what is the speed of force?


Valued Senior Member
Now suppose there are two oppositely charged particles with one having say +q and other -q charge.see the whole thing(i mean the whole system) on a page.now both are miles apart so they follow coulumbs law of attraction,since they are point masses.now one the particle is experiencing a force due to another.now say i move one particle with -q charge horizontally by a small distance,now for the big one,will the particles change in position affect its force,what i mean is that the particle with +q charge,will it shift its postion simultaneously so as to make it (the one having -q charge) experience the same force as it was earlier.reports say that it will take some time for the particle with -q charge to experience same force.does that mean force has speed?if yes what is the speed of the force?.In resnick and halidey its written that speed of force is infinite.what does it mean?
As far as I know the electro-magnetic force (EMF) of charged particles propagates at the speed of light (c) and has a range of infinity.
Interesting subject...

Hi Zion,

The reason why the textbook you read says the speed of a force is infinite is because it reasons in a Newtonian context.

Newton assumed that a force immediatelly acts on an object at a distance; eg. if you would consider a lead ball, and would all of the sudden put a bigger lead ball 1 lightyear away, the two lead balls would immediatelly start attracting eachother in his view. The same goes for two electrons: if you suddenly put one electron next to another, they would immediatelly repell eachother according to Newton.

However, nowadays we know (or at least: we think) that electrons repel eachother through the exchange of photons. This means that the electromagnetic repulsion (or attraction for that matter) propagates at the speed of light.

It was actually because of the work of Einstein (who taught us that no information can travel faster than light) that we now assume that all forces have a finite propagation speed (the speed of light). However, this seriously complicates even a simple calculation like two electrons repelling eachother. Therefor, in simple calculations, or calculations that not need an accuracy of 10 digits after the decimal, physicists assume that forces act immediatelly (propagate at an infinite speed), even though we know it is wrong. Either your textbook assumes this, or it is a textbook on Newtonian mechanics, where the idea of immediatelly acting forces is an historical artefact.


Speed of force

it is about equal to the speed at which a fart can be smelled after it has been ripped...He who smelt dealt it...in other words there is no answer as there are to many unknowns! Speed of what force? my fart , a rock falling, a feather falling, a fart in a hurricane?

What about quantum entanglement of photons or electrons? Using an electron or photonic pair that is entangled at the quantum level, isn't it possible to transmit information instantaneously?
Tricky question

Hi SeekerOfTruth,

Very good question indeed, but I am not able to answer it. There is still a lot of research being conducted on quantum entanglement, and from what I've understood, it indeed seems to violate the laws of special relativity (let me note that there have been other quantum experiments that seem to violate relativity as well).

It could be a very promising way of communication (if we forget about practical problems about getting electrons or photons entangled), but I am afraid it will not be for the next 20 years or so. The effect is still not accepted by the general scientific community, even though more and more experiments are being conducted that point in favor of the quantum entanglement effect.

Anyway, I expect a major breakthrough to be made on that front somewhere soon (maybe in the next two years or so), so a little more patience before we get more information on entanglement ;).



In "Quantum Entanglement" the two photons or electrons are the same particle in another dimension/s. Since they are in the same location, in another dimension, the force and interactions of these particles would be instantaneous. Maybe one day, when someone creates a split-quantum transmitter, this type of information transfer would be possible.


That seems like an interesting reply considering entangled photons have sucessfully been created in the proton teleport experiment conducted last year by 2 different groups - one at the Universtiy of Innsbruck and the other at the University of Rome.


( a brief mention in the 4th paragraph from the bottom - cant find a link to the original report atm )

Both EPR photons did seem to be in our current dimension ?
or am i not reading your reply correctly ?


I meant that photons are a dual particle. They would exist in two dimensional planes. While in our dimensional plane(three dimensions + time) there would be two photons, in the other dimensional plane they may be only one particle. Since energy transfer can occur between these planes, one photon would always know what the other is doing.