Freethought & Rationalism Archive

Late_Cretaceous · 08-27-2002, 02:01 PM

This guy told me the other day that "Gravity is the absence of force". Has anyone heard anything like this? I never have. I think he may have misunderstood something he saw on NOVA or read in Sky and Telescope.

Abacus · 08-27-2002, 02:34 PM

The absence of what force?

Vibr8gKiwi · 08-27-2002, 02:46 PM

That guy hasn't taken even a basic physics course. Gravity is a force. It's the force of attraction between bodies that have mass. There's even a (weak) force of gravity between that guy and his blind, three legged dog, "lucky."

[ August 27, 2002: Message edited by: Vibr8gKiwi ]

Starboy · 08-27-2002, 03:20 PM

He might be talking about GR. In that case gravity is not a force, it is the shape of space-time itself.

Starboy

bd-from-kg · 08-27-2002, 03:35 PM

Actually there's a serious question lurking here. According to GR, gravity isn't really a force, but a curvature in the space-time continuum. But according to the particle physics geniuses, gravity can only be reconciled with QM by positing the existence of gravitons which carry or mediate the gravitational force. However, if gravity is a curvature in the space-time continuum it would seem that there is no force to carry or mediate. Anything in the curved portion of space-time should be affected immediately and continuously by the curvature; it shouldn't depend on whether or when it happens to interact with any gravitons. How can a curvature in a field be "carried" by particles? How can GR and QM be reconciled by throwing out GR? I'm baffled.

Jesse · 08-27-2002, 04:37 PM

It seems to be sort of up in the air right now as to what a theory of quantum gravity would say about curved spacetime, "gravitons," and so on. Here's something from an <a href="http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html" target="_blank">FAQ on virtual particles</a>:

Quote:

I hear physicists saying that the "quantum of the gravitational force" is something called a graviton. Doesn't general relativity say that gravity isn't a force at all?

You don't have to accept that gravity is a "force" in order to believe that gravitons might exist. According to QM, anything that behaves like a harmonic oscillator has discrete energy levels, as I said in part 1. General relativity allows gravitational waves, ripples in the geometry of spacetime which travel at the speed of light. Under a certain definition of gravitational energy (a tricky subject), the wave can be said to carry energy. If QM is ever successfully applied to GR, it seems sensible to expect that these oscillations will also possess discrete "gravitational energies," corresponding to different numbers of gravitons.

Quantum gravity is not yet a complete, established theory, so gravitons are still speculative. It is also unlikely that individual gravitons will be detected any time in the near future.

Furthermore, it is not at all clear that it will be useful to think of gravitational "forces," such as the one that sticks you to the earth's surface, as mediated by virtual gravitons. The notion of virtual particles mediating static forces comes from perturbation theory, and if there is one thing we know about quantum gravity, it's that the usual way of doing perturbation theory doesn't work.

Quantum field theory is plagued with infinities, which show up in diagrams in which virtual particles go in closed loops. Normally these infinities can be gotten rid of by "renormalization," in which infinite "counterterms" cancel the infinite parts of the diagrams, leaving finite results for experimentally observable quantities. Renormalization works for QED and the other field theories used to describe particle interactions, but it fails when applied to gravity. Graviton loops generate an infinite family of counterterms. The theory ends up with an infinite number of free parameters, and it's no theory at all. Other approaches to quantum gravity are needed, and they might not describe static fields with virtual gravitons.

Starboy · 08-27-2002, 04:39 PM

bd-from-kg, IMHO it only means the current crop of theories need much more work if they can be salvaged at all. Remember a theory of reality is not reality.

Starboy

Jonesy · 08-28-2002, 06:59 AM

Quote:

Originally posted by Late_Cretaceous:
This guy told me the other day that "Gravity is the absence of force". Has anyone heard anything like this? I never have. I think he may have misunderstood something he saw on NOVA or read in Sky and Telescope.

Mankind has not yet explained gravity. Answering "Why do we not fall off the planet into space?" with "Because of gravity" is incomplete. The person who fully explains gravity will be a genius, because a full understanding of gravity will open up possibilities such as 'controlling gravity' - meaning that you can control 'the gravity force' locally and thus achieve ' antigravity'. When this happens, oil companies are finished (for example), transport with wheels is finished, etc...

We cannot delude ourselves that we 'know' what gravity is, when we don't.

Infinity Lover · 08-28-2002, 12:53 PM

I think gravity is the result of inward and outward infinity fighting each other, or rather put the forces that opperate on a cosmological scale, and the forces that opperate on a quantumlevel working against each other.

But then again I also think it's a cool tune by none other than the Godfather of Soul himself James Brown!
Graaavuh-teeeee!
G. R. A. V. I. T. Y.
Uh! Good Goh! Uh! Waitaminute! WHaaAAA!

Friar Bellows · 08-28-2002, 02:22 PM

Quote:

Originally posted by Jonesy:
The person who fully explains gravity will be a genius, because a full understanding of gravity will open up possibilities such as 'controlling gravity'...

Not at all. To know something fully is not necessarily to have total control over it. A final "theory of everything" will not guarantee a spaceship that gets us to the Andromeda Galaxy in a human lifetime. Sure, science opens up opportunities, but it also sets definite limits.

08-27-2002, 02:01 PM	#1
Late_Cretaceous Veteran Member Join Date: Oct 2001 Location: Alberta Posts: 1,049	The Nature of Gravity This guy told me the other day that "Gravity is the absence of force". Has anyone heard anything like this? I never have. I think he may have misunderstood something he saw on NOVA or read in Sky and Telescope.

08-27-2002, 02:46 PM	#3
Vibr8gKiwi Senior Member Join Date: Jul 2000 Location: CA, USA Posts: 543	That guy hasn't taken even a basic physics course. Gravity is a force. It's the force of attraction between bodies that have mass. There's even a (weak) force of gravity between that guy and his blind, three legged dog, "lucky." [ August 27, 2002: Message edited by: Vibr8gKiwi ]</p>

Thread Tools	Search this Thread
Show Printable Version	Search this Thread: Advanced Search

08-27-2002, 02:34 PM	#2
Abacus Veteran Member Join Date: Mar 2002 Location: South Dakota Posts: 2,214	The absence of what force?

08-27-2002, 03:20 PM	#4
Starboy Banned Join Date: Jun 2002 Location: Tallahassee, FL Reality Adventurer Posts: 5,276	He might be talking about GR. In that case gravity is not a force, it is the shape of space-time itself. Starboy

08-27-2002, 03:35 PM	#5
bd-from-kg Veteran Member Join Date: Jul 2000 Location: King George, VA Posts: 1,400	Actually there's a serious question lurking here. According to GR, gravity isn't really a force, but a curvature in the space-time continuum. But according to the particle physics geniuses, gravity can only be reconciled with QM by positing the existence of gravitons which carry or mediate the gravitational force. However, if gravity is a curvature in the space-time continuum it would seem that there is no force to carry or mediate. Anything in the curved portion of space-time should be affected immediately and continuously by the curvature; it shouldn't depend on whether or when it happens to interact with any gravitons. How can a curvature in a field be "carried" by particles? How can GR and QM be reconciled by throwing out GR? I'm baffled.

08-27-2002, 04:39 PM	#7
Starboy Banned Join Date: Jun 2002 Location: Tallahassee, FL Reality Adventurer Posts: 5,276	bd-from-kg, IMHO it only means the current crop of theories need much more work if they can be salvaged at all. Remember a theory of reality is not reality. Starboy

08-28-2002, 12:53 PM	#9
Infinity Lover Veteran Member Join Date: Jan 2002 Location: The Netherlands Posts: 1,047	I think gravity is the result of inward and outward infinity fighting each other, or rather put the forces that opperate on a cosmological scale, and the forces that opperate on a quantumlevel working against each other. But then again I also think it's a cool tune by none other than the Godfather of Soul himself James Brown! Graaavuh-teeeee! G. R. A. V. I. T. Y. Uh! Good Goh! Uh! Waitaminute! WHaaAAA!

Freethought & Rationalism Archive

The archives are read only.