When you beam 2 photon streams at one another, a non-zero differential cross section would mean they interact and scatter one another. If the cross section is zero, they are not interacting.
Gluons are talked about like they have been proven yet there is a lack of definite terms when talking about them. They may exist but what we think of as gluons may be something else entirely.
Gluons are 'seen' by their products and interactions. You dont' see the gluon directly but see particles feeling their effects and by jets of particles produced by the gluon.
True it could be something different, but then you can say that about pretty much all of theoretical physics. Most people prefer to consider the physics model to be what is really going on but you don't have to.
cefarix
29th November 2006 - 06:36 PM
Nick, I think it's high time that you realized that gravity is not acceleration in GR. Gravity is caused by the curvature of spacetime, which in turn is caused by the flow of energy in 4-dimensions. You cannot equivocate gravitation with acceleration, because acceleration is a 3-dimensional concept whereas space-time is in 4-dimensions. We can, however, derive the normal acceleration (which has components of space and time, which mind you, is different from space-time), by defining it as the rate at which a test particle deviates from the geodesic.
For example, around the Earth, geodesics lead toward the center of the Earth in space-time. An object in freefall therefore has no forces acting upon it --- because it has no acceleration --- because it is not deviating from the geodesic. The acceleration "g" that we define is a convenient measure, because being the egocentric beings we are, we tend to define our state of being as "point zero". So we consider ourselves, standing on the Earth's surface, to have zero acceleration, and the things free falling out of the sky to have non-zero acceleration. In fact, it's the other way around. We are being forced out of the equilibrium of following the geodesic to the center of the Earth by the fact that there is a solid ground beneath which does mutual electromagnetic repulsion against our atoms. This is why we feel the ground pushing up on us. It is actually we who are accelerating. Also, because of the curvature of space-time, you can have non-zero acceleration (deviation from the geodesic), and still maintain a constant distance from some point, and you can also have zero acceleration (free fall, or follow the geodesic without any hindrance), and have non-constant distance from a point (this is actually trivial, since ds/dt can be non-zero but ds^2/dt^2 can be zero).
Nick
29th November 2006 - 07:38 PM
QUOTE (cefarix+Nov 29 2006, 06:36 PM)
Nick, I think it's high time that you realized that gravity is not acceleration in GR.
For GRAVITY and ACCELERATION Einstein found THEIR EQUIVALENCE as - the rate of change of velocity
I found that they are not exactly the same in their equivalence.
One is rate of change of velocity. That's free fall or an accelerating frame.
The other is simply an acceleration equivalent to - CHANGE OF VELOCITY alone.
That other is revealed in weight (gravity) which is equivalent to an acceleration that has no duration(or time rate) Again this is simply change in velocity.
And since velocity has a light speed limit change in velocity does also.
AlphaNumeric
29th November 2006 - 07:42 PM
QUOTE (Nick+Nov 29 2006, 08:38 PM)
I found that they are not exactly the same in their equivalence.
Obviously they are not literally the same but you haven't understood it properly and you haven't 'found' anything other than your own lack of understanding.
Nick
29th November 2006 - 07:49 PM
Can something at rest be said to have a rate of change of motion?
What about the rocket on a launch pad? It has the equivalent of acceleration in that it has WEIGHT yet it has no motion relative to the earth. This is a different kind of Acceleration but acceleration nonetheless. --- IN IT NO TIME RATE IS APPLICABLE
AlphaNumeric
29th November 2006 - 08:02 PM
You and Zanket seem to have the exact same conceptual problem. I suggest you read the thread she started and all the replies of people explaining to her why she was wrong.
Nick
29th November 2006 - 08:14 PM
QUOTE (AlphaNumeric+Nov 29 2006, 08:02 PM)
You and Zanket seem to have the exact same conceptual problem. I suggest you read the thread she started and all the replies of people explaining to her why she was wrong.
YOU SHOW ME WHERE I AM WRONG ALPHA NUMB-ER.
NoCleverName
30th November 2006 - 12:44 AM
Force without movement is definitely a subtle concept. The fact that force is frequently defined as dp/dt (time-varying change in momentum) doesn't help, either! So "movement" seems instrinically bound up with force. So Nick's question deserves an answer.
Force, as exhibited in nature, is really a property of a vector field (like the gravitational and electric fields). For gravity, a formula like F = ma describes the manifestation of that field on an unconstrained mass located somewhere in that field. The field itself doesn't have to be described in terms of acceleration, just force alone. In fact, the gravitational field is really described by F = Gmm/r^2.
The field itself, with it's "tugging" is always present, whether anything is there to "feel it" or not. It's just easier to describe the magnitude of that field by what it would do to an object placed in it. So feeling "weight" on the earth is just the gravitational field working on you (nothing new there).
Newton's laws were first discovered by investigating the gravitational field.
How do we get from vector fields of force to, say, statics or gas pressure? And why should the laws valid in fields carry over when there are no fields present?
If you studied the motion of objects (separately from gravitational influence) with just the law of conservation of momentum handy and the three laws of motion, I believe you can derive pretty much all the needed machinery. Now, it turns out the the laws of non-gravity motion look the same as those in a gravitational field. One subtle difference is that gravity acts on the mass of an object while the laws of motion work on its inertia.
Since both the mass and inertia of an object seem to be the same (as far as we can measure), it's convenient to use the same equations for both situations (using mass, by convention, in both).
So that's why you get force measured by ma even though nothing is moving. There's a convenient equivalency but I believe the distinction between mass and inertia still remain.
At least that's my story (from what I can remember from the dim past). I'm sure someone else can do better.
Nick
30th November 2006 - 12:56 AM
Force in gravity OR WEIGHT necessarily needs no timerate required.
This changes EINSTEIN'S Equivalence Principle. Both sides- gravity and accelerated frames - are not exactly the same in their equivalence.
AlphaNumeric
30th November 2006 - 12:59 AM
QUOTE (Nick+Nov 29 2006, 09:14 PM)
YOU SHOW ME WHERE I AM WRONG ALPHA NUMB-ER.
WhY DoNt YoU rEaD tHe ThReAd ZaNkEt StArTeD WhIcH ExPlAiNs It AlL??
Or Is ThAt 2 MuCh LiKe WoRk?
QUOTE (Nick+Nov 29 2006, 09:14 PM)
This changes EINSTEIN'S Equivalence Principle. Both sides- gravity and accelerated frames - are not exactly the same in their equivalence.
Just repeating yourself doesn't make you right. Show specifically the resultant contradictions in relativity is the EP is not valid.
$10 says you can't say anything quantative and just wave your arms and talk vaguely.
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