Does a finite universe make sense to you?

[DaveC426913]

I compare the Big Bang event to someone chewing bubblegum and then blowing a big bubble that expands forever. The "Bang part" itself happened at the person's lips and as he blew the bubble this became our ever expanding "3-D space".

The trouble with this analogy is that in the universe, there is no "at the person's lips". Your analogy suggests that there is a part of the bubble that could be identified as the origin, and this is not true in the BB.

Think of an analogy more like a sealed ball that has no spigot/nipple/whatever you want to call it - say, a beach ball. The sun heats the air inside the ball and that is what causes the expansion. The advantrage of this analogy is that the expansion occurs without having a single spot where it's expanding form.

 

[marcus]

very true.

it is of course still an analogy.

some people like the raisin / bread analogy better, but i don't like it as much as the balloon because it implies a finite distance to the crust/edge of the bread/universe unless you assume the bread is infinite.

the balloon allows a seemingly infinite universe containing a finite amount of matter/energy.

...and all it requires is an additional dimension.

:)

I'm with you on this. the raisinbread analogy doesn't contain the idea of curvature and how something can be finite volume without having any edge. it is more just a local image of expanding distances. you have to assume the dough is infinite.

the balloon analogy is more useful (even though space is only 2D in that analogy).

the additional dimension is not known by the 2D creatures to exist so it can be considered purely formal mathematical. the radius of the balloon is what is called the radius of curvature.

in our case we don't know it exists in some higher dim. surrounding, but we can calculate its length in various cases and estimate it based on CMB data and galaxy redshift survey data (numbers of galaxies counted at various distances)-----ways that have been devised to measure curvature, essentially like experimentally measuring the interior angles of large triangles.
==================

if the radius of curvature is R, then simple high school or college geometry can estimate the volume of 3D space to be 2 pi² R³
this is just the volume of a 3D sphere of radius R (pictured in 4D)
=================

I see some people in this thread are now getting hung up on asking how the balloon begins to expand!
that is not covered in classical (nonquantum) cosmology. It is the business of quantum cosmology to explore that and model it. That field has really taken off in the past 2 or 3 years. I don't know of any up-to-date popularization, but you can get a rough idea by skimming the abstracts in a keyword search of the technical literature using keywords "quantum cosmology". This is using the Stanford database:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=DK+quantum+cosmology+and+date+%3E+2005&FORMAT=WWW&SEQUENCE=citecount%28d%29

You can change the information in the search box and look at a longer timeframe like "date > 2001" or change the keywords and so on.
What I put in was "date > 2005" and asked for the papers to be sorted by how often they have been cited in other research, so the first ten or twenty that come up are probably the most important and representative of where the field is currently going.

this is the field of research grappling with the problem of modeling time and conditions right around the big bang or beginning of expansion

to me it seems inefficient to try to speculate on one's own about this before finding out what the relevant mainstream research community in that field is working on---but that seems to be what many of us (including in this thread) typically do

I suggest you sample it, Junglist, no need to delve unless you want, just read a few of the abstracts (the summaries) and get some impression---ask some questions here if something doesn't make sense. that is, if you are curious about current models of the big bang. Not to necessarily believe, but to sample what the professional mainstream is working on.

 

[BoomBoom]

the additional dimension is not known by the 2D creatures to exist so it can be considered purely formal mathematical. the radius of the balloon is what is called the radius of curvature.

I understand this analogy and the 2D people would understand that if they were to go in a straight line they would eventually come back around to where they started. But what if, since they knew what this curvature was, they decided to head out on a trajectory that countered the curvature so that it really was a straight line? I guess this would be a tangent line to the sphere?

Taking that analogy to our 3D universe and taking the same strategy, where would that take us?

 

[marcus]

... But what if, since they knew what this curvature was, they decided to head out on a trajectory...

you aren't empathizing with the too-dees (the 2D creatures). need to carefully put yourself in their shoes.

all trajectories lie in the 2D surface
all directions they can point in are in the 2D surface
any way you point, that direction extends in a geodesic (like a great circle on Earth surface) that stays in their world

they have no indication that any higher dimension surround exists, and it may not. We did not assume that they live in a 2D that is surrounded by an actual 3D. It might not be.

curvature is an intrinsic property that depends on internally measured distance and angle measurements. A surface can be curved without living in a higher dim surround. Riemann and Gauss realized this in 1850. You've got to realize it too, Boomboom.

Try to imagine yourself as a Toodee. No directions take you out of your world. Moving around and measuring let's you determine curvature by certain vintage 1850 formulas. Yet this does not prove that a higher dim exists. You might get it by thinking along these lines, Boomboom

 

[yuiop]

I understand this analogy and the 2D people would understand that if they were to go in a straight line they would eventually come back around to where they started...

On a slightly different tangent .. what if the ants left a trail ..then eventually if they continue in a straight line they could come across their original trail and begin to suspect their universe is not infinite.

Now extend this idea to the ants being on an expanding balloon. If the balloon radius expanded at the speed of light and if the ants moved in a great circle (their idea of a straight line) would they get back to their marked starting point in a finite time even if they moved around the circumferance at the speed of light (maybe they send a light beam around and see if it returns). Anyone care to work that one out, taking the spiral path into account?

 

[DaveC426913]

If the balloon radius expanded at the speed of light

The circumference of their spherical universe will increase at 2*pi*r per unit time. Since they are traveling at no faster than r per unit time, then no, they will never arrive back at their starting point.

 

[yuiop]

The circumference of their spherical universe will increase at 2*pi*r per unit time. Since they are traveling at no faster than r per unit time, then no, they will never arrive back at their starting point.

Thanks :) Obvious when you put it that way. I had a hunch it was true when I posed the question. So, in a way the finite (but expanding) surface of the balloon would be an infinite surface to the ants, because neither the ants nor any signals they send, can go round the balloon in a finite time. :)

 

[MiltMeyers]

BoomBoom Does this make sense. If we were living on the surface of a 2d world, the ballon. The balloon would be a finite world but now let's start out with a singularity of a balloon and the balloon inflates and keeps getting bigger. The galaxys are scattered about on the surface now if light left a galaxy and while it was in in flight the 2d universe exspanded. Now since the light came from inside the 2d world it came from a new dimension a 3d direction and would look straight but in fact it is bent in the 3d. Now change the balloon to what we live in what looks like a 3d world but in truth it is really 4d. Space is curved in 4d. Light is coming from a 4d direction and we see it as straight when in fact it is curved. Think this as we see further back in time the smaller the universe is so the space is curved to fit the now of space into the smaller now of time past. Now does that answer what I think to me is the effect of moving to 4d space time with the balloon analogy? I hope I have it figured out as to me it is simple but if you point out were I'm wrong I'll explode and keep my mouth shut. Bubble gum or bowling balls, hmmmmm, interesting ideas.

 

[DaveC426913]

Now since the light came from inside the 2d world it came from a new dimension a 3d direction and would look straight but in fact it is bent in the 3d.

Light does not come from inside the 2D world; it comes from any point on the surface of the 2D world. Light - like everything else - is constrained to the surface. Light beams follow world lines around the 2D world. When the Twodees measure anything in their world, their measurement tools (including the best ones - lasers) will follow the surface.

Now change the balloon to what we live in what looks like a 3d world but in truth it is really 4d. Space is curved in 4d. Light is coming from a 4d direction and we see it as straight when in fact it is curved.

Light is coming from any point in our 3D world and follows lines that we measure as straight, even if, when measured in 4space, those lines can be seen to curve.

 

[BoomBoom]

Try to imagine yourself as a Toodee. No directions take you out of your world. Moving around and measuring let's you determine curvature by certain vintage 1850 formulas. Yet this does not prove that a higher dim exists. You might get it by thinking along these lines, Boomboom

Yes, I believe I do get it... thank you Marcus.

Apologies for any frustration that trying to describe this may have caused...cheers! :)

 

[MiltMeyers]

Dave The beam of light followed the surface of the balloon but when it arrived it came from a point that is now inside the balloon. Now this curve is in the 3rd dimension. Scaling that up to our 4d world the light beam would have come from a point in a smaller universe. In fact all light beams would come from points in a smaller universe and that is in any direction we look. That is why we can only go to a smaller and smaller universe till we are back to the time just after the start were the universe is really small. That is our 4d universe. Finite and holding every bit of junk ever condensed out of the big bang. Our lives and posts and fights with that significant other.

Now let's look at what we see when we look out into space. We see star light coming to our eye in a straight line and it is red shifted and also is is from a smaller universe. That means it followed a curve in space. ie; a 3D straight line that is curved in the 4D time and space. Now does it make sense that there is no outside to the universe and no time or space before zero time and space? Due to relativity there is no now all over and what we see is what we get.

 

[DaveC426913]

Dave The beam of light followed the surface of the balloon but when it arrived it came from a point that is now inside the balloon. Now this curve is in the 3rd dimension. Scaling that up to our 4d world the light beam would have come from a point in a smaller universe. In fact all light beams would come from points in a smaller universe and that is in any direction we look. That is why we can only go to a smaller and smaller universe till we are back to the time just after the start were the universe is really small. That is our 4d universe. Finite and holding every bit of junk ever condensed out of the big bang. Our lives and posts and fights with that significant other.

Now let's look at what we see when we look out into space. We see star light coming to our eye in a straight line and it is red shifted and also is is from a smaller universe. That means it followed a curve in space. ie; a 3D straight line that is curved in the 4D time and space. Now does it make sense that there is no outside to the universe and no time or space before zero time and space? Due to relativity there is no now all over and what we see is what we get.

OK, I see what you're getting at. We're talking about two different things. I'll drop it.

 

[BoomBoom]

I was getting a sense of dejavu, then realized we have covered this ground before, as in this thread: (which may help others still struggling with the concept)
https://www.physicsforums.com/showthread.php?t=178063"

Again, apologies for the density of my skull... :O

 

[marcus]

Again, apologies for the density of my skull... :O

we can't easily gauge skull thickness here, with different people operating on different amounts of sleep and competing job-demands etc.
what I do get from you is a sense of good will. fair-mindedness

about repeating. yes we do go over this periodically
I don't know if that is bad, though. Or if we should try to avoid it by citing earlier discussion threads. sometimes new people need a fresh discussion
and old people (who were new last time) jump in and give them a workout

and old olds like me can sit back much of the time and watch with interest
it probably does no great harm to repeat stuff now and then, with a different cast of characters

 

[MiltMeyers]

Dave sorry I missed your point. The question; Does a finite universe make sense to you? I would say yes it does. I'm new to the forum and tend to jump in and say what I think. I didn't do any research(past posts) into balloons as universe models and if I had I would have held my post. Finite now what about if the space time exspanse and pushes a galaxy beyond light speed? Is that possible? In other words is there a horizon of visible light and the universe only appears to be finite?

 

[sketchtrack]

A finite universe only makes sense to me if there is something out there other than the universe. Maybe multiple finite universes, but that idea clashes with one definition of universe which is describes as everything that exists.

 

[epkid08]

I would define our universe as anything that's bounded by our universal dimensions.

 

[NYSportsguy]

The trouble with this analogy is that in the universe, there is no "at the person's lips". Your analogy suggests that there is a part of the bubble that could be identified as the origin, and this is not true in the BB.

Think of an analogy more like a sealed ball that has no spigot/nipple/whatever you want to call it - say, a beach ball. The sun heats the air inside the ball and that is what causes the expansion. The advantage of this analogy is that the expansion occurs without having a single spot where it's expanding form.

DaveC426913 - Dave the big question that is confusing many people is where the the "Big Bang" and it's rapid expansion originate from. That is why I brought up the "bubble gum" analogy because if you see this link below and read how most cosmologists think the "bang" happened...it is similar to my "bubble gum" analogy up top.

http://www.astro.princeton.edu/~aes/AST105/Readings/misconceptionsBigBang.pdf

 

[NYSportsguy]

By the way - It should be noted that from the article in that link, that galaxies can recede away FASTER that the speed of light without violating and special relativity laws because the expansion of space itself is not the same as traveling through space ALREADY CREATED.

So for all we know, the universe is actually expanding at speeds faster than "c" already. If that's the case we will NEVER catch up to the outer "surface" of this ball even if we could move at "c".

 

[NYSportsguy]

Spelling Correction: without violating any special relativity laws*

 

[DaveC426913]

DaveC426913 - Dave the big question that is confusing many people is where the the "Big Bang" and it's rapid expansion originate from. That is why I brought up the "bubble gum" analogy because if you see this link below and read how most cosmologists think the "bang" happened...it is similar to my "bubble gum" analogy up top.

http://www.astro.princeton.edu/~aes/AST105/Readings/misconceptionsBigBang.pdf

And they've done a terrible disservice to their readers by taking a loose analogy and replicating it too literally. Their image should not have a spigot. And yours should not have a pair of lips. It defeats the lesson of the analogy.

 

[epkid08]

Just an added note, I've always thought that if one part of the universe is infinite, then many parts are infinite; On the contrary, if one part is not infinite, then infinity doesn't exist in the universe, and furthermore doesn't need to exist and be applied in nonsensical ways. Am I right in assuming this?

...But the thing that gets me is the fact that zero is shows up in math, and also in the universe; Its cousin infinity, shows up in math, why wouldn't it show up in the universe as well?

 

[marcus]

DaveC426913 - Dave the big question that is confusing many people is where the the "Big Bang" and it's rapid expansion originate from. That is why I brought up the "bubble gum" analogy because if you see this link below and read how most cosmologists think the "bang" happened...

http://www.astro.princeton.edu/~aes/AST105/Readings/misconceptionsBigBang.pdf

Great article! Lineweaver and Davis "Misconceptions..." article in the March 2005 SciAm, if I remember correctly. It has often been recommended here at the forum.

It explains a lot of mainstream cosmology without depending on mathematical language, hope everybody has read it. Worth reading carefully...

NYSports, I don't recall the Lineweaver article offering any idea about where the material and space and rapid expansion ORIGINATE from.
(that is quantum cosmology, the models are fairly new, Lineweaver and Davis are giving an account of CLASSICAL, non-quantum, cosmology which goes back almost to the start of expansion but then stops giving answers)

Classical (non-quantum) cosmology is based on standard vintage-1915 Einstein General Relativity, which breaks down right at the start of expansion. It simply does not say. It takes the beginning of expansion for granted and unfolds from there.

Quantum cosmology is a fairly new field, with no popular-written non-mathematical book. The field arose in an effort to study behavior right around the onset of expansion, and to develop models which would make testable predictions about what we can observe now (going beyond the predictions of the classical model.)

Here is the Amazon blurb about a new book collecting many experts writings about their different ways of modeling the start of the big bang. there are about 20 authors. the editor who collected and put the book together is R. Vaas. The book will be too technical and expensive to be useful to most of us but checking out the Amazon page will give you an idea of the existence of this as a new field of scientific research.

This forum thread gives more information than the Amazon page
https://www.physicsforums.com/showthread.php?t=216219
It includes the table of contents, and even links that enable one to see preprints of some of the contributed chapters by the various authors.

But the Amazon page gives the essentials in brief
https://www.amazon.com/dp/3540714227/?tag=pfamazon01-20

I see that the production schedule for the book has slipped. The publication date is now March 1, 2009. Academic book publication is notoriously slow---everybody wants to keep revising his own chapter to make it have the latest and greatest. every footnote has to checked etc etc. Anyway I hope they get it out by March 2009

The trouble with analogies, like your bubblegum, is that the experts themselves haven't settled on a preferred model (of the expansion-start) yet. So if there is no preferred mainstream model, then what is the analogy supposed to be an analogy OF?

 

[marcus]

So for all we know, the universe is actually expanding at speeds faster than "c" already. If that's the case we will NEVER catch up to the outer "surface" of this ball even if we could move at "c".

You recommended people read the Lineweaver and Davis SciAm article. It gives a pretty good treatment of classic mainstream cosmology. Have a careful look at the article you recommended.

I think you will see that in their picture there is no outer surface.
And distances have always been expanding faster than c. Since they expand by a certain percentage each year, you just have to take a distance that is long enough and it will be expanding faster than c.

For example, in earlier times distances were expanding one percent per year. So if you took a distance of 100 lightyears, it would expand by one lightyear in a year. But increasing by one lightyear in a year means increasing at the speed of light!

And if you took a distance of 200 lightyears, it would be increasing by 2 lightyears every year, so it would be increasing at TWICE the speed of light. This is routine stuff.

At present the percentage rate is much smaller. The percentage increase is only 1/140 of a percent every million years. But still, if you take long enough distances----the same thing applies but just for longer distances. We are getting light from stuff today that is receding from us at twice c. Lineweaver and Davis explain how the light manages to get here from rapidly receding stuff.

Important thing, though, is not to picture the expanding universe as a BALL of material expanding into a void. The standard picture does not have an outer surface. In the standard picture the universe is both the space and the material more or less uniformly distributed throughout it. There are nonstandard cosmology models, but in the standard version there is no surface and no surrounding void.

 

[sketchtrack]

Would mass expand with space? How can an expansion of space be postulated when space is nothingness.

 

[NYSportsguy]

Would mass expand with space? How can an expansion of space be postulated when space is nothingness.

Empty space (a.k.a. a Vacuum) is never totally void of "energy". It has zero point energy which gives it the "quantum jitters". The laws of thermodynamics and E = MC^2 say that anything with at least zero point energy (the least amount of energy above absolute zero) will have some minimal amount of mass as a result.

So, basically everywhere we see empty vacuum space, there is also energy and thus mass and thus a gravitational force present.

Hope this helps some.

MARCUS - I remember reading that part of the website where it said how light from the past still somehow reaches us even though it is traveling through the expanding space medium at rates faster than "c". You have to eventually day that if the very first light from the original big bang still has not reached us yet that it will be slower and slower and probably increasingly impossible for that light to ever reach us because as time increases the distance it has to travel and cover more ground increases exponentially.

At that rate, it will never reach us and will be similar to the effects that a black hole has on light.

 

[NYSportsguy]

SketchTrack - Mass isn't necessarily expanding, the is just more of it being created as spaces continues to expand because of the explanation I gave above.

 

[NYSportsguy]

Inclination and expansion are equal. This might be the next general relativity type of theory that needs to be formulated.

If so it would explain how light can never escape a black hole in the same way light cannot reach us as the universe recedes from us at accelerating velocities. I might probably b wrong here but perhaps this can put someone on the right track...who knows?

 

[marcus]

Would mass expand with space? How can an expansion of space be postulated when space is nothingness.

"expanding universe" is shorthand for the average regular expansion of large distances.

It isn't postulated. It is derived from solving equations, comes out of the math.

I don't ordinarily say expansion of space. I don't think of space as a material. So the phrase expansion of space can be misleading, if it makes you think of a material expanding. for me it is the sum total of all the distance relations between things, between events---the web of distances and angles and areas that make up geometry

If I sometimes said expansion of space, what I meant, or should have said, is the increase in distances.
(between, for example, two widely separated galaxies which are both stationary with respect to the microwave background.

the gradual percentage increase in distances is not POSTULATED it is an unavoidable consequence of the most accurate theory of gravity we have. Nobody has proposed a theory of gravity that predicts more accurately than the present theory. And the present gravity theory, applied to fit the data, tells you largescale distances increase according to a certain rule (the Hubble speed/distance formula) and it checks.

so it is not a postulate. it is an OUTCOME of using the most accurate theory of gravity that we have. (the theory that predicts the motions of objects and the bending of light most correctly)

have to accept the increase of distance at least until we get a better theory of gravity (which people have been trying to invent one for almost 100 years without success)

in any case it doesn't affect the distances within our own group of galaxies, they are too small to be affected by the rule-----only very largescale distance is involved.

 

[robheus]

Read How the Universe Got Its Spots by Janna Levin and then go read Ned Wright's Cosmology Tutorial website again. I swear to you that you will have a tough time believing the universe can be endless. It’s funny how that happens. Janna’s book is thin and easy. There’s no college math, no raisin bread and no balloons. Instead, it’s all the different possibilities and how to interpret the CMB and that kind of thing.

An endless universe has its issues. It needs an infinite mass at the time of the Big Bang. That means infinite galaxies and infinite worlds. So there must be one just like ours, in fact infinite worlds just like ours. Even so, I prefer an infinite universe too. But it’s nothing more than a preference.

Perhaps, but how do you conclude/proof that?

And in the case of a finite spatial universe, this would lead to finite time also because time would run in an endless loop.

So, that is basically the same.

 

[NYSportsguy]

Expansion of Space is another way of saying "creation of space". Something doesn't necessarily have to expand to be have more of it created. Space is "growing" at a rapid rate because it is being created so fast and thus expanding.

 

[NYSportsguy]

NYSports, I don't recall the Lineweaver article offering any idea about where the material and space and rapid expansion ORIGINATE from.
(that is quantum cosmology, the models are fairly new, Lineweaver and Davis are giving an account of CLASSICAL, non-quantum, cosmology which goes back almost to the start of expansion but then stops giving answers)

The trouble with analogies, like your bubblegum, is that the experts themselves haven't settled on a preferred model (of the expansion-start) yet. So if there is no preferred mainstream model, then what is the analogy supposed to be an analogy OF?

Good point. I however, from all the facts and figures I have read about, am going to say that my "bubble gum" theory is probably going to turn out to be more correct than some of the other answers I have been seeing for now. I also like the "eternal expansion" theory and the possibility of there being multi-verses as part of a Cosmic Landscape. To me these seem to make the most sense as of right now.

The article from Lineweaver and Davis state that "This ubiquity of the big bang holds no matter how big the universe is or even whether it is finite or infinite in size. Cosmologists
sometimes state that the universe used to be the size of a grapefruit, but what they mean is that the part of the universe we can now see—our observable universe—used to be the size of a grapefruit."

I do not find this theory to be plausible. The initial "Bang" had to originate from some sort of singularity or collision between other dimensional universes or branes of some kind to start ours.

 

[marcus]

...
The article from Lineweaver and Davis state that "This ubiquity of the big bang holds no matter how big the universe is or even whether it is finite or infinite in size. Cosmologists sometimes state that the universe used to be the size of a grapefruit, but what they mean is that the part of the universe we can now see—our observable universe—used to be the size of a grapefruit."

I do not find this theory to be plausible. The initial "Bang" had to originate from some sort of singularity or collision between other dimensional universes or branes of some kind to start ours.

Sounds like you have made up your mind already on some of these issues
But the first scholarly book on the subject Beyond the Big Bang isn't due to be published until March 1 of 2009. It will have chapters written by leading experts about the various ideas and it will include some you just mentioned.

You might be jumping the gun. This thing is just beginning to get the focus of scientific attention it deserves and studying conditions around the big bang (by whatever means can be devised) is going to be high on the scientific agenda for the next 10 years or so for sure.
Might be good to withhold judgment for a while longer. Hear what the various ideas are, and what various other people say.

 

[marcus]

Expansion of Space is another way of saying "creation of space"...

Doesn't make sense to me. Space is not a substance or material that needs to be produced. The words you use make it sound like a material.
I try to avoid using the words "expansion of space". Distances increase, that's all.

Nothing is created, nothing swells up, or stretches, or rises like yeasty bread-dough. Distances just increase.

There are no new distances that have to be made somehow---it's the same old distances as always---just that many of them, the longrange ones, increase by some percentage per year on average.
Like money in your savings account

 

[BoomBoom]

Nothing is created, nothing swells up, or stretches, or rises like yeasty bread-dough. Distances just increase.

I must confess that this is an issue I have the most problems with comprehending.

As distances increase the result is more space in between the matter than was there before, yet at the same time it is said that the matter does not travel THROUGH space. It seems to me that the matter MUST be traveling through empty space for the amount of space to increase. Space is, after all, nothing...and the percentage of nothing is continually increasing.