Big Bang: Discovering the Reasons Behind Its Occurrence

[DaveC426913]

I hope you realize that this has been tested? That people haven't merely taken this on faith?

I don't know what you mean by 'tested'. We can't test the physics of BHs, but our mathematical models of them do explain what we see via (albeit rather remote) observation.

 

[Chalnoth]

I don't know what you mean by 'tested'. We can't test the physics of BHs, but our mathematical models of them do explain what we see via (albeit rather remote) observation.

Well, theories are only really tested in science through the collection of a variety of independent sources of evidence. When the evidence from many directions all agrees with a given theory, and no compelling alternatives are presented, most scientists become convinced that the theory is at least approximately true. From what I gather from those who study this sort of thing, black holes passed that point some time ago.

Now, we may speculate wildly as to whether or not the objects we currently call black holes may be something that we haven't thought of yet. And they may be. But there isn't really a good way to actually go out and investigate the vague notion of, "something we haven't thought of yet," so it only makes sense to provisionally accept the theory we have until such time as evidence is presented that contradicts this.

Edit: And I'd like to point out that I purposely don't often express this level of skepticism, because it turns out that once a majority of scientists become reasonably convinced something is true within their own field of study, that is almost never overturned. In fact, I can't think of a single situation where this has occurred since the onset of modern science (say, about 150 years ago for physics, give or take). The possibility always remains, of course, but it's just unlikely.

 

[AWA]

I'd like to point out that I purposely don't often express this level of skepticism, because it turns out that once a majority of scientists become reasonably convinced something is true within their own field of study, that is almost never overturned. In fact, I can't think of a single situation where this has occurred since the onset of modern science (say, about 150 years ago for physics, give or take). The possibility always remains, of course, but it's just unlikely.

How about the aether, energetic versus atomic theory of matter (Boltzmann suicide included), blackbody radiation continuous emission, static universe... just to name a few that come to mind.
You haven't given your assertion much thought, have you?

 

[Chalnoth]

How about the aether, energetic versus atomic theory of matter (Boltzmann suicide included), blackbody radiation continuous emission, static universe... just to name a few that come to mind.
You haven't given your assertion much thought, have you?

Demonstrate that a majority of scientists were convinced of any of these things at one time.

Yes, there have been many ideas in science that turned out to be false. But it seems to me that the majority of them never passed the level of, "Well, maybe this explains things, let's test it!" Many others stem from pre-science concepts, and weren't overturned until we developed the ability to actually investigate them (thus they couldn't be rightly considered conclusions of science, and instead just suppositions).

 

[AWA]

Demonstrate that a majority of scientists were convinced of any of these things at one time.

Demonstrate? As if this was some math theorem? Go to a public library and read some History of Physics book. It is public knowledge available to anyone with a little interest in learning about past mistakes. That a majority of the academy favors one theory guarantees nothing about the validity of the theory.

Yes, there have been many ideas in science that turned out to be false. But it seems to me that the majority of them never passed the level of, "Well, maybe this explains things, let's test it!" Many others stem from pre-science concepts, and weren't overturned until we developed the ability to actually investigate them (thus they couldn't be rightly considered conclusions of science, and instead just suppositions).

You are describing models such as L-CDM in this paragraph "they are at the level of, "Well, maybe this explains things, let's test it!", or "waiting until we developed the ability to actually investigate them ,thus they can't be rightly considered conclusions of science, and instead just suppositions"(Dark matter, Dark energy...). Exactly like the examples I showed, and exactly like them they are supported by the majority of scientists. Certainly we have better technology now but our current technology is in its infancy to deal with such entities as black holes, dark matter and dark energy too so they can'be rightly considered conclusion of science, just suppositions.
Only time will tell which way they are considered in the future. Let's not be so naive as to believe everything is settled.

 

[Chalnoth]

Everything is certainly not settled. Dark energy I would also place in the same category of these things that later turned out to be false. But not dark matter or black holes. There's a lot we don't know about dark matter in particular, and a fair amount we don't know about black holes, but there really isn't much of a question any longer that both of these things exist (at least as a very good approximation to the real objects).

Perhaps more importantly, dark matter and black holes are supported by a wide body of mutually-corroborating evidence. This is something that none of your examples had.

With the aether, for instance, this was merely assumed to exist based on existing theory, and it quickly became apparent that its properties were becoming more more magical all the time. When it was finally looked for, though, the search came up empty, and so it was (correctly) dropped.

With the continuous black body spectrum, it was immediately obvious that something had to be wrong with that idea, as it predicted infinite emission of energy (I would also note that this one also turns out to be approximately correct, as it is accurate for low frequencies/long wavelengths compared to the temperature).

Given that observational cosmology began with Edwin Hubble, in essence, I don't see how a static universe could ever have been considered a majority view.

 

[AWA]

Everything is certainly not settled. Dark energy I would also place in the same category of these things that later turned out to be false. But not dark matter or black holes. There's a lot we don't know about dark matter in particular, and a fair amount we don't know about black holes, but there really isn't much of a question any longer that both of these things exist (at least as a very good approximation to the real objects).

There is not any question they exist as theoretical entities, not as physical entities. They could exist as physical objects, we don't know yet, believing on it is just a matter of personal election. Many physicists even those actively publishing papers on this subjects consider them theoretical constructs as long as no direct physical evidence for them is available and just think of it as the most plausible explanation so far.

Perhaps more importantly, dark matter and black holes are supported by a wide body of mutually-corroborating evidence.

They are suported by theoretical models, and are not contradicted by observation (basically they can't be with current technology, so as long as this state of things doesn't change, they are actually unfalsiable and therefore not real science for the moment, they might be in the near future)

With the aether, for instance, this was merely assumed to exist based on existing theory, and it quickly became apparent that its properties were becoming more more magical all the time. When it was finally looked for, though, the search came up empty, and so it was (correctly) dropped.

You are describing again something very similar to things like strings, WIMPS,etc, let's give it some time and they may or may not be dropped.

With the continuous black body spectrum, it was immediately obvious that something had to be wrong with that idea, as it predicted infinite emission of energy (I would also note that this one also turns out to be approximately correct, as it is accurate for low frequencies/long wavelengths compared to the temperature).

Well, "inmediately" took at least 30-40 years. Certainly little in geological terms but not so little in the history of modern science.

Given that observational cosmology began with Edwin Hubble, in essence, I don't see how a static universe could ever have been considered a majority view.

You lack in imagination and notions of science history, a static universe was not a majority view, it was the only view since the first concepts of a universe outside the Earth was formed by ancient astronomers to 1922 when a universe of changing radius was theoretically hypothesized by Friedmann, and certainly it was stil the majority view until a few years after the 1929 Hubble observation of the redshift-distance law. When Einstein in 1917 proposed the first modern model of universe he reccurred to the static universe even if his equations allowed other solutions because that was the standard view at the time, this can be read in most books on the matter.

 

[Chalnoth]

They are suported by theoretical models, and are not contradicted by observation

This is a statement that is true about any theoretical model ever produced that has yet to be falsified. The point remains that a wide body of observations have consistently followed the expected results based upon these theoretical models. This is what science is, this is how it works, this is how we can be reasonably confident that they are at least approximately correct.

And yes, we are talking about real objects here. There is some possibility that what we know of as a black hole is in reality some other compact object. But there is no question that these compact objects we think are black holes exist. With dark matter there is very little known about its specific nature, but there is no serious question that there is some form of non-luminous matter out there, and none of the standard model particles fit. With dark energy we are less sure, but that's largely because it's an observationally difficult problem.

It is true that there are dissenters for both dark matter and black holes, but they are a strong minority. Most in the requisite subfields of cosmology/astrophysics are quite convinced that dark matter and black holes are real (caveat: I'm sure this is true about dark matter, but black holes are a bit outside my field, so I am less sure they're this confident...I think it's true, but it's a more vague impression on my part, sadly).

(basically they can't be with current technology, so as long as this state of things doesn't change, they are actually unfalsiable and therefore not real science for the moment, they might be in the near future)

This isn't correct. There are a number of observations that could, in principle, have falsified black holes and dark matter. They haven't. Now, we may not have the ideal observations that some people might prefer, but this is often not an option in science. We work with the evidence we have, not the evidence we wished we had. Yes, it would be nice to get a picture of a black hole's event horizon (this may happen relatively soon, actually, which would be rather exciting). Yes, it would be nice to detect and measure the properties of whatever particle it is makes up dark matter. But it is foolish to think that without a specific sort of observation that we might like to have that we can't be reasonably confident as to whether or not the model is at least approximately accurate.

Well, "inmediately" took at least 30-40 years. Certainly little in geological terms but not so little in the history of modern science.

Huh? I'm pretty sure the ultraviolet catastrophe was known about from the start, even though they didn't know the solution at the time.

You lack in imagination and notions of science history, a static universe was not a majority view, it was the only view since the first concepts of a universe outside the Earth was formed by ancient astronomers to 1922 when a universe of changing radius was theoretically hypothesized by Friedmann, and certainly it was stil the majority view until a few years after the 1929 Hubble observation of the redshift-distance law. When Einstein in 1917 proposed the first modern model of universe he reccurred to the static universe even if his equations allowed other solutions because that was the standard view at the time, this can be read in most books on the matter.

And this would impact upon my point how? Obviously before Hubble, there was no observational cosmology, so there could be no science-based conclusion on whether or not the universe was static. This seems to me a case of science overcoming the presumptions that came before, not a case of science giving the wrong answer.

 

[AWA]

Look, you made a silly statement (or bad informed)in post 52, and I pointed it out, you might as well admit it, if you don't I couldn't care less, to go on would be a waste of time since it all should be clear for anyone with a minimum discernment.

 

[Chalnoth]

Look, you made a silly statement (or bad informed)in post 52, and I pointed it out, you might as well admit it, if you don't I couldn't care less, to go on would be a waste of time since it all should be clear for anyone with a minimum discernment.

I don't think it was a silly statement at all. It may have been a bit short and poorly-explained, but I don't think it was silly.

Every field of science has had a period of "growing pains" where people were just settling into the field and learning how things work. Lots of bad ideas abounded and it took time to expunge them with experimental data. But once that initial period of "growing pains" passed, as happened with cosmology some time ago, I'm not aware of a single instance of an evidence-supported theory being widely-held as true that was overturned.

There are some important qualifiers there, of course, and you may argue that those qualifiers are invalid/inconsistent, but I have seen you present nothing that makes that case.

 

[AC130Nav]

I don't think it was a silly statement at all. It may have been a bit short and poorly-explained, but I don't think it was silly.

Every field of science has had a period of "growing pains" where people were just settling into the field and learning how things work. Lots of bad ideas abounded and it took time to expunge them with experimental data. But once that initial period of "growing pains" passed, as happened with cosmology some time ago, I'm not aware of a single instance of an evidence-supported theory being widely-held as true that was overturned.

There are some important qualifiers there, of course, and you may argue that those qualifiers are invalid/inconsistent, but I have seen you present nothing that makes that case.

So cosmology is fine and just needs a little tweaking? Isn't that what they said about epicycles? Again a case where math tried to trump reason.

 

[Chalnoth]

So cosmology is fine and just needs a little tweaking? Isn't that what they said about epicycles? Again a case where math tried to trump reason.

People have been making this sort of accusation for some time about dark matter and dark energy in particular. But I have been quite confused as to why they think the situation is in any way reasonable.

To take the example of epicycles, for instance, there were some massive conceptual problems. The first one is that when the observations became more and more precise, more and more epicycles had to be added to make them work. To contrast this with dark matter, the simplest model for dark matter, a perfectly collisionless, zero-temperature massive particle, has passed with flying colors every observation that it so far would have impacted. There are potential issues where our understanding of the physics in question is otherwise poor (such as the centers of galaxies), but in every case where the physics is relatively well-controlled, where we have a reasonably good handle on the systematic errors, this simplest model of dark matter works fantastically.

Of course, for theoretical reasons we don't expect any real dark matter to actually have zero temperature or be perfectly collisionless. And we hope to one day be able to exploit these non-idealities in order to determine more explicitly the nature of dark matter. But there most definitely hasn't been a need to continually add new properties to dark matter to explain observations.

With dark energy you might have more of a point, but there I'm starting to think that our original assumption that the cosmological constant just had to be zero was based on faulty thinking. Since we actually have no indication from theory that this parameter should have been zero, we should have expected a non-zero value, and thus should, had we paid attention to our equations, have expected to at some point observe some accelerated expansion.

Edit: I'm also confused that when claiming that we can be pretty sure dark matter is a WIMP, and dark energy is the cosmological constant, that this is equated to "everything being okay" with cosmology. No, not at all. Provided you are talking in terms of knowing everything about cosmology, just knowing that dark matter is some sort of WIMP doesn't in any way say what dark matter actually is, it just narrows down the possibilities. Stating that dark energy is actually the cosmological constant doesn't in any way say why it takes this particular value, something which definitely would require new physics to explain. It just narrows the focus to what sorts of new physics we should be looking for. Observational cosmology is by no means close to finished, but we have answered some questions.

 

[finiter]

And this would impact upon my point how? Obviously before Hubble, there was no observational cosmology, so there could be no science-based conclusion on whether or not the universe was static.

Is it not better to take that observational cosmology started from Galileo? He was the first one to use a telescope for that purpose. In that case, static universe can be taken as a science-based conclusion of the past.The expanding universe of ours may be a part of still bigger static entity, the Ensemble containing the multiverses. Or, being static can be a concept of the future also.

 

[Chalnoth]

Is it not better to take that observational cosmology started from Galileo? He was the first one to use a telescope for that purpose. In that case, static universe can be taken as a science-based conclusion of the past.The expanding universe of ours may be a part of still bigger static entity, the Ensemble containing the multiverses. Or, being static can be a concept of the future also.

That would have been astronomy. Modern cosmology didn't really start until we had an inkling that our universe extended beyond our own galaxy, which was what Hubble's observations showed.

Yes, in a way cosmology was what Galileo was dealing with, but that was only because at the time, they thought our universe was smaller than our own solar system turned out to be! Modern cosmology didn't really start until we started to get hints as to the true extent of our universe.

 

[budrap]

To take the example of epicycles, for instance, there were some massive conceptual problems. The first one is that when the observations became more and more precise, more and more epicycles had to be added to make them work.

To make the analogy between Ptolemaic Cosmology and Modern Cosmology more precise you only need to substitute ad hoc modifications for epicycles in the second sentence above. The ad hoc modifications of MC would be Inflation, Dark Matter and Dark Energy all three of which have been added to compensate for predictive failures of the model.

Also analogous is the failure of MC to reexamine it's underlying premises as a consequence of those predictive failures. PC was premised on an Earth centric cosmology with all extraterrestial objects orbiting the Earth in perfect circles.

MC is premised on the existence of a Universe, meaning the existence of a singular space-time reference frame encompassing all of the observable and unobservable cosmos and a corollary assumption that the observed cosmological red-shift is the product of a recessional velocity.

...the simplest model for dark matter, a perfectly collisionless, zero-temperature massive particle, has passed with flying colors every observation that it so far would have impacted.

This is hardly surprising since Dark Matter is by design without interactive properties other than the gravitational (and otherwise unobservable) mass necessary to bring the MC model into conformance with observation.

 

[Chalnoth]

To make the analogy between Ptolemaic Cosmology and Modern Cosmology more precise you only need to substitute ad hoc modifications for epicycles in the second sentence above. The ad hoc modifications of MC would be Inflation, Dark Matter and Dark Energy all three of which have been added to compensate for predictive failures of the model.

By this logic, anything that we ever learn that is new would be just another epicycle.

For dark matter and inflation in particular, they were each proposed as a potential solution to a particular puzzle. Dark matter was initially proposed because galaxy clusters appeared to be far, far more massive than could be explained by their stars. Inflation was initially proposed to solve the flatness and homogeneity problems inherent in the big bang theory. Each made very specific predictions about future observations, predictions that could, in principle, have turned out some other way, but were nevertheless borne out by observations.

This is the exact opposite of epicycles, because the simplest version of the original idea has been continually borne out by observation (for inflation, that's chaotic inflation, for dark matter, that's cold, collisionless massive particles).

Dark energy is rather more difficult, just because it's an extremely weak effect. However, our best test of this that we know of so far will come in the relatively near future with weak lensing observations that measure the growth of structure (that is, how quickly the universe becomes more clumpy). This sort of observation turns out to be very sensitive to the nature of dark energy. It's also a difficult observation to do correctly, so we should expect it to take a little while to hammer out all of the systematic errors.

This is hardly surprising since Dark Matter is by design without interactive properties other than the gravitational (and otherwise unobservable) mass necessary to bring the MC model into conformance with observation.

Nobody expects dark matter to be completely collisionless. Many models of dark matter, for instance, interact with the weak nuclear force in the same way that neutrinos do. It just turns out to be rather difficult to rule out any particular model. Fortunately, however, current dark matter searches are actually starting to rule out some significant regions of parameter space. Perhaps in a few years we'll get lucky. We'll see.

 

[budrap]

By this logic, anything that we ever learn that is new would be just another epicycle.

No, what we learn when the model fails is that it is inadequate. It is the ad hoc hypothesis that is "just another epicycle". This doesn't make the hypothesis necessarily wrong but unless the model's underlying premises are simultaneously reexamined to see if they are still sound in the light of new data then there is always the danger that the MC model will suffer the same fate as the Ptolemaic - wrong for a millenium but still capable of cranking out a right answer.

Like the Earth centric perfect circles of Ptolemy the "Universe" as a singular container of the cosmos is a vestigal concept from deep in our cultural history. It desperately needs to be reconsidered.

 

[AC130Nav]

Nobody expects dark matter to be completely collisionless. Many models of dark matter, for instance, interact with the weak nuclear force in the same way that neutrinos do. It just turns out to be rather difficult to rule out any particular model. Fortunately, however, current dark matter searches are actually starting to rule out some significant regions of parameter space. Perhaps in a few years we'll get lucky. We'll see.

At least we get decent answers from you--not true in other portions of the Physics Forum where the current dogma is viciously defended.

However, I do not see how anything with mass (unlike the poster to whom you responded) could fail to to have collisions. Mass implies a gravitational field, and this is what collisions are about not surfaces.

Question: I have read that the "expansion" of the universe has been found not to be uniform. (I put it in quotes not because I don't believe in it, but because I don't think that's the right word--more like rapid decompression in aeronautical terms). Is it uniform at all distances from us?

 

[Chalnoth]

However, I do not see how anything with mass (unlike the poster to whom you responded) could fail to to have collisions. Mass implies a gravitational field, and this is what collisions are about not surfaces.

Collisions among matter which we are familiar with are driven by the electromagnetic force, not the gravitational force. Basically, when atoms get squeezed together, the electrostatic repulsion of the electrons prevents too much compression, or the atoms passing through one another, even though atoms are mostly empty space.

We already have a relatively familiar particle, after all, that has mass, interacts gravitationally, and yet passes through matter all the time: the neutrino. Neutrinos don't have enough mass to explain dark matter, but we expect that whatever particle actually makes up the dark matter would turn out to be much like the neutrino in its interactions, just with more mass.

Question: I have read that the "expansion" of the universe has been found not to be uniform. (I put it in quotes not because I don't believe in it, but because I don't think that's the right word--more like rapid decompression in aeronautical terms). Is it uniform at all distances from us?

The expansion of our universe is quite uniform to within experimental tests. Here's one measure using supernovae as a test:
http://www.pnas.org/content/101/1/8/F3.expansion

This diagram, termed a "Hubble diagram", which is a diagram of velocity vs. distance, shows a linear relationship out to about 650Mpc, or a little over 2 billion light years. That's pretty uniform. We also have measures that go even further out, but this is one that I found quickly and felt it was good enough to drive the point home.

 

[Chalnoth]

No, what we learn when the model fails is that it is inadequate. It is the ad hoc hypothesis that is "just another epicycle".

But the accusation of inflation, dark matter, and dark energy being "ad hoc" is entirely specious. Yes, they were each initially proposed as a possible explanation for a particular inadequacy in the model. If you'll look at the history, there were a number of competing models for each of these things. But those competing explanations have been knocked out one by one by subsequent observations, and now only inflation, dark matter, and dark energy have survived (though granted, modified gravity still remains a possibility for the explanation of the accelerated expansion, it isn't looking good for that possibility).

You might wish to claim that maybe there is some explanation that we haven't thought of yet, but that isn't science. One of the primary driving forces of scientific work stems around simple practicality. You can't do work on, "maybe it's something we haven't thought of yet," as you have to have a specific idea to at least get started. If you have a specific idea of an alternative, then great! Work on it! Flesh it out! See if it is self consistent, see if it is consistent with past observations, see if it provides testable predictions for future observations.

But don't just stand on the sidelines and say, "Yeah, I think it's something else." That isn't science.

 

[finiter]

You can't do work on, "maybe it's something we haven't thought of yet," as you have to have a specific idea to at least get started. If you have a specific idea of an alternative, then great! Work on it! Flesh it out! See if it is self consistent, see if it is consistent with past observations, see if it provides testable predictions for future observations.

Cold energy, where temperature go below 0K, I think, could explain a black hole. I don't know whether anybody else have made such a suggestion earlier. Can you confirm? However, I have been working on that for some time.

 

[Chalnoth]

Cold energy, where temperature go below 0K, I think, could explain a black hole. I don't know whether anybody else have made such a suggestion earlier. Can you confirm? However, I have been working on that for some time.

Temperature can't go below zero. Temperatures that are numerically below zero turn out to act, thermodynamically, as temperatures that are hotter than positive infinity.

 

[budrap]

[

But the accusation of inflation, dark matter, and dark energy being "ad hoc" is entirely specious. Yes, they were each initially proposed as a possible explanation for a particular inadequacy in the model.

These two sentences are mutually contradictory, like claiming to be a God-fearing atheist.

You might wish to claim that maybe there is some explanation that we haven't thought of yet, but that isn't science. One of the primary driving forces of scientific work stems around simple practicality. You can't do work on, "maybe it's something we haven't thought of yet," as you have to have a specific idea to at least get started. If you have a specific idea of an alternative, then great! Work on it! Flesh it out! See if it is self consistent, see if it is consistent with past observations, see if it provides testable predictions for future observations.

But don't just stand on the sidelines and say, "Yeah, I think it's something else." That isn't science.

The objection I raised was not vague I thought but very specific. Let me restate:

1. As with the Ptolemaic model the proponents of the Modern Cosmological model only patch the existing model when it encounters a predictive failure.

2. In and of itself this is not wrong just inadequate. Whenever a model fails it's fundamental assumptions should be re-evaulated in light of that failure. If a model fails repeatedly the imperative to re-evaluate should become evermore scientifically compelling.

3. The specific underlying assumption of the MC model that I feel is most in need of re-examination is that there exists a singular "Universe" which encompasses all of the observable and unobservable cosmos. This concept of "Universe" has never been scientifically vetted, only assumed. It appears to be a vestigal cultural concept much like the the Earth centric perfect circles of Ptolemy.

If you choose not to address these points that is certainly your perogative. If you wish to argue them please do. But please, spare the strawman arguments. Thanks.

 

[Chalnoth]

These two sentences are mutually contradictory, like claiming to be a God-fearing atheist.

The key point is initially. If people had said they were true only based upon the initial evidence, yes, I might agree with you.

2. In and of itself this is not wrong just inadequate. Whenever a model fails it's fundamental assumptions should be re-evaulated in light of that failure.

The funny thing is that you think this hasn't actually been done.

3. The specific underlying assumption of the MC model that I feel is most in need of re-examination is that there exists a singular "Universe" which encompasses all of the observable and unobservable cosmos. This concept of "Universe" has never been scientifically vetted, only assumed. It appears to be a vestigal cultural concept much like the the Earth centric perfect circles of Ptolemy.

While I happen to agree with that this is often speciously assumed, it in no way places doubt upon these three models. This is, by large, a separate issue related to how we go about determining whether a particular model is likely or unlikely, but it doesn't really effect the observational evidence in favor of inflation, dark matter, and dark energy.

 

[budrap]

The funny thing is that you think this hasn't actually been done.

The funny thing is that you seem to be agreeing that it hasn't actually been done with respect to the concept of "Universe" here:

While I happen to agree with that this is often speciously assumed, it in no way places doubt upon these three models. This is, by large, a separate issue related to how we go about determining whether a particular model is likely or unlikely, but it doesn't really effect the observational evidence in favor of inflation, dark matter, and dark energy.

As far as I can see there is only one model (Modern Cosmological) with three patches (Inflation, Dark Matter, Dark Energy) required by predictive failures of the MC and there is no direct observational evidence for any of them nor is there likely to be any time soon. The best that can be said is that there are no contradictory observations.

The interesting thing about a cosmology devoid of a singular all encompassing "Universe" is that both Inflation and Dark Energy would be irrelevant in the same way that epicycles became irrelevant after Copernicus/Kepler. Dark Matter might still be an interesting hypothesis depending on whether or not the new model directly clarified the gravitational issues DE seeks to address.

 

[jtbell]

The interesting thing about a cosmology devoid of a singular all encompassing "Universe" is that both Inflation and Dark Energy would be irrelevant in the same way that epicycles became irrelevant after Copernicus/Kepler.

Can you provide a reference to a publication in a reasonably current peer-reviewed journal, or possibly on arxiv.org, that proposes or uses such a cosmology? (Note that arxiv.org carries less weight because it is not peer-reviewed.)

I'd like to remind participants in this thread about the Physics Forum rules which are accessible by clicking the "Rules" link at the top of every page here, in particular the section Overly Speculative Posts. It is not part of the mission of PF to promote challenges to currently generally-accepted theories based on pure speculation. If a viewpoint is in fact part of current scientific discussion, as reflected in professional literature, even if it is a minority viewpoint, then it's OK to discuss here. If it's an outdated viewpoint that is not supported by current evidence, then it's not appropriate to harp on it here, just as we don't support promotion of classical luminiferous-aether theories against relativity.

 

[Chalnoth]

The funny thing is that you seem to be agreeing that it hasn't actually been done with respect to the concept of "Universe" here:

Huh? No, a number of people have looked into a variety of possibilities of what may lie beyond our observable universe. But these have very little bearing on dark matter, dark energy, and inflation, which are invoked to explain observations within our own observable universe. I think that the opposition to many such ideas is a bit too vociferous myself, but that doesn't mean the investigations aren't being carried out.

What is clear, though, is that you're extremely off-base. Investigations into what may or may not occur beyond our cosmological horizon has very little bearing on inflation, dark matter, and dark energy. There are some model selection arguments that depend upon what occurs outside of our cosmological horizon, but there is no way in which what occurs beyond our cosmological horizon can possibly do away with these models.

The only somewhat reasonable alternative explanations to these models today lie in modifications to gravity. Today we've ruled out the possibility of observational artifacts accounting for dark matter/dark energy. So it just becomes a question of whether we understand the matter content of our universe, or whether we understand gravity (since gravitational measurements are the only situation in which these discrepancies arise). As of today, nobody has yet produced a compelling modification of gravity to explain either dark matter or dark energy.

As for inflation, the horizon problem essentially proves that it or something like it must necessarily have occurred. The only reasonable alternative to inflation so far is the ekpyrotic model.

 

[budrap]

Can you provide a reference to a publication in a reasonably current peer-reviewed journal, or possibly on arxiv.org, that proposes or uses such a cosmology? (Note that arxiv.org carries less weight because it is not peer-reviewed.)

Hm, this is a peculiar request. My point is precisely that the merits of the singular Universe concept that undergirds the currently accepted cosmological model have never been scientifically evaluated. Therefore it is highly unlikely that there would be a paper proposing an alternative to this unacknowledged and unexamined a priori assumption that the cosmos is comprised of a singular reference frame such that it may be considered a singular entity or Universe.

The very fact that you are obviously unaware of any such an alternative cosmology is illustrative of my point. None exists because none has ever been considered. I don't see how that disqualifies my comments under the rules you mention unless you wish to dismiss them simply on the grounds that they are novel. Hopefully the bar for Overly Speculative Posts is not quite that low.

 

[budrap]

Huh? No, a number of people have looked into a variety of possibilities of what may lie beyond our observable universe. But these have very little bearing on dark matter, dark energy, and inflation, which are invoked to explain observations within our own observable universe. I think that the opposition to many such ideas is a bit too vociferous myself, but that doesn't mean the investigations aren't being carried out.

What is clear, though, is that you're extremely off-base. Investigations into what may or may not occur beyond our cosmological horizon has very little bearing on inflation, dark matter, and dark energy. There are some model selection arguments that depend upon what occurs outside of our cosmological horizon, but there is no way in which what occurs beyond our cosmological horizon can possibly do away with these models.

I guess I am not expressing myself very clearly. I at no point meant to imply knowledge of or a theory about what lies beyond the cosmological horizon. What I am attempting to convey is the idea that the cosmos we observe may not be all or part of a singular entity commonly called the Universe. Put another way I am simply stating that the question of whether or not there exists a universal space-time reference frame needs to given a proper scientific evaluation. As of now its existence is merely an a priori feature of the MC model.

So it just becomes a question of whether we understand the matter content of our universe...

Therein lies the problem sir, you assume the existence of a "Universe" where none in fact may exist.

 

[AC130Nav]

I guess I am not expressing myself very clearly...
Therein lies the problem sir, you assume the existence of a "Universe" where none in fact may exist.

Haven't got a clue what you're saying.

At first I thought you were a multiverse type; now I think you're a nihilist. That last doesn't belong here but might explain why you make no sense.

 

[DaveC426913]

Therein lies the problem sir, you assume the existence of a "Universe" where none in fact may exist.

AC130Nav is correct. This is the Cosmology Forum; the universe exists here by definition.

Philosophy Forum is two doors over. You may deny existence there.

 

[budrap]

AC130Nav is correct. This is the Cosmology Forum; the universe exists here by definition.

Philosophy Forum is two doors over. You may deny existence there.

Yes, this is the Cosmology Forum but it is not the existence of the cosmos (or anything else that can be empirically demonstrated) that I am questioning. What I do question is the assumption that the cosmos is possessed of a universal space-time reference frame which consequently renders it a "Universe" or singular entity. It is my contention that said assumption is unsupported by any empirical evidence.

If you wish disagree then produce the empirical evidence that supports the assumption of a universal space-time reference frame. Scientifically speaking you can't just insert it "by definition" except as hypothesis and if it's only a hypothesis then it must be subject to review or discussion.

If the distinction I am drawing between the cosmos and its characterization as a singular "Universe" is lost on you perhaps you should avoid discussions of matters that tax your ability to think and stick to comedy. But just to be clear here, I don't object to your disagreeing with me, only please offer scientific objections not quasi-religious arguments from authority. That is not the way of science.

 

[AC130Nav]

Yes, this is the Cosmology Forum but it is not the existence of the cosmos (or anything else that can be empirically demonstrated) that I am questioning. What I do question is the assumption that the cosmos is possessed of a universal space-time reference frame which consequently renders it a "Universe" or singular entity. It is my contention that said assumption is unsupported by any empirical evidence.

If you wish disagree then produce the empirical evidence that supports the assumption of a universal space-time reference frame. Scientifically speaking you can't just insert it "by definition" except as hypothesis and if it's only a hypothesis then it must be subject to review or discussion.

If the distinction I am drawing between the cosmos and its characterization as a singular "Universe" is lost on you perhaps you should avoid discussions of matters that tax your ability to think and stick to comedy. But just to be clear here, I don't object to your disagreeing with me, only please offer scientific objections not quasi-religious arguments from authority. That is not the way of science.

Actually there are good arguments against "quasi-religious arguments from authority," but your nonsense is giving them a bad name.

Let me be specific in one regard, "produce the empirical evidence that supports the assumption of a universal space-time reference frame." I'm not sure that's part of the current theories (I like it though, as long as 4 dimensions is not the limit). But it has nothing to do with science, which is restricted to what can be demonstrated. It is not that ONLY four dimensions must be demonstrated, but that AT LEAST four dimensions must be demonstrated (more to be proven by experiment).

 

[FizixFreak]

Now if you use for instance a Fermi normal coordinate chart in curved spacetime or simply a rest frame in Cartesian coordinates in flat space you can use time (which is then proper time) on one axis so it looks like it is a separate dimension. But just by using such a charts does not make it a dimension.

There is a distinction between the manifold and a choordinate chart and it is a mistake to assume that any of the dimensions of the manifold is time.

according to the einstine picture of space and time any thing having a mass can curve the space time fabric but since time is not a spatial dimension how can it be curved by any body??

 

[DaveC426913]

according to the einstine picture of space and time any thing having a mass can curve the space time fabric but since time is not a spatial dimension how can it be curved by any body??

You answered your own question.

As you said, mass curves spacetime (not just space). A massive object curves all 4 dimensions.

 

[finiter]

It is not part of the mission of PF to promote challenges to currently generally-accepted theories based on pure speculation. If a viewpoint is in fact part of current scientific discussion, as reflected in professional literature, even if it is a minority viewpoint, then it's OK to discuss here.

I think that PF does allow questions that may challenge the validity of the generally-accepted theories? Questioning the existing concepts is different from arguing on the basis of an un-accepted theory.

 

[AC130Nav]

You answered your own question.

As you said, mass curves spacetime (not just space). A massive object curves all 4 dimensions.

It might have been better to say (or at least mention) that time slows in the vicinity of a mass and then have given an example (from experimental data).

 

[jackmell]

What I do question is the assumption that the cosmos is possessed of a universal space-time reference frame which consequently renders it a "Universe" or singular entity. It is my contention that said assumption is unsupported by any empirical evidence.

May I ask what are the consequences if the cosmos does not have a universal space-time reference? I would guess from your dialog you suggest this would imply the cosmos then would not be a single entity, a "Universe", but would rather be somehow "disjointed" or separated in some way. If so, could you explain what that would mean.

 

[budrap]

May I ask what are the consequences if the cosmos does not have a universal space-time reference? I would guess from your dialog you suggest this would imply the cosmos then would not be a single entity, a "Universe", but would rather be somehow "disjointed" or separated in some way. If so, could you explain what that would mean.

What it would mean, I think, is that the early astronomers were correct in their first impression that galaxies are Island Universes. Meaning that galaxies each have their own unique reference frames because they each have unique origins relative to other galaxies. If that is true of course, we should expect to see evidence of galactic formation and evolution as we survey the cosmos. The observations of the astronomer Halton Arp support this view though they are widely ignored since they also cast doubt on the redshift as recessional velocity assumption that is the fundamental basis of the Big Bang model.

There is really nothing that novel in idea that there is no universal spacetime reference frame; it arises directly within the context of Special Relativity. A universal reference frame reappears in discussions of General Relativity, however not as a direct consequence of the theory but is simply imposed as a matter of convenience. If you apply the GR equations to the "Universe" you are inherently invoking a universal reference frame regardless of whether or not one actually exists. That, I think, was Einstein's greatest mistake.

 

[Chalnoth]

What it would mean, I think, is that the early astronomers were correct in their first impression that galaxies are Island Universes. Meaning that galaxies each have their own unique reference frames because they each have unique origins relative to other galaxies. If that is true of course, we should expect to see evidence of galactic formation and evolution as we survey the cosmos. The observations of the astronomer Halton Arp support this view though they are widely ignored since they also cast doubt on the redshift as recessional velocity assumption that is the fundamental basis of the Big Bang model.

Halton Arp's views are flatly contradicted by the existence of the CMB. Full stop. Nothing more needs to be said about his views unless he (or somebody else) can demonstrate a thermal distribution for such CMB light stems directly from his model.

Because the best he's been able to do so far is claim that his model predicts a "nearly uniform background light", which I consider a very spotty claim, but in any case there is no expectation of anything like a thermal distribution.

There is really nothing that novel in idea that there is no universal spacetime reference frame; it arises directly within the context of Special Relativity. A universal reference frame reappears in discussions of General Relativity, however not as a direct consequence of the theory but is simply imposed as a matter of convenience. If you apply the GR equations to the "Universe" you are inherently invoking a universal reference frame regardless of whether or not one actually exists. That, I think, was Einstein's greatest mistake.

Huh? This is flatly wrong. General Relativity contains even more freedom in reference frame than special relativity did. One can even do a number of calculations in GR without using any reference frame at all. This is useful, for instance, in demonstrating whether or not any weird features you see in your current equations are just a result of a bad choice of coordinates, or whether they actually exist in the model.

Of course, when it comes to understanding cosmology, it turns out that there exists a very convenient coordinate system (comoving coordinates). This is most certainly not a preferred reference frame, just a convenient one when talking about the expansion of the universe and its effects. In other areas, different coordinates are preferable.

 

[budrap]

Halton Arp's views are flatly contradicted by the existence of the CMB. Full stop. Nothing more needs to be said about his views unless he (or somebody else) can demonstrate a thermal distribution for such CMB light stems directly from his model.

I said nothing about Halton Arp's views. It is his observations that I explicitly referred to and his observations clearly contradict the assumption that the cosmological redshift is due to a recessional velocity. In science observations carry more weight than theory.

Huh? This is flatly wrong. General Relativity contains even more freedom in reference frame than special relativity did. One can even do a number of calculations in GR without using any reference frame at all. This is useful, for instance, in demonstrating whether or not any weird features you see in your current equations are just a result of a bad choice of coordinates, or whether they actually exist in the model.

I clearly said that a universal reference frame does not arise as a consequence of GR theory so what are you complaining about here?

Of course, when it comes to understanding cosmology, it turns out that there exists a very convenient coordinate system (comoving coordinates). This is most certainly not a preferred reference frame, just a convenient one when talking about the expansion of the universe and its effects. In other areas, different coordinates are preferable.

This is a distinction without a difference. Your comoving coordinates which consist of a universal origin at t=0 and a series of universal epochs (inflation, decoupling, galaxy formation and the universal simultaneity of now) constitutes a universal spacetime reference frame whether you want to call it that or not.

 

[Chalnoth]

I said nothing about Halton Arp's views. It is his observations that I explicitly referred to and his observations clearly contradict the assumption that the cosmological redshift is due to a recessional velocity. In science observations carry more weight than theory.

No, these are just his views. His observations say nothing of the sort (they were suggestive once upon a time, but we've much better observations today). It is only his opinion (and those of a few of his followers) that they do. Halton Arp may have done some good science in decades past, but for some time now has been nothing but a pseudoscientific crackpot, continually making wild claims that are completely disconnected from reality.

I clearly said that a universal reference frame does not arise as a consequence of GR theory so what are you complaining about here?

That you are complaining about it in the first place, that you think that this is a "blunder" at all and not simply a matter of convenience.

This is a distinction without a difference. Your comoving coordinates which consist of a universal origin at t=0 and a series of universal epochs (inflation, decoupling, galaxy formation and the universal simultaneity of now) constitutes a universal spacetime reference frame whether you want to call it that or not.

1. The origin at t=0 is not considered to be valid.
2. These other physical processes in no way require a universal space-time reference frame, but describing them is definitely more convenient in such a frame.

 

[budrap]

No, these are just his views. His observations say nothing of the sort (they were suggestive once upon a time, but we've much better observations today). It is only his opinion (and those of a few of his followers) that they do. Halton Arp may have done some good science in decades past, but for some time now has been nothing but a pseudoscientific crackpot, continually making wild claims that are completely disconnected from reality.

I am citing only Arp's observations of high redshift quasars in close proximity to and in some cases even apparent interaction with low redshift galaxies. I am not interested in discussing Arp's theories about the same. It is his theories that have been shown to be in error not the underlying observations.

That you are complaining about it in the first place, that you think that this is a "blunder" at all and not simply a matter of convenience.

OK, let's take it from the top and try again. It falls out (meaning it is a consequence not an a priori assumption) of the theory of Special Relativity that there is no universal spacetime reference frame. The further elaboration of SR into GR did not alter this state.

However, assuming the existence of a "Universe" and consequently a universal reference frame that contains it and then applying the equations of GR to said "Universe" was indeed a "blunder" as you would have it. If you want claim this is a valid scientific approach then cite the empirical evidence supporting the assumption of this "Universality". Cite evidence that this issue was ever scientifically vetted. Show me where it was scientifically proven and not merely assumed that the cosmos constitutes a singular entity that you like to think of as the "Universe". If you are saying that the assumption was "simply a matter of convenience" I would have to agree.

1. The origin at t=0 is not considered to be valid.
2. These other physical processes in no way require a universal space-time reference frame, but describing them is definitely more convenient in such a frame.

1. If by not valid you mean it doesn't make any sense we are in complete agreement. It is however a logical consequence of the Big Bang model and ducking that inconvenient fact doesn't change the necessary conclusion that the BB model leads straight back to an illogical absurdity.

2. I'm not saying that they require a universal spacetime reference frame. I'm saying that they constitute a universal spacetime reference frame. Calling them comoving coordinates is simply a semantic dodge.

 

[Chalnoth]

I am citing only Arp's observations of high redshift quasars in close proximity to and in some cases even apparent interaction with low redshift galaxies. I am not interested in discussing Arp's theories about the same. It is his theories that have been shown to be in error not the underlying observations.

Higher-resolution observations (e.g. from the HST) show that there is no reason to believe these are anything but chance correlations, and that there isn't actually any interaction. The information is available on the Internet if you're willing to look for it. Just pick a specific observation and go hunting.

However, assuming the existence of a "Universe" and consequently a universal reference frame that contains it and then applying the equations of GR to said "Universe" was indeed a "blunder" as you would have it.

That's just plain false, though. First, the results only become inconsistent between different reference frames when you start run into irregularities in the coordinate system (typically singularities). Thus taking, as a tentative hypothesis, the proposal that there exist reference frames for which the universe appears homogeneous and isotropic is a perfectly reasonable thing to do. You can't trust the behavior of the result in the vicinity of any singularities in the coordinate system (which would be at t=0), but other than that it doesn't mess anything up.

The question, then, is whether or not there actually is a reference frame for which our universe is approximately homogeneous and isotropic. The second part to that is, today, trivial to answer, just by looking at the CMB. The CMB is uniform to about one part in one thousand in each direction. Once we take out the dipole of the CMB (presumably due to our own motion with respect to it), the CMB is uniform to about one part in one hundred thousand.

That is pretty darned isotropic.

So, the only question remains, is the assumption that there exists a reference frame for which our universe is also homogeneous valid? First, the default answer to this would most definitely be yes, for the simple reason that a universe that appears isotropic, but isn't actually homogeneous, would indicate that we are extremely near the center of an extremely big universe. And that is something that is rather ridiculous on its face. However, can we test it?

Indeed we can!

You see, for a while some cosmologists thought that it was possible to explain the acceleration of our universe due to our universe being isotropic but not homogeneous. This would indicate that we live near the center of a very large, underdense region (a void). Well, this hypothesis does provide some definite predictions that don't line up with observation, as seen here:
http://arxiv.org/abs/1007.3725

Thus, with all of the other observations that do make sense when we keep the assumption of homogeneity, we can be pretty darned confident that this assumption is accurate. And since there are no singularities in the coordinate system far from t=0, we don't have to worry about it giving us incorrect results due to picking a bad coordinate system.

We should obviously be careful not to extrapolate it too far beyond our cosmological horizon, or too close to t=0. And we certainly wouldn't want to use these coordinates to attempt to describe behavior too close to overdense/underdense regions. But other than that it isn't a concern.

1. If by not valid you mean it doesn't make any sense we are in complete agreement. It is however a logical consequence of the Big Bang model and ducking that inconvenient fact doesn't change the necessary conclusion that the BB model leads straight back to an illogical absurdity.

The big bang model is not expected to be complete. General Relativity itself is the problem here: GR predicts that there will be a singularity in the finite past, almost no matter what sort of physical model we use. We expect that a correct theory of quantum gravity will correct this flaw in GR.

2. I'm not saying that they require a universal spacetime reference frame. I'm saying that they constitute a universal spacetime reference frame. Calling them comoving coordinates is simply a semantic dodge.

Except they don't. You're mixing different terms here. The very idea of a universal reference frame is one that if you are within a perfectly-insulated, closed container, you can tell how fast you are moving. Picking a particular coordinate system within which to do calculations doesn't change the fact that we can't do this. In the FRW universe, we would still have to look outside to see the CMB, for instance. There would be no way to determine our motion without looking outside.

 

[AWA]

So, the only question remains, is the assumption that there exists a reference frame for which our universe is also homogeneous valid? First, the default answer to this would most definitely be yes, for the simple reason that a universe that appears isotropic, but isn't actually homogeneous, would indicate that we are extremely near the center of an extremely big universe. And that is something that is rather ridiculous on its face.

That is simply false.There is a growing bibliography(Sylos-Labini, Pietronero,Mittal,Barrett) with very good observational support that points to a fractal structure of the universe on large scales. And a fractal dispositon of matter may indeed be isotropic and not homogenous. Ever heard of Mandelbrot "conditional cosmological principle?
Not only that, there is a whole family of spacetimes (Stephani) that includes the FRW universes that also allows inhomogenous isotropic solutions. You call yourself "science advisor"?. Why do yo make such categorical assertions when they are not backed up by sound science? That shows either ignorance if you don't know or dishonesty if you choose to ignore those facts that disprove your arguments.

Thus, with all of the other observations that do make sense when we keep the assumption of homogeneity, we can be pretty darned confident that this assumption is accurate. And since there are no singularities in the coordinate system far from t=0, we don't have to worry about it giving us incorrect results due to picking a bad coordinate system.

Yeah, nice and easy.

 

[Chalnoth]

That is simply false.There is a growing bibliography(Sylos-Labini, Pietronero,Mittal,Barrett) with very good observational support that points to a fractal structure of the universe on large scales. And a fractal dispositon of matter may indeed be isotropic and not homogenous. Ever heard of Mandelbrot "conditional cosmological principle?

This isn't actually a disagreement. Everybody agrees that our universe is inhomogeneous on small scales. The very existence of planet Earth is proof positive of that. The question isn't that, rather, but whether we can accurately describe our universe as homogeneous on large scales. And that certainly seems to be what all of our observations have shown us to date. The CMB is nearly anisotropic. Galaxies are, on large enough scales, distributed homogeneously (though are obviously very inhomogeneous on smaller scales). The details of the expansion rate and other observations rule out any major deviations from homogeneity with distance.

There may be some corrections we should apply to our equations for expansion that assume perfect homogeneity due to the fact that it's not really homogeneous on smaller scales, but there really isn't any question that the picture is approximately accurate.

Not only that, there is a whole family of spacetimes (Stephani) that includes the FRW universes that also allows inhomogenous isotropic solutions. You call yourself "science advisor"?. Why do yo make such categorical assertions when they are not backed up by sound science? That shows either ignorance if you don't know or dishonesty if you choose to ignore those facts that disprove your arguments.

I don't call myself anything. The staff here at PF were kind enough to place this label on my account. I neither requested it nor sought it out, though I do thank them. And I am making this sort of assertion because it is, to my knowledge, backed up by solid evidence. The possibility of galaxies distributed in a fractal pattern is potentially interesting, as it would be telling us something specific about the nature of gravity, but doesn't undercut this view at all.

Unfortunately I don't feel like taking the time to search out the evidence for every forum post I make, but if we get into a solid disagreement I am willing to do so (though I will note: you also presented bald assertions without evidence, so please don't act self-righteous here).

 

[finiter]

And that certainly seems to be what all of our observations have shown us to date.

If the universe is homogeneous, on a large scale, at every instant, can we regard it as a system in which the members interact gravitationally? Or is it just an absurd collection of galaxies and that the actual reason why it remains uniform remains unknown?

 

[Chalnoth]

If the universe is homogeneous, on a large scale, at every instant, can we regard it as a system in which the members interact gravitationally? Or is it just an absurd collection of galaxies and that the actual reason why it remains uniform remains unknown?

Well, if the uniformity were perfect, you can still calculate the gravitational interaction. That's precisely what the Friedmann equations are.

When you look into the system in a bit more detail, and properly consider the fact that it isn't actually uniform, you end up with some interesting behavior: on very large scales, you get what is called "linear evolution of structure". This can be rather simply calculated, and you get that small inhomogeneities to start with become small inhomogeneities later on: you don't get, on large scales, very huge deviations from a homogeneous universe.

But on smaller scales the picture is entirely different. Once the matter in a given region goes above a certain density relative to the surroundings, it starts to collapse in on itself. This is non-linear evolution, and it can't be so easily computed, but must be simulated. From this you end up with the more dense places in the universe collapsing and forming galaxies, galaxy clusters, and superclusters, complete with interesting-looking structures visible on larger scales, but the statistical properties on even larger scales left undisturbed.

The way this sort of thing works in a bit more detail is that they divide the matter in the universe up into small particles, and start with a slightly inhomogeneous distribution of said particles (based upon, for example, CMB data). They then run the simulation forward, calculating the gravitational attraction between the different particles at each step. Here's a video flythrough of the end result of one such simulation for how matter tends to clump:

 

[finiter]

Well, if the uniformity were perfect, you can still calculate the gravitational interaction. That's precisely what the Friedmann equations are.

Then, can the expansion be regarded as three dimensional, the shape of the universe remaining either spherical or as a spherical surface?

But on smaller scales the picture is entirely different. Once the matter in a given region goes above a certain density relative to the surroundings, it starts to collapse in on itself. From this you end up with the more dense places in the universe collapsing and forming galaxies, galaxy clusters, and superclusters, complete with interesting-looking structures visible on larger scales, but the statistical properties on even larger scales left undisturbed.

Then can we simplify the whole thing as: once matter particles were formed, matter started contracting due to gravity while the universe continued expanding.

 

[Chalnoth]

Then, can the expansion be regarded as three dimensional, the shape of the universe remaining either spherical or as a spherical surface?

The expansion was in three dimensions, yes. But we don't know the overall shape.

Then can we simplify the whole thing as: once matter particles were formed, matter started contracting due to gravity while the universe continued expanding.

Unfortunately, it's not quite that simple. When the dark matter first condensed, yes, it started to clump. But, at the time the normal matter condensed, our universe was still a plasma, which meant that the protons and electrons were separated from one another, and interacted very strongly with the photons around them. This meant that they felt pressure, so they might start to fall into a gravitational potential well, but then they'd bounce right back out again. It wasn't until the protons and electrons became neutral atoms that the normal matter started to become clumpy.