[james Muirhead]

james  Muirhead asked the Naked Scientists:
   
What is the source of the force of gravity or what is it that reaches up from the Earth to pull the apple downward?
What do you think?

[Bill S]

hi James.  This is just a thought from a non-expert.

If two, or more, massive objects are moved apart they are given gravitational potential energy.  If you pick up a rock, you are the source of that GPE, which causes the rock to return to the surface when you let go.

Extrapolate to the Big Bang, when all matter/energy was in intimate contact.  The expansion of the Universe moved all that apart, presumably, imparting GPE, so all the matter of the Universe has the energy to return to its original compact state if nothing prevents it from doing so.

This would mean that the Big Bang was the source of gravitational energy.  Naturally, that leaves the question of the source of the force that drives expansion, but that's another problem.

Hopefully, someone with more knowledge than I have, will come in on this.

[PmbPhy]

The source of gravity is mass. To be precise its active gravitational mass. The mass generates a gravitational field and the field exerts a force on whatever is in the field. The mechanism to do this is currently unknown. All we know is how it works, not why it works.

[zx16]

I thought it had been recently established, that it's all due to the Higg's boson.  This boson creates a "field" which has a "dragging" effect on particles,  which we perceive as "mass".

And this "mass" produces a "heaviness", which we used to attribute to a "gravitational force", but now we know it isn't, it's just the result of the Higg's boson's "field".

I mean how much clearer can you get?

[PmbPhy]

I thought it had been recently established, that it's all due to the Higg's boson.  This boson creates a "field" which has a "dragging" effect on particles,  which we perceive as "mass".

And this "mass" produces a "heaviness", which we used to attribute to a "gravitational force", but now we know it isn't, it's just the result of the Higg's boson's "field".

I mean how much clearer can you get?

You appear to be confusing inertial mass with active gravitational mass. The Higgs boson is part of particle physics which is a quantum theory of particles. As of yet there is no quantum theory of gravity. The reality will certainly be clearer than your belief as stated above.

[jeffreyH]

With the electromagnetic field the force carrier is the photon. For the gravitational field the force carrier is the hypothetical graviton. This has been described as a two copy gluon. However, the graviton cannot be made of gluons since the force is inverse square. The gluon is the reverse. It gets stronger with distance. Gluons can absorb and emit other gluons. This could be the same for gravitons. None of this speculation about the graviton should be taken as the truth.

[geordief]

I thought the current theory of gravity was geometrically based (GR) and that the mass of objects did not cause an "attraction" effect as all objects appear to be attracted whether or not they were massive.

Now I  have heard that massive objects are indeed responsible for the way  the co ordinates used to model space time  become curved locally.

Is it  the mechanics of this action which are not understood?

All we have is the description that (loose quote) "mass curves space and curved space tell mass how to move" ,it seems to me.

[Bill S]

I thought it had been recently established, that it's all due to the Higg's boson.  This boson creates a "field" which has a "dragging" effect on particles,  which we perceive as "mass".

I don’t think the boson creates the field.  Doesn’t the particle arise as a disturbance in the field?

The idea that the Higgs field gives mass via a drag effect is misleading.  This arose from an analogy thought up by David Miller when William Waldgrave, (science minister in John Major's Government, needed a layman-level explanation of the Higgs mechanism in order to make a case for continuing the British share of funding for the CERN project).  It’s the one about a famous person crossing a room full of people.  This is not how the Higgs field works.   

BTW. It won Miller a bottle of Champagne, but his family beat him to it – he got none.

[zx16]

Frankly, I'm disappointed.  I thought the Higg's Boson would explain the cause of mass.  That's to say, mass is caused by the "dragging-effect" of a field caused by the Higgs thing.
But apparently it's not so simple, and nobody knows what they're talking about.

Is 21st century physics in a crisis?

[Colin2B]

Is 21st century physics in a crisis?

No, but the popular press like to oversimplify it.

[zx16]

The crisis of 21st century physics is this:

It has produced two different, and entirely irreconcilable, descriptions of what happens in the Universe:

1. Relativity Theory

2. Quantum Mechanics

They don't agree with each other.  Therefore there is something wrong about both of them.

[evan_au]

Relativity and Quantum Mechanics... don't agree with each other.  Therefore there is something wrong about both of them.

General Relativity describes the universe on a large scale, which is dominated by the force of gravity.
Quantum Mechanics describes the universe on a very small scale, which is dominated by forces much stronger than gravity.

They both work extremely well in the universe we see around us:
- in the LHC, which studies the world of the very small (and uses the principles of Relativity to do it),
- and in Astronomy, which studies the world of the very large (and uses the principles of Quantum Mechanics to do it)

However, at the event horizon of a black hole, the effects of gravity rivals the forces normally studied in Quantum Mechanics.
- It is in this (to date) unseen domain that General Relativity and Quantum Mechanics contradict
- Theoreticians are working on various approaches to a unified theory
- Rather than consider this conflict a disaster, researchers consider it an opportunity!
- Fortunately for us, applied physicists don't currently have any nearby black holes to study in microscopic detail, to resolve these open questions!

But for the rest of the universe outside a black hole, we think that both theories are happily compatible, and explain events in our solar system and beyond with great precision.

[yor_on]

Want to hear something weird
What if 'space' is 'gravity'?

I've started to wonder, I find 'vacuums' very bothersome myself.

[geordief]

General Relativity describes the universe on a large scale, which is dominated by the force of gravity.

What is the reasoning behind describing Gravity as a force?I thought GR  viewed  it through the prism of the geometry of spacetime.

Is there  a reason it can be called a  "force"? It is not the same as Newtonian force ,is it?

[jeffreyH]

General Relativity describes the universe on a large scale, which is dominated by the force of gravity.

What is the reasoning behind describing Gravity as a force?I thought GR  viewed  it through the prism of the geometry of spacetime.

Is there  a reason it can be called a  "force"? It is not the same as Newtonian force ,is it?

F = ma
g = Gm/r²
g = a
F = force

[jeffreyH]

In a gravitational field that is uniform everywhere you get a linear acceleration.
If the potential of the field varies from place to place this is not the case.

When the potential varies a graph of acceleration is curved and not a straight line.

Remembering that acceleration is the derivative of the change in velocity with respect to time.

[geordief]

F = ma
g = Gm/r²
g = a
F = force

Those are Newtonian equations. Is the concept of force limited to the mathematics of Newtonian gravity and so inapplicable to areas where Newtonian gravity  does not apply?

EDIT: we cross-posted..

[jeffreyH]

Incidentally the derivative of acceleration is jerk. The derivative of jerk is snap.

This adequately sums up tidal forces.

[jeffreyH]

F = ma
g = Gm/r²
g = a
F = force

Those are Newtonian equations? Is the concept of force limited to the mathematics of Newtonian gravity and so inapplicable to areas where Newtonian gravity  does not apply?

EDIT: we cross-posted..

They are approximations. You have to understand what is meant by curvature.

Since time dilates and length 'contracts' neither time nor space are linear.

This means that things don't happen simultaneously everywhere.

Add in the speed limit on information transfer (the speed of light) and viola!

Curved
 spacetime.

[geordief]

Add in the speed limit on information transfer (the speed of light) and viola!

Curved
 spacetime.

What ,not the whole orchestra (or even the string section) ?   

PS still no formatting on the site?