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Effort to get us all on the same page (balloon analogy)

by marcus
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3112100000
#217
Jan11-12, 09:06 PM
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Quote Quote by Drakkith View Post
What do you mean by "expanding from a given dense source"? I don't understand your analogies.
im too confused now i actually meant it like explosion of a bomb or fireworks but i now doubt it

if universe is just full of vacuum or space with no particles that is how universe is supposed to be i mean space doesnt need to be created anything created will be finite if space does not existed then we need space to put in space so only paradox in my view which need to be solved is matter particles and life/consciousness

bigbang i think is only created matter and matter life how could space expand if its expanding then it must be finite that doesnt make sense i cant digest expansion of space
Drakkith
#218
Jan11-12, 09:37 PM
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The universe isn't "supposed" to be like anything, it exists as it is. The rest of your post can be answered by looking at the FAQs in the cosmology section. Your view on it is not anything like the current scientific model.
3112100000
#219
Jan11-12, 10:32 PM
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Quote Quote by Drakkith View Post
The universe isn't "supposed" to be like anything, it exists as it is. The rest of your post can be answered by looking at the FAQs in the cosmology section. Your view on it is not anything like the current scientific model.
universe is supposed to be vacuum with no matter or energy or nothing but perfect nothing i cant take universe as it is like now how did all these stuff come in to existence out of nothing

i had read quantum fluctuations proton is made of 90% nothing ?and bigbang it says star burns for abt 10 billion years but bigbang is predicted to be happened only 13 billion years ago ?

these theories and explanations is still building up and people with basic understanding can make assumptions
i have doubts which cannot be cleared with current understsnding of universe i dont think any significant breakthrough in cosmology will be made in my lifetime
Drakkith
#220
Jan11-12, 10:53 PM
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Quote Quote by 3112100000 View Post
universe is supposed to be vacuum with no matter or energy or nothing but perfect nothing i cant take universe as it is like now how did all these stuff come in to existence out of nothing
No one anywhere who knows what they are talking about will tell you that they are sure that the universe came from nothing. That isn't even possible to verify. The truth is that we simply don't know. And please, don't try to tell me the universe is supposed to be vacuum with no matter or energy. You have absolutely no way of knowing that.

i had read quantum fluctuations proton is made of 90% nothing ?and bigbang it says star burns for abt 10 billion years but bigbang is predicted to be happened only 13 billion years ago ?
Attempting to ask what a proton is made up is inherently complicated unless you understand quantum mechanics. At that scale things are NOT like they are for us in our everyday life. Saying that is 90% empty space is a very limited way of looking at it and probably isn't correct.

And I'm not sure what your problem with stars burning for 10 billion years is. If the universe is 13 billion years old it is possible to have stars which have already burned that length of time.

i have doubts which cannot be cleared with current understsnding of universe i dont think any significant breakthrough in cosmology will be made in my lifetime
It sounds to me like you simply don't have a good grasp of the basics and are getting confused. I suggest you just keep learning the basic concepts.
3112100000
#221
Jan11-12, 11:49 PM
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Quote Quote by Drakkith View Post
No one anywhere who knows what they are talking about will tell you that they are sure that the universe came from nothing. That isn't even possible to verify. The truth is that we simply don't know. And please, don't try to tell me the universe is supposed to be vacuum with no matter or energy. You have absolutely no way of knowing that.
matter has to be created it is the product of some process like life which is a product of matter that we can say for sure .so matter has to be churned out i know you dont agree im also not sure of this, im talking probablities

there got to be something incredible that we dont know yet
if physicist can tell what causing strong nuclear force & gravity rather than how these force works
Drakkith
#222
Jan12-12, 02:14 AM
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Quote Quote by 3112100000 View Post
matter has to be created it is the product of some process like life which is a product of matter that we can say for sure .so matter has to be churned out i know you dont agree im also not sure of this, im talking probablities

there got to be something incredible that we dont know yet
if physicist can tell what causing strong nuclear force & gravity rather than how these force works
Our current knowledge can only get us so far. Instead of saying "this MUST be true" you would be much better off learning about what we currently know and how we know it.
alphachapmtl
#223
Feb17-12, 02:24 PM
P: 81
Quote Quote by 3112100000 View Post
i have this understanding plz correct me if im wrong im taking the mental freedom

expansion of universe is causing the galaxies to move away...
Maybe galaxies are not moving away but shrinking.
The end result would be the same (redshift , etc...)
alphachapmtl
#224
Feb17-12, 02:27 PM
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Quote Quote by Zygsterz View Post
As I understand it, the further we look out into the universe, the faster objects are accelerating...
Moving away, not accelerating.
Drakkith
#225
Feb17-12, 03:25 PM
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Quote Quote by alphachapmtl View Post
Maybe galaxies are not moving away but shrinking.
The end result would be the same (redshift , etc...)
This is not an accepted view.
salvestrom
#226
Feb17-12, 04:52 PM
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Quote Quote by Drakkith View Post
This is not an accepted view.
Doesn't it actually require the complete opposite of the bing bang: a large space with diffuse matter that slowly coalleces overtime and shrinks into a denser and denser state?
zbe
#227
Feb26-12, 10:02 AM
P: 9
Hi everyone.

I have a question. As already mentioned the measurments tell us the universe is flat or nearly flat. It was also stated that only closed universe would be spatialy finite and both the open and flat one would be infinite. My question is: How can universe have a beginning and is spatialy infinite? It is widely accepted that our universe has a beginning so wouldn't that suggest that our universe is either closed or that flat/open universe doesn't have to be infinite, somehow? =)

Please, tell me if I am missing something.

Regards.
marcus
#228
Feb27-12, 09:25 AM
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Quote Quote by zbe View Post
... It was also stated that only closed universe would be spatialy finite and both the open and flat one would be infinite.
There are so many concepts here it makes for confusion. I'm not sure what you mean by "open" and "closed".
Let's talk about the meaning of words another time. I understand you when you say spatially finite and spatially infinite. Either could be the case. We don't know yet which is more supported by the evidence. I don't believe either. I am waiting to see more evidence.

It is widely accepted that our universe has a beginning
I don't think there is any scientific evidence that our universe had a beginning. The "big bang" is not necessarily the beginning of time. It could have been preceded by a contraction. All that the evidence suggests is that the expansion that we see apparently had a beginning. We can follow time back to a very dense state. I am waiting for the models/theories to be tested, that go back further.

My question is: How can universe have a beginning and is spatialy infinite?
I don't see any contradiction. Personally I do not believe the U had a beginning because I do not see any observational evidence to support that belief. It is always possible that what we can understand and explain will go back farther in time as our science gets better. There is no fixed limit on how far back in time we can discover explanations and causes.

Understanding is a gradual step-by-step process. Perhaps it never ends. Right now our job is to understand what caused the start of expansion (the "big bang").

But maybe you know somebody who believes the U had a beginning! There are people who believe this! Let's say this person is named Bob. If Bob is able to imagine that the U had a beginning, then why can't he also imagine that the U is spatially infinite? What is the problem? Both things are hard to imagine, I admit. (And I prefer not to believe either, since there is no hard evidence for either.) But I don't see any contradiction.

If someone is able to believe that the U had a beginning, and wants to believe that, then why can't they also believe that it is spatially infinite, if they want? We should just let them think what they want.
cepheid
#229
Feb27-12, 10:26 AM
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Quote Quote by marcus View Post
But I don't see any contradiction.
The contradiction would seem to be that the scale factor goes to 0 as t → 0. That seems to suggest that as you go back in time, everything collapses down to a singular point. For any finite spatial volume, that sort of almost even works, because it means that the universe contracts to zero size as you go back in time to the beginning of the expansion. I suppose you could view this as the expansion of spacetime from some "initial singularity" of infinite density, but that sounds like nonsense -- what does it even mean? So what it really seems to mean is that our current physics breaks down and is incapable of describing what happens at t = 0. This is my view, actually. For me a singularity is just a mathematical problem having no physical significance other than, "your equations don't work here."

For an infinite spatial volume, even if the scale factor goes to zero, it doesn't mean that the universe goes to zero size. It just means that what happens as t → 0 is undefined. (Even more undefined than in the finite case). So the point is, since the universe having a beginning (or at least a beginning of the expansion) seems to require the scale factor going to zero, and since it's undefined what happens to a infinite spatial volume under these circumstances, it seems that (spatially infinite universe + beginning of expansion) doesn't make sense conceptually. (Then again, neither does "initial singularity.")

Am I thinking of this along the right lines? I really could use your insight here.
marcus
#230
Feb27-12, 11:06 AM
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I think along similar lines. GR develops a singularity. A singularity means the theory is breaking down and you have to stop trusting it. Any manmade theory will have a limited "domain of applicability" and will give a worse and worse approximation to nature as you approach where it breaks down.

I'd say you are thinking along the right lines, but I'm not an authority on this or anything really. All I can do is observe that what you say makes perfectly good sense to me. (You may know more than I do about this in fact.)

I think we are in a transitional situation where everybody realizes that classical GR has limited applicability and we need a quantum theory of the U's changing geometry. So various theories are being developed and replacements and no one stands out as favorite.
GR is a non-quantum vintage 1915 theory of dynamic geometry (how it changes and interacts with matter). It's beautiful and exquisitely accurate over its vast range of applicability. Only a few flaws and blemishes at the extreme limits.

So people are now proposing quantum geometry theories that attempt to extend the domain of applicability. Cover for classical everywhere that classical is good PLUS push the bounds of what we understand just a little bit further, to understand better around the start of expansion and the pits of black holes.

It would be nice if a quantum geometry could also explain the cosmological constant too (maybe it arises in some natural way from the quantum theory, a natural tendency for expansion to accelerate? well...) It would be nice if a quantum geometry would tell us that tiny microscopic primordial black holes don't evaporate quickly (classically or semiclassically they do so we wouldn't expect to see any, but what is "dark matter"?)

Lots of things would be nice. But the main thing is to resolve the "initial" singularity and get a testable model of what was happening around the time expansion started.
A testable model that also reproduces the beautiful classical picture, with the same fine accuracy.

We're talking attitudes/opinions at this point. I told you mine. it's similar to what you said, I think.
marcus
#231
Feb27-12, 11:30 AM
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Wow! I just looked at your "about me". You picked really interesting things to get a PhD in!
That stuff has the potential to really open up and get increasingly significant over the next 20 years IMHO. I'm just a retired mathematician who loves cosmology. I should be listening to you, not the other way around Good career and life choices!
zbe
#232
Feb27-12, 03:47 PM
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Quote Quote by marcus View Post
There are so many concepts here it makes for confusion. I'm not sure what you mean by "open" and "closed".
By "open" and "closed" (or flat) I mean the curvature of the universe. And (on page 3 or 4) it was said that only closed universe would "guarantee" finite space --- but it looks like it is infinite since we most likely live in a flat universe.

I don't think there is any scientific evidence that our universe had a beginning. The "big bang" is not necessarily the beginning of time. It could have been preceded by a contraction.
I think that all our knowledge ATM goes towards notion that the beginning of our universe (big bang) is the most acceptable truth unless I am missing something here. It could have been preceded by a contraction indeed but that would not change the contradiction.


All that the evidence suggests is that the expansion that we see apparently had a beginning. We can follow time back to a very dense state. I am waiting for the models/theories to be tested, that go back further.
Exactly. That is my point. How could you follow - in a finite amount of time - infinitely big universe to a finite (or infinitely small, it doesn't matter) universe.

Understanding is a gradual step-by-step process. Perhaps it never ends. Right now our job is to understand what caused the start of expansion (the "big bang").
I couldn't agree more. The only thing that bothers me is why could there even be a possibility that universe is infinitely large since it has a start - of expansion.

But maybe you know somebody who believes the U had a beginning! There are people who believe this! Let's say this person is named Bob. If Bob is able to imagine that the U had a beginning, then why can't he also imagine that the U is spatially infinite? What is the problem? Both things are hard to imagine, I admit.
IMHO both things aren't hard to imagine unless they are both true for the same thing. =) Look at it that way: A 1x1x1 (cm, doesn't matter) cube is born.=) It grows. In what time does it reach infinity? Never! Or better - in infinite time. I say F*** infinity since it has nothing to do in physics.=)

Also, I would guess my point is somehow the other way around of the cepheid's one.

I strongly agree with everything known in cosmology, this is just one of the rare questions that popped in my mind while reading this thread. =)

Regards.
cepheid
#233
Feb27-12, 04:36 PM
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Quote Quote by marcus View Post
Wow! I just looked at your "about me". You picked really interesting things to get a PhD in!
That stuff has the potential to really open up and get increasingly significant over the next 20 years IMHO. I'm just a retired mathematician who loves cosmology. I should be listening to you, not the other way around Good career and life choices!
Thanks for the kind words. I'm not a theorist and don't have really in-depth knowledge of General Relativity, just the basics and certain things that are applicable to cosmology. But I'm trying to learn it, over and above "building stuff" to collect more data via observations which is my main pastime, as you probably gathered.
mysearch
#234
Feb28-12, 05:03 AM
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Quote Quote by cepheid View Post
The contradiction would seem to be that the scale factor goes to 0 as t → 0. That seems to suggest that as you go back in time, everything collapses down to a singular point......It just means that what happens as t → 0 is undefined.
Quote Quote by marcus View Post
I don't think there is any scientific evidence that our universe had a beginning.
Quote Quote by zbe View Post
I say **** infinity since it has nothing to do in physics.
Hi,
I hope the extracts above and the highlighted words from previous posts do not misrepresent the original context, as they seem to capture some key issues, which I would like to raise. In the first quote, the key word appears to be whether ‘everything’ in the totality of the universe expanded from some conceptual singularity? In my own personal review of the various cosmology models, there seems to be plenty of scope to, at least, speculate that the expansion of what we often describe as the universe is only part of some larger process/universe.

I agreed that what happens as t->0 is ‘undefined’ in terms of current science, i.e. both GR & QFT, although we might be allowed to speculate that our ‘universe’ could have been triggered by some sort of quantum process within some larger definition of the universe.

In this respect, the speculative larger universe might not have any obvious ‘beginning’, although it might still be correct to say that our ‘local’ universe came into existence some 13.7 billion years ago.

However, there still appears to be the troublesome issue of infinities, which I am not sure that physics or the maths can ultimately avoid. If the common description is taken at face value, then you have to explain a universe, which is 13.7 billion years old, created from a singularity of near ‘infinite’ density that would conceptually occupy a near infinitely small volume, outside of which ‘absolute’ nothing exists or has ever existed. In this context, the issue of ‘creation’ from absolute nothing always seemed a bit metaphysical for my taste. Of course, the speculative model suggested cannot really avoid infinities, as the idea of an extended universe suggests a possibly infinite size and infinite age. Maybe Marcus, as a mathematician, and Cephid, as an astrophysicists, might like to comment further on such issue. Thanks


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