• 0 Posts
  • 7 Comments
Joined 1 year ago
cake
Cake day: July 6th, 2023

help-circle
  • Copy paste top answer from the original question is below.

    I find it refreshing that there are actually people out there who are smart and understand this stuff, when I am constantly surrounded by stupid people like myself.

    For an exact calculation we need to address a few choices: (you can change them, the answer will not be tremendously affected)

    1. What is the receiver? Let’s assume a 70 m dish, like this one [CDSCC] in the Deep Space Network.
    2. [Voyager 1] can transmit at 2.3GHz or 8.4GHz. Let’s assume 8.4GHz, for better beam forming (but probably it can only use the lowest frequency at the highest power, so this could be too optimistic).
    3. Does “received” mean all photons hitting the antenna dish, or only those entering the electronic circuit of the first LNA? A similar question can be asked for the transmitter in the space craft. We’ll ignore this here since losses related to illuminators or Cassegrain construction will not even be one order of magnitude, insignificant compared with the rest. Answers:\

    A) Voyager sends 160 bits/second with 23W. Using 8.3GHz this is 4⋅1024 photons per second, or 2.6⋅1022 per bit, because for frequency f the energy per photon is only Eϕ=ℏω=2πℏf=5.5⋅10−24J  or  5.5 yJ (yoctojoule).

    B) The beam forming by Voyager’s d=3.7mdish will direct them predominantly to Earth, with (πd/λ)2 antenna gain, but still, at the current distance of R=23.5 billion kilometers, this only results in 3.4⋅10−22 Watt per square meter reaching Earth, so a receiver with a D=70m dish will collect only 1.3 attowatt (1.3⋅10−18W), summarized by: Preceived=Ptransmit (πdλ)2 14πR2 πD24 Dividing by Eϕ we see that this power then still corresponds to c. 240000 photons per second, or 1500 photons per bit. If we assume f=2.3GHz this becomes 415 photons per bit. And if we introduce some realistic losses here and there perhaps only half of that.

    C) (Although not asked in the question) how many photons per bit are needed? The [Shannon limit] C=Blog2(1+SN), relates bandwidth B, and S/N ratio to maximum channel capacity. It follows that with only thermal noise N=kTnoiseB, the required energy per bit is: Ebit=SC=kTnoise 2C/B−1C/B ⇒ limC≪B  Ebit=kTnoiselog2, where C≪B is the so-called “ultimate” Shannon limit. With only the CMB (Tnoise=3K)we would then need 41yJ, or 41⋅10−24J, per bit. That’s only 7.5 photons at 8.3GHz. But additional atmospheric noise and circuit noise, even with a good cryogenic receiver, could easily raise Tnoise to about 10K and then we need 25photons per bit at 8.3GHz, and even 91 at 2.3GHz. So clearly there is not much margin.




  • Nofx - you’re wrong:

    You’re wrong about virtues of Christianity And you’re wrong if you agree with Sean Hannity If you think that pride is about nationality, you’re wrong

    You’re wrong when you imprison people turning tricks And you’re wrong about trickle down economics If you think that punk rock doesn’t mix with politics, you’re wrong

    You’re wrong for hating queers and eating steers If you kill for the thrill of the hunt You’re wrong 'bout wearing fur and not hating Ann Coulter Cause she’s a cunted cunt

    You’re wrong if you celebrate Columbus Day And You’re wrong if you think there will be a Judgement Day If you’re a charter member of the NRA, you’re wrong

    You’re wrong if you support capital punishment And you’re wrong if you don’t question your government If you think her reproductive rights are inconsequent, you’re wrong

    You’re wrong fighting Jihad, your blind faith in God Your religions are all flawed You’re wrong about drug use, when its not abuse I hope you never reproduce

    You’re getting high on the downlow A victim of Cointelpro You’re wrong and will probably never know



  • AI is a really bad term for what we are all talking about. These sophisticated chatbots are just cool tools that make coding easier and faster, and for me, more enjoyable.

    What the calculator is to math, LLM’s are to coding, nothing more. Actual sci-fi style AI, like self aware code, would be scary if it was ever demonstrated to even be possible, which it has not.

    If you ever have a chance to use these programs to help you speed up writing code, you will see that they absolutely do not live up to the hype attributed to them. People shouting the end is nigh are seemingly exclusively people who don’t understand the technology.