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Author Topic:   what is the big bang and how do i understand it?
Son Goku
Inactive Member


Message 76 of 122 (240567)
09-05-2005 12:32 PM
Reply to: Message 75 by RAZD
09-03-2005 9:35 PM


Re: The Cosmic Fudge Factory and Empirical Candy
quote:
can also be modelled in other ways (such as the universal constant)
Do you mean omega or something else?
quote:
Why assume this? Perhaps GR will be like Newtonian Physics: close enough in controlled conditions to use for workable solution, or perhaps it will be replaced entirely if the new theory is much easier to use.
It's unlikely that the new theory will be easier to use if its limiting case is a non-linear theory.
The new theory won't change the gross nature of General Relativity because "Quantum Gravity" (or whatever its eventual name is) only applies in areas where General Relativity breaks down.
Which is inside black holes and at the Big Bang, which are places predicted by GR in the first place.
So Quantum Gravity won't really be a replacement of General Relativity, rather it will (probably) explain how spacetime emerges from something more fundamental, which won't change GR, it being the theory of spacetime itself.
quote:
Try any other field with a theory that only explains (what is it 4% total?) of the known behaviour, but which then claims to be the best theory ....
Occams razor tells me that when {the adjustment to the data} gets to be more than {the data} to make the theory work, that the theory is wrong.
To me this is one of the great unknowns, and this shouldn't be glazed over by any pretending that dark stuffs is really the answer.
That isn't the real motivation behind dark matter.
General Relativity has so far perfectly predicted all gravitational systems we have ever observed.
So it is an excellent theory of local gravity.
When it comes to cosmological scales General Relativity still explains the properties of accelerative expansion.
The only difference is that a special case of lambda = 0 is sufficient for local/closed systems, but the dynamics of the cosmos requires the field equation in all generality.
The question is what couples to lambda, what is lambda's origin.
It can be Dark Matter, it could be anything, General Relativity doesn't care because it's still right.
We haven't observed any situation in which General Relativity breaks down, from 6 micrometers up to billions of light years and that is the reason it has not been replaced.

This message is a reply to:
 Message 75 by RAZD, posted 09-03-2005 9:35 PM RAZD has replied

Replies to this message:
 Message 77 by RAZD, posted 09-05-2005 3:59 PM Son Goku has replied

  
RAZD
Member (Idle past 1395 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 77 of 122 (240629)
09-05-2005 3:59 PM
Reply to: Message 76 by Son Goku
09-05-2005 12:32 PM


Re: The Cosmic Fudge Factory and Empirical Candy
The new theory won't change the gross nature of General Relativity because "Quantum Gravity" ... only applies in areas where General Relativity breaks down.
You could also say that GR only applies in areas where Newtonian physics breaks down and that GR doesn't change the gross nature of Newtonian Physics.
So Quantum Gravity won't really be a replacement of General Relativity, rather it will (probably) explain how spacetime emerges from something more fundamental, which won't change GR, it being the theory of spacetime itself.
I prefer to think that a whole new way of looking at Quantum Gravity could replace GR rather than cling to the "standard" - and I have to wonder if this kind of clinging doesn't obscure some of those new ways.
It can be Dark Matter, it could be anything, General Relativity doesn't care because it's still right.
um, isn't this begging the conclusion?
General Relativity has so far perfectly predicted all gravitational systems we have ever observed.
So it is an excellent theory of local gravity.
We haven't observed any situation in which General Relativity breaks down, from 6 micrometers up to billions of light years
I have some real problems with this insistance that GR covers {all\every} situation, when the result of the theory is that we only know about 4% of everything: knowing {all\everything} about only 4% of a system is a far way from knowing the system with any kind of confidence.
For all you know we could be looking at the side effect of some other process all together, like assuming that the light from "St Elmo's fire" is the sum all and be all of the process.
To me that says that it is more likely that any new theory will be significantly different.
Enjoy.

we are limited in our ability to understand
by our ability to understand
RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.

This message is a reply to:
 Message 76 by Son Goku, posted 09-05-2005 12:32 PM Son Goku has replied

Replies to this message:
 Message 78 by Son Goku, posted 09-05-2005 6:11 PM RAZD has replied

  
Son Goku
Inactive Member


Message 78 of 122 (240658)
09-05-2005 6:11 PM
Reply to: Message 77 by RAZD
09-05-2005 3:59 PM


Re: The Cosmic Fudge Factory and Empirical Candy
quote:
You could also say that GR only applies in areas where Newtonian physics breaks down and that GR doesn't change the gross nature of Newtonian Physics.
GR doesn't change the gross nature of Newtonian Physics, but there is a difference between the relationship between Newtonian Physics and GR and GR and "Quantum Gravity".
Newtonian Physics is very much a variable->0 type limit, where as GR isn't a limit in that sense of Quantum Gravity.
quote:
I prefer to think that a whole new way of looking at Quantum Gravity could replace GR rather than cling to the "standard" - and I have to wonder if this kind of clinging doesn't obscure some of those new ways.
What I mean is that it won't replace it in a computational sense.
It will supersede it on explanatory power, but unless you've got time to kill you're going to use GR for the calculations of the majority of gravitational systems.
quote:
um, isn't this begging the conclusion?
No, I can see why you're reading that way though.
I don't mean "right" in the absolute sense, simply that General Relativity doesn't care about lambda's origin.
It still matches observational evidence perfectly, it is a current goal in observational and theoretical cosmology to fully account for all the quantum or classical effects which couple or contribute to lambda.
Basically we don't have lambda's source but General Relativity is still right.
Dark energy is a possible source of lambda and the Casimir experiments make it a safer bet than most of the current alternatives.
quote:
I have some real problems with this insistence that GR covers {all\every} situation, when the result of the theory is that we only know about 4% of everything: knowing {all\everything} about only 4% of a system is a far way from knowing the system with any kind of confidence.
What do you think General Relativity is a theory of and what do you think it tries to explain?
General Relativity is not a theory of matter, it is a theory of how spatio-temporal geometry couples to matter.
In a local system it requires only the Einstein Tensor and Stress-Energy Tensor of the source.
At the cosmological distance it requires the Einstein Tensor plus a scalar multiple of the metric, this multiple being lambda.
Although only a certain percent of the matter can be directly accounted for, this percentage is the dominant form of Stress-Energy in the universe.
It is the source of the Gravitational field.
The remaining percentage only interact to give lambda.
Whatever the remaining percent is, it results in a scalar field permeating the cosmos, however that scalar field isn't a source of gravity.
Rather it changes the geometries matter is permitted to mould, rather than fixing the geometry itself.
General Relativity isn't leaving out this remaining percent, it has it there by default, but it doesn't discuss the nature of the remaining percent because it isn't a theory of matter, it's a theory of what geometries the material content of the universe spits out.

This message is a reply to:
 Message 77 by RAZD, posted 09-05-2005 3:59 PM RAZD has replied

Replies to this message:
 Message 79 by cavediver, posted 09-05-2005 6:56 PM Son Goku has not replied
 Message 86 by RAZD, posted 09-11-2005 5:58 PM Son Goku has replied

  
cavediver
Member (Idle past 3633 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 79 of 122 (240675)
09-05-2005 6:56 PM
Reply to: Message 78 by Son Goku
09-05-2005 6:11 PM


Re: The Cosmic Fudge Factory and Empirical Candy
General Relativity is not a theory of matter, it is a theory of how spatio-temporal geometry couples to matter.
Bullseye!
General Relativity isn't leaving out this remaining percent, it has it there by default, but it doesn't discuss the nature of the remaining percent because it isn't a theory of matter, it's a theory of what geometries the material content of the universe spits out.
Couldn't have said it better myself... well, perhaps I won't go quite that far but right to the heart of the matter.
I will still expand on this when I've got a moment's break.
The key point is that GR, unlike Newton, is not a theory. It is a theory of theories, a mini-TOE in its own right. Every problem that RAZD has talked about are problems with theories (or solutions as we would refer to them) that sit within the framework of GR. SG is quite right when he says that nothing contradicts GR, we just have some problems identifying the correct solutions within GR.
(as an aside... Platonistic-type thinking arises precisely because of this theory-of-theories nature of reality)
RAZD is looking for aesthetics of the solutions , where-as the aesthetics lies in the orginal equations. This is no more evident than in the standard model of particle physics. QCD and electroweak are mind-blowingly aesthetic... but look at the low-energy results and it's ugly as hell. RAZD, if you think we have epicycles in cosmology, you should take a look at the standard model Lagrangian... it's over a page long. Compare that to GR: L = sqrt(g)R. You cannot get more simple than GR.
One of the reasons you aren't too convinced with GR is because you aren't convinced about SR. If you understood what SR implies, you would understand that we are stuck with some form of GR-type theory. And don't forget that SR is tested to unbelievable accuracy every day at CERN and Fermilab amongst others. That is why we hang on to a GR-type framework... we are forced to. GR not only has to reduce to Newton, but it must reduce to SR. To reduce to Newton is exceptionally simple. To reduce to SR pretty much dictates what GR must be.

This message is a reply to:
 Message 78 by Son Goku, posted 09-05-2005 6:11 PM Son Goku has not replied

Replies to this message:
 Message 80 by RAZD, posted 09-05-2005 9:14 PM cavediver has replied

  
RAZD
Member (Idle past 1395 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 80 of 122 (240714)
09-05-2005 9:14 PM
Reply to: Message 79 by cavediver
09-05-2005 6:56 PM


Re: The Cosmic Fudge Factory and Empirical Candy
tag-teamed again
I will still expand on this when I've got a moment's break.
good enough - I need to be away for a couple days on business, I'll get back to this after that.

This message is a reply to:
 Message 79 by cavediver, posted 09-05-2005 6:56 PM cavediver has replied

Replies to this message:
 Message 81 by cavediver, posted 09-06-2005 4:11 AM RAZD has replied

  
cavediver
Member (Idle past 3633 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 81 of 122 (240762)
09-06-2005 4:11 AM
Reply to: Message 80 by RAZD
09-05-2005 9:14 PM


Re: The Cosmic Fudge Factory and Empirical Candy
Hey, you should try being an evolutionist in a church full of creationists... then you'd learn about tag-teaming
I've realised how disjointed all of this is. I'm used to teaching GR, not defending it. Thus my arguments are not as streamlined as I would like. However, my last post started to get to the root problems. I will try to put this all back together into a coherent whole.
Have a good trip!

This message is a reply to:
 Message 80 by RAZD, posted 09-05-2005 9:14 PM RAZD has replied

Replies to this message:
 Message 85 by RAZD, posted 09-11-2005 4:05 PM cavediver has not replied

  
JustinC
Member (Idle past 4834 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 82 of 122 (241989)
09-09-2005 8:36 PM


Cavediver,I have a question about GR and didn't want to start a new thread, so I'll post it here. I'm sure you can answer it easily.
In GR, the curveture of spacetime, expressed as excess radius of a sphere, is given by the formula:
Radius excess= (GM)/(3c^2)
(This is according to Feynman's "Six Not So Easy Pieces", though in the preface it's noted that he leaves out the sum of the pressures in this statement.)
Then, it's stated that this excess radius will be independent of frames of reference. How is this so, since mass is dependent on the frame of reference?
My guess is that although the frames of reference will get a different mass, they are using different coordinate systems, and in their coordinate system they will get the same excess radius. Is this correct?

Replies to this message:
 Message 83 by cavediver, posted 09-11-2005 1:55 PM JustinC has replied

  
cavediver
Member (Idle past 3633 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 83 of 122 (242269)
09-11-2005 1:55 PM
Reply to: Message 82 by JustinC
09-09-2005 8:36 PM


How is this so, since mass is dependent on the frame of reference?
Easy, it's not! This is the big misunderstanding with SR. Velocities do not add. Naively: we see a spacecraft (mass M, velocity V<~c) exert thrust F for time T. The spacecraft deltaV is F/M x T, so we expect to see new velocity = V + F/M x T. We don't because veocities don't add. We see something smaller than this. The false conclusion is that M has increased.
they are using different coordinate systems, and in their coordinate system they will get the same excess radius.
This is the key. In different 4d coordinate systems, 4d vectors (and tensors) will have different components, and if we are measuring one of these components as if it were a scalar, we get upset when it changes in odd ways (length intervals, time intervals). The trick is to look for real 4d scalars that do not change when we change coordinate system. Curvature is one, measured by the Ricci curvature scalar. You can relate this directly to your excess radius. You can then relate that to your mass. So your "mass" when measured correctly, will not change in different coord systems - as in, different frames of reference - as in, when moving at different velocities.

This message is a reply to:
 Message 82 by JustinC, posted 09-09-2005 8:36 PM JustinC has replied

Replies to this message:
 Message 84 by JustinC, posted 09-11-2005 3:02 PM cavediver has replied

  
JustinC
Member (Idle past 4834 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 84 of 122 (242283)
09-11-2005 3:02 PM
Reply to: Message 83 by cavediver
09-11-2005 1:55 PM


quote:
Easy, it's not! This is the big misunderstanding with SR. Velocities do not add. Naively: we see a spacecraft (mass M, velocity V<~c) exert thrust F for time T. The spacecraft deltaV is F/M x T, so we expect to see new velocity = V + F/M x T. We don't because veocities don't add. We see something smaller than this. The false conclusion is that M has increased.
I think you've been saying this all along, but I'm just beginning to understand it. So let me see if I have a good grasp of time dilation, lenght contraction, and mass increase.
These concepts are the result of only looking at the 3D components of a 4D vector. Whereas length of an object shoots off to zero as an obsever sees the object increase in speed, this is only a result of just looking at the 3D vectors. In spacetime, the term (c^2)(t^2) will compenstate for lenght going to zero.
Also, is relativistic mass just a result of maintaining Newton's laws? Because, as you said, the only way to interpreted the nonadditive velocities in terms of Newton's laws would be to suppose the mass has increased.

This message is a reply to:
 Message 83 by cavediver, posted 09-11-2005 1:55 PM cavediver has replied

Replies to this message:
 Message 87 by cavediver, posted 09-11-2005 6:37 PM JustinC has replied

  
RAZD
Member (Idle past 1395 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 85 of 122 (242288)
09-11-2005 4:05 PM
Reply to: Message 81 by cavediver
09-06-2005 4:11 AM


Re: a church full ...
cavediver writes:
try being an evolutionist in a church full of creationists...
actually I just finished living in the center of dutch reform church west michigan for 8 more years than I thought I could endure ...
http://truthinheart.com/Zondervan.htm

we are limited in our ability to understand
by our ability to understand
RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.

This message is a reply to:
 Message 81 by cavediver, posted 09-06-2005 4:11 AM cavediver has not replied

  
RAZD
Member (Idle past 1395 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 86 of 122 (242304)
09-11-2005 5:58 PM
Reply to: Message 78 by Son Goku
09-05-2005 6:11 PM


Re: The Cosmic Fudge Factory and Empirical Candy
Son Goku, msg 78 writes:
It will supersede it on explanatory power, but unless you've got time to kill
I can see this point being unresolvable until such time as the next theory comes along, at which time the answer will become self-evident.
It still matches observational evidence perfectly, ... Dark energy is a possible source of lambda ...
But it's only perfect once both dark matter and dark energy are invoked to explain the discrepancies. Each discrepancy found has resulted in new levels of dark stuffs, first the matter and now the energy ... what's next?
quote:
... knowing {all\everything} about only 4% of a system is a far way from knowing the system with any kind of confidence.
What do you think General Relativity is a theory of and what do you think it tries to explain?
The question is what do we know about gravity and how assured are we that what we know is valid?
If the theory that we think explains gravity "perfectly" ends up reducing {everything we know about the universe} to ~1/25th of the whole then we effectively do not know anything about gravity.
At the cosmological distance it requires the Einstein Tensor plus a scalar multiple of the metric, this multiple being lambda ... Whatever the remaining percent is, it results in a scalar field permeating the cosmos, however that scalar field isn't a source of gravity ... it changes the geometries matter is permitted to mould ...
Now this sounds like chucking out the dark stuffs and adjusting the formula to make the calculations match the observations. How is this different? Why assume that {something unobserved} is responsible for this lambda rather than {some relationship} that is not yet {theorized\observed}?
... it isn't a theory of matter, it's a theory of what geometries the material content of the universe spits out.
and you get upset when I think that this branch of physics is getting more concerned with working out the mathematics of the theory than with explaining the physical universe?
cavediver, msg 79 writes:
GR, unlike Newton, is not a theory. It is a theory of theories, a mini-TOE in its own right. Every problem that RAZD has talked about are problems with theories
Let's stick to gravity, what we know about it and what we don't know, or have to assume to use current theory to predict what is observed.
RAZD is looking for aesthetics of the solutions, where-as the aesthetics lies in the orginal equations.
I'm looking for a theory that predicts observed gravitational behavior with a minimum of assumptions or theoretical complications, especially related to the amount of the universe that we know about. Adding unobserved matter or energy or dimensions just to make the equations "balance" seems to beg the question on how much we really know.
To me that means starting with the observed behavior and then generating the formulas to match that behavior instead of starting with formulas and then adjusting the universe to match the calculated results.
It seems to me that we are lost in a "snapshot" perspective of the universe, that all the calculations are done as if only any one instant were involved in the computations. Whether you use Newtonian or Einsteinian formulas for the calculations.
If I take two snapshots and lay them one on top of the other and then perform the calculations as if they are both present at the same snapshot instant, the result will not be very different ... other than some "adjustment" to the coefficients ...
If I do this with 4 or 5 or 10 it will still not be very different, but extend that out to 100 or 1,000 or 10,000 ... or 3e8? ... there will begin to be a difference in the calculated results.
This is sort of what I mean by "time shadows" ...
As another example with a simplified approach:
I can measure the attraction between an electron and a positron at distance d and can describe it as
f=kP/d2
I can measure the attraction between a wire with a negative current and a parallel one with a positive current at distance d and can describe it as
f=kL/d
And I can skew one wire from the other and get some combination of the two
Thus as I pile on the snapshots I begin to change from f=kP/d2 to f=kL/d similar to what you see with the skewed wires.
I don't need to add any matter or energy to change the calculated result, just the way I look at the picture.
That should be enough to set you both off again

we are limited in our ability to understand
by our ability to understand
RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.

This message is a reply to:
 Message 78 by Son Goku, posted 09-05-2005 6:11 PM Son Goku has replied

Replies to this message:
 Message 88 by cavediver, posted 09-11-2005 7:16 PM RAZD has not replied
 Message 89 by cavediver, posted 09-11-2005 7:33 PM RAZD has not replied
 Message 90 by cavediver, posted 09-11-2005 8:00 PM RAZD has replied
 Message 95 by Son Goku, posted 09-12-2005 2:38 PM RAZD has replied

  
cavediver
Member (Idle past 3633 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 87 of 122 (242313)
09-11-2005 6:37 PM
Reply to: Message 84 by JustinC
09-11-2005 3:02 PM


Look like you've got it!
Also, is relativistic mass just a result of maintaining Newton's laws? Because, as you said, the only way to interpreted the nonadditive velocities in terms of Newton's laws would be to suppose the mass has increased.
Yep, that's pretty much it.

This message is a reply to:
 Message 84 by JustinC, posted 09-11-2005 3:02 PM JustinC has replied

Replies to this message:
 Message 91 by JustinC, posted 09-12-2005 1:12 AM cavediver has replied

  
cavediver
Member (Idle past 3633 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 88 of 122 (242325)
09-11-2005 7:16 PM
Reply to: Message 86 by RAZD
09-11-2005 5:58 PM


Re: The Cosmic Fudge Factory and Empirical Candy
This is my rant post. I will follow it with a more calm approach
Ok, RAZD, you've got to understand that we are 110 years beyond looking for a nice empirical adjustment to Newton. If that's what you want, go to the MOND site where you found that 1e-10m/s/s value. That's a good old "just modify the formula and it will all be alright. As long as we have a formula that fits the data, that's great because we can make predictions". Long before GR, there was the infamous Newtonian modification to F=GMm/r^(2.0001) or whatever it was, that accounted nicely for the advance of perihelion of Mercury.
That's all well and good, but these days we're in the business of understanding this universe, not just being able to perform accurate calculations of celestial mechanics.
and you get upset when I think that this branch of physics is getting more concerned with working out the mathematics of the theory than with explaining the physical universe?
Upset? Damn right! I hate to break it to you but GR is an area of mathematics, an area of geometry. WTF do you think is the only thing we have with any explanative power in the universe? What explanations do you have? Physics is about breaking apart black boxes to discover the black boxes within. However, in SR, GR and quantum theory, we have opened up boxes and found maths within. I don't mean maths relating black boxes to black boxes, which is the role of mathematics in every other area of science, but maths relating to maths relating to maths. Where do you think the whole of our understanding of particle physics has come from? ALL of it was predicted from the mathematics. There are NO physical principles in particle physics, and there is ONE physical principle in GR... the linking to matter via the Newtonian limit. All the physical understanding we have is in our pictures of the mathematics. Every physical principle you think you have heard about in these subjects is a layman's picture of the behind-the-scenes mathematics.
Now you may say (along with many others on this site) that I am confusing the model with reality. But I don't hear that from anyone working at this fundemental level, just those that are way up the ladder.

This message is a reply to:
 Message 86 by RAZD, posted 09-11-2005 5:58 PM RAZD has not replied

  
cavediver
Member (Idle past 3633 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 89 of 122 (242335)
09-11-2005 7:33 PM
Reply to: Message 86 by RAZD
09-11-2005 5:58 PM


A theory of gravity
1) it must reduce to "Newton's Law of Gravity" 'cos that's what we see around us.
2) it MUST reduce to Einstein's Special Relativity 'cos that's what my friends at CERN and FermiLab see every day around them. There is a not a single iota of evidence against SR, and mountains of evidence for.
3) if, from the outset, we cannot satisfy 1) and 2), chuck it out
4) if you don't know yet whether you will satisfy 2) because you are not too sure what satisfying 2) entails... give up, it's a non-starter... go and study 2) for a year or two and go back to stage 1)
5) you are now left with a viable thory of gravity. However, you will have come up with a theory that has come up before, as 2) is such a strong requirement that it makes it not too diffuclt to narrow down the possibilities. We've been doing it for precisely 100 yrs so we've had plenty of time.
6) Check out your theories gravitational predictions around the solar system... earth-moon, mercury anomaly, etc
7) your theory, by having to satisfy 2), will have some weird predictions. Check them out. Do you see them? Bending of light, frame-dragging, gravitational time dilation, etc
8) If you have got this far, you can be happy.
9) If you notice odd things in the universe on very large distance scales causing anomalies... chuck out all of your work and go back to 1). Oh, sorry, that's RAZD's approach...
9a) If you notice odd things in the universe on very large distance scales causing anomalies... what might be causing them? Is there anything already within your theory (Lambda) that explains some or all of this behaviour? Are there quantum extensions (which MUST be incorporated at some point) to your theory that might explain some of this behaviour (quintessence).

This message is a reply to:
 Message 86 by RAZD, posted 09-11-2005 5:58 PM RAZD has not replied

  
cavediver
Member (Idle past 3633 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 90 of 122 (242343)
09-11-2005 8:00 PM
Reply to: Message 86 by RAZD
09-11-2005 5:58 PM


Re: The Cosmic Fudge Factory and Empirical Candy
But it's only perfect once both dark matter and dark energy are invoked to explain the discrepancies. Each discrepancy found has resulted in new levels of dark stuffs, first the matter and now the energy ... what's next?
This keeps going round. Dark energy is NOT a newly invoked dark stuff. That's your layman terminology for you. It is part of GR, and also part of the quantum extensions to GR (supergravity, string theory, etc). The only problem is on galactic scales with galactic rotation curves, and intergalactic proper motions, which is where dark matter is introduced. There is one and one only discrepancy and this is it. The Cold Dark Matter model is the answer to this.
If the theory that we think explains gravity "perfectly" ends up reducing {everything we know about the universe} to ~1/25th of the whole then we effectively do not know anything about gravity.
But this is pure bs. The "dark energy" component is explained. It is part of the theory. GR explains perfectly the Solar System. It explains why we have time dilation, light bending & gravitational lensing, frame dragging, grav radiation loss by binary neutron stars, and a Special Relativistic limit. None of these have anything to do with the precise level of gravitational attraction. None of the modified newtonian theories can address any of these, even if they can produce nice rotation curves through complete fudging (see the MOND site).
As SG says, GR is not a theory of the matter in the universe, it is a theory of the geometry of the universe based upon that matter. It is not empirical. When I mentioned the A,B,C,D,E, etc in the GR metric, you mentioned how these were then empirically fitted. There is not the slighest bit of empiricism in working out those coefficients. They are predicted by the maths. Input your mass distribution, and GR spits out the coefficients. You are not fitting to observation here. The only fit to observation is getting the correct gravity strength through the Newtonian Limit: one number. Everything else comes from the theory. It is that powerful... these coefficients then predict the local gravitational attraction, the time dilation, the frame-fragging, the light-bending, etc, etc. Again and again the theories predictions are confirmed. Where is the empiricism?
The only anonaly is the galactic stuff, which can be rectified by assuming a larger mass input originating from CDM. That is it. Is that enough to reject the whole of GR?
Now this sounds like chucking out the dark stuffs and adjusting the formula to make the calculations match the observations.
No, it's already part of the formula of GR. Ever hear of Einstein's "greatest mistake". It was his use of Lambda to explain the non-expansion of the universe...
I'm looking for a theory that predicts observed gravitational behavior with a minimum of assumptions or theoretical complications, especially related to the amount of the universe that we know about
And the light-bending, and the time-dilation, and the frame-dragging, and SR limit, and the grav radiation slow down... does this theory predict all of these as well?
[ABE If I sound ratty, it's 'cos I'm very very tired... look how many times I've writen theories, not theory's... must sleep]
This message has been edited by cavediver, 09-11-2005 08:41 PM

This message is a reply to:
 Message 86 by RAZD, posted 09-11-2005 5:58 PM RAZD has replied

Replies to this message:
 Message 98 by RAZD, posted 09-18-2005 9:09 PM cavediver has replied

  
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