Thought experiment: how would physics develop without Einstein?

[Strange]

1 hour ago, swansont said:

If the latter - basically you are discussing alternatives to GR that are ultimately incorrect. According to the link, GEM was introduced a few decades before GR was finalized. What were the reasons it was not pursued further? I see nothing in the link about it explaining the advance of the perihelion of Mercury. This was a problem known in 1915, and solved by GR. Would an alternative theory have taken hold in a GR vacuum, if it could not explain this effect? Anything that could not would start out with the handicap of knowing it was not complete.

It is a long time since I studied the history of science at this period but I remember mention of other attempts to formulate alternative gravitational moulds to explain Mercury's perihelion but none of them were satisfactory.

[Duda Jarek]

The main question to discuss here is if without Einstein we (or some other civilization) would get to GR.

Alternative way is introducing succeeding terms of Taylor expansion of GR - the question is what could be the "extraordinary evidence" to convince that it is necessary to introduce intrinsic curvature of spacetime in non-renormalizable theory (GR).

 

Finally some experiments, so let's discuss them:

- from https://en.wikipedia.org/wiki/Tests_of_general_relativity :

so it is mainly about gravitoelectric effects - isn't it part of GEM?

Imagine analogous EM situation: circulating charge produces magnetic field, which leads to Lorentz force precessing the orbit.

I don't know why they didn't use Heaviside? Maybe they just were not aware (?), he is not mentioned in https://en.wikipedia.org/wiki/Two-body_problem_in_general_relativity

It seems Heaviside's paper had one citation before 1950: https://scholar.google.pl/scholar?hl=en&as_sdt=2005&sciodt=0%2C5&cites=5741552482440482063&scipsc=&as_ylo=1800&as_yhi=1950

Anyway, if Heaviside's GEM is approximation, then just use the proper one from Taylor expansion of GR.

 

- regarding light bending, we observe it also e.g. in water - due to different propagation speed. 

Without Einstein one could use this explanation - requiring some slowing down of EM propagation in gravitational field - some coupling between EM and gravity.

 

These are low field effects - can be explained by using a few first terms of Taylor expansion of GR - one could estimate/use them not being aware of complete GR.

I am afraid that to get to really convincing arguments, we would need to go to high field effects - like distinguishing neutron star from black hole - how such argument could look like?

 

Edited August 17, 2020 by Duda Jarek

[Strange]

10 minutes ago, Duda Jarek said:

The main question to discuss here is if without Einstein we (or some other civilization) would get to GR.

Then why do you keep bringing up your false and off-topic claims about GEM.

11 minutes ago, Duda Jarek said:

- regarding light bending, we observe it also e.g. in water

Space is not full of water.

 

[Duda Jarek]

1 minute ago, Strange said:

Then why do you keep bringing up your false and off-topic claims about GEM.

I am just referring to Wikipedia (e.g. copy&pasted table), which uses GEM all around for low field GR effects ... and don't see any "off topic claims" - please specify.

4 minutes ago, Strange said:

Space is not full of water.

Bending wave is universal for propagation with different speeds - is not limited to water, or EM waves:

https://en.wikipedia.org/wiki/Refraction

https://en.wikipedia.org/wiki/Structural_acoustics

[swansont]

2 hours ago, Strange said:

It is a long time since I studied the history of science at this period but I remember mention of other attempts to formulate alternative gravitational moulds to explain Mercury's perihelion but none of them were satisfactory.

That would be true of any model that was incorrect. It works for one phenomenon, but fails elsewhere. We see this today with e.g. MOND to explain what GR explains with dark matter. It works at one range of parameter, but not others.

1 hour ago, Duda Jarek said:

The main question to discuss here is if without Einstein we (or some other civilization) would get to GR.

I think there is little doubt that we would. It would be a matter of when.

 

1 hour ago, Duda Jarek said:

Alternative way is introducing succeeding terms of Taylor expansion of GR - the question is what could be the "extraordinary evidence" to convince that it is necessary to introduce intrinsic curvature of spacetime in non-renormalizable theory (GR).

 

Finally some experiments, so let's discuss them:

- from https://en.wikipedia.org/wiki/Tests_of_general_relativity :

so it is mainly about gravitoelectric effects - isn't it part of GEM?

Was GEM advanced as a solution to this issue?

 

 

[Duda Jarek]

Searching for materials about Mercury precession, they usually refer to GEM, e.g.:

https://www.worldscientific.com/doi/abs/10.1142/S2010194517600527

Quote

The Gravitomagnetism in the Solar System

In 1918, Joseph Lense and Hans Thirring discovered the gravitomagnetic (GM) effect of Einstein field equations in weak field and slow motion approximation. They showed that Einstein equations in this approximation can be written as in the same form as Maxwell’s equation for electromagnetism. In these equations the charge and electric current are replaced by the mass density and the mass current. Thus, the gravitomagnetism formalism in astrophysical system is used with the mass assuming the role of the charge. In this work, we present the deduction of gravitoelectromagnetic equations and the analogue of the Lorentz force in the gravitomagnetism. We also discuss the problem of Mercury’s perihelion advance orbit, we propose solutions using GM formalism using a dipole-dipole potential for the Sun-Planet interaction.

But Heavisides' 1893 GEM paper has only citation before 1950 (now 315):

https://scholar.google.pl/scholar?hl=en&as_sdt=2005&sciodt=0%2C5&cites=5741552482440482063&scipsc=&as_ylo=1800&as_yhi=1950

It looks like just nobody was aware of this paper back then (?)

 

Update: from https://arxiv.org/pdf/gr-qc/0207065.pdf

Quote

In 1893 Oliver Heaviside[6] [7] investigated the analogy between gravitation and electromagnetism; inparticular, he explained the propagation of energy in a gravitational field, interms of a gravitoelectromagnetic Poynting vector, even though he (just asMaxwell did) considered the nature of gravitational energya mystery. Theformal analogy was then explored by Einstein [8], in the framework of GeneralRelativity, and then by Thirring [9] who pointed out that thegeodesic equationmay be written in terms of a Lorentz force, acted by a gravitoelectric andgravitomagnetic field.

 

Edited August 17, 2020 by Duda Jarek

[Phi for All]

2 hours ago, Duda Jarek said:

The main question to discuss here is if without Einstein we (or some other civilization) would get to GR.

!

Moderator Note

You've had two pages of exactly this, but since you ignore all the arguments that don't support your own, these threads just keep going with no resolution. More like a blog than a discussion when you keep soapboxing your ideas without taking replies on board. It's a bad habit, it's frustrating to those taking their time to respond, and that's why it's against the rules of this science discussion forum. 

If this doesn't improve quickly, I'm closing the thread. More rigor, please.

 

[Duda Jarek]

But finally from general comments that "everything confirms Einstein", we are getting to real discussion - about concrete experiments, as this is a bit more complex.

[Phi for All]

15 minutes ago, Duda Jarek said:

But finally from general comments that "everything confirms Einstein", we are getting to real discussion - about concrete experiments, as this is a bit more complex.

!

Moderator Note

Try NOT responding to modnotes, and use your time for discussing the counter-arguments posed by the members. It shouldn't be this difficult.

 

[Strange]

3 hours ago, Duda Jarek said:

Bending wave is universal for propagation with different speeds - is not limited to water, or EM waves:

There is nothing in space to cause refraction. And refraction does not behave like gravitational lensing. 

[Duda Jarek]

Wave propagation is usually governed by Fermat's principle (similar to the least action principle):

Quote

the path taken by a ray between two given points is the path that can be traversed in the least time

leading for example to refraction due to slow down in some medium, allowing e.g. to build lenses - not necessarily using strong boundaries between materials, can be gradient like in gravitational case.

GR uses intrinsic curvature instead, but in Fermat's principle it can be interpreted as slowing down in presence of gravitational field.

 

Here is some related paper: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.96.104037

Gravitomagnetic bending angle of light with finite-distance corrections in stationary axisymmetric spacetimes

 

Anyway, bending we observe is low field effect - can be obtained by replacing GR with first terms of its Taylor expansion.

The big question is how to conclude non-renormalizable GR from them? I am afraid that convincing arguments might require strong field effects like black holes ...

[Strange]

3 minutes ago, Duda Jarek said:

leading for example to refraction due to slow down in some medium, allowing e.g. to build lenses - not necessarily using strong boundaries between materials, can be gradient like in gravitational case.

Gravitational lensing does not behave like refraction. (Maybe because the light does not slow down.)

Your anti-GR preaching is getting tedious.

[Duda Jarek]

Are you claiming that light in gravitational lensing do not behave accordingly to Fermat's principle? Interesting, could you support it somehow?

I don't know what do you mean by anti-GR preaching, but let me remind: this thread was supposed to be focused on argumentation to convince to GR (non-renormalizable, without Einstein).

Once again, using low field arguments would not work as, without Einstein, there could be just developed succeeding terms of Taylor expansion of GR instead.

We need strong field arguments like black hole - how they could be used to convince that a given object is not just a heavy neutron star?
 

update: just found some "Introduction to Gravitational Lensing Lecture scripts" http://www.ita.uni-heidelberg.de/~massimo/sub/Lectures/gl_all.pdf

Quote

1.2 Fermat’s principle and light deflection

Starting from the field equations of general relativity, light deflection can be calculatedby studying geodesic curves. It turns out that light deflection can equivalently be described by Fermat’s principle, as in geometrical optics. This will be our starting point

Mathematics is the same, especially for all low field approximations as first Taylor terms.

Edited August 17, 2020 by Duda Jarek

[Strange]

11 minutes ago, Duda Jarek said:

Are you claiming that light in gravitational lensing do not behave accordingly to Fermat's principle?

No.

12 minutes ago, Duda Jarek said:

I don't know what do you mean by anti-GR preaching, but let me remind: this thread was supposed to be focused on argumentation to convince to GR (non-renormalizable, without Einstein).

Then why are you continuously taking it off topic?

 

[Duda Jarek]

Just now, Strange said:

Then why are you continuously taking it off topic?

What do you mean? We are discussing experiments like gravitational lensing you have brought up - I have just linked some lecture in previous post.

[Strange]

7 minutes ago, Duda Jarek said:

What do you mean? We are discussing experiments like gravitational lensing you have brought up - I have just linked some lecture in previous post.

Your repeated claims that GEM can replace GR, despite all the explanations that it can't.

Your claims that gravitational lensing could be explained by refraction, when obviously it can't.

This is clearly just an attempt to promote alternative crackpot theories outside of the Speculations forum.

[Duda Jarek]

Without Einstein (situation this thread was supposed to be focused on) we would add corrections to Newton - first terms of Taylor expansion of GR ... mathematically getting agreement of low field effects.

I have a feeling that you don't believe in Taylor expansion, Fermat principle ... here is this lecture again:

40 minutes ago, Duda Jarek said:

just found some "Introduction to Gravitational Lensing Lecture scripts" http://www.ita.uni-heidelberg.de/~massimo/sub/Lectures/gl_all.pdf

Quote

1.2 Fermat’s principle and light deflection

Starting from the field equations of general relativity, light deflection can be calculatedby studying geodesic curves. It turns out that light deflection can equivalently be described by Fermat’s principle, as in geometrical optics. This will be our starting point

 

And generally this is not discussion but bullying by moderators - not even trying to respond to arguments, only shooting some general remarks without any support.

I am going to sleep now, would gladly discuss it tomorrow - but using argumentation instead ... low field is not enough, we need to go to high field like black hole - how exactly could such argument look like: to experimentally distinguish black hole from heavy neutron star?

[Markus Hanke]

6 hours ago, Duda Jarek said:

how exactly could such argument look like: to experimentally distinguish black hole from heavy neutron star?

Neutron stars generate strong magnetic fields around them, whereas black holes don't (only their accretion disks do, but those fields have different geometry). This is directly observable. Even for neutron stars themselves, gravity is strong enough to have an influence on the geometry of their magnetic fields, as well as their rotational frequency - both of which are strong field GR effects, and directly observable. And then of course you have gravitational wave signatures of the mergers of such objects, which are different for black holes and neutron stars. 

All of this has been mentioned before, so I don't know why you keep going on about this.

[Duda Jarek]

Observational effects of strong magnetic fields are e.g. jets - are saying that their presence excludes possibility of black hole? I don't know - there are theoretized Kerr's black holes and I think they have magnetic field, also from acreting matter: https://en.wikipedia.org/wiki/Rotating_black_hole ?

And the question is for the other side: imagine civilization without Einstein - developing low field corrections: succeeding terms of Taylor expansion of GR, not being aware that they should sum up to GR. Having QFT, they see renormalizability as crucial - how to convince them that non-renormalizable GR is the only way?

For this purpose we need observational effect of black hole - convincing that it definitely isn't just a heavy neutron star, maybe using event horizon.

Maybe Hawking radiation? How far are we from its direct observation?

[Markus Hanke]

9 hours ago, Duda Jarek said:

Observational effects of strong magnetic fields are e.g. jets - are saying that their presence excludes possibility of black hole?

No, you get magnetic jets in both black holes and pulsars - but what I am saying is that their dynamics are different, because the former arises from accretion disks, and the latter from the dipole field of the neutron star itself. They are observationally different.

9 hours ago, Duda Jarek said:

For this purpose we need observational effect of black hole - convincing that it definitely isn't just a heavy neutron star, maybe using event horizon.

Yes, this is essentially what we have been saying for the past two pages.

[Phi for All]

On 8/18/2020 at 7:29 AM, Markus Hanke said:

Yes, this is essentially what we have been saying for the past two pages.

!

Moderator Note

And since the repetition, vagueness, and lack of rigor seems to be essential to this topic, I'm going to close it now.