[nilak]

The proof centrifugal force is not fundamental.

A satelite orbiting the Earth is always in free fall.
A roket that uses its thrusters to hover at the same hight without orbiting the Earth is not in free fall.
That is the difference.

The rocket requires constant power. The satelite doesn't.
If you go there to feel the effects you will definitely notice the difference.
In the rocket you will feel a little gravity (in fact is the force from the thrusters equal to gravity)
In the satelite you will feel free falling.

That is simple newtonian.

In GR you replace gravity with falling space itself (equivalent to curved spacetime) and its the same thing.

[jerrygg38 (OP)]

#103 Nilak
Certainly ... Though somebody will tell you light can also be bent by sufficiently massive objects.
But what you say is sufficiently accurate for our "needs"
Newton´s Principles break down that "inertial" fact. But, watch out!, that adjective means just that it is related to "inertia" ... Somebody could relate it to "an inertial system of reference", and try to convince us those reaction forces (f.e.) are only fictitious ...

Obviously what I wanted to point out is, light travels straight when there are no external factors. To bend light you need to do something and that translates to energy.
I've mentioned light, because it is not newtonian principles that makes it go straight. Moment of inertia is not mass preserving its velocity. The motion must have a different explanation. I believe it lies in the way electric and magnetic fields propagate. QM doesn't include these fields which are real, and combines newtonian physics with other properties that can't be expalained claasically resulted from experiments.
I aslo think that all particles in the Standard Model are similar to classical waves and not travelling as separate entities. For example if you make photons go orbiting arround each other you will create the illusion of a particle, but in fact there is an orbital wave that will travel in a spiral and making it slowing down proportionaly to the orbial radius.
If we can't measure to the deepest level what is going on the only option is to create different modes and put them to the test. Until now none has passed  all the tests. This discussion about centrifugal force could, in fact, give us some new clues.

Nilak said: Obviously what I wanted to point out is, light travels straight when there are no external factors. To bend light you need to do something and that translates to energy.
Jerry replied: That is not necessarily true. When light encounters a gravitational field gradient it may gain energy or lose energy. However to bend light no energy is required. You only need a gradient differential in momentum.  The light around the sun will absorb some  sub-photonic particle/waves circling around the sun and some emit straight line sub-photonic particle/waves. Thus there is a transfer of momentum but not energy.
Nilak said: I've mentioned light, because it is not newtonian principles that makes it go straight. Moment of inertia is not mass preserving its velocity. The motion must have a different explanation. I believe it lies in the way electric and magnetic fields propagate. QM doesn't include these fields which are real, and combines newtonian physics with other properties that can't be expalained claasically resulted from experiments.
Jerry replied:Yes, photons travel in a straight line by the geometric structure of the light wave. The photons in my opinion have two parts which attract each other. When on part is enlarging, the other part is shrinking. One reaches maximum radius and the other reaches a point. And the cycle continues. The result is that the pattern always forms a perfect straight line. Pure simple geometry. And because both halves exist in different small time dimensions, they can never destroy each other. But they can turn into mass which involves a spherical energy configuration.
Nilak said:I aslo think that all particles in the Standard Model are similar to classical waves and not travelling as separate entities. For example if you make photons go orbiting arround each other you will create the illusion of a particle, but in fact there is an orbital wave that will travel in a spiral and making it slowing down proportionaly to the orbial radius.
If we can't measure to the deepest level what is going on the only option is to create different modes and put them to the test. Until now none has passed  all the tests. This discussion about centrifugal force could, in fact, give us some new clues.
Jerry replied: I am certainly learning a lot from it. I see certain possibilities but the various answers may only be partial components of the centrifugal force. But to maintain Newton, it must be an equal and opposite force. Yet this force could have several components.  When we swing the rock on a rope, something is pulling against us. And at the moment the best I can think of is the rock is interacting with its own gravitational field. Yet that may only be a partial solution and the rock may be interacting with the gravitational field of the Earth which is a stronger field. What happens aboard a spaceship where the Earth’s field is low?

[rmolnav]

#119 Nilak
What you quoted is not what I mainly wanted to show from what  linked, which is just before:
"According to Newton's third law of motion, for every action there is an equal and opposite reaction. The centripetal force, the action, is balanced by a reaction force, the centrifugal ("center-fleeing") force. The two forces are equal in magnitude and opposite in direction. The centrifugal force does not act on the body in motion; the only force acting on the body in motion is the centripetal force. THE CENTRIFUGAL FORCE ACTS ON THE SOURCE OF THE CENTRIPETAL FORCE to displace it radially from the center of the path. Thus, in twirling a mass on a string, the centripetal force transmitted by the string pulls in on the mass to keep it in its circular path, while the centrifugal force transmitted by the string pulls outward on its point of attachment at the center of the path".
But you talk of two forces acting on same unique rotating object: centripetal f., and an inertial f. which you, and many others, consider to be the centrifugal f.
As I have said many times, that is NOT the REAL centrifugal force, which comes from 3rd Newton´s Principle, as a reaction to centripetal f., and should not be considered acting on the very rotating object ...
That´s why many people say centrifugal f. is just apparent, fictitious ... And it originates an unbelievable confusion out there !!

[nilak]

Jerry replied: That is not necessarily true. When light encounters a gravitational field gradient it may gain energy or lose energy. However to bend light no energy is required.

You are right, no energy is required.
When light is curved under a gravitational field, we can still say it travels straight. The space itself is dynamically modifying its geometry.
Since the gravity is not a force, in this context it means the centrifugal force does not exist in planetary system under gravity.

The problem is, we don't have a theory of everything and we keep crossing between newtonian mechanics and GR.

[jerrygg38 (OP)]

Jerry replied: That is not necessarily true. When light encounters a gravitational field gradient it may gain energy or lose energy. However to bend light no energy is required.

You are right, no energy is required.
When light is curved under a gravitational field, we can still say it travels straight. The space itself is dynamically modifying its geometry.
Since the gravity is not a force, in this context it means the centrifugal force does not exist in planetary system under gravity.

The problem is, we don't have a theory of everything and we keep crossing between newtonian mechanics and GR.

Nilak said: You are right, no energy is required.
When light is curved under a gravitational field, we can still say it travels straight. The space itself is dynamically modifying its geometry.
Jerry replied: To say that space itself is modifying its geometry  presents something mysterious called space. All we know is that the photon is traveling along a gravitational field that changes the vector angle of the light without changing its energy level. What happened? The intensity of the gravitational field is stronger toward the sun and weaker away from the sun. The stronger side will gain energy and the weaker side will lose energy. The net gain and loss will be zero. This will cause the photon vector to change and the light will bend around the sun. Once you leave the strong gravitational field of the sun, the photonic vector will equalize and the photon will continue on a straight line. No strange space is required, just simple Newtonian type physics.
Nilak said: Since the gravity is not a force, in this context it means the centrifugal force does not exist in planetary system under gravity.
Jerry replied: Just as the photon will bend due to differential gravity, the Earth will  curve around the sun. So the mechanism for planetary orbits is that the momentum of the earth has a twist in it due to the gravitational field differential. It is just a classical physics problem with Einsteinian velocity corrections.
   You may be correct in saying that this is not a regular centrifugal force problem because scientists have not considered the twist of objects moving in a gravitational field. There is no such thing as a object moving in a straight line forever. An object will always curve due to the gravitational field gradient.
Nilak said:The problem is, we don't have a theory of everything and we keep crossing between newtonian mechanics and GR.
Jerry replied: Newtonian mechanics is good engineering analysis. GR is a mathematicians analysis. Both are good but as an Engineer I want to know what is happening and GR does not explain the twist of objects moving in a gravitational field. GR mathematically stays that space is curved but that is false. The gravitational field causes space to appear curved. So Einstein is mathematically correct but from a nuts and bolts engineering understanding Einstein does not explain what is happening.

[nilak]

Nilak said: You are right, no energy is required.
When light is curved under a gravitational field, we can still say it travels straight. The space itself is dynamically modifying its geometry.
Jerry replied: To say that space itself is modifying its geometry  presents something mysterious called space. All we know is that the photon is traveling along a gravitational field that changes the vector angle of the light without changing its energy level. What happened? The intensity of the gravitational field is stronger toward the sun and weaker away from the sun. The stronger side will gain energy and the weaker side will lose energy. The net gain and loss will be zero. This will cause the photon vector to change and the light will bend around the sun. Once you leave the strong gravitational field of the sun, the photonic vector will equalize and the photon will continue on a straight line. No strange space is required, just simple Newtonian type physics.
Nilak said: Since the gravity is not a force, in this context it means the centrifugal force does not exist in planetary system under gravity.
Jerry replied: Just as the photon will bend due to differential gravity, the Earth will  curve around the sun. So the mechanism for planetary orbits is that the momentum of the earth has a twist in it due to the gravitational field differential. It is just a classical physics problem with Einsteinian velocity corrections.
   You may be correct in saying that this is not a regular centrifugal force problem because scientists have not considered the twist of objects moving in a gravitational field. There is no such thing as a object moving in a straight line forever. An object will always curve due to the gravitational field gradient.
Nilak said:The problem is, we don't have a theory of everything and we keep crossing between newtonian mechanics and GR.
Jerry replied: Newtonian mechanics is good engineering analysis. GR is a mathematicians analysis. Both are good but as an Engineer I want to know what is happening and GR does not explain the twist of objects moving in a gravitational field. GR mathematically stays that space is curved but that is false. The gravitational field causes space to appear curved. So Einstein is mathematically correct but from a nuts and bolts engineering understanding Einstein does not explain what is happening.

Space is something misterious but GR amost solved the mistery.
Curved spacetime is equivalent to space that is changing geometry in time. I prefer to present it first time like a changing geometry in time rather spacetime block.  After visualizing this space vs. time concept, you can go interpret spacetime concept.
Light can travel in a space that is changing geometry but cannot travel in spacetime. In spacetime light is a static single 4d picture. If you ommit z axis, and use a 2d +1t spacetime you get a block 3d spacetime. Nothing moves there because time is already included.
An object  following a geodesic line is misleading.

In our universe there is nothing moving in a perfect straight line of course. However in a hypothetical scenario a beam o light in a static space will move in a straight line. The static space can have different energy densities, but light will still go straight if the geometry of space is fixed. Notice I used the notion of space not spacetime. If you use spacetime, then you know what happens to the space over time.

Newtonian mechanics cannot be used for explaining reality at a fundamental level. The closest thing to fundamental level is GR and Einstein equations.
To solve fundamental problems we can use GR and perhaps make some speculations. But in my opinion newtonian mechanics is obsolete for solving problems at a fundamental level.

[jerrygg38 (OP)]

Nilak said: In our universe there is nothing moving in a perfect straight line of course. However in a hypothetical scenario a beam o light in a static space will move in a straight line. The static space can have different energy densities, but light will still go straight if the geometry of space is fixed. Notice I used the notion of space not spacetime. If you use spacetime, then you know what happens to the space over time.
Jerry replied: You have interesting points in your understanding of Einsteinian space time. It makes for a very complex universe that few can understand.  I believe that the universe is a much more simple place that many, many people can readily understand.
   You say that light will go straight in the geometry of space is fixed.  When I look at a photon traveling through a parallel to a fixed gravitational field, if we look inside the photon we will find (in my opinion) that the energy density is higher on the side facing the stronger gravitational field. Thus the photon may maintain the same total energy but it has more energy on the side facing the stronger field. In effect there was an energy shift within the photon itself and the photon will curve.
  For our universe with the center of the gravitational field at the big bang, the light will curve around the universe. Thus fancy space time is not necessary to explain the universe.
  Classical theory with added Einsteinian velocity corrections and elements of string theory small dimensions plus the strange quantum mechanical effects produce a universe from an engineering perspective. Then the question becomes if the universe is an engineering marvel or a mathematical puzzle. Both are possible  but I like the former.

[nilak]

Actually light cannot move in a static space beacause it automatically changes the geometry of space as it travels but you can imagine a static homogeneous infinite space before you release a EM wave, which will go straight.
All I want to say is that deviation of light occurs only where and while space changes geometry. Of course if you treat the photon quantum mechanically things get a bit messed up but again the probability to go straight is the highest.

[nilak]

By newtonian mechanics, an object that travels in a gravitational filed gains kinetic energy and loses potential energy, hence no energy input. But in there is no gravitational field the object goes straight. If you magically introduce a large object with mass that createa a gravitational filed, the object will deviate from a straight line. The introduction of the massive object means introducing energy into the system. This means the object genuinely travels straight. To deviate it you need energy.
If the massive object was already present the deviation was already in progress hence no energy transfer.
That is the difference.

[jerrygg38 (OP)]

Nilak said: Actually light cannot move in a static space beacause it automatically changes the geometry of space as it travels but you can imagine a static homogeneous infinite space before you release a EM wave, which will go straight.
All I want to say is that deviation of light occurs only where and while space changes geometry. Of course if you treat the photon quantum mechanically things get a bit messed up but again the probability to go straight is the highest.
Jerry replied: The question is “To be or not to be”. Does space really exist? Is space something? Somehow magical space does something. If space does not exist and only the electromagnetic fields and the gravitational field exists, plus dark matter and low energy  dark energy photons, then we have to define how things operate in terms of these things. That leads us to classical engineering  type problems and solutions.  So we can look at the universe in terms of properties of space and time or in terms of the stuff within space. We then have two choices, a mathematical solution defined by the properties of space and time and an engineering solution where we seek to understand what is happening within the stuff within space.
  So for the mathematical solution you say that light cannot move in static space because it changes the geometry of space as it travels.  At first these words were strange to me but as I dwell on them for the mathematical solution a light wave must react with space in order to survive. Ok that makes sense for the case where space is something.
Nilak says” By newtonian mechanics, an object that travels in a gravitational filed gains kinetic energy and loses potential energy, hence no energy input. But in there is no gravitational field the object goes straight. If you magically introduce a large object with mass that creates  a gravitational filed, the object will deviate from a straight line. The introduction of the massive object means introducing energy into the system. This means the object genuinely travels straight. To deviate it you need energy.
If the massive object was already present the deviation was already in progress hence no energy transfer.
That is the difference.
Jerry says: There are two possibilities. An object can have its own gravitational field that travels with it or space creates the gravitational field. If an object has its own gravitational field then this field is 13.78 billion light years in size.  Thus what we see in a particle is a focal point of what it is. An alternative is that a particle interacts with the dark energy photonic field to create the gravitational field. In either case space has no properties. Other alternatives is that the various fields are physically separated from each other by tiny differences in time. Thus the positive and negative electric fields never coexist.
  We then have many possibilities from space is nothing to space is everything. Photons can interact with space or photons can be independent of space. Another possibility is that space is merely a different state of the gravitational field. We say that the gravitational field has  deviation in intensity and thus a direction. Yet it is possible for the field to be neutral. Thus the gravitational field can be looked upon as clay that can be molded and twisted into interesting shapes. There are many interesting possibilities for sure.

[nilak]

Nilak said: Actually light cannot move in a static space beacause it automatically changes the geometry of space as it travels but you can imagine a static homogeneous infinite space before you release a EM wave, which will go straight.
All I want to say is that deviation of light occurs only where and while space changes geometry. Of course if you treat the photon quantum mechanically things get a bit messed up but again the probability to go straight is the highest.
Jerry replied: The question is “To be or not to be”. Does space really exist? Is space something? Somehow magical space does something. If space does not exist and only the electromagnetic fields and the gravitational field exists, plus dark matter and low energy  dark energy photons, then we have to define how things operate in terms of these things. That leads us to classical engineering  type problems and solutions.  So we can look at the universe in terms of properties of space and time or in terms of the stuff within space. We then have two choices, a mathematical solution defined by the properties of space and time and an engineering solution where we seek to understand what is happening within the stuff within space.
  So for the mathematical solution you say that light cannot move in static space because it changes the geometry of space as it travels.  At first these words were strange to me but as I dwell on them for the mathematical solution a light wave must react with space in order to survive. Ok that makes sense for the case where space is something.
Nilak says” By newtonian mechanics, an object that travels in a gravitational filed gains kinetic energy and loses potential energy, hence no energy input. But in there is no gravitational field the object goes straight. If you magically introduce a large object with mass that creates  a gravitational filed, the object will deviate from a straight line. The introduction of the massive object means introducing energy into the system. This means the object genuinely travels straight. To deviate it you need energy.
If the massive object was already present the deviation was already in progress hence no energy transfer.
That is the difference.
Jerry says: There are two possibilities. An object can have its own gravitational field that travels with it or space creates the gravitational field. If an object has its own gravitational field then this field is 13.78 billion light years in size.  Thus what we see in a particle is a focal point of what it is. An alternative is that a particle interacts with the dark energy photonic field to create the gravitational field. In either case space has no properties. Other alternatives is that the various fields are physically separated from each other by tiny differences in time. Thus the positive and negative electric fields never coexist.
  We then have many possibilities from space is nothing to space is everything. Photons can interact with space or photons can be independent of space. Another possibility is that space is merely a different state of the gravitational field. We say that the gravitational field has  deviation in intensity and thus a direction. Yet it is possible for the field to be neutral. Thus the gravitational field can be looked upon as clay that can be molded and twisted into interesting shapes. There are many interesting possibilities for sure.

Yes, I agree. Space as everything is an alternative but not necessarily the best one, it just, for me makes more sense.

[rmolnav]

Let us go BACK TO BASICS.
We don´t know what the root essence of gravity, and space, actually is.
But for most of our practical applications Newton´s theories are sufficient.
Following them, and as far as I can understand, if an object with a mass A is in a certain point of space (in an instant of time), it WOULD exert a gravitational pull on another object with mass B IF the second WERE placed in another point, directly proportional to both masses A and B, and inversely to the square of their separation.
Then somebody thought it could be mathematically useful a tool such as vector field, now gravitational field of A, formed by all vectors representing the pulls that A WOULD exert on objects of a unit of mass, IF they WERE situated in every point around A.
Those capital letters are there to put emphasis on the fact that gravitational field is actually an abstraction, not a physical reality. In the infinite number of points around A where no massive object in considered instant, the field has only a “potential” reality.
If A changed position, ALL pull vectors would change accordingly, in value and direction (only in value where in line with both positions of A). Initial gravitational field of A, not being something real but just an abstraction, “dies” same moment when mass A changes position.
To consider a gravitational field is something real, can drive people to say nonsenses, such what has often been said here.
E.g. "Another possibility is that space is merely a different state of the gravitational field ..."
That is similar to saying that my face could be a different state of the image I see when looking at a mirror ...

[jerrygg38 (OP)]

Nilak said: Yes, I agree. Space as everything is an alternative but not necessarily the best one, it just, for me makes more sense.
Jerry replied: The only thing that appears correct to me is that space is not a checkerboard upon which the universe exists. That is only a measurement. This means that at big bang or maximum compression, the universe existed within a much smaller volume. Outside that volume was nothing at all. Thus space itself has no properties but only possibilities.
  Now we compress what you call space. Okay that is good. But what did we really compress? I believe it is the gravitational field that we compressed. At that time this field is the substance of everything. It is amorphous. It can produce mass. It can produce the gravitational field that we measure. It can produce the two electric fields of positive and negative. It can produce the tiny time dimensions (alternatively the positive dimension and the negative dimension.
  Thus the electric fields and the associated magnetic fields are derived from the amorphous gravitational fields. Mass is merely the compressed amorphous gravitational field.
  To make sense of things I need a positive dimension and a negative dimension. Alternately these could be considered tiny time dimensions. So the string theory scientists have conceived of many tiny dimensions. The amorphous gravitational field when compressed can produce many of these dimensions.
  The only thing that bothers me about Einstein’s work is the lack of a differential mass in the forward and rearward directions. And we always have the possibility that mass/energy is slowly radiating into the world of dark energy. This would cause the universe to expand and the back pressure would be gravity.
  Thus many possibilities exist. Einstein’s work provide us with the binding energy of the hydrogen atom as the differential energy of the electron in the first Bohr orbit. His equations provide us with the energy level or the neutrino as the electron is crushed toward the proton. Thus his mathematics is the basis of the big world of the universe and the tiny world of the atom.
   I have been studying this since 1981 as a hobby and I see many possibilities. It is an interesting puzzle.

[jerrygg38 (OP)]

Rmolnav said: Let us go BACK TO BASICS.
Those capital letters are there to put emphasis on the fact that gravitational field is actually an abstraction, not a physical reality. In the infinite number of points around A where no massive object in considered instant, the field has only a “potential” reality.
If A changed position, ALL pull vectors would change accordingly, in value and direction (only in value where in line with both positions of A). Initial gravitational field of A, not being something real but just an abstraction, “dies” same moment when mass A changes position.
Jerry replied: For any electrical type phenomenon there is a transient solution. The movement of a stationary mass at point A to point B causes the gravitational field to shift. In general there will be a time delay while the shift is taken place. Since the field reaches quite far out, the transient will take quite a long time to settle. In general the field from the mass around point A combines with other fields from nearby masses so it is difficult to find the individual field. However as we see from the gravitational field sensors, we can pick up the field of rotating black holes very far away. Since we can measure such things, the gravitational field is a reality and not an abstraction.
Rmolnav said: E.g. "Another possibility is that space is merely a different state of the gravitational field ..."That is similar to saying that my face could be a different state of the image I see when looking at a mirror ...
Jerry replied: In my prior write up I used the term amorphous gravitational field. So I believe that you are correct. If we compress this field, we get mass and the ordinary gravitational field which I call a bipolar field and the positive and negative electric fields.

[rmolnav]

#133 jerrygg38
Firstly, I was referring to gravitational fields, not electrical type phenomena. And within Newton´s Mechanics, which, according to all I´ve read so far, is sufficiently accurate for most of let us say "normal" cases ...
And I find very surprising that somebody who said here (#12):
"... you say General Relativity causes space time to curve. How can general relativity cause space time to curve? Why? This makes no sense. Somehow there is a Sky God called "general relativity" that causes planets and photons, etc. to move in curved paths. This is pure magic and very unscientific for sure. The mathematicians may be happy so say such things but as an Engineer I do not believe it"
NOW finds that:
"...we can pick up the field of rotating black holes very far away. Since we can measure such things, the gravitational field is a reality and not an abstraction".
What detected by LIGO were the so called gravitational waves, considered to be fluctuations in the curvature of spacetime which propagates as waves, traveling outward from the source. Predicted by Einstein's theory of general relativity, the waves transport energy known as gravitational radiation. Sources of gravitational waves include binary star systems composed of white dwarfs, neutron stars, or black holes. Other much less massive objects, as our sun, could also be a source, but they would be too tiny to be detected.
Do you choose from relativity theory only what seems to match your bizarre ideas?
Do you really think that even a toddler, when he finds difficult to accelerate a little bit, it is because when he reaches another position he continues being gravitationally attracted by “himself" situated at his initial position ??… That would mean that gravitons, or whatever actually “transmitting" gravity, are slower than the toddler !!!
You know, somewhere I read the transmission of gravity has same velocity as light. They had found that measuring delays of sun and moon related earth tides … It could not be not so much, but slower than a toddler

[jerrygg38 (OP)]

Rmolnav said: What detected by LIGO were the so called gravitational waves, considered to be fluctuations in the curvature of spacetime which propagates as waves, traveling outward from the source. Predicted by Einstein's theory of general relativity, the waves transport energy known as gravitational radiation. Sources of gravitational waves include binary star systems composed of white dwarfs, neutron stars, or black holes. Other much less massive objects, as our sun, could also be a source, but they would be too tiny to be detected.
Jerrygg38 replied: The question is what is the curvature of space time? To me it is the concentration of the gravitational field. Thus the intensity of the field is greater at the point of curvature. So it is the field that is curved. Another possibility is that the curvature of Einsteinian space time means that the gravitational constant G is a variable. Of course over time a variable G will help the universe to oscillate from min to max to min again.
Rmolnav said: Do you choose from relativity theory only what seems to match your bizarre ideas?
Jerrygg replied: I seek to understand the physical meaning of what the theory predicts.  To use the term space time does not tell us what is happening from a physical viewpoint.
Rmolnav said: Do you really think that even a toddler, when he finds difficult to accelerate a little bit, it is because when he reaches another position he continues being gravitationally attracted by “himself" situated at his initial position ??… That would mean that gravitons, or whatever actually “transmitting" gravity, are slower than the toddler !!!
Jerry replied: It is all happening at the speed of light so the initial position fades away quite rapidly and we get an interaction between the present position and the prior position of a split second ago.

[rmolnav]

#135 jerrygg38
I must say I find your last post more let us say reasonable than others. Perhaps the problem is that you are trying something kind of impossible.
You say:
"To use the term space time does not tell us what is happening from a physical viewpoint"
I fully agree with you. But you know,  I´ll never forget (long ago) my best teacher of Maths at the University, late Julio Fernández Biarge (google it and you´ll see ...), telling us something like:
In a plane, a two dimension space, if the addition of the squares of two variables has to keep constant, all we know all points satisfying that condition make a circumference ...
If in our three dimension space, the same has to happen with three variables ... a sphere (very "similar" to a circumference)
We can extrapolate that to a four dimension "imaginary" (not sure whether he used that word), with the addition of the squares of four variables having to keep constant. We could call that "abstract" object a four dimension sphere (a hypersphere in a four dimension space? ) ...
But please, DON´T TRY TO IMAGING AND "SEE" IT IN YOUR MINDS, EVEN AS SOMETHING SOMEHOW SIMILAR TO THE "NORMAL" THREE DIMENSION SPHERE. IT WOULD BE REALLY FRUSTRATING ... 

[puppypower]

Centrifugal force appears anytime something rotates or revolves around an axis. Therefore, centrifugal force has a connection to angular momentum. Since centrifugal force does not appear during linear motion, but only starts to appear if the path shows the slightest curvature, suggests that linear momentum is a ground state that gains potential when centrifugal force appears.

If we look at GR and the curving of space-time, since paths in space-time are no longer linear, GR adds centrifugal force because space-time deviates from the ground state of linear motion, where there is no curvature; of space-time. The expansion of the universe is causing universal gravity to curve space-time less and less; space-time expands while mass remains constant. This action is removing centrifugal force potential, back toward the linear momentum ground state. The loss of centrifugal force, with energy conserved, equals an accelerated expansion.

[rmolnav]

#136 (Continuation)

I consider that the problem is not in the "use of the term space-time" but in how they try to explain us its curvature and its relation to gravitational atraction.

E.g. there are typical analogies such as:

"main-qimg-65276e2942c653d621e0bd0ac1d665ef

… the presence of body/mass bends the space around it forming a curvature, formation of gravitational well … space time gets bent around Earth and moon revolving around it.

...a free body falls in this gravitational well ... for a body in order to save itself from falling into this well , the body should revolve around planet into circular path. Certain tangential velocity v should be maintained by the body and a is the gravitational acceleration with which it is falling (?) into the well".

They show the bending of a two dimension "space" by our Earth, considering it similar to what theoretically happens to the four dimension space-time.

So far so good. But they introduce our Moon, and, as "a free falling body falls in this gravitational well" ... they say that is the gravitational attraction from Earth …

I must say that is just for naive people. To explain Earth gravity (by an analogy) they consider the Moon, if not rotating, would fall into the well, thanks to what we could call “radial inclination” of the bent surface … But that slope drives things “downward” ONLY if there is some other massive object below, another Earth or similar massive object !!!

[nilak]

If we look at atoms inside a rotating object, the sum of these atoms orbital momentum gives the total orbital momentum of the object. If the atoms have their own angular momentum(from rotating around their own axis) it doesn't influence the orbital momentum of the object. So it is clear that centrifugal force appears  when you try to change direction of motion and the same kind of force oposes acceleration.
The atom  or any mass particle angular momentum must work the same way, as summation of orbital momentum of the internal  components.
Bosons shouldn't have angular momentum, only spin.