# Bob_for_short

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344

2. ## What is Gravity?

??? RTG admits existence of heavy objects which gravitationally affect light. How could you see them, "especially if so massive"? RTG does not predict a point-like singularity situated inside the horizon. Any heavy body has a radius exceeding the gravitational one in RTG. Of course. Light bending is predicted by RTG with no problem.

5. ## Is it possible to build a giant particle accelerator in space?

Yes, why not? It would be much more expensive though. Besides, the accelerated particles should be stopped somehow after passing the target and returned in the system (a closed current circuit). Otherwise your accelerator would get extremely charged with time which is not good at all.
6. ## What is more "real" - the retarded or instant data?

Let us take an observatory with a certain clock and space axes. We may have many still objects in our space with known positions (distances, angles). All of them belong to and constitute our observatory. We observe a moving body by recording time and observed positions, thus we obtain r(t), v(t), where r and v are 3D vectors. Now we may have two situations: non-relativistic and relativistic. In the non-relativistic situation the observed r(t) and v(t) are the instant, actual body data. In the relativistic one r(t) and v(t) are the retarded data. Knowing the light velocity we can always recalculate the “instant” data from retarded r(t), v(t). For directly observed data we must use the Lorentz transformations if we want to recalculate our observed (retarded) data from one observatory to another (where the other data are also retarded or "directly observable" ones). But transforming the “instant” or “actual” data from one RF to another is different: it is just the Galilean transformations. There is no c in the “instant” data by definition. So which data are more fundamental, real or reliable – instant or retarded?
7. ## What is Gravity?

I spoke of massive particles first of all, not of gravitons. Anyway, in QED and in GR the exact equations are coupled and non linear. So even photons can scatter photons - there is no superposition principle, to be exact. The same is in GR: any stuff that possesses energy or mass is the field source. And this field gets in the particle equations as well as in the field equations. Linear is the zeroth approximation after equation linearization.
8. ## What is Gravity?

Non perturbative gravity, similarly to non perturbative CED, is possible in some approximation, when neglecting the back reaction, for example. The renormalization group is good if it does not violate the good sense. It is not the case in QED, in my opinion.
9. ## Late PhD, idealistic?

Well, I did not do a heavy but technical and formal work for my PhD defence (preparation of the manuscript, etc.) because the advantages of being a PhD were canceled in the USSR at that time (1989). I just saved some time for my fundamental researches instead. Before that time the advantages were: increased salary and the freedom to choose your own research direction. This meant independence in researches so it was very attractive for ambitious people.
10. ## What is Gravity?

I did not get the meaning of the first phrase. For example, in CED one can try to solve numerically the exact equations with the jerk and one obtains a runaway solution. So CED is not renormalizable exactly. I do not follow the "assymptotic safety" advancements but I thought that this term was related so far to GR without matter.
11. ## Late PhD, idealistic?

Well, I finished a post-graduate program at the Kurchatov Institute of Atomic Energy in Moscow, passed the corresponding qualification exams but I decided not to defend my PhD. At that time it had no meaning because of many reasons. Yes, I have my own publications with quite original results in academic journals, that is why I consider myself as a PhD de facto.
12. ## What is Gravity?

Oh, the famous self-action! I hope you know Classical Electrodynamics, the Principle of least action, and the Noether theorem. The latter provides the conservation laws from some symmetries under condition that the field and mechanical equations have finite and meaningful solutions. In electrodynamics the charge motion is affected with the fields, and the fields are “sourced” with charges. So the mechanical and field equations are coupled. According to H. Lorentz, the electron “feels” the total field – the external and that created by itself. When one makes a detailed derivation of the self-acting force for a point-like charge, one obtains first an infinite value plus some finite addendum. The infinite part is a rather impractical – it is impossible to make calculations with it so it is discarded. The finite reminder is the charge jerk – the acceleration of acceleration. It leads to self-accelerating (runaway) solutions which are also impractical and non-physical. So it is also discarded in practice. Thus the Noehter theorem remains in CED a nice but not fulfilled statement – just because the solutions are not reasonable. In the field theories of Gravity we proceed from the same principle – the particles create field that acts on particles. The same self-action difficulty is unavoidable in the frame of point-like particle model. That is what we see in quantum gravity - the theory is not even renormalizable.
13. ## Late PhD, idealistic?

I am 52 and I still hope to get a PhD some day.
14. ## What is Gravity?

In my opinion, RTG is better than GR since it deals with a fixed geometry. It is not clear to me how to compare curves in different geometries (light bending in GR, for example). It is better to have one, plane geometry and attribute the light bending to the gravity force rather than geometry. RTG gives different predictions in so impractical cases - big bang, black holes, that it is not really essential. (Difficult to verify and impossible to use in a daily life.) In my opinion, RTG, as any classical field theory, should have self-action problems, but it is only my opinion.
15. ## What is Gravity?

Any data are "understood" via the prism of a theory. If you have GR, you try to find BH and BB, but you need black matter and energy to make ends meet. If you have a string theory, you look for signs of additional dimensions in nature, etc. Which our ideas are correct? How to understand the observations? We cannot escape from this or that interpretation.
16. ## What is Gravity?

OK, let us ask ajb to read or browse the book rapidly and make a judgment - if he encounters something unreasonable. I am sure ajb is qualified enough to notice an obvious flaw in this theory. As far as I know, nobody found any flaw in this theory so far. It is just not taught and discussed in the literature. I think it is so because of too high authority given to A. Einstein as an absolute genius with absolutely right theories.
17. ## What is Gravity?

As to the Universe, there are oscillations from some maximum matter density to some minimum. Pleas read the book; I cannot retype it here. As to ignoring, ask yourself if you want to read the Logunov's book and papers. Nobody cares, everybody is busy with his own things. Rush for Nobel prizes makes people busy with Quantum Gravity and Theories of Everything.
18. ## What is Gravity?

A BH is a mass inside the Schwarzchild radius, isn't it? In RTG massive bodies are larger than this radius so the filed solution in presence of matter is different from solutions with a point-like BH. See details on arXiv: http://arxiv.org/abs/gr-qc/0210005.
19. ## Quick question about Bernoulli principle and resistance?

If you mean molecules, then no. Their motion is chaotic with some average velocity along the pipe axis. If you speak of fluid micro-volumes, then yes, but the friction is determined with the average relative fluid-wall tangent velocity. So in a narrower section the friction is higher. Even solid bodies have friction when move along each other being in a close contact.
20. ## What is the frame of reference?

A frame of reference is an observatory. It is furnished with means to measure everything in question.
21. ## What is Gravity?

Good point. Reformulations, different constructions are normally a way to advance physics. We cannot stick to GR as if it were the ultimate truth. Astronomers observe BH candidates, not BH. From far distances, with help of indirect observations, and with BH idea in the head one can mistake a massive body without horizon for a BH with a horizon. Believing in BH is similar to believing in the classical mechanics with the Galilean group. It is a sequence of a theory but not an experimental fact. Take, for example, two gravitating elementary point-like particles. Their potential energy is 1/R. That means they can collapse in a point with releasing an infinite amount of energy. The same remark is valid for charged particles. Obviously such infinities are unphysical. They are not observed although they are solutions of very nice physical models. QM resolves the problem of particle collapse and explains the matter stability. GR has also pathological solutions - black holes with horizons. It is because the theory fails at short distances, just like classical examples given above. What is observed is not black holes for sure but massive objects. People study everything, including BH, it is normal. It does not mean that their mathematical exercises are always physical solutions.
22. ## 't Hooft's guide to becoming a bad theoretical phyicist

I am certainly a bad physicist, at least in the following sense: I cannot explain even simple things. What is evident to me is not evident to others and I always run on misunderstandings.
23. ## Quick question about Bernoulli principle and resistance?

The wall friction depends on the fluid velocity. A narrow section is "equivalent" to locally higher wall friction. As well, after a narrow section the flow may become turbulent - with additional wall friction due to locally higher velocities. According to Bernoulli, the velocity should decrease but it happens only in sufficiently smooth diffusors with small angles and at relatively small velocities. A turbulent flow may begin at high Reynolds numbers even in a straight pipe.
24. ## What is Gravity?

Yes, Logunov mentions many previous attempts to build a gravity theory in a flat space-time by others. The trick is that the gravity is a universal force and it looks indeed as a geometry of space-time. As soon as one geometrizes the space-time, one deals inevitably with a Riemann geometry: R>0. In RTG the gravity is not fully geometrized. It creates an effective Riemann space-time for matter but it is decoupled from the Minkowski metric in some field equations. So the Minkowski metric becomes the real geometry of space-time (R=0), it is observable (via laws of conservation, for example), but effects of gravity are taken into account as universal too. As to "gauge principle", it is not obligatory to follow it literally but as a hint in a phenomenological approach. Any good theory is phenomenological - it is based on experimental observations first of all. Otherwise a theory becomes a mathematical topic of some mathematical constructions - it may have many consequences but not related to observations.
25. ## I can't remember...

Luminescence? Fluorescence?
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