Einstein, Gravity And Space-Time In 3 Dimentions

[I_Hate_Infinity]

Hi,

My very first question, if this site returns the educated, logical people to answer this for me, there may well be more to follow.

Einstein showed us that time and space were one and that space time was like a fabric, stretched to the ends of the Universe. (2D example to represent a 3D environment) And when he showed that gravity was not so much a force, but the effects of matter distorting the fabric of space-time and with massive objects, the effect can be to initiate an orbit with another object. When this is demonstrated, often a bowling ball is placed in the centre of an elastic 2D surface which shows this 'fabric' bending around it and therefore creates a warped trajectory for the second object introduced which although is only travelling in a straight line, conforms to the shape of its environment in its path.

The demonstration perplexes me... The bowling ball distorts the 'trampoline' because it is itself under the force of gravity (which the demonstration tries to explain.) I can understand it working on a 2D surface but, even though we believe the Universe is flat, the Universe is a 3D space. We see stars and galaxies in every direction and they are all spinning in complete random axis compared to each other, not a uniform plain on which they distort space-time.

Am I missing something here? How is it possible for space to shaped like the demonstration when applied in the 3rd dimention?

I'd really like someone's help and patience to explain Einstein's Theory of General Relativity to me. I'm well versed in physics and thinking outside the box, and I'm even looking into Quantum Mechanics to pass the time... Just can't get my head around a few practical problems :)

Apologies for the essay. Hope you can help.

Infinity

[Old_Geezer]

That is very kind of you, to ask more if you get a decent answer from educated folk. We will look forward to it.

I think that when an analogy is used to pass knowledge a certain amount of acceptance and imagination is required to overcome the imperfect comparison but to use the similarities shown to gain a better understanding. If you get hung up on an unimportant aspect then you may have difficultly progressing.

Remember you are trying to understand the action in 4 dimensions using a model that is in 3 (or two if looking at an animation). The gravity used in the demo should not be taken to be the same influence as you know it in 3D as it provides in the model of 4 dimensions.

No apology needed but it is something you just need not to get stuck on. It is demonstrates the thinking behind it then it is good for that. If you need more you probably need to study the mathematics rather than look for a visualisation.

That's my take on it anyway.

[Old_Geezer]

"If it demonstrates" >:-(

[Old_Geezer]

As an afterthought: try not to think about what is causing the deformity in the 2D 'rubber sheet', just accept that something is deforming it and that it merely represents 3D space being deformed by mass.

[I_Hate_Infinity]

Thank you sir for you answer but it saddens me. I fear you're right that I must accept the demonstration as a tool to visualise and if I get hooked up on this issue I can't move on.

In my minds eye, I visualise an Earth sized sphere surrounded by Einstein's space-time and as the observer, I see the 'fabric' being bent and distorted to a centre point at the Earth's core (the end point of Newtons apple if there were no crust/resistance.) So why does space-time react to matter in this way as to 'attract' other matter by folding in on itself (presumably to point the size of a Quark)... Why does this pinch of the fabric create a 'plug hole' effect for surrounding matter helplessly falling and falling and falling toward the centre...

Again i'm rambling. My point is, why must we lose Newton's idea of an attractive fundamental force of gravity, opposed to Einstein's warping, distorting and pushing of space-time. Why must mass be pushed toward each other rather than pulled?

I fear I'm looking like a fool not to grasp this. As only a self-taught Physics student, I really need to ask the questions that I can't find the answer to.

Infinity

[Old_Geezer]

Newton's laws are fine for "rough" day to day practical use, and probably always will be. But they don't gve the right answer with a close enough precision for other things, so we must look for better explanations.

[Clanad]

While I sympathize with your perplexion.... fact is, you're mixing philosophy with mathematics, when you state "...So why does space-time react to matter in this way as to 'attract' other matter by folding in on itself (presumably to point the size of a Quark)..."

The fact that it does react in such a fashion is totally separate from "why" does it do so. I would postulate the effect is due to high design, but others would simply state "It is what it is" and be satisfied with the known results.

It's a good thing, in my humble estimation, to do as you have in asking "why", but, divorced from the reality of physics and its tied-at-the-hip brother, mathematics,, any answers are an oasis of nugacity, no?

[I_Hate_Infinity]

You've been excellent in both my posts Clanad, but I must stand my ground here. I don't believe that the "why" and the "how" should ever remain separate. The progress of human civilisation and the development of physical science depends on why...

"Why does the Sun go round the sky" "How does the Sun go round the sky" (excuse the poor example) Isaac Newton first wondered why the apple fell, he then began his quest to resolve how...

I seem to be presented with a situation here, where we've figured out the how, but no one knows "why" the "how" works? I'm sure I've missed something and I'm sorry if I'm wasting your time, but do you understand my point and do you have an answer (ono)

Infinity

[mibn2cweus]

While I don't know the mechanism behind gravity, I do agree with you philosophically on the means by which answers are obtained. When you try to separate the 'why' from the 'how' you end up with the arbitrary assertions of religion. In science the 'how' is the 'why'. Science, unlike religion, does not posit the 'why' as an a prior to obtaining the knowledge of 'how'. When you know 'how' then and only then do you know the 'why'.

[jim360]

Gravity is difficult and I won't pretend to be a world expert. One way of perhaps trying to extend the "ball bending the sheet" picture to 3, and then 4, dimensions is to imagine several such sheets in which the ball is resting. In the ideal case each sheet will be bent in the same basic way, and then you can say that the 3-d space bending is just all the possible 2-d space bendings put together. That's not quite right of course, but in truth these things are almost impossible to fully visualise and we have to resort to diagrams that try desperately to capture as much of the behaviour of 4 dimensional gravity as possible on 2-dimensional paper. No wonder your head hurts trying to move in the other direction...

And you are quite right, never stop thinking about these sorts of things, and don't pretend that philosophy and maths and physics can be separate.

[mibn2cweus]

The marriage of philosophy with science is essential to subduing the tantrums of their evil step-child . . . religion.

[I_Hate_Infinity]

Thank you for your answers and I'm glad you agree with me on the how/why issue.

I understand that at the moment of creation, it is believed the the four fundamental forces (n/strong, n,weak, electro-magnetism and gravity) split to assume their place in our sustainable Universe. And it has been shown that gravity compared to the rest is remarkably weaker, whilst the other 3 share similar strengths.

Bearing in mind what has already been discussed, is it right for me to conclude that Gravity isn't really a fundamental force at all? And that's why is has no resemblance to the other three forces. And gravity's lack of a carrier particle (such as the electron for e/m), further shows it's actually categorised wrongly as a force? If so, is it time to reduce the fundamental forces from 4 to 3?

Thoughts please.

Infinity

[jim360]

Well, perhaps. On the other hand, although the theories are not yet complete, it is possible to show that you might be able to quantise gravity which leads naturally to it having force carriers (gravitons) in the same way that the other forces do. So maybe it is a force after all. Things are sort of messy, and it's not clear to me or anyone else if we'll show that gravity is a force in the same way as the other forces are. But I believe there are strong reasons to believe that it should be in the end, in a "complete" theory. Time only will tell.

[jim360]

Another subtlety worth mentioning is that if you want a gravitational field to exist in empty space, that is, in between stars and planets, then you can show from the equations that this can only happen in 4 dimensions or more - so space-time doesn't work in three dimensions.

[I_Hate_Infinity]

Thank you Jim360. It's relieving to know I'm not alone in wanting the answers, and that modern science hasn't got a full explanation to why Einsteinian gravity works either. And my apology for the question title because I am fully aware that space in 4D is necessary and correct. Might I propose a question branching off what you have said?

If the graviton particle is discovered and gravity, despite its other oddities, is confirmed to be a force, what might be the mechanism to which this particle interacts with matter to push/attract atoms together. Isn't a force the exchange of its particle between two sources so it may complete a circuit which allows it to serve its function? (I am leaping into the field of ignorance here) If not, do the other forces (although stronger) work on distances greater than gravity in 4D space?

Infinity

[I_Hate_Infinity]

I know this thread has long been dead, but, I have finally got my head around it and propose a better reall world example for demonstration.

If one imagines a cubed space such as a Rubiks cube and have an object on the outside edge with no momentum, and a suddenly introduce a large massive object in the cube's centre, the 'pinching' of space-time it creates, stretches space into a focal point and therefore stretches the grid our out-lying, momentumless object occupies. It then has motion because the warping enourages the object to return to the grid coordinates it once occupied, eventually falling victim to the every increasing warped path its now on.

Therefore, gravity doesn't pull, space pushes... Right? (It's taken we 2 weeks to get my head around and find a suitable example, so my apologies to my educated AB peers who already know this, if my explanation isn't perfect.)

IHI

[jim360]

That sounds not too far off the traditional Schwarzchild solution of space-time and solving for a particle at rest. You can think of it a number of ways. Gravity pulls, space pushes (not sure I like this one, actually, but if it works for you...), or space bends and the object rolls down the newly-created "hill" in space. Space-time is bent rather than pinched, I'd say, but the analogy seems otherwise fairly close.