[Pmb (OP)]

I'm curious as to what the average Joe thinks when he hears the term spacetime curvture. What did think when you heard of it the first time. By this I mean what did the concept bring to mind when you first learned about it? If you've studied it for some time now then what do you think it means now as compared to when you first started learning it?

My impression is that many people believe that spacetime curvature refers to the curving of a worldline in spacetime caused by a gravitational field. Am I close? I, of course, know what it means. I just want to know if people have the right idea about it. It seems to me that when people think of spacetime curvature and the phrase gravity is a curvature in spacetime that they think that the gravitational field we all know and love and have grown up in and live with all of our lives are the same thing.

What do you think? And than you for your thoughts in advance.

[galaxysim]

from my experience on other forums....and my oft quoted phrase 'cant count or wont count ? '  im pretty sure the 90% and perhaps 95%+ of the populace suffer brain implosion the moment things go beyond their tangible experience


You have to have what i call the maths gene AND an ability to carry out thought experiments AND a good instinct for self checking your progress.

Most lay peoples knowledge comes from opinion, rather than an internal matchstick pyramid of knowledge that they have painstakingly built from the ground up....this is why 'does not compute' is a common theme. Its very easy to get confused if you don't have the guardrails of science based education.

The mindset required to 'get laid and paid' is of a very different architecture to that of the scientific method. Thus if your new to science it can take some time to wrap your head around what might be a relatively straight forward scientific concept...this is of course frustrating for all parties in the discussion....people are impatient and the human mind tends to over simplify in when facing complexity.

A long winded reply to your OP

I think very few peoples understanding of Spacetime Curvature goes beyond ye olde cannon ball and rubber mat
http://en.wikipedia.org/wiki/Spacetime [nofollow]

 Joe Average meets the train in a tunnel paradox....paradox wins every time.



@Pmb says your a physicist ? curious what field ? casual or pro

....Mine is AI and general science Astronomy to zoology

[Pmb (OP)]

A long winded reply to your OP

I think very few peoples understanding of Spacetime Curvature goes beyond ye olde cannon ball and rubber mat
http://en.wikipedia.org/wiki/Spacetime

That doesn’t tell me what they think it is though. For example; take a look at the uniform gravitational field inside a spherical cavity that was hollowed out from a spherical homogenous distribution of matter. The center of the cavity is offset from the center of the sphere.

http://home.comcast.net/~peter.m.brown/gr/grav_cavity.htm

Is the spacetime associated with the gravitational field inside the cavity curved? Hint: The field inside the cavity is uniform, i.e. the tidal force tensor is zero. If you don’t know what that tensor is then please see

http://home.comcast.net/~peter.m.brown/mech/tidal_force_tensor.htm

Is this leading up to affine connections?

Not really but thanks for asking. I’m not sure whether the connection coefficients are geometric objects or not.

I was surprised to read Edwin Taylor say of John wheeler non-use of tensors.

Yeah. I know that about Edwin. I can never talk to him about anything to do with tensors. I think that after a while he developed a phobia about them. The same thing happened to me with the multiplication table. Lol!

[yor_on]

The way matter moves seems to be the best answer there, but it also connects to what you define as a universe, and its dimensions. As for a space without gravity? Can you get both? Defining it as the way matter moves, and also draw 'boundaries', as a ball shaped 'universe'. What defines that 'ball', a 'flat space'? The universe we have seem to 'stretch out', but if we use the 'ball' as our referee, the first thing to question should be. What defines that 'ball'? mass-'energy'? Matter? Gravity? Depending on choice, as for example me expecting gravity being the metric defining a 'shape', one then have to define what this stretched out universe is defined by, gravity too? If that is so, what is a 'flat space'?

[Pmb (OP)]

You didn't answer my question. There are only three possible responses to my question

Is the spacetime corresponding to the gravitationa field inside the cavity curved?

(1) Yes
(2) No
(3) I don't know

[yor_on]

How about a fifth?
5. it depends on the distribution of matter, and also from 'where' you define it, as well as what scale you use

You make hard questions Pete. You yourself has pointed out that you can transform away gravity, by 'free falling'. That's why I haven't found any better approximation for it than a 'preferred direction'. But 'free falling' and a 'flat space' is still questions unanswered to me, wondering what defines a universe. If gravity defines a shape, and have a infinite reach, then it shouldn't matter what 'shape' we define a universe to, should it? And whatever is meant by a 'flat space' it still must contain that metric, as I think for now, to exist.

[yor_on]

Ahh sorry, I was still stuck on your first there.  The Meaning of "Spacetime Curvature"  . As for the later, I would assume the space to be 'flat' and so 'non curved', but still containing a gravitational metric. And no, I don't think a space need to be curved as long as we have matter defining gravity. But it seems that some define a 'flat space' as something not using the metric of gravity? And that one is weird to me.

[Pmb (OP)]

Ahh sorry, I was still stuck on your first there.  The Meaning of "Spacetime Curvature"  . As for the later, I would assume the space to be 'flat' and so 'non curved', but still containing a gravitational metric. And no, I don't think a space need to be curved as long as we have matter defining gravity. But it seems that some define a 'flat space' as something not using the metric of gravity? And that one is weird to me.

Do you understand that spacetime curvature is merely a fancy name for tidal force?

[Bill S]

Do you understand that spacetime curvature is merely a fancy name for tidal force?

No;  but I would like to!

[Pmb (OP)]

No;  but I would like to!

Okay. It will help me if I knew where you are with math, Newtonian mechanics, gravity, tensors etc. I.e. can you follow these two pages
http://home.comcast.net/~peter.m.brown/mech/tidal_force_tensor.htm
http://home.comcast.net/~peter.m.brown/gr/geodesic_deviation.htm

See if you can find the subject in Taylor and Wheeler's new version of Exploring Black Holes at http://exploringblackholes.com/

[Pmb (OP)]

I think very few peoples understanding of Spacetime Curvature goes beyond ye olde cannon ball and rubber mat
http://en.wikipedia.org/wiki/Spacetime

Strangely enough those diagrams are really embedding diagrams and weren't supposed to represent spacetime curvature unfortunately it didn't work out that way.

[yor_on]

Sure. everything defining a direction is 'gravity' Pete, and it's no 'force' either, as I get it. And all this about gravitomagnetic forces is just confusing to me, it splits gravity into two parts as I get it. One part of it being some 'component' making you anchored to earth (analogue to electricity) the other treating tidal forces (magnetic part), suggesting you can see it as some sort of electromagnetism. You can't have it as a force, as far as I see it's just a preferred direction. And we're all following geodesics. A force is what intrudes on a geodesic in this case, breaking it.
=

Who 'invented' gravitomagnetism btw? I just can't make me believe it was Einstein that created that slogan, someone clever did it, and it has caught on, but it don't fit Einsteins thoughts, to me that is.

[yor_on]

Ahh, think I found him?

http://en.wikipedia.org/wiki/Gravitoelectromagnetism

"The analogy and equations differing only by some small factors were first published in 1893, before general relativity, by Oliver Heaviside as a separate theory expanding Newton's law."

http://en.wikipedia.org/wiki/Oliver_Heaviside

On the other hand, this was before GR, so some must have reused it, banking into skulls using equations for electromagnetism, as presumed of a idea of all 'forces' coming from one origin, at some temperature for example (regime / symmetry breaks). If fits a Higg explanation, possibly? But I still don't see it fit Einsteins GR?

[Pmb (OP)]

Sure. everything defining a direction is 'gravity' Pete, and it's no 'force' either, as I get it.

Not according to Einstein. GR states gravity is an inertial force rather than a 4-force like the Lorentz force.

For more on inertial forces and how some physicists percieve them as being "real" please see the web page I created on this subject at
http://home.comcast.net/~peter.m.brown/gr/inertial_force.htm0

For example please see the quote on that page from Introducing Einstein's Relativity, by Ray D'Inverno, Oxord/Clarendon Press, (1992) page 122

Notice that all inertial forces have the mass as a constant of proportionality in them. The status of inertial forces is again a controversial one. One school of thought describes them as apparent or fictitious which arise in non-inertial frames of reference (and which can be eliminated mathematically by putting the terms back on the right hand side). We shall adopt the attitude that if you judge them by their effects then they are very real forces. [Author gives examples]

Other quotes are like that.

Here's what Einstein said about this point

From an article in the February 17, 1921 issue of Nature by Albert Einstein

Can gravitation and inertia be identical? This question leads directly to the General Theory of Relativity. Is it not possible for me to regard the earth as free from rotation, if I conceive of the centrifugal force, which acts on all bodies at rest relatively to the earth, as being a "real" gravitational field of gravitation, or part of such a field? If this idea can be carried out, then we shall have proved in very truth the identity of gravitation and inertia. For the same property which is regarded as inertia from the point of view of a system not taking part of the rotation can be interpreted as gravitation when considered with respect to a system that shares this rotation. According to Newton, this interpretation is impossible, because in Newton's theory there is no "real" field of the "Coriolis-field" type. But perhaps Newton's law of field could be replaced by another that fits in with the field which holds with respect to a "rotating" system of co-ordinates? My conviction of the identity of inertial and gravitational mass aroused within me the feeling of absolute confidence in the correctness of this interpretation.

[Pmb (OP)]

Sure. everything defining a direction is 'gravity' Pete, and it's no 'force' either, as I get it.

Everything? The electric field defines a direction. Are you saying that the electric field is a gravitational field?

Anyway, not according to Einstein (and me) it's not. GR states gravity is an inertial force rather than a 4-force like the Lorentz force.

For more on inertial forces and how some physicists percieve them as being "real" please see the web page I created on this subject at
http://home.comcast.net/~peter.m.brown/gr/inertial_force.htm

For example please see the quote on that page from Introducing Einstein's Relativity, by Ray D'Inverno, Oxord/Clarendon Press, (1992) page 122

Notice that all inertial forces have the mass as a constant of proportionality in them. The status of inertial forces is again a controversial one. One school of thought describes them as apparent or fictitious which arise in non-inertial frames of reference (and which can be eliminated mathematically by putting the terms back on the right hand side). We shall adopt the attitude that if you judge them by their effects then they are very real forces. [Author gives examples]

Other quotes are like that.

Here's what Einstein said about this point

From an article in the February 17, 1921 issue of Nature by Albert Einstein

Can gravitation and inertia be identical? This question leads directly to the General Theory of Relativity. Is it not possible for me to regard the earth as free from rotation, if I conceive of the centrifugal force, which acts on all bodies at rest relatively to the earth, as being a "real" gravitational field of gravitation, or part of such a field? If this idea can be carried out, then we shall have proved in very truth the identity of gravitation and inertia. For the same property which is regarded as inertia from the point of view of a system not taking part of the rotation can be interpreted as gravitation when considered with respect to a system that shares this rotation. According to Newton, this interpretation is impossible, because in Newton's theory there is no "real" field of the "Coriolis-field" type. But perhaps Newton's law of field could be replaced by another that fits in with the field which holds with respect to a "rotating" system of co-ordinates? My conviction of the identity of inertial and gravitational mass aroused within me the feeling of absolute confidence in the correctness of this interpretation.

[niebieskieucho]

I'm curious as to what the average Joe thinks when he hears the term spacetime curvture. What did think when you heard of it the first time. By this I mean what did the concept bring to mind when you first learned about it? If you've studied it for some time now then what do you think it means now as compared to when you first started learning it?

It's a double rubbish. Spacetime is a sick idea. It's just space that has nothing to do with time (of what BTW?), as time spontaneously does not exist. As to the second rubbish, i.e. alleged curvature of space, it's simply impossible. Space does not undergo deflection, is indestructible, does not expand, is of the same volume as it was before origin of matter.

My impression is that many people believe that spacetime curvature refers to the curving of a worldline in spacetime caused by a gravitational field. Am I close? I, of course, know what it means. I just want to know if people have the right idea about it. It seems to me that when people think of spacetime curvature and the phrase gravity is a curvature in spacetime that they think that the gravitational field we all know and love and have grown up in and live with all of our lives are the same thing.

What do you think? And than you for your thoughts in advance.

The only curvature of space I can accept is due to spherical shape of the (finite) universe. But this is its natural shape.

[Pmb (OP)]

It's a double rubbish. Spacetime is a sick idea. It's just space that has nothing to do with time (of what BTW?), as time spontaneously does not exist.

From these comments its clear that you don’t know what spacetime is. Please learn about these things before you make another attempt at commenting on them. I.e. please study what spacetime is. I created the following for this purpose
http://home.comcast.net/~peter.m.brown/sr/spacetime.htm

Whether spacetime is curved or not is not up for debate. It’s an observable fact. It’s a measurable phenomena. But until you learn what it really is as opposed to what you think it is (which you’ve proven that what you think it is is wrong) you won’t be able to understand that very simple fact. If you had chosen to first learn about the subject that you’re criticizing then you wouldn’t have made these mistakes. I showed you where to read about it online. Please do so before you make another attempt to argue that it’s wrong.

As to the second rubbish, i.e. alleged curvature of space, it's simply impossible. Space does not undergo deflection, is indestructible, does not expand, is of the same volume as it was before origin of matter.

These comments also tell me that you don’t know what space curvature is. You incorrectly assumed that it meant that space is deflected. It doesn’t. It has to do with the measured distance between various points in space. The amount of deflection of star light by the sun is a measure by how much space is altered by the sun’s gravitational field.

My impression is that many people believe that spacetime curvature refers to the curving of a worldline in spacetime caused by a gravitational field. Am I close?

No. You’re way off. A charged particle moving in flat spacetime in an electric field will have a worldline that curves. That in no way shape or form means that the spacetime is curved.

If the particle’s worldline is a geodesic (i.e. the 4-force on it is zero – only inertial forces are acting on it) and it curves then all that tells you is that you’re observing the motion of the particle from a non-inertial frame of reference. Spacetime curvature pertains to the divergence of two geodesics which start out parallel and deviate. See
http://home.comcast.net/~peter.m.brown/gr/geodesic_deviation.htm

The only curvature of space I can accept is due to spherical shape of the (finite) universe.

Then why not choose to learn about it and learn what it really means as opposed to what you think it means.

If you really want to learn what spacetime curvature is then read Exploring Black Holes at http://exploringblackholes.com/

Or read
http://home.comcast.net/~peter.m.brown/sr/sr.htm
http://home.comcast.net/~peter.m.brown/gr/gr.htm

I know it’s a lot but nobody said that learning about spacetime curvature could be easy to learn.

Unless you really don’t want to learn it?


I'm sorry if I come across as being rude to you. I don't mean to be. I simply get irritated when people claim that things are wrong when it's also clear that they've never learned what it is in the first place.

[yor_on]

"The electric field defines a direction. Are you saying that the electric field is a gravitational field?"

No, I was talking about what you discussed, 'gravity', but there are several descriptions to it. gluing a name to it, as gravitomagnetism, doesn't catch it for me though. I think I prefer it as a direction so far

[Pmb (OP)]

"The electric field defines a direction. Are you saying that the electric field is a gravitational field?"

No, I was talking about what you discussed, 'gravity', but there are several descriptions to it. gluing a name to it, as gravitomagnetism, doesn't catch it for me though. I think I prefer it as a direction so far

Gravitomagnetism refers to a specific gravitational effect. It's about a velocity dependant gravitational force just like the magnetic force is velocity dependant. The direction of the gravitational force depends on the direction of the velocity of the particle. So what direction are you talking about?

[yor_on]

Fictitious force is a very nice description of it Pete. As you can transform it away by a free fall. If I assume that all matter in the universe has a preferred direction (geodesic) in where no forces act on it, then I suppose this should be 'gravity'. And that should be a preferred direction to me, or 'SpaceTime curvature'. Even though uniform motion is a relative motion, we still can use fixed stars, CBR, etc to define a direction for it. But if I go strictly by what 'relative motion' state, that you can redefine any (uniform) motion by just changing a reference frame? Then I'm not sure how to describe the 'direction' of matter, because you need a 'motion' to have a direction. And that one is intuitively weird to me, and in some way more correct, although I can prove motion just by introducing more uniformly moving objects in a 'system' and so be able to define different speeds relative those objects. If I can find that, then motion should exist, as I think for now