How many photons are received per bit transmitted from Voyager 1? • Hacker News Board

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

#191

Post by jessriedel » Tue, Jun 04, 2024, 6:16 PM UTC

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…

You're confusing the quantum-classical transition with the quantum-gravity to classical-gravity transition. (People understood the relativistic-Galilean transition before they understood the QFT-classical-field-theoy transition.)

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

#192

Post by forgot-im-old » Tue, Jun 04, 2024, 6:46 PM UTC

stracer wrote: post #189

forgot-im-old wrote: post #132

Earlier quoted context omitted.

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…

By adding additional degrees of freedom in the transmission through 'analog modulation' you increase the transmission rate. This is certainly possible, for example FM is more robust than AM, but at the expense of bandwidth. In the presence of a thermal (Gaussian) limited noise model, the Shannon capacity always applies regardless of the modulation.

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

#193

Post by empyrrhicist » Tue, Jun 04, 2024, 9:01 PM UTC

nico wrote: post #187

empyrrhicist wrote: post #182

Earlier quoted context omitted.

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…

I'm not trying to be mean, it just struck me as kind of a funny position.

"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"

Like, that's well and good, but in general we just can't do that without hand-waving, period. This is true all over the place (biology/physics, psychology/neuroscience/physics). It's sort of true, but not in a useful way.

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

#194

Post by jessriedel » Tue, Jun 04, 2024, 10:32 PM UTC

empyrrhicist wrote: post #193

nico wrote: post #187

Earlier quoted context omitted.

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…

I'm not trying to be mean, it just struck me as kind of a funny position. "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" Like, that's well and good, but in general we just can't do that without hand-waving, period. This is true all over the place…

Rigorous things can be done in physics and mathematics, and the fields benefit greatly from this.

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

#195

Post by empyrrhicist » Tue, Jun 04, 2024, 10:47 PM UTC

jessriedel wrote: post #194

empyrrhicist wrote: post #193

Earlier quoted context omitted.

I'm not trying to be mean, it just struck me as kind of a funny position. "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" Like, that's well and good, but in general we just can't do that without hand-waving, period. This is true all over the place…

Rigorous things can be done in physics and mathematics, and the fields benefit greatly from this.

What does that even mean, and how is it a response to my point that choosing an appropriate level of abstraction for the problem at hand is a good idea?

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

#196

Post by lebed2045 » Wed, Jun 05, 2024, 1:00 AM UTC

Strilanc wrote: post #140

Sharlin wrote: post #133

Earlier quoted context omitted.

> Stuff like DRAM storing a 0 or 1 via the presence or absence of 40K electrons I'd assume that these days it's a couple of orders of magnitude fewer than that (the cited source is from 1996). Incidentally, 40k e- is roughly the capacity of a single electron well ("pixel") in a modern CMOS image sensor [1] – but those 40k electrons are able to represent a signal of up to ~14 bits, around 10k distinct luminance values…

If you have a more modern estimate I'll take it. Very interesting about the CMOS sensors distinguishing +- 2 electrons (40K / 2^14).

not 2 but around 10 seems possible https://www.mdpi.com/2079-9292/9/5/757

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

#197

Post by lebed2045 » Wed, Jun 05, 2024, 1:09 AM UTC

eru wrote: post #175

codedokode wrote: post #158

Earlier quoted context omitted.

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?

In principle, you can send more than one photon per bit on average. Photons have a lot of ways they can encode additional bits, eg frequency, polarisation, timing. You are right that you can randomly lose some photons. That's what error correcting codes are. See https://en.wikipedia.org/wiki/Error_correction_code As an example, assume every photon can encode 10 bits without losses, but you lose 10% of your photons. T…

*typo: you can send more than one bit per photon on average

I'm very curious to learn more about 1cm, what is the math behind it? Do you speak about classical music CD with ±700mb of capacity? I was always fascinating by ability of old super scratched optical disks still functioning without problems.

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

#198

Post by eru » Wed, Jun 05, 2024, 4:18 AM UTC

lebed2045 wrote: post #197

eru wrote: post #175

Earlier quoted context omitted.

In principle, you can send more than one photon per bit on average. Photons have a lot of ways they can encode additional bits, eg frequency, polarisation, timing. You are right that you can randomly lose some photons. That's what error correcting codes are. See https://en.wikipedia.org/wiki/Error_correction_code As an example, assume every photon can encode 10 bits without losses, but you lose 10% of your photons. T…

*typo: you can send more than one bit per photon on average I'm very curious to learn more about 1cm, what is the math behind it? Do you speak about classical music CD with ±700mb of capacity? I was always fascinating by ability of old super scratched optical disks still functioning without problems.

> I'm very curious to learn more about 1cm, what is the math behind it?

So I actually got that from a cool math talk I attended about 20 years ago. At the end the professor had a cool demonstration where he glued paper strips of various sizes radially on the CD, and exactly as the math he spend an hour explaining predicted, the CD player could cope with up to a 1cm width strip, but no more.

Let me try to find some written material.

https://en.wikipedia.org/wiki/Cross-interleaved_Reed%E2%80%9... is a good start, but doesn't go into the details. https://en.wikipedia.org/wiki/Reed%E2%80%93Solomon_error_cor... might also be worth a read.

In a nutshell, you arrive at the 1cm like this: you can look up what proportion of 'wrong' bits the CD's coding can correct and other overhead. Then you look up the circumference of a CD (about 28 cm), then you do some multiplication, and figure out that you can lose about 1cm out of every 28cm, and still be able to correct.

Most of the interesting math happens at the first step of 'what proportion of errors can the music CD correct?' and more interestingly 'how does the CD player do that?'

> I was always fascinating by ability of old super scratched optical disks still functioning without problems.

Keep in mind that CD-ROMs have one additional layer of coding on top of what music CDs have. That's because if a bit error slips through the error correction chances are it still won't be audible to the human ear for music, but software might still crash with a single wrong bit.

> Do you speak about classical music CD with ±700mb of capacity?

Yes, that's because that's what I heard the talk about. I am sure more modern formats also have interesting error correction, but I don't know what they use and how much you could cover up.

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

#199

Post by jessriedel » Wed, Jun 05, 2024, 4:13 PM UTC

empyrrhicist wrote: post #195

jessriedel wrote: post #194

Earlier quoted context omitted.

Rigorous things can be done in physics and mathematics, and the fields benefit greatly from this.

What does that even mean, and how is it a response to my point that choosing an appropriate level of abstraction for the problem at hand is a good idea?

You said

> in general we just can't [describe a system in the limiting regime using the fundamental theory] without hand-waving, period...It's sort of true, but not in a useful way.

And I am saying that it in fact can be done, and has been done, in physics and math in a very non-hand-waving way. One can show rigorously when a certain abstractions is accurate.

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

#200

Post by empyrrhicist » Wed, Jun 05, 2024, 7:46 PM UTC

jessriedel wrote: post #199

empyrrhicist wrote: post #195

Earlier quoted context omitted.

What does that even mean, and how is it a response to my point that choosing an appropriate level of abstraction for the problem at hand is a good idea?

You said > in general we just can't [describe a system in the limiting regime using the fundamental theory] without hand-waving, period...It's sort of true, but not in a useful way. And I am saying that it in fact can be done, and has been done, in physics and math in a very non-hand-waving way. One can show rigorously when a certain abstractions is accurate.

Well... sure, but I think you're still almost purposely missing the point. Take this example - can we prove that a system of differential equations emerges in a meaningful way from discrete systems? Yes, obviously. That's a far cry from the OP's "if you think about it, all things are quantum", which is where this thread started and what I'm talking about.

It also illustrates the actual point pretty well - when you have a good set of differential equations that describe observed phenomena, that higher level of abstraction gives MORE insight into the processes at play, even when we know that it emerges from something more fundamental. Only when that model is a poor approximation do we need to appeal to the more fundamental regime (or when that fundamental regime is what we're studying).