thus, time and space are interconnected... However, can I just say that space gets bent by presence of mass... Because somewhere I read that it is incorrect to say space gets bent because it is the space time that is bent... What is the difference? Because to me adding mass to bend the space is perfectly OK and time is just a side effect of it.
 
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Premanand said:
What is the difference?
Space time curvature has a very precise meaning and it is perfectly possible to have a curved space time with a flat space. GR is about curved space-time, not about curved space. Space may be curved as well, but you reqlly cannot neglect the time part.

Premanand said:
Because to me adding mass to bend the space is perfectly OK and time is just a side effect of it.
Then you would be wrong.
 
Orodruin said:
Space time curvature has a very precise meaning and it is perfectly possible to have a curved space time with a flat space. GR is about curved space-time, not about curved space. Space may be curved as well, but you reqlly cannot neglect the time part.Then you would be wrong.
Thank you... Could u answer one more question please? Does adding mass to the object bends the space? Is the bent space a reason for increase in force of attraction when mass is increased?
 
Premanand said:
Sorry... This question may be very basic. As a self taught, I understand that the mass will bend the space around it such that any other mass entering the bent space will immediately be pushed towards the center because of the bent space. Higher the mass, higher will be the bent (if that is the right word)... and since speed of light is constant, the 'experience' will also vary accordingly as all our nerves and all other biological activity happens by electromagnetic waves... Thus, time and space are interconnected... However, can I just say that space gets bent by presence of mass... Because somewhere I read that it is incorrect to say space gets bent because it is the space time that is bent... What is the difference? Because to me adding mass to bend the space is perfectly OK and time is just a side effect of it.
It is possible to imagine "bent space" without "bent time" (note that these expressions refer to the mathematics). If you have the concept that "bent time" is a necessary effect of "bent space" then the result is the same.
 
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harrylin said:
It is possible to imagine "bent space" without "bent time" (note that these expressions refer to the mathematics). If you have the concept that "bent time" is a necessary effect of "bent space" then the result is the same.
Thank you... So on conceptual level... I can bend the space further by adding more mass? ... I mean adding mass increases 'the force of attraction' by bending the space 'more' ?
 
Premanand said:
I mean adding mass increases 'the force of attraction' by bending the space 'more' ?
No, the effect of "attraction" is mostly related to the time distortion (gravitational time dilation). The spatial curvature only causes minor effects. See link in my previous post.
 
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As you posted, time and space ARE interconnected...here are a few insights.

You can picture the paths of a particle as curves in special relativity as you would curves on a flat graph paper. SR involves relative motion and relative time,and one type of curvature but not gravity. When gravitational curvature is involved, as in general relativity the graph paper itself on which the curved paths are drawn is itself curved. That's not obvious and is why it took an 'Einstein' to figure it out.

In general, when relative motion and mass is involved, both space and time are distorted, that is, 'bent' or 'curved'. And there are lots of types of curvature!
 
Premanand said:
Higher the mass, higher will be the bent (if that is the right word)... and since speed of light is constant, the 'experience' will also vary accordingly as all our nerves and all other biological activity happens by electromagnetic waves... Thus, time and space are interconnected..

yes space and time ARE interconnected. But don't think 'experience' is all about electromagnetic waves, or light. If you bump your head on a door in the dark, there are no electromagnetic waves, but you'll not like that experience, right? And what about loud firecrackers...those are SOUND waves [air molecules hitting your eardrum] not electromagnetic waves and you might not like those either; but music, now those are nicer sound waves. And don't forget about taste and smell either..not electromagnetic in nature.

As already noted 'curvature' of space and time often goes together. One way I have found to think about 'distortion' of time is that near big masses, lots of gravity, time is 'distorted' a lot. Time runs slower in higher gravity [potential] when viewed from a distance. Another way to think about curvature or distortion is to remember there are three dimensions of space [up/down,left/right, in/out, or x,y,z]; by analogy just think of time as a fourth component and you have 'spacetime'...and all four components can be 'curved'.
 
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Finny said:
And don't forget about taste and smell either..not electromagnetic in nature.
(My emphasis)
Careful here, while not electromagnetic waves, all of the phenomena which are mentioned here are mainly electromagnetic in nature, just like all forces we experience on the molecular level. If not for the electromagnetic force, air molecules hitting an eardrum would pass right through it. From when you go away from internuclear forces to when you arrive at scales at which gravity plays a role, all forces are electromagnetic in nature.
 
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