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TDL 76
2008-May-17, 05:41 PM
What is The Universe?

schlaugh
2008-May-17, 07:11 PM
Basically, everything. All matter, energy and space. Time too, I suppose. Even that which we haven't seen or measured yet.

dcl
2008-May-19, 05:02 PM
The question is what IS the Universe, not what WAS it or what WILL it BE. So the answer is that the Universe IS the totality of all matter and energy everywhere as it exists NOW and involves cosmology. What it WAS and what it WILL BE are two additional questions. They DO involve time and have entirely different answers involving cosmogony.

speedfreek
2008-May-19, 07:47 PM
"Now" is an interesting concept if you try an apply it across the cosmos.

dcl
2008-May-20, 03:20 AM
speedfreak is right. NOW is an interesting concept when applied to the Universe as a whole. We do not see the Universe as it is now. Because of the finite speed of light, we see nothing as it now, not even the moon. We see the moon as it was about 1.3 seconds ago, the sun as it was 8.3 minutes ago, the planet Neptune as it was about four hours ago, the nearest star other than the sun as it was 4.3 years ago, the Andromeda galaxy as it was about 2.6 million years ago, and the edge of the observable Universe as it was about 13.7 billion years ago.

damian1727
2008-May-20, 07:02 AM
so whens tea time ?:eek:

Drunk Vegan
2008-May-20, 08:08 AM
Time is an illusion. Tea time doubly so.

jokergirl
2008-May-20, 08:47 AM
42.

I can't believe nobody answered that yet.

;)

rreppy
2008-May-21, 08:16 PM
So, my 'now' and your 'now' can never be the same 'now'.
...Now I get it! Oops! I meant NOW I get it. No - NOW! Awww, forget it!

dcl
2008-May-23, 08:22 PM
jokergirl, what is the question you feel nobody has answered yet? If it's "What is the Universe?", It seems to me that both schlaugh and I answered it. If you feel that something is missing, I urge you to explain why. Hopefully, one of us or someone else can supply whatever you sense te be lacking.

Drunk Vegan
2008-May-23, 10:09 PM
jokergirl, what is the question you feel nobody has answered yet? If it's "What is the Universe?", It seems to me that both schlaugh and I answered it. If you feel that something is missing, I urge you to explain why. Hopefully, one of us or someone else can supply whatever you sense te be lacking.

She wasn't saying that, she was saying she was surprised that no one had answered "42" yet.


You know, the meaning of life, the universe, and everything.

dcl
2008-May-23, 11:47 PM
thanks, Drunk Vegan.

damian1727
2008-May-24, 07:24 AM
the clue's in the name....

damian1727
2008-May-24, 07:39 AM
so all matter and energy? is space/time a ''thing'' ? or do we just have ratio's between things?

i kinda agree with lee smolin... ie that question needs an answer..:think::think::think::think:

dcl
2008-May-24, 03:02 PM
damian 1727, you ask, "Is space/time a "thing?" The indefiniteness of the meaning of the word "thing" makes your question hard to understand. Everything is a "thing" in one sense or another. That the Universe is made up of all matter and energy is about the most that one can say in answer to the question of what the Universe is. As for a ratio between mass and energy, it's not clear to me that there is any answer to that question since special relativity reveals that both are forms of the same thing. I really don't believe that anything more can be said in answer to your question.

KaiYeves
2008-May-24, 03:34 PM
The Universe is every place,
Including all the e m p t y space
It's every star and galaxy
All objects of astronomy
Geography, zoology
(Each cat and dog and bumblebee),
All persons throughout history
Including you,
Including me.
From Douglas Florian's book of space poems Comets, Stars, the Moon and Mars.

ravens_cry
2008-May-25, 08:33 AM
SimUniverse - Make Your Cosmos!

Includes Planet Maker add-on, as well as Life 4.0.
*MindMaker 0.6b not supported, not resonsible for loss of data, files, programs or any damage to hardware resulting
from installation/use of MindMaker 0.6b with above software.*

SimUniverse - Make Your Cosmos!

damian1727
2008-May-25, 09:02 AM
:Dim talking about background independent" theories -- ones where there is no framework of absolute time and space for particles to move against, but rather ones where space and time themselves are integral, evolving, changing parts of the cosmos, and in which there are no static things, only dynamic processes....

being as there can be no outside to the universe....:D

damian1727
2008-May-25, 09:16 AM
http://www.edge.org/3rd_culture/smolin03/smolin03_print.html

:)

ravens_cry
2008-May-25, 09:26 AM
Call me kooky, but as I understand it, there MUST be something outside the universe, for the matter and energy in the universe to exist.

damian1727
2008-May-25, 09:52 AM
by definition the universe is eveything so there can be no outside...:neutral:

ravens_cry
2008-May-25, 10:05 AM
Then if energy/matter can neither be created or destroyed in our universe, then how come it is here at all?

Dumb Amateur Astronomer
2008-May-25, 11:09 AM
Wow, this is the most arrogant reply I have seen in a long time. Not only did you not get the reference to "42", but you think you answered the question. Correctly, even. :clap:



jokergirl, what is the question you feel nobody has answered yet? If it's "What is the Universe?", It seems to me that both schlaugh and I answered it. If you feel that something is missing, I urge you to explain why. Hopefully, one of us or someone else can supply whatever you sense te be lacking.

damian1727
2008-May-25, 11:42 AM
yes but we like him as he is as dry as dry and knows a thing or two.....

damian1727
2008-May-25, 11:43 AM
Then if energy/matter can neither be created or destroyed in our universe, then how come it is here at all?

as nothing is less stable than something?

damian1727
2008-May-25, 12:01 PM
and also i guess in the past universe ment everything now we have multiverses .bubble universes and all sorts....

i myself like the infinite inflation model as its mind numbing in its scope !!

:)

dcl
2008-May-25, 03:48 PM
Dumb Amateur Astronomer: this is the most arrogant reply I have seen in a long time. Not only did you not get the reference to "42", but you think you answered the question. Correctly, even.

dcl: I'm sorry that you found my reply arrogant. I also regret that I did not and still do not recognize the reference to "42", whatever that means. In fact, I must admit that I didn't even notice it when I submitted my comment. I suspect it refers to something in "A Hitchhiker's Guide to the Galaxyi", but, never having read that beyond something at the beginning about, as I recall, bulldozing of a house, I don't even know that much, so all I can do is congratulate you on your superior knowledge.

damian1727: if energy/matter can neither be created or destroyed in our universe, then how come it is here at all?

dcl: Science has no answer for that question. Science observed that the Universe is expanding, inferred that it was smaller in the past and, using what is known about the behavior of matter and energy, in effect ran the movie backward as far as knowledge would allow and sensibly stopped there to avoid uninformed speculation. That took it back to 10-43 sec, at which time the size of the eniverse appeared to be as close as can be imagined to that of a dimensionless point and at a temperature so high that no matter of any kind could exist, not even protons, neutrons, electrons, etc., so that what was to become matter had to all be in the form of energy at a temperature of at least trillions of kelvins, the only form of energy possible at such temperatures being electromagnetic with black-body spectrum, the temperature being too high for any of the other three basic forms of energy. No one knows enough about the nature of energy to be able to run the "movie" any further back into the past, in particular to say anything about where that energy came from in the first place.

ravens_cry
2008-May-25, 10:14 PM
Then if energy/matter can neither be created or destroyed in our universe, then how come it is here at all?

as nothing is less stable than something?
I don't see your logic, could you explain?:question:
From where I stand, you can squeeze the universe back together again in a Big crunch, to 'get back' usable energy for the next Big Bang, but that still doesn't explain where it comes from. And if one says it has always existed, well that's the same answer theologians have been using for thousands of years. And if it doesn't work for HIM, why should it work for things moderately more concrete? :wall:

dcl
2008-May-26, 09:00 PM
damian 1727: You asked, "Is space/time a 'thing'? or do we just have ratios between things?" i kinda agree with lee smolin... ie that question needs an answer.

dcl: Special relativity introduced the concept of spacetime, written as a single unhyphenated word. Spacetime is seen as a four-dimensional entity and is visualized in terms of four mutually perpendicular directions, three of which are spatial and the fourth temporal, that is, forward and backward directions in time. Collectively, I suppose the four of them could be regarded as a thing, but it's not a material thing that you can touch or see. A common application of the concept is a two-dimensional diagram that can be drawn on a sheet of paper. It's called a "spacetime diagram". It can also be called a "space/time diagram" if one wishes. People will understand you whichever form you use. Both names appear in books and technical articles. The horizontal coordinate is a spatial direction with left and right. The vertical coordinate is time, with past downward and future upward. Light is depicted as a pair of lines at 45-degree angles to the vertical and horizontal lines. A special version of this diagram used to illustrate the meaning of the Lorentz transformation in special relativity is called a Minkowski diagram.

I don't understand your reference to Lee Smolin. The only context in which I've encountered Lee Smolin is string theory, and I don't think that's what you're referring to.

dcl
2008-May-27, 02:44 AM
The universe is a fragment of the multiverse. Hope that was helpful to you.

It is not useful to make controversial statements without backing them up with arguments for why you think they are valid. In the present instance, the first sentence in your statement is highly controversial. You need to provide an argument for why you think it is valid.

damian1727
2008-May-28, 03:49 PM
its better than the alternative tho....

or how else do you explain the 'fine tuning'?.....

dcl
2008-May-28, 10:56 PM
In what context are you referring to "fine tuning"? If you answer that, I may be able to explain what "fine tuning" is.

damian1727
2008-May-29, 04:06 PM
:):):)

http://en.wikipedia.org/wiki/Fine-tuned_universe

dcl
2008-May-30, 03:32 PM
:):):)

http://en.wikipedia.org/wiki/Fine-tuned_universe

I believe there is no need to account for the fine-tuning. If it hadn't happened, we wouldn't be here to ask the question. The best we can do is to assume that it happened through sheer chance. To ask why it happened is like asking why a fair coin landed on heads rather than tails. I see no reason for supposing that the fine-tuning was more than the chance outcome of a seriers of random events.

By the way, I appreciate your response to Dumb amateur astronomer's accusing me of arrogance.

damian1727
2008-May-31, 03:30 PM
no problem...

i would beg to differ on ''fine tuning'' ... as i understand it the universe or our part of it came into being as a quantum event with as we understand at present the constants masses forces getting their values ''at random''

we are here to ask the question so it did happen and the question asked !!

i like it as it suggests many many ''universes''

:)

sheer chance is not very likely when you look at the odds...

i dont have them in front of me but its like the biggest number you ever saw!

i'll look them up if you like
:shifty:

dcl
2008-May-31, 09:12 PM
damian 1727: i would beg to differ on ''fine tuning'' ..as i understand it the universe or our part of it came into being as a quantum event with as we understand at present the constants masses forces getting their values ''at random''. we are here to ask the question so it did happen and the question asked !!

dcl: I know of no reason for supposing that the "quantum event" occurred other than as a spontaneous event. The world is full of spontaneous events. Ancient peoples attributed such events to the actions of capricious gods, but modern people attribute them to sheer chance. I still say that if not for that event, we would not be here to argue about why it happened.

damian 1727: i like it as it suggests many many ''universes''

dcl: I see no reason for postulate other universes, presumably one corresponding to each of the infinity of other alternate events that could have happened but, as far as we are aware, didn't. Suppose that a mouse nibbled at the cheese in a mouse trapped and was caught. The trap could have been defective and allowed the mouse to enjoy its meal and go home to tell its family about it, but that doesn't imply that there is another entire universe in which this actually happened.

damian 1727: sheer chance is not very likely when you look at the odds...

dcl: The fact that it happened nullifies the odds against its happening.

damian 1727: i dont have them in front of me but its like the biggest number you ever saw!

dcl: I agree.

damian 1727: i'll look them [odds against the quantum event's having happened] up if you like

dcl: Don't bother. I agree that the number is horrendously large, but that fact implies nothing about the possible existence of that alternate universe as existing somewhere as a real universe. An alternate universe is only an idea, not something that actually exists. The very word "alternate" implies the actual occurrence of one of a number of possibilities and the nonexistence of all contrary possibilties.

damian1727
2008-Jun-01, 04:18 AM
dcl The fact that it happened nullifies the odds against its happening.


me huh ? i never understood this it makes no sense

i might win the lottery but the odds of me doing so are as they were..

and it also makes sense that if something happened once it could happen twice....or that big number we agreed on


we are not aware they did or did not

as i see it if quantum fluctuations in a void can do this then im sure they do
and as i see it fine tuning most certainly raises an eyebrow (!!) and i feel better with the very logical and beautiful explanation that is the multiverse

also on a completely personnel level i kinda take it as a an act of faith that the world is always far more complex and amazing than i could ever possibly imagine so i would not choose to limit myself to one universe if in fact i could have many for the same price ;)

and it shuts (no it doesnt) the god squad up

:whistle:

dcl
2008-Jun-01, 04:30 PM
damian1727, I agree. The chance against our Universe's having come into existence already fine-tuned for human life to arise was extremely high. It happened, the high probability against its happening notwithstanding.

jseats
2008-Jun-01, 07:23 PM
If the universe by definition is 'everything', then what is the rationale for the term coined 'multiverse'. I never quite understood how that came about. Perhaps it is just semantics, but if we want to define 'universe' to mean all that is, then we should not refer to supersets of that. Granted it gets tedious to always say things like 'our observable universe' or 'all space-time that is causally connected'. I think if you allow existence of the concept of potentially disconnected spacetimes, then 'universe' as stated cannot be given the definition of 'all matter and energy' without a little refinement.

damian1727
2008-Jun-01, 10:08 PM
true dat

:P

dcl
2008-Jun-01, 10:37 PM
damian1727, I just discovered that I committed a monstrous goof in my statement responding to your statement about fine-tuning of the Universe. By saying "high" when I meant to say "low", I said precisely the opposite of what I intended to say: a horrific example of careless forgetting to proof to assure that I was saying what I meant to say. Sorry, people. I meant to say that I agree with you that the probability of the Universe's coming into existence fine-tuned for human life to occur was highly IMprobable.

As for the term "multiverse", I want no part of it. I know of no evidence for there being more than the one Universe that we know, the "branes" of string theory notwithstanding.

jseats, I agree wholeheartedly with your rejection of the concept of multiverses. I see no useful purpose in speculating about the existence of universes other than the one we know unless there is a possibility of our being able to test for their existence. On the other hand, I do feel that it is important to distinguish the universe and the observable universe because they are drastically different, and it is often important to know which one is being referred to.

Drunk Vegan
2008-Jun-02, 06:19 AM
The universe is a big ball of wiggley-wobbley... timey-wimey... stuff.

damian1727
2008-Jun-02, 11:05 AM
dcl i may be wrong but i dont think jseats was saying that there was no multiverse per say he/she was saying that if we stick with the original definition of universe to mean EVERYTHING EVER .. including different space time bubbles and dimensions then your original deffinition ... all matter and energy... was oversimplistic

i think thats what he/she said

:)

the multiverse is the simplest explanation for fine tuning

dcl
2008-Jun-02, 08:46 PM
dcl i may be wrong but i dont think jseats was saying that there was no multiverse per say he/she was saying that if we stick with the original definition of universe to mean EVERYTHING EVER .. including different space time bubbles and dimensions then your original deffinition ... all matter and energy... was oversimplistic

i think thats what he/she said

:)

the multiverse is the simplest explanation for fine tuning

jseats said, "If the universe by definition is 'everything', then what is the rationale for the term coined 'multiverse'. I never quite understood how that came about. Perhaps it is just semantics, but if we want to define 'universe' to mean all that is, then we should not refer to supersets of that." This seems to me to be an argument against use of the term "multiverse" as being more inclusive than the term "universe".

He went on to say, "Granted it gets tedious to always say things like 'our observable universe' or 'all space-time that is causally connected'. I think if you allow existence of the concept of potentially disconnected spacetimes, then 'universe' as stated cannot be given the definition of 'all matter and energy' without a little refinement." This seems to me to be no more than an argument against saying "our universe" when one means "our observable universe".

damian1727
2008-Jun-02, 09:30 PM
he would call the multiverse .. universe.. as it means everything....

if you allow for disconnected spacetimes..(universes to us) then .....

nevermind :)

dcl
2008-Jun-03, 05:49 PM
I believe that I failed to make it clear in my last remark that I am in agreement with jseats regarding ambiguity in the way the term "universe" is frequently used to refer to less than the entire Universe, the latter referring to everything, excluding nothing.

damian1727
2008-Jun-03, 06:42 PM
sooooooooo what i and many others term the multiverse you would would call universe?......?

and what would the word for the individual ''bubbles' be?

even tho you dont think they exist you would dtill need a word to tell me ~!!!!

lol

way to confuse ourselves!

when i say universe i mean the whole of space time that came into being 13.7 billion years ago

but i believe *scarey voice* there IS soOoO mucH mOreee....

dcl
2008-Jun-03, 09:45 PM
sooooooooo what i and many others term the multiverse you would call universe?......?

and what would the word for the individual ''bubbles' be?

even tho you dont think they exist you would dtill need a word to tell me ~!!!!

lol

way to confuse ourselves!

when i say universe i mean the whole of space time that came into being 13.7 billion years ago

but i believe *scarey voice* there IS soOoO mucH mOreee....

As far as I know, there is no evidence for more than the single universe that we live in. Any speculation to the contrary is only that and is backed by no evidence whatever. I feel that such speculation remains sterile until at least some evidence has been found for it. Until individual bubble universes are found, I wouldn't worry about what to call them. If someone wants to believe in bubble universes, I'll be content to let him devise a name for them. When I say "universe", I, too, mean the whole spacetime that appears to have come into existence 13.71 billion years ago. I, too, suspect that there is much more to the Universe than we know about or can even guess at at present.

speedfreek
2008-Jun-06, 05:56 PM
A lot of science or cosmology is based on the concept that "If it can happen here, it can happen somewhere else". Why not apply this to the universe itself?

The simple reason for the multiple universe idea is that it removes the fine tuning problem.

If this seems too speculative, consider that the fine tuning problem itself is really a philosophical question - you are asking why all the physical constants are at those particular values rather than other values - you are asking what mechanism defined those values - you are asking about the mechanism responsible for our universe being the way it is...

We now have a few contenders in cosmology that might take the time-line back further than the beginning of "our" universe, things like M-theory and Loop Quantum Gravity, but we have no way so far to test these ideas and they only take the "mechanism behind" question back along the time-line with them anyway.

dcl
2008-Jun-09, 03:45 PM
A lot of science or cosmology is based on the concept that "If it can happen here, it can happen somewhere else". Why not apply this to the universe itself?

The simple reason for the multiple universe idea is that it removes the fine tuning problem.

If this seems too speculative, consider that the fine tuning problem itself is really a philosophical question - you are asking why all the physical constants are at those particular values rather than other values - you are asking what mechanism defined those values - you are asking about the mechanism responsible for our universe being the way it is...

We now have a few contenders in cosmology that might take the time-line back further than the beginning of "our" universe, things like M-theory and Loop Quantum Gravity, but we have no way so far to test these ideas and they only take the "mechanism behind" question back along the time-line with them anyway.

"here" and "somewhere else" in the expression "If it can happen here, it can happen somewhere else" do not usually refer to locations in different universes. There is no basis for supposing that multiple universes would remove the fine-tuning problem. I am not asking why all of the physical constants have the values that they do. I think these values have the values that they do merely because we wouldn't be here to ask the question if they different, We shouldn't ask for causes when there were none. I'm not aware that M-theory and quantum gravity offer to take the time line back before the Big Bang.

speedfreek
2008-Jun-09, 05:33 PM
Well, M-Theory proposes the possible existence of multi-dimensional membranes which interacted, causing our universe.

As for Loop Quantum Gravity, Abhay Ashtekar and Martin Bojowald have released papers stating that according to loop quantum gravity, the singularity of the Big Bang is avoided. What they found was a prior collapsing universe. Since gravity becomes repulsive near Planck density according to their simulations, this resulted in a "Big Bounce" and the birth of our current universe. These topics are an active research in loop quantum cosmology.

By the way, I wasn't implying that you were asking about the fine-tuning problem, that was bad wording on my part. I was just referring to the fine tuning problem in of itself. I agree with you regarding the lack of a need for a cause.

damian1727
2008-Jun-09, 08:39 PM
dcl ..... I am not asking why all of the physical constants have the values that they do. I think these values have the values that they do merely because we wouldn't be here to ask the question if they different,

me .... that is not a very satisfying argument ... how does it feel as a physicist having to put all the force ratios ..constants ..partical masses into your equations by hand ... they should arise from the theory and in an ideal world not be able to take any other values

then we could say ''see there you go thats explained ''

just to say well im here so that explains it is just utter nonsense imho

we need to understand how the universe came to be the way it is...thats physics...so the search continues and we have yet to explain how the
force ratios ..constants ..partical masses came to hold the values they do..

im sure that the future will make great in roads in our understanding

but it wont be im here so thats no suprise !!!! it is a suprise.!!!
:D:D:D:
:D:D:D:D:p

the anthropic principle says i find myself in a universe i can be in

it DOES NOT say that the values are such SO I CAN BE HERE..... think these values have the values that they do merely because ....it is no reason

bugbear of mine

speedfreek
2008-Jun-09, 09:39 PM
Perhaps there are/have been billions of universes (but where did they come from?). Perhaps the laws of physics are different in each and where a universe works properly life will arise to ask these questions. Perhaps the current universe is part of a single sequence of universes that gradually settle towards the ideal laws of physics (but where did it come from?). Perhaps the universe was designed by an intelligence (but who designed them?). Perhaps multi-dimensional membranes clash together and form universes (but where did the 'branes come from?).

The "what is the mechanism behind it?" question just gets moved backwards.

damian1727
2008-Jun-09, 10:37 PM
works properly ???ideal laws of physics???

lets just keep open minds and rely on science to let us know what we know and be big enough to know what we dont

you sound as if you think further investigation is not worth it

folk always put something called god into gaps in knowlege....so what?

lets push the gaps back

ultimatley you seem to be asking the ancient question WHY SOMETHING AND NOT NOTHING?

for now i live with the fact that NOTHING is unstable and liable to fracture into something ;) the fact that this question is along way away from being know should not stop us thinking

:):):D

Cougar
2008-Jun-10, 02:25 AM
damian1727: if energy/matter can neither be created or destroyed in our universe, then how come it is here at all?

dcl: Science has no answer for that question.

Here, your answer is correct. I think accomplished physicists may ask themselves the same question - "Why is there anything at all?" or "Why isn't there nothing?" but only when they're in philosophical moods, I suppose.


...ran the movie backward as far as knowledge would allow and sensibly stopped there to avoid uninformed speculation. That took it back to 10-43 sec....

Here your answer is incorrect. We can't get anywhere near 10-43 sec. From my recent reading on the subject, many major names in the field all seem to agree on how the movie would rewind back to 1 second. If I'm not mixing my units, I believe our most powerful accelerators can simulate conditions somewhere around 10-15 sec. Beyond that, we have no observational data, and various physicists have different ideas.

Cougar
2008-Jun-10, 03:12 AM
Beyond that, we have no observational data, and various physicists have different ideas.

They are different ideas, but they all seem to be dealing with the apparent failure of string theory to derive a single, unique solution that explains our universe. As Lee Smolin points out in The Trouble With Physics [2006], after about 30 years of effort developing string theory and its offshoots, the theory turns out to be just TOO successful. (Well, he doesn't put it that way, but I think it's applicable.) Some have estimated the number of string theory solutions at 10500. Note the number of particles in our universe is 'only' around 1080.

Leonard Susskind, the "father" of string theory points out in his 2006 book, The Cosmic Landscape, that this suggests there are 10500 possible universes allowed by the theory, and there's no reason to think that many of the longer-lived ones aren't actually existing, similarly to how ours happens to be.

I kind of like the picture painted by Alex Vilenkin in his remarkably well-written entry, Many Worlds in One [2006]. If I haven't mixed up my authors, Vilenkin does a masterful job in his explanation of eternal inflation, where the "whole universe" is in constant, exponential expansion, and what we call the big bang is just one bubble universe that "gracefully exits" the background frenetic inflation and proceeds to evolve according to the physical laws and constants that were set in the first seconds of the so-called "bang." And there's untold number of such bubble universes, which will unfortunately never be able to interact in any fashion with any other due to the superluminal expansion going off between them.

Though Vilenkin's description seems plausible, Smolin is quite right in his criticism of the craft that seems to more commonly be positing schemes that have no fair chance of finding any observational support. The space between theory and experiment seems to be undergoing.... exponential inflation.

To Vilenkin's credit, he does predict some fundamental of his idea may be distinguishable from other theories by a close analysis of the gravitational wave background. Of course, we are currently having a hard time detecting the gravitational wave foreground, so....

damian1727
2008-Jun-10, 07:14 AM
i would just like to say i never said this...

damian1727: if energy/matter can neither be created or destroyed in our universe, then how come it is here at all?


it got confused in all the cut and paste and was said by RAVENS CRY

it got in my post so i could answer it... (tho i cant lol )

glad thats clear :D

speedfreek
2008-Jun-10, 12:27 PM
works properly ???ideal laws of physics???

lets just keep open minds and rely on science to let us know what we know and be big enough to know what we dont

you sound as if you think further investigation is not worth it

folk always put something called god into gaps in knowlege....so what?

lets push the gaps back

ultimatley you seem to be asking the ancient question WHY SOMETHING AND NOT NOTHING?

for now i live with the fact that NOTHING is unstable and liable to fracture into something ;) the fact that this question is along way away from being know should not stop us thinking

:):):D

Damian, it was you who introduced the fine-tuning problem into this thread, and once this has been introduced, it sends the discussion tumbling inevitably towards the "why something and not nothing" question.

I was just suggesting a number of alternative possible solutions to the fine-tuning problem, but all they do is push the question further away - the question is still there, lurking!

Now, dcl is happy to leave the question unanswered, and I tend to agree with him, but I see no problem in investigating further if you want, which is why I mentioned things like M-Theory and Loop Quantum Gravity. M-Theory allows multiple universes ('branes bang together and cause universes), and Loop Quantum Gravity allows a sort of cyclical universe (no big-bang, but a previous contracting universe).

Cougar
2008-Jun-10, 03:29 PM
...i never said this...


Oh, sorry, Damian and Raven. It's certainly a question that I've seen toward the beginning of numerous books and articles. "Why is there something instead of nothing?" The various multiverse and bubble universes ideas do provide an answer to this question: There are zillions of different bubbles, all with different qualities, and ours happens to allow for life to evolve, obviously. End of answer. Unfortunately, such an answer has no observational support, is not falsifiable, and therefore has kind of left science behind. But apparently scientists are tired of sweeping the fine-tuning question under the rug....

dcl
2008-Jun-10, 06:06 PM
In this contribution, I'll respond on some of the things said by others regarding my contributions since my last contribution. Each entry will start with the pseudonym of the person on whose entry I'm commenting immediately followed in a new paragraph starting with my own pseudonym followed by my comment.

speedfreek: M-Theory proposes the possible existence of multi-dimensional membranes which interacted, causing our universe.

dcl: Let's not lose sight of the fact that, as attractive as M-theory may be in some respects, there is absolutely no evidence for or against it. So let's remember that at best it is only a hypothesis awaiting the first evidence that it may be valid. I'm under the impression that the same must be said for loop quantum gravity.

speedfreek: As for Loop Quantum Gravity, Abhay Ashtekar and Martin Bojowald have released papers stating that according to loop quantum gravity, the singularity of the Big Bang is avoided. What they found was a prior collapsing universe.

dcl: I, too, think it plausible that the present expansion was preceded by a bounce from a previous contraction, but I'm not aware that there is any evidence for a bounce, so we should not seize on the idea that there was one.

damian1727: "I am not asking why all of the physical constants have the values that they do. I think these values have the values that they do merely because we wouldn't be here to ask the question if they were different" is not a very satisfying argument ... how does it feel as a physicist having to put all the force ratios ..constants ..partical masses into your equations by hand ... they should arise from the theory and in an ideal world not be able to take any other values

dcl: Physicists agree that values for physical constants should ideally arise from the theory, but most theories aren't as complete as we'd like them to be in that respect.

damian1727: just to say well im here so that explains it is just utter nonsense imho

dcl: I don't know where you got that quote. My being here explains nothing.

damian1727: we need to understand how the universe came to be the way it is...thats physics...so the search continues and we have yet to explain how the force ratios ..constants ..partical masses came to hold the values they do.

dcl: We'd like to understand how the universe came to be the way it is, but we don't need to.

damian1727: you sound as if you think further investigation is not worth it

dcl: It's not clear that that remark was addressed to me, but it appears to me that it was. I feel that further investigation in some areas is pointless. For example, the idea that the Universe has the shape of a cube, a 3-torus, a doughnut, or a dodecahedron is pointless because the suggestion that the Universe has any of those shapes seems preposterous to me. The shape that seems plausible to me is that of an expanding four-dimensional hypersphere.

damian1727: ultimatley you seem to be asking the ancient question WHY SOMETHING AND NOT NOTHING?

dcl: I am not asking that question and am curious as to why you think I am.

Cougar: Here [in runningn the movie backward] your answer is incorrect. We can't get anywhere near 10-43 sec. From my recent reading on the subject, many major names in the field all seem to agree on how the movie would rewind back to 1 second.

dcl: I suggest you broaden your reading. There are any number of respected sources that give that 10-43 figure. That figure comes from the Standard Model of particle physics, not from accelerator experiments.

damian1727
2008-Jun-10, 07:01 PM
dcl all the posts in my post below speedfreeks where aimed at him

dcl you said... I think these values have the values that they do merely because we wouldn't be here to ask the question if they were different,,,,,

which i translated into ... just to say well im here so that explains it...

anyway i tend to agree with all of you great posts guys esp cougar ,,,thanks 4 the
Alex Vilenkin mention.... i like this idea..

:)

speedfreek
2008-Jun-10, 08:47 PM
speedfreek: M-Theory proposes the possible existence of multi-dimensional membranes which interacted, causing our universe.

dcl: Let's not lose sight of the fact that, as attractive as M-theory may be in some respects, there is absolutely no evidence for or against it. So let's remember that at best it is only a hypothesis awaiting the first evidence that it may be valid. I'm under the impression that the same must be said for loop quantum gravity.

speedfreek: As for Loop Quantum Gravity, Abhay Ashtekar and Martin Bojowald have released papers stating that according to loop quantum gravity, the singularity of the Big Bang is avoided. What they found was a prior collapsing universe.

dcl: I, too, think it plausible that the present expansion was preceded by a bounce from a previous contraction, but I'm not aware that there is any evidence for a bounce, so we should not seize on the idea that there was one.

Of course, both M-Theory and Loop Quantum Gravity are hypotheses awaiting a mechanism to test them with. I agree we should not seize upon the idea that either is correct, as we have no evidence. I presented them simply as valid possibilities (ones being pursued seriously, rather than pie in the sky ideas), hence my repeated use of the term "perhaps" in my post above. :)



I feel that further investigation in some areas is pointless. For example, the idea that the Universe has the shape of a cube, a 3-torus, a doughnut, or a dodecahedron is pointless because the suggestion that the Universe has any of those shapes seems preposterous to me. The shape that seems plausible to me is that of an expanding four-dimensional hypersphere.


The idea that any shape other than a four-dimensional hypersphere seems implausible to you and is therefore preposterous to you is essentially irrelevant. Cosmologists are searching for evidence of a shape, and one method is to look for matching areas in the WMAP data. Any valid shape with a non-trivial topology (and that includes a hypersphere, amongst others) might show up as repeated inhomogeneous regions in the CMBR, where these non-uniform regions were introduced during inflation. The relative positions of these regions would indicate the topology involved, but only if the fundamental domain of the universe was smaller than our observable universe.

It may indeed seem doubtful that the fundamental domain (the whole universe) is smaller than our observable universe, but we have to do what we can to test for it and the least we can do is search our observable universe for evidence for it so that we can count it out. So far we have only counted it out across a co-moving diameter of 78 billion light years and our observable universe has a co-moving diameter of 92 billion light years so there is a little way to go yet before we can confidently state that the whole universe is larger than our observable portion of it. Until we can, there remains the possibility that we might find evidence for a non-trivial topology.

Should we only look for evidence for the most plausible model? Is that good science?

As you are so convinced that the hypersphere is the only plausible shape for the universe I must assume you have studied the mathematics of hyperspheres and so you should be familiar with both the Poincaré conjecture (http://en.wikipedia.org/wiki/Poincar%C3%A9_conjecture) and, perhaps more pertinently, the Poincaré homology sphere (http://en.wikipedia.org/wiki/Poincar%C3%A9_dodecahedral_space#Poincar.C3.A9_hom ology_sphere), which is also known as Poincarés dodecahedral space.

damian1727
2008-Jun-10, 09:39 PM
:clap::clap:

hurrah

(does that mean edges are back in with a shot?) :D

Cougar
2008-Jun-10, 10:27 PM
Cougar: Here [in runningn the movie backward] your answer is incorrect. We can't get anywhere near 10-43 sec. From my recent reading on the subject, many major names in the field all seem to agree on how the movie would rewind back to 1 second.

dcl: I suggest you broaden your reading. There are any number of respected sources that give that 10-43 figure. That figure comes from the Standard Model of particle physics, not from accelerator experiments.

Ha ha! Now that is truly funny. Would you like to peruse my Recent Reading list?



# Chaos, Making a New Science [1987] -- James Gleick

# Complexity, Life at the Edge of Chaos [1992] -- Roger Lewin

# Complexification -- John Casti

# Journey to the Great Attractor [1994]-- Alan Dressler

# The Science of Fractal Images -- Peitgen, Saupe, eds.

# Hyperspace, A Scientific Odyssey Through Parallel Universes, Time Warps, and the 10th Dimension [1994] -- Michio Kaku

# The Matter Myth -- Paul Davies

# The Cosmic Blueprint, New Discoveries in Nature's Creative Ability to Order the Universe [1988] -- Paul Davies

# God and the New Physics -- Paul Davies

# The Red Limit [1977]-- Timothy Ferris

# Coming of Age in the Milky Way -- Timothy Ferris

# The Mind's Sky, Human Intelligence in a Cosmic Context -- Timothy Ferris

# The Key to the Universe [1977] -- Nigel Calder

# QED, The Strange Theory of Light and Matter -- Richard Feynman

# Surely Your Joking, Mr. Feynman! -- Richard Feynman

# What Do You Care What Other People Think? -- Richard Feynman

# Cosmic Catastrophes [1989] -- Clark Chapman, David Morrison

# Searching For Certainty, What Scientists Can Know About the Future [1990] -- John L. Casti

# Dreams of a Final Theory [1992] -- Steven Weinberg

# The Cosmic Code [1982] -- Heinz Pagels

# Sympathetic Vibrations, Reflections on Physics as a Way of Life [1985] -- K.C. Cole

# The God Particle, If the Universe is the Answer, What is the Question? [1993] -- Leon Lederman with Dick Teresi

# Genius, The Life and Science of Richard Feynman [1995] -- James Gleick

# At Home in the Universe, The Search for the Laws of Self-Organization
and Complexity [1995] -- Stuart Kauffman

# The Origin of The Universe [1994] -- John D. Barrow

# The Quark and the Jaguar, Adventures in the Simple and the Complex [1995] --
Murray Gell-Mann

# The Last Three Minutes, Conjectures About the Ultimate Fate of the Universe [1994] --
Paul Davies

# Flyby, The Interplanetary Odyssey of Voyager 2 [1987] -- Joel Davis

# The Nemesis Affair, A Story of the Death of Dinosaurs and the Ways of Science [1986] -- David M. Raup

# Bully for Brontosaurus -- Stephen Jay Gould

# Eight Little Piggies, Reflections in Natural History [1993] -- Stephen Jay Gould

# On a Piece of Chalk [1868, republished 1967] -- Thomas Henry Huxley

# Cosmic Coincidences, Dark Matter, Mankind, and Anthropic Cosmology [1989] --
John Gribbin and Martin Rees

# The Collapse of Chaos, Discovering Simplicity in a Complex World [1994] --
Jack Cohen and Ian Stewart

# The Milky Way, Fifth Edition [1941-1981] -- Bart Bok, Priscilla Bok

# A Hundred Billion Stars [1984] -- Mario Rigutti

# The Lighter Side of Gravity [1982] -- Jayant V. Narlikar

# Chaos in the Cosmos [1996] -- Barry Parker

# A Brief History of Time -- Stephen Hawking

# Black Holes and Baby Universes [1993] -- Stephen Hawking

# Exploring the Galaxies [1976] -- Simon Mitton

# The Three Big Bangs, Comet Crashes, Exploding Stars,
and the Creation of the Universe [1996] -- Dauber and Muller

# Mysteries of the Milky Way [1991] -- Goldsmith and Cohen

# The Edges of Science [1990] -- Richard Morris

# The Privilege of Being a Physicist [1989] -- Victor Weisskopf

# Feynman's Lost Lecture [1996]

# Cosmic Rays, Tracking Particles From Outer Space [1989] -- Michael Friedlander

# Quarks, The Stuff of Matter [1983] -- Harald Fritzsch

# How Nature Works, The Science of Self-Organized Criticality [1996] -- Per Bak

# In The Beginning, After COBE and Before The Big Bang [1993] -- John Gribbin

# The Secret Melody [1995] -- Trinh Xuan Thuan

# Neils Bohr, A Centenary Volume [1985] -- French and Kennedy, eds.

# The Particle Garden, Our Universe
as Understood by Particle Physicists [1995] -- Gordon Kane

# The Edge of the Unknown,
101 Things You Don't Know About Science
And No One Else Does Either [1996] -- James Trefil

# Einstein's Legacy -- Julian Schwinger

# The Whole Shebang,
A State-of-the-Universe(s) Report [1997] -- Timothy Ferris

# Creation, The Story of the Origin and Evolution of the Universe [1988] -- Barry Parker

# In Quest of Quasars, An Introduction to Stars and Starlike Objects [1969] -- Ben Bova

# The Twin Dimensions, Inventing Time & Space [1986] -- Geza Szamosi

# Blind Watchers of the Sky, The People and Ideas that Shaped Our View of the Universe [1996] -- Rocky Kolb

# Heisenberg Probably Slept Here, The Lives, Times, and Ideas of the Greatest Physicists of the 20th Century [1997] -- Richard P. Brennan

# Beyond the Known Universe, From Dwarf Stars to Quasars [1974] -- I.M. Levitt

# The Dark Side of the Universe [1988] -- James Trefil

# Perfect Symmetry [1985] -- Heinz Pagels

# The Very First Light, The True Inside Story of the Scientific Journey Back to the Dawn of the Universe [1996] -- John C. Mather and John Boslough

# The First Three Minutes,
A Modern View of the Origin of the Universe [1977] -- Steven Weinberg

# Scientific Autobiography and Other Papers [1949] -- Max Planck

# The Cosmos from Space [1987] -- David H. Clark

# Rain of Iron and Ice, the very real threat of comet and asteroid bombardment [1996] -- John S. Lewis

# Worlds Unnumbered, the Search for Extrasolar Planets [1997] -- Donald Goldsmith

# Why People Believe Weird Things, pseudoscience, superstition, and other confusions of our time [1997] -- Michael Shermer

# The Threat and the Glory [1959-90] -- Peter B. Medawar

# Gšdel, Escher, Bach: an Eternal Golden Braid [1979] -- Douglas Hofstadter

# The Inflationary Universe, the quest for a new theory of cosmic origins [1997] -- Alan H. Guth

# Wrinkles in Time [1993] -- George Smoot, Keay Davidson

# The Meaning of It All, Thoughts of a Citizen-Scientist [1998] -- Richard P. Feynman

# The Light at the Edge of the Universe [1993] -- Michael D. Lemonick

# Chaos and Harmony [2001] -- Trinh Xuan Thuan

# The Fifth Miracle, The Search for the Origin of Life [1998] -- Paul Davies

# Paradigms Regained, A Further Exploration of the Mysteries of Modern Science [2000] -- John Casti

# The Essence of Chaos [1993] -- Edward N. Lorenz

# Thinking in Complexity, The Complex Dynamics of Matter, Mind, and Mankind - 3rd Ed. [1997] -- Klaus Mainzer

# Gravitation and Cosmology, Proceedings of the ICGC Conference Held at IUCAA, Pune, India, in December 1995 [1995] -- Dhurandhar and Padmanabhan (eds.)

# The Social Meaning of Modern Biology, From Social Darwinism to Sociobiology [1986] -- Howard L. Kaye

# Origins of Life [1985] -- Freeman Dyson

# In Search of the Ultimate Building Blocks [1997] -- Gerard 't Hooft

# The Large, the Small and the Human Mind [1997] -- Roger Penrose

# The Structure of Scientific Revolutions [1962, 1970] -- Thomas S. Kuhn

# Beyond the Black Hole, Stephen Hawking's Universe [1985] -- John Boslough

# The Thermodynamics of Pizza, Essays on Science and Everyday Life [1991] -- Harold J. Morowitz

# Billions and Billions, Thoughts on Life and Death at the Brink of the Millenium [1997] -- Carl Sagan

# Beyond the Quantum Paradox [1994] -- Lazar Mayants

# Guns, Germs, and Steel, The Fates of Human Societies [1997] -- Jared Diamond

# Einstein, A Centenary Volume, [1979] -- A.P. French, ed.

# Science and Beyond [1986] -- Steven Rose and Lisa Appignanesi, eds.

# Science a la Mode, Physical Fashions and Fictions [1989] -- Tony Rothman

# Goodbye, Descartes, The End of Logic and the Search for a New Cosmology of the Mind [1997] --Keith Devlin

# The Runaway Universe, the Race to Find the Future of the Cosmos [2000] -- Donald Goldsmith

# General Relativity From A to B [1978] -- Robert Geroch

# Quantum Reality, Beyond the New Physics [1985] -- Nick Herbert

# The Flamingo's Smile, Reflections in Natural History [1985] -- Stephen Jay Gould

# Science, Computers, and People, From the Tree of Mathematics [1986] -- Stanislaw Ulam; Marc C. Reynolds, Gian-Carlo Rota, Eds.

# The Flight From Science and Reason, Annals of the New York Academy of Sciences, Vol 775 [1996] -- edited by Paul R. Gross, Norman Levitt, and Martin W. Lewis

# Doing Science, The Reality Club [1991] -- edited by John Brockman [not recommended]

# A Tour of the Calculus [1995] -- David Berlinski

# A Beautiful Mind, The Life of Mathematical Genius and Nobel Laureate John Nash [1998] -- Sylvia Nasar

# Euler, The Master of Us All [1999] -- William Dunham

# Thomas Kuhn: A Philosophical History for Our Times [2000] -- Steve Fuller

# The Fabric of the Cosmos; Space, Time, and the Texture of Reality [2004] -- Brian Greene

# The Life of the Cosmos [1997] -- Lee Smolin

# The Universe at Midnight, Observations Illuminating the Cosmos [2001] -- Ken Croswell

# Galaxies and Quasars [1979] -- William J. Kaufman

# Conflict in the Cosmos, Fred Hoyle's Life in Science [2005] -- Simon Mitton

# Big Bang, the origin of the universe [2004] -- by Simon Singh

# How The Universe Got Its Spots, Diary of a finite time in a finite space [2002] -- Janna Levin

# From Quarks to the Cosmos, Tools of Discovery [1995] -- Leon Lederman, David Schramm

# The Big Questions, Probing the promise and limits of science [2002] -- Richard Morris

# Alpha and Omega, The search for the beginning and end of the universe [2004] -- Charles Seife

# Supersymmetry, Unveiling the ultimate laws of nature [2000] -- Gordon Kane

# Black Holes and Time Warps, Einstein's Outrageous Legacy [1994] -- Kip Thorne

# The Universe, the 11th Dimension, and Everything, What we know and how we know it [1999] -- Richard Morris

# Faster, The Acceleration of Just about Everything [2000] -- James Gleick

# Before the Beginning, Our Universe and Others [1997] -- Martin Rees

# The Life of the Cosmos [1999] -- Lee Smolin

# The Cosmic Landscape String theory and the illusion of intelligent design [2006] -- Leonard Susskind

# Chasing Hubble's Shadows, The Search for Galaxies at the Edge of Time [2006] -- Jeff Kanipe

# Cosmic Clouds: Birth, death, and recycling in the galaxy [1997] -- James Kaler

# Many Worlds in One [2006] -- Alex Vilenkin

# Endless Universe, Beyond the Big Bang [2007] -- Paul Steinhardt and Neil Turok

# Origins: How the Planets, Stars, Galaxies, and the Universe Began [2006] -- by Stephen Eales

# Poetry of the Universe: A Mathematical Exploration of the Cosmos [1995] -- by Robert Osserman

# Extreme Stars, At the Edge of Creation [2001] -- by James Kaler



Add to that The Trouble With Physics by Lee Smolin and Madmen Dream of Turing Machines by astrophysicist Janna Levin.

I believe the misunderstanding about what we currently know when the universe was 10-43 seconds old is yours.

speedfreek
2008-Jun-10, 10:31 PM
(does that mean edges are back in with a shot?) :D

These shapes we are discussing don't have "edges" as such. You might try to visualise an expanding 4-dimensional hypersphere as having our 3D universe as its surface.

dcl
2008-Jun-11, 01:36 AM
Cougar: Here [in running the movie backward] your answer is incorrect. We can't get anywhere near 10^-43 sec. From my recent reading on the subject, many major names in the field all seem to agree on how the movie would rewind back to 1 second.

dcl: I suggest you broaden your reading. There are any number of respected sources that give that 10^-43 figure. That figure comes from the Standard Model of particle physics, not from accelerator experiments.

Cougar: Ha ha! Now that is truly funny. Would you like to peruse my Recent Reading list? I believe the misunderstanding about what we currently know [about] when the universe was 10^-43 seconds old is yours.

dcl: I note your long list of references, most of which appear to be either outdated or totally irrelevant to the question of how far back in time the history of the Universe has been traced via the Standard Model of particle physics. It suffices for me to cite just one reference to rebut your assertion that the movie can be rewound only to 1 second. On page 155 of James S. Trefil, "The Moment of creation", Macmillan, New York, 1983. You can find the following statement, quoted verbatim from page 155 of this book.:

. "We will call the period from 10^-43 second to 10^-35 second after the Big Bang the GUT, or Grand Unification Theory, era."

Trefil is a professor of physics at Stanford University. Perhaps you'd like to challenge him on that figure. His response should be even funnier than was yours to my earlier statement.

damian1727
2008-Jun-11, 02:12 AM
oooo come on guys lets not fall out over less than no time !!!

cougar i did not realize that there were so many books....

speed ... i am i want an edge :D

Cougar
2008-Jun-11, 03:02 AM
"We will call the period from 10^-43 second to 10^-35 second after the Big Bang the GUT, or Grand Unification Theory, era."

Being able to name something doesn't mean we know much about it. Please note that the GUT era is completely inaccessible to current particle accelerators, and though several GUTs have been proposed, there is little or no data to distinguish which is supportable.

The quote was:


...ran the movie backward as far as knowledge would allow....

We don't yet have "knowledge" of the state of the universe during the GUT era. Inflation (around 10-33) is looking pretty good, but even it is fairly far from a done deal.

dcl
2008-Jun-12, 12:17 AM
It's deductions from the Standard Model of particle physics, not accelerator data, that tell of what we think we know about conditions in the early Universe. I am not a particle physicist, so I am not qualified to judge how valid these deductions are, but when the community of particle physicists tells us that they are confident that theory has enabled them to extrapolate physical phenomena back to 10^-43 second, I'm inclined to accept their statements at least tentatively as well-founded. These statements are not made lightly: They are not published in reputable journals until other physicists up to date on the latest findings endorse them through the peer review process. I cited only one place where the 10^-43 second figure for the beginning of the GUT era can be found. I've seen it in a number of different publications.

dcl
2008-Jun-12, 02:31 AM
speedfreek: Your reference to the Poincare conjecture induced me to Google it to find out what it claims. I had of course heard of it earlier but had never managed to find out what it claimed, even after it had made a big splash in the news several years ago on finally being proven. I had supposed it to be an abstract idea in pure mathematics of no immediate interest to cosmologists.

The same seemed to apply to the supposed relevance of the dodecahedron to cosmology. From the reference you cited, I learned that the conceivable relevance of the dodecahedron is the same as for the 3-torus when parallel faces or the former are "glued" in the topological sense. I still feel that the glued dodecahedron, like the 3-torus, is too implausible to be taken seriously as a possible model for the Universe.

speedfreek
2008-Jun-12, 05:23 PM
Well sometime around 2003 we found what looked like a repeating pattern in WMAP data that indicated that the universe might be shaped like a Poincare dodecahedral space, which is why we were investigating these models. There was some observational evidence of a non-trivial topology that required further investigation and that investigation isn't finished yet.

If you were in charge, would you have said the shape is too implausible to investigate, bearing in mind that we already had some data that seemed to indicate that shape?

Cougar
2008-Jun-12, 06:05 PM
...when the community of particle physicists tells us that they are confident that theory has enabled them to extrapolate physical phenomena back to 10^-43 second, I'm inclined to accept their statements at least tentatively as well-founded.

I don't believe any particle physicist has said that, certainly not confidently. 10-43 is the Planck Time. (Actually, it's 5.39 x 10-44.) It is supposedly a barrier beyond which measurement cannot go, even in principle.

See Timeline of the Big Bang (http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang). Note the caveat at the beginning of the section on the very early universe:



All ideas concerning the very early universe (cosmogony) are necessarily speculative. As of today no accelerator experiments probe energies of sufficient magnitude to provide any insight into the period. All proposed scenarios differ radically, some examples being: the Hartle-Hawking initial state, string landscape, brane inflation, string gas cosmology, and the ekpyrotic universe.

dcl
2008-Jun-12, 08:11 PM
In the following, I quote speedfreek and Cougar and comment on their comments: The first paragraph by one of us is preceded by that person's pseudonym. Succeeding paragraphs by the same person are not so labeled.

speedfreek: Well sometime around 2003 we found what looked like a repeating pattern in WMAP data that indicated that the universe might be shaped like a Poincare dodecahedral space, which is why we were investigating these models. There was some observational evidence of a non-trivial topology that required further investigation and that investigation isn't finished yet.

If you were in charge, would you have said the shape is too implausible to investigate, bearing in mind that we already had some data that seemed to indicate that shape?

dcl: Without meaning to be derogatory in any way, I'm interested in knowing whether by "we" you mean a research group of which you are a member. If so, I am impressed and hope to learn from you. Can you refer me to a description of what was found in 2003 that would be accessible on the Internet? Alternatively, can you summarize briefly what was found? What group is or was doing this investigation?

Cougar: I don't believe any particle physicist has said that, certainly not confidently. 10-43 is the Planck Time. (Actually, it's 5.39 x 10-44.) It is supposedly a barrier beyond which measurement cannot go, even in principle.

See http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang Note the caveat at the beginning of the section on the very early universe:

"All ideas concerning the very early universe (cosmogony) are necessarily speculative. As of today no accelerator experiments probe energies of sufficient magnitude to provide any insight into the period. All proposed scenarios differ radically, some examples being: the Hartle-Hawking initial state, string landscape, brane inflation, string gas cosmology, and the ekpyrotic universe."

dcl: I've seen the equivalent of that statement and number in a large enough number of different sources that I've assumed, possibly erroneously, that it was factual. I'd appreciate your citing statements to the contrary if you can.

I appreciate your referring me to the Wikipedia article you cited. Incidentally, it gives 10 exp -43 second not as the Planck era but as the end of the Planck era. It gives the interval starting at 10 exp -43 second and ending at 10 exp -36 second as the Grand Unification Era.

speedfreek
2008-Jun-12, 08:50 PM
dcl: Without meaning to be derogatory in any way, I'm interested in knowing whether by "we" you mean a research group of which you are a member. If so, I am impressed and hope to learn from you. Can you refer me to a description of what was found in 2003 that would be accessible on the Internet? Alternatively, can you summarize briefly what was found? What group is or was doing this investigation?

No, I mean we as in the human race! :lol: Sorry if it misled you, I often write that way when the subject is about scientific discoveries - "We have discovered a new planet", "We think the universe is 13.7 billion years old" etc.

This is the original story - Is the universe a dodecahedron? (http://physicsworld.com/cws/article/news/18368)

And the paper that followed the original story -
A Hint of Poincaré Dodecahedral Topology in the WMAP First Year Sky Map (http://arxiv.org/abs/astro-ph/0402608)

A research group then pursued the issue but they found no evidence for any non-trivial topology across a diameter of 78 billion light years (24 Gigaparsecs) and so we can confidently state that the fundamental domain of the whole universe is at least that large. These figures are based on the WMAP data representing a sphere around us that has now grown to 46 billion light years in radius (92 billion light years diameter). They intend to continue the search until they have reached ~28 Gigaparsecs. They have discounted the dodecahedral model as the universe would have had to have had a fundamental domain only 30 billion light years across for that to work.

This is the paper with their findings - Extending the WMAP Bound on the Size of the Universe. (http://arxiv.org/abs/astro-ph/0604616)

I actually agree with you about the universe probably being a hypersphere but if the fundamental domain of the universe is indeed larger than our observable portion of it, as seems likely, we will never know for sure. If the fundamental domain were smaller however (and that is a possibility), we might find evidence that allows us to determine the overall topology. (See I'm doing the we thing again - I just fall into it naturally!)

Until they have finished the study, I wouldn't want to commit myself either way, even if I thought the most plausible shape was an S3 hypersphere. The reason is simple - if they find no evidence for a non-trivial topology at all then the whole universe must be larger than our observable portion of it. The topology will therefore always be subject to speculation.

dcl
2008-Jun-13, 02:37 PM
Thank you, speedfreek, for your references. The article cited in the following is from one of them.

--------

"We use optimal filtering and the combination statistic to rule out the infamous 'soccer ball universe
model'"

This statement is quoted directly from the last sentence in the abstract for the article entitled "Extending the WMAP Bound on the Size of the Universe" by Joey Shapiro Key, Neil J. Cornish, David N. Spergel, and Glenn D. Starkman, submitted in Apr 2006, downloadable from http://arxiv.org/abs/astro-ph/0604616).

Until this article is withdrawn by the authors or its substance refuted by other articles, I'd think it should stop speculation about the Universe's having the geometry of a dodecahedron with opposite faces "glued" in the topological sense, which had impressed me from the first time I heard of it as too improbable to be taken seriously. I see the possibility of Universe's having the geometry of either a 3-torus or Dr. Gay's doughnut as equally improbable. I'm not at all convinced that the Universe has the geometry of a four-dimensional hypersphere either, but I've tried unsuccessfully to find any plausible argument for rejecting it and find that it seems to readily provide plausible answers to every question I've been able to come up with..

If anyone can provide a plausible argument against the four-dimensional hypersphere Universe, I'd like to be told of it. It envisages the Universe as having originated at a point or at least within an extremely small three-dimensional volume at the center of a four-dimensional hypersphere the three-dimensional "surface" of which is the curved and finite expanding three-dimensional Universe that we seem to find ourselves in.

I feel that people are too quick to jump on the infinite flat Universe model that people have read into the WMAP data. As I see it, WMAP has thus far found the Universe so nearly flat as to be unable to detect any curvature, allowing people to jump to the unwarranted conclusion that the Universe is precisely flat and infinite.

I'd like to consider any plausible models for which others would argue.

speedfreek
2008-Jun-13, 06:23 PM
Yes, as I said in my above post they have discounted the "soccer ball universe" (dodecahedral space) as the fundamental domain seems too large to allow it. They have not so far been able to totally discount other non-trivial topologies.

My original point was that it seems to me if it were up to you they shouldn't have even been following up possible evidence of the dodecahedral model as you deem that model implausible and preposterous and I am wondering if that is good science or not.

That paper also states that they have only found space to be within 2% of being flat, so there may indeed be large scale curvature but the radius of that curvature would be larger than our observable universe.

The paper below may interest you - it examines and eliminates some other non-trivial topologies but concludes that although we still have no evidence for a non-trivial topology, we still cannot discount it. However, the best fit to the data is the flat, simply-connected Lambda-CDM model.

Imprints of spherical non-trivial topologies on the CMB (http://arxiv.org/abs/astro-ph/0702436)

dcl
2008-Jun-14, 12:59 AM
I would want to eliminate the simplest possibilities before turning to more complex ones.

speedfreek
2008-Jun-14, 10:30 AM
Unfortunately, it seems that the simplest possibilities are the hardest to eliminate.

If we never find enough evidence to confidently state the shape of the universe, but along the way we find hints for some of the less simple topologies, are you saying that we shouldn't investigate these, if not just so that we can eliminate them? This is what we (humans!) have been doing.

dcl
2008-Jun-14, 09:13 PM
speedfreek, I think your thinking is sound, and I have no problem with it. In particular, I have no problem with people wanting to test hypothetical models for shape of the Universe that can be eliminated or confirmed as plausible only through a reasonable amount of testing. If they test those models and find persuasive evidence for their validity, the effort will have been justified. If the effort fails, the onus will be on them and the sponsors of their research to justify the cost, time, and manhours spent on the effort that might have been expended on some other research. I would not deny them the right to test their ideas, no matter how outlandish they seem to me.

I'm saying only that all of the models of the Universe that I am aware of as having been proposed other than the four-dimensional hypersphere that I and presumably others have proposed impress me as being so improbable that I myself dismiss them out of hand, but I have no problem with others who feel differently looking for evidence to support their models.

As for what constitutes good science, I'll leave that to others to say. If people want to invest time, effort, and money on studies that seem to others to be destined to produce negative results, I say let them go ahead if those with the money to fund the effort are willing to provide the money. If they fail, they will at least have provided an answer to a question.

As for the glued dodecahedron model, I would have been most astonished if convincing evidence had been found for it.