3
$\begingroup$

As per my imagination any thing can't impose force on the other by not giving even a touch(i,e action at a distance). So I thought there must be some physical existence of lines of force. Although virtual particles hypothesis has been proposed. Up to my knowledge virtual particles are just said to be disturbance (field) and not the one what we thought as materialistic "particle". Anyway I have heard about Faraday speaking about such similar view about there physical existence. But I do have a naive idea about it. I would greatly appreciate if any one can input something about your view on the physical existence of force lines. It would be more appreciable if any one can speak about Faraday's and Maxwell's approach on this concept. enter image description here

I am providing Faraday's and Maxwell's basic views about the concept, so that anyone can speak about it.

FARADAY'S VIEWS: At first Faraday considered the physical reality of the lines of force as a possibility, yet several scholars agree that for Faraday their physical reality became a conviction. One scholar dates this change in the year 1838. Another scholar dates this final strengthening of his belief in 1852. Faraday experimentally studied lines of magnetic force and lines of electrostatic force, showing them not to fit action at a distance models. In 1852 Faraday wrote the paper "On the Physical Character of the Lines of Magnetic Force" which examined gravity, radiation, and electricity, and their possible relationships with the transmission medium, transmission propagation, and the receiving entity.

MAXWELL'S VIEW: Initially, Maxwell took an agnostic approach in his mathematization of Faraday's theories. This is seen in Maxwell's 1855 and 1856 papers: "On Faraday's Lines of Force" and "On Faraday's Electrotontic State". In the 1864 paper "A Dynamical Theory of the Electromagnetic Field" Maxwell gives scientific priority of the electromagnetic theory of light to Faraday and his 1846 paper "Thoughts on Ray Vibrations". Maxwell wrote: Faraday discovered that when a plane polarized ray traverses a transparent diamagnetic medium in the direction of the lines of magnetic force produced by magnets or currents in the neighborhood, the plane of polarization is caused to rotate. The conception of the propagation of transverse magnetic disturbances to the exclusion of normal ones is distinctly set forth by Professor Faraday in his "Thoughts on Ray Vibrations." The electromagnetic theory of light, as proposed by him, is the same in substance as that which I have begun to develop in this paper, except that in 1846 there were no data to calculate the velocity of propagation.

I hope anyone from quantum physics can speak about virtual particles.
Here is a opinion of Matt Strassler (click on this) about Virtual particles hypothesis

$\endgroup$

closed as primarily opinion-based by Emilio Pisanty, Jon Custer, stafusa, Rory Alsop, sammy gerbil Jan 8 '18 at 1:14

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 6
    $\begingroup$ "As per my imagination any thing can't impose force on the other by not giving even a touch" You should know that what you call "touch" is just the electric forces of outer electrons acting at extremely small distances. $\endgroup$ – Ataraxia Oct 16 '13 at 2:31
  • 4
    $\begingroup$ Field lines are a mathematical representation of the vector field created by a charged object. That's the only sense in which field lines "exist." $\endgroup$ – Dmitry Brant Oct 16 '13 at 2:42
  • $\begingroup$ @Dmitry Brant.If field lines were just a mathematical representation,then why there is similar pattern arising when iron fillings are sprinkled over a magnet.There might be some more explanation to be given on that particular formation of lines.I would expect you go through the link suggested to dmckee. $\endgroup$ – Immortal Player Oct 16 '13 at 4:23
  • 4
    $\begingroup$ @CURIE When you throw a ball in the air and let it drop, it makes the shape of a parabola. Did that parabola exist before you threw the ball? $\endgroup$ – Dmitry Brant Oct 16 '13 at 13:43
  • 7
    $\begingroup$ What does "physically exist" mean? This is a question about philosophy, not physics. $\endgroup$ – Ben Crowell Oct 17 '13 at 3:41
19
$\begingroup$

The electric and magnetic fields are real things: they can store energy and transfer momentum.

"Field lines" or "lines of force" are a visualization tool suitable for drawing vector fields. They are maps of the fields and the fields are real things. Is that good enough for you?


And, yes, the electromagnetic interaction can be described in another (more fundamental) way as exchange of bosons in a quantum field theory. But that does not change the fact they these fields store energy and transfer momentum.

$\endgroup$
  • $\begingroup$ @CURIE electromagnetic waves prove that an electromagnetic field in fact has to contain energy and momentum for interactions between charged particles to make any sense. There is a real "flow", but choosing particular field lines is an arbitrary illustration of that flow. $\endgroup$ – Robert Mastragostino Oct 17 '13 at 4:13
  • $\begingroup$ Isn't it possible to fully dispense with the concept of electric/magnetic fields though? $\endgroup$ – Ayesha Jan 17 '14 at 23:38
  • $\begingroup$ @Ayesha Er...no. They can be re-expressed in quantum field theory terms, but they're still there. And that is as it should be because they are "really real": as I say, they carry both energy and momentum. $\endgroup$ – dmckee Jan 17 '14 at 23:42
  • $\begingroup$ @dmckee I read a textbook (Griffith's) which stated that it is possible to dispense with field concepts entirely and formulate electrodynamics as an "action-at-a-distance" theory. Could you please clarify? Thank you! $\endgroup$ – Ayesha Jan 17 '14 at 23:45
  • $\begingroup$ @Ayesha Far be it from be to argue with the great man, but I don't see where he is going with that (that's not a book I have used): energy and momentum exist in free space, disconnected from any material object while the wave travels. That's not a problem on the light-cone (where time does not pass), but to us poor, leaden creatures it surely is. $\endgroup$ – dmckee Jan 17 '14 at 23:47
8
$\begingroup$

Does the fact that every rain drop falls in their respective straight lines all parallel to one another imply that those lines are physically real?

No. It is just the tendency of gravity to act between two massive objects--a straight line is simply the least inaccurate way to describe this interaction. You can also draw additional curved lines linking the sides and tops of the drop to the earth, but these cancel out because of symmetry.

If you were to observe the rain drops on an enormous scale--large enough to have to account for the curvature of the earth, you would then realise the lines are indeed not parallel, but converge to the earth's core. While this is another story, it helps to illustrate that gravitational field lines link two massive objects together and a billion water droplets are well described with a billion straight field lines connected to the earth.

The difference for magnetic field lines is that they are not formed between two independent magnetic monopoles (not yet confirmed to exist), but by one magnetic dipole. In this way magnetic field lines do not originate or terminate between two independent objects, but forms a closed loop with itself. By this logic the lines will never be straight but always curved--if they look straight it is only due to extreme magnification, such as looking at rain and thinking they all fall parallel when they are actually converging to one point. You may also get the impression that field lines are straight by dropping filings between the gaps of two magnets--they form a straight line of filings, but are in fact only highlighting a small portion of a large closed loop.

When you look at iron filings they do not show you field lines existed before the filings arrived, lines which must be obeyed, rather they draw field lines which exist now both because of the electrons in the magnet and because of the filings themselves which alter the closed field. So when you shake everything up...you will not get the exact same pattern, but you will still be able to see traces of closed loops.

$\endgroup$
  • $\begingroup$ Your statement that field lines not existing before iron fillings were sprinkled does not convince me.Because,field exist around a magnet even if there is no particle to experience it.And,comparison of lines of drops and the field lines doesn't hold good.Because,field lines have their physical significance(not to be confused with physical existence),but lines of drops has no physical significance.I meant to say that lines formed by drops doesn't exist,if there were no drops,but field exist even if there were particles(existence can be tested by sprinkling iron shavings) $\endgroup$ – Immortal Player Oct 16 '13 at 3:51
  • 4
    $\begingroup$ yes there exists a field before the filings come into the picture, but i am saying the picture does not even show this prior field because the filings themselves alter it (there is no way to depict a field except with a series of vectors or points, both of which betray the actual story and are only used because mathematics require them), causing field concentration near iron, and field gaps where there is no iron, and if you shook everything up, you would not get an identical picture. those lines you see only appear after the fact. $\endgroup$ – gregsan Oct 16 '13 at 4:35
  • 1
    $\begingroup$ Is it still thought that these field lines from the Sun snap? can they form a straight line then? $\endgroup$ – Jitter Oct 16 '13 at 4:37
  • $\begingroup$ straight field lines for magnetic fields are just a small sections of infinitely long magnetic field loops. $\endgroup$ – gregsan Oct 16 '13 at 4:38
  • $\begingroup$ Are they then distorted infinite loops at the so called snapping point? $\endgroup$ – Jitter Oct 16 '13 at 4:42
2
$\begingroup$

Field lines are created and located by people to demark measurable points in field strength according to some selected unit of measure, and also to show the direction/polarity of the magnetic field. Polarity exists, differences in field strength exist, field lines do not exist other than as a mental construct. The analogy to drops of rain describing non-paralel lines towars the center of the attractive body is a good one, as there are in that case no actual lines at play, just as magnetic field lines are also not at play, or at work, in any phsical sense whatsoever. The fact that they are useful in treating magnetic fields mathematically should not lead to their reification.

$\endgroup$
1
$\begingroup$

No, they don't exist physically (in macroscale). Magnetic field is changing gradually from point in space to another point in space (if you go subatomic, then I guess at some point it will be changing in Planck quanta, so I guess at that really small scale you could say that field lines do physically exist :)).

If you would measure the magnetic field around the magnet with say a Hall probe, and you would observe the magnetic field intensity as you move the probe slowly around the magnet, you would see only gradual change, not some "jumps" up and down as would be suggested by physical existence of those "lines of force".

Problem with visualizing with iron fillings or ferrofluid is that you don't really see magnetic field of the big magnet, what you actually observe are iron fillings turning into minimagnets which then cluster together. That cluster granularity has to do with physical properties of iron fillings and the surface they are on. Same goes for ferrofluid. The ferrofluid spikes are actually minimagnets created from ferrofluid particle clusters. If you drop another ferrofluid particle there, it will stack to whichever minimagnet is closer, it will not stand on its own. EDIT: in other words, with iron fillings you will see different lines than with say nickel fillings, also depending on filling sizes of course.

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.