Can Space Appear Curved Due to Forces Similar to Magnetism?

[only_theory]

I've thought about this one a few times in the past and can't wrap my head around it, how can space or rather nothing actually curve to cause the effect of gravity?

Is it possible that it just looks like space curves and it's actually caused by something similar to magnetism?

Think about it, if something like magnetism worked similar to the effect of gravity, would it look any different to space curving? I am sure they would look the same but one is reality and one is theory!

Interesting thought to consider, note I am not suggesting anything is wrong with current theory etc I am just curious, thanks.

 

[A.T.]

I've thought about this one a few times in the past and can't wrap my head around it, how can space or rather nothing actually curve to cause the effect of gravity?

Curved space-time is just a mathematical model used to quantify the observed effects of gravitation. Humans invented it just like numbers and forces to describe what they observe.

 

[Dmitry67]

Curved space-time is just a mathematical model

As well as flat spacetime...

 

[Dale]

I think the premise is a little off. Empty spacetime does not curve. Spacetime is only curved in the presence of some stress-energy.

 

[Dmitry67]

DaleSpam, what's about gravitational waves?

 

[robphy]

"EFE in empty space"
https://www.physicsforums.com/showthread.php?t=199485

 

[dx]

Is it possible that it just looks like space curves and it's actually caused by something similar to magnetism?

Space never looks curved, no matter what. Our brains will always interpret anything that we see in a flat euclidean space framework.

 

[Dale]

DaleSpam, what's about gravitational waves?

"EFE in empty space"
https://www.physicsforums.com/showthread.php?t=199485

Yeah, but the Schwarzschild solution requires some energy at the center and gravitational waves require some quadrupole (whatever that means) mass. Similarly with other vacuum solutions. So unless I am missing some subtelty here spacetime still doesn't curve except in the presence of some stress-energy.

 

[robphy]

Given a spacetime (M,g),
one can excise portions of it and end up with a spacetime (M',g').Here are discussions of this idea [in the context of causal structure and singularities]:

http://books.google.com/books?id=k_...fferential+topology&source=gbs_search_s&cad=0
"The Space-time M is Minkowski space with one point removed. "

http://books.google.com/books?id=Wf...X&oi=book_result&ct=result&resnum=1#PPA130,M1

http://books.google.com/books?id=hs...vbz0Bw&sa=X&oi=book_result&ct=result&resnum=6
"..but such points can be excised from the manifold, leaving a spacetime... "

So, if there is a source somewhere... and one cuts out a portion of the curved but matter-free [i.e. zero-ricci but nonzero weyl] section. That section, together with its metric, is itself a curved vacuum spacetime.

 

[samalkhaiat]

Like Maxwell's, Einstein's equations have non-trivial solutions (waves) in the absence of matter! Indeed, Einstein's equations can be written in the equivalent (Maxwell-Like) form

$$(-g)[ T^{ab} + t^{ab}] = \partial_{c}h^{abc}$$

where t is the energy-momentum pseudotensor of the gravitational field, and $h^{abc} = -h^{acb}$ is the spin pseudotensor. The vacuum solutions (i.e., when T = 0)of this equation describe the so-called gravitational waves.

regards

sam

 

[Dale]

Given a spacetime (M,g),
one can excise portions of it and end up with a spacetime (M',g').
...
So, if there is a source somewhere... and one cuts out a portion of the curved but matter-free [i.e. zero-ricci but nonzero weyl] section. That section, together with its metric, is itself a curved vacuum spacetime.

Is there any reason to believe that the resulting boundary conditions would represent any "massless" physical situation? In other words, is there any reason to believe that you could physically have a Schwarzschild spacetime without the presence of a mass?

 

[StatusX]

Einstein's equation in vacuum is $R_{\mu \nu} = R^\rho_{\mu \rho \nu} = 0$, while the condition for zero curvature is $R^\mu_{\nu \rho \sigma} = 0$, which is strictly stronger, so it's possible for there to be curvature in a vacuum. Whether there's matter far away does not pertain to the original question, but in principle it is possible to have curvature in an empty ($R_{\mu \nu} = 0$ everywhere) universe. Whether such a universe is physically reasonable depends on what you mean: in a certain sense, any universe without matter is unphysical.

 

[robphy]

Is there any reason to believe that the resulting boundary conditions would represent any "massless" physical situation? In other words, is there any reason to believe that you could physically have a Schwarzschild spacetime without the presence of a mass?

I'm not qualified to fully address that question.
However, one thing I learned in this line of thinking is
that such a question relies on formulating mathematical statements
that try to "capture the physics", then prove theorems based on what was formulated.

This might be worth browsing over to get a sense of this line of thinking,
http://philsci-archive.pitt.edu/archive/00004506/01/PhysReas.pdf ,
which quotes a paper by Geroch [which I can't find online]

"The space-times obtained by cutting and patching are not normally
considered as serious models of our universe. However, the
mere existence of a space-time having certain global features suggests
that there are many models--some perhaps quite reasonable physically--with similar properties."

 

[only_theory]

Curved space-time is just a mathematical model used to quantify the observed effects of gravitation. Humans invented it just like numbers and forces to describe what they observe.

Ah i see, so If space itself doesn't curve what does or just gives the appearance of it?

 

[Niles]

Ah i see, so If space itself doesn't curve what does or just gives the appearance of it?

The way I have understood it (someone please correct me if I am wrong), space-time does curve, but what we are "seeing" is just the projection of the curved space-time onto a 3D space.

 

[A.T.]

Ah i see, so If space itself doesn't curve what does or just gives the appearance of it?

The way I have understood it (someone please correct me if I am wrong), space-time does curve, but what we are "seeing" is just the projection of the curved space-time onto a 3D space.

If you assume a flat space-time around a mass like Newton did, then the path of a falling object in space-time (its worldline) is curved. So the object is accelerated (by Newtons force of gravity). But you could just as well assume (like GR does) that space-time is curved in such a way, that the worldline of the free faller is straight. So it is not accelerated anymore by any force.

 

[Dale]

I'm not qualified to fully address that question.

That's OK, I am probably not qualified to fully understand the answer anyway

 

[only_theory]

When talking about space what are most peoples definitions of it? To me space means just an area of nothing that can contain stuff, if this is correct how can nothing curve?

On the other hand if you're to say that something occupying space causes gravity that would make more sense to me.

 

[A.T.]

how can nothing curve?

How can nothing be flat?

 

[Naty1]

When talking about space what are most peoples definitions of it? To me space means just an area of nothing that can contain stuff, if this is correct how can nothing curve?

Some even perhaps many here will answer that space is just a mathematical model... I say it IS something...it just doesn't seem "empty" to me...you can use Penrose twister theory, geodesics, quantum spinfoam and/or branes as representations...all are related views...whether any of those ARE "something" is an open issue.

Space seems like one form of a once unified entity that spawned the universe...mass,time,energy,etc are other vestiges of that very high energy and unstable but unified initial condition...

On the other hand if you're to say that something occupying space causes gravity that would make more sense to me.

Whatever space(time) really might be, mass,energy and pressure cause our mathematical models of it to deform...to curve...keep in mind these entities curve time as well...Einstein viewed "empty" spacetime, meaning spacetime without these three entities, as flat..no curvature...

I don't know what "occupying space" means...mass would "occupy" space in laymens terms, likely pressure and energy would not...but Nobody knows precisely how mass relates to space since nobody knows precisely what either is!

 

[only_theory]

How can nothing be flat?

Exactly, so nothing is just that, nothing, so what i want to know is what actually is causing gravity and the appearance of curving space time, I am talking about reality here, not mathematical models and such stuff, sure that's great to make predictions etc but its not how i or most people think like.

I don't know what "occupying space" means...mass would "occupy" space in laymens terms, likely pressure and energy would not...but Nobody knows precisely how mass relates to space since nobody knows precisely what either is!

I mean the stuff in the vacuum, energy fluctuations, virtual particles etc, perhaps you could call it the fabric?

 

[jtbell]

im talking about reality here, not mathematical models and such stuff,

How would we recognize "reality" if we found it?

 

[Dale]

I don't think the concept of curved spacetime is that complicated (although the math is). When you are talking about physics then spacetime is the geometrical relationship between physical events. When we say that the spacetime between some events is curved that simply means things like two "straight" lines can intersect in more than one point and the sum of the angles of a triangle is not 180º.

 

[only_theory]

The concept isn't that hard, what I am getting at is how if the definition of space is an empty area that stuff can occupy, how does this empty area curve in the presence of mass exactly? or is there something unseen in space causing the effect of curved space?

 

[Dale]

if the definition of space is an empty area that stuff can occupy,

I just told you that is not the definition of spacetime. At least it would not be the Machian definition that most physicists would use.

how does this empty area curve in the presence of mass exactly? or is there something unseen in space causing the effect of curved space?

How does one object know the equal and opposite force to apply to another? How does the electron get its charge? Fundamental physics principles are always descriptive rather than explanatory.

 

[only_theory]

I just told you that is not the definition of spacetime. At least it would not be the Machian definition that most physicists would use.

Oh right, so what's your definition of empty space then? I am not talking about models here, what is curving in reality exactly?

 

[StatusX]

An equally good question is "how can empty space be flat?". That is, how is it that in a region particles have never been before, particles that enter it "know" to travel in straight lines. More to the point, how do they know what "straight lines" are? If you think this is trivial, note that we just use inertial coordinates for convenience; if we had instead chosen to describe this flat region of space with rotating coordinates, the particles would have to know how to curve appropriately.

The point is, physics doesn't attempt to answer questions about what things really are, just what they do. As we uncover more relations, we seem to be describing things as they really are (eg, heat is molecular motion), but really we're just grouping unknowns together. Perhaps we will uncover relations between space and other physical things (eg, matter) in the future, but for now space is a primitive element.

 

[jnorman]

empty space is not "nothing". and the analogy to magnetism is quite appropriate. space comprises overlying fields, and it is the gravitational field which is curved. sadly, we do not understand what a field is, and we do not understand how a magnet works any more than we understand how a gravitational field works. even those entities which we call particles are not really things - they are the manifestations of fields.

keep in mind that while in the early 20th century, it was accepted that there was no longer a need to explain things in terms of an underlying "ether", einstein later, during development of GR, reinstated the concept of an ether as part of the foundation of GR.
http://www.mountainman.com.au/aether_0.html

 

[Dale]

Oh right, so what's your definition of empty space then?

See post 23 above.

Im not talking about models here, what is curving in reality exactly?

I don't know what you mean by "in reality". I am talking about the geometry of physical objects and events.

When I make a geometrical statement about something physical (eg. "the table leg is perpendicular to the table top") I believe that is a physical statement and not purely a mathematical model. Do you agree or would you consider that to be "just a mathematical model"?

 

[Anticitizen]

Exactly, so nothing is just that, nothing

Well, there's obviously something there, as there is some mechanism by which information is passed in the space between events. Curvature's what we're calling it.

 

[Feullieton]

I think the premise is a little off. Empty spacetime does not curve. Spacetime is only curved in the presence of some stress-energy.

_______

Exactly. I think I should note here that actually there is no such thing as empty space. I found my statement on observed cosmic microwave background radiation (CMBR) and continuous particle - antiparticle birth and annihilation throughout all observable universe. If we are to speak of empty space and nothingness or universe beyond observation we are obligated to recognize our action as intrusion into realm of metaphysics.

Acordingly we can develop further understanding of general ralativity and spacetime curvature based on CMBR. I believe we can achieve quite reasonable discription based on that universe has matter/energy all throughout it. It's just that for human point of view (which is traditionan euclidian space) matter/energy is concentrated more in one areas than others - that being planets, stars and black holes opposed to what we call vacuum. As for the spacetime point of view all universe has equally distributed matter/energy all throughout it. Therefore spacetime is not curved in itself. However it appears to be curved for us exactly because we doesn't share the same point of view. Additionally CMBR allows us to bypass earlier problem of explaining presence of gravity in empty space.

Let's conclude: More matter/energy means more spacetime.

(This is why light travels slower in densier and lower energy - temperature close to zero kelvin, materials. It just needs to cover more spacetime.)

Even furthermore we can explain gravitational phenomena using same developments in quantum mechanics. I refer to particle potentionality to be anywhere in space, and that means anywhere with only restriction being speed of light which sets horizon of potentiality. So as for massive objects which has way more spacetime, according to my improvised underlined theorem above, statistically particle has much greater potential to end up in or closer to massive object in space than further away from it. If particle is continuously subjected to such potentiality over time it ends up being pulled closer to object.

This is rather rough outline of my poor understanding of subject, so any discussion is appreciated.