25 ph is like massive SNR! Let's talk about 30ps timing and 3 photons & you have insight into my daily work!
How many photons are received per bit transmitted from Voyager 1?
151–160 of 205 posts
Re: How many photons are received per bit transmitted from Voyager 1?
#152Could we e.g. decrease the bit rate, and in effect send less information but for longer?
Eg send a continuous wave with low signal beyond its phase, and measure at a rate of (digital) bits per month?
Re: How many photons are received per bit transmitted from Voyager 1?
#153The overwhelming loss in this calculation is from the antenna’s radiated energy spreading out over a larger and larger area (despite the directional “gain” factor). I’m wondering: would a probe launched today instead employ a laser to communicate? This would seem to offer many orders of magnitude improvement in the directionality of the signal.
Not an expert but I imagine it just doesn't matter much. It's able to do incredible things with just 24 watts of power.
Re: How many photons are received per bit transmitted from Voyager 1?
#154Earlier quoted context omitted.
Is there some fundamental limit to the number of bits per photon that can be communicated via EM radiation? I think it does not exist, because photons aren't all equal, we can use very high frequency and X-ray quantum can probably carry much more information than RF quantum.
Send three photons A B C. They arrive at times ta, tb, tc. Compute fraction (tc - tb) / (tb - ta). This can encode any positive real number with arbitrary precision. But clearly you need either very precise measurements or send the photons at a very slow rate.
Special relativity will give limits on how aligned the clocks can be (which should be a function of the distance between the clocks). So there will be precision limits.
Re: How many photons are received per bit transmitted from Voyager 1?
#155Super interesting! But I feel like there is a bit of a conclusion missing for me. So 1500 Photons hit the receiver per bit send, but this is obviously way to few to keep processing the signal and it will just be drowned out by noise? Where do we go from here? Does voyager repeat its signal gazillions of times so we can average out the noise on our end? Where can I find more information on what is done with these few…
Look up Solomon Reed erasure coding. Voyager uses it, so does qrp Ham radio operators.
Re: How many photons are received per bit transmitted from Voyager 1?
#156I was trying to answer a question about the Voyager space probe and got our of my depth, BUT I found this great PDF in the process.
Covers a lot of technical details at the level a person without much specific training can understand.
https://voyager.gsfc.nasa.gov/Library/DeepCommo_Chapter3--14...
Re: How many photons are received per bit transmitted from Voyager 1?
#157Earlier quoted context omitted.
But we are classical, so I think it's wrong (or at least confusing) to talk about the many photons as repetition codes. Then we might as well start to call all classical phenomena repetition codes. Also how would you define SNR when doing this? Repetition codes have a very clearly defined meaning in communication theory, using them to mean something else is very confusing.
> Then we might as well start to call all classical phenomena repetition codes All classical phenomena are repetition codes (e.g., https://arxiv.org/abs/0903.5082 ). And this is perfectly compatible with the meaning in communication theory, except that the symbols we're talking about are the states of the fundamental physical degrees of freedom. In the exact same sense, the von Neumann entropy of a density matrix is…
> All classical phenomena are repetition codes
Could you ELI5 this "bit"?
Thanks
Re: How many photons are received per bit transmitted from Voyager 1?
#158Actually the limit predicted by Shannon can be significantly beaten, because Shannon assumes gaussian noise, but if we use photon counting receivers we need to use a poisson distribution. This is the Gordon-Holevo limit. To beat Shannon you need PPM formats and photon counters (single photon detectors). One can do significantly better than the numbers from voyager in the article using optics even without photon cpunt…
I am not sure if you can use 1 photon per bit because (as I understand) emitting and capturing photons is a probabilistic process and when you have 1 photon, there is a probability that it will not be captured by an antenna, but rather will be reflected or will turn into heat. Or am I wrong here?
Re: How many photons are received per bit transmitted from Voyager 1?
#159Earlier quoted context omitted.
Very cool. It’s interesting to realize that at some level, every system is a quantum system if you “zoom in” enough
> at some level, every system is a quantum system if we consider "quantum" to mean our quantum theory, at the level of general relativity, gravity is not a quantum system. and the qualifier "yet" is also not known.
I wonder very much about that statement. So far it is not merging into one theory. Hence one may try to help the OP every physical system if zoom in will be better modelled asking the quantum …
But quantum field actually is a universe model like GR and hence you have this issue of sort of action in a distance by superimposition.
Hence zoom in is not helping.
Re: How many photons are received per bit transmitted from Voyager 1?
#160Earlier quoted context omitted.
> Then we might as well start to call all classical phenomena repetition codes All classical phenomena are repetition codes (e.g., https://arxiv.org/abs/0903.5082 ). And this is perfectly compatible with the meaning in communication theory, except that the symbols we're talking about are the states of the fundamental physical degrees of freedom. In the exact same sense, the von Neumann entropy of a density matrix is…
> All classical phenomena are repetition codes Could you ELI5 this "bit"? Thanks
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