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Author Topic:   General Relativity, Gravity, Help!!
JonF
Member (Idle past 167 days)
Posts: 6174
Joined: 06-23-2003


Message 16 of 20 (64890)
11-07-2003 9:09 AM
Reply to: Message 15 by Rrhain
11-07-2003 7:45 AM


Gravitons do not emit gravitons.
But can we think of gravitons as splitting and recombining and all sorts of weird stuff as photons "do" on Feynman diagrams?

This message is a reply to:
 Message 15 by Rrhain, posted 11-07-2003 7:45 AM Rrhain has replied

Replies to this message:
 Message 17 by Rrhain, posted 11-07-2003 10:55 AM JonF has not replied

  
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 17 of 20 (64928)
11-07-2003 10:55 AM
Reply to: Message 16 by JonF
11-07-2003 9:09 AM


JonF responds to me:
quote:
quote:
Gravitons do not emit gravitons.
But can we think of gravitons as splitting and recombining and all sorts of weird stuff as photons "do" on Feynman diagrams?
I'm not sure. I may have to qualify my statement.
More specifically, things with mass do not emit gravitons merely from their existence. It is the motion of the mass that causes the emission of the gravitons. Gravitons, however, are massless.
When a charged particle moves, it emits photons. But static charges do not emit photons.
------------------
Rrhain
WWJD? JWRTFM!

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 Message 16 by JonF, posted 11-07-2003 9:09 AM JonF has not replied

  
Tsegamla
Inactive Member


Message 18 of 20 (64996)
11-07-2003 4:12 PM


Thanks, Rrhain! Just one question about string theory, does it suggest that quarks are strings, or that quarks are made up of many strings?

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 Message 19 by Rrhain, posted 11-08-2003 6:49 AM Tsegamla has not replied

  
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 19 of 20 (65101)
11-08-2003 6:49 AM
Reply to: Message 18 by Tsegamla
11-07-2003 4:12 PM


Tsegamla responds to me:
quote:
Just one question about string theory, does it suggest that quarks are strings, or that quarks are made up of many strings?
My understanding is that quarks are made of strings.
One of the big problems with string theory is that it predicts strings to be so small that there would be no way to directly detect them. Thus, this makes it very difficult to produce a testable theory of strings. With quarks, there are ways to make testable predictions, even though we can't "see" the quarks in the common sense of the word. Strings, being so much smaller, are that much harder to deal with.
The reason why we like string theory is that it is mathematically elegant and helps to combine what are seemingly conflicting aspects of physics. And that's a great way to get something studied, but that doesn't make it true.
As one of the scientists on the recent Nova program on strings said, if string theory cannot be validated in the laboratory, then nobody should believe it.
------------------
Rrhain
WWJD? JWRTFM!

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 Message 18 by Tsegamla, posted 11-07-2003 4:12 PM Tsegamla has not replied

  
JIM
Inactive Member


Message 20 of 20 (65325)
11-09-2003 1:30 PM


Not sure if this will help but;
You can get a more accurate picture from the famous "rubber sheet" analogy by picturing what it would look like if you are looking straight down from above it. This has two major advantages, the first being that the object which appears spherical in the original diagram would look like a disk when viewed from directly above. This makes the illustration more integrated since it is a two-dimensional object on a two-dimensional surface. The other advantage is that, from this angle, the grid lines on the flat surface all appear to curve toward the object from all directions. This is the proper meaning of the rubber sheet analogy, it is a two-dimensional representation of what happens in three dimensions.
On the two-dimensional surface, the disk (as it appears from this angle) represents the heavy ball in the original diagram, perhaps a cannon ball. A smaller ball (like a marble) that tries to roll passed this large ball can only go by in one of the directions afforded by the two dimensions of its environment. That is, it can only go in front or behind or to the left or the right of the cannon ball. But whichever way it's going, its trajectory will be curved toward the cannon ball. Now, even though you can only see the lines running along the two directions (left to right or front and back), in your mind you are aware that the curvature of these lines is a result of the surface being bent in a third direction, up and down.
This, then, is what gravity does to three-dimensional space. It causes a curve in a fourth direction which is at a 90o angle to the three with which we are commonly familiar.
The two-dimensional curved surface is supposed to be analogous to three-dimensional curved space; we can't visualize three-dimensional curved space directly very well. It is not correct to think of objects like the Sun as spheres sitting on top of the 2D surface, though; the 2D surface is space, and all objects lie within space. So within this analogy, the Sun would have to be a 2D disc sitting at the bottom of the 2D "well".
An illustration of the way 'warping' occurs is to consider setting out on a journey into into space. If you set out in a straight line you wouldn't expect to end up where you started from would you?
However, mass can warp space time, as illustrated by the rubber sheet analogy, and if warped enough you can end up back where you started. It is like a minute creature walking on the surface of a large sphere - it looks flat on his scale, but having walked onwards in a straight line, it would end up back where it started.
Light follows a straight line path in space, but if mass distorts that spacetime, then it follows a curved path - ie it appears to be attracted by mass.
The warping effect idea can also solve the 'action at a distance' problem of how masses can interact over large distances. There is no Force, just curved paths!
[This message has been edited by JIM, 11-09-2003]

  
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