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I always have a question in my mind when I think about the big bang. It is that if the universe has expanded from a tiny singularity by an explosion to the universe of today, why didn't it expand into a uniform sphere with everything distributed uniformly. There wasn't any force present already before the starting of the universe.

The Galaxies and different things don't seem to be uniform. And also where does this randomness of every planet, every star being different from others come from.

Could anyone help me in understanding this?

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  • $\begingroup$ The world is still searching for an answer to this. $\endgroup$
    – Lelouch
    Commented Mar 5, 2017 at 12:44

2 Answers 2

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enter image description here

The comment by AFT above, referring to a duplicate is correct, as regards Why is the universe not perfectly uniform but I thought including the image above might add to John's answer.

This is an representation of the Cosmic Radiation Background distribution, not at the time just after the Big Bang, but about 400,000 years later.

The important part of this picture is that it is not uniform, you can clearly see differences in color, representative of differences in temperature. Please read the answer by anna v.

The link I provide above gives more details, and I don't want to repeat the duplicate, but I wanted to illustrate that even at this early stage of the universe, it was not homogeneous, and reading the other answer, and the Wikipedia article should list some of the reasons we believe this occured.

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  • $\begingroup$ These answers seem to satisfy me. Does this mean that randomness is inbuilt in the physics of the universe? @Countto10 $\endgroup$ Commented Mar 5, 2017 at 13:15
  • $\begingroup$ To me, and I am not an expert by a long way, it would seem that ANY initial deviations in matter density would be amplified by gravitational effects, so that clumping of matter, once it started to occur, would be bound to increase, and lead to the inhomogeneous state of the observable universe we see today. I don't know enough about the subject to say anything other that at a small enough scale, probability was involved. What is still unexplained is why the universe started in a low entropy state and this would seem to be linked to your question. $\endgroup$
    – user146020
    Commented Mar 5, 2017 at 13:26
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Well, it is practically uniform to supplement the graph of Countto10.The cosmic microwave background radiation plot is the best fit for a black body radiation formula by far.

cmb

Graph of cosmic microwave background spectrum measured by the FIRAS instrument on the COBE, the most precisely measured black body spectrum in nature. The error bars are too small( fluctuations order of 10^-5) to be seen even in an enlarged image, and it is impossible to distinguish the observed data from the theoretical curve.

In effect, it is this uniformity detected in radiation that left at 300.000 years after the Big Bang that made necessary the introduction of a fuzziness at the beginning of the universe, and not the singularity of the classical general relativity model. A quantum mechanical regime is posited at the beginning introducing the homogenizing effect of an inflaton field, with quantum fluctuations which became the seeds for the nonuniformity at 10^-5 level in the CMB plot.

These seeds are the ones that started the gravitational regions which became clusters of galaxies, galaxies and stars.

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  • $\begingroup$ +1 thanks for supplementing my supplement to John's answer ; ), seed is the word I just blanked on and I should have stated that the CMB is also based on tiny , tiny differences. Rgds $\endgroup$
    – user146020
    Commented Mar 5, 2017 at 13:55

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