Idea: how to simulate gravity effects without "traditional gravity"

[KC001]

About 15 years ago or so I had this idea how gravity could be simulated without traditional gravity itself being used at all. Thought I would share the idea with you to see if it raises any interesting discussions:

 

Imagine space as a 2D grid on a paper.

Make the grid/paper scale larger and larger every second.

All matter you put on the paper would also scale larger and larger at the same rate as the paper/grid does.

This means that nothing out of ordinary would be happening from the point of view of a human standing on that paper: everything seems to stay the same size and at equal distance to other objects on that paper. No gravity effects would be seen.

For the outside observer though the paper and the human standing on the paper would get larger and larger.

 

NOW:

All matter you put on the paper/grid, would slow down the expansion of the grid under and near that matter.

The more matter/mass the area has, the more the expansion slows down.

The matter itself would still get larger and larger at equal rate to the general expansion of the paper itself.

 

Now for the person standing on that paper, the nearby objects would seem to start moving towards each other (gravity kind of effect) since they get larger and larger faster than the paper/grid is expanding around them.

So the objects are basically “growing larger, thus seemingly getting closer”.

 

Still no proper gravity that accelerates thing towards each other, even though now nearby objects would seem to be slowly getting closer and closer, as they get larger and the paper/grid expands too slowly for the objects not to eventually touch each other.

 

To get the nearby objects to accelerate towards each other (just like regular gravity works) the paper/grid expansion rate itself would need to be accelerating. Just like regular space seems to be doing according to astronomers.

 

Black hole sitting on the paper/grid would have enough mass to be hitting brakes to the paper/grid expansion altogether OR at least enough so the expansion would be dramatically slower compared to surrounding areas.

 

I believe this can be simulated on a computer fairly easily.

 

Any thoughts about this idea?

Extra idea: I'm not intimately familiar with dark matter's effects, but maybe it could be simulated by strong masses "carving" permanent (or semi permanent) bumps/wrinkles into the grid and/or paper as the masses move around the paper?

 

[Strange]

!

Moderator Note

Moved to Speculations. Please read the specific rules for this section of the forum, particularly the need to provide evidence or other support.

 

[Endy0816]

I think 'model' would probably have been a better choice of words.

I would say you probably could model gravity this way on a computer though would need to confirm your model still matches with reality.

[Ghideon]

 

3 hours ago, KC001 said:

gravity could be simulated without traditional gravity itself being used at all

Ok!

3 hours ago, KC001 said:

Any thoughts about this idea?

What is the purpose, an alternative to the rubber sheet model* and similar?  I might give this some thought, the idea may be interesting depending on the purpose.

 

*) https://www.scienceforums.net/topic/111238-the-rubber-sheet-analogy/

 

[Strange]

32 minutes ago, Endy0816 said:

I think 'model' would probably have been a better choice of words.

I agree that "model" might be a better description

Quote

I would say you probably could model gravity this way on a computer though would need to confirm your model still matches with reality.

I'm sure something like this could be the basis of model, bit it would probably require all sorts of ad-hoc things added, because what you are actually modelling is the way gravity works!

For example:

3 hours ago, KC001 said:

All matter you put on the paper/grid, would slow down the expansion of the grid under and near that matter.

The more matter/mass the area has, the more the expansion slows down.

Why would that slow down the expansion of the grid? There is nothing inherent in the grid model that requires this; it is just added because it seems to be necessary to make the model accurate. There are a few other things like that.

But it may not be a completely mad idea. After all, in GR, when you are stationary on the surface of the Earth you are accelerating upwards continuously (which is why you feel like you are being pressed into your chair: just like when a car accelerates). 

3 hours ago, KC001 said:

Now for the person standing on that paper, the nearby objects would seem to start moving towards each other (gravity kind of effect) since they get larger and larger faster than the paper/grid is expanding around them.

It isn't obvious (to me) that "things getting bigger" is equivalent to "things staying the same size but moving closer together". (I can't think of a compelling counter-argument either. ) It may just be a change of coordinates. But how does it fit with the inverse square law? And would things free-falling at different distances need to be expanding at different rates (because they are approaching each other at different rates)?

How would orbits work in this model? The size of the orbit would have to increase at the same rate that things were expanding; is there a mechanism for that?

The model might work conceptually, but I would like to see some quantitative results from it. 

You might also want to look at the "waterfall" model of space where, instead of representing gravity as spacetime curvature it is represented as space "falling" towards massive objects.

[Ghideon]

9 hours ago, Strange said:

It isn't obvious (to me) that "things getting bigger" is equivalent to "things staying the same size but moving closer together". (I can't think of a compelling counter-argument either. )

Maybe OP should clarify, but it seems to make sense if the following is considered:

13 hours ago, KC001 said:

All matter you put on the paper/grid, would slow down the expansion of the grid under and near that matter.

Some (ugly) pictures:

First picture: At time t there is one large and one small on the grid. The small ball mass has negligible effect on grid expansion to simplify. Large balls' mass considerably slows down expansion of grid. The distance between the balls is 1/2 square.

Some time later the grid has expanded to approx double size. The balls have also expanded. Since the mass slows down the expansion under the large ball, the grid has not expanded so much, so the large ball does not fit in one square.

 

If you zoom out so that the apparent sizes of the balls are the same then it looks as if they are closer than in the first picture? The distance between the balls is now less than 1/2 square. But one would notice that the square under the big ball seems smaller.

 

Not sure if this is what @KC001 meant or if it makes any sense. I just got curious and tried to figure it out

 

 

Edited June 2, 2019 by Ghideon
zoom out picture + comments

[Strange]

29 minutes ago, Ghideon said:

f you zoom out so that the apparent sizes of the balls are the same then it looks as if they are closer than in the first picture? The distance between the balls is now less than 1/2 square.

I can see that this might work (qualitatively, at least) if you just consider two objects. 

But say you have three objects: the Earth, the Moon and a meteor in space falling towards the Earth. If we describe gravity in terms of the objects getting bigger (and so the relative distance decreasing) doesn't this imply that the meteor will also be getting closer to the Moon?

[Ghideon]

9 hours ago, Strange said:

But say you have three objects: the Earth, the Moon and a meteor in space falling towards the Earth. If we describe gravity in terms of the objects getting bigger (and so the relative distance decreasing) doesn't this imply that the meteor will also be getting closer to the Moon?

Good point! My interpretation of the idea probably don't work at all for several objects in relative motion. I think I'll have to wait for clarifications* from OP before further comments.

*) and a response to my question regarding the purpose of the idea

[KC001]

Ghideon got my idea right.

And as Strange pointed out: there could be a problem with more than one object floating in the gravitational field. :-/ I would need to think about this idea/model some more to see how the problem manifests itself.

 

Here's a quick stream of mind. I'm thinking as I'm writing:

Example #1: Meteor sits between moon and Earth in such a place that Earth+Moon gravity would cancel each other out (for the meteor that is). Moon/Earth/meteor would all start their journey from standing still. Then the Moon and Earth slowly start "accelerating" towards the meteor in between them as they slowly "eat up" the paper/grid that's left underneath them while getting bigger. Eventually all three would crash together.

Example #2: Earth/Moon/meteor form a 90 degree angle (meteor is on the side of Earth compared to the Moon). Each object stands still before the simulation starts. As the grid/paper expands, both Earth and Moon "hit brakes" from their own respective direction to the location of paper/grid where the meteor is at any given moment. If I can visualise it properly in my head, the meteor should start "falling" to the side of the Earth where the Moon is. 

 

I think I visualize this in my head in a very similar way to the "space falling into mass"/waterfall approach, but by doing it kind of the opposite way: space and matter expands and mass hits brakes to the expansion.The visualizations would be fairly similar between waterfall and this model.

 If I remember my own idea correctly (it's been many years, note), my original idea was that it could be the time itself slowing down and thus also slowing down the expansion of the grid near masses. I.e. time moves slower so the paper/grid expansion can't keep up with the expansion of the matter over it. So slight changes in "local speed of time" would eventually cause the gravity effects. This was the point when my brain started hurting by thinking how to simulate it and I opted to the simpler version I presented in this thread

 

 

Edited June 4, 2019 by KC001

[Strange]

1 hour ago, KC001 said:

If I remember my own idea correctly (it's been many years, note), my original idea was that it could be the time itself slowing down and thus also slowing down the expansion of the grid near masses.

I remember (half-remember) a discussion on another forum that you can do a coordinate transform from our usual "expanding space" model to "slowing time"(*). But it isn't used because it is less intuitive (to most people) and introduces complications like a variable speed of light. 

Of course, you need something to explain why the rate of change (whether expansion, time, or size) has increased. We can explain this with "dark energy" (even though we don't know what that is). Changing coordinates to another system doesn't solve that problem.

You can obviously tweak your grid model to make it reproduce the effects we observe, but then it just becomes an ad-hoc model, rather than an explanation.

(*) actually, wouldn't time have to be getting faster so that photons from the past appear to have a lower frequency?

[Ghideon]

1 hour ago, KC001 said:

Ghideon got my idea right.

Thanks for clarifying!

I see some challenges regarding how practical the idea will be. Once you start to build mathematical formulas for simulation and tune the parameters for the expansion of the grid and breaking effect of mass doesn't that result in a "copy" of a gravitational model that uses gravity? If the end result of the computer simulation should look like gravity and behave like gravity it pretty much would require something based on the math for actual gravity? 

2 hours ago, KC001 said:

Here's a quick stream of mind. I'm thinking as I'm writing:

Example #1: Meteor sits between moon and Earth in such a place that Earth+Moon gravity would cancel each other out (for the meteor that is). Moon/Earth/meteor would all start their journey from standing still. Then the Moon and Earth slowly start "accelerating" towards the meteor in between them as they slowly "eat up" the paper/grid that's left underneath them while getting bigger. Eventually all three would crash together.

Example #2: Earth/Moon/meteor form a 90 degree angle (meteor is on the side of Earth compared to the Moon). Each object stands still before the simulation starts. As the grid/paper expands, both Earth and Moon "hit brakes" from their own respective direction to the location of paper/grid where the meteor is at any given moment. If I can visualise it properly in my head, the meteor should start "falling" to the side of the Earth where the Moon is. 

I think both cases could be drawn in a similar way as in my pictures, with the grid will be more distorted by the added mass of the moon. But in reality the moon is in orbit around earth, and comets doesn't pop into existence being stationary at some point in space. Is idea intended to take motion and orbits into account? 

 

 

Side note: I initially imagined some kind of physical contraption for demonstration purposes. A grid painted on a stretching rubber sheet, expanding balls and movement of the rig so the grid visually seems to have the same size even when expanding. Not a successful line of thought...

[KC001]

On 6/4/2019 at 10:30 PM, Strange said:

I remember (half-remember) a discussion on another forum that you can do a coordinate transform from our usual "expanding space" model to "slowing time"(*). But it isn't used because it is less intuitive (to most people) and introduces complications like a variable speed of light. 

Of course, you need something to explain why the rate of change (whether expansion, time, or size) has increased. We can explain this with "dark energy" (even though we don't know what that is). Changing coordinates to another system doesn't solve that problem.

You can obviously tweak your grid model to make it reproduce the effects we observe, but then it just becomes an ad-hoc model, rather than an explanation.

(*) actually, wouldn't time have to be getting faster so that photons from the past appear to have a lower frequency?

Unfortunately this is where we are exceeding my physics and math skills and I don't have any answer to your questions :-/

On 6/4/2019 at 11:16 PM, Ghideon said:

I see some challenges regarding how practical the idea will be. Once you start to build mathematical formulas for simulation and tune the parameters for the expansion of the grid and breaking effect of mass doesn't that result in a "copy" of a gravitational model that uses gravity? If the end result of the computer simulation should look like gravity and behave like gravity it pretty much would require something based on the math for actual gravity? 

I think both cases could be drawn in a similar way as in my pictures, with the grid will be more distorted by the added mass of the moon. But in reality the moon is in orbit around earth, and comets doesn't pop into existence being stationary at some point in space. Is idea intended to take motion and orbits into account?

I was trying to figure out an alternative way to simulate the gravity effects without calculating the traditional force/acceleration vectors for the simulation animation frames. In my model you obviously still need to calculate some parameter (based on distance and mass from all objects) how much the paper/grid expansion slows down at any given point of the paper/grid. To get this right, the values would need to be adjusted so that they match observations of the real world (as in any model, really). This should result in a similarly shaped curve as traditional gravity's strength at any given point in space (but with the value being a scalar instead of a direction/force vector). I guess this means you could say that my model is using traditional gravity as a starting point, but tries to reach it's actual effects by different means.

Hmm. That being said, I think my original post might then have been somewhat misleading: If the slowdown of the paper/grid expansion depends on the mass and distance of the objects, it sounds like it's most probably going to be based on the traditional gravity formula. But then again, as mentioned above, the forces wouldn't be used as directional vectors, but as a scalar value which hits brakes to the expansion of the paper. I think this is the exact point of my model which needs a closer look to see if it breaks down into non working model or if it has potential to work in a simulation.

The idea intends to take motion and orbits into account. If I can simulate this model properly in my head, I think the orbit should happen something like this:

Earth sits stationary on the paper. Meteor is passing by the Earth. As the grid around Earth expands slower around the Earth, the passing meteor gets pulled towards it. The accelerating expansion of the paper curves the path of the meteor even more and thus it starts going around the Earth.

Note that this is where my powers of imagining the simulation in my head start to have their limits and the whole thing should be made into a proper computer simulation to verify if it actually works in practise or not. I'm now entering the "guessing zone".

Edited June 9, 2019 by KC001

[Ghideon]

1 hour ago, KC001 said:

I was trying to figure out an alternative way to simulate the gravity effects without calculating the traditional force/acceleration vectors for the simulation animation frames. In my model you obviously still need to calculate some parameter (based on distance and mass from all objects) how much the paper/grid expansion slows down at any given point of the paper/grid. To get this right, the values would need to be adjusted so that they match observations of the real world (as in any model, really). This should result in a similarly shaped curve as traditional gravity's strength at any given point in space (but with the value being a scalar instead of a direction/force vector). I guess this means you could say that my model is using traditional gravity as a starting point, but tries to reach it's actual effects by different means.

Hmm. That being said, I think my original post might then have been somewhat misleading: If the slowdown of the paper/grid expansion depends on the mass and distance of the objects, it sounds like it's most probably going to be based on the traditional gravity formula. But then again, as mentioned above, the forces wouldn't be used as directional vectors, but as a scalar value which hits brakes to the expansion of the paper. I think this is the exact point of my model which needs a closer look to see if it breaks down into non working model or if it has potential to work in a simulation.

The idea intends to take motion and orbits into account. If I can simulate this model properly in my head, I think the orbit should happen something like this:

Earth sits stationary on the paper. Meteor is passing by the Earth. As the grid around Earth expands slower around the Earth, the passing meteor gets pulled towards it. The accelerating expansion of the paper curves the path of the meteor even more and thus it starts going around the Earth.

Note that this is where my powers of imagining the simulation in my head start to have their limits and the whole thing should be made into a proper computer simulation to verify if it actually works in practise or not. I'm now entering the "guessing zone".

(Bold by me above)

Quick question, how is velocity and movement of the celestial bodies taken into account using only scalars and no vectors? How do you calculate the direction the meteor is supposed to move? I do not claim it to be not possible, just that my (limited) math skills does not make it obvious how it would work.

 

[KC001]

On 6/9/2019 at 12:44 PM, Ghideon said:

(Bold by me above)

Quick question, how is velocity and movement of the celestial bodies taken into account using only scalars and no vectors? How do you calculate the direction the meteor is supposed to move? I do not claim it to be not possible, just that my (limited) math skills does not make it obvious how it would work.

 

The idea is that as the paper/grid expands into all directions, the scalar value at point X of the paper/grid describes how much the mass of the celestial body decreases the expansion speed in that point of space. So it affects the expansion paper/grid only, not the regular movement vector of the celestial body. 

The more I think of this, it's the exact inverse presentation of "space curving or falling into the mass" model. Instead of space falling into the mass, it expands as does all the matter and at the same time some of the space gets "overridden" by the expanding mass.

 

Edited July 5, 2019 by KC001