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We are still exploring the universe along with the contrary of multi-verse, then how one estimated total no. of atoms? Is it just consideration of matter or also anti matter?

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  • $\begingroup$ We can't count antimatter atoms because we don't know if they exist, or if they do, where they are located $\endgroup$ – user108787 Aug 13 '16 at 23:56
  • $\begingroup$ Then atoms estimated are just of the observable universe matter, how correct are they with accuracy of same binding elements? $\endgroup$ – Karan Nadagoudar Aug 14 '16 at 0:03
  • $\begingroup$ I am not sure I understand the second part of your question, but the visible universe is estimated to contain between 10$^{78}$ and 10$^{80}$ atoms. $\endgroup$ – user108787 Aug 14 '16 at 0:12
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    $\begingroup$ And BTW, I remember seeing an estimate of the number of atoms, or maybe it was particles (close enough) in the (observable?) universe around 1960 in reading either Eddington or Gamow's 1-2-3 Infinity. Can't remember exactly but think it was around $10^{80}$. $\endgroup$ – Bob Bee Aug 14 '16 at 4:54
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    $\begingroup$ It's not clear what this question is asking about - are you talking about the matter content in the observable universe? Please make it clearer which figure you're talking about and where you got it from. $\endgroup$ – ACuriousMind Aug 14 '16 at 11:15
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There are up to $100$ billion galaxies in the observable universe. Let me assume each of these has $100$ billion stars with a mass comparable to the sun $2\times 10^{30}kg$. A proton weighs about $10^{-27}kg$. So with a total of $10^{22}$ stars this is $10^{52}kg$ and so there are on the order of $10^{79}$ protons in the observable universe.

There are more however, for the CMB is at $45\times 10^{10}$ light years and our survey of stars goes out to about $12$ billion light years. This is a volume increase of $52$, which means an estimate of around $10^{81}$ protons on the Hubble frame is not a bad estimate. Yet there is even more, for the CMB is just a period in the past where the radiation dominated universe was opaque. The number could then actually be infinite if the universe is flat. However, for the CMB the redshift factor is $z~=~1100$, and we could guess what it would take to redshift the Planck scale to some figure. The Planck epoch might have Planck scale quanta (gravitons etc) red shifted by a factor of $10^{30}$ or so. There might then be proportionately more volume expanded by $\sim~10^{100}$ on the Hubble frame.

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  • $\begingroup$ @lawrence-b-crowell: Wow, those are some big numbers. It's amazing to ponder what we don't know about the Universe considering how much we do know already... $\endgroup$ – pr1268 Aug 14 '16 at 1:56
  • $\begingroup$ Hypothesis: The universe is merely 1% larger than the visible universe. Can you rule this out with a model independent measurement? :-) $\endgroup$ – CuriousOne Aug 14 '16 at 1:59
  • $\begingroup$ Anything outside the observable universe (maybe what visible really is meant to be) obviously can not be measured. We always depend on models. And sometimes we get surprised. $\endgroup$ – Bob Bee Aug 14 '16 at 4:50
  • $\begingroup$ @Crowell. The observable universe has a radius of 46 billion light years, not 450 billion. Your volume increase though is right, maybe just fix the typo $\endgroup$ – Bob Bee Aug 14 '16 at 5:03
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"Multiverse" is more like a sci-fi or phylosophic thing as mainstream physics.

The size of the whole Universe is unknown, maybe infinite.

The total number of atoms in the visible universe is estimated by adding the stars (with their known sizes), the interstellar gas, the intergalactic gas, etc.

Note, only around 5% of the matter in the Universe is baryonic (= can produce atoms). Btw, most of it isn't part of atoms, because it is plasma in the stars.

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    $\begingroup$ Isn't plasma still composed of atoms? (Assuming that we can consider atomic nuclei to be atoms, er, ionic atoms stripped of their electrons.) $\endgroup$ – pr1268 Aug 14 '16 at 2:08
  • $\begingroup$ @pr1268 Well, assuming this it is composed of atoms. :-) $\endgroup$ – peterh - Reinstate Monica Aug 14 '16 at 10:11

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