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Author Topic: Big Bang & depiction of universe - two part question  (Read 10603 times)

Offline Merccooper

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I'm sure this has been asked, but searching for the answer has proven difficult.
First part:
If the Big Bang theory is true, why can we not say the universe is spherical?

Second part:
Why, in relation to the Big Bang, is the universe depicted in a cone shape (as attached) and not some other shape?





 

Offline JohnDuffield

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Re: Big Bang & depiction of universe - two part question
« Reply #1 on: 07/02/2015 17:52:01 »
If the Big Bang theory is true, why can we not say the universe is spherical?
I think we can. See this article where cosmologist Neil Cornish claims that the universe is at least 156billion light years wide. See this bit:

"It can be thought of as a spherical diameter is the usual sense," Cornish added comfortingly. (You might have heard the universe is almost surely flat, not spherical. The flatness refers to its geometry being "normal," like what is taught in school; two parallel lines can never cross.)"

Why, in relation to the Big Bang, is the universe depicted in a cone shape (as attached) and not some other shape?
I don't know. I suppose they've dropped one dimension such that the physical shape of the universe is circular, then they're showing how it gets bigger over time from left to right.
 

Offline PmbPhy

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Re: Big Bang & depiction of universe - two part question
« Reply #2 on: 08/02/2015 18:09:50 »
I'm sure this has been asked, but searching for the answer has proven difficult.
First part:
If the Big Bang theory is true, why can we not say the universe is spherical?

Second part:
Why, in relation to the Big Bang, is the universe depicted in a cone shape (as attached) and not some other shape?

The reason these kinds of questions don't get answered is because it's apparent from the question that the person asking it won't understand the answer. The questions which thus follow  become harder and harder to answer due to the lack of understanding of the physics.

For example: The universe can't be spherical because when the matter distribution is placed into Einstein's field equations the result yields various solutions, none of them being spherical. How could anybody, in words, explain why a certain solution to Einstein's field equation be as it is? Especially since it's well known as being the hardest equation to solve in all of the laws of classical physics!


If the mass density is too small then the universe will be closed meaning that a path leading off in one direction ends up coming back to where it started, regardless of the direction. If the mass density is too large then those paths go off into infinity and never come back. In that case the universe is infinite in size.
 

Offline Bill S

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Re: Big Bang & depiction of universe - two part question
« Reply #3 on: 08/02/2015 19:01:47 »
Quote from: Pete
For example: The universe can't be spherical because when the matter distribution is placed into Einstein's field equations the result yields various solutions, none of them being spherical.

Is it possible that confusion could arise because of a distinction between geometry and topology when talking about the shape of the Universe?
 

Offline Merccooper

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Re: Big Bang & depiction of universe - two part question
« Reply #4 on: 08/02/2015 23:56:53 »
Thanks for that input John.

PmbPhy, I'm sorry if I have wasted your time and bits of data by showing my lack of in-depth knowledge of Einstein's field equations asking that question. I thought this site's purpose was, in part to, "....help the general public to understand and engage with the worlds of science, technology and medicine". Am i wrong about that?
So, my question now is, if the universe can not be spherical, what is it?
 

Offline PmbPhy

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Re: Big Bang & depiction of universe - two part question
« Reply #5 on: 09/02/2015 03:05:02 »
Quote from: Merccooper
PmbPhy, I'm sorry if I have wasted your time....
I never suggested that you wasted my time. I was merely explaining the reason why questions like this don't get many answers.

Quote from: Merccooper
and bits of data by showing my lack of in-depth knowledge of Einstein's field equations asking that question.
I understand. I'm assuming that you came here to learn that stuff.

Quote from: Merccooper
I thought this site's purpose was, in part to, "....help the general public to understand and engage with the worlds of science, technology and medicine".
That's quite correct.

Quote from: Merccooper
Am i wrong about that?
No. In fact I answered your question and explained why the answer would be difficult to understand.

Quote from: Merccooper
So, my question now is, if the universe can not be spherical, what is it?
The best description of the universe that we have today is that it's flat, i.e. like a plane.

I'm sorry that you got a wrong impression from my response.
 

Offline JohnDuffield

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Re: Big Bang & depiction of universe - two part question
« Reply #6 on: 09/02/2015 14:18:59 »
The best description of the universe that we have today is that it's flat, i.e. like a plane.
With respect Pete, that's wrong. See this article where cosmologist Neil Cornish was saying he thought the universe was at least 156billion light years wide:

"It can be thought of as a spherical diameter is the usual sense," Cornish added comfortingly. (You might have heard the universe is almost surely flat, not spherical. The flatness refers to its geometry being "normal," like what is taught in school; two parallel lines can never cross.)"

A spherical universe is a "flat"universe if parallel light beams stay parallel and go straight. As for what happens if you try shining those light beams 78 billion light years from here, I don't know.   
 

Offline yor_on

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Re: Big Bang & depiction of universe - two part question
« Reply #7 on: 09/02/2015 16:05:38 »
Nah Pete, a perfectly good answer. And Mer :)
Don't get too prickly about it, sometimes the answers need a redefinition of the question.
That's just another way of getting it right.
 

Offline yor_on

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Re: Big Bang & depiction of universe - two part question
« Reply #8 on: 09/02/2015 16:09:10 »
And John :)
No such thing as your spherical universe, unless you refer to the 'light sphere' we observe from here? Assuming there was though, one now will have to explain why there is no 'edge'.

However one try to do that, it's not simple. Physics always go for the simplest definition possible.
 

Offline yor_on

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Re: Big Bang & depiction of universe - two part question
« Reply #9 on: 09/02/2015 16:13:25 »
Lookiong at his definition, I would call it 'pop science', good enough for CNN and Fox possibly?
 

Offline yor_on

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Re: Big Bang & depiction of universe - two part question
« Reply #10 on: 09/02/2015 16:20:31 »
As for number one Mer.
"If the Big Bang theory is true, why can we not say the universe is spherical?"

That one is best explained by thinking two dimensionally about it. Using the surface of a inflatable balloon. the beginning is 'no balloon' but as soon as you find your surface the 'inflation' starts 'everywhere on it'. The balloon, looked on that way, also becomes a representation of a later expansion. If there is no defined 'origin', how can you get to your 'balloon', you may ask? :) Well, you can't, but it's the definition that fits best, just the same.
=


There is a alternative way though, to think about it, naively. Imagine it as a mathematical space, not a geometrical nota bene. In that 'space' you find 'points' that's 'disconnected', as defined from us. When they start to 'connect' you will get your inflation, and expansion, and 'space' as in 'universe', assuming it to happen 'simultaneously'. To make it happen you need one more thing, a local arrow, that also are a local constant, namely 'c'. They all need that one, equivalently. And it needs its equivalence, to create those 'repeatable experiments' we define physics from.
« Last Edit: 09/02/2015 16:35:13 by yor_on »
 

Offline Bill S

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Re: Big Bang & depiction of universe - two part question
« Reply #11 on: 09/02/2015 18:50:45 »
Hi Merccooper, welcome.

I have to say that Pete can come across as a bit curmudgeonly at times, but tap into the patience Ė itís there.  Donít be put off posting questions.  Iíve sampled a few science discussion forums and this is the best I have found.

As is well known in this forum, I am not a scientist, and am inclined to try the patience of experts by persistently working at problems until I feel at least reasonably happy that either I have grasped the solution, or that I never will.  (The latter is rare, but thatís just conceit.)

Like so many things in science, talking about the shape of the Universe is not intuitively straightforward.  Cosmologists tend to link the shape to the density/critical density ratio.  In order for a cosmologist to accept that the Universe was spherical, it would have to be established that the density was greater than the critical density.  That seems to be the scientific definition of a spherical universe; itís certainly the image that goes with the ďopen/closed/flat universe scenario.

By the same token, a flat universe is depicted as a flat rectangular shape.  I doubt that we are expected to believe that the physical universe has right-angled corners, so defined shape may not always be the same as actual shape.  We also have to remember that these images are analogies.  Sometimes we non-scientists have to put our intuitive thoughts on the back burner and just try to understand what the experts are saying. 

Donít get rid of those intuitive thoughts completely, though; they might come into fashion (again) one day.   :)
 

Offline JohnDuffield

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Re: Big Bang & depiction of universe - two part question
« Reply #12 on: 09/02/2015 21:17:33 »
I think it's important to point out that "the shape of the universe" can be very misleading. If you take a look at the Wikipedia article of that name, you can see this picture:



However it isn't depicting the shape of the universe at all. It's depicting the geometry via "two-dimensional surfaces". The "flat" universe is the third of the shapes above, but don't think the universe is shaped like a flat board. It isn't two-dimensional, it's three-dimensional. And note that the simplest three-dimensional shape you can come up with is spherical.

Like so many things in science, talking about the shape of the Universe is not intuitively straightforward.
I think it is. To be honest, I don't know why anybody ever entertains the first two options above. On the large scale space is homogeneous and isotropic. And if space is like this, light moving through it doesn't curve. Einstein said as much in his Leyden Address, but he didn't apply this to cosmology. When it comes to cosmology it was as if he totally lost his usual confidence in his own theory. IMHO it's rather strange, and maybe it's related to the fact that he didn't achieve much after about 1920. One guy I was talking to said it was as if he'd had a stroke or a breakdown or something.
« Last Edit: 09/02/2015 21:34:14 by JohnDuffield »
 

Offline Merccooper

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Re: Big Bang & depiction of universe - two part question
« Reply #13 on: 09/02/2015 22:13:41 »
Thank you for your encouragement Bill. I enjoy thinking about and reading about various aspects of science. The universe and gravity have always kept my attention. Then, by chance, I read some articles about quantum physics and was amazed about Heisenbergís uncertainty principle and other aspects of quantum physics. I know I will never have the mathematical smarts to even come close to understanding these things from that aspect, but was hoping to talk about them in more basic terms. My wife and kids roll their eyes when I want to talk about these subjects, which is why I turned to the naked scientists.

Anyhow, that aside, I apologize to Pete that I have taken is input out of context.

Now, that aside, Iíve read about the balloon analogy before but will hold my questions until I put more thought into it. I also found an article about Einsteinís Equations that suggests to explain his equations in ďplain EnglishĒ. I say this with a smile as even this has why too much math for me! But, Iím going to try and absorb some of it. Here is the article: newbielink:http://math.ucr.edu/home/baez/einstein/ [nonactive]

At the risk of asking a poor question, to what extent has it be proven that light beams traveling through space do not 'ever' curve? I assume 'ever curve' implies without the influences of gravity from massive objects. (I just read John's post so have not yet had the chance to "research" it, so if it isn't a valid question, feel free to ignore).



 

Offline jccc

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Re: Big Bang & depiction of universe - two part question
« Reply #14 on: 09/02/2015 23:14:08 »
I second to Bill. This is the best science forum I found.

My thought, the space/universe we can detected today, maybe just a sand on the beach.
 

Offline JohnDuffield

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Re: Big Bang & depiction of universe - two part question
« Reply #15 on: 09/02/2015 23:18:38 »
Merc: I think most cosmologists are happy that space is "flat" such that light doesn't curve. WMAP demonstrated this, see for example this article. It gives the illustration as above, and says this:

"The WMAP spacecraft can measure the basic parameters of the Big Bang theory including the geometry of the universe. If the universe were flat, the brightest microwave background fluctuations (or "spots") would be about one degree across. If the universe were open, the spots would be less than one degree across. If the universe were closed, the brightest spots would be greater than one degree across. Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error."

All that is fairly reasonable, and is backed up by the Planck mission. However the next bit of the WMAP article isn't reasonable:

"This suggests that the Universe is infinite in extent; however, since the Universe has a finite age, we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe."

This is a non-sequitur. A flat universe does not suggest that the universe is infinite in extent. We cannot truly conclude is that the universe is much larger than the volume we can directly observe. If anybody says we can, ask them to explain this conclusion. They will not be able to.
 

Offline Bill S

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Re: Big Bang & depiction of universe - two part question
« Reply #16 on: 09/02/2015 23:51:59 »
Quote from: John
A flat universe does not suggest that the universe is infinite in extent.

It risk of seeming like a stuck record, I would think it quite reasonable to consider that a flat universe would be unbounded, but not necessarily infinite.  Is that too nice a distinction? 
 

Offline yor_on

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Re: Big Bang & depiction of universe - two part question
« Reply #17 on: 10/02/2015 10:40:15 »
I'm with you too there John. Myself I think of it as undefinable, meaning that whatever size we would like to put to it will be found wrong. It's 'dynamically existing' in my thoughts, using 'c'. But the 'light sphere' existing will be there wherever I go, defining a envelope of time.
 

Offline JohnDuffield

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Re: Big Bang & depiction of universe - two part question
« Reply #18 on: 10/02/2015 11:11:16 »
It risk of seeming like a stuck record, I would think it quite reasonable to consider that a flat universe would be unbounded, but not necessarily infinite. Is that too nice a distinction?
IMHO it's perfectly reasonable to consider anything. That's kind of my point, the "infinite universe" non-sequitur arises because people are asserting things without considering the alternatives.

Quote from: yor_on
I'm with you too there John. Myself I think of it as undefinable, meaning that whatever size we would like to put to it will be found wrong. It's 'dynamically existing' in my thoughts, using 'c'. But the 'light sphere' existing will be there wherever I go, defining a envelope of time.
And if we could take a snapshot of the universe as it exists now? What shape is it? Since it's space expanding, how can it be expanding into anything? What would you see if you were 76 billion light years away from here? A black half to the sky? One half of the sky looking like a mirror image of the other? None of the above? It's interesting stuff, far more interesting than the "infinite universe" non-answer that just doesn't square with big-bang cosmology.
 

Offline phyti39

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Re: Big Bang & depiction of universe - two part question
« Reply #19 on: 10/02/2015 20:23:06 »
The pictures from the Hubble telescope show composite objects in any selected direction, which would seem to indicate a 3D volume for the universe. In addition to the CMB analysis, if space is not approx. flat or euclidean, we would not have the those detailed photos. The resolution would deteriorate over many lightyears.
 

Offline jeffreyH

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Re: Big Bang & depiction of universe - two part question
« Reply #20 on: 10/02/2015 20:57:08 »
If spacetime is not flat due to gravity and space is flat then it is not spacetime that is being affected. Space is part of spacetime, it can't exist without both space and time. For time we have experimental evidence that it isn't 'flat' although flat is not a good term for time. We do not have evidence of space contraction. Length contraction is more an effect on mass. If we measure 1 metre what are we actually measuring? We usually measure objects. You wouldn't normally show someone a metre of empty space. Some of the concepts have to be thought of as conveniences that are used because they work out in the equations. We never properly describe a phenomena in all its aspects as that is far too complex an exercise.
 

Offline Bill S

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Re: Big Bang & depiction of universe - two part question
« Reply #21 on: 10/02/2015 22:21:13 »
Quote from: Jeffrey
Length contraction is more an effect on mass. If we measure 1 metre what are we actually measuring? We usually measure objects. You wouldn't normally show someone a metre of empty space.

That's an interesting point. Jeffrey.  If we consider an object that is 1m long, it occupies 1m of space.  if the object is subjected to length contraction, does the space it occupies contract as well?  It would seem logical to assume it would, but how could we tell, one way or the other? 
 

Offline JohnDuffield

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Re: Big Bang & depiction of universe - two part question
« Reply #22 on: 10/02/2015 23:13:00 »
If spacetime is not flat due to gravity and space is flat then it is not spacetime that is being affected. Space is part of spacetime
I'm afraid it isn't. Space is space. Spacetime is a mathematical abstraction in which there is no motion. You can draw worldlines in it to depict motion through space over time, but it models an "all times at once" block universe. So it's static. So you cannot move through it. You move through space, and when you change your state of motion, your measurements of distance and time change. And how did you make these measurements? Using light, moving through space.

Quote from: Bill S
That's an interesting point. Jeffrey. If we consider an object that is 1m long, it occupies 1m of space. If the object is subjected to length contraction, does the space it occupies contract as well?
No, because the object is moving through space. Besides, length contraction is a can of worms. If you accelerate such that you see everything length-contracted to half its former length, what do you think changed? Everything? Or you?
 

Offline jeffreyH

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Re: Big Bang & depiction of universe - two part question
« Reply #23 on: 11/02/2015 01:14:45 »
If spacetime is not flat due to gravity and space is flat then it is not spacetime that is being affected. Space is part of spacetime
I'm afraid it isn't. Space is space. Spacetime is a mathematical abstraction in which there is no motion. You can draw worldlines in it to depict motion through space over time, but it models an "all times at once" block universe. So it's static. So you cannot move through it. You move through space, and when you change your state of motion, your measurements of distance and time change. And how did you make these measurements? Using light, moving through space.

Why would you make measurements using light? You can use the speed of light as a reference point but this tells you nothing about the spacetime in your own frame of reference. It looks like any other frame you have passed through. Light speed is a very bad indicator. The shifting of the wavelength of light can tell you what the state of a remote frame may be but that is inferred from the assumed behavior of light.

Quote from: Bill S
That's an interesting point. Jeffrey. If we consider an object that is 1m long, it occupies 1m of space. If the object is subjected to length contraction, does the space it occupies contract as well?
No, because the object is moving through space. Besides, length contraction is a can of worms. If you accelerate such that you see everything length-contracted to half its former length, what do you think changed? Everything? Or you?

Define space. In the vacuum there is an energy present so can that be described as space. Like time, space is a concept we have developed to aid us in understanding the physical world. When we talk about empty space what do we mean? A void? If space is empty of everything then that is what it must be considered to be. As for a static spacetime, that can't be true when considering massive bodies moving through the coordinates of the system. The nature of the spacetime events change the nature of the spacetime.
 

Offline JohnDuffield

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Re: Big Bang & depiction of universe - two part question
« Reply #24 on: 11/02/2015 13:42:16 »
Why would you make measurements using light?
Because it's "the most fundamental" way of doing it, and it's what you do in practice. The most accurate clocks are optical clocks, and you measure distance using radar. The electromagnetic waves pinging  back and forth are light in the wider sense. 

You can use the speed of light as a reference point but this tells you nothing about the spacetime in your own frame of reference. It looks like any other frame you have passed through. Light speed is a very bad indicator. The shifting of the wavelength of light can tell you what the state of a remote frame may be but that is inferred from the assumed behavior of light.
Your own frame of reference is little more than your state of motion. A reference frame is not something that exists in its own right.

Define space. In the vacuum there is an energy present so can that be described as space.
Yes, in some respects energy and space seem to be the same thing. But it's difficult to define them. Light is essentially E=hf waves in space, and we can make matter out of light. So you could say matter is made of waves in space. But what do you say space is? It isn't made out of matter or waves. Instead those things are made of it.

Like time, space is a concept we have developed to aid us in understanding the physical world. When we talk about empty space what do we mean? A void? If space is empty of everything then that is what it must be considered to be.
No, it isn't a void. It's a something. Read Einstein's Leyden Address where he describes space as a thing that can have a state: "This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that "empty space" in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gmn), has, I think, finally disposed of the view that space is physically empty."

As for a static spacetime, that can't be true when considering massive bodies moving through the coordinates of the system. The nature of the spacetime events change the nature of the spacetime.
It's true Jeffrey. Pay attention to Einstein's use of the words space and spacetime. He didn't confuse the two, but some people do. They forget that spacetime is not something you can move through. Have a google on no motion in spacetime. I'm afraid some of the links are where I say it, but plenty are where somebody else is saying it.   
« Last Edit: 11/02/2015 13:43:54 by JohnDuffield »
 

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Re: Big Bang & depiction of universe - two part question
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