- 03 Mar '07 01:00Genuine question for the physicists out there. One of those abstract pub questions cropped up and we found that not one of us around the table could explain it. The attraction isn't electromagnetic as far as we knew, or is it?

Can anybody explain not what it does, we witness or think we witness its action every day, but why does it occur?

Avoiding tautologies, if possible, please? - 03 Mar '07 01:28

http://en.wikipedia.org/wiki/Gravity*Originally posted by jatrius***Genuine question for the physicists out there. One of those abstract pub questions cropped up and we found that not one of us around the table could explain it. The attraction isn't electromagnetic as far as we knew, or is it?**

Can anybody explain not what it does, we witness or think we witness its action every day, but why does it occur?

Avoiding tautologies, if possible, please?

I wish I had a good answer for that one. As far as I know, electromagnetism and gravity are still considered to be two entirely separate things. "Why" gravity occurs I have no idea though. I recall in one of my physics classes, a professor quoting some other physicist as saying something like (with a heavy German accent), "Vvvee ask Vvvhat, not Vvvhy!" And then I think continuing on along the lines of, "if you want to know why, try the Philosophy dept. (or was it theology?). I found this an entirely unsatisfactory attitude for a scientist, but what do I know--I'm just a lowly an engineer. - 03 Mar '07 02:40

Mass bends space-time, just as a ball on a rubber sheet will cause a depression. If you roll a marble at such a ball it will tend to fall towards the mass.*Originally posted by leisurelysloth***http://en.wikipedia.org/wiki/Gravity**

I wish I had a good answer for that one. As far as I know, electromagnetism and gravity are still considered to be two entirely separate things. "Why" gravity occurs I have no idea though. I recall in one of my physics classes, a professor quoting some other physicist as saying something like (with a heavy Ge ...[text shortened]... tisfactory attitude for a scientist, but what do I know--I'm just a lowly an engineer.

That's the best explanation I've heard, but to me it sounds like using gravity to explain gravity... - 03 Mar '07 03:50The question of "why" can only be guessed at. I was always told that mass attracted mass and that was the reason for gravity. However, that is very vague. Be it known that gravity is probably the weakest of the basic forces (Electromagnetic, Weak, Strong).

Maybe that's one of those points where "why" becomes unanswerable (because for every answer to the question "Why?" is at least one other question "Why?"

My answer is that it was the way this universe was made, and maybe one day I'll get to ask that question and a million other like it. (Warning: this statement contains a presupposition.) - 03 Mar '07 09:48We can always describe the "what" part, by observing and from that build mathematical formulae.

But what about the "why" part? String theory might give the 'answer' to that.

Let me make an analogy first: You can always measure the velocity of light. But in the Maxwells equations of electromagnetic fields the velocity of lights pops out as an solution of certain formulas. So by studying the formulas you can predict the velocity of light and the observations will confirm it.

When we've set up the 'formulas of universe' (pardon me for not finding the right words) it turns out that the solution of certain equations gives the values of the 'constants of nature', like the strengths of the weak and strong forces, boltzmans constant, and more. But only if you tune the parameters correctly, and this is the problem. So if the formulas are correct, and the parameters are correct, the gravity pops out as an solution of these equations, and also with the correct strength of force.

So this is the "why". Gravity is there because it is the solution of the 'formulas of universe'. When we know these formulas more properly, we can also (perhaps) discover more basic forces, not discovered until then, purely theoretical. We can explain everything in our universe, and we can (perhaps) discover the very reason that our universe exists, and with which reason.

String theory is not complete, yet. We are nearing the Truth asymptotically. It is a hard work. New branches of mathematics are in need to develop and to be invented. Only a handful of people know and understand the frontline of this research. But in hundred years from now, I’m sure that it will be in the college textbook of physics.

I don't pretend that I understand string theory, not at all. When I write we, I mean mankind as a whole. Mostly I don't know anything for myself, I've read it in books, articles, internet, and from those who has capabilities beyond mine.

The "what part" is interesting, but the "why" part is even more so, and this without any theology. - 03 Mar '07 15:44interestingly - the formulae predicts that only if one of the two bodies so attracted is sufficiently large - then the force between those bodies becomes sufficiently large in itself

of an even more interesting note is that an object within a sphere - creates the disturbing effect of no gravitational attraction between the two objects - centre of gravity focii not relevent in this situation

somewhat similar i believe to electromagnetic conditions

so G=6.673 x 10 ^(-11) Nm^(2)/kg^(2)

big deal - WHY - is a good question - 04 Mar '07 08:41

I can't quite understand this post.*Originally posted by olddog***interestingly - the formulae predicts that only if one of the two bodies so attracted is sufficiently large - then the force between those bodies becomes sufficiently large in itself**

of an even more interesting note is that an object within a sphere - creates the disturbing effect of no gravitational attraction between the two objects - centre of gravity f ...[text shortened]... netic conditions

so G=6.673 x 10 ^(-11) Nm^(2)/kg^(2)

big deal - WHY - is a good question - 04 Mar '07 18:14

The speed of light is an input into Maxwell's equations it's not really predicted by them, unless you regard the permittivity and permeability of free space as more fundamental constants - which most people don't.*Originally posted by FabianFnas***Let me make an analogy first: You can always measure the velocity of light. But in the Maxwells equations of electromagnetic fields the velocity of lights pops out as an solution of certain formulas. So by studying the formulas you can predict the velocity of light and the observations will confirm it.**

In answer to the person who started the thread, the explanation for gravity is that massive objects cause the spacetime around them to be curved, which alters the path of things moving through the space near them. There isn't an answer as to why, it's more that that's the observation - things are as they are. You may as well ask why one and one make two. - 04 Mar '07 18:44

It depends how you see at things. 1+1=2 is a result of deeper rules of the number system and its operations. 1+1=2 is not at all a basic rule. Mathematics is an axiomatic system.*Originally posted by DeepThought***The speed of light is an input into Maxwell's equations it's not really predicted by them, unless you regard the permittivity and permeability of free space as more fundamental constants - which most people don't.**

In answer to the person who started the thread, the explanation for gravity is that massive objects cause the spacetime around them to be c ...[text shortened]... s the observation - things are as they are. You may as well ask why one and one make two.

I see, and some others, physics as axiomatic too. In my philosophy there are some very basic rules that governs the universe, the axioms of the Universe. And this is what the string theory is all about.

Is velocity of light a basic constant of nature? Or is it a result of more basic constants or parameters in the equations of string theory? Does the velocity of light really have to be (near to) 300 000 km/s? Or does the Universe permit it to be faster or slower? Is it even a constant over times? No observational proofs are given, perhaps the equations can give some answers.

The same thing about gravity. Is there a reason for the gravitational constant to be what is is? Does it change over times? Does it have to be a gravitation at all? Is there a negative gravitation (like the magnetic force)?

I say that gravity is only a solution of the equations of string theory. There are more basic reasons to the existence of gravity and its force. I say that there are axioms, known by mankind, not yet known by mankind, or perhaps, not ever known by mankind but still there. These axioms can be described by equations where the solutions explains it all.

Gravity is there because it cannot be otherwise due to equations. that's why. - 05 Mar '07 00:25
In answer to the person who started the thread, the explanation for gravity is that massive objects cause the spacetime around them to be curved, which alters the path of things moving through the space near them. There isn't an answer as to why, it's more that that's the observation - things are as they are. You may as well ask why one and one make two.[/b]

Thanks to everybody who answered on this thread. Certainly a great deal of food for thought. It's a freaky thought that no scientist has as yet devised a satisfactorily verifiable view as to why masses attract.

I certainly didn't mean to stir up a hornet's nest but I did make the plea for no tautologous answers, if that were possible. I've always been a big fan of Popper's falsifiability axiom. To ignore this leads us down the path of a priori reasoning and the point has been made that that way leads to theology and/or madness.

I've never been happy with,"It just IS, ALRIGHT!!" as an answer to anything, and I think that history bears out that most innovators within science concurred with this view. I'll just have to recognise my own ignorance of the the probabale true meaning of the question I'm asking. I'll just leave it at that with having to agree that mass bends the space-time continuum and that a larger mass will make a bigger dent in this.

I'll sign off with one last conundrum put to me by one of my comrades at the initial evening where the issue cropped up.

If we could locate an empty corner of the universe and send out two mirror image space craft to approach it from opposite trajectories and they each had a Galilean cannonball on the end of a probe arm and released them at the same time close to each other, having achieved a relatively static position with regard to each other and then the rockets vamoosed. Would they stay equidistant or would they attract each other? (Uniform balls, same mass, density etc.) - 05 Mar '07 08:16

Neither do I. So I have an open mind and have the antennae out. Because if there is an answer, I'll pick it up eventually. I am happy if a can understand that there is an answer, even if I don't have the knowledge to understand the answer itself. String Theory and Quantum Gravitation I believe have the answers to these kind of deep questions.*Originally posted by jatrius***I've never been happy with,"It just IS, ALRIGHT!!" as an answer to anything** - 05 Mar '07 19:50

1 + 1 = 2 is pretty fundamental. Mathematicians just like to make things obscure to justify their research grants*Originally posted by FabianFnas***It depends how you see at things. 1+1=2 is a result of deeper rules of the number system and its operations. 1+1=2 is not at all a basic rule. Mathematics is an axiomatic system.**

I see, and some others, physics as axiomatic too. In my philosophy there are some very basic rules that governs the universe, the axioms of the Universe. And this is what the ...[text shortened]... plains it all.

Gravity is there because it cannot be otherwise due to equations. that's why.

Physics is not axiomatic, I used to think like that but it's getting the whole thing on it's head. Physical theories are axiomatic though; special relativity is a good example - the two assumptions are that the speed of light is the same in all intertial reference frames, and that there is no way to distinguish between inertial reference frames. You can then compare what the theory says about the world with some experiments or observations, and try and think of some tests to invalidate it, but all you can do is say that the theory is either good (describes the results of experiments well) or bad (gets the wrong answers).

The theory isn't the thing itself, it is a description of what it's going to do and what it's like. There's a tendency to blur the theory and the thing in itself which causes us to fetishize theories - so that instead of looking at General Relativity to see if it it's wrong they've postulated dark matter (of which there is bound to be some, but there'd have to be too much for various cosmological bounds) in an attempt to keep the existing theories going when they aren't producing the right answers. This isn't the first time either, at the end of the 19th century they were talking about an aether to try to cope with the fact that the speed of light didn't seem to change with the observers speed, Einsteins genius was to turn the whole thing on it's head - the mathematical structure of the theories (Lorentz transforms and so on) were already worked out, he just made it all make sense by believing what the experiments were saying to him.

The universe isn't axiomatic, it just is. We have theories to describe how it behaves but you fall just as fast whether your theory is a good or a bad one. - 05 Mar '07 20:06

You can prove with Peanos 5 axioms of the natural number system that 1+1=2 with more basic rules than this. 1+1=2 is not fundamental, it is provable.*Originally posted by DeepThought***1 + 1 = 2 is pretty fundamental.**

...

The universe isn't axiomatic, it just is.

Whether the nature laws of universe is axiomatic or not will the future tell. Until then it is only a hypothesis that I happen to believe in. I think that a handful of axiomatic laws of nature is enough to describe the whole universe. What I've seen of String Theory supports this idea. - 05 Mar '07 21:31

Well very possibly, but the natural numbers are a human construction, they only really became relevant to us when accountancy became neccessary to keep track of production. Natural numbers are artificial.*Originally posted by FabianFnas***You can prove with Peanos 5 axioms of the natural number system that 1+1=2 with more basic rules than this. 1+1=2 is not fundamental, it is provable.**

Whether the nature laws of universe is axiomatic or not will the future tell. Until then it is only a hypothesis that I happen to believe in. I think that a handful of axiomatic laws of nature is enough to describe the whole universe. What I've seen of String Theory supports this idea.

You are confusing theories about the thing with the thing. You don't need to invoke string theory for your argument, the Standard Model of Particle Physics and General Relativity describe what we can see in particle accelerators and the bulk properties of the cosmos very well. Quantum Electro-dynamics has been tested to fifteen significant figures. It is a very good theory. Saying that the universe can be described by theories which have few axioms is very different from saying that the universe has a bunch of laws that it obeys.

You need to be wary of String Theory, it looks quite promising but there are problems with it, and it is diverting resources away from potential alternatives. The basic problem with string theory, and it's modern successor M-theory is that although it predicts the right low energy particle spectra, that's all it does. It doesn't give us anything that we can use to distinguish it from the standard model, so it's actually no better than the standard model - and a total pig to do any practical calculations with. Also it predicts too many dimensions, they may well be there, but unless we find a way of seeing them that strikes me as a problem. Quantum Field theories (at least the SU(N) ones used in the standard model) have the appealing property of only working properly in four dimensions, whereas M-theory needs eleven. - 06 Mar '07 00:59

Really? So before the human construct of natural numbers existed how many was 2?*Originally posted by DeepThought***Well very possibly, but the natural numbers are a human construction, they only really became relevant to us when accountancy became neccessary to keep track of production. Natural numbers are artificial.**