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B Hydrogen times Pi

  1. Nov 12, 2015 #1
    Dear PF Forum,
    Why in "Contact" film in 1997 if I remember. The frequency for receving signal from aliens is Hydrogen times Pi?
    I can understand, at least grasp, that the frequency uses Hydrogen frequency, because it's the most simple element. Can't use 92.0 MHz as Sonora Radio in Jakarta, because 92,000,000 is too human. Elshinta's 90.0 Mhz can't be used either.
    So it's hydrogen, considering the alien will use other than base 10 number.
    Why Pi?
    Because the scientist afraid that the hydrogen frequency will be altered by the frequency of the stars. So, times Pi to avoid confusion. Since Pi is irrational. (Is it? But I think that belongs to Math forum to prove it :smile:)
    Of course we can't use Hubble constant, or Avogadro number.

    [EDIT:]Why not Phi?
    Golden ratio is irrational, too. Or because golden ratio is too simple ##\frac{\sqrt{5}+1}{2}##?
    Why not Euler number? or Natural Log(2) or square root of 2?
    Do SETI also monitor Hydrogen times Phi and Hydrogen times Euler?

    Why Pi?
    Thanks for any discussion.
  2. jcsd
  3. Nov 12, 2015 #2


    Staff: Mentor

    The wiki article talks about in the SETI section. The idea is that an advanced civilization would know the H lines and PI so that using a frequency which is the product of the two would not be of natural origin and would signify an advanced civilization sent the signal.
  4. Nov 13, 2015 #3


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    Interesting though, that we expect aliens to have a concept of pi. Either numerical relationships and ratios are the abstract products of pure human imagination which have no actual connection to the physical universe... OR we can expect aliens to have a grasp of mathematics.

    Not both though.
  5. Nov 13, 2015 #4
    I think it's a safe assumption that any creatures capable of broadcasting has to have some understanding of mathematics. It's not possible to get past certain technological milestones without it. Aliens live in the same spacetime that we do, and their space will have the same laws that ours does, geometry is part of that.

    @Stephanus, look at why we use base 10, there is a very specific reason for it, and it's not what you're taught in school. I was taught in school that we use base 10 because we have 10 fingers. Complete nonsense, humans have actually used many bases throughout history, base 10 became popular because it works so nicely with logarithms. You might find this interesting:

    There are lots of special values: if I really wanted to know how far along a species was, I'd use the ratio between the mass of an electron and that of a proton.
  6. Nov 13, 2015 #5
    Other bases work with logarithms nicely as well.
  7. Nov 13, 2015 #6
    Higher bases like base 16 also seem like likely candidates for alien math because those bases compress more information with fewer digits. However, aliens probably don't use just one base. Its convenient to use many different bases for a variety of different tasks. No need to just stick with one base;I think its a false dilemma to say that aliens should be using a certain base when they could be sophisticated enough to use like 10 different bases or something in different circumstances in order to convey information in a more efficient manner. Because of computers, many humans are just now learning hex and octal in addition to base 10 for instance. Its possible in a hundred years that humans are as familiar with octal and hex as they are with base 10.
  8. Nov 13, 2015 #7

    Vanadium 50

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    You're right - that is complete nonsense. Base 10 works so nicely with logarithms base 10. Base 12 works nicely with logarithms base 12. Base 16 works nicely with logarithms base 16. Base 60 works nicely with logarithms base 60. Furthermore, logarithms were invented more than 400 years after base 10 numbers were introduced in Europe.
  9. Nov 21, 2015 #8
    Thanks for the replies. I'm out of town so I can't respond sooner.

    What about golden ratio and euler number?
    If there's a signal with hydrogen times Phi and hydrogen frequency times euler number is it safe to assume that the signal is not of natural origin?
  10. Nov 21, 2015 #9


    Staff: Mentor

    The question is why not PI? It is the most pervasive in our math theory today and likely forever. Hence we make the assumption that other alien civilizations would have the same kinds of math.
  11. Sep 14, 2016 #10
    Because it's completely wrong. The natural circle constant is circumference / radius, not circumference / diameter. If aliens are transmitting on an "obvious" frequency, it's tau * hydrogen, not pi * hydrogen.

  12. Sep 14, 2016 #11
    Right, f is in Hertz
    Angular frequency.
    Last edited by a moderator: May 8, 2017
  13. Sep 24, 2016 #12


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    Has anyone considered that frequency in Hertz involves seconds. Seconds are roughly based on the properties of the rotation of earth. Why and how would an alien technology use our unit of measure?

  14. Sep 24, 2016 #13
    They would transmit with whatever units they use.
    We would interpret that using the units we use.

    As Omegatron says " aliens are transmitting on an "obvious" frequency, it's tau * hydrogen".
  15. Sep 24, 2016 #14
    They wouldn't, that's why you pick something natural like the hydrogen line times a mathematical constant. That's the wavelength, not the frequency. Whether you measure that distance in meters or Planck lengths or Vulcan standard distance it's still the same size.

    It's a special point on the electromagnetic spectrum. It's a photon with the exact energy that it takes to jump an electron orbiting a proton from its lowest orbit to its second. That's the same everywhere in the universe.
    Last edited: Sep 24, 2016
  16. Sep 24, 2016 #15


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    Now I understand. It always seemed odd that seconds would come into it especially written by Sagen. I guess i wasn't paying enough attention.

  17. Sep 24, 2016 #16
    Considering aliens would most likely NOT use decimal base 10, they would have to send some natural frequency. So why not the frequency used in hydrogen atomic clocks, I think in our talk around 9.8 Ghz, wouldn't matter what duration their equivalent of seconds are or what base they use, however it came out in their time base and number base, it would still be 9.8 Ghz in ours. I guess that is the frequency they were talking about in the transition from one energy level to another, right?

    If we received a signal and it was on some number like exactly 10.0000000000 Ghz, that would be highly suspicious of Earthy origin of some kind, errant satellite like the last wow signal turning out to be some kind of military sat.
  18. Sep 25, 2016 #17
    @256bits and @newjerseyrunner have already answer that. I think you have understood, too.
    It's Hydrogen times Pi, because if it's purely hydrogen frequency, it can be confused with the other outerspace object frequency.
  19. Sep 25, 2016 #18


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    I'm not into science fiction, but this gave me an idea. When we eventually meet an alien civilisation, we find that they do, indeed, use ##\tau## instead of ##\pi##. This results in the so-called ##pi##-wars, where the rightness or wrongness is eventually determined, as with all things, by military supremacy.
  20. Sep 25, 2016 #19
    Ahh, ##\tau## is actually ##2\pi##. So, they use Hydrogen times tau.
    I think SETI should also check Hydrogen per tau or per pi as well.
    There are two frequencies in Contact 1997 (movie). First is hydrogen times pi. It's audio and introduction messages. Then, one of the scientist Kent Clark, (yep, not Clark Kent) finds another wave. It's Hydrogen times pi double, or I think it's hydrogen times tau.
  21. Sep 26, 2016 #20


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    It's been done. https://en.wikipedia.org/wiki/Lilliput_and_Blefuscu -- the big endian controversy.
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