My Cosmological Musing

  • #1
lets say we have a ball with no air in it, so it is no bigger than a dot. now we attach a pump to it that pumps air into this very elastic ball at a relativistic speed.

1) there are an infinite number of 2-dimensional universes within the ball. all of them are of course at some radial distance from the singularity. but the singularity is not actually a part of any of these 2-dimensional universes.

2) an observer on a surface sees himself as being in the middle of his universe.

3) his universe is expanding at unbelievable rates.

4) he measures his universe to have no edges.

5) he has no concept of the 3rd dimension of volume, as he is a flatlander, and only sees in 2 dimensions.

does this not have some eerie similarities to our own situation ? now what sort of 4th dimension do an infinite number of spheres fit into ? i have no more chance of visualizing that geometry than the flatlanders have of visualizing a sphere. but it makes me wonder.

one thing i agree with qm - i suspect that the totality of it all is stranger than we can even ponder about.
 

Answers and Replies

  • #2
hi chronos,

i am assuming your post was intended for this musing thread ? i dont see how you are making any conclusions about mathematics, or lack of it.

i simply compared a 2-dimensional viewpoint with a 3-dimensional viewpoint.

i suspect that the flatlanders may have mathematics to explain their universe. it may or may not be anything like our mathematics. likewise, the mathematics that we use in 3 dimensions may be like or unlike the math that is used by a 4-dimensional creature. or maybe something else completely replaces mathematics in 4 dimensions ? i dont know.

i think the mistake you are making is one that many scientists make. they assume they can learn everything. i dont assume this at all. in fact, just the opposite - i suspect that we cant learn anything at all about a 4th dimension, if there even is one. but if there is one, i dont think it would even make any sense to us, any more than the flatlander could think about volume.
 
  • #3
just to add some clarification on what i was thinking.

in the way that my limited 3-dimensional brain can think, i was guessing that the flatlanders mapped their universe with x and y coordinates. and that the 4-dimensional guys mapped their universe with x, y, z, and alpha coordinates (whatever spatial dimension alpha might be).

and because we developed math for our universe, i was guessing that the other 2 also had their math. but i realize that these guesses are merely because of my 3-dimensional experience, and with time manifested as it is. all this may or may not have relevance in other universes. there is nothing that i would want to say with any degree of certainty.

but i found it compelling that this 2-dimensional universe travelling through a 3rd dimension would seem to have many of the same conclusions as we have about our 3-dimensional world.

i was simply positing "could there be a connection ?" could we be travelling through a 4th dimension ? could this curvature of spacetime have anything to do with it ? these flatlanders, if sophisticated enough, would find curvature in their world as well. but depending on how big their surface area was, it would get harder and harder for them to tell, as it would look flatter and flatter, as the surface grew.

also, they may or may not be under the same restrictions as we are, in regard to information speed. just because we cant get info faster than C in our universe, does not NECESSARILY mean that would be true in other universes. does light and EM even exist in other universes ? i just dont think we can conclude that anything is the same, just because we experience such and such in our universe.

another thing about mathematics that my physics teacher used to tell me. math is supposed to explain what we have experienced, not the other way around. mathematicians seem to like to develop mathematics and then assume there must be some real-world connection somewhere. this is not always the case.
 
  • #4
marcus
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- i suspect that the totality of it all is stranger than we can even ponder about.

With due respect, IMO you must be speaking for yourself. You can't see into other people's minds and decide what they can or can not ponder about.

In the modern cosmology research that I follow---the line that seems to me to be making the most progress these days---there is no singularity (at the point where the singularity used to be in the old model).

In the new model, time keeps evolving back and a picture emerges of the universe prior to the beginning of expansion.

I think it would be great if we could stop using the word "singularity" as if it were something real, and not just a feature some particular theory. AFAIK there is no scientific reason to suppose that a "singularity" actually occurred in nature.
 
  • #5
Chronos
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I agree we live in a shy universe who clever conceals her many secrets. The mathematical part must, however, be consistent in a causal universe. While the 2D observers and 3D observers will have different coordinate systems, they will [assuming no errors] agree that both models are consistent when compared
 
  • #6
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... shy universe who clever conceals her many secrets...

:wink:

downright provocative of her
could be a bit of a tease
 
  • #7
hi marcus,

i stick with my statement. i dont need to be able to peer into someone else's mind to suspect that we can not understand a 4th spatial dimension, or that flatlanders can not understand volume.

i havent read the articles presented to me by hellfire, but i was thinking that he said that according to quantum cosmology, the singularity had quantum effects that were trying to be determined. at least to me, this seems to say that this theory treats the singularity as something. of course, that is not to say that the theory is correct.

i am merely trying to make sure i am understanding what both of you are saying.
 
  • #8
hi chronos,

i did some searches on the net for "causal universe", but could not find any that talked about it from a physics perspective. what that implies to me is that for every effect, there is a cause. is this what is meant by this term ? or are you referring to something else ?

i cant agree or disagree with your statement, only to say that i dont know. i suspect that it is the only thing that makes sense to us. whether it would actually be true or not, i cant say (about math in a 2 dimensional world.)

we cant really imagine a 2-dimensional object, any more than we can a 4-dimensional one. sure, we understand what width and length are. and we have mathematical constructs, called planes, which have no thickness.

but if that sort of 2-dimensional world actually exists, we could not see any sort of object, touch it, or anything else about it. it has absolute no thickness. we need all 3 dimensions to actually make sense out of a physical object.

everything we have come to know is part of our 3-dimensional universe. i just dont think it is safe to conclude with certainty that anything is the same in another universe.

if light exists in a 2-dimensional world, how so ? is it not a particle ? or would the 2-dimensional world see only facets of light, but not the whole thing ? and better yet, could that also be our situation ? could we only be seeing a facet of light, not its whole character ? much like when we see a shadow of a building, instead of its actual volume ?

what about time ? is that merely something that occurs because there is motion in the universe ? there is already a huge connection between speed and time. and that changes our perception of even the reality in which we live. so if there was no motion, therefore no speed, perhaps there would be no time.

i highly suspect that there are higher dimensions in what i refer to as the super-universe (all that is). and i also suspect that each of us is trapped within the universe in which we reside (assuming of course that there are other universes).

we probably also tend to assume that a 2-dimensional world contains x and y. what if it contains x and alpha, or beta and alpha, dimensions that we dont understand even in our 3-dimensional world ?

you guys all have better physics knowledge than i do at this point, so i surely cant debate that with you. i am lucky that i have found a forum that i can learn about what some of the most current thought patterns about phsyics are - from you guys.

but if i can impart only a little bit of wisdom - it would be to not be as sure as you seem to be. i can recall when i felt that way, so i certainly relate. but i see the continual evolution of what was once thought to be so, not to be so any longer.

i think we have deluded ourselves into thinking that we can discover a lot more than we actually can. LOL. but perhaps a little bit of arrogance is needed to keep us searching. after all, there is no way for us to know what we cant know, so we just continue to figure out what we can.
 
  • #9
marcus
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i havent read the articles presented to me by hellfire, but i was thinking that he said that according to quantum cosmology, the singularity had quantum effects that were trying to be determined. at least to me, this seems to say that this theory treats the singularity as something...

AFAIK the standard understanding in any kind of science is that singularities do not exist in nature.
a singularity is where a man-made THEORY breaks down and fails to compute or gives meaningless results.

I don't know what hellfire said that gave you the impression that a singularity is a real "something". Sometimes people talk like that when trying to communicate to a lay person. In any case I'm afraid i don't have time to go back and track down what people said and get the verbal semantic stuff sorted out

So I have to withdraw and let you sort it out yourself, or with chronos and hellfire. You can ask someone directly "is a singularity a real something that exists in nature independently of flaws in theory?" and see what they say. Maybe they'll say yes!:smile:
 
  • #10
hi marcus,

that is a bit of a catch-22 question. most of us think of nature as being part of this universe. or according to the big bang theory, that from which this universe arose.

in the past, i have read where the "singularity" is considered as part of this universe, and also as not. however, in either case, i dont believe we can ever answer the question "do singularities exist as a real thing ?" because to do so, would require us to jump out of the black box (our universe) that we are in, and somehow make observations about the super-universe. imo, an impossibility for us in this universe.

lets assume that the singularity is not a real thing. does that conflict with the big bang theory ? all the mass of this universe was supposed to be just a dot, and then exploded, for some reason. this mass, matter, stuff, or whatever you want to call it, existed.

did it not exist in the singularity ?

we have matter and energy in this universe, today. from where did it come from, then ? i guess this is the question. if it came from the singularity, then you would be hard-pressed to explain that the singularity was not something.
 
  • #11
after reading this article, i would assert that the author would have to describe the singularity as a "real something".
 
  • #12
hellfire
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I don't know what hellfire said that gave you the impression that a singularity is a real "something".
I used the term singularity to mean a point or a state in which the classical notion of space-time breaks down. In this sense a singularity is something real that exists. You probably use the term singularity to generically mean some kind of infinite value for a truly dynamical variable.
 
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  • #13
marcus
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most people including scientists use the word inconsistently
which causes ambiguity

a major theme in quantum cosmology is to remove singularities singularities

singularities exist in the former theory

(i.e. points where the older theory breaks down)

when one cures the singularity one does not remove the point from spacetime,
one does not do anything at all to Nature or physical reality

one cures the singularity by modifying the theory

============

one can, in a loose way of speaking, refer to the PLACE in some coordinate system where the difficulty with the old theory happened

and one can call that PLACE the "singularity"

where the place is will depend on the system of coordinates and the geometrical model they are used in and will be subject to a fair amount of ambiguity as well

but people do talk like that, informally, which is fine (but it can confuse a lay audience)
 
  • #14
i just see in my last post, that i forgot to put in the url of the article that i had just read. i cant find it any more.

well marcus, i am confused. LOL.

to be or not to be - that is the singularity question of the day. LOL.

i dont know how it can be nothing, if at the same time we claim in contains something.
 
  • #15
marcus
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i dont know how it can be nothing, if at the same time we claim in contains something.


nobody claims that AFAIK
but you basically are stuck with the language that you use
(I can't reform you :-) you just have to keep on using words the way youve learned them)

If you want to, listen and watch the videos of a recent conference at SantaBarbara

"The quantum nature of spacetime singularities"

there it is said clearly at the outset by the MC Gary Horowitz what the usual understanding is
IF A THEORETICAL MODEL OF THE WORLD EXHIBITS SINGULARITIES THAT IS A SIGN THERE IS SOMETHING WRONG WITH THE THEORY.

the name of the game is how to fix the theory or replace it by an improved theory so the singularities (blow-ups, glitches) no longer occur.

==============

also Einstein made this point long long ago----owing to general covariance the POINTS in the spacetime continuum have no objective reality

all that one can attribute reality to are events

there is no THERE in spacetime, in the prevailing way (Gen Rel) we have modeled it since 1915

so there is no objective reality to the spacetime point or points where the classical theory had a blow-up

and the classical theory, we know, is wrong

(it works fine in more normal situations but it gives no realistic picture of what happens to spacetime in certain extreme situations-----it has a limited applicability)

Nice Einstein quote about general covariance
“Dadurch verlieren Zeit & Raum. den letzter Rest von physikalischer Realität. ..."

“Thereby time and space lose the last vestige of physical reality”.

mere points in spacetime do not have physical existence, space is more like the relations between real events

many possible sources of quote including Rovelli's book Quantum Gravity but for an online source see page 43 of
www.tc.umn.edu/~janss011/pdf%20files/Besso-memo.pdf[/URL]

117 In the introduction of the paper on the perihelion motion presented on 18 November 1915, Einstein
wrote about the assumption of general covariance “by which time and space are robbed of the last
trace of objective reality” (“durch welche Zeit und Raum der letzten Spur objektiver Realität beraubt
werden,” Einstein 1915b, 831). In a letter to Schlick, he again wrote about general covariance that
“[t]hereby time and space lose the last vestige of physical reality” (“Dadurch verlieren Zeit & Raum
den letzter Rest von physikalischer Realität.” Einstein to Moritz Schlick, 14 December 1915 [CPAE 8,
Doc. 165]).
 
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  • #16
well, you are telling me that it is not a real thing. hellfire is telling me that the field of quantum cosmology is about trying to understand what the actual quantum effects of the singularity were - so as to make better guesses about it.

i am not sure what language you are referring to, but anyone using english is gonna come up with the same conclusion that i did. it is nonsense to be studying the quantum effects of nothing.

i dont think it takes a rocket scientist to figure that one out.

now that does not mean that your thought processes about the singularity are wrong - simply that they do not coincide with quantum cosmology.

as i have said before, i suspect that neither thought process has any chance of being proven, any more than my thought process of thinking that god exists, is true. the only difference as far as i can tell, is that i am willing to admit it. LOL.
 
  • #17
hellfire
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There is actually no confusion. The definition of singularity in general relativity is a very difficult one, but for our discussion you can assume that it is a infinite value for some invariant that can be computed from the curvature tensor. From this point of view, there exists a state at which general relativity breaks down. This state is scope of quantum gravity theories. It is assumed that in a more fundamental theory of quantum gravity there will be no infinites in dynamical variables that describe the gravitational field. From this point of view this "infinite" will be removed and the infinite does not exist. marcus follows quantum gravity very closely, so he will know better than me the most used definition for singularity.
 
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  • #18
marcus
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Hi hellfire, thanks for clarifying and moderating (which as guru you do very well!)

There is a kind of simple rough and ready way to put the issue in a way that may suit P-L needs. this is really for him:

In science you can have two or more models that fit the data (observed so far) equally well. then you need more observations to distinguish
and you don't have rational grounds to prefer one over the other until you get more decisive observations (of find a logical inconsistency).

right now we have at least two consistent models in cosmology that fit all the observations equally well---both models allow you to extrapolate backwards into the past

A. in one model, based on vintage 1915 einstein, when you run it backwards in the past, it breaks down at a time about 14 billion years ago.
blows up and fails to work any further (you can say that in the classic einstein model "time stops" cause you cant run it any further back into the past)

B. in several other models, in particular Ashtekar's 2006 "new dynamics" model, that problem has been cured and the model keeps on running back in time past the 14 billion year mark.

Both models are equally good at matching all sky observations made by people so far, because the Ashtekar model REDUCES to the old einstein a few instants after the start of expansion and gives the same numbers, as close as can be measured so far.

Martin Bojowald should be given credit because he constructed the first model of this type in 2001 and Ashtekar's is an improvement on that.

The conclusion, I would say to P-L, is that there is at present no scientific reason to assume that time-evolution breaks off as you go back in time. Since both models fit the data, one can't rationally prefer one over the other.

So I don't assume that "time stops" as you go back to around 14 billion years ago, or that "time began" at some moment. That would be assuming more than we know.

But a lot of lay people have a bad mental HABIT of assuming a beginning of time AS IF it was justified on scientific grounds. I object to this, and I attribute it to the influence of obsolete cosmology popularizations written back in the 1980s and 1990s. Not too long ago, a decade or so, the scientists themselves had a mental habit of assuming a beginning of time and they would write these bestsellers popularizing a simplified version of then-current (now out-moded) cosmology. And it seems to have really sunk in. So we have our work cut out for us, to torpedo that unjustified assumption.
 
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  • #19
marcus
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in case anyone is curious, here is a basic paper:
http://arxiv.org/abs/gr-qc/0607039
Quantum Nature of the Big Bang: Improved dynamics
Abhay Ashtekar, Tomasz Pawlowski, Parampreet Singh
Revised version to appear in Physical Review D
Phys.Rev. D74 (2006) 084003

"An improved Hamiltonian constraint operator is introduced in loop quantum cosmology. Quantum dynamics of the spatially flat, isotropic model with a massless scalar field is then studied in detail using analytical and numerical methods. The scalar field continues to serve as 'emergent time', the big bang is again replaced by a quantum bounce, and quantum evolution remains deterministic across the deep Planck regime. However, while with the Hamiltonian constraint used so far in loop quantum cosmology the quantum bounce can occur even at low matter densities, with the new Hamiltonian constraint it occurs only at a Planck-scale density. Thus, the new quantum dynamics retains the attractive features of current evolutions in loop quantum cosmology but, at the same time, cures their main weakness."

Just a reminder: You don't have to BELIEVE either Einstein 1915 Gen Rel, or Ashtekar 2006 "new dynamics" quantum cosmology. So far, both fit the data. It will take more work deriving and testing predictions, to see which is the better fit. In the mean time I'd say best reserve judgment.
 
  • #20
hi marcus and hellfire,

i didnt want to read 40 pages of really technical stuff. i had never heard of anyone thinking that time didnt start at the big bang. from everything that i had read, energy, matter, time and everything else in our universe was created by the big bang and that which followed. but that is just a theory to explain our own universe. it certainly does not explain what or if something existed or occurred before the creation of our universe.

both of you guys have implied though, that scientists are trying to go back before the big bang. hellfire, with quantum cosmology, and marcus, with his previous post.

i say good luck. as i said before, i dont think scientists have any better chance of doing that than they do of proving that god exists. that is not to say i want it so. i would love to know if god exists, and what exists outside of this universe. but wanting to know, and being able to know - arent the same thing. LOL.

i have no idea what time is. i dont think anyone else does, either. so from my perspective, i dont know if time, matter, energy, space, etc. are local to this universe, or whether they exist in some fashion in the super-universe.

we cant think in 4-dimensions. we dont know what the 4th spatial dimension is. but we can at least have musings about 2 dimensions. so i will go there, again.

if a 2-dimensional world exists, nothing in our universe can be the same as it would appear to flatlanders. because everything here has length, width, and depth. so if what we refer to as matter is present in some form in FLATLAND, then said flatlanders would only be able to see a part of its true dimension. for sake of argument here, i am calling our perspective its true dimension - although of course we dont know that.

so again, i posit - could this also be the same for us ? what we describe as light, time, matter, energy, etc. - are we only "seeing" 3 dimensions of things that have a higher order dimension, if their true reality could be known ?

i dont know that time is real. but i am pretty sure that energy, matter, and space are real. i think there is at least a chance that time exists only because motion exists. one can find quite a few articles on the net about it. it certainly can not be discounted. we just simply dont know enough.
 
  • #21
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singularity

I think it would be great if we could stop using the word "singularity" as if it were something real, and not just a feature some particular theory. AFAIK there is no scientific reason to suppose that a "singularity" actually occurred in nature.

Very glad with your proposal which IMO is an attempt to bring physics back to reality.

kind regards
hurk4
 
  • #22
marcus
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Thanks hurk4, I appreciate the moral support!
I want to emphasize in blue something I said in an earlier post. There is no scientific reason to suppose time stops at 14 billion years, going back. If you assume that, then you are moving into the realms of prejudice and superstition.

in case anyone is curious, here is a basic paper:
http://arxiv.org/abs/gr-qc/0607039
Quantum Nature of the Big Bang: Improved dynamics
Abhay Ashtekar, Tomasz Pawlowski, Parampreet Singh
Revised version to appear in Physical Review D
Phys.Rev. D74 (2006) 084003

"An improved Hamiltonian constraint operator is introduced in loop quantum cosmology. Quantum dynamics of the spatially flat, isotropic model with a massless scalar field is then studied in detail using analytical and numerical methods. The scalar field continues to serve as 'emergent time', the big bang is again replaced by a quantum bounce, and quantum evolution remains deterministic across the deep Planck regime. However, while with the Hamiltonian constraint used so far in loop quantum cosmology the quantum bounce can occur even at low matter densities, with the new Hamiltonian constraint it occurs only at a Planck-scale density. Thus, the new quantum dynamics retains the attractive features of current evolutions in loop quantum cosmology but, at the same time, cures their main weakness."

Just a reminder: You don't have to BELIEVE either Einstein 1915 Gen Rel, or Ashtekar 2006 "new dynamics" quantum cosmology. So far, both fit the data. It will take more work deriving and testing predictions, to see which is the better fit. In the mean time I'd say best reserve judgment.

P-L seems to be protecting himself from reason by complaining that this paper is too technical. You can always look at the non-technical introduction and conclusion parts, and skip the math.

But here is a less technical paper, in case anyone finds that one too hard to follow. This has some math parts too, but you can skip them and still get the gist.

http://arxiv.org/abs/physics/0605078
The Issue of the Beginning in Quantum Gravity
Abhay Ashtekar
15 pages, 2 figures. History and Philosophy of Physics. Based on an invited talk at the 7th International Conference on the History of General Relativity (HGR7), "Einstein and the Changing World View of Physics, 1905-2005", held at Tenerife, Canary Islands in 2005

"The goal of this report is to provide an up to date account of results on the quantum nature of the big bang, obtained in loop quantum cosmology. They suggest a radical modification of the paradigm provided by general relativity for the issue of the Beginning. The article is addressed primarily to historians and philosophers of science."

This article is aimed not at other quantum gravity experts, but at an audience of historians and philosophy people.
 
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  • #23
protecting myself from reason ? where did you come up with that one ? i have given you very simple examples, with solid reasoning behind them. you have failed to even acknowledge them. i will read the 15 pages. i have read the first one. the other article i did read the intro, which is what told me that i was never gonna finish 42 pages of what would even become much more technical.

but if the future is anything like the past, marcus the 10th will be explaining to PL the 10th how physics theory number 1052 is correct, and how general relativity, quantum loop cosmology, and classical physics were all wrong, although they were good attempts.

PL the 10th will still be positing questions like "are the realities of our universe merely just 3-dimensions of a higher order of things ?". to which marcus the 10th will ignore and tell PL the 10th that he wants to avoid reason, because he does not necessarily subscribe to physics theory number 1052.

if one ignores the mistakes of history, one is apt to repeat them.
 
  • #24
hi marcus,

well, i made it thru the first 3 pages. it may not have calculus equations, but it is still a highly technical piece of writing. i am comparing that to the thousands of articles on the net that talk about the big bang theory. one can be an average joe, and still understand them. with this current article, i am skipping over some stuff, because it would take forever and a day if i examined each sentence to make sure i knew exactly what was meant.

there are probably some of your forums where being a physics or math graduate are necessary. i dont recall anything about differential equations, except i got an A in it about 30 years ago. which is also about the last time i saw one. LOL.

i was hoping that at least many of these forums were not geared toward actually being a physicist, etc. questions about cosmology and such are topics that people from lots of professions are interested in. however, we like shows like discovery and such, that still bring over the ideas, without all the technical PERBATIVE mumbo-jumbo.

i was close to a 4.0 student, so i am no dummy. i have just been away from all that technical stuff for what seems like a lifetime ago, now. but if an article seems technical to me, you can be sure that it is gonna be that way to the masses of people who are still interested.

where we came from, why we are here, what is the universe, how does the universe work, etc. are not just topics of interest to physicists, but to just about everyone who has ever looked up at the stars.
 
  • #25
hi marcus,

it got more and more technical. became disinterested.

here is an article about the big bang, written in everyday english.

http://www.big-bang-theory.com/

i am sure that you dont believe in everything that it says about singularities. but my point of showing you the article is that this is the type of article i want to read about, with regard to complexity, about quantum cosmology or any other physics topic. i want to get the gist of what they are talking about without getting into all of the complex details.

hellfire gives me basic info. a singularity, at this point, seems to have infinite values with regards to density, which basically means we dont know what it is ? physicists are attempting to acquire theories such that they can explain the infinity away, and get a better understanding of what it is, or if they exist at all ? is this it, in a nutshell ?
 
  • #26
marcus
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a singularity, at this point, seems to have infinite values with regards to density,..

the bigbang singularity exists in a certain theory and, as you say, it is a point where this particular theory's model predicts infinite density.

on the other hand, if you work with Ashtekar's QG model there is no point where the density is infinite.

the lesson to learn is that a singularity is a manmade thing. It exists in a manmade theory, not in nature. And it represents a failure of that particular manmade theory that you are talking about.

The singularity may not exist in other manmade theories. Whatever it is, it is theory-dependent. It does not have a real physical existence.
==============

Another way to describe what a singularity is, is that it is a point in a certain model (the model that has the singularity) where TIME (the time of that particular model) STOPS

that is just a nice way of saying that the model breaks down :smile:
"time stops" means that particular model is giving meaningless answers like infinite density and so that particular model just quits.

Again, you see that the idea of a singularity is model-dependent.

In another model, time MIGHT NOT stop---the model might keep chugging along.

So again you see that a singularity is not something that has physical existence. It does not exist in nature, but rather is a feature of what model you happen to use.

I'm glad you have provided an opportunity to emphasize these points. I hope you are learning, but even if you personally are not yet ready to learn it is still useful to have an occasion to make these points emphatically and clearly, so thanks.
 
  • #27
Chronos
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I've never known a physicist who thought 'singularities' were anything more than mathematical artifacts - the 'ultra-violet catastrophe' problem in classical physics is a good analogy.
 
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  • #28
okay, i buy that. (in regards to singularities being an artifact that exists because the theory breaks down). pretty hard to imagine infinite anything, since by its very definition, something can not be infinitely anything.

what do you think about the following link ? i am guessing you would say that there is some mis-information in it ?

http://www.physlink.com/Education/AskExperts/ae649.cfm
 
  • #29
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  • #30
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limits observing the 4th dimension

Hello to all,

Having read Flatland a long time ago, I have recently developed a belief that there may be problems in percieving the higher dimensions.

Physics-Learner said "I suspect that we can't learn anything at all about a 4th dimension." I believe we can learn somethings about the 4th dimension, but not all there is to "know".

In Flatland a 3D sphere passes thru a 2D plane. The flatlanders first observe a point, then a circle that increases to the diameter of the sphere, then the circle decreases back down to a point before disappearing. If the 3D object is regular in shape, then eventually the flatlander may infer the shape (providing he observes the complete passing).If the 3D shape is irregular and the time the flatlander has to observe it is limited, then it becomes impossible to infer the true shape.

In trying to understand the 4th dimension, I find that in General Relativity, time is considered a dimension while in quantum physics time is defined as a measure of change. Can we completely reconcile these two different perceptions of time?

Here are the limits I think need to be addressed (they may or may not be related to the 4th dimension, with incomplete knowledge who can tell for sure).

1) In Relativity space-time is considered a priori, (undefineable). We are limited to observations within our space-time continuim.Is there more?

2) The speed of light limits us to direct observation within our local observable universe (we may infer some aspects beyond this).

3) The uncertainty principle. I believe being uncertain is a limit unto itself.

4) Blackholes, dark matter, and dark energy. We are limited in our ability to observe these by their very nature.

Are these limits related? Could it be the missing knowledge is due to our inability to percieve a higher dimension? I've read about a hypothesis called the singular singularity where all singularities are believed to be connected. Can this occur in another unobservable aspect of time? Who knows?

I don't claim to have any answers, only questions as I'm not schooled in the higher levels of math, but like Physics-Learner I wonder if there could be anything to this line of thinking. Any enlightenment will be greatly appreciated.
 
  • #31
hi wil,

interesting post. my thought process was along the lines of the 2-dimensional spherical surface travelling thru the third dimension of volume, as the sphere expanded. said flatlander would seem to make many of the same conclusions about his universe, as we seem to be making about our universe.

so we would never have a 3-dimensional object travelling thru a 2 dimensional surface area.

but i would question one thing. from our perspective, your geometry is correct, in terms of planes, points, etc. but i am not sure we could make those same conclusions about a real physical object. while we understand width and length, we can at least have some sort of musings about FLATLAND.

but i am not sure that we can actually conclude that this is what flatlanders would observe. we really cant understand a world without depth. so from our perspective, it seems as if it would form a dot, and then a circle, if it was a sphere - but i would hesitate in saying that the flatlander would conclude this. all of our ideas and understanding involve all 3 dimensions. we really can not conceive of an object with truly 2 dimensions. it is a non-sequitor in our world.

i highly suspect that the whole super-universe (everything that is) is so far beyond us, that we arent even amoebas yet - and information about it is beyond our reach.

some of the more technical types here are talking about being able to find out what occurred before the big bang. they could have theories that sound pretty good at some point in time - but how do we test them for absolute certainty ? are we able to jump out of our universe to make actual tests ? and how do we jump back in time before the existence of our universe to see what was there ? i dont believe we can ever know about what is outside of this universe.

but in using logic and the physics of this universe, i believe it can be demonstrated that something outside of this universe was responsible for its creation. i just dont believe we will ever have access to it, while in this universe.
 
  • #32
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Physics-learner,

First of all, you can't have a 2D observer on the surface of a sphere. Or a 1D observer. As soon as you consider the curve you introduce a 3rd dimension. Your observer is restricted to a point (zero dimensions).This analogy fails to represent anything except the expansion of the universe and it doesn't do a very good job of that. To avoid the center of the universe question, I suggest the loaf of raisinbread expanding as it cooks, where the raisins represent the galaxies. This too is inadequate in that it is a 3D analogy representing a 4D expansion.

I find it hard to believe you are willing to accept the 2D sphere analogy but reject the conclusions made using euclidean geometry.The flatlander is a 2D observer, and is observing the 2D aspects of a 3D object, that are available to it. As a 3D observer do you have problems observing 3D objects. As 3D observers we we can observe some aspects of the 4th dimension (gravity is a prime example). I believe time dialation is another. To observe the entire 4th dimension, I believe is impossible.

One more thing. I see no need for a super-universe since "universe" already represents "everything that is". As does cosmos, if you prefer. Some people equate "universe" with the local observable area of the universe, this I believe is wrong. To equate universe and our space-time continuim is more correct, as this is all we can hope to observe and understand. I however distinguish between the two in that I see no reason there would not be more beyond our space-time continuim.

There can't be anything outside of the universe because just by "being" it would be considered as part of the universe. If you can use logic and physics to demonstrate that something external to our space-time continuim was responsible for its creation, then please do.

Physics Learner,

I must apologize. After reconsidering the sphere, I will accept a line segment that curves with the sphere as a 2D object and therefore accept your analogy as valid and a closer representation of our difficulty in observing a higher dimension. I hope you see the validity of the one I took from flatland. I think we agree it is not possible to fully percieve time.

Sincerely trying to understand,

Wilgory
 
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  • #33
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Hi Kittani,

I'm not a cosmologist, this is just my understanding.

Singularities are predicted when a theory's math breaks down (goes to infinity). In addition to the one at the begining of the universe, they are also predicted to exist in the center of black holes. Whether they exist or not, they can't be observed or validated. So to speculate about their exact construction is fruitless.

As far as I know, the Cosmic Background Radiation (CBR) is everywhere, so to use it to find "the center of the universe" is impossible.

Space and time, as we know it, was created with the "big bang" and like the CBR there is no center. The expansion of the universe is not like that of an explosion. It is more like the way a loaf of raisinbread expands as it cooks. The raisins being the galaxies. We are on a raisin looking out. All other raisins are seen moving away from us. An observer on a distant raisin sees the same movement.

The speed of light limits us to observing our area of the universe (local observable area). There is likely to be very much more that we will never observe.
 
  • #34
hi wil,

when i first read your reply, i wasnt sure what to say, because i sensed a defensiveness that i was not sure why.

i will come back and reply to many of your points, as i think it makes for good discussion. but for the time being, i wanted to make one thing clear.

i did not reject what you said. nor have i rejected what marcus, hellfire, and chronos have said. to reject something means to say that it is provably wrong. for example, i reject the concept that 2+2 = 5.

what i am telling you is the same thing that i have told marcus, hellfire, and chronos. we are making assumptions about things with a much higher degree of correctness than we should be.

it took over a century before anyone questioned newton. is his definition of gravity incorrect ? most scientists today would say so. another century from now, i suspect that scientists will be saying the same thing about relativity theories.

in our specific example, i did not reject your euclidean example in 2 dimensions. i even said that to us 3-dimensional beings, it seems like it would be true. however that does not mean THAT IT IS TRUE.

none of us can imagine a 2-dimensional object any more than we can imagine a 4-dimensional object. what you said seems entirely likely, given the way our brains can think. but i suspect that our brains are very limited, if we compare it to the totality of it all.
 
  • #35
marcus
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what i am telling you is the same thing that i have told marcus, hellfire, and chronos. we are making assumptions about things with a much higher degree of correctness than we should be.

...

I think you must SPEAK FOR YOURSELF, Phyz. You don't know what assumptions I make. You don't know enough about me to give me useful advice about what I "should be" doing or "should not be"

You don't give evidence of
1. having moral authority
2. understanding the skeptical attitude towards theory that is common among astronomers and I gather many other scientific communities.

So when you say "we" are making assumptions all you can really talk about is what you assume, or believe.

I follow the field of cosmology----that means I study various competing models and I am really interested in seeing those models TESTED. I would like to see some shot down and others pass. And when a model passes a test, I don't go and believe it (like a layperson might). It has passed this test and it might fail the next. At any one time we do the best we can, doubting everything (to greater or lesser extent) and ultimately believing nothing.

General Relativity is pretty darn near perfect:!!) but even GR has places where it breaks down! Provisionally you could say I believe it, but only up to a point:smile: So basically I believe nothing totally, not even GR, and I think that is not unusual for working cosmologists (which I'm not, I'm merely an onlooker who follows the field.)

Periodically we get religious-motivated people coming here exhibiting a kind of naive arrogance not unlike yours when you caution people not to believe science because "we" are incapable of understanding the universe.

I know my mental limitations, you know yours. Please don't try to define what "we" can or cannot understand. whether it is 3 or 4 dimensions or whatnot---you've been talking about a lot of things that "we" supposedly cannot understand. Please just speak for yourself.

And don't worry about my or anyone else here being too credulous. Just worry about your own credulity and let other people be in charge of theirs.

It is possible that you are pointing out a mote in someone else's eye whilst you have a beam in your own. i.e. that you are warning folks not to swallow mainstream science because it might contain baloney, and all the while you are consuming a truckload of baloney from other sources.

I say possible:smile: because I don't know how much you actually believe of what is on the webpages you give links to.
 

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