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What is gravity?
Posted: 05 November 2011 11:59 PM   [ Ignore ]   [ # 91 ]
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kkwan
Newton’s insight into the nature of mass and gravity implies that with one solitary body, mass can be defined as “quantity of matter” independent of gravity or force.

What about a massless (or negative mass) particle?  Would that remove it from the list of physical matter?  If so would it be a metaphysical particle?

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Posted: 06 November 2011 01:17 AM   [ Ignore ]   [ # 92 ]
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kkwan - 05 November 2011 10:01 PM

Thus, if there is only one piece of matter in the universe, it will have mass and inertia but no gravity because it is solitary.

What is inertia of a single piece of matter in the universe?
You must separate between what Newton says, and what is correct.

kkwan - 05 November 2011 10:01 PM

So, gravity can be considered an emergent property of mass iff there is more than one piece of matter in the universe to interact with each other.

Think about it. Isn’t the same true for inertia?

What one needs to determine if an object has mass is a force.

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Posted: 06 November 2011 01:18 AM   [ Ignore ]   [ # 93 ]
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Write4U - 05 November 2011 11:59 PM

What about a massless (or negative mass) particle?  Would that remove it from the list of physical matter?  If so would it be a metaphysical particle?

No.  cool smile

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Posted: 06 November 2011 02:16 AM   [ Ignore ]   [ # 94 ]
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GdB - 06 November 2011 01:18 AM
Write4U - 05 November 2011 11:59 PM

What about a massless (or negative mass) particle?  Would that remove it from the list of physical matter?  If so would it be a metaphysical particle?

No.  cool smile

Does the ‘no” mean that there can be massless matter?  If there is massless matter how can it generate a gravity field? By its speed alone?
But does that have the same effect on spacetime as real rest mass (matter)?  Does a photon create a gravitational field?

http://knol.google.com/k/dark-energy-does-light-create-a-gravitational-field

[ Edited: 06 November 2011 02:26 AM by Write4U ]
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Posted: 06 November 2011 06:48 AM   [ Ignore ]   [ # 95 ]
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Write4U - 06 November 2011 02:16 AM

Does the ‘no” mean that there can be massless matter? 

No

Write4U - 06 November 2011 02:16 AM

Does a photon create a gravitational field?

Yes

Negative mass is an absurdity: if a force is expressed on a negative mass, it would accelerate opposite to the direction of the force. I think our energy problems would be solved for ever!

Do not mix up anti-matter with ‘matter with negative mass’. Anti-matter has mass, just as normal matter.

Just to add: tachyons are mathematical possible solutions to relativistic equations, but they would disobey causality when they would interact with our world where the speed of light is the upper limit.

Doug describes very nice what metaphysics in in this posting. What the heck would then a metaphysical particle be?

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Posted: 06 November 2011 12:54 PM   [ Ignore ]   [ # 96 ]
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Write4U - 05 November 2011 11:59 PM

kkwan
Newton’s insight into the nature of mass and gravity implies that with one solitary body, mass can be defined as “quantity of matter” independent of gravity or force.

What about a massless (or negative mass) particle?  Would that remove it from the list of physical matter?  If so would it be a metaphysical particle?

Light has no mass but it has momentum and interacts with matter.

A negative mass particle (if it can exist) is exotic matter.

From the wiki on exotic matter

 
* Hypothetical particles which have “exotic” physical properties that would violate known laws of physics, such as a particle having a negative mass.
  * Hypothetical particles which have not yet been encountered, such as exotic baryons, but whose properties would be within the realm of mainstream physics if found to exist. It has been speculated that by the end of the 21st century it may be possible by using femtotechnology to create new chemical elements composed of exotic baryons that would eventually constitute a new periodic table of elements in which the elements would have completely different properties than the regular chemical elements.
  * States of matter which are not commonly encountered, such as Bose–Einstein condensates and quark–gluon plasma, but whose properties are perfectly within the realm of mainstream physics.
  * States of matter which are poorly understood, such as dark matter.

Such particles are hypothetical particles.

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Posted: 06 November 2011 01:35 PM   [ Ignore ]   [ # 97 ]
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Write4U - 06 November 2011 02:16 AM

Does a photon create a gravitational field?

http://knol.google.com/k/dark-energy-does-light-create-a-gravitational-field

From the link you posted above:

From the abstract:

Light traveling freely in space does not produce a gravitational field - contrary to most “establishment” thinking.

And from the introduction:

The problem seems to begin with Einstein’s E = mcc; from this justly famous equation it seems everyone assumed, including Einstein, that light has mass and so produces a gravitational field. But light obviously does not have mass, it has momentum and energy (E = hv), which is equivalent to mass (hv = mcc), but is not mass itself. (“Mass” is the source of inertial resistance or gravitational “weight” (or gravitational field energy) of any energy form.)

And the wiki on the photon

Experimental checks on photon mass

The photon is currently understood to be strictly massless, but this is an experimental question. If the photon is not a strictly massless particle, it would not move at the exact speed of light in vacuum, c. Its speed would be lower and depend on its frequency.

However:

Photons inside superconductors do develop a nonzero effective rest mass; as a result, electromagnetic forces become short-range inside superconductors.

OTOH, light can apparently be converted to matter and be regenerated from matter. From this article HERE

Physicists have for the first time stopped and extinguished a light pulse in one part of space and then revived it in a completely separate location. They accomplished this feat by completely converting the light pulse into matter that travels between the two locations and is subsequently changed back to light.

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Posted: 06 November 2011 01:42 PM   [ Ignore ]   [ # 98 ]
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GdB - 06 November 2011 01:17 AM

What is inertia of a single piece of matter in the universe?

It will be proportional to its mass.

Think about it. Isn’t the same true for inertia?

No. From the wiki on inertia

Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object’s mass.

Thus, a solitary object with mass in the universe inherently has inertia but no gravity.

What one needs to determine if an object has mass is a force.

No, it is not a force if mass is defined as quantity of matter.

[ Edited: 06 November 2011 01:54 PM by kkwan ]
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Posted: 07 November 2011 12:22 AM   [ Ignore ]   [ # 99 ]
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kkwan - 06 November 2011 01:42 PM
GdB - 06 November 2011 01:17 AM

1. What is inertia of a single piece of matter in the universe?

It will be proportional to its mass.

2. Think about it. Isn’t the same true for inertia?

No. From the wiki on inertia

Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object’s mass.

Thus, a solitary object with mass in the universe inherently has inertia but no gravity.

3. What one needs to determine if an object has mass is a force.

No, it is not a force if mass is defined as quantity of matter.

1. That is not an answer.
2. I said think, do not throw citations. If a solitary body of mass does not exert gravity, because one needs a second body of mass, then it also has no inertia, because I also need something additional to it that can exert a force. And how should I measure the movement of the object when there are no other objects around to which I can compare?
3. Again (you are running in circles): how do you determine the quantity of matter without a force? (Note: you might not even know what the substance is made of, counting atoms does not help then. Or, if you know what the substance is, without previous measurements of the mass of its components).

Your running in circles is a nice demonstration of the circularity in the definitions of force, mass, matter and gravity.

kkwan - 06 November 2011 01:35 PM

Experimental checks on photon mass

Try to think, kkwan.
Imagine, I have a huge sphere with a perfect mirroring inside. Exactly in the centre I have a little matter and anti matter, exactly mirrored (Say 1 kilogram of your silicon ball, and exactly the same silicon ball but then made up of anti matter). I bring he silicon balls together, and they are completely changed in radiation (photons). These photons are perfectly reflected again and again (which also means the big mirror ball does not absorb any energy from the explosion. All the energy stays in the big ball.). Now, from the outside, does one measure a decrease of gravity, in line with the disappearance of 2 kilograms of matter?

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Posted: 07 November 2011 12:58 AM   [ Ignore ]   [ # 100 ]
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kkwan - 06 November 2011 01:35 PM
Write4U - 06 November 2011 02:16 AM

Does a photon create a gravitational field?

http://knol.google.com/k/dark-energy-does-light-create-a-gravitational-field

From the link you posted above:

From the abstract:

Light traveling freely in space does not produce a gravitational field - contrary to most “establishment” thinking.

That page is not serious.

Think again. First: a photon has no rest mass. But it has impulse momentum. Now think about the famous Eddington experiment, showing that light is bent by the gravity of the sun. When photons are attracted, their momentum changes. Because of the law of conservation of momentum, the sun will get the same change in momentum in the opposite direction as the change in momentum of the light. But a change in momentum means exerting of a force. Which force? The gravitational force of the light.

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Posted: 07 November 2011 02:09 AM   [ Ignore ]   [ # 101 ]
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Why would a massive object be affected by a non massive object?  It seems entirely possible to me that light bends in a gravitational field but that it does not create a gravitational field of its own. There is no mutual attraction, as in magnetism. A massive object distorts spacetime and affects everything that falls within that field, including non massive objects which of themselves may not generate a gravitational spacetime distortion

I am not claiming this is the case, but that IMO it is theoretically possible.
How is it that a neutrino is attracted by the gravity of earth but can pass through the earth itself, without “disturbance”. That is why they are so hard to find!

Seems to me, the change in momentum you cite is an example of relative speed, not an example of gravity.

[ Edited: 07 November 2011 03:02 AM by Write4U ]
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Posted: 07 November 2011 05:30 AM   [ Ignore ]   [ # 102 ]
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C’mon, Write4U, this is basic physics:

1. Momentum is conserved in all physical processes (it is in classical mechanics, in relativity and in QM)
2. Photons bear momentum (special relativity)
3. If the trajectory of a photon is bent, its momentum has changed, and therefore the momentum of something else must have changed momentum too.

Neutrinos interact with matter only by their gravitation and the weak nuclear interaction. As this interaction is really very weak, most neutrinos pass through the earth without interacting with its matter.

You must not mix up what is scientific fact, scientific speculation, philosophy and free wheeling ideas. Studying the first three is a good antidote against the last. Just putting Googlings together, as kkwan does, is no replacement for real understanding.

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Posted: 07 November 2011 02:29 PM   [ Ignore ]   [ # 103 ]
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GdB - 07 November 2011 05:30 AM

C’mon, Write4U, this is basic physics:

1. Momentum is conserved in all physical processes (it is in classical mechanics, in relativity and in QM)
2. Photons bear momentum (special relativity)
3. If the trajectory of a photon is bent, its momentum has changed, and therefore the momentum of something else must have changed momentum too.

Neutrinos interact with matter only by their gravitation and the weak nuclear interaction. As this interaction is really very weak, most neutrinos pass through the earth without interacting with its matter.

You must not mix up what is scientific fact, scientific speculation, philosophy and free wheeling ideas. Studying the first three is a good antidote against the last. Just putting Googlings together, as kkwan does, is no replacement for real understanding.

I am not disputing any of your observations. My question is , what does it have to do with “gravity” (spacetime distortion)?

3) if I turn the corner with my car, does the corner house change momentum (except relatively)?

And there is this, which does not mention anything about gravity.
http://en.wikipedia.org/wiki/Virtual_particle

[ Edited: 07 November 2011 02:51 PM by Write4U ]
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Posted: 08 November 2011 01:22 AM   [ Ignore ]   [ # 104 ]
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Write4U - 07 November 2011 02:29 PM

I am not disputing any of your observations. My question is , what does it have to do with “gravity” (spacetime distortion)?

In the example of the sun bending the trajectory of a photon gravity is the interaction that transfers some momentum from the sun to the photon and the other way round (action = -reaction).

Write4U - 07 November 2011 02:29 PM

3) if I turn the corner with my car, does the corner house change momentum (except relatively)?

No, the earth as a whole does. Here it is the friction that transfers the momentum, not gravity. So to be very exact, the corner house changes a tiny bit of the momentum, reverse proportionally to the mass of the house to the mass of the rest of the earth.

Write4U - 07 November 2011 02:29 PM

And there is this, which does not mention anything about gravity.
http://en.wikipedia.org/wiki/Virtual_particle

I have no idea about virtual particles. And I think you don’t either…

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Posted: 08 November 2011 02:15 AM   [ Ignore ]   [ # 105 ]
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I respect your knowledge and the best I can do for now is take your word for it, but I am not convinced.

I am not convinced that when a particle enters the gravity field of a massive body (which may extend for millions of miles), that massive body is affected by the gravity field of that particle (which may extend less than millimeter).   


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Perhaps Ive been watching too many ads for Posturepedic mattresses….. cheese

[ Edited: 08 November 2011 02:29 AM by Write4U ]
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