Is Gravity Really a Fundamental Force?

[Searching]

I am an engineer with a Learning Channel level of knowledge of physics. I can't get past the idea that gravity is not a fundamental force. Can someone help me?

Hear is my problem:
If gravity is truly a fundamental force, why can we not find the particle associated with it? Why is so much weaker than the other forces? Should we really need 11 dimensions connect it to the others?

It makes logical sense to me that gravity is merely an effect. Perhaps space-time is made up of these "string" or similar particles that have properties of matter and energy (dark matter/dark energy), but are too small to be detected. We observe dark matter (by its effects) clustered around black holes at the center of galaxies. Perhaps is only more dense do to the black hole and is actually everywhere and makes up the fabric or space.

Otherwise, are we saying that space-time is made of nothing? It seems logical that there may be no such thing as empty space.

Can someone help me understand in a way that I can comprehend why we are some certain gravity is a fundamental force?

Sorry in advance for the simplicity, but play that cards we have.

 

[pallidin]

Welcome to PF and do enjoy it !

Gravity is, apparently, difficult to nail-down. We can readily observe it's effects but seem hard-pressed to come-up with some type of accepted theory as to "cause"

Perhaps in time we will understand.

 

[guillefix]

But doesn't general relativity says that gravity is not a force but just a deformation of sapce-time caused by energy-mass?

 

[WannabeNewton]

Gravity is weak on the small scale because elementary particles have small masses as relative to elementary charge. If you want to define gravity rigorously you have pick what framework of gravity you wish to look at. Newtonian mechanics classifies gravity as a force that attracts objects based on potentials but in GR gravity not a force but rather the effect of falling in arbitrarily curved spacetimes.

 

[pallidin]

But doesn't general relativity says that gravity is not a force but just a deformation of sapce-time caused by energy-mass?

That's the problem. We do NOT understand the cause of "mass"

 

[Polyrhythmic]

That's the problem. We do NOT understand the cause of "mass"

What do you mean by the "cause" of mass? Mass is, just like charge, a fundamental property of matter.

I also don't see a reason why one shouldn't call gravity a force. The "fact" that gravitational effects can be traced back to a curvature in spacetime doesn't change what we actually experience: particles being accelerated in the presence of other masses. If this is not the mechanism of a force, I don't know what a force is.

 

[Polyrhythmic]

I am an engineer with a Learning Channel level of knowledge of physics. I can't get past the idea that gravity is not a fundamental force. Can someone help me?

Hear is my problem:
If gravity is truly a fundamental force, why can we not find the particle associated with it? Why is so much weaker than the other forces? Should we really need 11 dimensions connect it to the others?

It makes logical sense to me that gravity is merely an effect. Perhaps space-time is made up of these "string" or similar particles that have properties of matter and energy (dark matter/dark energy), but are too small to be detected. We observe dark matter (by its effects) clustered around black holes at the center of galaxies. Perhaps is only more dense do to the black hole and is actually everywhere and makes up the fabric or space.

Otherwise, are we saying that space-time is made of nothing? It seems logical that there may be no such thing as empty space.

Can someone help me understand in a way that I can comprehend why we are some certain gravity is a fundamental force?

Sorry in advance for the simplicity, but play that cards we have.

Since virtual particles mediating forces are just mathematical constructs and nothing more, I don't see why the presence of such a gauge boson would be a criteria for the existence of a force.

You mention the possibility that it is just an effect. Isn't anything just an effect of something? For example lectromagnetic interaction being the effect of particles having charge?

 

[MegaDeth]

What do you mean by the "cause" of mass? Mass is, just like charge, a fundamental property of matter.

I also don't see a reason why one shouldn't call gravity a force. The "fact" that gravitational effects can be traced back to a curvature in spacetime doesn't change what we actually experience: particles being accelerated in the presence of other masses. If this is not the mechanism of a force, I don't know what a force is.

I agree, to me, it's just an effect of the mass of objects in space. Big objects anyway.

 

[WannabeNewton]

What do you mean by the "cause" of mass? Mass is, just like charge, a fundamental property of matter.

I also don't see a reason why one shouldn't call gravity a force. The "fact" that gravitational effects can be traced back to a curvature in spacetime doesn't change what we actually experience: particles being accelerated in the presence of other masses. If this is not the mechanism of a force, I don't know what a force is.

GR states that there is no acceleration due to any "Force" when a particle in free fall enters the presence of a mass; particles in free fall simply start following the geodesics of the curved geometry due to whatever mass - energy distribution is causing the curvature. The equation of geodesic deviation is what quantifies "force" or acceleration in the sense that it gives deviations from this kind of free fall due to the presence of tidal gravitaitonal forces and one can add other forces to the equation.

 

[Polyrhythmic]

I agree, to me, it's just an effect of the mass of objects in space. Big objects anyway.

Small objects as well, it's just that the effects become rather small.

 

[Polyrhythmic]

GR states that there is no acceleration due to any "Force" when a particle in free fall enters the presence of a mass; particles in free fall simply start following the geodesics of the curved geometry due to whatever mass - energy distribution is causing the curvature. The equation of geodesic deviation is what quantifies "force" or acceleration in the sense that it gives deviations from this kind of free fall due to the presence of tidal gravitaitonal forces and one can add other forces to the equation.

That is correct, yet I'd still say that the effect of one mass on another (be it through a curvature of spacetime) qualifies as some kind of interaction, or force (I think the term should be applied more loosely in this case). Even though its nature may be different than for example in the electromagnetic case.

 

[guillefix]

Why do we have to think about the cause of mass (which might be the Higgs boson), why couldn't it be that it's not mass which causes space-time curvature, but that mass is space-time curvature, i.e. we call mass points to bumps in the shape of the four-dimensional universe? I don't know the technical stuff of GR but I am just wondering..

 

[Polyrhythmic]

Why do we have to think about the cause of mass (which might be the Higgs boson), why couldn't it be that it's not mass which causes space-time curvature, but that mass is space-time curvature, i.e. we call mass points to bumps in the shape of the four-dimensional universe? I don't know the technical stuff of GR but I am just wondering..

I'm not sure how the statement "mass is space-time curvature" could make sense. The concept at hand, which general relativity gives us seems sufficient. It kind of works two ways: mass moves through spacetime and mass curves spacetime.

 

[LostConjugate]

The problem is that space-time curvature is simply an elegant mathematical solution to, typically round, gravitational objects. It does not give us any hints as to WHY gravity exists.

 

[Debt]

course so. Is em a force? I mean we have an understanding of physics, so what. gravity will pull your butt to the ground, it's a force.

 

[MegaDeth]

Small objects as well, it's just that the effects become rather small.

Oh right, do objects on the Earth curve space time as well or does it only account for in space?

 

[Polyrhythmic]

Oh right, do objects on the Earth curve space time as well or does it only account for in space?

Yes. Everything that carries mass, or energy, curves spacetime. Even if it is not as heavy as a planet or a sun.

 

[MegaDeth]

Ahh right, thanks for your help. Oh yeah, one thing I don't understand is, you know you see diagrams of curved spacetime, well, how would you perceive that curvature in 3 dimensions? As in, what would the curvature look like all around a planet/object?

 

[Polyrhythmic]

Ahh right, thanks for your help. Oh yeah, one thing I don't understand is, you know you see diagrams of curved spacetime, well, how would you perceive that curvature in 3 dimensions? As in, what would the curvature look like all around a planet/object?

Do you mean three space dimensions or two space + one time dimension?
In any case, the popular picture that is often used to describe curvature isn't accurate. It's rather misleading. I personally don't know how to accurately visualize spacetime curvature, since time is something we usually don't "see".

This is the misleading picture I was referring to: http://www.netzartig.org/wp-content/uploads/2010/06/Spacetime_curvature.png"

 

[WannabeNewton]

Ahh right, thanks for your help. Oh yeah, one thing I don't understand is, you know you see diagrams of curved spacetime, well, how would you perceive that curvature in 3 dimensions? As in, what would the curvature look like all around a planet/object?

Talking specifically for a typically spherical planet you can perceive the spatial geometry of the curved space - time as a 3 - sphere.

 

[MegaDeth]

Do you mean three space dimensions or two space + one time dimension?
In any case, the popular picture that is often used to describe curvature isn't accurate. It's rather misleading. I personally don't know how to accurately visualize spacetime curvature, since time is something we usually don't "see".

This is the misleading picture I was referring to: http://www.netzartig.org/wp-content/uploads/2010/06/Spacetime_curvature.png"

I actually mean 3 dimensions of space. Because in the picture, it only shows what happens at the bottom half of the Earth.

 

[MegaDeth]

Talking specifically for a typically spherical planet you can perceive the spatial geometry of the curved space - time as a 3 - sphere.

So how does gravity actually work in the case of a 3-sphere?

 

[Polyrhythmic]

Talking specifically for a typically spherical planet you can perceive the spatial geometry of the curved space - time as a 3 - sphere.

And how would you visualize that? A 3-sphere is a threedimensional object in a four dimensional space.

 

[WannabeNewton]

So how does gravity actually work in the case of a 3-sphere?

Much like that of Newtonian gravity with some more subtleties like the bending of light, gravitational time dilation, gravitational redshift etc. I don't know how much of the schwarzchild metric you already know but try this website it might help: http://casa.colorado.edu/~ajsh/schwp.html

 

[WannabeNewton]

And how would you visualize that? A 3-sphere is a threedimensional object in a four dimensional space.

You can't really visualize the temporal geometry so just for the purpose of visualization you can suppress the time dimension and view the curvature of space - time to be that of a 3 - sphere.

 

[Polyrhythmic]

You can't really visualize the temporal geometry so just for the purpose of visualization you can suppress the time dimension and view the curvature of space - time to be that of a 3 - sphere.

And what does a three-sphere look like? I've never seen one and I guess it's quite hard to visualize since we can only perceive objects embedded in three-dimensional space.

 

[MegaDeth]

And what does a three-sphere look like? I've never seen one and I guess it's quite hard to visualize since we can only perceive objects embedded in three-dimensional space.

Use google images.

 

[Polyrhythmic]

Use google images.

Google images is quite reliable, especially since the first result shows some business strategy stuff. ;)

Anyways, it's not possible to take a picture of a three-sphere, since it is by definition a three dimensional object which can be embedded in a four dimensional space. What we can see is a two-sphere, a two dimensional object which we can embed in a three dimensional space. It is very familiar to us: it's basically the surface of a ball.

 

[DaveC426913]

It is possible to create an image showing a gravity well in three dimensions.


You still have the xyz grid but, rather than joining points on the grid with lines, you put a little vector at each intersection pointing in the direction of the apparent force.

Maybe someday I'll sit down and make it.

 

[WannabeNewton]

You can naturally think of the 3 - sphere as a boundary/ surface in 4 - space and in terms of the space - times in question I'm not sure there is a good physical interpretation, maybe a 2 - sphere evolving in time (although in this space - time there exists time - like symmetry so the sphere would look the same as time varies)?

 

[Polyrhythmic]

It is possible to create an image showing a gravity well in three dimensions.


You still have the xyz grid but, rather than joining points on the grid with lines, you put a little vector at each intersection pointing in the direction of the apparent force.

Maybe someday I'll sit down and make it.

Drawing force lines sounds possible. Have fun ;)

 

[Searching]

I'm not sure how the statement "mass is space-time curvature" could make sense. The concept at hand, which general relativity gives us seems sufficient. It kind of works two ways: mass moves through spacetime and mass curves spacetime.

First of all, thanks you guys. This place is great! But to the question of what is spacetime. It seems that everything is matter/energy. Wouldn't space time also have to be? Otherwise, what is it made of?

Before we could detect the atmosphere people must have thought the it was empty space. Couldn't the same be true for the matter/energy that makes up spacetime?

 

[maverick_starstrider]

Oh right, do objects on the Earth curve space time as well or does it only account for in space?

FYI, you're never going to find a fundamental theory in physics where something only happens "in space" and not "on earth" (or vice versa), i.e. that there is anything special about Earth vs. anywhere else in the universe. The laws of physics (as far as we know) are the same everywhere. All of them.

 

[maverick_starstrider]

I actually mean 3 dimensions of space. Because in the picture, it only shows what happens at the bottom half of the Earth.

You can't visualize 3 dimensional surfaces, we only see 3 dimensions, so we can only visualize 2-dimensional surfaces. However, MATHEMATICALLY it's quite easy to work with such things. This is a point that never comes across when PBS Nova or whatever talks about higher dimensions and such. Physicists don't VISUALIZE 11 dimensions or any such nonsense, it's all in the math, and the math of higher dimensions isn't particularly difficult and ideally (stressing ideally) you then get some number which predicts the value of a certain experiment, if you then do the experiment and get that value then you may have been on to something with your higher-dimensional theory.

However, to get some idea of how space-time curves in 3 dimensions look at this: http://en.wikipedia.org/wiki/File:Black_hole_lensing_web.gif this is an example of what is called gravitational lensing. Light (photons) have no mass and thus if gravity really worked like Newton thought (G M m/r^2) it would not feel gravity, but GR says gravity is really a distortion of space-time and thus light, just light everything, just travels in a straight line, except in the presence of mass a "straight" line becomes curved by the distorted geometry. So what you're seeing there is the light from some far-away galaxy or nebula being curved around the space-time distortion caused by some large mass between us and the galaxy in the background (like a lense).

 

[Polyrhythmic]

First of all, thanks you guys. This place is great! But to the question of what is spacetime. It seems that everything is matter/energy. Wouldn't space time also have to be? Otherwise, what is it made of?

Before we could detect the atmosphere people must have thought the it was empty space. Couldn't the same be true for the matter/energy that makes up spacetime?

I'm not sure how the statement "space is matter/energy" makes sense. Space is what contains matter/energy. It's some kind of dynamical background everything takes place on. If space actually was something, you could ask even further: What contains space?