Jump to content

What is Gravity?


ions
 Share

Recommended Posts

ajb: The spin-2 attribute of the graviton arises from the quadrupole character of gravitational waves, as I understand it.

 

Ok, you can understand this in terms of representations of the Lorentz group and the fact the graviton couples to the energy-momentum, i.e. it has two indices.

Link to comment
Share on other sites

  • Replies 67
  • Created
  • Last Reply

Top Posters In This Topic

Thus by Occam's Razor general relativity is chosen.

 

Occam's razor is obviously not enough to cut off singularities. Alexander's sword is best (to cut the gordian knot).

 

Seriously, what is the problem with Logunov's theory?

 

A theory without singularities (no black holes) is quite remarkable, especially when hundred of astronomers are observing in their telescopes manifestations of BH that respectable professors like Hawking have spend a lifetime on studying their properties.

 

There must be something wrong in it.

Link to comment
Share on other sites

we know that gravity is,,,,this is obvious,,,,as in magnets steel is attraction to itself,this also shows that in gravity there is a force we call gravity like a magnet only its in matter itself-this shows itself in mass attracting to mass the grater the mass the greater the force of gravity-in the same way that the bigger the magnet the bigger the magnetic force,,,so this shows that even in the least amount of matter is the force of gravity,,,without this force matter would not be matter,,,,in fact all things that are matter would not be with this force-the gravity force is,,,,no doubt about it,,,the deeper question might be how can you find out more about this force,,,,has anyone had any new ideas to help explain the force of gravity?Mike

Link to comment
Share on other sites

Occam's razor is obviously not enough to cut off singularities. Alexander's sword is best (to cut the gordian knot).

Good point. Reformulations, different constructions are normally a way to advance physics. We cannot stick to GR as if it were the ultimate truth.

Seriously, what is the problem with Logunov's theory?

 

A theory without singularities (no black holes) is quite remarkable, especially when hundred of astronomers are observing in their telescopes manifestations of BH that respectable professors like Hawking have spend a lifetime on studying their properties.

 

There must be something wrong in it.

 

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.

Edited by Bob_for_short
Link to comment
Share on other sites

Horizons are not the same as singularities. Does Logunov's theory say no singularities and/or no horizons?

 

One issue is that singular spaces are not so obvious to define in general relativity. I have no idea about Logunov's theory.

Link to comment
Share on other sites

Horizons are not the same as singularities. Does Logunov's theory say no singularities and/or no horizons? I have no idea about Logunov's theory.

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.

Link to comment
Share on other sites

I repeat myself: there must be something wrong in this theory. i cannot believe that the west is simply ignoring something so big. that is too sad. As AJB asked, no singularities? That means no Big Bang either. So what?

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.

Edited by Bob_for_short
Link to comment
Share on other sites

As to the Universe, there are oscillations from some maximum matter density to some minimum. Pleas read the book; I cannot retype it here.

 

I will.

 

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.

 

I can't believe that.

Link to comment
Share on other sites

...I can't believe that.

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.

Edited by Bob_for_short
Link to comment
Share on other sites

Me thinks that in the beginning it was not a big bang-it was matter everywhere mixed in space-fairly evenly through out-then gravity this force began-sepperation occcured between space and matter-via the force of gravity-without this force no matter would be as it is today-call it the energy force that holds or seperates space and matter-causeing also time-in the process-the big bangs occur when in space time-they are overwhelmed by the collection of to much mass-in one spot-and thus Bang-it explodes with energy!


Merged post follows:

Consecutive posts merged

Mass origanally was in its finest form smaller than dust-most likely atom sized all through the space-evenly there-then this force began to seperate space thus we have gravity-and time was started at this place too-because of distance between massive objects-in space-with light at a speed of light-made time but only relative to any physical body-for there are things that are not subject to these things-as we see-Mike

Link to comment
Share on other sites

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.

 

There are a couple of generic questions about these kinds of gauge theories of gravity that I have. They may well be answered in the book or other papers. I'd have to read thought them. Though I am no expert in these kinds of formulations of gravity.

 

I am sure that Logunov either directly addresses these or is aware of the limitations or issues of his theory.

Link to comment
Share on other sites

No Big bang, No black holes, no expansion, no acceleration. Is that in concordance with data's?

from Logunov's http://arxiv.org/abs/gr-qc/0210005. Preface p6,7,8. Emphasis by me.

 

"RTG introduces essential changes into the character

of the development of the Universe and into the collapse of

large masses.

Analysis of the development of a homogeneous and isotropic

Universe within RTG leads to the conclusion that the Universe

is infinite, and that it is “flat”. Its development proceeds cycli-

cally from a certain maximum density down to a minimum and

so on. Thus, no pointlike Big Bang occurred in the past. There

existed a state of high density and high temperature at each

point in space.

According to RTG, the so-called cosmological “expansion”

of the Universe, observed by the red shift, is explained by

changes in the gravitational field, but not by relative motion

— galaxies escaping from each other, which actually does not

take place. Matter in the Universe is in a state of rest relative

to an inertial coordinate system. The peculiar velocities

of galaxies relative to an inertial system arose owing to a certain

structure of the inhomogeneity of the distribution of matter

during the period, when the Universe became transparent.

This means that in the past the distance between galaxies was

never zero. The theory predicts the existence in the Universe

of a large hidden mass of “dark matter”. According to RGT,

“black holes” cannot exist: a collapsing star cannot disappear

beyond its gravitational radius. Objects with large masses can

exist, and they are characterized not only by mass, but also

by a distribution of matter density. Since, in accordance with

GRT, objects with masses exceeding three solar masses transform,

at the conclusive stage of their evolution, into “black

holes”, an object found to have a large mass is usually attributed

to “black holes”. Since RTG predictions concerning

the behaviour of large masses differ essentially from GRT predictions,

observational data of greater detail are required for

testing the conclusions of theory. Thus, for example, in RTG

spherically symmetric accretion of matter onto a body of large

mass, that is at its conclusive stage of evolution (when the nuclear

resources are exhausted), will be accompanied by a significant

release of energy owing to the fall of matter onto the

body’s surface, while in GRT the energy release in the case of

spherically symmetric accretion of matter onto a “black hole”

is extremely small, since the falling matter takes the energy

with it into the “black hole”. Observational data on such objects

could answer the question whether “black holes” exist in

Nature, or not. Field concepts of gravity necessarily require introduction

of the graviton rest mass, which can be determined

from observational data: the Hubble “constant” and the deceleration

parameter q. According to the theory, the parameter

q can only be positive, at present, i.e. deceleration of “expansion”

of the Universe takes place, instead of acceleration.

For this reason, the latest observational data on acceleration

of the “expansion” must be checked carefully, since the conclusions

of theory concerning “deceleration” follow from the

general physical principles mentioned above."

Link to comment
Share on other sites

No Big bang, No black holes, no expansion, no acceleration. Is that in concordance with data?[/i]

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.

Edited by Bob_for_short
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

What do you mean with "self-action problem"?

 

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.

Edited by Bob_for_short
Link to comment
Share on other sites

Not perturbativly renormalisable. GR (+ other terms) may be asymptotically safe.

 

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.

Link to comment
Share on other sites

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.

Edited by Bob_for_short
Link to comment
Share on other sites

In the field theories of Gravity we proceed from the same principle – the particles create field that acts on particles.

 

Just cannot understand.

I thought gravitons were considered massless particles. How can they create a field?

It looks evident to me that if you give mass properties to the particle itself you will get an increasing field of increasing value instead of a field of finite value expanding through spacetime.

Link to comment
Share on other sites

Just cannot understand. I thought gravitons were considered massless particles. How can they create a field?

 

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.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share


×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.