# Why two mass attracts each other?

Discussion in 'Physics & Math' started by hansda, Mar 19, 2013.

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1. ### FarsightValued Senior Member

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It's because electromagnetism has a chirality or "handedness". Check out Maxwell's On Physical Lines of Force. On wiki page 53 he says this:

"A motion of translation along an axis cannot produce a rotation about that axis unless it meets with some special mechanism, like that of a screw.

This is why we have dynamos and electric motors. You push current up the wire and the motor turns, and vice versa. Note Maxwell's mention of "vortices" in his title. You can emulate electromagnetic attraction and repulsion with opposite and similar vortices. Two opposite vortices move together, two similar vortices move apart.

Gravity isn't like electromagnetism in that it doesn't have a chirality. It's usually depicted via the bowling-ball-on-the-rubber-sheet analogy. The problem with this is that it uses gravity to "explain" gravity, so remove the bowling ball. Your rubber sheet is flat. Now emulate an electron by grabbing the rubber sheet with your left hand and twisting it anticlockwise. Emulate a proton by grabbing the rubber sheet with your right hand and twisting it clockwise. Now take a look at the sheet. It's a bit screwed up where your "hydrogen atom" hands are, but away from your hands, there's no twisting because the two opposite twists cancel. However there is still a resulting tension. This reduces with distance, altering the motion of waves traversing the rubber sheet, causing them to veer a little towards your hands. That's like light bending when it passes the sun. You have emulated a gravitational field. For matter falling down, you need to know about the wave nature of matter. See if you can work it out.

3. ### AlphaNumericFully ionizedModerator

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Farsight, chirality in particle physics is a difference concept to that. The fact a number of things in electromagnetism involves the cross product and the curl operator doesn't make it a chiral theory. Chirality in particle physics is like the concept in chemistry, the system is not invariant under a mirror reversal. The weak force is chiral in that when you split a particle state into its left and right handed chiral pieces using a chirality projector you find that only one of those two pieces arises in the system. This is experimentally seen in the weak force where certain decay processes have a directional preference. The electromagnetic field doesn't have that. The fact terms like $\nabla \times B$ turn up in Maxwell's equations is something else.

If all you can do is argue your case using analogies then you don't have a case. Multiple times you've had your misunderstandings of the curl operator and magnetic fields explains, as well as it being pointed out to you that the 'ball on a rubber sheet' analogy only gets you so far, the details of gravity's behaviour are not 100% encapsulated by that illustration.

When are you going to stop with this "I have all the answers, provided you accept arm wavy word salad devoid of any quantitative details or viable model" nonsense? Basic vector calculus and electromagnetics isn't difficult, on the grand scheme of things, it's beginnings are taught to first year undergraduates. If you only faced up to the fact analogies are, by their very nature, superficial in their insight and that your approach thus far has amounted in absolutely zero working models you might be able to start down the road of doing something constructive. You have sunk years and a lot of money into developing something with less applicability than even 'not even wrong' string theory, which you repeatedly hold up as a joke and a farce for, so you perceive, its lack of real world applicability. Come on now, electroamagnetics and vector calculus are fun and intellectually rewarding, you have nothing to lose but your ignorance.

5. ### OnlyMeValued Senior Member

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Rita, it really is not so complicated.

Gravity does pull two masses toward one another. The reason planets don't just all get pulled into stars, is because they are moving. Everything that is moving has momentum. You have heard I am sure, that an object in motion tries to stay in motion. If something small and light is moving and runs into you, (like a butterfly) it has little momentum and not much happens to you..., but if it were a car, which has far more mass.......

So planets are flying thorugh space at pretty fair velocities, (the earth travels at just a little less than 1000 MPH), and they have a lt of mass and a lot of momentum. It (the planet) tries to go straight but the sun, or star's gravity pulls on it and causes it to curve around the sun in an orbit. The planet's momentum and the gravitational force between the star and planet, balance out.

There are situations where things are pulled into massive stars.., neutron stars and black holes, where the gravitational forces are very large, but for the most part in our solar system and for most of the stars with planets we know of, the balance between the gravitational force and the momentum of the planets balances and the planets wind up in generally stable orbits.

It really is a lot like having a weight on a string or rope and twirling it around. The rope pulls on the weight keeping it from flying off. The pull you feel on the rope as you twirl the weight around is the force of the weight trying to go straight instead around. Here the rope plays the part of gravity and the pull of the weight you feel is the momentum of the weight.., resisting gravity.

Remember the earth weighs a lot and is moving around 1000 MPH through space.., that's a lot of momentum and there isn't very much left in space (in a planet's orbit), to slow it down.... So gravity and the planet's momentum balance out in an orbit. The planet does not get to go straight, as it would like... And the sun or star's gravity does not get to pull the planet in.

7. ### FarsightValued Senior Member

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It isn't a different concept. Google on say "positron chirality" and you soon appreciate that the electron and positron have the opposite chirality.

The analogy is apt, and it's appropriate to the question and gives a fair answer that can be readily understood. A better answer would step up the dimensionality and move from a rubber sheet to a bulk. I'll offer that if hansda requests it.

Cut the carping. What you offered in post #8 was hopeless because you have no understanding of electromagnetism. See Minkowski's Space and Time and look towards the end, opposite figures 3 and 4. Note this:

"In the description of the field caused by the electron itself, then it will appear that the division of the field into electric and magnetic forces is a relative one with respect to the time-axis assumed; the two forces considered together can most vividly be described by a certain analogy to the force-screw in mechanics; the analogy is, however, imperfect."

Note that the electron has one field, the electromagnetic field, that field interactions result in electric and magnetic force, and the two forces are related via a screw analogy. What I said was no word salad. And we don't refer to spinor fields (ie matter like electrons etc) for nothing.

8. ### Markus HankeRegistered Senior Member

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381
The answer to both of these is no. I implied no such things. I was merely attempting to illustrate a geometric concept through the use of a highly simplified, and thus limited, analogy.

9. ### Markus HankeRegistered Senior Member

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AlphaNumeric is of course correct, the chirality of an elementary particle like the positron has no connection whatsoever to the vector cross product. They are very different concepts.
A system is chiral if and only if it cannot be mapped to its mirror image by only rotations and translations, i.e. if and only if its symmetry group does not contain any orientiation-reversing isometries. This is the official definition, nothing at all to do with vectors and cross products.

Since electrons and positrons are invariant under parity transformations ( in the sense that their spin flips its sign ), they thus possess chiral symmetry. The same would, by that definition, not be true for an abelian gauge theory like QED with its U(1) symmetry group, hence electromagnetism does not possess chirality. This is not surprising since the mediating vector boson, the photon, is its own anti-particle.

In either case, chirality has nothing whatsoever to do with vector cross products.

EDIT : There is a concept in electromagnetism called helicity, which is related to the polarization of an electromagnetic wave. This just as an aside.

10. ### Markus HankeRegistered Senior Member

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I think there is only one person here who should cut the carping, and it is certainly not AlphaNumeric. Post #8 was well written, physically and mathematically spot on, and very insightful. You have no hope of ever matching his understanding of the underlying physics. Trying to explain to you the concepts he alluded to seems a bit like throwing pearls in front of a sow, in my mind.

11. ### FarsightValued Senior Member

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With respect Markus, the picture you have of QED is incorrect. The mediating vector boson is a virtual particle, a "field quantum" sometimes described as a chunk of field. There are no actual photons flitting back and forth between the electron and the proton in the hydrogen atom. Matt Strassler wrote a pretty good article on virtual particles here. Note this:

"But if two electrons pass near each other, as in Figure 1, they will, because of their electric charge, disturb the electromagnetic field, sometimes called the photon field because its ripples are photons. That disturbance, sketched whimsically in green in the figure, is not a photon. It isn’t a ripple moving at the speed of light; in general isn’t a ripple at all, and certainly it is under no obligation to move at any one speed..."

The two electrons move apart because of an electromagnetic field interaction, not because they're flashing at one another. And the electromagnetic field really does have a "screw" nature like Maxwell and Minkowski said. And see wikipedia, screws can be left handed or right handed. Note the illustration. In electromagnetism we use the right-hand rule for good reason. And the electron and the positron have the opposite chirality for good reason too. If they had the same chirality they'd have the same charge. Doubtless the teaching you've received has left you with the impression that the electron is a point particle, but remember electron diffraction, the Einstein-de Haas effect, and the fact that a point particle can't have magnetic moment. Remember that "spinor" and remember the ethos of QFT: everything is field. So the electron's electron's electromagnetic field is part of what it is. The E and B vector fields don't actually describe this field, they describes the linear and/or rotational force that results from electromagnetic field interactions. See wiki, remember what Minkowski said, and then see section 11.10 of Jackson's Classical Electrodynamics: "one should properly speak of the electromagnetic field Fuv rather than E or B separately". Also note the mention of handedness in the wikipedia cross-product article and the reference to chiral in Curl (mathematics). The best analogy I can give for the underlying chirality touches on topological charge and employs a cubic lattice. Reach in with your right hand, grasp the lattice, and turn it clockwise. Then reach in round the side with your left hand, and again grasp the lattice to deliver an orthogonal rotation. You can do this clockwise or anticlockwise to yield two different chiralities. Find some pictures of electron-positron pair production in a magnetic field within a cloud chamber. They leave curved tracks. The electron curves one way, the positron curves the other. Throw electrons and positrons through a solenoid and note the opposite helicities. It doesn't happen for nothing.

EDIT: I see you've added the word helicity. See above. It isn't just related to the polarization of the electromagnetic wave.

12. ### Markus HankeRegistered Senior Member

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That is fine, the important point in the context of the thread is the symmetry group, which is U(1) with the electromagnetic 4-potential being the underlying field. This symmetry group is achiral, so there is no chirality within the framework of QED. You may wish to address this very simple point.

13. ### FarsightValued Senior Member

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It's rather straightforward. See the wiki derivation from electromagnetic theory and note this: "the curl operator on one side of these equations results in first-order spacial derivatives of the wave solution, while the time-derivative on the other side of the equations, which gives the other field, is first order in time". I would caution that "the other field" is somewhat inaccurate because this presents E and B as two separate fields when the field concerned is Fuv. Nevertheless, consider the typical sinusoidal electromagnetic sine wave, and plot the integral to draw a "hump" of potential. The top of the hump is in the middle of the wavelength where the sine goes to zero, and is related to the Aharonov-Bohm effect. It isn't chiral. But look at the left and right sides of your hump. Where the sine wave is below zero the hump curves this way /. Where the sine wave is above zero the hump curves this way \. Apologies for the flat symbols, but I hope you can see what I mean. Pair production essentially separates the electromagnetic field-variation and the net zero curvature into two standing electromagnetic fields. These feature curl and chirality rather than mere curvature, being three-dimensional rather than two dimensional. The chiralities are opposite, as per my lattice analogy. Note The Role of Potentials in Electromagnetism by Percy Hammond where you can read "We conclude that the field describes the curvature that characterizes the electromagnetic interaction." All this may be unfamiliar to you Markus, but I'm not making it up.

14. ### Markus HankeRegistered Senior Member

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381
I have already given you the definition of chirality, and shown you quite clearly that it has nothing whatsoever to do with cross products of vectors, but rather with the isometries of the underlying symmetry group of the system. Why are you still trying to argue the point with statements like

which is entirely without physical or mathematical meaning. The article you referenced is about the derivation of the EM wave equation from Maxwell's equations ( a standard excercise for any undergrad physics or maths student ), and again has nothing whatsoever to do with chirality.

Btw, I am quite familiar with the maths and physics of electrodynamics, both its vector field and tensorial formulations. Currently I am studying its description in terms of differential forms, which is extremely interesting and incredibly powerful. In either case, chirality is not involved here; you might be confusing this with helicity, which is a different concept.

15. ### wellwisherBannedBanned

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5,160
If you follow mass, in general, to its inevitable conclusion, mass spontaneously heads in the general direction of the speed of light reference. This is easier to see if you scale up to larger mass first.

Energy does not net condense into mass in our real time universe. That is the exception. The net direction is mass back to the speed of light reference, via fusion into energy, or the space-time contraction of mass into black hole points.

Here is a reference example to approach this from another angle. Say you were on a moving train. If you stuck your head out the window and looked forward, in the direction of travel, you will notice the forward scenery appears to be expanding in an integrated way (getting closer). If we look backwards, toward the caboose, we will notice the scenery appears to contract in an integrated way (getting farther away). This is based on our reference velocity vector normalized to zero.

Next, I would like to plot these train observations as a function of time, with the zero point being the point in time we stick our head out the window and begin looking. Forward is positive time (future places we will be) while looking back to where we have already been will is negative time (past).

In terms of our analogy, mass attraction and gravity is heading back to the past; BB starting point. Mass exists in time. This negative direction of time means it existence is losing potential in time; back toward C where time is not a factor. Time is only important to inertial reference not the speed of the light reference.

The future we see from the train is in the direction of increasing time or time potential. This heading away from the speed of light reference is implicit of the expansion of space-time even further from C.

The variable of science that is closest to time is entropy. The entropy of the universe has to net increase, just as time as to move forward. Energy is conserved which is not how time works. Time is only conserved at C; eternal clock. But in finite reference, both entropy and time move forward with both increasing.

Gravity is interesting because it can lower mass entropy, via pressure. For example, turning water into solid state water in the mantle lowers entropy. If we equate entropy with time (time potential) gravity by lowering entropy with pressure, brings mass back into time; lower entropy of the past. Mass tries to return from where it came; energy.

16. ### hansdaValued Senior Member

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Consider a practical example of gravitational force between the Sun and the Earth in terms of GR.

The Earth will cause curvature of space-time for its movement. The Sun also should affect this curvature of spacetime around the Earth, so that the Earth remains in the orbit of the Sun otherwise the Earth may go out of the Sun's orbit.

17. ### FarsightValued Senior Member

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Try it for the Earth and an electron instead of the Sun and the Earth. Remember pair production and electron diffraction and the wave nature of matter. Look at the rubber sheet analogy again. What would happen to a ripple that was stuck in a little square path?

18. ### OnlyMeValued Senior Member

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This seems to be noting more than argumentative and misdirection.., because no one has yet come up with a successful model of quantum gravity.... We cannot yet model how the electron may or may not curve spacetime....., relative to gravitation.

You might ask how a free electron would be affected as it travels through the spacetime curvature of a star, but when you begin to interject, things like pair production, electron Difraction and the "wave" nature of matter, you start mixing GR and QM, which as yet do not agree on the character and nature of space and time, let alone spacetime and gravitation.

You are mixing quantum mechanics with general relativity, without first laying the ground work for a common understanding of space and time let alone gravitation.

19. ### FarsightValued Senior Member

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I'm not offering misdirection, nor am I mixing quantum mechanics with general relativity. I'm referring to classical electromagnetism and relativity. Don't forget that Einstein's special relativity paper was On the electrodynamics of moving bodies, and the Minkowski quote I gave was from Space and Time. The wave nature matter is nothing new either. See wiki: The de Broglie hypothesis, formulated in 1924, predicts that particles should also behave as waves. De Broglie's formula was confirmed three years later for electrons... This is all plain-vanilla physics. I can't explain why a lot of people don't seem to know about it.

One thing that's fairly interesting is the Aharonov-Bohm effect which is "a quantum mechanical phenomenon". However it was predicted by Ehrenberg and Siday in their 1948 classical electromagnetism paper The Refractive Index in Electron Optics and the Principles of Dynamics. Sorry, I can't find n open-access version online. There's quite a lot of overlap between classical electromagnetism and quantum mechanics, IMHO more than most people appreciate. See for example this bit lower down on the wiki Aharonov-Bohm article: "In fact Richard Feynman complained [citation needed] that he had been taught electromagnetism from the perspective of electromagnetic fields, and he wished later in life he had been taught to think in terms of the electromagnetic potential instead, as this would be more fundamental."

Anyway, you know light curves in a gravitational field, and you know about the wave nature of matter. Try drawing a light beam going round a square path. Now draw it again, only this time curve the horizontals downwards a little. Then without lifting your pen off the paper, draw it again and again. It doesn't matter whether you draw the square path clockwise or anticlockwise.

20. ### OnlyMeValued Senior Member

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The question seemed to involve the gravitational interaction between the sun and earth. You were suggesting to substitute the earth and an electron....

How exactly we're you intending to model the way the electron curves spacetime? You cannot use GR and there is no successful QM model that models either.., any spacetime curvature due to the electron.., or the spacetime curvature due to the earth.

There is no common theory to model the gravitational interaction of an electron and the earth.., that is consistent with GR.

Trying to invoke how light is affected and curved as it moves through a gravitational field, does not apply. The photon is considered massless, while the electron has mass... And we have no example of a free electron's path through a gravitational filed.., as we do for photons. We don't even see electrons naturally moving at relativistic velocities.

The hypothetical you propose requires some model for gravitation that can be applied at both the macroscopic and quantum scales, for it to be comparable to the GR model describing the interaction of the sun and earth, stars and planets, planets and moons.., etc..

As long as speculation is the intent of the hypothetical, it is far more likely that the electron would be affected electromagnetically, than gravitationally. There is no similar issue dealing with gravitationally significant objects (stars, planets, moons etc.), since for stars, planets and moons (except in rare circumstances), any electromagnetic interaction can be ignored... Not so with a free electron.

What you are doing is cramming bits and pieces of information and theory from disparate sources..., theories, models and experiment..., without first defining a common model.

21. ### FarsightValued Senior Member

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I wasn't. The gravitational field of an electron is so slight as to be immeasurable.

GR is a successful theory that models the motion of light in the Earth's gravitational field. Light curves towards the Earth. We know that we can make an electron (and a positron) from light in pair production, we know we can diffract an electron, and we know it's got a magnetic moment, and we know it's got its spin. My illustration of light stuck in a square path was a primitive simplification of the electron intended to show why it falls to Earth. The horizontals bend towards the Earth, the verticals don't. And light is affected by gravity twice as much as matter.

It does apply. You could trap a massless photon in a gedanken mirror-box, and it adds mass to that system. You can contrive the box so that the photon follows a square path. When you open the box it's a radiating body which loses mass, as per Einstein's E=mc² paper. Again it's plain-vanilla relativity, and again I can't explain why a lot of people don't seem to know about it.

Not so. All it requires is the wave nature of matter. The horizontal component of the wave path is bent in a gravitational field.

Given a large gravitating body with no electromagnetic field, an electron will not be affected electromagnetically.

What I'm giving here is relativity with a bit of wave nature of matter backed up by references. Don't forget that Einstein refers to the electron in his E=mc² paper, and in his special relativity paper. If you search the latter, it's in there 33 times. Also bear in mind what Newton said in his letter to Richard Bentley on 25 February 1692: “That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it”. Why do you think an electron falls down? Magic?

22. ### OnlyMeValued Senior Member

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And yet electromagnetically it is not insignificant! Your example included the Earth and an electron where the interaction would involve the electromagnetic interaction. You cannot model how a free electron interacts gravitationally..., likely with anything... Even in a laboratory setting, neutrons are used.., not electrons or protons. At quantum scales charge dominates.

Again, desparate information and "quantum" leaps in assumptions. You CANNOT use what we experience and measure with light and photons, to describe how an electron interacts gravitationally...

As far as your "gedanken mirror-box" and a photon's mass is concerned.., Prove it! (You seem to be elevating a hypothetical-theoretical to the level of an assumed fact...) And while doing so try not to read history to meet your own ends and interpretations. While Einstein's paper introducing E = mc^2, predicts that the mass of an atom is increased and decreased by the absorbtion and emission of a photon, it does not suggest that the free photon has any inherent mass. It is the change in the energy state of the involved electron, as a part of the atom which is associated with the change in the atom's mass.

As far as why a lot of people don't know about it..., most try to read historical documents with an attempt to understand the original intent, and with some understanding of at least some part of what we know know that they (Einstien and Newton) did not. You seem to be projecting conclusions beyond the original intent.., to meet your own purposes.

You CANNOT assume that an electron and a photon are equivalent ether gravitationally or electromagnetically... Even given evidence suggesting a wave charcteristic of electrons. Photons have no charge—Electrons do. Electrons have mass—photons are massless. Photons move at c. Free electrons do not, under any observed natural conditions.

While there is some experimental evidence to support wave charateistics of free electrons, the wave nature of "matter" (protons, neutrons and complex atoms and molecules) remains theoretical.

Your example included the Earth, which has a magnetic field. Even so the electron will always be electromagnetically affected by any interaction with complex matter (atoms and molecules). The proximity at which that electromagnetic interaction occurs is the only issue. In practice the whole of the solar system is a charged environment where a free electron is concerned. The solar wind is heavily ionized.

Newton's contribution on this issue is of no significance. As for Einstein's contributions your are reading into his statements, your own conclusions. You don't seem to take into consideration the contextual environment of the times or the fact that much of what you reference lies within the early formation of the subjects they addressed. Knowledge advances and today we know far more than was available to Einstein, even ore so Newton.

Still my original intent remains.., you are mixing quantum conditions and the macroscopic environment of GR and gravitation, without first introducing or even referencing a unifying model.

You can describe how a photon moves through a gravitational field.., not why it does so... the curvature of spacetime describes that.., but it does not explain why it is curved.., just that it is. You cannot extend the photon's interaction to an electron or any massive particle or object. Likewise, though we can describe how a massive object moves through a gravitational field, we cannot extend that to free subatomic particles, with the possible exception of the neutron. All ionized particles which include electrons and protons are also affected by their electromagnetic environment.., and almost always to a greater extent than they are affected by gravitation.

23. ### FarsightValued Senior Member

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A neutron has spin half and a magnetic moment. The same principle applies.

I described it. We make electrons (and positrons) out of photons in pair production. We annihilate the electron and the positron and we get photons. The electron has spin half and a magnetic moment. And look at atomic orbitals. See the bit that says "The electrons do not orbit the nucleus in the sense of a planet orbiting the sun, but instead exist as standing waves". Why do you think we can diffract electrons? Because they're point particles? No. Because of the wave nature of matter.

What are you on about? I never said the photon has any inherent mass. However Einstein did say "It is not impossible that with bodies whose energy-content is variable to a high degree (e.g. with radium salts) the theory may be successfully put to the test. If the theory corresponds to the facts, radiation conveys inertia between the emitting and absorbing bodies". Isn't that good enough for you? Or would you dismiss Einstein because you don't understand this simple physics?

I suggest you read that original material.

I certainly didn't say electrons move at c. But I will say that a 511keV photon has the same active gravitational mass as an electron.

No it doesn't. Go and look up neutron diffraction. And fullerene diffraction. We can diffract buckyballs.

Oh that's quite enough. You dismiss robust experiment evidence and known facts, and Einstein, and Newton. I can't help you further.