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How many photons are received per bit transmitted from Voyager 1?

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Re: How many photons are received per bit transmitted from Voyager 1?

#181

Post by ballooney »

djha-skin wrote: post #155
tb0ne wrote: post #119

Super 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.

[Reed-Solomon is the more conventional formulation if you do end up going looking]

Re: How many photons are received per bit transmitted from Voyager 1?

#182

Post by empyrrhicist »

jessriedel wrote: post #113
empyrrhicist wrote: post #58

Earlier quoted context omitted.

I think the point is the model though - if a system's behavior can be modeled/described classically, it's a bit silly to to call it a "quantum" system in the same way that it's reductive to say Biology is just applied particle physics. Sure, but that's not a very useful level of abstraction.

If you want to understand the transition between a fundamental theory and its effective description in some limiting regime, you need to be able to describe a system in the limiting regime using the fundamental theory. It's not "silly" to talk about an atom having a gravitational field even if it's unmeasurably small (currently).

Lol, so you've got a working theory to bridge the quantum and classical worlds? That is, you've figured out how to make general relativity and quantum mechanics emerge from a more fundamental theory? Somebody get this person a Nobel!

We're at the phase where we know the world is quantum, but we also simply don't have the ability to bridge that set of observable phenomena to what we know about macroscopic things. That's what makes this exercise "silly".

Re: How many photons are received per bit transmitted from Voyager 1?

#183

Post by Out_of_Characte »

superposeur wrote: post #81
Out_of_Characte wrote: post #72

Earlier quoted context omitted.

There's several projects for laser-based communication and research. It would also make it really difficult to aim since you can miss your target now. https://www.jpl.nasa.gov/news/nasas-deep-space-optical-comm-... https://en.m.wikipedia.org/wiki/Laser_Interferometer_Space_A...

Interesting about the JPL program and I’m amazed this prototype was only launched last year! Apparently the answer to comms laser use is “not yet but soon”.

Its certainly exiting that we'll have laser based communication in the near future. its like all ingredients for interplanetary missions are slowly coming together. all we're missing now is a very high specific impulse engine that could push the several tons for human habitation to another planet.

Re: How many photons are received per bit transmitted from Voyager 1?

#184

Post by [deleted] »

mr_toad wrote: post #166
somat wrote: post #99

An interesting thing about photons (which may not be true, I just enjoy this stuff amateurishly, that is, without the effort or rigor to actually understand it.) is that they might not exist. the em field is not quantized, or at least is not quantized at the level of photons. A "photon" only exists where the em field interacts with matter, where the electrons that create the disturbance can only pulse in discrete lev…

Existence is a difficult concept for something moving at the speed of light. Light follows a null geodesic through space-time with zero (space-time) length and no proper time. Past, future, and causality have no meaning to a photon. We think of photons travelling through space because our symmetry is broken, we have mass, and we and experience time and space. Observers like us will see light follow the same world-lin…

[deleted]

Re: How many photons are received per bit transmitted from Voyager 1?

#185

Post by imoverclocked »

eru wrote: post #172
imoverclocked wrote: post #161

Earlier quoted context omitted.

I think what they mean is that classical systems use more than a single packet of energy to represent a state. Our “digital systems” are actually analog systems in saturation states. Each time you want to set a bit in memory, you need enough energy to fill up a capacitor (or similar related concept) which is far more than a single electron. This methodology from the viewpoint of quantum systems is repetition/redundan…

Going off on a bit of a tangent: Some people suggest that digital computing and neural networks are a bit fit, and that would should be using analog devices. That sounds very appealing at first. But we have (at least) two problems: First, our transistors dissipate almost no energy when they are either 'fully open' or 'fully closed'. Because either there's approximately no current, or approximately no resistance. Hold…

I love tangents!

I think all of your points are valid. I also think that we have optimized heavily for this state of technology. If we figured out that analog computing was somehow superior in a big way, I bet we would find ways of reducing power etc in analog designs.

One way that analog computing would be really neat for neural networks is in speed. The way it might not be so great is in reliability (or repeatability, specifically.) Analog systems are more susceptible to noise as well as variation from fabrication processes. Running things at saturation makes them easier to design, test and mass produce.

Re: How many photons are received per bit transmitted from Voyager 1?

#186

Post by olddustytrail »

PeterCorless wrote: post #129

I just wanted to chime in with a reminder that though Voyager 1 is speeding away from Sol at a constant velocity because of the Earth's revolution around the sun it can be up to ±1 AU closer or further away, depending on the time of the year. This article is for Voyager 2, but the issue is the same. For a brief moment every year we actually get closer to Voyager 1, then we pivot away in our revolution around the sun…

Surely 2AU depending on whether we're on the same side of the sun or we're on the dark side.

Re: How many photons are received per bit transmitted from Voyager 1?

#187

Post by nico »

empyrrhicist wrote: post #182
jessriedel wrote: post #113

Earlier quoted context omitted.

If you want to understand the transition between a fundamental theory and its effective description in some limiting regime, you need to be able to describe a system in the limiting regime using the fundamental theory. It's not "silly" to talk about an atom having a gravitational field even if it's unmeasurably small (currently).

Lol, so you've got a working theory to bridge the quantum and classical worlds? That is, you've figured out how to make general relativity and quantum mechanics emerge from a more fundamental theory? Somebody get this person a Nobel! We're at the phase where we know the world is quantum, but we also simply don't have the ability to bridge that set of observable phenomena to what we know about macroscopic things. That…

No need to be sarcastic. We are trying to develop ideas and have a conversation

We are not trying to prove who is right and who is wrong

Regardless of whatever the mainstream agreement in physics might be regarding a preferred model for reality, everyone experiences reality directly, without any need for science or math. And they can express those experiences and ideas in their own way

If you don’t agree with someone else’s ideas, please just explain why politely, and also maybe even try to understand their point of view. What would things look like if they were actually right? How might theirs be a good idea?

Thank you

Re: How many photons are received per bit transmitted from Voyager 1?

#188

Post by nico »

immibis wrote: post #179
nico wrote: post #76

Earlier quoted context omitted.

Maybe I’m mixing Shannon’s limit with the sampling rate imposed by the Nyquist-Shannon Sampling theorem > Around 2004, Emmanuel Candès, Justin Romberg, Terence Tao, and David Donoho proved that given knowledge about a signal's sparsity, the signal may be reconstructed with even fewer samples than the sampling theorem requires.[4][5] This idea is the basis of compressed sensing … > However, if further restrictions are…

Consider the simple example of frequency aliasing. If you sample a 3.2MHz sine wave at a 1MHz sample rate, it looks the same as a 0.2MHz wave. But if you know a priori that the signal only has frequency components between 3 and 3.5 MHz, then you know the 0.2MHz you are measuring is actually 3.2MHz - you can fully reconstruct the original signal even though you are not sampling it fast enough.

Exactly

Interestingly, in a philosophical way, you might never be able to know the “original signal”, since any signal can also technically be the alias of an infinite number of other signals, including the one used for sampling

Re: How many photons are received per bit transmitted from Voyager 1?

#189

Post by stracer »

forgot-im-old wrote: post #132
stracer wrote: post #80

Earlier quoted context omitted.

All transmitted bits are also received, at least when everything works as intended.

No, with error correction, not all transmitted bits are received, but the message bits can be recovered.., and if not they must retransmit later.

I meant the message bits carried by the emission, but you're right, the way things are done, more bits are prepared at first, to make the message more resilient against noise, and only then all the bits are modulated onto the EM emission. So while not all emitted bits do come correctly, all data bits can be reconstructed.

Which makes me wonder, whether this way of achieving resilience against changes along the way is necessary. Maybe the data bits can be modulated directly onto analog current, and error resilience can be achieved by remodulating it on the analog level. Then, the emission would have as many bits as there are in the message, error-resilience (modulating, demodulating) would be done strictly using analog electric circuits.

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