10 replies to this topic

[Parsec]

Hi,

I'd like to ask a question to those who're more into Astronomy than I'm:
taken for valid the Big Bang theory, we, like the rest of the universe's mass, come from a specific point in space.
According to the cosmological principle, on a macro-scale the universe is homogeneus and isotropic. The cosmic background radiation is uniform, wherevere we see, since it should represent a uniformly distributed hot gas that has expanded to the current size of the universe.
As far as I understand, this size represents the borders of our universe, and it's ever growing (to the extreme point that will lead to the Big Crunch or the Big Freeze); thus, at the moment we're moving towards somewhere.
On an observational point of view, the universe isn't homogeneus, since there're clusters of galaxies and matter isn't equally distributed. Thus, some galaxies should be farther from the "point of origin", and some should be closer.
Can we know from observations where we're? Are we placed in the head, the body or the tail of this run?
In the same way, can we detect where this initial point in space was?


Thank you in advance

[Hilander]

There are no stupid questions but you can get some stupid answers.  So here's my stupid answer.

I imagine the scientist have a pretty good idea about where we are located but I doubt they are exact.

[Hilander]

Looks like they can't pinpoint as to what side of the universe we are on.  Just where we are in relation to other galaxies.  Not a stupid question I learned something here.

Is it possible to pin point Milky Way in the Universe Map?

I found many articles on this question.

[sepulchrave]

Parsec, on 16 September 2012 - 11:33 PM, said:

In the same way, can we detect where this initial point in space was?

According to the Big Bang theory, there is no ``initial point'' in space.

The Big Bang occurred simultaneously in every point in space at the same time. Galaxies, nebulae, etc. didn't expand into space, space itself expanded.

The ``balloon analogy'' is often used in this situation: As a balloon inflates, is it possible to find the point on the surface of the balloon from which the inflation began? The answer is ``no'', because the point of inflation was the centre of the balloon, at point that does not exist on the surface.
(In this analogy the 2D surface of the balloon is analogue to our 3D space.)

[Parsec]

Thank you Hilander and sepulchrave for your answers, they both helped me in clearing this subject.

About what you wrote sepulchrave: following the logic of the Big Bang theory as you expained, it's actually intuitive that, since space didn't exist before the Big Bang, there was no "space" where the singularity could be. You've been very incisive.

As you wrote, space during the Big Bang expanded: does it mean that actually the cbr isn't moving, but it's space itself?

And thus, another stupid question (althougt I think it's more phylosophical than scientific at this point): if space is expanding, where? Or better, if space is growing, can it mean that's contained in something bigger? I know that our space is everything there is (or everything we can detect), but what if there could be an higher level of space, containing our? I guess this could lead to an infinite "chinese box" universe, so maybe it's pointless.

[sepulchrave]

Parsec, on 18 September 2012 - 11:22 PM, said:

As you wrote, space during the Big Bang expanded: does it mean that actually the cbr isn't moving, but it's space itself?

It isn't space, it is the ``echo'' of the big bang. As space expands, what used to be short wavelength (high energy) radiation became ``stretched'' out into long wavelength (low energy) radiation.

The CMB is composed of lower energy radiation, but exists over a much larger volume; if you total the CMB energy over all of space this gives you an estimate of what the energy (i.e. temperature) was like when the Universe was much smaller (the CMB energy is basically conserved).

Parsec, on 18 September 2012 - 11:22 PM, said:

And thus, another stupid question (althougt I think it's more phylosophical than scientific at this point): if space is expanding, where? Or better, if space is growing, can it mean that's contained in something bigger? I know that our space is everything there is (or everything we can detect), but what if there could be an higher level of space, containing our? I guess this could lead to an infinite "chinese box" universe, so maybe it's pointless.

Possible, but unlikely, in my opinion.

Space (and time) are internal parameters of the system (the system begin the Universe, in this case).

Perhaps it is like baking a cake: as the cake finishes baking, it increases in flavour. Some cake-dwelling philosopher might ask, ``if the cake is increasing in flavour, is this pushing the flavour out of whatever surrounds the cake?''
Of course not, flavour has only to do with the internal arrangement of the cake (raw dough, vs. fresh baked, vs old and stale, etc.).

Likewise, if there is anything ``outside'' our Universe, it (almost by definition) could not share any of our internal dimensions like space, time, colour, temperature, mass, etc.

[Imaginarynumber1]

sepulchrave, on 19 September 2012 - 06:37 PM, said:

Possible, but unlikely, in my opinion.

Space (and time) are internal parameters of the system (the system begin the Universe, in this case).

Perhaps it is like baking a cake: as the cake finishes baking, it increases in flavour. Some cake-dwelling philosopher might ask, ``if the cake is increasing in flavour, is this pushing the flavour out of whatever surrounds the cake?''
Of course not, flavour has only to do with the internal arrangement of the cake (raw dough, vs. fresh baked, vs old and stale, etc.).

Likewise, if there is anything ``outside'' our Universe, it (almost by definition) could not share any of our internal dimensions like space, time, colour, temperature, mass, etc.

Just wanted to say that I really liked the way that you explained this.

[the L]

I dont get this. If balloon explode and we can trace it parts and where are going and on what speed then...I dont see why not know center. I dont agrees its baloon. It was a seed. Zen seed. Which wanted to disordered order. Asymetrycal seed. More matter then anti matter.

[sepulchrave]

the L, on 08 November 2012 - 12:11 AM, said:

I dont get this. If balloon explode and we can trace it parts and where are going and on what speed then...I dont see why not know center.

We do know the centre... in our local coordinate frame it was everywhere and 13.5 billion (or whatever) years ago.

the L, on 08 November 2012 - 12:11 AM, said:

I dont agrees its baloon. It was a seed. Zen seed. Which wanted to disordered order. Asymetrycal seed. More matter then anti matter.

Of course it wasn't a balloon. The balloon analogy is just used to help laypeople visualize a very limited case of how one could interpret the Universe.

(And of course it only works if one assumes that the spatial extent of the Universe is closed, which is probably, but not necessarily, the case.)

I don't disagree with you saying that it was a ``seed'', I just don't see how that imagery helps interpret the expansion that preceded the Big Bang.

--------
Edited to amend the part that I struck out above, because I realize it sounds kind of condescending...

What I meant to say is ``the balloon analogy only works to illuminate how the Universe could expand from a single point without that point existing within the (current) Universe''.

On almost every other level the balloon analogy fails to explain or give any insight.

I guess your seed analogy - assuming I understand it - also works; a tree can grow from a single seed but that seed is not at any particular location within the grown tree...

Edited by sepulchrave, 08 November 2012 - 05:10 AM.

[Parsec]

Sepulchrave, we can say that the universe at the beginning was like a picnic tablecloth, those with the plates sewed on it.
At the beginning the tablecloth was in the basket, then it has been pulled out: the fabric is the space fabric, while the plates are the galaxies and the matter. Before the tablecloth is pulled out, everything is in the same spot and the fabric is folded on itself; when it comes out, there's no "place of origin", since the fabric is "everything that matters" to us (who live and can see only inside, or over, the tablecloth) and it stratches in all directions, taking the matter with it.
Does it work? Should I eat less and read more?

[sepulchrave]

Parsec, on 13 November 2012 - 01:01 AM, said:

Sepulchrave, we can say that the universe at the beginning was like a picnic tablecloth, those with the plates sewed on it.
At the beginning the tablecloth was in the basket, then it has been pulled out: the fabric is the space fabric, while the plates are the galaxies and the matter. Before the tablecloth is pulled out, everything is in the same spot and the fabric is folded on itself; when it comes out, there's no "place of origin", since the fabric is "everything that matters" to us (who live and can see only inside, or over, the tablecloth) and it stratches in all directions, taking the matter with it.
Does it work? Should I eat less and read more?

Yeah, it works about as well as any other analogy, I guess.

The one nice thing about the balloon analogy is that you can visualize time as a spatial direction: The balloon more-or-less describes a 2+1 spacetime, the 2 spatial dimensions are described by the surface of the balloon, the 1 time dimension is directly out from the balloon's surface. For a spherical balloon you can ``see'' the origin of time, at the very centre of the balloon.