What is a force ?

[Cath]

As in the fundamental forces .. electro magnetic, strong and weak nuclear and gravity (if you consider gravity as a force).

I know opposite magnetic poles attract, potential difference causes attraction etc, but what really is a 'force' ?

What is it about a 'force' that gives it the ability to create the attraction or repulsion, what's actually going on there ?

[ronin]

I suppose that it has to be considered as a reduction in potential energy of a system.

Such that the final system is lower in energy and so more "stable".

Just thinking and I suppose "energy" is the wrong term, just no idea of another.

I do suspect that you are considering here something we see and can describe on the macro scale that has an explanation in the quantum scale, not sure about field theory.

So if you want the unified theory I ain't giving you it :eek: . Well not for less the  5 boxes of Jaffa cakes :grin: :grin: .

[JamesF]

I think the Standard Model associates forces with "carrier" or "messenger" particles called the gauge bosons, the exchange of which creates the forces we perceive.  My head started to hurt when I tried to understand any more than that though.  I'm really not sure at all how the Higgs boson fits into that, nor whether gravitons are somehow related to the HIggs boson, or as far as we're aware entirely fictional for the moment.

Which probably doesn't help at all, does it?

James

[Cath]

It may do James, it may do!

5 boxes of Jaffa cakes ! .. you drive a hard bargin Ronin !

[ollypenrice]

It's a darned good question!

 An influence tending to change the motion of a body or produce motion or stress in a stationary body. 

OK, so what's an influence???     

Olly

[Ouroboros]

"What really is a force?"

Oh dear! I'm not sure we will ever answer that question. In fact I'm not sure it's a question that has an answer.

We can describe a force. We can say a lot about it in tremendous detail. We can measure it. But what it actually is ..... who knows?

[Cath]

Exactly Olly

[Paul M]

Maybe we are back in wave-particle duality territory again.

I can visualise "fields" such as elecromagnetic or gravitational interacting and being perceived by us as forces.

I struggle to visulise their quantum counterparts, photon's and gravitons, interacting and how those interactions are perceived as forces.

I know that when I rest my arm on this couch I'm sat the atoms of the two "solid" masses don't physically collide. There is electromagnetic repulsion between their constituent atom I think? I 'm ok with that. 

When opposing magnets repel each other at a non-contact distance it's just the same force in action but acting at much greater distance? I'm ok with that.

The nuclear forces just befuddle me! Gravity more so!!

I wish someone would hurry up and unify them

[Tiki]

We can describe a force. We can say a lot about it in tremendous detail. We can measure it. But what it actually is ..... who knows?

We can also use force to define fields. Eg. Lorenz force in elecro-magnetic theory.

[Macavity]

My best inklings (only!) of the Higgs - Its necessity to standard model came from this blog:

http://www.quantumdiaries.org/2011/11/21/why-do-we-expect-a-higgs-boson-part-i-electroweak-symmetry-breaking/ (From the "Quantum Diary" of one Philip Tanedo)

He produces entertaining (fun figures) and meaningful explanations of "dead hard sums".

Further useful stuff in cross references too. Mere mortals begin at the bottom (it's a blog) 

[Ouroboros]

I'm rather ashamed to say as a trained physicist I have difficulty in fitting the weak nuclear force into my rough and ready concept of force, which is something that pulls or pushes things.

Gravitation, electromagnetism and the strong nuclear force fit with my crude conceptions. But not the weak interaction, which is responsible for things like radioactive decay.

My excuse is that I never had anything much to do with particle or nuclear physics. I should really read up on it.

[ollypenrice]

I'm rather ashamed to say as a trained physicist I have difficulty in fitting the weak nuclear force into my rough and ready concept of force, which is something that pulls or pushes things.

Gravitation, electromagnetism and the strong nuclear force fit with my crude conceptions. But not the weak interaction, which is responsible for things like radioactive decay.

My excuse is that I never had anything much to do with particle or nuclear physics. I should really read up on it.

Forces for courses?

S rry!

Olly

[Ouroboros]

:-) as you say, forces. Or are they manifestations of the same thing. Ooops .... off topic.

[Owmuchonomy]

I ran into these guys contemplating the very same question in Nagano....

..

[Ptarmigan]

I think 'force' and 'reactions to' is Newtonian speak, action at a distance is long gone.

These days it is all about fields and manifolds and other confusing ideas

For example : the mass of the sun no longer exerts a force on the earth, yeh 'onest !

It creats a gravity field which the earth kinda slips and slides about in.

Sorry for those technical terms

[Paul M]

I ran into these guys contemplating the very same question in Nagano....

..image.jpg

Beautiful image.

I wonder what they are contemplating?

Also reminds me that our hot tub needs filling. I may have some answers yet!

[ronin]

I think 'force' and 'reactions to' is Newtonian speak, action at a distance is long gone.

These days it is all about fields and manifolds and other confusing ideas

For example : the mass of the sun no longer exerts a force on the earth, yeh 'onest !

It creats a gravity field which the earth kinda slips and slides about in.

Sorry for those technical terms

That is the problem, Newton described gravity as a force, Einstein treats it as a simple distortion/effect.

So I assume that means gravity is not a force and so does it exist as such.

The effect of a gravity well can be described as if it were a force but that is just an analogy.

Hence my simplistic statement of "potential" all you do in any gravity well is fall down "the slope" and so your potential is reduced.

Maybe that is why Gravity always seems to be the odd force out, it isn't one and is incorrectly named as such. (All Newtons fault)..

Has anone ever tried unifying the others and just ignoring gravity?

Not here but in some institute elsewhere?

As in gravity is not a "force" so leaving it out of the equation?

Gravity would appear to be a candidate to be described as not a force but an effect that can be described in force like terminology.

[Ptarmigan]

Has anone ever tried unifying the others and just ignoring gravity?

Oh yes.

The electric force, as it was then called, and the magnetic were the first fields to be unified by Maxwell into the electromagnetic, which explained how radio (and TV !) work 'at a distance'

Then came the electroweak unified field which added the weak nuclear to the electromagnetic in the 1960s, which is where I came in ! , by Steven Weinberg and Abdus Salam.

Then it all got a bit complicated I think the strong nuclear has been added recently ( there were several competing ideas since the '60s )

But yes, you are right, gravity is the odd one out in that there is no GUT including it, but the rest have been.

( needs a quantum theory of gravity to be invented yet, watch this space so to speak )

Edited to add Steven, I knew I'd remember it soon !

old age never comes alone

[Tiki]

Maybe that is why Gravity always seems to be the odd force out, it isn't one and is incorrectly named as such. (All Newtons fault)..

The gravitational force is of course relatively weak. eg. The ratio of the gravitational force to the electrical force is of the order -10^43 for two electrons.

[Tiki]

Gravity would appear to be a candidate to be described as not a force but an effect that can be described in force like terminology.

Isn't this what Einstein did: he expressed the curvature of spacetime in terms of local tidal forces.

[ollypenrice]

Maybe forces were first identified when they did something. Faraday and then Einstein described them before they did anything. I'm waffling!! 

Olly

[Ptarmigan]

What is it about a 'force' that gives it the ability to create the attraction or repulsion, what's actually going on there ?

How about this :

Imagine you are in a field and there's a bull and a cow looking at you and the field has a bit of a slope.

Now imagine instead two pith balls, one is charged positive and the other negative, one of them slides one way and the other heads off in the other direction, looks like they are being pushed by a force, but no, they are just sliding about in a muddy field

Now imagine instead that they are a North pole and a South pole, one goes off one way and , what's that you say,  not yet discovered any isolated monopoles, hmmm,

it gets worse no negative gravity neiver !!!

Oh bother,

goes back to scratching head

nurse, nurse, help !

[ollypenrice]

Something I read in a text book regarding general relativity; two people set out heading due north from the equator, separated by a thousand miles. They maintain a course perpendicular to the equator but they collide at the north pole. They conclude that some force pulled them together. Discuss!

Olly

[acey]

"Force" is a term of Newtonian physics, meaning something that can cause acceleration (there are other equivalent ways of defining it too). Einstein showed that this concept is actually invalid: you cannot define "force" (in the Newtonian sense) within any theory that obeys special relativity.

In common parlance we still speak of the "force" of gravity, and for most purposes Newtonian physics is good enough. Einstein showed how to model gravitational interaction in a different way. So really we should speak of "interactions" rather than "forces", the known fundamental ones being gravity, electromagnetism and the strong and weak nuclear interactions.

Einstein modelled gravity "geometrically" whereas quantum theory models interactions by means of intermediate particles which transfer momentum. The "force carrying" particles are photons for electromagnetism, W and Z for weak interaction, and gluons for strong interaction. It is hypothesised that gravity would be mediated by "gravitons", but a proper theory for this has not been achieved.

The electromagnetic and weak interactions have been shown to be aspects of a single underlying interaction ("electro-weak"), and it is believed that all the fundamental interactions should be unified in this way. In the first moment after the big bang there would have been a single kind of interaction which then "split" into the ones we know as the universe expanded and cooled. Gravity would have been the first to become "frozen out". But the existing theory of the big bang is based on general relativity, i.e. gravity, so in order to get the full picture it is assumed that one should first understand quantum gravity (the theory of gravitons).

[Astrodob]

Not a good question..

It's a form of energy that moves objects in certain directions.