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Mordred

Cosmological Principle

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Right, but this is according to the classical theory of gravity. The presence of such a singularity signals that the classical theory breaks down as we approach this singularity.

Then if you need to abandon the singularity because the theories predictions are self defeated, you should abandon the entire theory itself. Or atleast understand it is a poor aproximation of reality.

I think it was general relativity or is that what you mean by classical?

What is with the 10-49 Seconds anyway, why isn't that 0 then? Is that the time it takes for POINT to become a sphere with a planck length diameter?

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Then if you need to abandon the singularity because the theories predictions are self defeated, you should abandon the entire theory itself.

This would mean abandoning general relativity as a whole. We know that under rather generic conditions singularities are an inevitable feature of the theory. Much like the infinities that arise in classical electromagnetic theory due to the electron's self-interactions.

 

Or atleast understand it is a poor aproximation of reality.

General relativity is a good approximation of reality as long as we are not near the scale of quantum gravity. Similarly, the standard model of cosmology is a good model, but we know it breaks down when we are close to the singularity.

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This would mean abandoning general relativity as a whole. We know that under rather generic conditions singularities are an inevitable feature of the theory. Much like the infinities that arise in classical electromagnetic theory due to the electron's self-interactions.

 

 

General relativity is a good approximation of reality as long as we are not near the scale of quantum gravity. Similarly, the standard model of cosmology is a good model, but we know it breaks down when we are close to the singularity.

Well that's been the idea for a few decades now I guess. Yes I agree its a good aproximation, but, the good and poor adjectives are subjective, I think approximation is the key word.

What is with the 10-49 Seconds anyway, why isn't that 0 then? Is that the time it takes for POINT to become a sphere with a planck length diameter?

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Well that's been the idea for a few decades now I guess. Yes I agree its a good aproximation, but, the good and poor adjectives are subjective, I think approximation is the key word.

By 'good' we mean that the theory agrees well with nature taking into account experimental errors and the domain of validity of the theory. Where there is some subjectiveness is in the 'agrees well'; we define that ourselves though typically one would set that to mean within the experimental errors. For example, there are no known phenomena that do not agree with general relativity to within the experimental errors and the theory has been tested to some huge degree of accuracy (I forget the figures, but it is on par with the standard model of particle physics).

 

Similarly, when dealing with the lambda CDM model, which has general relativity as part of its 'backbone', we have nice fits for the parameters. The theory seems to fit nature generally very well, just not so in the very very very early universe.

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I would be hard to conduct experiements under the conditions that existed in the first 10-49 seconds after the big bang though, so our testing is inherently rather biased.

Edited by Sorcerer

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That was pointed out the theory only describes the universe from a time of 10-49 seconds onwards (according to what Mordred posted before). But the reasoning that lead to the creation of the idea, inevitably leads to the crossing of spacetime at the origin, where it has no volume and is infinitely dense.

 

No it doesn't. A naive extrapolation of GR to scenarios where it may not be valid does that. Which is why no (other than science journalist) does it.

 

There are several models which avoid a singularity entirely.

Then if you need to abandon the singularity because the theories predictions are self defeated, you should abandon the entire theory itself. Or atleast understand it is a poor aproximation of reality.

 

ALL theories are approximations of reality with limited domains of applicability.

 

What is with the 10-49 Seconds anyway, why isn't that 0 then? Is that the time it takes for POINT to become a sphere with a planck length diameter?

 

That is the state at which energies exceed those at which current theories can be applied with confidence.

Edited by Strange

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I would be hard to conduct experiements under the conditions that existed in the first 10-49 seconds after the big bang though, so our testing is inherently rather biased.

Indeed, so the best one can really hope for is some imprint of this epoch that we can detect in observational cosmology. This is one of the problems with formulation a quantum theory of gravity, nature just does not want to give us hints.

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So, it could be the flying spaghetti monster for 10-49 seconds then.

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So, it could be the flying spaghetti monster for 10-49 seconds then.

 

This is the "god of the gaps" argument (or "FSM of the gaps" argument :)).

 

Just because we don't (yet) have a theory for the earlier state of the universe doesn't mean that anyone can just make up their own explanation(*). "Don't know" is always a valid result in science.

 

(*) Well, obviously, they can. It just isn't science. Related to which, I am always surprised when religious people with an anti-science agenda object to the big bang model. I would have thought they would jump on the pop-sci version as a "creation story" (and highlight that one of the founders of the theory was a Catholic priest).

Edited by Strange

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I was thinking about the objection to there being a singularity based on the cosmological principle and realised how this violates the isotropic and homogenous nature. I was thinking of 3D from 1 moment to the next, but not of the following moments in 4D, so missed that it was an anomally, which stands out against the rest of time. So for example at no other point in 4D does the universe gain dimensions and this makes that moment anisotropic.

However, there are a few moments like this at the beginning of the universe which also are anomalous. For instance at no other point in time does the universe undergo recombination change phase from plasma to gas and have photons decouple from matter. So this moment, ironically, being anisotropic in time also creates evidence for isotrophy.

All I can really say on these anomalies to resolves them with regards to the cosmological principle is that just as we ignore the small scale fluctuations over 3D which statistically even out so we can regard the universe as isotropic and homogenous. So too we can ignore the few points in the universes evolution where anomalous events occur, because on the larger scale of time, these events are statistically irrelevant.

So again I come to the conclusion that the cosmological principle does not deny there being a change from a singularity to a 3 dimensional universe at the first moment of time.

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You might want to study which type of singularity.

 

1.the state of being singular, distinct, peculiar, uncommon or unusual

2.a point where all parallel lines meet

3 a point where a measured variable reaches unmeasurable or infinite value

4. the value or range of values of a function for which a derivative does not exist

5 a point or region in spacetime in which gravitational forces cause matter to have an infinite density; associated with Black Holes.

 

The universe singularity case is number 3 as opposed to 5. As mentioned though this depends on the metrics used. Some examples that avoid or solve number 3 have been mentioned. A notable one being the bounce of LQC.

Edited by Mordred

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Yes Mordred, but what in the cosmological principle says that, that is not allowed?

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Nothing Its still an important point to mention as this is also commonly misunderstood. It's more an FYI, as the universe can be infinite its singularity cannot be accurately thought of as a BH style point like singularity if you include the universe beyond our observable universe. We still don't know if the universe is finite or infinite. Though our observable universe is finite

 

You'd be amazed how often this is misunderstood.

Edited by Mordred

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I'm not so much amazed at how often it is misunderstood, but rather how often it isn't even considered as a thought at all.

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PMJI, but "Cosmological Principle" is the correct spelling. It could even be called "Principal Cosmological Principle" were it the most popular of several competing theories.

 

So, could we please change the spelling in the title?

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Lol good catch I'm surprised I, and everyone else missed that. Title error fixed. +1

Edited by Mordred

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Mordred makes some very good points, but I would like to make some things absolutely clear.

 

The big bang can be thought of as a black hole, but there are differences, the horizon for instance, is different, where a black holes horizon is a true boundary. The universe has no boundary.

 

It is also true from the mathematics of a black hole that from inside, the universe would not appear very dense. This is also true from our perspective, since matter makes up about 1% of all of spacetime and then there is the space outside the observable horizon, which could be much larger and devoid of any matter or energy.

 

Another problem, is that the big bang doesn;t quite match the physics of a black hole, since its easier to argue it makes better sense for its time reversed partner, a white hole. Some notable scientists have speculated this and even wrote papers on it. Mordred is like me, we entertain theories we may not even agree with. 

On 08/06/2015 at 11:36 AM, ajb said:

Indeed, so the best one can really hope for is some imprint of this epoch that we can detect in observational cosmology. This is one of the problems with formulation a quantum theory of gravity, nature just does not want to give us hints.

 

You should have been harsher, I think I know what you mean though :P We won't get to observe anything beyond the radiation phase of the universe. It would completely smear anything that existed with structure before it. Besides I guess it is hard to say anything with structure existed before the universe became transparent for light, but who cares really lol... 

 

I will ask though, what are your opinions on a quantum theory of gravity?

 

I have not much confidence at all for the gauge theory of quantization. I was made aware by Mordred though that the spin-2 statistics should remain in the wave formulation. I think Mordred is intelligent, but not been terribly sure this should be the case. I can understand though why, because I know some background of that field and the spin -2 field does give rise naturally to an attractive field. But there are other ways that doesn't involve a concept of spin and are purely classical.

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Well the spin 2 statistics of GR is contained in numerous textbooks of GR and cosmology. ( usually in the introductory textbooks. Later when I have time I will post the series of calcs from Matt Roose.

However the spin 2 arises from the two linear polarizations of a GW wave.  (H+ and H×) under Noether  ( uses the Gell Mann matrixes ) The electromagnetic field is dipolar one linear field with two polarity states.( uses the Pauli matrixes)

Edited by Mordred

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Mordred, the problem of course is that we now know from WMAP and many other sources of data that there is in fact large-scale anisotropy to the universe, in both baryonic matter and CMB. So there is a growing view that the Cosmological Principle has been falsified, but this fact doesn't seem to have been internalized in our theories yet. 

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No WMAP, COBE and Planck all agree with the cosmological principle despite the pop media coverage of those studies. This includes the great attractor etc. 

The consensus is that 100 Mpc may not be a sufficient volume where the principle becomes applicable below this scale obviously you have LSS anistropy but just like looking at an ocean with waves the larger the volume, the less the waves on the surface matters in terms of applying a uniformity.

 Some papers suggest upgrading the scale to 120 or as high as 150 Mpc. This is the trick many fail to see, usually from efforts to self teach.

 Barbera Ryden "Introductory to Cosmology" has an excellent descriptive of the size to uniformity relations. 

Cosmologists  obviously understand the gist of the principle as being one of scale.

Think of the ocean analogy the further you are away from the surface and the larger the view, the more uniform the ocean appears. The closer you are the smaller the view the more chaotic the surface appears.

The Principle is the same. Secondly 1/1000th of a degree difference in the temperature variation studies of the CMB certainly supports the uniformity. The planck anistropy of evil was a dipole anistropy calibration error. (Matt Roose Introductory to cosmology) has an excellent coverage of dipole anistropy including the basic calibration formula to account for Earths motion effects on redshift. Which is written long before Planck even published its data.

 Never trust pop media or heuristic explanations, they will mislead you every time...

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On 6/8/2015 at 5:04 AM, ajb said:

This would mean abandoning general relativity as a whole. We know that under rather generic conditions singularities are an inevitable feature of the theory. Much like the infinities that arise in classical electromagnetic theory due to the electron's self-interactions.

General relativity is a good approximation of reality as long as we are not near the scale of quantum gravity. Similarly, the standard model of cosmology is a good model, but we know it breaks down when we are close to the singularity.

General relativity is only a good approximation for extremely limited scales, on the order of solar systems.

It's applicable area of operation is .1% of the universe.

This is easily demonstrated. The theory by itself is 99.9% accurate within the solar system without adding any other theory to it. But the second one attempts to apply what was just shown to be 99.9% accurate in describing planetary systems (non-ionized matter) to the rest of the universe (ionized matter) one suddenly has to add 96% ad-hoc theory to make what was just tested to a 99.9% accuracy without it to make it even fit a semblance of reality.

So the question is really, are we using the wrong physics for the wrong state of matter to begin with in our attempt to describe the rest of the universe, and so end up needing that 96% ad-hoc theory leading to singularities?

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29 minutes ago, Justatruthseeker said:

General relativity is only a good approximation for extremely limited scales, on the order of solar systems.

It's applicable area of operation is .1% of the universe.

This is easily demonstrated. The theory by itself is 99.9% accurate within the solar system without adding any other theory to it. But the second one attempts to apply what was just shown to be 99.9% accurate in describing planetary systems (non-ionized matter) to the rest of the universe (ionized matter) one suddenly has to add 96% ad-hoc theory to make what was just tested to a 99.9% accuracy without it to make it even fit a semblance of reality.

So the question is really, are we using the wrong physics for the wrong state of matter to begin with in our attempt to describe the rest of the universe, and so end up needing that 96% ad-hoc theory leading to singularities?

Your reasonings and assumptions seem to defy what we have observed and the reasonable assumption of the isotropic and homegenous nature of the observable universe. 

 

https://phys.org/news/2018-07-einstein-againweak-strong-gravity-fall.html

 

https://www.nature.com/articles/s41586-018-0265-1

 

And of course gravitational lensing of distant objects as dictated by GR have been confirmed many many times.

Obviously the answer to your final question is that while certainly GR is an excellent aproximation  that at this time we are unable to improve on, then certainly, no, it is not the wrong physics.

Edited by beecee

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1 hour ago, Justatruthseeker said:

General relativity is only a good approximation for extremely limited scales, on the order of solar systems.

It's applicable area of operation is .1% of the universe.

This is easily demonstrated. The theory by itself is 99.9% accurate within the solar system without adding any other theory to it. But the second one attempts to apply what was just shown to be 99.9% accurate in describing planetary systems (non-ionized matter) to the rest of the universe (ionized matter) one suddenly has to add 96% ad-hoc theory to make what was just tested to a 99.9% accuracy without it to make it even fit a semblance of reality.

So the question is really, are we using the wrong physics for the wrong state of matter to begin with in our attempt to describe the rest of the universe, and so end up needing that 96% ad-hoc theory leading to singularities?

!

Moderator Note

If you wish to discuss this, start up a thread in the speculations forum. Be sure to bring more evidence and detail than you have presented here. In this thread, it's hijacking.

edit: since you've hijacked another thread, it has been split. Make your case there

https://www.scienceforums.net/topic/115265-dark-matter-split-from-is-this-the-dark-matter-particle/

 

 

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13 minutes ago, swansont said:
!

Moderator Note

If you wish to discuss this, start up a thread in the speculations forum. Be sure to bring more evidence and detail than you have presented here. In this thread, it's hijacking.

edit: since you've hijacked another thread, it has been split. Make your case there

https://www.scienceforums.net/topic/115265-dark-matter-split-from-is-this-the-dark-matter-particle/

 

 

What more evidence do you need than what was once just 99.9% accurate no longer is the second you apply it outside the solar system?

But sure, whatever you need

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On 6/8/2015 at 11:53 AM, Sorcerer said:

That was pointed out the theory only describes the universe from a time of 10-49 seconds onwards (according to what Mordred posted before). But the reasoning that lead to the creation of the idea, inevitably leads to the crossing of spacetime at the origin, where it has no volume and is infinitely dense.

 

This logical consequence was abandoned because we lack the tools to describe it with our current knowledge. But that doesn't necessarily mean it isn't what happened before that. It doen't necessarily mean it is either, however that would be the conclusion from the reasoning which first created the theory.

 

The fact that you need to give a time of 10-49 seconds, implies that time before it.

I wouldn't get hung up on the fact that it's 10^-49 seconds that defy our current understanding of physics. Also, Big Bang is an historic misnomer

Quote

He coined the term "Big Bang" on BBC radio's Third Programmebroadcast on 28 March 1949. It was popularly reported by George Gamov and his opponents that Hoyle intended to be pejorative

From Wikipedia - Fred Hoyle.

But this term has lead many people to imagine the beginnig of the universe as an explosion from a single point.

But now just imagine that you could appoint an infinitely large amount of numbers to every real number. Every real number here is a single point, on a scale consisting of an infinite amount of points. Our observable universe might have sprung from a single point, but it needn't have been the only point that was there at the "beginning", so even though this point would be special to our observeable universe, it would be utterly insignificant among a lot of insignificant points, and the cosmological principle would continue to hold

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