[Harri (OP)]

I'm not sure why I'm so fascinated by gravity but ... as a non scientist I'm a little confused about what to conclude about gravity.
From my limited reading I'm thinking there must be one type of gravity that attracts matter to matter like an invisible magnetic. Hence the formation of planets and we are all pulled down on the earth.
And another form of gravity that is a warping of space that keeps our planets in motion around each other.
I guess my question would be is all gravity a result of a warping of space ?

[Kryptid]

So far as we can tell, all gravity is the same. The equations that describe a ball falling towards the Earth are equally valid for the orbits of the planets. They are, in fact, the exact same thing. The planets actually are falling into the Sun, but they keep missing it:

[Harri (OP)]

Gravity... what a beautiful thing!

[PmbPhy]

I'm not sure why I'm so fascinated by gravity but ... as a non scientist I'm a little confused about what to conclude about gravity.
From my limited reading I'm thinking there must be one type of gravity that attracts matter to matter like an invisible magnetic. Hence the formation of planets and we are all pulled down on the earth.
And another form of gravity that is a warping of space that keeps our planets in motion around each other.
I guess my question would be is all gravity a result of a warping of space ?

In a certain approximation in GR the gravitational field can be placed in the form of Maxwell's equations. In that sense one speaks of a gravitomagnetic field and a gravitoelectric field.

[Bill S]

The planets actually are falling into the Sun, but they keep missing it:

And the moon is falling towards the Earth....no, wait, it's moving away! I guess that's due to tidal forces. 

Does that mean that there are tidal forces involved in planetary orbits, but they are, relatively, so small that we can ignore them?

[guest45734]

I guess my question would be is all gravity a result of a warping of space ?

Dont let the maths obfiscate the truth,  According to Einstein, gravity is not a force – it is a property of space-time itself, and yes it warps space time.

Basically all mass sucks space  time warping it.

[Bill S]

Dont let the maths obfiscate the truth,  According to Einstein, gravity is not a force

Have you actually found a quote in which Einstein said that gravity is not a force?

[Kryptid]

Does that mean that there are tidal forces involved in planetary orbits, but they are, relatively, so small that we can ignore them?

Depends on what you mean by "ignore". The tidal forces on the Earth due to its orbit around the Sun are significant enough to contribute noticeably to the tides.

[Bill S]

The tidal forces on the Earth due to its orbit around the Sun are significant enough to contribute noticeably to the tides.

But not enough to cause the Earth to move away from the sun?

[guest45734]

Have you actually found a quote in which Einstein said that gravity is not a force?

I am strugling to find an actual qoute, but there are lots of hits on google, which appear to be qoutes and are not on closer inspection.

BUT qouting from wikiqoute "Gravity is most accurately described by Albert Einstein's general theory of relativity, which describes gravity not as a force but as a consequence of the curvature of spacetime caused by the uneven distribution of mass/energy; and resulting in gravitational time dilation, where time lapses more slowly in lower (stronger) gravitational potential." https://en.wikiquote.org/wiki/Gravity

You will also find in the above link lots of references to various different theories on gravity ranging from newtons theories to string theories.

[yor_on]

It's tricky Bill. Einstein didn't consider it a geometry, as far as I get it,. He used calculus and thought of gravity and inertia in those terms. the geometric interpretation was something that came without him, not meaning that he didn't see the implications, just that he found it questionable. " he thought that General Relativity was no more and no less geometrical than Maxwells theory of electromagnetism; and that the important achievement of GR was the advancement of the unification programme in direct continuation of special relativistic electrodynamics. Einstein thought that the special theory unified electricity and magnetism, the general theory inertia and gravity. Yet, we shall see that, unbeknown to most scholars, Einstein was emphatic in his belief that this should not be interpreted as a ‘geometrization’of gravity, especially if ‘geometrization’was seen as a reduction of gravity/inertia to spacetime geometry

.... As early as 1926 Einstein insisted, explicitly, that his work should not be understood as reducing physics to geometry, either his work on GR or his (and Weyl's and Eddington's) work on a unified field theory of gravitation and electromagnetism. Interestingly, what seems to be Einstein's first clear statement on the matter was prompted by a letter from Hans Reichenbach. Reichenbach was at the time engaging with Weyl's and Eddington's theories, and wrote Einstein that he thought that seeing electricity as geometrical in Weyl's theory is not more than an illustration (Veranschaulichung), one that, he argued, is equally possible (and equally trivial) in GR. Einstein agreed wholeheartedly, writing ' You are completely right. It is wrong to think that ‘geometrization’ is something essential. It is only a kind of crutch (Eselsbrücke) for the finding of numerical laws. Whether one links ‘geometrical’ intuitions with a theory is a … private matter. '   "

So when speaking about a geodesic it's not a geometric path in his terms, " Already in the first papers in which Einstein starts making use of the metric tensor to give an account of gravitation, he is at pains to establish the status of the geodesic equation as describing the motion of particles as “straight and uniform” (geradlinig und gleichförmig) even when subject to gravity. This would lead him to call the geodesic equation a “generalized law of inertia”; redefining inertial paths such that the category includes motion under the influence of gravity. ..... Already in a note added in proof to Einstein (1912), Einstein had stated that equation (1) gives the equation of motion of point particles “not subject to external forces”.

Thus, it was clear that already in 1912, before even embarking on a metric theory of gravitation, Einstein thought of (static) gravitational fields not as invariant force fields diverting particles from inertial motion. Already, in 1912, he thought of equation (1) as describing inertial motion on one hand, and as describing motion in the presence of (static) gravitational fields on the other. "

"  Einstein effectively states that the very distinction between ‘gravity’ and ‘inertia’ is useful only for relating the theory to its predecessor theories; it is not a distinction from within the theory itself. Put differently, if one just looks at the theory without relating it to predecessor theories, there is no need whatsoever to distinguish ‘inertial terms’ and ‘gravitational terms’ in the geodesic equation. "

By that I understand he meaning that talking about gravity as a force directing the inertia (willingness to keep on indefinitely) of a test particle made little sense to him.

"  In Einstein's mind, the unification was very similar indeed, as the December 1919/January 1920 text on the development of relativity shows. There, he recalls the magnet-conductor thought experiment described in the first paragraph of his 1905 paper on special relativity, from which he concludes. ' The existence of the electric field is a relative one, depending on the state of motion of the coordinate system used; only the electric and magnetic field together can be attributed a kind of objective reality, independent of the state of motion of the observer, i.e. of the coordinate system. '

Einstein then describes how he worked on a review article of special relativity in 1907, and links the above realisation regarding the electric and magnetic field to another thought experiment regarding inertia and gravity: ' Then I had the most fortunate thought of my life in the following form: The gravitational field only has a relative existence in a manner similar to the electric field generated by electro-magnetic induction. Because for an observer in free fall from the roof of a house, there is during the fall — at least in his immediate vicinity — no gravitational field. Namely, if the observer lets go of any bodies, they remain, relative to him, in a state of rest or uniform motion, independent of their special chemical or physical nature '

quotes taken from " Why Einstein did not believe that General Relativity geometrizes gravity " By Dennis Lehmkuhl.

[yor_on]

It's pretty cool, isn't it :)
He defined it as relativity joining inertia and gravity into one entity as I gather.

This " Already, in 1912, he thought of equation (1) as describing inertial motion on one hand, and as describing motion in the presence of (static) gravitational fields on the other. "

And notice how he then treat 'motion'
=

Actually it's more than tricky.   " Already in the first papers in which Einstein starts making use of the metric tensor to give an account of gravitation, he is at pains to establish the status of the geodesic equation as describing the motion of particles as “straight and uniform” (geradlinig und gleichförmig) even when subject to gravity."

What that states to me is that even if there is no 'force' acting he presumably still could consider it a 'field', in where what we would call a 'force' became induced by what frame of reference you choose. You can always take away a gravitational 'field' by being in a free fall, the 'force' of gravity only exist as long as long as you're without that free fall. Earth may be in a geodesic, but we're not. Ah, well we are, but we aren't :)

[Kryptid]

But not enough to cause the Earth to move away from the sun?

That's a little tricky because it's not a good analogy for the Moon moving away from the Earth. The fact that the Earth has continents that get in the way of the oceanic tides acts as a mechanism for "braking" the Earth's spin. This, in turn, transmits momentum to the Moon that raises its orbit. The Sun, unlike Earth, is completely fluid. If any such tidal energy transfer occurred between the Sun and Earth, it would be much less efficient.

[Harri (OP)]

If we are expecting rising waters as a consequence of global warming and melting ice caps, will that in anyway affect the mechanism that brakes the earths spin?

[Bill S]

I am strugling to find an actual qoute

I'm not surprised.

BUT qouting from wikiqoute "Gravity is most accurately described by Albert Einstein's general theory of relativity, which describes gravity not as a force but as a consequence of the curvature of spacetime....

Not quite what Einstein said, perhaps.

[Bill S]

It's tricky Bill

Did you mean that finding a quote in which Einstein said that gravity is not a force, would be tricky?

Perhaps my interpretation is skewed, but your excellent posts seem to say quite clearly that Einstein saw gravity as a force, albeit one that was more complex, and perhaps less mysterious, than "simple" Newtonian gravity.

[guest45734]

I am strugling to find an actual qoute

I'm not surprised.

BUT qouting from wikiqoute "Gravity is most accurately described by Albert Einstein's general theory of relativity, which describes gravity not as a force but as a consequence of the curvature of spacetime....

Not quite what Einstein said, perhaps.

Here is some more quotes by Einstein for light reading. several amused me but taking them out of context you can have fun.
" We can't solve problems by using the same kind of thinking we used when we created them".
Read more at: https://www.brainyquote.com/authors/albert_einstein

None of the points made above point out that current theories on gravity might just be being stretched beyond breaking point, ie there may not be random amounts of dark matter in the universe to make EFE equations work. MOND was one of the first to dare to point this out, currently various other theories also support this idea ie dark matter does not exist. Verlindes emergent gravity is one such theory, which seems to be passing all the tests.Both space and time appear to be emergent phenomina based on entanglement perhaps

[Bill S]

These comments by Chris Baird are interesting. They also deal with the "get-out clause" that gravity is a fictitious force.

Yes, gravity is a force. But it is a force that is more completely described by spacetime curvature and not Newton's law. The fact that gravity is caused by spacetime curvature means ultimately that it can be viewed as an inertial force, meaning that it arises from the inertia of an object as viewed from a non-inertial frame. But it is indeed a real force. It's not just a classical force. You will see some places call it a "fictitious force" which can be misleading. The word fictitious is not used by physicists in this context to mean fake, imaginary, or pretend. Rather it means that the force arises from the way the inertia of an object is being viewed in a non-inertial frame. For instance, the centrifugal force is a "fictitious" force, but it is a very really force indeed in the rotating reference frame which leads to measurable physical effects.

[Bill S]

Both space and time appear to be emergent phenomina based on entanglement perhaps

What would you see as being entangled, in order to give rise to space and time?

[guest45734]

Both space and time appear to be emergent phenomina based on entanglement perhaps

What would you see as being entangled, in order to give rise to space and time?

I will let Verlinde speak for himself
 https://insidetheperimeter.ca/a-new-view-on-gravity-and-the-dark-side-of-the-cosmos-erik-verlinde-public-lecture/?__hstc=261081490.b20e624ce3bbf82fcde9c8f1a30c5bc1.1533466440658.1533466440658.1533466440658.1&__hssc=261081490.1.1533466440658&__hsfp=2495466239

In the above lecture he refers to a 51 page paper he wrote, I think this is the paper  https://arxiv.org/pdf/1611.02269.pdf

Hossenfelder seems to support Verlindes ideas in this paper https://arxiv.org/pdf/1703.01415.pdf also in the following later paper ref reddhift https://arxiv.org/pdf/1803.08683.pdf she adds further credence to Verlindes theories.

I posted a lot of other stuff on various threads on this forum, to provoke a discussion on exactly this topic.

Oh ref time being emergent https://medium.com/the-physics-arxiv-blog/quantum-experiment-shows-how-time-emerges-from-entanglement-d5d3dc850933 this is the first of many links I hit, without even trying.

Space time may appear smooth but at the quantum level this is not the case.