Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 19/12/2005 11:31:32
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If you have a ball bearing, it will have a certain amount of gravitational force associated with it that acts as if concentrated at its centre of mass. Now, if you take a load of ball bearings & glue them together, the total gravity of your construction would act from the centre of mass of the whole.
As the gravitational attraction of this construction would be uniform in all directions, that implies that a ball bearing on the far side is contributing as much gravitational attraction as 1 on the near side. But, as gravity follows an inverse square law, the individual gravity of the ball bearing on the far side should be proportionately less than that of the ball bearing on the near side. This, in its turn, implies that whatever gravitational attraction each ball bearing has, is, as it were, sucked into the middle of the whole mass & then re-emitted. This would certainly appear to be the case were gravity a particle-based phenomenon.
Furthermore, the strength of the gravitational field of an object does not alter with time. The logical conclusion from this is either that no particles are being emitted or that for every particle that is emitted, another is absorbed. Any particle that is absorbed would have to have been emitted by another object. However, were our construction zapping out particles all over the place in the hope of finding another object to exchange with, that, surely, would gradually reduce its overall energy until, eventually, there were no more particles to emit. This is clearly not the case.
That means that somehow our construction "knows" when another object is close enough to exchange with. If that is so, it means that the force of gravity comprises 2 parts; the 1st, that which detects the other object and 2nd, the exchange of gravity particles. This would imply that gravity is not, in itself, a fundamental force and that something even more fundamental is at work. Hence, any theory that unites gravity, as no more than an attractive force between 2 objects, with the other forces must still be incomplete.
Another option is that there is no exchange of particles at all. Relativity says that mass distorts spacetime such that any object entering the gravitational field of another object is, in effect, going downhill (I know that's not a good analogy but it's the best I can manage). This means there is no actual attractive force between the objects; there is no direct interaction between them, no exchange of particle - just this "dip" in spacetime. Does this imply that gravity is the force that distorts spacetime? If so, that still means that gravity is not a force of attraction.
Right... that's the easy stuff out of the way. Now let's get to the dodgy bit! I'll use the rubber sheet analogy as I think everyone is familiar with that.
I've come across a few theories that propose that gravity leaks into the 4D universe with which we are familiar, from an extra dimension (I've seen recent reports of a forthcoming experiment to detect gravitons escaping back to their home dimension). However, to produce the effects of gravity as we see them, more must leak in where there is more mass.
So, what if all mass acts as a "gateway" into that extra dimension. Think of the rubber sheet - an extremely thin 1. Mass resting on that sheet causes it to "tear". Obviously, the greater the mass, the larger the tear. Now, gravity leaks in through that tear, so the bigger it is, the more can get through. This is where the sheet analogy fails. That tear is a function of the interaction between the mass and the whatever-it-is that separates us from the gravitic dimension. Therefore as the mass moves, the tear moves with it and so does the leakage of gravity.
But even this means that there is some force apart from gravity at work - the force that causes the tear. In conclusion, it seems to me that whichever you look at it, uniting gravity with the other forces will not produce a GUT.
I'm sure that more-able minds than mine have pondered this, but I can't find any mention of it anywhere.
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Am I alone in thinking that all gravity comes from the past, that being the singularity at the begining of our universe.
That while Time flows in one dirrection the attractive force of gravity acts as if it is trying to take us back in time.
Tomorrow lies outside our universe without it there would be no tomorrow.
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Yes, you probably are
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As far as I can tell, the difference is that if you have two ball bearing, a distance 2r separating them, and a distance d away from you, then the gravitational force should be: 2g/(r^2 + d^2).
If d is significantly larger that r, then this would approximate to 2g/d^2, which is what you would expect.
Clearly, if d is comparable in magnitude to r, then it would be a different matter, but then it is clear that in the extreme, that d is smaller than r (i.e. one ball bearing is one side of you, and the other is the other side of you) then it is logical that the approximation of assuming all the gravity emanating from the centre of gravity of the two ball bearings would obviously break down.
In other words, the assumption that the gravitational pull is from a point between the two ball bearings is only relevant at great distance.
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another_someone - I appreciate what you're saying, but I was thinking of a construction of many ball bearings pressed together. You wouldn't then be able to get between them. The gravitational attraction is measured as if it all emanated from a single point at the centre of mass.
However, in your example of being between 2 balls, your mass would have to be added to the system. If the balls were of equal weight and equidistant from you, then the centre of mass of the system would be somewhere inside you.
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quote:
Originally posted by DoctorBeaver
another_someone - I appreciate what you're saying, but I was thinking of a construction of many ball bearings pressed together. You wouldn't then be able to get between them. The gravitational attraction is measured as if it all emanated from a single point at the centre of mass.
However, in your example of being between 2 balls, your mass would have to be added to the system. If the balls were of equal weight and equidistant from you, then the centre of mass of the system would be somewhere inside you.
But the point still stands, that I would believe that the inverse square law (from a nominal centre of gravity) only applies when the distance between you and the object is large in comparison to the size of the object.
The inference is that the inverse square law would not neatly apply to object on the surface of the Earth. In fact, since gravimeters are used to measure variations of the Earth's gravity at its surface. Clearly, these variations could not exist if the gravity of the Earth was as if it originated from a point source. Thus the assumption that gravity works as if it was from a point source does not work when close up.
This is true, even if you are not actually getting below the surface of the Earth, or between the ball bearings of your example; but merely close enough that the size of the object is of the same order of magnitude as the distance between you and the object itself.
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But it has been shown that the gravitational pull of the earth is fractionally less at the top of a mountain than it is at ground level. That shows that gravity cannot be coming from the surface.
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quote:
Originally posted by DoctorBeaver
But it has been shown that the gravitational pull of the earth is fractionally less at the top of a mountain than it is at ground level. That shows that gravity cannot be coming from the surface.
What it shows, not surprisingly, is that much of the Earth's gravity does not emanate from the surface – because most of the Earth is below its surface. It does not show that the Earth behaves, at close quarters, like a point source of gravity.
If you were to say that gravity, as you ascend a mountain, were to accurately follow the inverse square law as if all the gravity emanated from the centre of the Earth, then you would have a point; but merely saying that it is less, without describing the rate at which it declines as you ascend, does not prove your point.
Even if all the gravity did emanate solely from the surface, you would still expect a reduction of gravity as you climbed a mountain in Scotland (even if only a very slight decline in gravity) as you move away from the gravitational pull of Australasia. But, in fact, you would anyway still expect a lot of gravitational pull from the solid mass of Earth all the way between Scotland and Australasia.
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Maybe I misunderstood what I read about going up a mountain:-
Your question is more complicated than it might appear. Gravity, as
best is known, is always attractive. Every particle in the Universe
attracting every other particle in the Universe. Newton's law:
F = G * M * m / R^2 where 'F' is the attractive force, 'M' and 'm' are the masses of two objects and 'R' is the distance separating the two objects.
The constant of proportionality 'G' = 6.67259x10^24 N*m^2/Kg^2. The AVERAGE radius of the earth is ~ 6.38 x 10^6 meters and its AVERAGE mass is such that: F = g * m where 'g' is the collection of AVERAGE constants G*Mearth/(Rearth)^2. has the familiar value 9.8 m/s^2. Among many web sites you can find the math worked out at http://hypertextbook.com/facts/2002/SamanthaDong2.shtml
Now this is the value used in introductory physics to work problems. In actual fact the force due to gravity varies with separation and the
density of the matter between the two bodies. Geologists use sensitive instruments that measure the change in the force of attraction at various places on the earth. For the purpose of your calculation, you only have to consider the 1/R^2 dependence to calculate the change in weight between a valley and a mountain, but "the real" calculation would have to take into account the fact that as you climb the mountain you are putting more "mass" between you and the center of the earth, so things are more complicated.
Vince Calder
Doesn't explain it in full, but does show that it's not at all straightforward. However, it says at the end "...between you and the centre of the Earth". Is that, then, not to be taken literally and is it, in fact, no more than a way of simplifying the maths?
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http://en.wikipedia.org/wiki/Gravity
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Thus gravity is proportional to the mass of each object, but has an inverse square relationship with the distance between the centres of each mass.
Strictly speaking, this law applies only to point-like objects. If the objects have spatial extent, the force has to be calculated by integrating the force (in vector form, see below) over the extents of the two bodies. It can be shown that for an object with a spherically-symmetric distribution of mass, the integral gives the same gravitational attraction on masses outside it as if the object were a point mass.
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OK. Thanks for the clarification.
However, it doesn't negate my original argument, it just alters it slightly & shows that I phrased it a bit wrong.
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As "another someone" has pointed out the description of gravity acting from the centre of mass of an object is a convenient simplification of what is really a very complex situation. Many of the familiar discriptions we use of physical phenomena are also similar approximations and only applicable within limited regions. Many of the ideas and discussions hre come as a result of extending simplifications like this beyond their region of applicability.
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God says so!
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One other very interesting simplification that is not always understood or used is the fact that if you have a hollow spherical shell of uniform density the gravitational field inside the shell is Zero! This means that the as you go down towards the centre of the rearth the acceleration due to gravity drops linearly to zero at the centre of the earth.
This fact also means that if you have a very large uniform body of indefinite extent (for example a simple universe!) the net gravitational field inside the body is zero. You would only get gravity if you could detect that you were nearer one edge than the other and if the universe had started expanding very rapidly (as ours appeares to do) this information may not have reached us yet and may never reach us. This is what is meant by having a flat universe
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Ian - thanks for that. So I can blame those buggers who over-simplified it in the 1st place! grrrrrrrr
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This is what is meant by having a flat universe
I thought that meant the geometry of the universe was basically Euclidean rather than Riemannian.
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quote:
Originally posted by DoctorBeaver
Ian - thanks for that. So I can blame those buggers who over-simplified it in the 1st place! grrrrrrrr
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This is what is meant by having a flat universe
I thought that meant the geometry of the universe was basically Euclidean rather than Riemannian.
But if there is no detectable gravity, then would we not in fact have a Euclidean geometry, since there would not be any gravity to curve space?
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But if there is no detectable gravity, then would we not in fact have a Euclidean geometry, since there would not be any gravity to curve space?
Good point [V]
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Beaver, Rules of thumb and approximations are very valuable when it comes to understanding something and doing a bit of original thinking its just that you've always got to remember the conditions in which they apply and not stray too far out of the box, or, if you do want to push the limits look for a new model or approximation. I have experienced more problems with mathematical pedants bashing their head against a brick wall of their own construction than I have with original thinkers getting an approximation wrong, finding out, and getting round the problem to create something worthwhile.
Learn, create, test and tell
evolution rules in all things
God says so!
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Eth,
going back to your original posting above, one thing occurs to me. (I'm not fully sure if this is one of the things you were getting at or not - the wording in your original posting was a little ... er ... confusing in places.[:)])
If you stick a million identical ball bearings together in a spherical shape, their combined gravitational attraction will be 1 million times that of a single ball bearing.
The ball bearings at the surface of the sphere will obviously be able to interact gravitationally with external bodies (i.e. other masses outside the sphere). But those trapped well inside the sphere will just spend their time interacting with others inside the sphere (especially if, as you say, the exchange of gravitational force might be mediated by particles - "gravitons" or whatever).
So the question is, how can the total gravitational attraction of the sphere be proportional to the total number of ball bearings in it (1 million)? How can the ball bearings on the inside contribute to the total attraction, given that the inner ones can’t “see out” to interact with the external world? Why isn’t the total gravitational attraction of the sphere proportional to the number of ball bearings (c.50,000) on the surface instead?
Or is this just a stupid question that betrays my complete ignorance of physics?[:I]
Can anyone help me to understand this?
Ta.
Paul.
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quote:
Originally posted by Solvay_1927
Eth,
So the question is, how can the total gravitational attraction of the sphere be proportional to the total number of ball bearings in it (1 million)? How can the ball bearings on the inside contribute to the total attraction, given that the inner ones can’t “see out” to interact with the external world? Why isn’t the total gravitational attraction of the sphere proportional to the number of ball bearings (c.50,000) on the surface instead?
Simple answer – do you know any way of blocking out gravity – if you do, I'd patent it real quick, you've just made a fortune inventing an anti-gravity machine [:)]
My impression of DoctorBeaver's thoughts on gravitons was that the balls on the outside would channel the gravitons in the same way that iron channels a magnetic field, but not that it would block the gravitons (maybe absorb and re-emit – he will have to explain that – but not just swallow up and not disgorge again).
quote:
Or is this just a stupid question that betrays my complete ignorance of physics?[:I]
Probably – but we'll allow you special dispensation for that [:D] (as if I don't ask enough stupid questions myself [:I]).
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Why does a compass point towards a mountain when close to it if the force at the top of a mountain is presumed to be less than at ground level? You may find that the actual gravitational force at the top of the mountain is greater, but counterbalanced by the centrifugal force of the planets rotation perhaps?
Eth, when people with multiple sclerosis experience high altitude standing on top of a mountain, their condition improves greatly. I found two cases in a magazine sharing their experiences, finding that they both could walk normally at the top of the mountain, leaving behind their sticks for support, yet when they got back to sea level they could not walk unaided. Fascinating when we were able to get the same results by tilting a bed to make use of gravity on the nervous system.
"The explanation requiring the fewest assumptions is most likely to be correct."
K.I.S. "Keep it simple!"
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Andrew what you are saying is not true and I doubt that any effects on people with MS have anything to do with gravity.
Learn, create, test and tell
evolution rules in all things
God says so!
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Or is this just a stupid question that betrays my complete ignorance of physics?
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Probably ...
I could go off you, another someone! [:p][:p][:p]
OK, so I know it was a really stupid question. But I suppose what I'm getting at is why can't you block gravity? How can the gravitational influence (on me, say) of each ball bearing not be affected in any way by the presence of other ball bearings which are in the way?
None of the other forces work like that, do they? (Magnetism/electromagnetism - or even the weak & strong forces?) And no particles can bypass all matter? (OK, neutrinos come close in that most of them can pass through the entire earth without intereacting with anything - but they don't all get through.)
Don't worry, I'm not expecting anyone to have an answer. I'm just thinking aloud.
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quote:
Originally posted by Solvay_1927
OK, so I know it was a really stupid question. But I suppose what I'm getting at is why can't you block gravity? How can the gravitational influence (on me, say) of each ball bearing not be affected in any way by the presence of other ball bearings which are in the way?
None of the other forces work like that, do they? (Magnetism/electromagnetism - or even the weak & strong forces?) And no particles can bypass all matter? (OK, neutrinos come close in that most of them can pass through the entire earth without intereacting with anything - but they don't all get through.)
Don't worry, I'm not expecting anyone to have an answer. I'm just thinking aloud.
OK, with my non-answer.
Gravity is a kind of peculiar force. Firstly, the quantum physicists have not really come to grips with it, so it clearly doesn't behave like anything else, but conversely, the relativity guys are really only able to deal with gravity.
Secondly, I don't know about how (or even if) you can block strong or weak forces (they're such short range that I can't imagine there's much practical need for it).
The electrical force can only be blocked by an opposite charge (i.e. a positive charge will attract a negative charge to cancel it out), but simply putting a piece of non-conducting material in the way of an electric field will not block an electric field. Gravity is totally different because it does not have an opposite (there is no positive and negative polarity of gravity – if there were, things could get very interesting).
Electromagnetism is something else, because it is an oscillating field, and it induces an opposing oscillating field (in the appropriate materials) which reflects the incoming field. What happens with gravity waves, assuming we ever get to see them, is another matter (maybe someone else knows the answer to that, but I don't).
One interesting question, since gravity is associated with mass, which is also associated with inertia; if you could somehow block out gravity, what would you expect to happen to inertia?
Another interesting question is what would the gravitation field of a tachyon look like? Ofcourse, how you might pin down a tachyon is another matter.
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quote:
Originally posted by Soul Surfer
Andrew what you are saying is not true and I doubt that any effects on people with MS have anything to do with gravity.
Learn, create, test and tell
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Local magnetic anomalies
(0-90 degrees; 3-4 degrees frequently)
Predictive geomagnetic models such as the World Magnetic Model (WMM) and the International Geomagnetic Reference Field (IGRF) only predict the values of that portion of the field originating in the deep outer core. In this respect, they are accurate to within one degree for five years into the future, after which they need to be updated. The Definitive Geomagnetic Reference Field (DGRF) model describes how the field actually behaved.
Local anomalies originating in the upper mantle, crust, or surface, distort the WMM or IGRF predictions. Ferromagnetic ore deposits; geological features, particularly of volcanic origin, such as faults and lava beds; topographical features such as ridges, trenches, seamounts, and mountains; ground that has been hit by lightning and possibly harboring fulgurites; cultural features such as power lines, pipes, rails and buildings; personal items such as crampons, ice axe, stove, steel watch, hematite ring or even your belt buckle, frequently induce an error of three to four degrees.
Anomalous declination is the difference between the declination caused by the Earth's outer core and the declination at the surface. It is illustrated on 1:126,720 scale Canadian topographic maps published in the 1950's, which included a small inset isogonic map. On this series, it is common to observe a four-degree declination change over 10 kilometers (6 miles), clearly showing local anomalies. There exist places on Earth, where the field is completely vertical; where a compass attempts to point straight up or down. This is the case, by definition, at the magnetic dip poles, but there are other locations where extreme anomalies create the same effect. Around such a place, the needle on a standard compass will drag so badly on the top or the bottom of the capsule, that it can never be steadied; it will drift slowly and stop on inconsistent bearings. While traveling though a severely anomalous region, the needle will swing to various directions.
A few areas with magnetic anomalies (there are thousands more):
-North of Kingston, Ontario; 90° of anomalous declination.
-Kingston Harbor, Ontario; 16.3° W to 15.5° E of anomalous declination over two kilometers (1.2 miles); magnetite and ilmenite deposits.
-Near Timmins, Ontario, W of Porcupine.
-Savoff, Ontario (50.0 N, 85.0 W). Over 60° of anomalous declination.
-Michipicoten Island in Lake Superior (47.7 N, 85.8 W); iron deposits.
-Near the summit of Mt. Hale, New Hampshire (one of the 4000-footers, near the Zealand Falls hut on the Appalachian Trail) ; old AMC Guides to the White Mountains used to warn against it.
-Around Georgian Bay of Lake Huron.
-Ramapo Mountains, northeastern New Jersey; iron ore; compass rendered useless in some areas.
-Near Grants, New Mexico north of the Gila Wilderness area; Malpais lava flows; compass rendered useless
http://www.geocities.com/magnetic_declination/
And gravity does have an effect on multiple sclerosis!
"The explanation requiring the fewest assumptions is most likely to be correct."
K.I.S. "Keep it simple!"
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quote:
So the question is, how can the total gravitational attraction of the sphere be proportional to the total number of ball bearings in it (1 million)? How can the ball bearings on the inside contribute to the total attraction, given that the inner ones can’t “see out” to interact with the external world? Why isn’t the total gravitational attraction of the sphere proportional to the number of ball bearings (c.50,000) on the surface instead?
That's sort-of what I was getting at.
Let's see if I can explain things better.
Instead of a sphere of ball bearings, just take 3 joined in a line across in front of you. Assume you are 4r from the centre of the middle bearing, therefore 4r from the centre of mass of the 3-bearing structure. The gravitational attraction would therefore be 3m/4r^2.
Now, turn the structure so that it's lengthwise away from you but still at 4r to the centre of the middle bearing, hence still 4r from the centre of mass. The calculation, therefore, is still 3m/4r^2, so the gravitational attraction should still be the same. But do the calculations individually for each bearing and it doesn't add up (g=m/2r^2+m/4r^2+m/6r^2). If you assume m=1 and r=1, you get a value for g of 0.1875 for the 1st calculation and 0.34 when you sum the individual values - almost twice as much!. (at least, they are the results from the spreadsheet I did)
Now, if you take a bar that is the same length and mass as the 3 bearings, what would be the result?
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Andrew. Magnetic anomalies have nothing to do with gravity. Gravitational anomalies associated with denser bits of material in the earth's crust exist and are an important technique used in prospecting for oil and other minerals.
Eotvos carried out many extremely accurate measurements of gravitational attractions of different materials and gravitational screening a long time ago and absolutely no gravitational dependance on material or screening down to parts per million has ever been detected.
Learn, create, test and tell
evolution rules in all things
God says so!
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Eth, to see your bull bearing paradigm work, you would have to place it in a location free from the earths influence. a better model would be the balloon popped during space flight when the water expanded outwards initially then all of it was attracted back to its somewhat distorted mass forming into its pre-popped state, this was shown on a goldfish in space discussion on here. Furthermore, the ball bearings are cast in steel, so can never interact properly with each other as each has a permanent state.
Maybe, if the ball bearings were polarised by magnetism prior to them being added to the mass it would give you a better picture of the way gravity aligns the particles.
I suspect this would indeed provide us with a better understanding of how it all works.
believing that gravity can only attract does not cut it for me also Eth. I am absolutely convinced that the pushing forces of gravity is responsible for the heating of the core in planets, as atoms unload their force against opposing atoms on the opposite side of the mass, not canceling it out, but interacting with each other to excite the atoms into producing an enormous amount of friction as they push against each other and jostle about.
Having offloaded the burden of the pushing force, the atoms jointly increase their pulling capabilities, bringing in more material from decaying planets.
Interesting post Eth, thanks
Hope the rib gets better soon, and I don't think you really hate me that much [8D]
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http://www.newmediaexplorer.org/sepp/SCIStudypart1.pdf
Soul
download the pdf file and scroll to the bottom to see how gravity affect multiple sclerosis. the tables are from an independent analasis of an early pilot study using a five degree head up tilt on a bad over a prolonged period to determine if gravity does play an important roll in the onset of many neurological conditions
"The explanation requiring the fewest assumptions is most likely to be correct."
K.I.S. "Keep it simple!"
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I have skimmed through your report and found it quite interesting. As far as I can see your thesis relates to the orientation of your body with respect to gravity particularly while sleeping. suggesting that it is best to sleep with ones head slightly uphill. I am quite prepared to accept that this could be slightly better than sleeping exactly flat. In fact most nights I sleep in an adjustable bed myself and find that having the head raised a bit is quite good.
However other aspects give me cause for concern. Firstly I see no reason why you should be so obsessive abouit small changes in the magnitude of gravity on the earth (which is where this discussion originated) Also your statistical presentations do not contain anything like enough data to be valid and look like a rather naive way to belabour a point that has been made at great length.
Finally your discussions with respect to densities of solutions being critical are not clearly expressed and appear at quick reading take little account of the osmotic pressure effects that are known to be important in fluid transport particularly in plants.
Learn, create, test and tell
evolution rules in all things
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Andrew I have now had time to look at other aspects of your work on the IOP and Tree huggers web pages. Although I would expect some cohesion between water molecules I am quite surprised you managed to get a sbig a value as you did. This discussion is way off the topic here and so is probably best continued elsewhere but I would like to know why you don't like the osmotic pressure aspects of physics. They are based on valid models and scientific demonstattions at least as effective as yours. Other important transport mechanismas inside cells are peristalsis and molecular ratchets.
To return to Dr Beaver's original gravity questions. You must remember that the gravitational field near to an irregularly shaped object (like your three ball bearing model) IS irregular it is only at large distances where the difference between squares of the distance to the nearest part and the most remote part can be neglected that the centre of gravity simplification is valid. The sphere is a special case because of its symmetry and the gravitational field over the surface of a uniform sphere is constant and equal to the effect of having all the mass concentrated at the centre.
Also looking at your original question there is some fundamental wrong thinking about quantum interactions when you talk about things "knowing" what to do,then exchanging particles this is not the way it is. The particle that is exchanged IS the knowledge that the other particle is near. This is best described aby two electrons colliding and bouncing off each other by coulomb repulsion the energy changes associated with the interaction are eplained in terms of the exchange of a photon between the two electrons.
Learn, create, test and tell
evolution rules in all things
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quote:
You must remember that the gravitational field near to an irregularly shaped object (like your three ball bearing model) IS irregular it is only at large distances where the difference between squares of the distance to the nearest part and the most remote part can be neglected that the centre of gravity simplification is valid. The sphere is a special case because of its symmetry and the gravitational field over the surface of a uniform sphere is constant and equal to the effect of having all the mass concentrated at the centre.
OK, thanks for the clarification.
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Also looking at your original question there is some fundamental wrong thinking about quantum interactions when you talk about things "knowing" what to do,then exchanging particles this is not the way it is. The particle that is exchanged IS the knowledge that the other particle is near. This is best described aby two electrons colliding and bouncing off each other by coulomb repulsion the energy changes associated with the interaction are eplained in terms of the exchange of a photon between the two electrons.
I understand that about electrons, but it's not really what I was getting at. Maybe my phraseology was a bit off.
What I meant was, if an object is sending out gravity particles willy-nilly, it will lose something unless an equivalent number of particles are captured. If gravitons are the particles that carry gravity and they're being emitted without a similar number being captured, the gravity of the object will gradually diminish. That is blatantly not the case. So, my point was, is there some other process involved that "tells" the object when to send out gravitons? Or are you implying that maybe there is a graviton cloud similar to, but obviously much larger than, an electron cloud?
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You've still not got it. Two gravitating objects are NOT sending out gravitons willy nilly. Nothing at all happens until they interact when they EXCHANGE gravitons to complete the interaction. the exchange of a graviton IS the knowledge of the interaction nothing else
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Hang on a mo, Ian.
If gravity is mediated by particles, how do the particles "know" when to interact? I would have thought it reasonable to assume that the gravitating objects have to be exchanging and receiving gravitons ALL the time. Otherwise, what would cause them to "switch on" the exchange and suddenly start interacting? And is that any different to the idea of the continuous sending out of gravitons in all directions (and receiving back different gravitons from different sources in every direction)?
Like with electromagnetic repulsion between two electrons - they never actually touch, so they must be continually sending out and receiving photons. (Like Eth talked about earlier, they're surrounded by a cloud of virtual photons - but I don't believe that's a cloud of finite size, that's just a probability cloud that continues into infinity, but very quickly gets very "improbable" as you move away from the electron.)
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If gravity is mediated by particles, how do the particles "know" when to interact? I would have thought it reasonable to assume that the gravitating objects have to be exchanging and receiving gravitons ALL the time. Otherwise, what would cause them to "switch on" the exchange and suddenly start interacting? And is that any different to the idea of the continuous sending out of gravitons in all directions (and receiving back different gravitons from different sources in every direction)?
That's my point
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Am I alone in thinking that all gravity comes from the past, that being the singularity at the begining of our universe.
That while Time flows in one dirrection the attractive force of gravity acts as if it is trying to take us back in time.
Tomorrow lies outside our universe without it there would be no tomorrow.
by Mad Mark
You're on similar lines to my idea. I think gravitational attraction is soething to do with our passage through time. Like maybe the vortex created by our wake.
And as for the singularity at the beggining of time; if such a thing as the singularity or even a beginning of time does exist, there is no denying the fact that it is, as you say the origin of gravity. And also everything else.
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You are all forgetting the effct of quantum mechanical uncertainty on the interaction. If you have large obects, OK they are exchanging gravitons and photons all the time however if you, for example have two electrons colliding with each other and changing direction as a result of electromagnetic repulsion the measurement limits imposed by uncertainty mean that you just can't tell how many photons that they exchange but the result is just the same as if they had only exchanged one during the interaction.
Learn, create, test and tell
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Ian - I think you're still missing my point. You keep talking about the actual exchange of particles. I'm asking about what happens BEFORE the exchange. Are gravity particles just emitted willy-nilly on the offchance of an exchange or is there a mechanism that initiates the exchange.
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Nothing happens before the exchange of particles. That's the point and one of the imnportant things about quantum wierdness.
It is possible to visualise an electron moving through the quantum mechanical vacuum as being surrounded by a haze of virtual photons but these are continually being emitted and reabsorbed. If they were emitted and lost the electron would loose energy and in the absence of anything else that just cannot (and does not) happen so they must be reabsorbed witihn the time and space limits set by the uncertainty principle. Things start happening only when two objects get close enough to interact.
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quote:
Nothing happens before the exchange of particles.
So the question then is, what triggers the exchange when it does occur? How do the particles "know" they're close enought to interact and start exchanging?
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If they were emitted and lost the electron would loose energy and in the absence of anything else that just cannot (and does not) happen so they must be reabsorbed witihn the time and space limits set by the uncertainty principle.
But what if the photons are lost and then replaced by other photons (from the ZPE / Quantum vacuum, or even from the photons that are constantly being emitted by everything around us that is above absolute zero)? How do you know the same virtual photons are re-absorbed?
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This is the best way of describing things as I understand them.
The terrible truth is that all the particles in the universe "exist" everywhere and at all times! It is just that it is very improbable that you will find them where they aren't supposed to be! that is one of the best ways of describing quantum wierdness. When two particles start to approach each other and interact the probability that they will interact rises and the way they will interact is defined by basic classical physics overlaid bt quantum uncertainty. At some point they interact witin the statistical range of their interaction and then it is possible to observe the effect of that interaction.
As far as emission and reabsorbtion this again is just a mental model and you just cant tell if it is the same photon or a different one the bookds just have to balance in the end
You have to be satisfied that there are some things that you just can't know.
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Everything has to have an opposite even gravity.The only problem is our understanding of gravity is so limited that until that question is fully answered we cannot begin to look for the opposite.
Is it not possible that the flow of time is the opposing force to gravity?
Tomorrow lies outside our universe without it there would be no tomorrow.
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Before energy had time to form into matter in our early universe time would have had a free run of the place and without that opposing force it ran away with itself.
Localy matter bends space in on itself but in the absence of matter time bends it outwards.
As for gravity and kenetic mass increase as you increase speed where you may expect the mass to effect gravity the opposite may happen, as the speed of the object will slow time locally its opposing gravity will decrease accordingly.
Tomorrow lies outside our universe without it there would be no tomorrow.
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I definitely think you've got an interesting theory, Mark. Mass in increasing gravity is like light in an increasingly dense medium, yeah? So if the mass or light is travelling perpendicular to the gravity or density gradient, it would (and does) turn towards the increase.
You're probably like me and don't know many details, just go with your gut.
unidirectional: Gravity (only attracts) Time (only forward)
two way : Electromagnetism (attracts/repels) Space (forward and back)
Parallels on a different scale. Maybe the medium in which gravity travels is time, not space. IN the same way that light doesn't experience time, gravity doesn't experience space.
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Mad Mark, you are absolutely correct! Gravity cannot simply attract, it has to repel also, just the same as a magnetic force.
With respect of gravity, the pushing force is occurring at the centre of the planet, generating the friction / reaction that maintains the heat at the Earth's core. Each atomic particle pushing against the opposing particles on the opposite side of the planet.
"The explanation requiring the fewest assumptions is most likely to be correct."
K.I.S. "Keep it simple!"
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Mark, rincewind and andrew what you are saying is a total load of tripe and has no foundation in physics.
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Okay, do you concede that, though relativity talks about space-time as one thing, it also states that anything travelling at the speed of light does not experience time, it exists in an instant (from its own point of view)?
So why couldn't the inverse be true (something experiencing time but not, from its own point of view, space)?
I'm not a highly trained physicist but I got an easy A at A level and had a ****in genius teacher who took us way beyond what was necessary for the exams. That was long ago and informal though.
I mean, gravity does not affect light's actual velocity. It just increases the frequency of the wave. In that respect it speeds it up. If you do the same thing to a massive body (ie increase the frequency of the wave associated with its kinetic energy), it increases its velocity.
I'm finding it hard to say what I'm trying to say. But I'm sure if we spoke face to face you'd have a fun, if turbulent time (depends how tired I am - I'm very tired at the moment so a bit all over the place).
It's like, 'stationary' matter can be thought of as travelling along the time axis of a space time graph. Light travels perpendicular to it, along the space axis. As matter accelerates, its direction (on the graph) rotates towards the direction of light. It tends towards being energy, all that anchors it is its rest mass. What would happen if matter turned the other way, from rest? It becomes energy/movement rather than acquiring more. Hmm. So what way is light travelling on the space axis again? Either, because time is not an issue. It doesn't know the difference between its start and its end.
These ideas that I throw out - they may be a bit far fetched and/or undisprovable and/or they don't add anything to accepted theories. To be honest I don't know (my maths is weak, I only got a B at A level and that was with hard work), but something I say might make a more adept physicist think along lines they wouldn't have, where they can make something useful out of it. You never know. They do have their foundation in physics, though more advanced physics might say they're stupid.
I have to say, a lot of accepted ideas in physics are complete tripe. Like the idea that there was 'nothing' before the big bang. 'Nothing', by definition, doesn't exist, never has, and never will. Just as an example.
If you didn't bother reading the rest read this:
Knowledge is a barrier to understanding. The more knowledge you have, the harder it is to understand. A lot of graduates come out of uni chock full of knowledge but without enough understanding (I'm not including you in this). Me and Mark, I think, understand all we know and our understanding has shot out the end of our knowledge, with momentum but no knowledge resisting it, just sparse factlets or whatever. So we have fun stringing together what we do know.
But sorry if we're inturrupting your discussion. I'll chill on the mad theories when I get a decent night's sleep:)
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I agree with you in that I see that as within our universe matter and energy are conserved there is no sense in thinking that it is not conserved within all space and time ie the appearance of our universe out if nothing is silly.
So the multiverse (everything there is including our universe and anything that may be outside of it) is of undifined (or infinite if you prefer it) space and time by definition. our universe is clearly defined in that it appears to have a dense hot and very smooth beginning and a cool quiet end. It appears to me and many other people that this is the simplest and most probable final cosmology. ie our universe is just one of many universes which start live for a while and then die (just like everything else) These are not parallel universes related to our own but totally independant and unknowable.
We are already aware of other "universes" spawning off from within our universe in the form of black holes the inside of which we cannot observe. These also have defined lives.
I realise the attraction that there must be a repulsive force to balance gravity but stop and think for a moment, gravity attracts very weakly at our scale but quite strongly when you think of stars and galaxies. Why don't they collapse immediately? what is the opposing force that stops them? The opposing force is angular momentum this is the reason why the universe continues to exist and in the words of a presentation that I am currently working on "Angular momentum the strongest force in the universe".
Look up and learn about the Virial theorem which describes how the conservation of angular momentum affects any distributed material that is trying to collapse under gravity. This has been known about and applied for more than 100 years
Also look up and learn about rotating black holes. Most of the descriptions of black holes talk about non rotating ones and it is just about impossible to create one of these. Rotating black holes are very different and much more complex.
Learn, create, test and tell
evolution rules in all things
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I'd be interested in reading/hearing your presentation (depending on who you're presenting it to cos it might go way over my head) because angular momentum is something that has recently started confusing me.
Why is linear movement apparently completely relative while angular movement seems to be absolute? What's the frame of reference? What are particles/planets/whatever rotating relative to?
Rotation, or a mismeasurement thereof, seems like another likely candidate for the reason behind dark matter/energy to me.
Do dark matter and energy seem just silly to anyone else? It really seems to me there must be a simple explanation for the gaps between theory and observation. It seems far more likely there's a problem with the theory rather than there's a load of matter and energy that we can't see for some reason.
Your summary of the lifetime of our universe made me think; space must have been/must be/must be going to be much bigger than what's in it, if you see what I mean. The cool end that you talk about is the ultimate heat death, right? Everything is much more spread out (obviously) than it was in the beginning. My question is, what's it growing in? What's it growing relative to? Because if it was hot in the very beginning when there was just energy, how can it be cool at the end, when it has all returned to energy. Where's the extra space come from? You say a black hole is a seperate universe from ours. The only way a black hole gets bigger is if we drop something into it, ay? The event horizon only expands because we've added to the mass and the internal density (presumably, insofar as we can say it exists) remains the same.
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Do dark matter and energy seem just silly to anyone else? It really seems to me there must be a simple explanation for the gaps between theory and observation. It seems far more likely there's a problem with the theory rather than there's a load of matter and energy that we can't see for some reason.
http://www.physorg.com/news9830.html
http://www.berkeley.edu/news/media/releases/2006/01/09_warp.shtml
http://physicsweb.org/articles/news/9/2/14
http://www.newscientist.com/article.ns?id=dn7056
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Cheers for those links Mickey, but I still think we're all gonna be laughed at by physicists of the future for this dark matter invention.
What evidence have we got that G, the 'universal' gravitational constant, is indeed universal and completely constant (for example, that's not my favourite possible explanation though)?
I'm gonna carry on reading (I got as far as the second one then branched off into MOND)
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Soul, what we are saying has no foundation in your interpretation of the literature. Gravity can not simply attract, the atomic particles that make up gravity have a repelling and attracting force. You cannot get rid of energy, so where has the repelling force gone?
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Originally posted by Soul Surfer
Mark, rincewind and andrew what you are saying is a total load of tripe and has no foundation in physics.
Learn, create, test and tell
evolution rules in all things
God says so!
"The explanation requiring the fewest assumptions is most likely to be correct."
K.I.S. "Keep it simple!"
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I am quite happy with the concept that Modified Newtonian Dynamics (MOND) may represent some or all of the dark matter anomalies obseved altough it appears to many that the balance of probabilities are against it. I have in fact posed questions relating to this elsewhere in these pages. I posted "Is there a lower limit to quantum interactions?" back on 29 dec 2005. this could be a physical justification for MOND type limitations
You are still making a big mistake in the roots of your thinking though. No energy exists in an electrical, magnetic gravitational or any other field itself of right. The only energy exists in the interaction of other objects with the source of the field via the field mediating bosons.
You are all thinking of a gravitating source as emitting gravitons like a light source emits photons. This is definitely not the case. You need to have two bodies orbiting each other or a non uniform object rotating before you start generating gravitational waves. Most normal objects of any size will redistribute themselves to become uniform and minimise the radiation they generate hence the reason why large planets are approximately spherical.
Learn, create, test and tell
evolution rules in all things
God says so!