6 ms·

If you know the diameter of the observable Universe and you want to calculate its circumference with the accuracy of the diameter of a proton, the number of dig

If you know the diameter of the observable Universe and you want to calculate its circumference with the accuracy of the diameter of a proton, the number of digits of pi that you need is 43.

deleted 11y ago
[deleted]
mabbo 11y ago
I've always heard the number is around 50, but do you have any references to show that as being correct?
- delecti 11y ago
  This [1] puts it at 44. [1] http://www.wolframalpha.com/input/?i=observable+universe+diameter+%2F+proton+diameter http://www.wolframalpha.com/input/?i=observable+universe+dia...
  - deleted 11y ago
    [deleted]
  - deleted 11y ago
    [deleted]
jasonkostempski 11y ago
Would have been so much better if that answer was 42.
- zhte415 11y ago
  It was 42, but in the time it came to get that answer, it kept expanding. So we need a new computer.
  - taneq 11y ago
    Gonna have to think deeply about the design of this new computer. ;)
- cJ0th 11y ago
  Well, reality can be inaccurate at times.
diskcat 11y ago
I think this assumes the order of magnitude of the size of the observable universe. Clearly if the diameter of the universe is smaller than a proton then you don't need 43 digits of pi to calculate its circumference to smaller than the diameter of a proton. So if the diameter of the universe is 10^1000000^100000000 proton wide the precision you need for pi would be way higher than 43?
- hanniabu 11y ago
  It does depend on the size of the observable universe, which we do know because, well, it's observable.
  - diskcat 11y ago
    The post i replied to started off with "If you know the diameter of the observable Universe" but if the result it depends on the size of the observable universe then you ought to say "given the size of the observable universe". Starting with 'if' would imply that the result only requires you 'knowing' the size of the obsv. unv. but does not depend on its actual size.
    - singlow 11y ago
      I think the meaning of "If you know," in this case was more like, "If you take as an input."
      - coldtea 11y ago
        Yep. "If you know X" is commonly used as "given X".
- GFK_of_xmaspast 11y ago
  There's a difference between "the size of the universe" and "the size of the observable universe", see also "cosmic microwave background", "dark energy", and "inflation."
gmuslera 11y ago
The smallest possible distance is the Plank lenght, 1,610^-35 (110^-15 is the diameter of a proton). And for that you only need around 60 digits of pi to calculate the circumference of the universe. Of course, that is just for the simple operation of calculate the circumference given the diameter, more complex operations with pi may require more precision.
- ghayes 11y ago
  Never heard it stated that way. Can you elaborate on "the smallest possible distance is Plank's length"? Is that the smallest observable distance?
  - jaseemabid 11y ago
    If you have some time to spare, watch this talk "The astonishing simplicity of everything" by Neil Turok. He explains all this so beautifully. https://www.youtube.com/watch?v=f1x9lgX8GaE https://www.youtube.com/watch?v=f1x9lgX8GaE
    - mstade 11y ago
      Well presented and really gets you thirsty for more, excellent talk – thank you very much for sharing!
    - acqq 11y ago
      He was painful to watch, I gave up after a while. Maybe it's just me.
  - CoryG89 11y ago
    > According to the generalized uncertainty principle (a concept from speculative models of quantum gravity), the Planck length is, in principle, within a factor of 10, the shortest measurable length – and no theoretically known improvement in measurement instruments could change that. At least according to Wikipedia, it seems it is indeed the smallest observable distance. Although it has never been proven and follows from the theoretical generalized uncertainty principle. https://en.m.wikipedia.org/wiki/Planck_length#Theoretical_significance https://en.m.wikipedia.org/wiki/Planck_length#Theoretical_si...

If you know the diameter of the observable Universe and you want to calculate its circumference with the accuracy of the diameter of a proton, the number of digits of pi that you need is 43.

deleted 11y ago

[deleted]

mabbo 11y ago

I've always heard the number is around 50, but do you have any references to show that as being correct?

delecti 11y ago
This [1] puts it at 44. [1] http://www.wolframalpha.com/input/?i=observable+universe+diameter+%2F+proton+diameter http://www.wolframalpha.com/input/?i=observable+universe+dia...
- deleted 11y ago
  [deleted]
- deleted 11y ago
  [deleted]

jasonkostempski 11y ago

Would have been so much better if that answer was 42.

zhte415 11y ago
It was 42, but in the time it came to get that answer, it kept expanding. So we need a new computer.
- taneq 11y ago
  Gonna have to think deeply about the design of this new computer. ;)
cJ0th 11y ago
Well, reality can be inaccurate at times.

diskcat 11y ago

I think this assumes the order of magnitude of the size of the observable universe. Clearly if the diameter of the universe is smaller than a proton then you don't need 43 digits of pi to calculate its circumference to smaller than the diameter of a proton. So if the diameter of the universe is 10^1000000^100000000 proton wide the precision you need for pi would be way higher than 43?

hanniabu 11y ago
It does depend on the size of the observable universe, which we do know because, well, it's observable.
- diskcat 11y ago
  The post i replied to started off with "If you know the diameter of the observable Universe" but if the result it depends on the size of the observable universe then you ought to say "given the size of the observable universe". Starting with 'if' would imply that the result only requires you 'knowing' the size of the obsv. unv. but does not depend on its actual size.
  - singlow 11y ago
    I think the meaning of "If you know," in this case was more like, "If you take as an input."
    - coldtea 11y ago
      Yep. "If you know X" is commonly used as "given X".
GFK_of_xmaspast 11y ago
There's a difference between "the size of the universe" and "the size of the observable universe", see also "cosmic microwave background", "dark energy", and "inflation."

gmuslera 11y ago

The smallest possible distance is the Plank lenght, 1,610^-35 (110^-15 is the diameter of a proton). And for that you only need around 60 digits of pi to calculate the circumference of the universe. Of course, that is just for the simple operation of calculate the circumference given the diameter, more complex operations with pi may require more precision.

ghayes 11y ago
Never heard it stated that way. Can you elaborate on "the smallest possible distance is Plank's length"? Is that the smallest observable distance?
- jaseemabid 11y ago
  If you have some time to spare, watch this talk "The astonishing simplicity of everything" by Neil Turok. He explains all this so beautifully. https://www.youtube.com/watch?v=f1x9lgX8GaE https://www.youtube.com/watch?v=f1x9lgX8GaE
  - mstade 11y ago
    Well presented and really gets you thirsty for more, excellent talk – thank you very much for sharing!
  - acqq 11y ago
    He was painful to watch, I gave up after a while. Maybe it's just me.
- CoryG89 11y ago
  > According to the generalized uncertainty principle (a concept from speculative models of quantum gravity), the Planck length is, in principle, within a factor of 10, the shortest measurable length – and no theoretically known improvement in measurement instruments could change that. At least according to Wikipedia, it seems it is indeed the smallest observable distance. Although it has never been proven and follows from the theoretical generalized uncertainty principle. https://en.m.wikipedia.org/wiki/Planck_length#Theoretical_significance https://en.m.wikipedia.org/wiki/Planck_length#Theoretical_si...