Gravity. Please knock this down

[mistermack]

I enjoy building up speculative ideas and knocking them down again. I find that I often do learn a bit in the process.

I wrote this about six months ago, as an attempt to make a mental picture of how gravity could work. Then I found a flaw that killed it, so I left it at that. Now, I read it again, and can't remember what knocked it on the head, for me. I think it was something to do with gravitational time dilation, but can't remember what. And it turns out I had the wrong idea about that anyway.

So please feel free to pull it apart, I'm not begging or pushing it as anything other than a thought experiment, that you might enjoy taking apart, as I like to do.

So this is it, copied and pasted from six months ago: 

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What would happen if every particle of matter in the Universe is actually constantly sucking in and absorbing space from around it?

On objects that have a huge mass, like a planet, there would be a great inward flow of space, because there are so many particles concentrated in one place.

 Here on the surface of the Earth, we would be living in a high-speed flow of space, as it was sucked past us into the Earth. 

How could you tell that this was happening? If you move at a constant speed through space, there is no indication or sensation of speed.

You can’t tell if you are moving, or staying still. So, if space was whizzing past us at high speed down into the Earth, we wouldn’t feel anything.

 

However, one thing about moving fast relative to space, is that time slows. The faster you move, the slower your clock will run. The effect is called time dilation.

So if space is being sucked into the Earth, whizzing past us on the surface at high speed, a clock that is positioned here on the surface of the Earth should have space whizzing past faster, and so run slower than one that is out in the depths of space, well away from the Earth.

 Does this actually happen? Yes, it does. It’s called gravitational time dilation under General Relativity. It happens close to any substantial massive object. It’s been accurately measured many times over, so it’s not a controversial idea, it’s a known fact. The only difference in GR is that it’s attributed to gravity, rather than relative motion through space. But time dilation has the same effect, whether it’s gravitational, or through motion.

 It should be possible, if we know the gravitational time-dilation figure for the surface of the Earth, compared to remote space, to work out the speed that space would need to be passing us by, to cause the same time-dilation. So if this is actually happening, it should be an easy calculation to give a figure for the speed at which space is being sucked past us on the surface of the Earth.

 But, what if here on the surface of the Earth, space is not just being sucked into the planet at a constant speed, but at the surface, the space is actually accelerating at a rate of 9.81 metres per sec² ?

So, without the support of the Earth beneath you, you too would fall downwards with an acceleration of 9.81 mps². This is exactly what does happen, and we experience it as gravity.

You would expect this to be the case, if space from a practically infinite volume was being sucked into a smaller and smaller volume. Like water approaching a sink hole. It has to speed up as it gets concentrated into a smaller and smaller volume.

 In other words, what we think of as gravity on Earth, could actually be space that is accelerating downwards.

The pull of gravity on Earth, and an acceleration in space of 9.81 mps² are indistinguishable. They feel exactly the same. It’s called artificial gravity. And it also works the other way. In planes that are used to train astronauts, they produce artificial gravity pointing away from the Earth of 9.81 mps², and for a short while, the trainees are weightless and floating.

The gravity due to the Earth, and the opposite artificial gravity due to the plane’s acceleration, are an exact match and cancel each other out.

 So gravity and acceleration feel exactly the same. Maybe, it’s because they ARE the same.

 If this sucking in of space were actually happening, then two massive objects freely floating in space would accelerate towards each other because they are both trying to pull in the same bit of space.

Also, any light that was passing close by a very massive object, like a super-massive black hole, would be deflected, as the space that it was passing through would be in accelerating motion, towards the black hole. So you would be able to see multiple images of objects that were directly behind the black hole.

This happens too and is known as gravitational lensing.

 The obvious question that arises, is what happens to the space that is being sucked into matter? If the Earth has been sucking in space for 4 billion years, where has it gone?

 I don’t have an answer for that, except to point out that according to big bang theory, all of the universe was once smaller than a pin head, and space is basically nothing, so there is nothing that appears obviously impossible about the concept from that angle.

 One interesting consequence of this notion, is that if it’s right, then space can and must ‘pull’ on its neighbouring space.

If the Earth is sucking in space in its immediate vicinity, then that would be resulting in the adjoining space moving to replace it, and the space adjoining that space moving to replace that, and so on.

As the process radiates outwards from the Earth, it’s happening over a bigger and bigger area, as the process radiates outwards, like an inflating bubble.

So, the strength of the effect in any one place diminishes in line with the growing surface area of a sphere, in relation to its distance from the centre.

Space will be moving slower and slower, the further you get from the Earth. This is why the space would be accelerating as it moves in, and the rate of acceleration rises, as you get nearer to the Earth.

 Also, any sudden change in the position of large amounts of mass will result in a ripple in the normally constant and even pulling of space on its neighbouring space.

This ripple should travel at the speed of light, in line with other massless disturbances in space.

This would be an equivalent of gravitational waves, which were predicted by Einstein, and are just recently being confirmed.

 

I thought of a problem with this idea, but I can’t remember it at the moment. But it did knock it on the head, as far as I was concerned.

I’ll try to recall what it was. Should have written it down. I think it’s to do with gravitational time dilation. 

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That's what I wrote back then. Janus just put me right about time dilation in a gravitational well, and at first sight, it doesn't conflict with this scenario, as the deeper you are in the gravitational well, the faster space  will be passing you by, and hence, the slower your clock.  I wish I could remember what I saw originally wrong with this, but it's gone from my head. I should have written it down. Another lesson learned.

Anyway, I hope you can have a bit of fun with this.

 

[mistermack]

I should have included the pretty obvious point, that this scenario would predict the existence of black holes, if they hadn't already been predicted and detected. The more massive a body, the greater would the final velocity of space being pulled into it, and there would surely be an instance where a body was big enough to cause a final velocity approaching the speed of light.

A photon emitted at that stage would still travel at c, but wouldn't make any headway away from the massive body, so no light could escape.

In bodies more massive still, there would be a point in the gravitational well, at which c was reached, and that would be the event horizon, below which no light could escape the massive body. 

[studiot]

A problem with this, as I see it, is with the word 'suck'.

In conventional Physics there is no such thing as suction.

All instances without exception are the result of an excess of external pressure over internal.

Edited October 14, 2017 by studiot

[mistermack]

44 minutes ago, studiot said:

A problem with this, as I see it, is with the word 'suck'.

In conventional Physics there is no such thing as suction.

All instances without exception are the result of an excess of external pressure over internal.

Thanks, I take your point. It's just terminology, easily remedied. I wasn't trying to be precise with the word, but just to convey  the idea. You would need to know the precise mechanism, to be able to accurately describe it anyway. 

But does a magnet pull on iron, or is it pushed?

[J.C.MacSwell]

Is this a constant flow? That would be consistent with feeling a constant force while resisting gravity at the surface (like my butt in my chair right now), but if something was dropped would it not get up to flow speed and therefore stop accelerating? (even in a vacuum)

Or is it constantly accelerating flow, requiring more and more space to ingest, and why is my butt not feeling a constantly increasing pressure?

Edited October 14, 2017 by J.C.MacSwell

[geordief]

17 minutes ago, J.C.MacSwell said:

Is this a constant flow? That would be consistent with feeling a constant force while resisting gravity at the surface (like my butt in my chair right now), but if something was dropped would it not get up to flow speed and therefore stop accelerating? (even in a vacuum)

Or is it constantly accelerating flow, requiring more and more space to ingest, and why is my butt not feeling a constantly increasing pressure?

Didn't the OP suggest the flow would speed up as it approached the Earth owing to the space available being less and so sped up like water rapids.

Is space being pulled into space? A strange idea

 

[mistermack]

I think it's easier to picture in two dimensions first.

I was picturing something like a pipe near the surface of a  very shallow pond, down which water escapes. The water near the pipe will move faster towards the pipe, than water further away. The flow gets faster and faster as you get near the pipe, because all of the flow is concentrated.

If you imagine a sunken circular concentric string around the pipe, the flow down into the pipe has to be passing across that string. A bigger circle has a bigger circumference, and so the flow speed across it will be less. So it's directly related to the circumference of a concentric circle at any given radius.

If you then picture the same thing in 3D, then it's related to the surface of a concentric sphere, in the same way.

[geordief]

38 minutes ago, mistermack said:

I think it's easier to picture in two dimensions first.

I was picturing something like a pipe near the surface of a  very shallow pond, down which water escapes. The water near the pipe will move faster towards the pipe, than water further away. The flow gets faster and faster as you get near the pipe, because all of the flow is concentrated.

If you imagine a sunken circular concentric string around the pipe, the flow down into the pipe has to be passing across that string. A bigger circle has a bigger circumference, and so the flow speed across it will be less. So it's directly related to the circumference of a concentric circle at any given radius.

If you then picture the same thing in 3D, then it's related to the surface of a concentric sphere, in the same way.

Is it just space being sucked in or space and its contents?

[J.C.MacSwell]

OK. So you are required to resist the flow/gravity to stay stationary on the Earth's surface (presumably electromagnetic forces at play), and there appears to be a radial inverse square law effect, but how is there no drag tangentially, for orbits?

Also, what is the inflow velocity of the flow near the Earth's surface that would interact with matter to produce the 9.81 m/s2 acceleration? If something was already free falling at that speed would it then accelerate much less, only to match the inflow velocity gradient?

Edited October 14, 2017 by J.C.MacSwell

[mistermack]

3 hours ago, geordief said:

Is it just space being sucked in or space and its contents?

Not contents, or you would see solid objects shrinking. The force of gravity is very weak, compared to the other forces, at particle level.

1 hour ago, J.C.MacSwell said:

OK. So you are required to resist the flow/gravity to stay stationary on the Earth's surface (presumably electromagnetic forces at play), and there appears to be a radial inverse square law effect, but how is there no drag tangentially, for orbits?

Also, what is the inflow velocity of the flow near the Earth's surface that would interact with matter to produce the 9.81 m/s2 acceleration? If something was already free falling at that speed would it then accelerate much less, only to match the inflow velocity gradient?

I would expect the effect to be identical to gravity as we know it, so I don't see why there should be any drag effect, other than what we observe of gravity.

I don't think the inflow velocity has anything to do with acceleration. If the space at the surface of the Earth was accelerating downwards at 9.81 m/s2, then if you are standing stationary on the surface, you will be accelerating in an upward direction relative to the space that you occupy, (not relative to the Earth), and this would require a force, which is provided by the solid surface that you stand on.

[MigL]

Consider the Earth/Moon system, and assume the orbit is stable and unchanging.
 Both bodies are moving away from each other as fast as gravity is pulling them together, or in your thought experiment, as fast as space is falling 'into' each body.
We can go to a stable point between the two bodies, where you feel neither gravity, nor are constrained by 'in-falling' space to move towards either body; Yet if you move in one direction or the other, you begin falling in that direction towards that body. Or in your version, you follow space in the in-fall.
That suggests there is a 'source' of space at that stable point, which then falls, from that point, in both directions.

That is not the only issue; If a sink is an attraction, then a source is anti-gravity.
Yet , because of the inverse square dependency, you can have two smaller masses on either side of that stable point attract each other. Even though they surround an anti-gravity source.

Any thought experiment that relies on anti-gravity effects is a non-starter, as it doesn't match observation.

[mistermack]

I wouldn't picture it like that. I don't see the need for a source or anti-gravity. If you have two pipes draining water in an ocean, a certain distance apart, then there is no need for a source of water. The surrounding water of the ocean moves to occupy the space vacated by the water you are draining away.

[Mordred]

Replace the need to apply a materialistic analogy.

At every coordinate assign a vector. A vector field is converging if its  vectors are to a point.

Diverging if from a point outward . Now apply that to a freefall field. (converging, central potential CoM.)

Of course for dimension (ct) this takes a bit to understand. However don't think about cause, restrict yourself to the pure math relations first.

Compare Galilean relativity to SR (Lorentz transform). 

Study how gamma is a constant of proportionality (scale factor) between two spacetime graphs first. In order to preserve the Euclid (invariant/rest) frame.

 

Edited October 15, 2017 by Mordred

[mistermack]

I don't really see that there has to be contradiction, between this picture and the picture that general relativity paints.

If you say that space time curves, are you not saying that the shape of space is changing with time? So the idea of space in motion is inherent in GR. The stronger the gravitational field, the more curvature of space time. The more curvature of space time, the more space is in motion.

[Mordred]

One can model GR as a flow of reference frames as per the River model. One can also keep the coordinates static. Analogies are useful, but only to the type of treatment. 

 More often than not they mislead, so your better off not thinking about them to understand GR..Spacetime shrinking, stretching, flowing etc are all descriptives that while useful can be easily miss understood.

For example spacetime stretching implies that spacetime is materialistic. Fabric being another problematic analogy.

To understand time dilation properly study the transforms themselves in terms of vectors and vector fields. Don't rely on verbal descriptives. They are interpretations of the math.

 

[mistermack]

I suppose a fairly obvious way to prove this wrong, would be to set up a time dilation experiment, on the surface of the Earth, with one clock moving down, and the other moving upwards. Maybe that's already been done? 

[J.C.MacSwell]

9 hours ago, mistermack said:

I don't really see that there has to be contradiction, between this picture and the picture that general relativity paints.

If you say that space time curves, are you not saying that the shape of space is changing with time? So the idea of space in motion is inherent in GR. The stronger the gravitational field, the more curvature of space time. The more curvature of space time, the more space is in motion.

You haven't answered anything with regard to where the analogy clearly breaks down. Try explaining a simple orbit. In Relativity or Newton Gravity it's free fall. In this it is plowing along tangentially against the medium of the flow. Explain why there is no drag in the tangential direction. 

[mistermack]

I don't understand where you get the idea of drag from. There is no drag in empty space, no matter what your velocity.

I'm not proposing that there is some sort of substantial medium, any different to the space time that is currently accepted. 

If a solid body can continue in motion relative to space, without drag, then why should there be drag if space were to move relative to the body? It's the same situation.

[Strange]

Like this?

https://en.m.wikipedia.org/wiki/Gullstrand–Painlevé_coordinates

http://jila.colorado.edu/~ajsh/insidebh/waterfall.html

[mistermack]

Thanks Strange. I'm completely numb from the first link, but the second about the space waterfall into black holes is nice to see. It's not dissimilar to what I was picturing happening at a black hole so according to that writer, the maths match the hypothetical picture, in that case.

If a black hole CAN cause space to flow towards it, then I don't see why any source of gravity isn't doing the same thing, obviously at a lesser scale. After all, black hole gravity is no different to any other gravity, outside of the event horizon.

[J.C.MacSwell]

2 hours ago, mistermack said:

I don't understand where you get the idea of drag from. There is no drag in empty space, no matter what your velocity.

I'm not proposing that there is some sort of substantial medium, any different to the space time that is currently accepted. 

If a solid body can continue in motion relative to space, without drag, then why should there be drag if space were to move relative to the body? It's the same situation.

Ok. I guess I took your ocean analogy as how it might work. So the inflow of space somehow affects an object in free fall, but there is no resistance otherwise?

[mistermack]

40 minutes ago, J.C.MacSwell said:

Ok. I guess I took your ocean analogy as how it might work. So the inflow of space somehow affects an object in free fall, but there is no resistance otherwise?

Yes, if you read back through, I'm proposing that space is not only flowing inwards, but also accelerating all of the way, relative to the massive body that is causing the effect. (Earth, in our case)

So if you step off a cliff, then you free fall at 9.81 mps², because the space you occupy is doing exactly that. If you don't step off the cliff, then you are being accelerated at 9.81 mps² upwards, relative to the space that you occupy, and the force for that to happen is supplied by the Earth that you are standing on.

The speed of the flow past you would have no effect at all,  that you could feel. But it would explain why your clock runs slower than a clock in remote space.

[J.C.MacSwell]

3 hours ago, mistermack said:

Yes, if you read back through, I'm proposing that space is not only flowing inwards, but also accelerating all of the way, relative to the massive body that is causing the effect. (Earth, in our case)

So if you step off a cliff, then you free fall at 9.81 mps², because the space you occupy is doing exactly that. If you don't step off the cliff, then you are being accelerated at 9.81 mps² upwards, relative to the space that you occupy, and the force for that to happen is supplied by the Earth that you are standing on.

The speed of the flow past you would have no effect at all,  that you could feel. But it would explain why your clock runs slower than a clock in remote space.

So is the flow increasing at 9.81 mps² at that point? The ocean analogy would have increasing flow toward the centre, but constant speed at each point (this is why I assumed some kind of drag was at work)

Edited October 15, 2017 by J.C.MacSwell

[mistermack]

If you picture a funnel, which you keep filled with water, the water at the wide end moves down slowly, but much faster at the narrow end. If you picture a sphere as lots of funnels, bound together, then you have a picture of what I proposed might be happening. 

[J.C.MacSwell]

2 hours ago, mistermack said:

If you picture a funnel, which you keep filled with water, the water at the wide end moves down slowly, but much faster at the narrow end. If you picture a sphere as lots of funnels, bound together, then you have a picture of what I proposed might be happening. 

So steady state (not increasing overall, but just as it gets closer).In the funnel analogy, or your hypothesis, if something arrived with the flow from a distance (say dropped from well above the cliff), how would the movement compare to a second particle released at the cliff edge as the first particle arrived? And why?

Edited October 15, 2017 by J.C.MacSwell