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I'm confused, I know, I'm always confused

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Re: I'm confused, I know, I'm always confused
Post by Fox2!   » Mon Aug 01, 2022 12:25 am

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ThinksMarkedly wrote:
Joat42 wrote:Technically it's entirely correct using the term "sublight" since no lightspeed signal actually travels at lightspeed due to the fact that it doesn't travel through a perfect vacuum.


That's far more pedantic than my relay idea!

Of course, the above is just an esoteric nitpick and the use of the word in the way it was done was kind of strange. Sublight in SciFi is usually related to engines or movement, not communication which is usually classified as being at lightspeed or FTL.


The most likely in-universe explanation is that the speaker simply mis-spoke. As you say, sublight is more often used to talk about movement of ships, so it might be in actual use aboard ship. Misusing to mean a light-speed signal (compared to an FTL gravitic signal) is entirely possible.


I don't have Governor handy at the moment, but I believe RFC used "sublight" to refer to light speed comms there, also.
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Re: I'm confused, I know, I'm always confused
Post by zuluwiz   » Tue Aug 02, 2022 11:35 pm

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I notice nobody has mentioned bitrate in connection to this question. That would be a good reason for the data to come in slowly, especially if the recon drone was transmitting as it received and processed the data.
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Re: I'm confused, I know, I'm always confused
Post by tlb   » Wed Aug 03, 2022 8:28 am

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zuluwiz wrote:I notice nobody has mentioned bitrate in connection to this question. That would be a good reason for the data to come in slowly, especially if the recon drone was transmitting as it received and processed the data.

In the books it is more treated as a question of bandwidth. In The Honor of the Queen, the transmission was at the level of Morse Code, but it recent books we are getting audio and video.
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Re: I'm confused, I know, I'm always confused
Post by Theemile   » Wed Aug 03, 2022 9:36 am

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tlb wrote:
zuluwiz wrote:I notice nobody has mentioned bitrate in connection to this question. That would be a good reason for the data to come in slowly, especially if the recon drone was transmitting as it received and processed the data.

In the books it is more treated as a question of bandwidth. In The Honor of the Queen, the transmission was at the level of Morse Code, but it recent books we are getting audio and video.


That was FTL transmission speeds, not not normal space RF or lasers, which had a high bandwidth.

Technically, Sublight is correct terminology for all RF and laser communications - c (the speed of light) is defined as the speed of light in a vacuum, and space is not a perfect vacuum, so any communications will be "slightly" below the speed of light, or sublight.
******
RFC said "refitting a Beowulfan SD to Manticoran standards would be just as difficult as refitting a standard SLN SD to those standards. In other words, it would be cheaper and faster to build new ships."
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Re: I'm confused, I know, I'm always confused
Post by tlb   » Wed Aug 03, 2022 10:55 am

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zuluwiz wrote:I notice nobody has mentioned bitrate in connection to this question. That would be a good reason for the data to come in slowly, especially if the recon drone was transmitting as it received and processed the data.

tlb wrote:In the books it is more treated as a question of bandwidth. In The Honor of the Queen, the transmission was at the level of Morse Code, but it recent books we are getting audio and video.

Theemile wrote:That was FTL transmission speeds, not not normal space RF or lasers, which had a high bandwidth.

Technically, Sublight is correct terminology for all RF and laser communications - c (the speed of light) is defined as the speed of light in a vacuum, and space is not a perfect vacuum, so any communications will be "slightly" below the speed of light, or sublight.

True, but the question of bitrate was only significant for the early FTL drones, I believe. And that was not due to processing power. Anyway isn't bitrate largely independent of transmission speed?

Far outside any source of stellar wind, how much slower is light traveling than the theoretical value of "c"?

PS: shouldn't the term be "sub-c" then, since the speed of light is whatever it actually is and only in a vacuum is it really c?
Last edited by tlb on Wed Aug 03, 2022 11:36 am, edited 2 times in total.
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Re: I'm confused, I know, I'm always confused
Post by Joat42   » Wed Aug 03, 2022 11:03 am

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tlb wrote:
zuluwiz wrote:I notice nobody has mentioned bitrate in connection to this question. That would be a good reason for the data to come in slowly, especially if the recon drone was transmitting as it received and processed the data.

In the books it is more treated as a question of bandwidth. In The Honor of the Queen, the transmission was at the level of Morse Code, but it recent books we are getting audio and video.

It should be mentioned that bitrate actually only pertains to serialized communication (with some caveats), the correct terminology is symbol-rate I believe. The symbol-rate coupled with the symbol-size then determines the bandwidth. Of course, in general terms bitrate and bandwidth can be used interchangeably but when you dig down into how things are encoded and transmitted it becomes two different things.

If we consider the first iteration of the FTL-communication mentioned, bitrate was an acceptable metric. Lets say that the next iteration allowed them to send 2 streams simultaneously, double the bandwidth right? No, it's actually 4x the bandwidth because you combine each bit from the 2 streams into a symbol that can have 4 states (0+0,0+1,1+0,1+1). Each technological iteration of the FTL-communication system probably involved faster bitrates coupled with more bitstreams, so the practical bandwidth most likely increased geometrically for every iteration until they hit the point of diminishing returns. It's of course entirely possible that each bit can have more states than 0 and 1 which also increases the bandwidth, so if a bit can have 3 states, 2 bitstreams then allows for symbols that can have 9 (3^2) states.

So going from slow, morse-like communication to full audio/video could probably be done fairly quickly.

---
Jack of all trades and destructive tinkerer.


Anyone who have simple solutions for complex problems is a fool.
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Re: I'm confused, I know, I'm always confused
Post by Theemile   » Wed Aug 03, 2022 1:26 pm

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tlb wrote:
zuluwiz wrote:I notice nobody has mentioned bitrate in connection to this question. That would be a good reason for the data to come in slowly, especially if the recon drone was transmitting as it received and processed the data.

tlb wrote:In the books it is more treated as a question of bandwidth. In The Honor of the Queen, the transmission was at the level of Morse Code, but it recent books we are getting audio and video.

Theemile wrote:That was FTL transmission speeds, not not normal space RF or lasers, which had a high bandwidth.

Technically, Sublight is correct terminology for all RF and laser communications - c (the speed of light) is defined as the speed of light in a vacuum, and space is not a perfect vacuum, so any communications will be "slightly" below the speed of light, or sublight.

True, but the question of bitrate was only significant for the early FTL drones, I believe. And that was not due to processing power. Anyway isn't bitrate largely independent of transmission speed?

Far outside any source of stellar wind, how much slower is light traveling than the theoretical value of "c"?

PS: shouldn't the term be "sub-c" then, since the speed of light is whatever it actually is and only in a vacuum is it really c?


Exactly, FTL transmission bitrate picked up as the technology improved - However, Usually RF bitrate is limited by the signal frequency, or multiples there of (for-ex, the X-10 protocol places timed instructions at specific places in the waveform based on the powerline frequency)

Technically, you are correct for "Sub-c", but I've never heard the phrase. The speed of light in Copper can drop to as low as 72% but coax can be as high as 83% - Earth's atmosphere at sea level drops the speed of light by a factor of 1.0003, So anything interstelllar matter can do is almost insignificant - but from a physics point of view, it is sub-c. And at the distances we're discussing, timing signals will be distorted.
******
RFC said "refitting a Beowulfan SD to Manticoran standards would be just as difficult as refitting a standard SLN SD to those standards. In other words, it would be cheaper and faster to build new ships."
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Re: I'm confused, I know, I'm always confused
Post by tlb   » Wed Aug 03, 2022 2:10 pm

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Theemile wrote:Technically, you are correct for "Sub-c", but I've never heard the phrase. The speed of light in Copper can drop to as low as 72% but coax can be as high as 83% - Earth's atmosphere at sea level drops the speed of light by a factor of 1.0003, So anything interstelllar matter can do is almost insignificant - but from a physics point of view, it is sub-c. And at the distances we're discussing, timing signals will be distorted.

I am not saying that I have seen it; but in discussions of Čerenkov radiation, we are clearly talking about the speed of a particle being faster than the speed of light in the medium (both speeds being less than c).
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Re: I'm confused, I know, I'm always confused
Post by ThinksMarkedly   » Wed Aug 03, 2022 3:27 pm

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Theemile wrote:Technically, you are correct for "Sub-c", but I've never heard the phrase. The speed of light in Copper can drop to as low as 72% but coax can be as high as 83% - Earth's atmosphere at sea level drops the speed of light by a factor of 1.0003, So anything interstelllar matter can do is almost insignificant - but from a physics point of view, it is sub-c. And at the distances we're discussing, timing signals will be distorted.


I wonder what the effective speed is to Voyagers 1 and 2. Those would be good testbeds.

Except that we can't measure the one-way speed of light. We can only measure round-trip, so the error in the computer systems in those two probes sending any signal back to us would be orders of magnitude greater. It could be done with a differential approach (measure it at two different distances), but you can't be sure that the computers would react in the exact same amount of time every time. In fact, you know they won't, because they're ageing and their power sources are dwindling. You'd also need to account for the redshifting due to the probes' velocity relative to us (which will vary during the year too!).

Why No One Has Measured The Speed Of Light - Veritasium (YouTube)
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Re: I'm confused, I know, I'm always confused
Post by Louis R   » Thu Aug 04, 2022 1:08 am

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You have 2 additional issues to deal with:

Signal velocity is degenerate with range - to calculate the former you have to obtain the latter independently. As an example, using the [clearly rounded off] numbers for the range and round-trip time to JWST on DSN Now gives a light speed of 300,353km/s. Close, but rather off ;) The range uncertainty to either Voyager is going to be large enough to bury the effect you're looking for.

Also, the velocity isn't going to be constant. It depends on the plasma properties in a rather complex way [literally: complex analysis was fully developed because it's needed to solve problems in electrical engineering], and those properties can vary on rather short time scales. In fact, one of the probes of the interplanetary medium is observation of changes in the signals received from satellites with transmitters with very precisely known characteristics - with an error budget for changes since launch. So the differential method won't - and can't - give the same result twice, with no way to separate systematic and stochastic errors.

ThinksMarkedly wrote:
I wonder what the effective speed is to Voyagers 1 and 2. Those would be good testbeds.

Except that we can't measure the one-way speed of light. We can only measure round-trip, so the error in the computer systems in those two probes sending any signal back to us would be orders of magnitude greater. It could be done with a differential approach (measure it at two different distances), but you can't be sure that the computers would react in the exact same amount of time every time. In fact, you know they won't, because they're ageing and their power sources are dwindling. You'd also need to account for the redshifting due to the probes' velocity relative to us (which will vary during the year too!).

Why No One Has Measured The Speed Of Light - Veritasium (YouTube)
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