# Big Bang and Spherical Symmetry

If the universe did indeed start with the big bang why is the universe not spherically symmetric?

As per Wikipedia entry on Big Bang, (and my understanding as well) big bang is the best explanation as of now.

The Big Bang is the scientific theory that is most consistent with observations of the past and present states of the universe, and it is widely accepted within the scientific community.

Basically considering the universe as a sphere (all points equidistant from a center) for any given state at any given point, there should have existed an identical state at the other end (line passing through the center) of the sphere. Also, all points equidistant from the center should have had the same 'state'.

What is the explanation for the 'asymmetry' that we have today?

• Asymmetry as in ? As I see, if you cannot find the centre of universe how can you comment on its symmetry ? Commented Oct 27, 2013 at 9:52
• Since the big bang has a starting point, I consider that to be the center. Commented Oct 27, 2013 at 10:13
• @ Ravindra HV : Some theories say that it might have started as if it has started from a centre, those theories contradict big bang by saying that it might have started as if everything was once confined to a point from where it all originated, this states that there may not really be a centre. Also due to the expansion of universe I think one can not be sure of where this center may be now, had there been one originally Commented Oct 27, 2013 at 10:28
• @rijul gupta : I am more interested with the big bang model of the universe (more intuitive to me and also has wider acceptance) and that does indeed have a starting point . So I'll focus on that. Thank you though. Commented Oct 27, 2013 at 11:00
• @RavindraHV: I am more interested with the big bang model of the universe ... and that does indeed have a starting point . You have this backwards. Big bang models do not have a center.
– user4552
Commented Oct 27, 2013 at 14:14

The universe is spherically symmetric on the large scale - though it would be more precise to describe it as isotropic and homogeneous. You can choose any point in the universe and you'll find it is approximately spherically symmetric about that point

Obviously it isn't perfectly spherically symmetric on scales less that supercluster dimensions. Our current best explanation for this is that at the end of inflation quantum fluctuations introduced random variations in the universe density. These produced the inhomogeneities we currently see in the cosmic microwave background, and some millions of years later the first stars and galaxies.

• Just extending the question, is it proven to be spherically symmetric ? Please post some links to established work on the subject Commented Oct 27, 2013 at 10:01
• @rijulgupta: the measurements of the cosmic microwave background are the definitive measurement. They show that at the time of recombination the deviations from anisotropy were less than or equal to 1 part in 100,000. Although it's a long and hard business we can measure the current galaxy distributions and we find that on the large scale gaalxies are distributed evenly. See the Sloan Sky Survey (sdss.org) for more details. Commented Oct 27, 2013 at 10:08
• Thank you for explaining but since we can observe the universe only for a limited distance, is it a good decorum to assert that we do have spherical symmetry ? The results may extrapolate to the unobservable part of universe, but they just as well may not, right ? Commented Oct 27, 2013 at 10:13
• @John Rennie Is there any explanation to why the fluctuations were random? What 'broke' the symmetry to allow for (seemingly) random events? Commented Oct 27, 2013 at 10:26
• @RavindraHV: see en.wikipedia.org/wiki/Primordial_fluctuations for a good starting point on learning about the fluctuations. They were random because quantum fluctuations are inherently random. Commented Oct 27, 2013 at 10:58

Very few nuclear reactions are symmetrical. Objects spin and often, such as the planets and stars, have different equatorial and polar measurements. Pulsars emit energy in beams. Super Novae radiate out material in less than perfect symmetry.A galaxy tends to spin in a non-symmetrical way. It would therefore be more likely in the "Big Bang" for the result to be anything but symmetrical

• Please do elaborate. Commented Jan 14, 2018 at 14:45
• This doesn't really make sense. All the forces of nature conserve angular momentum, so they preserve spherical symmetry.
– user4552
Commented Jan 14, 2018 at 17:24
• @paul You're perspective is to start from the current state and try to retrace how it might have begun. I am trying to guess how it may have been at the very beginning and wondering how it is that we have come to be. As per me it should have been ideally be a homogeneous spherically symmetric force. Also, what triggered the event itself will likely never be answered (If we go by newton's third law and the big-bang was a 'reaction' then what was the 'action' that caused it? Big-bang as the action itself does not make sense after all..). Commented Jan 14, 2018 at 19:15

Coming back to this question, I am guessing the fact that pi is irrational has also something to do with it. This was the kind of answer I was looking for initially as well.

• How the fact that $\pi$ is not a rational number should correlate with primordial quantum fluctuations of the vacuum? Commented Apr 14 at 9:28
• The original question being why the universe is not spherically symmetric. The layman's version of the answer that I was looking for would revolve around the fact that its because there is no perfect sphere, owing to the fact that pi is irrational. Commented Apr 26 at 11:33