Incredibly huge inconsistency of modern physics

[Reality Check]

First rule of General Relativity is that apparent forces aren't so apparent. Gravity is one of them ...

First rule of General Relativity is to learn General Relativity, TheAdversary . Gravity is a fictitious force in GR. This does not mean that there are no fictitious forces in GR.
ETA: I suspect that the forces exerted on Gravity Probe B when it detected frame-dragging would be called fictitious.

 

[Ziggurat]

The observation is that gravity looks exactly the same as the fictitious force that appears in an accelerated frame of reference. Hence, Gravity is a fictitious force!
That's what I meant when I said apparent forces are not so apparent; I can't think of anything less real than gravity.

Gravity is real. Even in general relativity. The fact that it's a fictitious force doesn't mean it's not real, it just means that it's something different than a force, namely, it's space-time curvature. And that curvature is very, very real.

 

[W.D.Clinger]

Yes. I mean Einstein's Elevator Thought Experiment. Where acceleration is indistinguishable from gravity and should be treated equally. That's the basic assumption of
General Relativity.

Acceleration is locally indistinguishable from gravity, but that doesn't necessarily mean it should be treated equally. Indeed, since gravity (in the form of curved spacetime) is distinguishable from acceleration when you drop the "local" restriction, there are circumstances in which general relativity effectively says acceleration should not be treated the same as gravity.

The observation is that gravity looks exactly the same as the fictitious force that appears in an accelerated frame of reference. Hence, Gravity is a fictitious force!
That's what I meant when I said apparent forces are not so apparent; I can't think of anything less real than gravity.

Curvature of spacetime is real, not fictitious. It's an observer-independent invariant of general relativity.

First rule of General Relativity is to learn General Relativity, TheAdversary . Gravity is a fictitious force in GR. .

As stated above, I tend to disagree with the highlighted.

 

[Reality Check]

Einstein just rolled over in his grave. Isn't it enough that you're rolling dice?

Einstein certainly would roll over in this grave at someone thinking fictitious forces is not a human concept.
Einstein was wrong about rolling dice: Does God play Dice? by Stephen Hawking

Thus it seems Einstein was doubly wrong when he said, God does not play dice. Not only does God definitely play dice, but He sometimes confuses us by throwing them where they can't be seen.

That looks like an older lecture by Hawking where he was wrong in stating that Bell's inequalities were confirmed by experiments - there was enough loopholes until lately to make the experiments inconclusive.

 

[Ziggurat]

'I don't know what you mean by that. Do you?'

Yes. I mean Einstein's Elevator Thought Experiment. Where acceleration is indistinguishable from gravity and should be treated equally. That's the basic assumption of
General Relativity.

A uniform gravitational field is indistinguishable from acceleration.

But real gravitational fields are not uniform. They can be close to uniform locally, but not globally. That's what makes the whole thing so tricky.

 

[W.D.Clinger]

That looks like an older lecture by Hawking where he was wrong in stating that Bell's inequalities were confirmed by experiments - there was enough loopholes until lately to make the experiments inconclusive.

Technical correction: Bell's inequality is violated by experiments, not confirmed.

That violation confirms quantum mechanics and repudiates EPR.

ETA: Einstein is the "E" in "EPR".

 

[Reality Check]

As stated above, I tend to disagree with the highlighted.

Following TheAdversary invalid usage of terms was bad, W.D.Clinger.!
I meant that the force of gravity emerges when we look at the path of objects in curved space-time, see that the paths are curved and assign a force to explain this acceleration.

 

[TheAdversary]

Yes, I meant that gravity is very real. The fictitious force that is very real.
Could you say that Newtonian Mechanics was unable to handle gravity as a fictitious force and that GR basically made the formulation of gravity as a fictitious force possible?
That it turns out to have non-newtonian qualities I would expect then.

 

[W.D.Clinger]

I meant that the force of gravity emerges when we look at the path of objects in curved space-time, see that the paths are curved and assign a force to explain this acceleration.

Another technical point:

In the absence of real forces, those world lines are geodesics, which means they're as straight as it is possible for any path within the spacetime manifold to be.

The world lines are interpreted as curved only when someone uses a pseudo-Euclidean local coordinate patch to describe them. The apparent curvature of geodesic world lines is therefore only apparent, an artifact of some arbitrary coordinate system. I'm sure that's what you meant by saying "the force of gravity emerges"; I'm just trying to draw attention to the role of arbitrary coordinate systems in the "when we look at the path of objects" part of your statement.

I like Ziggurat's way of putting it: "The fact that [gravity is] a fictitious force doesn't mean it's not real, it just means that it's something different than a force, namely, it's space-time curvature. And that curvature is very, very real."

 

[Darwin123]

I'm not exactly sure what you're asking, but...

General relativity rejects absolute frames of reference.

In Newtonian mechanics, you may have fictitious forces related to gravity and acceleration. In GR, that distinction between real and fictitious forces dissolves rather neatly into a distinction between coordinate-independent (invariant) facts and coordinate-dependent artifacts.

I don’t think that is true. The difference between a real and a fictitious force does not 'dissolve'. Fictitious forces occur when there is a real force of interaction acting on the observer. If the hypothetic observer is in an inertial or free falling frame, then the observer can't observe a fictitious force.

The thrust of a rocket generates a 'proper acceleration' on the spaceman inside. The thrust is a very real force as seen from an inertial frame. This proper acceleration is breaks the symmetry in the so called twin paradox.

Force in relativity impacts reality through proper acceleration. Proper acceleration affects the world line of an observer. In fact, the concept of proper acceleration is necessary to resolve many conundrums in relativity, including the so called twin paradox.

Here is a link on 'proper acceleration'.

https://en.wikipedia.org/wiki/Proper_acceleration
‘In relativity theory, proper acceleration[1] is the physical acceleration (i.e., measurable acceleration as by an accelerometer) experienced by an object. It is thus acceleration relative to a free-fall, or inertial, observer who is momentarily at rest relative to the object being measured. Gravitation therefore does not cause proper acceleration, since gravity acts upon the inertial observer that any proper acceleration must depart from (accelerate from). A corollary is that all inertial observers always have a proper acceleration of zero.
…
n situations in which gravitation is absent but the chosen coordinate system is not inertial, but is accelerated with the observer (such as the accelerated reference frame of an accelerating rocket, or a frame fixed upon objects in a centrifuge), then g-forces and corresponding proper accelerations felt by observers in these coordinate systems are caused by the mechanical forces which resist their weight in such systems. This weight, in turn, is produced by fictitious forces or "inertial forces" which appear in all such accelerated coordinate systems, in a manner somewhat like the weight produced by the "force of gravity" in systems where objects are fixed in space with regard to the gravitating body (as on the surface of the Earth).’


The perception that there are no forces in relativity is one of the favorite factoids of the woo woos. Forces are very important in relativity.

Special relativity requires the concept of force just to distinguish inertial frames from accelerating frames. In order to determine whether a reference frame is an inertial frame, one has to demonstrate that the observer associated with that inertial frame has a zero value for proper acceleration. You can’t just assume that a reference frame is inertial.

 

[W.D.Clinger]

I can't think of anything less real than gravity.

I meant that gravity is very real.

 

[W.D.Clinger]

Special relativity requires the concept of force just to distinguish inertial frames from accelerating frames. ...snip... You can’t just assume that a reference frame is inertial.

In GR, which has been the context of this recent discussion, you can't even assume the SR notion of inertial reference frames makes sense.

 

[TheAdversary]

'Special relativity requires the concept of force just to distinguish inertial frames from accelerating frames.
In order to determine whether a reference frame is an inertial frame, one has to demonstrate that the observer associated with that inertial frame has a zero value
for proper acceleration. You can’t just assume that a reference frame is inertial.'

The velocity of a reference frame cannot be obtained by experiments inside of a box without looking outside; The laws of physics look the same. But acceleration can always
be detected by noticing a new force that starts acting; Pushing you in your seat. This is no different in SR I see and I don't think it's any different in GR.
This is what I wanted to know.

 

[TheAdversary]

'I can't think of anything less real than gravity.'

That should be I can't think of anything more real than gravity. I'm tired.

 

[Darwin123]

The observation is that gravity looks exactly the same as the fictitious force that appears in an accelerated frame of reference. Hence, Gravity is a fictitious force!
That's what I meant when I said apparent forces are not so apparent; I can't think of anything less real than gravity.

Many physics discussions can be clarified with a simple substitution. Replace the word 'real' with 'objective'. Replace the word 'illusion' with 'subjective'.

There isn't anything less objective than gravity. I don't think that is quite true, but it is sort of leaning in the direction of truth.

According to the equivalence principle, one can't distinguish with local measurements between a gravitational field generated by a large mass and the proper acceleration.

So if the equivalence principle is true, the gravitational field is subjective. It doesn't exist when the observer is not being acted on by a nongravitational force force, but does exists when the observer is being acted on by a gravitational force. So the existence of a gravitational field depends on who is trying to observe it.

If different observers disagree as to the existence of a physical entity, then the physical entity can't be objective. So the gravitational field can't be objective.

When I attack a physics problem, I like to distinguish between objective and subjective. Points of view in my 'philosophy' are real. I can imagine a point of view of any animal that I work with, and can even image a point of view for electronic equipment.

The use of the word 'objective' and 'subjective' automatically imply that there are observers in the universe other than myself. This hypothesis that there are other observers than myself generally results in a happier story than the solipsism.

I don't like to distinguish between real and unreal. The effort to distinguish between real and unreal always seems to disintegrate into the solipsistic argument. I can't shake the default hypothesis that the rest of you are merely fantasies in a dream. Following the logic of solipsism has often ended up in nightmare.

Daoism hasn't worked for me! I work with butterflies AND caterpillars, and neither appear very happy to me.