Big Bang Expansion: Is There A Centre Of The Universe?

[GreatScot]

If the Big Bang was really a big expansion and if the universe is still expanding, then surely that implies a central point from which it expanded from, right? I've read that there is no centre, how is that possible if the universe came from a single expansion?

 

[DrClaude]

There is a FAQ on the subject: https://www.physicsforums.com/showthread.php?t=506991

 

[fsujoseph]

First post! Anyways, how I understand it goes like this: if the Universe is infinite in all directions then any point in the Universe would be the center. If it's not infinite, then I suppose there is a defined 'center'.

 

[bapowell]

First post! Anyways, how I understand it goes like this: if the Universe is infinite in all directions then any point in the Universe would be the center. If it's not infinite, then I suppose there is a defined 'center'.

Not necessarily. Imagine the surface of a sphere: where's the center? If the universe is finite and closed, then it can be considered the 3-dimensional surface of a 3-sphere and therefore has no center.

 

[fsujoseph]

Not necessarily. Imagine the surface of a sphere: where's the center? If the universe is finite and closed, then it can be considered the 3-dimensional surface of a 3-sphere and therefore has no center.

Yeah that's true. And if space is expanding unevenly then that would be true. If it was finite, it probably would have to be a perfect sphere or whatever you want to call it. (to have a center)

 

[phinds]

If the Big Bang was really a big expansion and if the universe is still expanding, then surely that implies a central point from which it expanded from, right? I've read that there is no centre, how is that possible if the universe came from a single expansion?

As has been pointed out, this is a very serious misunderstanding of cosmology. I would add that it is a very COMMON misunderstanding, abetted by pop-science TV shows.

I recommend the link in my signature.

 

[JeremyPeel]

how i understand it is that everywhere was in the "center" all at the same time

 

[Drakkith]

how i understand it is that everywhere was in the "center" all at the same time

As far as we know, there is no center and there never was.

 

[Mordred]

along with the 2 articles mentioned above, the FAQ and Phind's balloon analogy in his signature I recommend the four articles in this related and recent post.

https://www.physicsforums.com/showthread.php?t=736246#post4649459

 

[aboro]

As has been pointed out, this is a very serious misunderstanding of cosmology. I would add that it is a very COMMON misunderstanding, abetted by pop-science TV shows.

I recommend the link in my signature.

Phinds, unfortunately for the profession of cosmology and to the surprise and disappoint of many layman, like me, it appears that cosmologists themselves are responsible for the "misunderstanding' by misdescribing cosmological events such as the Big Bang and the Singularity.

For example, just several weeks ago, a television special was aired on PBS concerning the life of Stephen Hawking. There, Hawking himself described the origin of the Universe as the result of an "explosion."!

He earlier described the Singularity as a tiny black hole that exploded to become the Universe.

Both descriptions are wrong, misleading, confusing and insulting as the cosmologists (including physics professors) assume that the layman-listener does not have the mental capacity to understand, in layman, non-mathematical terms, the emerging cosmological principles that were unknown to science until just recently.

Albert Einstein once said that "physics can be taught to a barmaid." In saying this, he was merely pointing out that his theories of relativity and other physical laws and theories, while complex subjects, are and should be capable of being taught to the layman if the person doing the teaching knows how to teach.

It is too bad that many cosmologists are not teachers.

 

[phinds]

It is too bad that many cosmologists are not teachers.

Sadly, even some of those who ARE teachers are known to have made insultingly dumbed-down (and blatantly incorrect) statements on pop-science TV shows. It seems to be part of their contract that in order to get paid they have to say at least one thing that they know to be incredibly stupid.

 

[glappkaeft]

It could be a case of them just reading what's in the script.

 

[bahamagreen]

Very sorry to report that it is still happening, today, even in unscripted presentations.
I watched the youtube of the big evolution debate the other night between Bill Nye and Ken Ham. This was 2 hours and 45 minutes; plenty of time to get things right and not gloss over a point or two with misconceptions, and yet...

Bill Nye ("the science guy") argued that since the universe is moving apart, it can be traced back to a single point (rather than the expansion occurring at all places and there being to single point). 1:21:25 in video
He also presented the expansion as the observasion that stars are moving apart (rather than distant galaxies, clusters, super clusters, etc.) 1:20:55 in video

This was very disturbing to me, as he should know better; he even mentioned that his teacher was Carl Sagan.

video is at youtube -

 

[aboro]

Very sorry to report that it is still happening, today, even in unscripted presentations.

I find this incredible and unacceptable! I do not understand why cosmologists, including Stephen Hawking, are making misleading statements in describing events like "the Big Bang" -- when our science is presently telling us that the Universe did not begin with an explosion of some sort or 'Singularity" -- when our science is presently telling us that the Universe did not have a centrally located "dot" which one day hemorrhaged and is so doing, the Universe came into existence.

I know that there are many in this forum who understand and teach cosmology and who patiently respond to posts made by layman like the one that is the subject of this thread. What I do NOT understand is how those who are in the profession of cosmology allow others in the profession to make representations that apparently not even those in the profession know to be true.

Why are these cosmologists doing this? Why is Stephen Hawking allowing the profession of cosmology, in general, and himself, in particular, to be cheapened and denigrated by saying things publicly which he knows to be untrue?? Why is he (and others in his profession) acting in such a condescending manner by assuming that it is beyond the ability of a layman to understand matters relating to the origin of the Universe except through the use of knowingly false and misleading statements??

 

[bahamagreen]

I have watched a lot of videos of Feynman and he always tried very carefully to not mislead his audiences or leave out critical details... and when he had to do so for the sake of the audience or students, he always said so and "drew the line" for them explicitly identifying the "slightly incorrect or incomplete" parts so they would not be misled, so they would know just what part of the explanation or demonstration had been "simplified" or "adapted" to their level of understanding.

 

[Mordred]

In many cases, when one tries to describe this or that aspect in cosmology. One either has to describe it using the math's involved or resort to use of an analogy. The maths would lose an audience rather quick, so the analogy method is usually used. Unfortunately every analogy is subject to misinterpretation. Unfortunately most programs do not take the time to point out those perils in their analogy usage. For one pointing them out could quickly get boring for viewers, one could spend a full hour covering the misconceptions involved with the balloon analogy as one example. lol

In media, most viewers are more interested in the quick and dirty explanations, as opposed to the nitty gritty details. That juggling act between ratings and accuracy is one major factor in why media cosmologists say what they do.

but take heart, the media method gains interest in the field of cosmology. This encourages more students to take up the field. Not to mention coming here for better clarity

 

[CCWilson]

The big bang was indeed an explosion - an explosion of spacetime. This concept isn't something that most lay people are going to understand. In fact, I suspect most of us can't visualize it either, and can only use the balloon analogy to sort of get it. Getting some of the public to at least know that at one time everything was compressed and then expanded dramatically - that's progress. Let's not knock people who simplify things a bit but get at least some of the idea across rather than make it totally incomprehensible by insisting that they have a full understanding or bust.

 

[bapowell]

Define "explosion"

 

[Drakkith]

The big bang was indeed an explosion - an explosion of spacetime.

I believe the general consensus, at least according to the guys here on PF who know much more than I do, is that we don't know what happened at the point in time that our math says a singularity occurred. We only know that the universe was once very dense and expanded from there.

 

[CCWilson]

One definition of explosion is a violent expansion. It's true that we can't know what happened exactly at the ?singularity but "explosion" seems appropriate if you're trying to get the concept across to non-scientists, and during and after inflation it was pretty rapid. Let's not be so literal. Just be happy that the lay public knows that the universe is expanding.

 

[Mordred]

One definition of explosion is a violent expansion. It's true that we can't know what happened exactly at the ?singularity but "explosion" seems appropriate if you're trying to get the concept across to non-scientists, and during and after inflation it was pretty rapid. Let's not be so literal. Just be happy that the lay public knows that the universe is expanding.

one problem with the word explosion is that it implies a central point of origin. In other words a preferred direction. Hence its often preferred to simply state a rapid expansion of space-time.

May sound nit picky, but after you answer as many questions as some of the older members have. You will quickly realize how misleading the term explosion is.

 

[bapowell]

I agree with a Mordred; the notion of explosion implies a localization of the initial expansion that is a fatal and sadly common misunderstanding of the Big Bang that persists stubbornly among laymen.

 

[phinds]

Very sorry to report that it is still happening, today, even in unscripted presentations.

I find this incredible and unacceptable!

...


Why are these cosmologists doing this?

In a word ... money.

 

[Flatland]

First post! Anyways, how I understand it goes like this: if the Universe is infinite in all directions then any point in the Universe would be the center. If it's not infinite, then I suppose there is a defined 'center'.

If the Universe is finite then it is closed and unbounded. In this case if you travel in 1 direction long enough you will eventually come back to your starting point and thus no center.

 

[Chronos]

I think the problem is cosmologists neglect to mention the 'size' of the BB is only relevant wrt the observable universe. It's an entirely natural assumption for a cosmologist, but, not so much for a layman.

 

[Chronos]

It would take so many billions of years to circumnavigate the universe, how would you ever know you returned to your staring point? Even if there were a 'center' it would impossible to locate.

 

[Adderall]

It would take so many billions of years to circumnavigate the universe, how would you ever know you returned to your staring point? Even if there were a 'center' it would impossible to locate.

I think the circumnavigation bit was meant to be a thought experiment that highlights that the universe (whether it's finite or not) can't have a center so we don't have to waste all that time you're referring to searching for the center.

 

[phinds]

I think the circumnavigation bit was meant to be a thought experiment that highlights that the universe (whether it's finite or not) can't have a center so we don't have to waste all that time you're referring to searching for the center.

Well put.

 

[aboro]

But all of this did not have a beginning in the form of an "explosion" or as a tiny dot (hence the use of the word "singularity"). The words "explosion" and "singularity" are entirely too misleading in describing what cosmologists think actually occurred and which we are witnessing today via the technology that is now available. Explosion implies a "center" where the so-called explosion had its origin. The Universe has no center. Too the contrary, every observer, no matter where located within the Universe, views himself as being at the center. That word also wrongly implies that there was once a time when objects were ejected from a center much like the bricks of a building became "ejected" as a result of a stick of dynamite exploding within the center of the building. It is also misleading to describe the beginning as being a "Singularity." Using that word implies that everything was once within the sphere of a tiny dot and that everything exploded out of that dot. What 'singularity" really means is that point in time beyond which our physical laws do not apply. Because our physical laws do not apply prior to that point in time, we are not able to say anything regarding what happened prior thereto. A witch doctor in Haiti apparently is just as qualified as Stephen Hawking in guessing what really happened.

It is regrettable that such misleading words have to be used in explaining things to a layman. We are not first graders. It is like a math teacher telling students in the 8th grade that the basics of math can be understood if you know the word 'addition."

 

[julcab12]

...We have data's suggesting that the universe is largely/almost flat > curvature. Integrating a euclidean solution (inclusion of very small curvature) in line with the data. We can say, that 'If' the Universe curves back and close on itself, its radius of curvature is at least many times as large as the part that’s observable to us.

With regards to center. Any discrete point selected anywhere of this universe is, by definition, an infinite distance from the (infinite)perimeter. Hence, 'every point' in an Observable universe can be thought of as its CENTER bec the one aspect of to be considered center is supposedly equidistant from every point on the proposed perimeter. Going back to Cosmology fact section https://www.physicsforums.com/showthread.php?t=506991 "Since realistic cosmological models are homogeneous, every point in space has the same properties as every other point, and therefore the models don't have a center."

 

[Bandersnatch]

It is also misleading to describe the beginning as being a "Singularity." Using that word implies that everything was once within the sphere of a tiny dot and that everything exploded out of that dot.

Does it really? I think it only has that connotation for most lay people, because the first and only time they've heard it before is when used to describe black holes, so they then imagine it being synonymous with something very small and dense.
Unlike with "explosion", it's a misunderstanding of the term by the listener, not a misrepresentation of facts. As such, I don't think it's wrong to use it, any more than it is wrong to call evolution a "theory", just because some people may think it means "unsupported speculation".
It would be great to properly explain an unfamiliar term when first introducing it, though.

 

[phinds]

But all of this did not have a beginning in the form of an "explosion" or as a tiny dot (hence the use of the word "singularity"). The words "explosion" and "singularity" are entirely too misleading in describing what cosmologists think actually occurred and which we are witnessing today via the technology that is now available. Explosion implies a "center" where the so-called explosion had its origin. The Universe has no center. Too the contrary, every observer, no matter where located within the Universe, views himself as being at the center. That word also wrongly implies that there was once a time when objects were ejected from a center much like the bricks of a building became "ejected" as a result of a stick of dynamite exploding within the center of the building. It is also misleading to describe the beginning as being a "Singularity." Using that word implies that everything was once within the sphere of a tiny dot and that everything exploded out of that dot. What 'singularity" really means is that point in time beyond which our physical laws do not apply. Because our physical laws do not apply prior to that point in time, we are not able to say anything regarding what happened prior thereto. A witch doctor in Haiti apparently is just as qualified as Stephen Hawking in guessing what really happened.

It is regrettable that such misleading words have to be used in explaining things to a layman. We are not first graders. It is like a math teacher telling students in the 8th grade that the basics of math can be understood if you know the word 'addition."

You completely misunderstand the meaning of the word "singularity". It does NOT mean explosion and it does NOT imply "point" it just means "the place where our math model breaks down" and it is exactly the right description for what was going on before one Plank time.

 

[julcab12]

You completely misunderstand the meaning of the word "singularity". It does NOT mean explosion and it does NOT imply "point" it just means "the place where our math model breaks down" and it is exactly the right description for what was going on before one Plank time.

--To extend the subject. How did they came up with singularity and what really is "breaking"?^^

--Singularity is what they've labelled to that limit in the actual Einstein Field Equation(spacetime theory). In a sense that the equation shows discontinuity(value of infinity is showing up in the equation). Example. the function f=1/x is singular when x = 0; resulting to undefined value. In the BB model as expressed by the metric tensor. The values of this tensor are given by the Einstein field equations, and solutions to these equations can be singular(infinitesimal density). The equation is entering to where things are undefined which some suggest that it is incomplete. QG is our best bet as far as i know.


http://arxiv.org/pdf/1308.1722.pdf

"I discuss singular spacetimes in the context of the geometrized formulation of Newtonian
gravitation. I argue first that geodesic incompleteness is a natural criterion for when a model
of geometrized Newtonian gravitation is singular, and then I show that singularities in this
sense arise naturally in classical physics by stating and proving a classical version of the
Raychaudhuri-Komar singularity theorem."




--Since GR represents spacetime in terms of a metric (on a manifold of points). We can assume that a feature of certain spacetime i.e singular in a geodesically is in an incomplete manner.

--The question remains whether we should take the singularities of general relativity to be features of our actual universe, or whether we should instead take these singularities as indicating limits in which the classical theory of gravity and spacetime breaks down. The latter option would then suggest that one would need a theory of quantum gravity to describe circumstances that classically lead to singularities. While singularities might be unavoidable in classical context, there are some reasons to suspect that quantum processes might prevent true singularities from developing.

 

[Mordred]

I posted this reply in another thread, as it is so appropriate to the OP of this thread I feel it deserves posting the reply here as well.

There is a simple proof you can perform yourself to see why the universe has no center.

draw on a piece of paper several circles, one within the other. Add as many contained circles as you like 2 will suffice. Draw lines at every 45 degrees. Where the circles cross the lines apply a coordinate letter assignment. Yo will quickly notice or should notice that two coordinates near the center of the circle will not increase in distance at the same rate as two coordinates near the outer circle.

In fact two coordinates at the inner circle will increase in distance at a slower rate than two coordinates at the outer circle.

In cosmology all coordinates separate from all other coordinates at the same rate. Much like coordinates drawn on the ( surface only) of a balloon.

in terms of density, the inner regions will be more dense than the outer regions in the first example.

in the Balloon analogy all points on the surface has the same density, only time varies the diameter of the balloon so as you go back in time the density increases.
the first example has no easy means to describe the time factor so it would be confusing to describe lol. At least I can't think of a way in the first example lol.

Thankfully that isn't important to understand how easy it would be to determine a center if there was one.

 

[CCWilson]

Personally I think "explosion" is an appropriate term. True, the explosions of our acquaintance are three dimensional explosions, but it's not much of a stretch to apply the term to four dimensions. After all, we use the balloon analogy and all sorts of other tricks to try and wrap our minds around spacetime, which - let's face it - is impossible to really visualize for most (maybe all) of us homo sapiens and our three dimensionally-limited brains. And of course the image of a stretched rubber sheet deformed by the mass of heavenly bodies is also not the real thing, just a trick to help us understand GR. If we're going to play with analogies like that, which I think are great, it seems odd to insist that "explosion" - defined as a violent expansion - can't be extended to include four dimensional spacetime.

By the way, the definitions I've seen of "explosion" don't mention a center, or how many dimensions can be involved. It's all just semantics, anyway.

 

[bapowell]

Semantics, yes -- words mean something. And that matters.

Explosions bring to mind material expanding out from a central point. If you polled the general public, I have a good feeling most would agree with this conception. This picture is utterly unlike the early expansion of the universe. If the big bang is considered analogous to an explosion, people will have in mind literally an explosion of matter occurring within pre-existing space. This is not a guess -- on these forums alone we address this misconception more frequently than I think we'd all like. If refraining from a bad analogy prevents people from going down that road, then I'm all for paying attention to semantics.

 

[phinds]

Personally I think "explosion" is an appropriate term. True, the explosions of our acquaintance are three dimensional explosions, but it's not much of a stretch to apply the term to four dimensions.

But it's NOT four dimensions. In the sense that you are using it, a normal fire-cracker is a four-dimensional explosion ... 3 space and 1 time ... from a point. It is too misleading to describe the early universe as an "explosion".

 

[ryan albery]

Let's not knock people who simplify things a bit but get at least some of the idea across rather than make it totally incomprehensible by insisting that they have a full understanding or bust.

good words.