What does superconductivity or resistance have to do with it?
There are still electrons, with an electric field, moving in the superconducting wire, causing the magnetic field.

Conventional superconductivity is a special QM case where the electrons are coupled into a singular state. The electron fluid cannot be resolved into individual electrons. It's not just a perfect conductor.

The electromagnetic force (field) is fundamental, separate electric and/or magnetic fields are the physical/mathematical manifestation we use. Superconductivity and resistance transform the EM force into the fields we use to describe interactions.
It's still the EM force, just expressed as magnetic energy using the electromagnetic force between the charge of electrons.
https://en.wikipedia.org/wiki/Electromagnetic_field#Static_E_and_M_fields_and_static_EM_fields

 

A electronics based Application Note about Gravity.
https://www.nxp.com/files-static/sensors/doc/app_note/AN3151.pdf

Detecting Freefall with Low-G Accelerometers

With an Accelerometer, gravity is simply a static acceleration.

 

But what 'forces' the apple to rush to earth in Curved Space Time (ST)...??

Does curved ST fabric 'forces' EVERYTHING to ALWAYS keep moving on straight paths in curved space time..???

An object in free-fall has no net forces and will follow a geodesic path through spacetime. This is the equivalent of a straight line in flat 3D space. If the Earth were not there, the apple would keep following this path. But the Earth is there, following its own geodesic;. Intuitively, we can say that the Earth gets "in the way" of the apple -- once the apple hits the ground, it experiences a normal force and is no longer in free-fall and no long following its free-fall geodesic.

 

An object in free-fall has no net forces and will follow a geodesic path through spacetime. This is the equivalent of a straight line in flat 3D space. If the Earth were not there, the apple would keep following this path. But the Earth is there, following its own geodesic;. Intuitively, we can say that the Earth gets "in the way" of the apple -- once the apple hits the ground, it experiences a normal force and is no longer in free-fall and no long following its free-fall geodesic.

Yes, that part I can somehow follow...!!!

But my question is that there can be two cases in Newtonian Physics for instance... A body in motion and A body at rest...!!

So when apple is dropped (rather released with zero initial velocity), Apple's first desire is to maintain its state of REST (Zero initial velocity)... It just doesnt want to move...!! But then Earth 'grabs' on the Apple and FORCES it to start moving...!! If we sample time into smaller and smaller segments, we will see that Apple at every instance of time, wants to maintain its previous state (of Rest or Motion) but earth somehow 'grabs' it and keeps pulling it down...!! So relative to earth, the apple seems accelerating downwards... Changes its state from REST to Motion...!!

But how does this description fit curved space time, which says that Apple doesnt accelerate... Hence it doesnt change its state of motion... As per our original assumption, Apple's initial state was REST (Zero Initial Velocity)....!! So how does the Apple come to motion as per Einstein...!! Or is it that the Apple never comes into motion, rather its the earth that moves up and bumps into the Apple (Like the space ship did...???)

 

The electromagnetic force (field) is fundamental, separate electric and/or magnetic fields are the physical/mathematical manifestation we use.

Exactly. The electromagnetic field is the physical "thing", an invariant that we can measure and do things with. The notion of distinct electric and magnetic fields are derived abstractions of convenience. Sometimes it's easier to analyze things strictly in terms of electric effects or magnetic effects, but the underlying thing is always the EM field.

 

But my question is that there can be two cases in Newtonian Physics for instance... A body in motion and A body at rest...!!

Newtonian mechanics assumes an absolute rest frame, from which one can say that an object is indeed at rest or in motion. With his special theory of relativity, Einstein showed that there is no preferred frame. For any object, one can always choose coordinates in which the object has any velocity whatsoever, including 0.

So when apple is dropped (rather released with zero initial velocity), Apple's first desire is to maintain its state of REST (Zero initial velocity)...

At rest with respect to what? With respect to the Sun, the apple is never at rest, neither when it is in your hand, nor when it is falling, nor when it's on the floor. With respect to the Earth, the apple is at rest at all times except when it is falling. Since both characterizations are equally valid, we need a coordinate-independent way to describe the physics. That's where GR and the metric tensor come in.

The salient point, however, is that you can't just assume that the apple (or anything else) is at rest or in motion. And if you work out the coordinate-independent geometry, you'll find like Einstein did that objects in free-fall follow geodesics through spacetime. Remember, physics cannot answer why the universe behaves as it does, it can only attempt to explain how it behaves.

 

I would think a stationary electron would have an electric field only, not an EM field.

 

Newtonian mechanics assumes an absolute rest frame, from which one can say that an object is indeed at rest or in motion. With his special theory of relativity, Einstein showed that there is no preferred frame. For any object, one can always choose coordinates in which the object has any velocity whatsoever, including 0.


At rest with respect to what? With respect to the Sun, the apple is never at rest, neither when it is in your hand, nor when it is falling, nor when it's on the floor. With respect to the Earth, the apple is at rest at all times except when it is falling. Since both characterizations are equally valid, we need a coordinate-independent way to describe the physics. That's where GR and the metric tensor come in.

The salient point, however, is that you can't just assume that the apple (or anything else) is at rest or in motion. And if you work out the coordinate-independent geometry, you'll find like Einstein did that objects in free-fall follow geodesics through spacetime. Remember, physics cannot answer why the universe behaves as it does, it can only attempt to explain how it behaves.

Lets say the Apple was in the middle of nowhere in some place in universe...!! There is no matter around to curve space time (or pull the apple)... And WRT to me standing very very far away, it was at rest....

Now suddenly a planet appears from nowhere in the vicinity of the apple...!!

So in this situation, Newtonian Apple wud immediately change its state of REST w.r.t me and rush to meet the planet...!! And we wud say that the Planet pulled the apple towards it...!!

But in Einstein's situation, wud the curvature caused by the planet become a reason for the apple to start falling freely along the geodesic, w.r.t to me, and ultimately crash into the surface of the planet....?? And if this wud happen, then the question is what caused the apple to start moving w.r.t me...!!

From my perspective, I will see the apple change its state of motion - or wouldnt I...?? Initially at rest w.r.t me standing far away, when there was no planet and then suddenly rushing toward the planet when it appeared...!!

 

Now suddenly a planet appears from nowhere in the vicinity of the apple...!!

Now that's a realistic setup to a thought experiment.

 

I would think a stationary electron would have an electric field only, not an EM field.

Even a "stationary" electron would still have a magnetic component, as it has spin (which interact with electromagnetic fields like a magnetic moment). This is called the "Bohr Magneton." It has an inherent angular momentum, so even if it's stationary, it has the inherent property of a magnetic moment.

 

bogosort said:-

‘If you didn't realize you were on a ship -- there were no windows and the capsule is sound- and vibration-proof -- you would have no way of determining whether you and the apple were feeling gravity or the normal force of an accelerating vessel.’

That is exactly what I am saying; one force is due to the acceleration of the vessel, the other is due to the force of gravity on earth. The OP is claiming that gravity is not a force, but this example shows that it is.

 

bogosort said:-

‘If you didn't realize you were on a ship -- there were no windows and the capsule is sound- and vibration-proof -- you would have no way of determining whether you and the apple were feeling gravity or the normal force of an accelerating vessel.’

That is exactly what I am saying; one force is due to the acceleration of the vessel, the other is due to the force of gravity on earth. The OP is claiming that gravity is not a force, but this example shows that it is.

Acceleration is NOT gravity. Einstein equivalence principle doesn't say they are physically the same so the force of gravity on earth has its own physical cause.

If you look at only a very small region of spacetime, then the laws of physics are those of special relativity. In other words, spacetime looks flat; if spacetime is flat, then there is no gravity, since gravity is curved spacetime. Therefore it is impossible to detect any gravitational field by performing local measurements.

https://aether.lbl.gov/www/science/equiv.html

 

In both cases (the rocket engines providing thrust, a force on the rocket and gravity providing force on the apple) a force is causing the apple to accelerate, due to Force = Mass x Acceleration.

The rocket engines are providing the force in one situation and gravity in the other.

 

In both cases (the rocket engines providing thrust, a force on the rocket and gravity providing force on the apple) a force is causing the apple to accelerate, due to Force = Mass x Acceleration.

The rocket engines are providing the force in one situation and gravity in the other.

You are addressing something not in dispute. This is irreverent to the explanation of Gravity in the context of spacetime.

https://www.einstein-online.info/en/spotlight/geometry_force/

So what is gravity, in Einstein’s universe? Generally speaking, any distortion of spacetime geometry. More precisely, there are two sides to gravity: In part, gravity is an observer artefact: it can be made to vanish by going into free fall. Most of the gravity that we experience here on earth when we see objects falling to the ground is of this type, which we might call “relative gravity”. The remainder of gravity, “intrinsic gravity”, if you will, manifests itself in tidal forces, and is associated with a specific property of geometry: The curvature of spacetime.

 

A mass experiencing constant acceleration not having some force applied, would break the fundamental laws of physics.

 

A mass experiencing constant acceleration not having some force applied, would break the fundamental laws of physics.

Newtonian gravity as a force is not wrong in the binary sense, it's just incomplete as an explanation of the physical universe. Gravity, in Einstein’s universe, is a super-set of Newtonian gravity, so the vast majority of though experiments that would break the fundamental laws of physics break under both systems.

 

Now suddenly a planet appears from nowhere in the vicinity of the apple...!!

Now that's a realistic setup to a thought experiment.

Sorry, I just picked up this 'planet's appearance' thing from the video, just to emphasize the two situations - one being at rest w.r.t to a distant observer and other changing the state from rest to motion, in a 'gravitating' environment... I am eager to know what effect caused the apple to start moving relative to the stationery distant observer...!! Newton's case is clear - He wud say, the Planet 'pulled' it...

Surely, I am not sure if it was right or sensible to use (or extend) that analogy to the apple's case...!! ...!!!

Regards,
Rahul

 

I would think a stationary electron would have an electric field only, not an EM field.

Stationary with respect to what? Let's say you choose the electron's rest frame to do your calculations, and you find that the magnetic field is zero. But I choose a frame in which the electron is moving; in my calculations, the magnetic field is nonzero. Which of us is right? Both of us! But the actual physics of the situation must be frame independent -- everyone has to agree, regardless of frame, or the universe is incosnsitent -- so our calculations must not be describing the physics of the situation.

If instead we had both calculated the electron's electromagnetic field, we'd arrive at equivalent answers.

 

Lets say the Apple was in the middle of nowhere in some place in universe...!! There is no matter around to curve space time (or pull the apple)... And WRT to me standing very very far away, it was at rest....

Even if the apple has zero velocity with respect to you, it is moving through spacetime (along the time coordinate). In any case, it won't be stationary in space for very long. To keep things simple, let's assume that you and the apple are the only things in the universe. Even if at some point the apple was spatially at rest with respect to your rest frame, both Newton and Einstein would agree that you and the apple would slowly begin to approach each other (though they would disagree on how long it would take).

Now suddenly a planet appears from nowhere in the vicinity of the apple...!!

Newton would say that the planet, being much closer and much larger than you, exerts a larger gravitational force and so causes the apple to change trajectories and head toward the planet. Einstein would say that the planet changed the geometry of spacetime, and so the apple followed a new geodesic. At all times, the apple was in free-fall.

It's important to understand that both theories of gravity predict the same motion (for low-gravity, low-speed events). Newtonian gravity was even used to predict black holes long before Einstein was born! In terms of apples, though, the big difference is that the Newtonian theory explains the apple's motion by way of an action-at-a-distance force, while Einstein's theory explains it geometrically, without any forces or interactions. But Einstein's theory explains more than Newton's, and does so in a frame-invariant way. I think people cling to the idea of gravity as a force because of familiarity and because the math is much simpler. It's also familiar and simple to treat electrons as tiny, charged billiard balls, but we need quantum mechanics if we want to really understand how the universe behaves.

 

That is exactly what I am saying; one force is due to the acceleration of the vessel, the other is due to the force of gravity on earth. The OP is claiming that gravity is not a force, but this example shows that it is.

You can't physically distinguish between the two scenarios. Suppose that Alice wakes up in a windowless, accelerating rocket ship far from any gravitational fields, and Bob wakes up on an identical rocket ship hovering over Jupiter. You claim that Alice can know that the normal force she feels is from acceleration, and that Bob can know that the normal force he feels is from gravity. But this isn't the case! There is no physical experiment that will tell them which ship they are in. So how can you claim definitively claim that two different "forces" are acting on the astronauts? You can't.

One approach around this connunudrum is to simply declare by fiat that the universe knows which is which, and that's enough. Bob is feeling the effects of a gravitational force, end of story. The problem with this is that if we try to calculate the physics of what's going on for each astronaut, we'll arrive at different answers depending on our choice of coordinates. To get consistent results, we need a frame-independent way to describe the situations. And when you work out all the details, like Einstein did, you end up with general relativity, i.e., a 4D spacetime geometry in which gravity is not some action-at-a-distance force but a characterization of how the distance between things changes with mass/energy.