A while ago I saw Neil deGrasse Tyson comparing the number of stars in the universe with the number of words spoken by all of humankind, ever since.

I realize both of these numbers are not strictly defined, but still, we can use our best observations together with our best guesses to find out which number is larger, and by how many magnitudes. It's a good example of making you realize the size of astronomical numbers in the true sense of the word.

What is your answer or guesstimate?


Number of stars in the observable universe

There are about 100 to 200 billion galaxies in the observable universe. Galaxies range in size from a few billion to hundreds of trillions stars. Using 100 billion galaxies and 1 trillion stars in a galaxy yields 1023 stars in the observable universe as a rough order of magnitude estimate. (After getting this result, I found multiple sources that give answers ranging from 1021 to 1024 stars in the universe.)

Number of words ever spoken

We're talkative, but we also sleep and eat and listen. Assuming we talk for the equivalent of 3 hours per day and we speak at about 150 words per minute, or about 10 million words per year. I recall 100 billion as being a rough estimate of the number of modern humans who have ever lived. Many of those people died during or shortly after childbirth. Assuming an average life expectancy at birth of 25 years (generous), that means humans have spoken 2.5×1019 words since we first gained the gift of gab.

That might be off by a factor of ten, but it's not off by a factor of ten thousand. There are a lot more stars in the observable universe than the number of words ever spoken by humans.

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    $\begingroup$ 10 million words per year means about one per 3 seconds - rather overestimation for me; on the contrary 25 years isn't probably that generous as one might think. $\endgroup$ – Mithoron Feb 19 '15 at 1:03
  • $\begingroup$ This recent piece at arXiv blog gives a figure of 10^25 stars in the universe: medium.com/the-physics-arxiv-blog/… $\endgroup$ – Wayfaring Stranger Feb 19 '15 at 1:15
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    $\begingroup$ @Mithoron - People are either silent or speaking at about 90 to 150 words per minute, or 1.5 to 2.5 per second. I intentionally picked the upper end. Three hours a day of speaking might be a bit high, but not by a factor of three. The 25 years is overly generous, by a factor of two. That 100 billion people includes a lot of people who died in their infancy and thus never said a single word. Except for the last few hundred years, life expectancy at birth has been about 12 years, and that's when most of those 100 billion lived. $\endgroup$ – David Hammen Feb 19 '15 at 1:44
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    $\begingroup$ Amusingly, though, at 2.5 words/sec, we can each speak as many words in half an hour as there are stars in the night sky (about 4,500 visible, on a perfectly clear black night). $\endgroup$ – Dewi Morgan Feb 19 '15 at 6:46

10^19 words have been spoken in all of human history. This accounts for 109 billion people who have ever lived and each speaking 309 billion words in their life time. The amount of stars in the universe in a very rough estimate is somewhere around 10^24. For every word spoken in human existence there are over 100,000 stars in the universe. In conclusion, there are more stars in the universe than for every word ever spoken by humankind as well as every grain of sand on all the beaches on earth and many many more.


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