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Author Topic:   General Relativity.
sidelined
Member (Idle past 5908 days)
Posts: 3435
From: Edmonton Alberta Canada
Joined: 08-30-2003


Message 106 of 129 (254356)
10-24-2005 1:00 AM
Reply to: Message 102 by simple
10-20-2005 2:11 AM


Re: limiting claims
simple
Same can be said of the merge idea, and who knows what else. Space time as we know it only applies to this universe after it came into being, whether created, of from the tiny universe you suggest
What is the merge idea? Spaceime is what we find ourselves in and the ability of the physical laws to descibe that spacetime operate down to the Planck time of 10 ^ -43 sec. that is 1/10^ 43 power or in longhand 0.0000000000000000000000000000000000000000001 sec which is a staggeringly tiny amount.The temperature of the universe is at that point 10 ^ 32 Kelvin which is a situation in which the forces of nature themselves are indistinguishable one from the other.
Well, since you really don't know, we could say that, or something else for that matter!
Yes but anything else must account for the physics as nature operates in regardless of what that model is. The dilemma is the same for any idea you would consider.
So there may be a part of the universe we don't really see, or are uncertain about, but when it comes to vanishing and appearing things, like ghosts, your theorries as to the real explanation are only as good as your imagination.
No the theories are only as good as the evidence they are supported by. In the case of vacuum energy we can measure the predicted work exerted by these virtual particles under the right conditions. and the measurements fall within the predicted amounts within the level of error of the experiment. If you wish to say there are ghosts then it is you that must show how they occur and produce the evidence to accompany your model for the phenomena.
I would openly delight in you being able to do so because it would mean something new and exciting. But you must pass muster on the skepticism people have. If the phenomena are real they will stand on the evidence not on the person making the claim or the number of letters after their name.
Speculation. You don't know the limits we can discover.
That is incorrect sir, as there are limitations imposed on us by the structure of the universe. We cannot with absolute accuracy predict the splashing of random water drops from a fountain ever. The structure of the universe does not allow for infinite accuracy by its very nature. Due to the limit on the speed of light we cannot ever have immediate information about an event at the spacetime it occurs.
These unknowns also may affect the knowns, and there is no way we can say, then, that there may this other dimension beyond these admitted limits.
Certainly there may. But mays are endless in their profusion. It may be that the world is run by labrats who are actually performing an experiment on us while disguised as terrstrial creatures.
This is a good description of what is being attempted with having things like a microscopic universe just appear on the scene, or life from non life.
But no one claims the universe just appeared on the scene and if they do you also have the right to ask for evidence. Life from non life though seems a natural progression and quite reasonable given what we do know.Try defining life yourself and see how difficult it is.

But I realize now that these people were not in science; they didn’t understand it. They didn’t understand technology; they didn’t understand their time.

This message is a reply to:
 Message 102 by simple, posted 10-20-2005 2:11 AM simple has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 107 of 129 (263278)
11-26-2005 11:41 AM


Evidence for General Relativity
Here's as good a place as any...
RAZD made the following remarks over in Biological Evolution: Peppered Moths and Natural Selection.
We have a theory of gravity, even though the evidence for it is scanty at best. There are some definite observed anomalies where observed behavior does not match predicted values, some involving satellites in the further reaches of the solar system.
I naturally blew my top at this, and RAZD came back with this
We have a large body of observational evidence of the effect we call gravity. We have {theory\on theory\on theory} built up from empirical data formulas to theories of how gravity acts and is effected. But as for evidence for how that {action\effect} actually {works\becomes\exists}, whether via space warping, gravity waves or gravitons or some other method, we have ... what? Theory.
My first remark is that there is confusion here between GR and cosmology. Our theory of gravity is General Relativity. There is no "theory\on theory\on theory". GR is not tailored by empirical data apart from the value of G. The interplay of "space warping, gravity waves" is all contained and explained within GR. Gravitons are going beyond into quantum gravity and theories of everything, but are not in any way contradictory with General Relativity.
Perhaps RAZD would like explain away all of the theoretical predictions of GR that have been observationally measured: equivalence principle, grav time-dilation, grav red-shift, bending of light, lensing of light, binary pulsar energy loss, corrections to planetary motions (perihelion of mercury as the original), frame dragging, and of course the entire world of special relativity. That is off the top of my head.
We have a theory of gravity, even though the evidence for it is scanty at best.
This message has been edited by cavediver, 11-26-2005 11:41 AM

Replies to this message:
 Message 109 by RAZD, posted 11-27-2005 3:59 PM cavediver has replied
 Message 113 by TimChase, posted 12-06-2005 12:27 AM cavediver has not replied

  
Son Goku
Inactive Member


Message 108 of 129 (263461)
11-27-2005 7:05 AM


We have a theory of gravity, even though the evidence for it is scanty at best.
RAZD, what kind of evidence do you want?
Do you require us to actually collapse a Star into a Black Hole and then start testing stuff a few meters above the horizon, because short of this we have tested it in almost every conceivable way.
There are some definite observed anomalies where observed behavior does not match predicted values, some involving satellites in the further reaches of the solar system.
The actual momentum imparted by the Pioneer Anomaly is 0.0000000258 kgm/s^2. Or 1/40 of the strength of a kick from a butterfly delivered every second or a headbutt from a gnat.
Now let's view this in perspective, the orbit of a craft which has travelled the extent of the whole solar system and beyond, going into the Oort cloud, is off on an unexpected trajectory.
The difference in this trajectory from the standard trajectory is the same as if the craft was being headbutted by a gnat all the way.
To me a million other things could explain this, in place of "new physics" and that is the opinion of everybody who examines it.
This message has been edited by Son Goku, 11-27-2005 07:06 AM

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 109 of 129 (263526)
11-27-2005 3:59 PM
Reply to: Message 107 by cavediver
11-26-2005 11:41 AM


gravity.
with all due respect, the issue is gravity. and we've been over this before.
the point is not that there is {no evidence at all}, but that the evidence we have is not sufficient to say that current theory covers the observed data ... and thus that we have a cohesive theory for how gravity works. we have anomalies. "dark matter" is not an actually observed piece of evidence but a hypothetical explanation for an observed large scale anomaly, where the current theory of gravity does not work.
and we have some right here in the solar system that are similar in effect to what has been observed at large galactic dimensions, but the explanations (hypothesis) for one are inconsistent with the explanations (hypothesis) for the other.
we also have predictions based on current theory that have not been observed, whether gravitons or gravity waves is irrelevant.
to me that adds up to something is missing.
now who plays tag-team first?

This message is a reply to:
 Message 107 by cavediver, posted 11-26-2005 11:41 AM cavediver has replied

Replies to this message:
 Message 110 by cavediver, posted 11-27-2005 4:17 PM RAZD has replied
 Message 112 by Son Goku, posted 11-28-2005 5:25 PM RAZD has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 110 of 129 (263528)
11-27-2005 4:17 PM
Reply to: Message 109 by RAZD
11-27-2005 3:59 PM


Re: gravity.
No time at the moment, but just to say that your post does not explain your use of the phrase "scanty at best".
Even if I accept your description of the "anomalies" (which I do not), how does that enable you to describe the evidence for our theory of gravity (General Relativity) as scanty?
You are correct, we have gone over this before and I have explained why the PA is not worth considering as it stands. You are misrepresenting my science and I find that highly objectionable. You have a little knowledge of the subject but you are presenting yourself as an expert to a gullible audience and making claims that are simply false. You have much to learn...
This message has been edited by cavediver, 11-27-2005 04:18 PM

This message is a reply to:
 Message 109 by RAZD, posted 11-27-2005 3:59 PM RAZD has replied

Replies to this message:
 Message 111 by RAZD, posted 11-27-2005 4:21 PM cavediver has not replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 111 of 129 (263529)
11-27-2005 4:21 PM
Reply to: Message 110 by cavediver
11-27-2005 4:17 PM


Re: gravity.
you are presenting yourself as an expert to a gullible audience
I have never claimed to have a degree in physics nor to know more than just enough to be dangerous. I don't claim to be an expert, just a skeptic.

This message is a reply to:
 Message 110 by cavediver, posted 11-27-2005 4:17 PM cavediver has not replied

  
Son Goku
Inactive Member


Message 112 of 129 (263853)
11-28-2005 5:25 PM
Reply to: Message 109 by RAZD
11-27-2005 3:59 PM


Re: gravity.
RAZD writes:
the point is not that there is {no evidence at all}, but that the evidence we have is not sufficient to say that current theory covers the observed data
The observed evidence is way more than sufficient, it is on par with QED for the most rigorously tested theory in modern physics.
RAZD writes:
... and thus that we have a cohesive theory for how gravity works. we have anomalies. "dark matter" is not an actually observed piece of evidence but a hypothetical explanation for an observed large scale anomaly, where the current theory of gravity does not work.
Okay, first General Relativity works for any Stellar system we have observed, emphasise on any.
That is more than enough to accept it as an intra-stellar theory of gravity.
Now for interstellar.
We can't use the full Einsteinian Field Equation, so we use the Post-Newtonian approximation and this is only off when we get to the galactic scale.
And is it off in a structural manner?
No, the galaxy has the same structure as the PN approximation predicts, it simply slowed in a rotational manner.
Now if we add to the simulations a certain amount of Dark Material we get the correct rotation curve.
There are no anomalies, either justified enough or blatant enough to warrant another theory of gravity.
So either:
a) every cosmologist is worshipping their doctrine of General Relativity because we love epicycles so much that we collect them.
or
b)General Relativity is actually supported by evidence and that is the reason it is the dominant theory of gravity.
And gravity waves are tremendously weak.
Einstein's equations combined with numerical analysis warned us how difficult to detect they would be, so that isn't a flaw.
Only now are places like Glasgow, Cardiff, e.t.c. finally reaching the level of technology were we can tune out the quantum "noise".

This message is a reply to:
 Message 109 by RAZD, posted 11-27-2005 3:59 PM RAZD has not replied

  
TimChase
Inactive Member


Message 113 of 129 (265928)
12-06-2005 12:27 AM
Reply to: Message 107 by cavediver
11-26-2005 11:41 AM


Re: Evidence for General Relativity
Quick Note of Agreement:
If you checkout "Gravitation" by John A. Wheeler, et. al., you will find that over 300 different gravitational theories have been proposed as alternatives to General Relativity, and all but one has been eliminated by various experiments or observations. And that was back in the 1980s.
There is a great deal of support for General Relativity.

This message is a reply to:
 Message 107 by cavediver, posted 11-26-2005 11:41 AM cavediver has not replied

Replies to this message:
 Message 114 by jmrozi1, posted 12-15-2005 6:01 PM TimChase has replied

  
jmrozi1
Member (Idle past 5893 days)
Posts: 79
From: Maryland
Joined: 12-09-2005


Message 114 of 129 (269739)
12-15-2005 6:01 PM
Reply to: Message 113 by TimChase
12-06-2005 12:27 AM


Attractive Force or Warping of Space Time?
I don't know if this would be one of the aforementioned discredited theories, but I started reading an article about a possible misconception of gravity, and it mentioned gravity as a warping of space time rather than an attractive force. Supposedly, this theory is supposed to work the same as gravity and meet most of the same predictions, but could explain a select few of the anomolies as well.
Now, I'm not a complete idiot, but this theory doesn't make sense to me. It seems that if there are two objects that are initially stationary to the inertial reference frame, there shouldn't be any reason for the space between them to decrease unless the warping is continual. If this is the case, how could space time continue to warp without the aid of some sort of attractive force?
Somehow I don't think a student who took one Physics course would be able to challenge a theory developed by a team of physicists, so I'm obviously missing something. If anyone knows how this theory is supposed to work, I'm all ears.

This message is a reply to:
 Message 113 by TimChase, posted 12-06-2005 12:27 AM TimChase has replied

Replies to this message:
 Message 115 by Wounded King, posted 12-15-2005 6:25 PM jmrozi1 has replied
 Message 117 by TimChase, posted 12-15-2005 8:08 PM jmrozi1 has not replied
 Message 119 by cavediver, posted 12-15-2005 9:22 PM jmrozi1 has not replied

  
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 115 of 129 (269746)
12-15-2005 6:25 PM
Reply to: Message 114 by jmrozi1
12-15-2005 6:01 PM


Re: Attractive Force or Warping of Space Time?
It sounds to me like you are describing the 'Rubber Sheet' view of gravity, the usual illustration being of a bowling ball sitting in a dip on a suspended rubber sheet. That mass distorts space time and a sufficient mass distorts space time sufficiently that other objects will be drawn towards it. I your example the space between the two objects may not diminish, it depends on whether either of them is massive enough that their distortion manages to affect the other.
As I understand it this model is based on Einstein's work on general relativity, though I doubt my physics is much more developed than yours.
TTFN,
WK

This message is a reply to:
 Message 114 by jmrozi1, posted 12-15-2005 6:01 PM jmrozi1 has replied

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jmrozi1
Member (Idle past 5893 days)
Posts: 79
From: Maryland
Joined: 12-09-2005


Message 116 of 129 (269777)
12-15-2005 8:07 PM
Reply to: Message 115 by Wounded King
12-15-2005 6:25 PM


Re: Attractive Force or Warping of Space Time?
It sounds to me like you are describing the 'Rubber Sheet' view of gravity, the usual illustration being of a bowling ball sitting in a dip on a suspended rubber sheet.
Yeah, that's the one.
In fact, the bowling ball analogy was precisely how I arrived at my question. The explanation was that a straight line would always gravitate towards the center, and though it seems that given the correct orientation it would escape regardless, I let it go considering that the analogy might fail because it only explains the warping of a 2-dimensional space. The part that still bothers me, however, is that the only reason a stationary object should move towards the center is because of the continual warping of space time.
If this is the case, I guess my question would be how is that different than simply calling it an attractive force?

This message is a reply to:
 Message 115 by Wounded King, posted 12-15-2005 6:25 PM Wounded King has not replied

  
TimChase
Inactive Member


Message 117 of 129 (269779)
12-15-2005 8:08 PM
Reply to: Message 114 by jmrozi1
12-15-2005 6:01 PM


Re: Attractive Force or Warping of Space Time?
I could go into this in a bit more depth later (going to catch the bus, shortly), but basically what you are dealing with here are two different languages for describing the same phenomena. For example, Newton's gravitational theory could be expressed without reference to "gravitational forces" if it were expressed in the language of curved spacetime. If one were to do this, the geometry of space itself would be Euclidean, but the geometry of spacetime would be curved with the curvature existing between the dimension of time and the dimensions of space. In either case, the phenomena which is described will be the same phenomena, but whether your are expressing it in terms of curved geometry or gravitational forces in a flat geometry may differ -- and this constitutes the form in which the theory is expressed.
However, when one expresses Newton's gravitational theory in terms of curved spacetime, the mathematics becomes a great deal more complicated. Expressing the theory in terms of no curvature with gravitational forces keeps the mathematics simple. However, in the case of General Relativity, the language of curved spacetime without gravitational forces is what keep the mathematics simple -- relatively speaking.

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 Message 114 by jmrozi1, posted 12-15-2005 6:01 PM jmrozi1 has not replied

Replies to this message:
 Message 118 by cavediver, posted 12-15-2005 9:15 PM TimChase has replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 118 of 129 (269811)
12-15-2005 9:15 PM
Reply to: Message 117 by TimChase
12-15-2005 8:08 PM


Re: Attractive Force or Warping of Space Time?
For example, Newton's gravitational theory could be expressed without reference to "gravitational forces" if it were expressed in the language of curved spacetime. If one were to do this, the geometry of space itself would be Euclidean, but the geometry of spacetime would be curved with the curvature existing between the dimension of time and the dimensions of space
Although Newtonian spacetime can be described as curved, it would be more appropriate to describe the bundle structure of spatial hypersurface fibres on the time base-space as having non-trivial connection. BUT I do not see how this can possibily give rise to Newtonian "gravitational force". Can you explain?

This message is a reply to:
 Message 117 by TimChase, posted 12-15-2005 8:08 PM TimChase has replied

Replies to this message:
 Message 120 by TimChase, posted 12-15-2005 11:58 PM cavediver has replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 119 of 129 (269814)
12-15-2005 9:22 PM
Reply to: Message 114 by jmrozi1
12-15-2005 6:01 PM


Re: Attractive Force or Warping of Space Time?
If this is the case, how could space time continue to warp without the aid of some sort of attractive force?
Good question. The answer is that not only is mass a warper of space-time, but so is warped space-time! Or as I would put it, both mass and curvature are sources of curvature. The rubber sheet analogy is particularly good in this instance. A mass dropped onto the sheet appears to deform the sheet at all points. In actuality, away from the mass, it is the sheet itself deforming neighbouring points. The deformations are generated locally and there is no action at a distance (no force, attractive or otherwise).

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 Message 114 by jmrozi1, posted 12-15-2005 6:01 PM jmrozi1 has not replied

Replies to this message:
 Message 121 by TimChase, posted 12-16-2005 12:25 AM cavediver has replied

  
TimChase
Inactive Member


Message 120 of 129 (269868)
12-15-2005 11:58 PM
Reply to: Message 118 by cavediver
12-15-2005 9:15 PM


Re: Attractive Force or Warping of Space Time?
Well, simply put, the geometry of space would still be Euclidean in much the same way as a Friedman model with critical mass density. However, there would exist curvature between the temporal dimension and the three spatial dimensions, such that the paths which maximize proper time through spacetime (given the metric tensor) would be the same as the paths of objects in free fall -- the same way as in General Relativity. Although I haven't actually seen the mathematics behind such an approach (I have only heard it briefly described in a textbook on General Relativity), I would assume that you could employ standard cartesian or polar coordinates to space with a metric tensor appropriate to a flat space, but the non-diagonal components where either the left or the right index corresponded to time would be non-zero.
As for a "bundle structure" of "hypersurface fibers" on the "time base-space" having a "non-trivial connection," I am not exactly sure what you mean by this. I have heard of "fiber-bundle theory," for example, but I haven't ever heard it in any way applied to a gravitational theory -- unless of course you mean Roger Penrose's "twistor theory" which I suppose could be described as something along these lines.

This message is a reply to:
 Message 118 by cavediver, posted 12-15-2005 9:15 PM cavediver has replied

Replies to this message:
 Message 123 by cavediver, posted 12-16-2005 5:39 AM TimChase has replied

  
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