Are there more theories about the start of our Universe?

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  • #1
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I have heard of and read about the big bang theory for the start of our universe. Are there other competing theories that I should look at.
Thanks
Chiefly
 

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  • #2
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Smolin's fecund universe (discretited if I remember correctly but still fun). Also Penrose's Cyclic Conformal thingy. Also discretited if memory serves me but still a fun intellectual exercise. Og i had to pick a religion it wpuld bedre Smolin's. Perhaps in it stronger tecgnological iteration. Ill ser og i Can dig up som papers. ....
 
  • #3
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I am quite a fan of Penrose so if you could provide more detail of his 'thingy' I would be delighted to read it.
Never heard of Smolin's theory so any details about that would be fun even though discredited.
 
  • #4
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I have heard of and read about the big bang theory for the start of our universe. Are there other competing theories that I should look at.
If by "competing" you mean "not already ruled out by evidence", then no, there aren't. The main alternative theory historically, steady state theory, had evidence mounting against it during the 1950s, and then was conclusively ruled out by the discovery of the cosmic microwave background radiation in the 1960s.

Smolin's fecund universe (discretited if I remember correctly but still fun). Also Penrose's Cyclic Conformal thingy.
Neither of these are competing with the standard hot big bang model of our universe. If they are competing with any theory, it is with inflation theory, which is a theory about what happened before the hot big bang (which is the hot, dense, rapidly expanding state that is the earliest state of our universe for which we have good evidence).
 
  • #5
ohwilleke
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Definitional Issues

A theory about the beginning of the Universe and similar matters is generally called a "cosmology" and a fairly complete, but not comprehensive, list can be found here.

Exactly how many alternatives there are to the Big Bang is more of a definitional issue than anything. Where a cosmology model, like the paradigm of the LambdaCDM model, and a "cosmology" itself begin and end is ill defined. A LambdaWDM model (with warm dark matter rather than cold dark matter which is identical except for the dark matter particle mass which is smaller in warm dark matter theories) might be viewed as a variant of the same cosmology or same class of cosmologies as a LambdaCDM model, for example.

Lumpers would call almost all observationally viable or not scientifically ruled out cosmologies variations on the Big Bang theory or versions of it. Splitters would argue that each variation is a different theory or class of theories.

Cosmologies To Ignore

Many cosmologies are patently unscientific and rooted in religion or mythology. Many other cosmologies are no longer accepted by the scientific community, even though they were once considered credible scientific theories until new information ruled them out, such as the steady state theory and tired light theories. Both have only historical interest from an astrophysicist's perspective.

Viable Cosmologies Compared

The differences between the cosmologies that remain viable in light of current observational and experimental evidence primarily differ from each other (1) with respect to cosmological inflation, which is an extremely rapid expansion of the Universe sometime in a first very tiny fraction of a second (of which there are hundreds of variations), and (2) with respect to what (if anything) the cosmology says about possible points of time prior to a "Big Bang"-like event, for example, in the case of bouncing/cyclic cosmologies, or in the case of two sided cosmologies (with a parallel universe in which time runs in the opposite direction from that of our own Universe and is matter dominated before the Big Bang, see, e.g. here).

There are also (3) various kinds of many-worlds cosmologies and (4) cosmologies in which other stuff outside the observable Universe (defined rather than mechanically to exclude various indirect hints of its existence) is important.

Likewise, cosmologies differ meaningfully in their dark sector (i.e. dark matter and dark energy) content, and in their operative laws of gravity to the extent that they derived from subtle modifications of general relativity that can't be ruled out experimentally. But the vast majority of these variations are still squarely within the overall larger Big Bang hypothesis. Whether a Big Bang-like cosmology model like LambadaCDM and a modified gravity cosmology without dark matter or dark energy count as subtypes of one Big Bang cosmology, or as two different cosmologies, is largely a matter of opinion.

One could also arguably call various string theory approaches (such as higher dimensional brane worlds in which our existence is confined to an observable four dimensional universe) a form of a cosmology, although again, this not really contrary to the Big Bang Theory so much as it puts the Big Bang in a large multidimensional context.

Why Consider Alternatives?

Generically, alternatives to the plain vanilla "Big Bang" with all things existing originating then, are devised to be subtly different from the Big Bang: (1) in order to solve issues that might otherwise be explained with cosmological inflation, (2) by addressing issues related to matter creation (e.g. the matter-antimatter asymmetry of the universe), (3) by explaining anisotropy (i.e. asymmetry in the distribution of mass and energy) or violations of the "cosmological principle" (i.e. that there are no observable irregularities in the large scale structure of the universe at a large enough scale) that astronomy observations may hint at, (4) by providing some sort of probabilistic motivation for the values of physical constants or (5) for some sort of explanation of the "weirdness" of quantum mechanics.
 
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  • #6
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Thanks ohwilleke.
Penrose and his cyclic cosmology proposed that all matter ends up in black holes, what happens to those black holes depended on the duration of the universe and it needs a long long time to meet the cyclic conditions of decay by Hawking radiation.
Penrose and Loeb (the physicist not the rally driver) argue that it is highly unlikely inflation occurs and that there are just too many problems with the theory. Of course the adherents argue for the theory and use modified models to solve some of the problems but not any way near all.
The oscillation cosmology supported by Friedmann or the big crunch/big bang seems a good solution considering the big bang alone has a super high density at the beginning and I haven't seen any thing describing its origins. Maybe that is why they support the big crunch as the source of mass.

Now there are some paradoxes with the early years of the universe as B Smethurst says that super massive black holes probably existed just 670 million years after the big bang but how a black hole got to be billions of our stars mass is a deep mystery and long before stars and galaxies were formed that are the normal food of black holes. Here we see the GWB which is supposed to be the merger of 2 super massive black holes but the parsec problem seems to disallow this interaction and leaves a giant hole in the theory of the early universe. Some purport that dark matter is the source but without any evidence and a theory that is hard to test it remains on the outskirts of where they came from. But still theories have to be explored till they are proved or disproved.
 
  • #7
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Cosmologies To Ignore

Many other cosmologies are no longer accepted by the scientific community, even though they were once considered credible scientific theories until new information ruled them out, such as the steady state theory and tired light theories. Both have only historical interest from an astrophysicist's perspective.

What is the main information that ruled out tired light theories? Kragh’s 2017 review article, Is the Universe Expanding? Fritz Zwicky and Early Tired-Light Hypotheses, has an interesting conclusion:

Tired-light hypotheses for the origin of the galactic redshifts are still considered as possible alternatives to the Expanding Universe, but they are no longer taken seriously in mainstream cosmology.​
 
  • #8
Buzz Bloom
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Are there other competing theories that I should look at.
Hi Chiefly:

I generally wonder whether the use of "theory" might be better replaced by "conjecture". The word "conjecture" clearly conveys that the concept does not have observational data to support it, while "theory" is ambiguous with respect to whether any observational data exists.

Regards,
Buzz
 
  • #9
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What is the main information that ruled out tired light theories?
See here:

http://www.astro.ucla.edu/~wright/tiredlit.htm

Tired-light hypotheses for the origin of the galactic redshifts are still considered as possible alternatives to the Expanding Universe
I'm not sure which hypotheses are being referred to here, since every specific tired light hypothesis has been ruled out. Perhaps the author is speculating that someone might invent a different tired light-type hypothesis that would not be ruled out by our current data.

Also note that "the origin of the galactic redshifts" is not the only piece of data that needs to be explained. So a tired light hypothesis that explained that data, but was inconsistent with other data, would still be ruled out.
 
  • #10
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Looking through the various most popular theories (or conjectures, thanks Buzz) I struggle to find one that seems to allow for the super massive black holes that were reported to be formed by Smethurst at around 670 million years from the start of the universe. Super massive BH being around 1 billion solar masses.

What is the most likely source of these BH's, accretion is discredited and a voracious BH eating its fill of stars is also discredited as time was not on the side of that possibility. So are there solutions that formed clumping of mass in the early stages of the formation of the universe that could explain this?
Best
Chiefly
 
  • #11
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Perhaps the author is speculating that someone might invent a different tired light-type hypothesis that would not be ruled out by our current data.

Also note that "the origin of the galactic redshifts" is not the only piece of data that needs to be explained. So a tired light hypothesis that explained that data, but was inconsistent with other data, would still be ruled out.

To keep an open mind is a sound attitude. Marmet’s 2018 article, On the Interpretation of Spectral Red-Shift in Astrophysics: A Survey of Red-Shift Mechanisms – II, compiles dozens of proposed physical mechanisms.

I think a tired light model that can explain the whole range of the observed distance modulus vs. redshift data and provide an alternative origin of the CMB including its blackbody nature is not out of the question.

Please let us know your own thoughts on the question, “What is the main information that ruled out tired light theories?”
 
  • #12
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To keep an open mind is a sound attitude.
Only if what you're keeping an open mind about, actually is open.

I think a tired light model that can explain the whole range of the observed distance modulus vs. redshift data and provide an alternative origin of the CMB including its blackbody nature is not out of the question.
You are entitled to your opinion, but we cannot base discussion in a PF thread on your opinion. Unless you can give a reference to a peer-reviewed paper that describes such a model which has not been ruled out by data, we cannot discuss this here.

Please let us know your own thoughts on the question, “What is the main information that ruled out tired light theories?”
You already asked for information about this, and I gave it in post #9.

Again, unless you can give a reference to a peer-reviewed paper that describes a "tired light" model that is not ruled out by data, discussion of such models is off limits.
 
  • #14
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I think that preliminary you would want to know about a model of the universe that doesn't have a start as it would be quite unimaginable how the universe (in the original meaning of "all there exists") could even be said to have a start (an absolute start of everything, including space, time and matter/energy), since the only way it could have started would be from nothing. But nothing is not a start of anything.

What we only can try to understand is how our OBSERVABLE part of the universe could have started or formed from some pre-existing material conditions.
And there are a lot of theories about the way our universe could have begun, like for instance cosmic inflation (starting our observable universe from a small patch of false vacuum that undergoes exponentially fast expansion, and after decays of the inflaton reheats and creates all matter, and gradually cools and expands, becomes transparant to light and structures start to form, etc.), cyclic universe model (collapse followed by expansion, then recollapse, etc.), ekpyrotic.M theory model of colliding branes, etc.
 
  • #15
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Definitional Issues

A theory about the beginning of the Universe and similar matters is generally called a "cosmology" and a fairly complete, but not comprehensive, list can be found here.

Some remark on this. I don't think you can state that cosmology is defined as a theory about the beginning of the universe, but rather about its development both in the past, present and future. [ For comparison, evolution theory is similarly defined as a theory about how life develops, and explicitly not about its origins. ] One can however properly claim to have a theory about the beginning of the observable universe. But even the Big Bang theory is not a theory about the origin of the universe, but only of its development from a point in cosmological history we can still probe back by either direct observation (the CMB) or theory.
 
  • #16
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You already asked for information about this, and I gave it in post #9.

Again, unless you can give a reference to a peer-reviewed paper that describes a "tired light" model that is not ruled out by data, discussion of such models is off limits.

The reference you gave in Post #9 is not a peer-reviewed paper; it is just a tutorial page used by Wright to express his opinions. I asked for your thoughts hoping that you might be able to give us some useful insights about why tired light models are Cosmologies To Ignore.
 
  • #17
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The reference you gave in Post #9 is not a peer-reviewed paper; it is just a tutorial page used by Wright to express his opinions.
It also gives references to things that are peer-reviewed papers or books (as does the rest of Wright's cosmology FAQ and tutorial). The article is simply a convenient summary reference.

I asked for your thoughts
My "thoughts" are irrelevant. The question is, what does the data say?

In looking through the Marmet paper you referenced, other than the Lambda CDM model, which is consistent with all of the data on angular size distance, luminosity distance, and magnitude distance that we have (which is the only data discussed in the paper), every model for which predictions are given for those distances fails to match the data for at least one of them (most often angular size distance). So the data says that all of those models are ruled out. Some models do not have predictions for those distances given in the paper (or at least not graphed; I haven't tried to work out the consequences of all of the mathematical formulas), so we have no way of judging those; but "no way of judging" does not necessarily mean "still worth taking seriously". From the conclusion of the paper, I get the impression that the author's take is similar to the one I have just expressed.
 
  • #18
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I have heard of and read about the big bang theory for the start of our universe. Are there other competing theories that I should look at.
Thanks
Chiefly

The Big Bang theory is the only theory in town without competition, the only alternative some decades ago was the Steady State cosmology which was ruled out by experimental data. But this is not yet the end of story, the problem remained what really happened near the beginning, as GR would predict there to be a singularity but which is physically impossible, and quantum effects should be important in those circumstances. Yet, we don't have a theory of quantum gravity, although there are two theories in development to combine quantum mechanics and gravity, namely string/M theory and Loop Quantum Gravity.

But even without such a fully developed theory, there are models of what could have happened near and/or before this singularity, evading the singularity, and they were necessary to explain some features of the universe which the big bang model at that time could not explain, namely its flatness, homogeneity and just the right amount of inhomogeneities to explain structure formation (galaxies and such) within the cosmological time frame, and also why there are no monopoles (hypthetical particle predicted to exist by particle physics).

The first model that tried to adress this problem was cosmological inflation, that explains how in a rather small patch of space, due to a scalar field, space expanded very rapidly, exponentially fast, and after this field decays, it releases its energy by reheating the universe, and particle/anti-particle creation and annihilation let to a small overshoot in regular matter (due to some anti-symetry), which later on due to expansion and cooling of the universe combined into atoms (nucleo synthesis) and after 380.000 year the universe became transparrent to light as the photons could freely move, which is known as the CMB or "surface of last scattering". Different models were developped for infation with different properties of the scalar field, some of which still comply with precission mesurements, and not yet ruled out.

But inflationary models have their own problems (like for instance the measure problem, how to calculate probalities in inflationary cosmology as inflation predicts there can be infinitely many universes) and there are competing models to adress solutions to the same problems inflationary cosmology was intended to. One alternative is a cyclic universe (contracting then expanding again in an eternal cycle) and ekpyrotic (collision of branes in higher dimensions, based on M theory), which are worked on.
 
  • #19
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elcaro - your post regarding 'taking the bang out of the big bang' was super interesting not just because P Steinhard was a great proponent of the big bang and has now changed to a cyclic concept but importantly the theory as he explains it does not have any of the problems associated with inflation. This certainly goes a long way in answering my OP.
But it still leaves one question unanswered - how did the supermasive black holes form so early on in time.
 
  • #20
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elcaro - your post regarding 'taking the bang out of the big bang' was super interesting not just because P Steinhard was a great proponent of the big bang and has now changed to a cyclic concept but importantly the theory as he explains it does not have any of the problems associated with inflation. This certainly goes a long way in answering my OP.
But it still leaves one question unanswered - how did the supermasive black holes form so early on in time.
I think you meant to say that Steinhard was a prominent and cofounder of cosmological inflation. He seemed to have changed his mind on this and is now working wih Neil Turok on a cyclic universe model.

About the supermassive black holes, I just finished watching a youtube video on black holes. This video claims that supermassive blackholes got so large because they developed inside supermassive stars that formed in the early years of the cosmos (generation 3 stars), the stars got so large that their interior collapsed into a black hole and then ate the supermassive star.
 
  • #21
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@elcaro - Do you have the link to that video.
 
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  • #22
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Looking through the various most popular theories (or conjectures, thanks Buzz) I struggle to find one that seems to allow for the super massive black holes that were reported to be formed by Smethurst at around 670 million years from the start of the universe. Super massive BH being around 1 billion solar masses.

What is the most likely source of these BH's, accretion is discredited and a voracious BH eating its fill of stars is also discredited as time was not on the side of that possibility. So are there solutions that formed clumping of mass in the early stages of the formation of the universe that could explain this?

This recent BBC article, The mysterious origins of Universe's biggest black holes, is interesting.
 

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