Timeline for Dumbed-down explanation how scientists know the number of atoms in the universe?
Current License: CC BY-SA 3.0
11 events
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| Apr 1, 2017 at 15:10 | comment | added | ProfRob | The number of galaxies in the (observable) universe is highly uncertain. The Sun isn't a typical star. The average galaxy does not contain a trillion stars. The fraction of atoms contained in stars is uncertain. You can't estimate the number of atoms in the Universe in this way (not even to an order of magnitude) without already knowing the answer. The alternative method you refer to is in fact the correct method. | |
| Nov 19, 2014 at 19:07 | comment | added | Johannes | @ArturoDonJuan - I didn't forget, I ignored it. The above is an order of magnitude estimate, relatively tiny contributions to the number of atoms in the universe are better ignored as these constitute no more than a distraction. | |
| Nov 18, 2014 at 23:43 | comment | added | Arturo don Juan | I think you forget every planet, nebula, asteroid, etc. in the universe. | |
| Feb 23, 2013 at 22:06 | comment | added | OmnipresentAbsence | @Johannes I think the claim that a galaxy contains on average 1 trillion stars is very bold. Our galaxy is a big one and it contains around 300 billion stars. Otherwise a good answer | |
| Dec 30, 2012 at 21:22 | comment | added | KDN | I'd hardly consider "between $10^{70}$ and $10^{80}$" to be a very precise estimate. We could be darn certain that the number of atoms in the universe is between $10^{50}$ (roughly the number of atoms in the earth) and $10^{150}$ (a ridiculously large number). This is a range of $\pm 50$ orders of magnitude, but it is fair to say that we know with virtual certainty that the number of atoms in the universe falls within that range. Somewhere between $10^{70}$ to $10^{80}$ is sufficiently vague as to be accurate, more precise than $10^{50-150}$, and a lot more useful than "unknown". | |
| Dec 30, 2012 at 18:45 | comment | added | Pacerier | I don't know whether the numbers are more likely for or more likely for not, hence the question in the very first place. I've edited the question to reflect this issue. | |
| Dec 30, 2012 at 18:44 | comment | added | Johannes | @Pacerier - what makes you say these numbers are more likely than not correct? It occurs to me that the confidence interval for the numbers of atoms in the universe to be within say $10^{78}$ and $10^{82}$ certainly exceeds 50%. | |
| Dec 30, 2012 at 18:39 | comment | added | Johannes | @Pacerier - That would be a gross violation of the cosmological principle which says 'Viewed on a sufficiently large scale, the properties of the Universe are the same for all observers.' In other words, our universe is homogeneous. Deep sky galaxy surveys, such as the Sloan Digital Sky Survey, but also cosmic microwave background observations, all confirm the cosmological principle. | |
| Dec 30, 2012 at 18:38 | comment | added | Pacerier | And if there's logically less than 50% chance that these numbers are right, isn't it more reasonable to say "the number of atoms in the universe is unknown" than to say "the number of atoms in the universe is ~$10^{70}$"? | |
| Dec 30, 2012 at 18:34 | comment | added | Pacerier | But how is it possible that "each containing on average close to a trillion stars" could be verified reasonably enough, for us to say with enough certainty and conviction that there's over 50% chance that it is correct? For all we know, out of this 100 billion galaxy there could be a single galaxy that already has over $10^{23}$ stars... just curious. | |
| Dec 30, 2012 at 17:37 | history | answered | Johannes | CC BY-SA 3.0 |