GRAVITY PROBLEMS -- off topic from {Falsifying a young Universe}

Yes Yes Yes Yes, it does...Now, just jump into your time-machine, race back 100 years, and it will be RAZDs General Theory of Relativity

If you want to know about gravity, I suggest not reading crank sites. It is all very well being critical of GR, but if one does not have a first clue about the nature of GR (vanFlandern) then one tends to look rather stupid...

No, not at all; just a dislike for his arrogance or ignorance displayed in not appreciating1) that all of these points are more than well understood and explained/refuted by the multitude of serious players in the field of GR and gravity;2) his own lack of understanding when it comes to GR.If there were such serious problems, do you not think that scientists would jump at the chance for some original research? Believe me, everyone working in the field of relativity would love to be the first to write about a real problem.GR does have a real problem, in that it doesn't quantise consistently. The bulk of the papers in theoretical physics are related to trying to sort out this problem... I was referring to vanFlandern, not you. I was urging you not to listen to his rubbish, which is totally contrary to GR, despite whatever he says on the matter. It's just been done so many times... I don't have the time or inclination. I'm sorry if my post came out as agressive towards you, that was not my intention. I would simply suggest (as a one-time professional in the field) that you not trust his "work". If you are interested in this area of science, search out a good book such as Brian Greene's, or of course there is always A Brief History of Time and The Universe in a Nutshell. Perahps others here can suggest some more titles. I tend not to be too aquainted with the popular texts. Objects curve their surrounding space-time. An object follows the straightest path it can find through space-time. The straightest path for a small object near a large object is directly towards the larger object, or around the larger object in what we call an orbit; which one depends upon the initial conditions of the objects.Your straight path through space-time is towards the centre of the Earth. However, the solid ground is preventing you from following your path by exerting an upwards force upon you. That force is what you call gravity. There is no pulling This message has been edited by cavediver, 10-10-2005 10:21 AM

Actually, its not, but now we are entering real quantum stuff. The fermions in each atom are effectively points, so fermionically, atoms are 100% empty! But when you take into account the gluons, the nucleons gain an actual size and thus so does the nucleus. In the same way, the photons bulk out the atom, giving it its size. So bosonically, the atom is 100% full We are too keen to say that fermion = matter and boson = force but it's not as simple as that. And your/my solidity is generated by the coupling of the two in what we call QED. SG called it Coulomb repulsion becasue that is what we call the bulk "emergent" behaviour of all of those QED interactions.The "force" of solidity is directly related to the strength of E/M. This is unfathomly greater than the strength of gravity, which is why we stand or sit rather than sink As to what makes a surface... I'm not sure to which level you're referring. The difference between solid and liquid is simply chemical bonding. And liquids can be rather solid. If you hit water faster than it can get out of the way, it hurts!

As I've said before, we have theories of a second, third, fourth and even fifth "gravity" particle! Trying to find one consistent with observations is the problem. Turning it the other way round, we can postulate a particle that will "fix" the galactic rotation curves but not affect local observations, but we find that it is totally inconsistent with all that we know of particle and gravitational physics.I completely understand your objections but what you have to realise is that just about every decent scientist out there in this field feels exactly as you do. It would be nice to have a tweak to GR or even a new theory of gravity that perfectly explains grav phenom on all scales. But it just isn't that easy. The conclusion to which the vast majority have arrived is that adding dark matter is by far the most simple solution.From bitter personal experience I offer the following advice: if you think something fundemental has been overlooked by every one of the professionals working in a field, you are mistaken. Simple as that I'm open to counterexamples...

Just a couple of after-thoughts...1) Don't think I'm defending CDM to the death. I am simply defending its rightful place in the Standard Model. I haven't worked within the SM since leaving astrophysics and moving into theoretical physics. I wouldn't be at all surprised if something like ekpyrosis wasn't behind the phenomenon. In fact, I would be delighted, because I share your dislike of CDM for the same reasons, and string/M-theory is one of my areas. Howvever, at present, CDM is the best solution we have.2) Don't get too hung up on differentiating gravity from matter... they are one and the same, whether by geometradynamics, string theory, supergravity, etc.

I like this point. I'm too keen to talk about "moving" along straightest paths (with a nod towards Newton I), but "moving" has too many layman ideas of "what's making it move?" (i.e. unaware of Newton I).

Simple, we know as much about gravity as we do power, energy and momentum. All of these are intimately connected. However, the level of understanding required to appreciate this is immense... far far beyond any layman's guide or popular book, or indeed any undergrad course. No you don't. You've been sold a plausible analogy of what actually happens, and you have accepted it and decided to not ask another "why". The why of the car moving is in fact far more complex than the planet orbiting the star.If you push the "why"s far enough you get down to mathematics. We don't have anything else.

No, I do not admit that. That is misleading. From the point of view of the layman or indeed anyone outside of the field of gravitational research, I understand gravity exceptionally well. Where I fail to grasp at what is going on is at such a fundemental level that it is not worth talking about outside of the professionals working in that area, other than to say we have trouble quantising gravity, it is an active area of research at this time, and we have several very promising ideas.This message has been edited by cavediver, 10-11-2005 09:51 AM

Welcome to quantum mechanics Photons. Remember the energy levels that the electrons occupy? How do these arise? Action at a distance It's all the photon-fermion interactions involving the electrons, the quarks, and the photons. The atom is much much more complicated than the simple atomic picture usually presented. Well surface physics is a whole area. [abe 'cos I forgot] Surfaces become surfaces precisely because they are not that reactive. I guess most solid surfaces are either "crystaline" (rock, metal) or biological, where the latter have evolved to be non-reactive. As two surfaces approach, electrostatic repulsion overcomes anything else. Bring two iron blocks together and they will stay as two blocks unless you heat them sufficiently to where the surface atoms are sufficiently energetic to overcome the repulsion and form new metal bonds. Friction arises from irregularities in the surfaces "catching" on each other. This is not my area, but it's not that deep and doesn't require any real quantum knowledge. I think we are approaching a consensus. I agree and it is not how I would present the situation. But I think this is the fault of the popular science press, and not of the scientists. Black holes do not differentiate matter and anti-matter... it's all energy. Anti-matter does not have anti-mass (although demonstrating this is exceptionally difficult given our lack of anti-matter to hand)... Anti-matter is always portrayed as this nemesis of matter, but it's not an accurate picture. Ant-matter is all around and in us all of the time. It's just not there in bulk. Mesons are what bind the protons and neutrons together in the nucleus, and a meson is a quark, anti-quark pair.So pouring anti-matter into a black hole just makes the balck hole fatter. There's only one way black holes lose mass and that is via Hawking radiation.BTW, you do know that anti-matter is just matter travelling backwards in time, don't you? Yes, I agree with all of this. If I sound dogmatic at times, it is my defending of the Standard Model as our publicity brochure. I admit that I have doubts about a good proportion of the physics I explain. But these doubts are concerned with far deeper issues that I do not have the time to explain. Without a similar background in my subject, no-one else would understand my doubts. There are only so many analogies you can pile on top of another without completely losing the plot! This was essentially my message to Simple.I guess my point is that very few ideas have ever occurred in isolation. The concepts that gave rise to Relativity were spread across many different physicists and mathematicians, not confined to Einstein, as was the case with qunatum theory. And today we have orders of magnitude more scientists working on this stuff.Pick any plausible idea and I can guarentee it has been beaten to death. The real discoveries are made at the coal face. 100 years ago, the coal face was SR/GR/QM. We are a lot deeper than that now.But you are right, the real insights do seem to come from taking a step back and reconsidering. It's just that one step back (or one hundred) from the coal face is still several miles deeper in the mine than anyone outside the field has ever ventured. India has produced some astounding mathematicians but I think the majority of the really weird stuff has come from the western world. I think this eastern/western view comes again from popular science. I know what it is implied, but the depth of the concepts in theoretical physics transcends any preconceptions of eastern/western philosophy! Remember And it's interesting that the majority of theoretical physicists that I know have strong Platonistic/pseudo-Platonistic leanings based upon their experience in the field. I have yet to meet anyone with serious exposure to theoretical physics who takes a strong counter-position.cheersThis message has been edited by cavediver, 10-12-2005 09:36 AM

Yes, it is called Special and General Relativity, mixed with Quantum Field Theory, Representation Theory, Group Theory, Algebraic Topology, etc Available to anyone willing to sign up for and capable of pursuing a maths/physics degree, followed by a masters in maths/physics, followed by a PhD in maths/physics, followed by active research in maths/physics. If it could be explained simply, why would all that maths/phsyics be necessary? Any layman explanation of this stuff is tantamount to lying. Too often I explain things in layman terms, and the recipient then somehow feels qualified to extrapolate from what I have said, producing utter gibberish. Or worse, they start criticising the theory based upon the analogies provided. That is the crime of vanFlandern.If you are interested, start with the basics: Special Relativity and then General Relativity. I have provided brief explanations to both on this site in the last few months, and you can read more in the books suggested. But believe me, this is merely for curing your curiousity. It will not give you a fraction of the knowledge required to advance these areas, nor even what I would consider a reasonable level of understanding. There are no short cuts... Yup, or put aside ten years of your life and go sign up for that course...

It has nothing to do with the creation/evolution debate. It does have something to do with discovering a spiritual realm behind the natural. There has always been a fundemental level of understanding, and there have always been those that have said that God would be discovered just beyond the next level. He has not been found there yet, so why should now be any different?

Yeah, but my suggestion of taking 10 years out will save him a lot of time compared to reading his way through MTW

Yep, the maths of special relativity... that same maths that gives the Lorentz-Fitzgerald contraction which obviously isn't real becasue how the f*** is anything going to actually shrink, huh? And time-dilation, ha ha, yeah right. That really is going to turn out to be a real effect. What next, Einstein, time travel??? Jeez, the way these mathmematicians actually believe that these things could be real in any way rather than just mathematical artifacts. It's time these idiots used a little common sense...

I was in the process of adding a line about how my copy underwent collapse, when I thought... no, a little too undergrad I found my copy for 25 in pristine condition on my first day of Part III. I took it as a good omen.Wheeler is idiosyncratic but have you tried Penrose and Rindler yet? You haven't lived until you've tried to fathom Penrose's tensor diagrams!