A little thought of before the Big Bang

[DJBracks]

I'm not exactly highly experienced, considering I'm only 17, but i was just curious what anybodies thoughts are regarding a little idea i had while reading a science fiction novel called A Signal Shattered

My thought was that if before the Big Bang, the Universe was infinitely small and infinitely dense, has anybody ever wondered that maybe if one took the idea of alternate universes seriously, than maybe that infinitely small point of mass that becomes "our" universe is a... leak, for lack of a better term, of matter between "our" universe and another. And maybe that leak slowly built up, eventually exploding through, and that leak of matter is what makes up our universe.

I know my idea lacks all the proper terminology, and it is probably thought of, but i don't really have a very valid source to give any kind of input on the thought, except for the internet of course...

 

[Chalnoth]

Well, one issue here is that there is no reason to believe that our region of the universe ever was infinitely dense. Granted, this is what our equations say when we take our known physical laws and extrapolate backwards in time, but this is just an indication that our equations aren't entirely accurate. Many think that a quantum theory of gravity will show us what happens when matter is really, really dense, and we won't get a singularity extrapolating backward in time (though it will obviously get really, really dense).

As for the parallel universe part of the idea, yes and no. The issue with "parallel universes" is that you don't get matter leaking from one to another. Instead, matter itself is what defines these parallel universes. This idea is another way of talking about the many worlds interpretation of quantum mechanics, where we take seriously the wave function dynamics of quantum mechanics and throw away wave function collapse. What we find when we do this is that the appearance of wave function collapse happens anyway, as when the different components of a wavefunction interact with a larger system, the different components lose coherence with one another, preventing further interference, which makes it so that the different components after the interaction might as well exist in different universes.

According to this, our whole universe is just one big wavefunction. Within that wavefunction are a large number of worlds. These are the parallel universes. So the matter that made up that original, extremely dense bit of matter didn't "leak" into other universes, rather it produced them as the matter interacted with itself and produced multiple, incoherent bits of its own wavefunction.

 

[Chronos]

Observational evidence distinguishes science from science fiction. What we don't see is scientifically irrelevant.

 

[Chalnoth]

Observational evidence distinguishes science from science fiction. What we don't see is scientifically irrelevant.

Well, in a sense. But we can use our understanding of what we do see to place limits upon what we don't see.

 

[justin johnso]

Time began when man invented it as a concept to usefully measure the passing of events and the measurement of events. Time can be ignored. Chain events happen and once they have that is that. We can put our clocks back an hour but it doesn't mean that the universe is younger, it is just our measure of orderly things. The universe and it's eventual extiction will take place at a point in the future and then something else will happen.

 

[marcus]

...we can use our understanding of what we do see to place limits upon what we don't see.

I agree with Chalnoth about this. There is no question---the great part of what scientfic theories tell us is about stuff and events which we don't see.
We test them by comparing what they predict about what we can see.
We cannot peer inside every proton to check that it is made of three quarks. There might be some protons in which there are little Mickey Mouse dolls instead if quarks. But we use the theory because it predicts effects we can see.

Likewise with the big bang cosmology, although we cannot see events before about 380,000 years of expansion, the model tells us about things in the first second, and we can check the model against other things that we can see.

So it will be likewise with the models that go back before the big bang. They still need to be tested to show that they predict better than the original big bang model. We will still only actually see back to year 380,000, but when we have a model that goes back further than the present one, and predicts better, then it will become conventional in the same way.

...
My thought was that if before the Big Bang, the Universe was infinitely small and infinitely dense, has anybody ever wondered ...

DJ there is currently a lot of research by reputable people into (eventually testable) models of cosmology that go back before the start of expansion. There are several main ideas, the dominant or most prevalent idea in current research is the bounce. A prior region of spacetime and matter (similar to ours in some basic respects) which collapses. And quantizing conventional general relativity/gravity theory leads to gravity being repellent at very high density---in some approaches---so at a certain very high density there is a bounce.
There are also quantum gravity explanations of socalled "inflation"---a very rapid expansion episode that may have occurred.

So in general yes people have wondered about a lot of ways it could have happened, a lot of mechanisms leading up to the big bang or start of expansion. I don't know if anyone has researched one that looks exactly like your idea. They have to be mathematical models that obey quantum mechanics and more or less imitate standard Gen Rel. It is hard to say whose research would match your idea as it is expressed in words.

There is a lot of this kind of research going on. Steven Weinberg, a nobel laureate, is involved in it.

Stephen Hawking used to be, back in the 1980s and 1990s but his ideas did not catch on and he has not been very active (especially with reaching retirement age etc.)

Another prominent person, the Indian-born Abhay Ashtekar, is involved. Actually there is quite a list of major physicists getting into this "before the big bang" business.

A popular book now selling pretty well on amazon, that deals with this, is called
"Before the Big Bang", by Brian Clegg.
I wouldn't necessarily want to buy it, or own it, but I plan to make sure my local public library has it on the shelf. It is the kind of thing not only a lot of scientists but a lot of everybody are curious about. Clegg sketches what some of the main theories say about conditions leading up to the start of expansion.

 

[ViewsofMars]

Observational evidence distinguishes science from science fiction. What we don't see is scientifically irrelevant.

I agree with you in respect to "theory" and "hypothesis". Nasa seems to agree us. We are in Physics Forums > Astronomy & Cosmology.

Theory
A scientifically testable general principle or body of principles offered to explain observed phenomena. In scientific usage, a theory is distinct from a hypothesis (or conjecture) that is proposed to explain previously observed phenomena. For a hypothesis to rise to the level of theory, it must predict the existence of new phenomena that are subsequently observed. A theory can be overturned if new phenomena are observed that directly contradict the theory.
http://wmap.gsfc.nasa.gov/site/glossary.html

Perhaps a review of an earlier topic that I contributed to might be helpful here too.
https://www.physicsforums.com/showthread.php?t=331380

 

[ViewsofMars]

“In the Big Bang theory the CMB Radiation is the relic radiation from the hot primeval fireball that began our observable universe about 13.7 billion years ago.” (Cosmic Microwave Background Radiation Anisotropies: their Discovery and Utilization, Nobel Lecture, December 8, 2006 by George F. Smoot iii, Lawrence Berkeley National Laboratory, Space Sciences Laboratory, Department of Physics, University of California. http://nobelprize.org/nobel_prizes/physics/laureates/2006/smoot_lecture.pdf)

I love science and technology!

 

[Chronos]

I did not mean to infer what we do not observe is scientifically irrelevant. I meant to point out it merely useful to refute irrelevant theories.

 

[marcus]

Excellent quote from George Smoot!

“In the Big Bang theory the CMB Radiation is the relic radiation from the hot primeval fireball that began our observable universe about 13.7 billion years ago.” ... Nobel Lecture, December 8, 2006 by George F. Smoot...

Does everybody understand the difference between the universe (which cosmologists model and study) and the observable subset of it? One learns to distinguish between the universe and the observable universe early on, e.g. in an intro cosmology course.

 

[_PJ_]

Something potentially similar in respects, and postulated as one of many theoretical ideas and possibilities hat have grown from various aspects of String theories and particularly, Brane theories, is that our 'universe' (observable and beyond), that is, our 3 dimensions of space, were, prior to the Big Bang, compactified dimensions. These dimensions, through some interaction/reaction, were then "released" from their compatified state, and the cosmic expansion is the result of the "unravelling" of these dimensions.
At least, it fits in with the notion of the expansion of cosmic structure.

 

[Chalnoth]

Something potentially similar in respects, and postulated as one of many theoretical ideas and possibilities hat have grown from various aspects of String theories and particularly, Brane theories, is that our 'universe' (observable and beyond), that is, our 3 dimensions of space, were, prior to the Big Bang, compactified dimensions. These dimensions, through some interaction/reaction, were then "released" from their compatified state, and the cosmic expansion is the result of the "unravelling" of these dimensions.
At least, it fits in with the notion of the expansion of cosmic structure.

Well, that's not quite it. Rather, the idea is that all of the dimensions were small and wrapped up. Then inflation happened. And when inflation happened, it only happened in three directions of all those available: those three dimensions didn't "unravel". They just expanded so dramatically that these small, wrapped up dimensions became absurdly large.

 

[ViewsofMars]

I did not mean to infer what we do not observe is scientifically irrelevant. I meant to point out it merely useful to refute irrelevant theories.

OH, I see what you are attempting to do.

Well, that's not quite it. Rather, the idea is that all of the dimensions were small and wrapped up. Then inflation happened. And when inflation happened, it only happened in three directions of all those available: those three dimensions didn't "unravel". They just expanded so dramatically that these small, wrapped up dimensions became absurdly large.

I'm not sure as you state Chalnoth, "the idea is that all of the dimensions were small and wrapped up. Then inflation happened." That is an idea of yours, Chalnoth.

“These concepts and ideas must pass muster – like a camel going through the eye of a needle – in agreeing with the multitude of precise observations and thereby yield an effective version of our now-working cosmological model. This is the key point of modern cosmology, which is fully flowering and truly exciting.” (George F Smoot, Lawrence Berkeley National Laboratory, CERN Courier, Jun 8, 2009. http://cerncourier.com/cws/article/cern/39163)

George F. Smoot's statement ties in so very nicely with my last two messages.

Let’s use this idea of mine taken from a plaque off my office wall, “When I dance, beautiful dreams begin to happen.” The last time I danced in high heels, I fell and injured my leg.Fortunately, my leg healed and I'm ready to dance again.

 

[Chalnoth]

I'm not sure as you state Chalnoth, "the idea is that all of the dimensions were small and wrapped up. Then inflation happened." That is an idea of yours, Chalnoth.

No, actually, it isn't. I was just attempting to clarify what this particular idea mentioned by _PJ_ was about.

 

[ViewsofMars]

Let's take a look at what Chalnoth and JP wrote and compare it to an article from CERN about String Theory. It appears to me that String Theory has nothing to do with the established Big Bang Theory or inflation.

Secret dimensions
In everyday life, we inhabit a space of three dimensions – a vast ‘cupboard’ with height, width and depth, well known for centuries. Less obviously, we can consider time as an additional, fourth dimension, as Einstein famously revealed. But just as we are becoming more used to the idea of four dimensions, some theorists have made predictions wilder than even Einstein had imagined.

String theory intriguingly suggests that six more dimensions exist, but are somehow hidden from our senses. They could be all around us, but curled up to be so tiny that we have never realized their existence.

Beyond the third dimension

Some string theorists have taken this idea further to explain a mystery of gravity that has perplexed physicists for some time – why is gravity so much weaker than the other fundamental forces? Does its carrier, the graviton, exist and where? The idea is that we do not feel gravity’s full effect in the everyday world. Gravity may appear weak only because its force is being shared with other spatial dimensions.

To find out whether these ideas are just products of wild imaginations or an incredible leap in understanding will require experimental evidence. But how?

High-energy experiments could prise open the inconspicuous dimensions just enough to allow particles to move between the normal 3D world and other dimensions. This could be manifest in the sudden disappearance of a particle into a hidden dimension, or the unexpected appearance of a particle in an experiment. Who knows where such a discovery could lead!
http://public.web.cern.ch/public/en/Science/Dimensions-en.html

I did find another article that peeked my interest. Perhaps others may like to read it.
http://blog.case.edu/case-news/2008/10/13/blackholes

I've contributed enough to this topic. Thanks for allowing me to share and learn. A valuable experience.

 

[Peter Watkins]

Re post#6 and the "bounce" theory; if our universe is the result of an earlier universe that collapsed, then we must be expanding from a single point, a fact that is constantly denied on this forum. It also means that the earlier universe had first expanded in order to then collapse, which meant that the gravitational energy content was greater than the kinetic energy content that would have driven the expansion. Energy conservation laws state that our universe could only be driven by the same energy content. Slowing expansion, causing an increased rate of galaxy separation, and collapse are therefore inevitable. Doubtless mathematics will be able to prove this, although it is hardly necessary.

 

[marcus]

Re post#6 and the "bounce" theory; if our universe is the result of an earlier universe that collapsed, then we must be expanding from a single point,

Why so, Peter? If you actually go and read the quantum cosmology papers where the bounce is studied, they never show the prior phase collapsing to a single point. Quantum corrections to normal gravity take over before infinite density occurs and start the re-expansion. This happens both in the computer simulations and in the solvable analytical models.

Expanding from a single point is exactly what does NOT happen in the bounce picture

...It also means that the earlier universe had first expanded in order to then collapse,...

Again, why do you suppose this? If you look at the professional literature you see various cases, in some the prior phase only contracts and there is only one bounce event.
In others there is an endless series of bounces. You seem to want to assume the latter but at present I don't think there is any reason to pick one over the other. In any event, the main thing is to verify (or falsify) and understand OUR bounce----see what observable features various models predict, look for them, test our ideas and equations about just this one brief episode in the early universe.

If you want to take a look at the current research literature, here is a keyword search ("quantum cosmology") of papers since 2006, ranked by how often they get cited.
Looking at the 50 top-ranking papers you will see that most focus on bounce models
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+COSMOLOGY+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29

To see a brief summary of any paper just click where it says "abstract".

 

[ViewsofMars]

Re post#6 and the "bounce" theory; if our universe is the result of an earlier universe that collapsed, then we must be expanding from a single point, a fact that is constantly denied on this forum. It also means that the earlier universe had first expanded in order to then collapse, which meant that the gravitational energy content was greater than the kinetic energy content that would have driven the expansion. Energy conservation laws state that our universe could only be driven by the same energy content. Slowing expansion, causing an increased rate of galaxy separation, and collapse are therefore inevitable. Doubtless mathematics will be able to prove this, although it is hardly necessary.

Obviously, I need to return to this topic. I'm going to stand behind my earlier messages from page 1. (It would be nice for new comers to review them.) Furthermore, I'm not aware of a "bounce" theory. I have searched extensively and have yet to find a "bounce theory" that will overturn the Big Bang Theory. (I will return later to another remark of Marcus on page 1 since no one has responded to it.) Nature and Science are internationally known peer-reviewed journals and I haven't noticed anything about the "bounce".

Here is a small snippet from a larger article worthy of review that might be helpful.

Certainty In Mathematics and Physics
Rigorous proof (of the kind that supposedly distinguishes math from physics) resides only within a formal system. Each theorem of a formal system can be viewed as just a single data point that either does or does not contradict some other theorem of the system. After we have explored a given formal system for a long time we may feel very confident that it is consistent but, needless to say, zillions of contradiction-free theorems don't constitute a PROOF of consistency. Our confidence in PA, ZFC, or any other formal system is necessarily based on an incomplete induction. It's always possible that a given formal system could exhibit an inconsistency at some point. In fact, it's been suggested that EVERY formal system, if pressed far enough, is inconsistent. Nothing guarantees us the existence of a consistent formal system with enough complexity to encompass arithmetic.

[snip]
Still, a physical theory is by definition a theory of knowledge that associates (or identifies) some of its elements with observable quantities. That identification is part of the theory, and is what makes it a physical rather than a purely mathematical theory. Newtonian mechanics, interpreted as a physical theory, DOES assert a correspondence between its elements and certain measureable quantities, and in this sense it fails (as a physical theory, not necessarily as mathematical theory) when pressed to extremes of relative velocities. Whether it also fails at some point as a purely mathematical theory is a separate (and interesting) question.

Perhaps a better example would have been the theory of general relativity, which predicts - and breaks down at - singularities in the spacetime field. In this case the breakdown is both physical and mathematical.
[snip]
http://www.mathpages.com/home/kmath372.htm

I highly recommend Math Pages! Please feel free to explore it and learn.
http://www.mathpages.com/home/index.htm

 

[friend]

Why so, Peter? If you actually go and read the quantum cosmology papers where the bounce is studied, they never show the prior phase collapsing to a single point. Quantum corrections to normal gravity take over before infinite density occurs and start the re-expansion. This happens both in the computer simulations and in the solvable analytical models.

In any event, the main thing is to verify (or falsify) and understand OUR bounce----see what observable features various models predict, look for them, test our ideas and equations about just this one brief episode in the early universe.

I'm not sure how you could possibly distinguish between a bounce and an original expansion since everything is crushed down to quantum corrections which is what must have originally taken place.

 

[Chalnoth]

I'm not sure how you could possibly distinguish between a bounce and an original expansion since everything is crushed down to quantum corrections which is what must have originally taken place.

That depends upon the type of bounce we're talking about. The only remotely-reasonable proposal I've heard to date is the ekpyrotic scenario, though I'm still a bit skeptical about that one. At least one nice thing about the ekpyrotic scenario is that it makes a very specific prediction: we shouldn't see what is known as B-mode polarization in the CMB. It can therefore be falsified by a positive detection of B-modes.

 

[Peter Watkins]

Re "collapse to a single point". I did not mean a point of infinite density but rather where collapse has brought all of the matter that constituted the previous universe, together. This would presumably be in as dense a state as is possible. Whether this would occupy the volume of our solar system, or our galaxy, or our local cluster could doubtless be calculated.
The supposition that an earlier universe had first to expand in order to collapse is based on my disbelief of both spontaneous and divine creation. For a universe to collapse, gravity has to overcome either it's expansion or it's static inertia. Therefore the only way that a universe could be large without having expanded, is for it to have popped into existence in it's large state. And as far as I am concerned, the only thing that comes from nothing, is nothing!

 

[marcus]

Re "collapse to a single point". I did not mean a point of infinite density but rather where collapse has brought all of the matter that constituted the previous universe, together. This would presumably be in as dense a state as is possible. Whether this would occupy the volume of our solar system, or our galaxy, or our local cluster could doubtless be calculated.

Peter, I understand what you are saying quite a lot better now. I tend to picture the universe as finite volume, like a 3-sphere (hypersphere) of changing circumference. That is not too out of line with your imagery. And mine is just a provisional picture, it is still possible that the universe is spatially infinite. But for the sake of definiteness suppose it is finite. And it collapses down to some very high density.

In what is now the most prevalent approach to quantum cosmology, at very high density (near Planckian) quantum corrections to the equations make gravity reverse and become repellent, so in that approach a bounce naturally occurs.

I don't follow your reasoning here. The traditional picture of eternal universe goes back at least to greeks and was shared by Newton---was also what Einstein originally had in mind. It is just an eternal universe, it doesn't have to "pop" into existence. It simply has to exist.

The only difference now is that this eternally existing universe changes density over time.

Either as a cyclic thing, resembling a string of beads. Or like an infinite hourglass, with one narrow waist.

So I don't follow what you say here:

... Therefore the only way that a universe could be large without having expanded, is for it to have popped into existence in it's large state. And as far as I am concerned, the only thing that comes from nothing, is nothing!

Geometrically it looks like our universe will expand forever, so it could equally well (by running the picture backwards) have contracted forever---and never have to pop into existence.

Or so it seems to me.

There is also the branching tree picture where black hole collapses in one region cause big bang starts of other expanding regions. No region needs to collapse, they just keep proliferating.

In all models there is the philosophical problem of why existence exists---that is on our plate whether we think of existence as eternal or time-limited---but there IMO physics doesn't cut it.

 

[marcus]

I highly recommend Math Pages! Please feel free to explore it and learn.
http://www.mathpages.com/home/index.htm

"Feel free" sounds like you feel comfortable speaking for the host of mathpages
http://www.kevinbrown.com/
who uses a lovely view of Mars as his graphic emblem, or webpage header. Perhaps you know him. It is a shot of a canyon with many side canyons. If not acquainted, check it out! We at PF have pointed people to mathpages or other Kevin S. Brown web resources on several occasions. As I recall, there was this discussion by Chris Hillman of who the guy is.
https://www.physicsforums.com/showthread.php?t=146391

... Furthermore, I'm not aware of a "bounce" theory. I have searched extensively and have yet to find a "bounce theory" that will overturn the Big Bang Theory. ...

There have been articles in Nature or Nature Physics (I don't remember which). You won't necessarily get hits using the keyword "bounce". A lot more publication is in Physical Review series D (abbr. PRD) and Physical Review Letters (PRL). Also Classical and Quantum Gravity (CQG).

Perhaps if you are anxious to find professional-level peer-review articles you should try this search at the Stanford-SLAC database called Spires:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+COSMOLOGY+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29

Currently this gives 240 papers listed by citation count (most often cited listed first).
If you look at the top 50, most will be about bounce-type cosmologies. "Bounce" is not the technical term, although you occasionally do see the word used in the main text body of an article, if not the title. It is an informal term for the way many researchers treat the big bang---how they often model the start of expansion and conditions prior to it.

I've just listed papers that appeared > 2006, that is they appeared 2007 or later. It is a fast-moving field of research so it's advisable to concentrate on the more recent publications. The "ekpyrotic" or "brane-clash" models have gone out of favor recently, they are less studied now (were more pre-2005). They had a kind of bounce in that bunch of models too. If you do the same search but instead of > 2006 you go back earlier, then you get Hawking stuff, and also you get some "ekpyrotic". All kinds of things, Andrei Linde "eternal inflation" etc etc. But it is cleaner and simpler to just focus on recent.

 

[apeiron]

I don't follow your reasoning here. The traditional picture of eternal universe goes back at least to greeks and was shared by Newton---was also what Einstein originally had in mind. It is just an eternal universe, it doesn't have to "pop" into existence. It simply has to exist.

In all models there is the philosophical problem of why existence exists---that is on our plate whether we think of existence as eternal or time-limited---but there IMO physics doesn't cut it.

This is not really right as the original Greek cosmology had the universe arise by the division of a "chaos". A vague somethingness that developed with a self-consistent logic. In the oldest mythology (Hesiod's Theogony), the tale was told as a division that produced a hierarchy of gods, running from the most general to the more specific. And then Anaximander, the first metaphysician, started recorded philosophy with a non-god based version of the same mechanism.

So the original view was first there was a vague everythingness - a naked potential - and then crisp somethingness developed out of it hierarchically.

You could say Anaximander even had a multiverse story as he felt logically the potential (the apeiron of course) was unbounded (in space or time) and so our universe was probably only one example of many of its localised and expanding "separations" (apokrisis). You will note Rovelli's book on Anaximander is due for translation and I will be interested to see how deeply he has researched this original metaphysics.

So the ancient Greeks (and Buddhists as it happens) have considered alternative metaphysical answers. And Peirce and others have returned to them in the modern era.

The atomists of course had a different view. A quite charming one in its own way. Epicurus said there was an infinite void and an infinite shower of atoms was falling like raindrops through it. Then by chance, one particle deviated, colliding with a fellow, thus sparking a pin-ball like richocheting that led eventually to clumped matter and the world as we know it. So a chance QM fluctuation in a scalar field that broke the symmetry!

You, like many, may feel the various alternative metaphysical views are irrelevant to physics that goes beyond the standard model. But they could not be more relevant.

For instance, everyone is talking about the issue of time at the moment - is it emergent, is it phenomenological (block time), is it real?

You can argue that the two choices of eternal time vs popping into existence time are simply the result of demanding that crisp outcomes have equally crisp beginnings. But the most ancient recorded metaphysics actually had another idea. Beginnings were vague potential and whatever emerges - such as space and time - has to develop as a limit state.

So the bounce model is consistent with one meta-physical outlook, and unlikely in another. My own hunch is that the universe is a one shot deal. Though possibly part of a larger spawning fabric in Lindean style. Like a phase transition, you start with a potential and then that gets dissipated just the once (yes, a temporal view of sorts - but the transition would include a move from vague time to a crisp time).

Of course, strong evidence for bounce cosmology would have to tilt opinion towards an eternal crisp existence viewpoint. It is great to live in an era where these 2500 year old ideas are being tested.

 

[oldman]

...It is great to live in an era where these 2500 year old ideas are being tested.

Tested just how exactly? By more speculation? I'm with Chronos here. But I'm in total agreement with the "great to live" bit.

 

[marcus]

Tested just how exactly? ...

You seem unable to believe that a model that does not have a singularity can be tested, oldman.

Your question sounds to me as if meant to be rhetorical. But models with bounce replacing singularity can in principle be tested just as models can be tested in which backwards time-evolution happens to stop. Any model of the past is tested by the predictions which that model makes about what is observable in the present.

If your question is not merely rhetorical, and you are interested in what people are currently exploring as possible ways to test, then I should hunt up some links for you. These are not recommendations--I include stuff I personally don't like. This is just a sampling of what ideas for testing are being investigated at present. You can draw your own conclusions.
https://www.physicsforums.com/showpost.php?p=2315830&postcount=946
Solar system tests of Hořava-Lifgarbagez gravity
https://www.physicsforums.com/showpost.php?p=2328966&postcount=957
The Observational Implications of Loop Quantum Cosmology
https://www.physicsforums.com/showpost.php?p=2331850&postcount=960
Observational constraints on a power spectrum from super-inflation in Loop Quantum Cosmology

Some readers might be interested in gravity wave imprint on the CMB, another window on the early universe---not specific to any particular QG approach---that may be opening up:
https://www.physicsforums.com/showpost.php?p=2263505&postcount=920
Stable indications of relic gravitational waves in Wilkinson Microwave Anisotropy Probe data and forecasts for Planck mission

 

[ViewsofMars]

"Feel free" sounds like you feel comfortable speaking for the host of mathpages
http://www.kevinbrown.com/
who uses a lovely view of Mars as his graphic emblem, or webpage header. Perhaps you know him. It is a shot of a canyon with many side canyons. If not acquainted, check it out! We at PF have pointed people to mathpages or other Kevin S. Brown web resources on several occasions. As I recall, there was this discussion by Chris Hillman of who the guy is.
https://www.physicsforums.com/showthread.php?t=146391

I don't know the host of mathpages.com. From the link you gave about Kevin Brown, he lives in California. The owner of mathpages.com lives in Seattle, WA. We don't know the name of the owner, creator, or administrator of mathpages.com as is noted in the following link.
http://www.alexa.com/siteinfo/mathpages.com

We do know that the related links off of mathpages.com are very impressive. That is why I commented, " I highly recommend Math Pages! Please feel free to explore it and learn."
http://www.alexa.com/siteinfo/mathpages.com

I will tell you what I do know Marcus. I think you have an imagination that zoars beyond reality at times. Like I said before to you, my nickname is Mars. You appear to me by your comment to be insinuating or associating my nickname given to me by a famous scientist with what you think is a graphic emblem of Mars. :rofl:LOL! Marcus, I will share with you this much. I have been told by many a man that I am a drop dead gorgeous very petite long blonde haired model with green eyes. I'll have to resume our conversation later. I have an important meeting to attend.

 

[marcus]

You are right! I mistakenly had a link to Kevin D Brown. Mathpages clearly says copyright Kevin S Brown. Also I trust Chris Hillman when he says Kevin S Brown is the author of mathpages because Math/Physics resources on the web is Chris' business. He did a major Relativity FAQ.
Beyond that, the obfuscation apparently gets Byzantine. I will just give this link to what Hillman says, again:

https://www.physicsforums.com/showthread.php?t=146391

==quote from Chris==

Not true; the author of mathpages.com is called KEVIN S. Brown, and in happier days his contact information (now very outdated) appeared in his website. Verification of the author's name can be found at websites like http://home.att.net/~numericana/fame/ .

(I can just hear some freshfaced InterNet newbie asking, "why would the author of a seemingly inoffensive pedagogical website remove his name from it after more than a decade of existence?" After some thought, and speaking as the author of some seemingly inoffensive pedagogical websites of my own, I would advise members of this forum to decline to speculate about his possible motivations.)

==endquote==

... Marcus, I will share with you this much. I have been told by many a man that I am a drop dead gorgeous very petite long blonde haired model with green eyes. I'll have to resume our conversation later. I have an important meeting to attend.

Thanks for sharing, Mars!

Your saying that the owner of mathpages lives in Seattle WA agrees with Chris' americana link information which locates Kevin Brown there. I have no more interest in the mathpages topic, at least for the moment. I recall BTW your saying you injured an ankle (?) by dancing in high heels. I hope the ankle is better now, or that whatever injury has healed.

 

[ViewsofMars]

Thanks for caring about my health. I'm fine. It was my thigh that was injured while doing the Conga. We all fell down.

I don't know Kevin Brown, but I would like to say to him, "Thanks and best wishes to you. I like your website."

Marcus, let's get back to our topic of discussion on Monday. I'm heading out to the beach for the weekend.

Take care and have a great weekend!

Mars

p.s. A friend did give me Kevin Brown's phone # in case I wanted to thank him on the phone.

 

[oldman]

You seem unable to believe ...

On the contrary, I can believe almost anything. The White Queen had it right:

"I can't believe that!" said Alice.
"Can't you?" the Queen said in a pitying tone. "Try again: draw a long breath, and shut your eyes."
Alice laughed. "There's no use trying", she said: "one can't believe impossible things."
"I daresay you haven't had much practice," said the Queen. "When I was your age, I always did it for half-an-hour a day. Why, sometimes I've believed as many as six impossible things before breakfast".

It's the testing that's the problem. I maintain that the only really trustworthy test of any idea, speculation or theory is the prediction of something not yet observed. And, as you say: "... Any model of the past is tested by the predictions which that model makes about what is observable in the present." Yes! -- observable, not already observed. The Philosophers of Ancient Greece were short on trustworthy tests of their speculations. Sadly, the Collapsing String Bubble shows that some modern theoretical physicists share this shortcoming. That's why the observations from satellite observatories are so important for cosmologists

Thanks for the links. They are interesting. I can only wish that the observational implications of Loop Quantum Cosmology were not just explanations of what we have observed about the lack of large-scale features in the the CMB, but predictions that could be tested. Rather than constraints on the "Barmero-Immirzi parameter". Too esoteric for my understanding.

 

[Peter Watkins]

Hello Marcus. RE #22. Is the universe that you are picturing, our universe or the one that may have existed, and collapsed, before ours? Your description, a 3d sphere of changing circumference, is how I picture our universe. The only difference is that I think that the increased rate of galaxy separation is caused by a slowing rate of expansion. However, that's by the by.
You say that it is thought that at high densities, gravity reverses and repels. So how come there are massive black holes at the centre of all galaxies? Density cannot be greater than within a black hole, be it large or small.
There is of course an eternal universe. It is the wider universe from whence we came!

 

[Chalnoth]

Hello Marcus. RE #22. Is the universe that you are picturing, our universe or the one that may have existed, and collapsed, before ours? Your description, a 3d sphere of changing circumference, is how I picture our universe. The only difference is that I think that the increased rate of galaxy separation is caused by a slowing rate of expansion. However, that's by the by.

It's also wrong. The rate of galaxy separation would only increase faster if the expansion rate (the Hubble parameter) was increasing. The expansion rate appears today to be asymptotically approaching a constant value (this is what it would do in the presence of a cosmological constant). At a constant expansion rate, the galaxy separation will still accelerate.

I'd like to mention, by the way, that I tend to expect that the overall geometry of our universe is highly, highly unlikely to be anything so simple and symmetric as a sphere. More likely it is some very irregular shape, perhaps with any number of twists and loops in higher dimensions. It's possible that it has the topology of a sphere, of course, but it's unlikely that it has the shape of one.

You say that it is thought that at high densities, gravity reverses and repels. So how come there are massive black holes at the centre of all galaxies? Density cannot be greater than within a black hole, be it large or small.

That just says that an expanding universe would, from the outside, look like a black hole. Just because it looks like a black hole from the outside doesn't mean there aren't interesting things going on inside, however.

There is of course an eternal universe. It is the wider universe from whence we came!

Possible, but not certain.

 

[apeiron]

I'd like to mention, by the way, that I tend to expect that the overall geometry of our universe is highly, highly unlikely to be anything so simple and symmetric as a sphere. More likely it is some very irregular shape, perhaps with any number of twists and loops in higher dimensions. It's possible that it has the topology of a sphere, of course, but it's unlikely that it has the shape of one.

.

What are the reasons for thinking this? If the curvature looks so flat to us, does this not imply that all irregularities will have been stretched smooth and so a simple hypersphere is the most probable story? What's your line of thought here?

 

[Chalnoth]

What are the reasons for thinking this? If the curvature looks so flat to us, does this not imply that all irregularities will have been stretched smooth and so a simple hypersphere is the most probable story? What's your line of thought here?

There are two main considerations here.

1. Inflation ensures that no matter how complicated or ugly the shape of the universe as a whole is, it still looks flat to any observers that appear from an inflated region.

2. Even if it started off as a hypersphere, different phase transitions in the early universe would have occurred differently in different locations, causing different expansion rates, which would cause the overall shape to diverge significantly from a perfect sphere.

 

[apeiron]

There are two main considerations here.

1. Inflation ensures that no matter how complicated or ugly the shape of the universe as a whole is, it still looks flat to any observers that appear from an inflated region.

2. Even if it started off as a hypersphere, different phase transitions in the early universe would have occurred differently in different locations, causing different expansion rates, which would cause the overall shape to diverge significantly from a perfect sphere.

Right, so the assumption is of Linde style inflation with multiple local coolings and phase transitions into expanding universe-lets? And you are speaking of the shape of the whole?

Or this is a domain type argument. One single inflation event with multiple regions crystalising out with different local organisations around the same time?

If this is Lindean, then is natural to think of such a pre-bang realm as either flat and infinite in extent, or closed and connected? The other two options would seem to be fractal or locally hyperbolic.