Which theory of gravity do you think explains the most about phenomenon?

[Probe]

Which theory of gravity do you think explains the most about the phenomenon?

1. Newton’s or Modified Newtonian dynamics?

2. Quantum Gravity?

3. Tensor-vector-scalar gravity?

4. Einstein's General Relativity or Special Relativity?

5. Other?

[Superewza]

As far as i'm aware Newtonian physics does not conflict with Einstein's General Relativity?

[Probe]

As far as I understand Newton described gravity by principle of action at a distance meaning a field - gravitational field between the Earth and the moon and similarly and two bodies in the universe exist. this in turn responsible for gravitation forces between and two bodies.

Einstein described gravity by suggesting that the space-time around any object is bent. The degree of bent is corresponding to how massive is the object. For example- Supposed you keep a plastic ball and an iron ball on a soft sofa. the space around the iron ball will naturally be bent more due to it been heavy. It is due to this bending that we feel that there is some sort of interaction between any two bodies. In short Einstein's explanation of gravity is more geometrical than actual physical interaction between any two objects.

[G4YVM]

Thats what I love about reading stuff on SGL; these lightweight throwaway questions. Pah!

David. Tongue firmly planted next to molars.

[Ben Ritchie]

From a CDM perspective Newtonian and MOND are rather different, not the same option

[StevieDvd]

5. Magic :-)

[Superewza]

As far as I understand Newton described gravity by principle of action at a distance meaning a field - gravitational field between the Earth and the moon and similarly and two bodies in the universe exist. this in turn responsible for gravitation forces between and two bodies.

Einstein described gravity by suggesting that the space-time around any object is bent. The degree of bent is corresponding to how massive is the object. For example- Supposed you keep a plastic ball and an iron ball on a soft sofa. the space around the iron ball will naturally be bent more due to it been heavy. It is due to this bending that we feel that there is some sort of interaction between any two bodies. In short Einstein's explanation of gravity is more geometrical than actual physical interaction between any two objects.

So could you not consider Newton's description to be an explanation of what happens, and Einstein's to be an explanation of how it happens?

[Probe]

So could you not consider Newton's description to be an explanation of what happens, and Einstein's to be an explanation of how it happens?

I have considered it, as did Mach and Einstein. It is very similar and it is possible to carry over the same mathematical arguments from curved two dimensional surfaces to higher dimensions. Einstein's theory of gravity reduces to Newtonian gravity when the gravitational field involved is not very intense, like in the solar system. Which is necessary given the successes of Newtonian gravity in explaining the motions of planets. As you should be aware, although I doubt it. Newtonian gravity fails at Mercury, closest to Sun, where the gravitational field is the most intense. The unexplained fast precession of Mercury is exactly what is to be expected once corrections due to Einstein's theory of gravity is taken into account.

[lukebl]

...er. You've lost me.

....I'll get me coat.

[Superewza]

I have considered it, as did Mach and Einstein. It is very similar and it is possible to carry over the same mathematical arguments from curved two dimensional surfaces to higher dimensions. Einstein's theory of gravity reduces to Newtonian gravity when the gravitational field involved is not very intense, like in the solar system. Which is necessary given the successes of Newtonian gravity in explaining the motions of planets. As you should be aware, although I doubt it. Newtonian gravity fails at Mercury, closest to Sun, where the gravitational field is the most intense. The unexplained fast precession of Mercury is exactly what is to be expected once corrections due to Einstein's theory of gravity is taken into account.

Thanks, that's rather interesting. You've got GCSE Physics to blame for that, got full marks in half the papers and still barely know anything useful

[Probe]

Thanks, that's rather interesting. You've got GCSE Physics to blame for that, got full marks in half the papers and still barely know anything useful

Superewza,

I have a second degree in Pure and Applied Physics. It's only a poll.

[Superewza]

Woa, sorry. I didn't realize it was such an insult to thank someone for trying to teach me something.

And FYI, i already did pass got something like - 50/50 in P1a, 45/50 in P1b, 90/100 in P2, 100/100 in P3 and 30 (or around there) in the coursework... which gets 6 added to it then multiplied by 2.5 or something. Grade boundary for an A* was 320/400 i believe. Go figure.

[Probe]

Woa, sorry. I didn't realize it was such an insult to thank someone for trying to teach me something.

And FYI, i already did pass got something like - 50/50 in P1a, 45/50 in P1b, 90/100 in P2, 100/100 in P3 and 30 (or around there) in the coursework... which gets 6 added to it then multiplied by 2.5 or something. Grade boundary for an A* was 320/400 i believe. Go figure.

national curriculum standards have slipped.

[Superewza]

Who ruffled your feathers? All i've done here is explain what i understood of the situation, asked a few questions (which is vitally important to the whole 'learning' process, i might add), then accepted your viewpoint and thanked you for the effort.

Where's this come from? I understand if you somehow projected some form of sarcasm or satire onto my words (as it is difficult to read and portray through text) but i definitely did not mean to offend you in any way.

[Nexus 6]

Having the knowlege is great, whether basic or expert, but it will never make up for the appreciation of the Cosmos and all that it contains and no one will ever understand it all.

are we all not astronomers to one extent or another? surely that is all that really matters

when one says Newton I think Gravity

when one says Einstien I think General Relativity

who will be next I wonder?

[meteoriot]

Gravity sucks!

[Nexus 6]

Gravity sucks!

[brantuk]

Folks - Comparing exam marks is about as sensible as comparing car engine sizes.

Please try and remember we are all here to help each other explore and develope our interest in astronomy. The best way to do this is "as friends".

So do try not to bicker if possible or I'll have to start sending people to bed early lol

[Probe]

Who ruffled your feathers? All i've done here is explain what i understood of the situation, asked a few questions (which is vitally important to the whole 'learning' process, i might add), then accepted your viewpoint and thanked you for the effort.

Where's this come from? I understand if you somehow projected some form of sarcasm or satire onto my words (as it is difficult to read and portray through text) but i definitely did not mean to offend you in any way.

Apology accepted

[Probe]

Folks - Comparing exam marks is about as sensible as comparing car engine sizes.

Please try and remember we are all here to help each other explore and develope our interest in astronomy. The best way to do this is "as friends".

So do try not to bicker if possible or I'll have to start sending people to bed early lol

Thanks brantuk

[Spare Tyre Nebula]

Thanks, that's rather interesting. You've got GCSE Physics to blame for that, got full marks in half the papers and still barely know anything useful

[George Jones]

I voted for general relativity.

Newton's theory of gravity was a work of stunning genius, but physical knowledge, both theoretical and empirical, is a lot different now than it was in Newton's day. General relativity has a wider domain of applicability than does Newtonian gravity. If I drop a brick, either general relativity or Newtonian gravity can be used to calculate the time taken for the brick to hit the Earth. The calculations are simpler for Newtonian gravity, but either theory can be used. For other observed phenomena, like Mercury's orbit (already stated by Rez), the expanding universe, gravitational lensing, the Global Positioning system (sat nav), orbital periods of binary pulsars, etc., Newtonian gravity either gives the wrong answer or remains silent.

MOdified Newtonian Dynamics (MOND) has had some successes, but seems rather ad hoc, and has some problems. For a critique of MOND and a bit of a debate (between Sean Carroll and Stacy McGaugh; in the comments after the article), see

Dark Matter: Just Fine, Thanks | Cosmic Variance | Discover Magazine.

Quantum gravity cannot be used to explain any phenomena, at least not in a quantitative way. We do not have a quantum theory of gravity with which we can do calculations. A future theory of quantum gravity will likely have a wider domain of applicability than general relativity, but I think it will be somewhere between 5 and 500 years before we will have a quantum theory of gravity with which we can do calculations that apply to observed physical phenomena.

The purpose of the creation of Tensor-vector-scalar gravity was to have a relativistic theory of gravity out of which MOND falls after appropriate approximations.

Within a decade, we should "image" the black hole at the centre of our galaxy, and this should allow us to observe many strong-field gravitational effects. There was an excellent article on this in the December 2009 issue of Scientific American. I expect general relativity to pass these strong-field observational tests with flying colours.

[Probe]

George

I agree, even today it is being questioned and refined by some physicists, general relativity, which states that gravity is caused by the curvature of spacetime around massive objects, has proven to be a great success, and a beneficial theory to science itself. Spot on about Tensor-vector-scalar gravity being a relativistic theory of gravity out of which MOND falls after appropriate approximations.. Loop quantum gravity predicts that the entropy of a black hole is proportional to the area of the event horizon, but does not obtain the Bekenstein-Hawking formula S = A/4 unless the Immirzi parameter is chosen to give this value.

A prediction directly from theory would be preferable.

Many Thanks for voting too!

Rez

[Photosbykev]

Gravity doesn't exist, the earth sucks

[Karlos]

They all indicate possible phenomenon, but they don't give us a greater understanding of the singularities i.e. of the very start of the big bang or the depths of a black hole, this is where we step back and rethink the steps we have taken so far, I personally think we are closer than ever to the next beautiful theory after Relativity. It will be more complete with no phenomenon as we would be able to perfectly describe them.

EDIT: I think also they really do have different applications, i.e. Newtons laws still used in building and architecture today, where as Einsteins Relativity is more applicable to astrophysics. When it comes to Quantum it has clever mechanics, which address issues with the preceeding theories, but we cannot know too much about a single moment in time, like where and how much.