4 ms·

I don't think there are many different ways to encode meaningful information. We all live in the same universe and I see no reason to believe that intelligent

by lusr 14y ago

I don't think there are many different ways to encode meaningful information. We all live in the same universe and I see no reason to believe that intelligent alien life won't be intellectually quite similar to us. While tricky without context, decoding extraterrestrial signals will inevitably produce something of interest (images, audio) even if understanding e.g. the audio itself will be tricky. That being said, while I suspect that meaningful, structured information will be, by definition, structured and therefore obvious to spot in a broadcast, the real problem is that these transmissions are likely to be (a) compressed and/or (b) encrypted. While compression formats may reveal a few hints that there is some structured information present, encrypted data will be all but impossible to distinguish from random transmissions. We may be picking up transmissions from alien life but be unaware simply because the data is encrypted. I have no idea what proportion of our broadcast signals are encrypted today, but I suspect it's a fairly significant and growing proportion (privacy and intellectual property concerns being the primary reasons).

mistermann 14y ago
> While tricky without context, decoding extraterrestrial signals will inevitably produce something of interest (images, audio) even if understanding e.g. the audio itself will be tricky. Serious question: How is it presumably simple to decode images and audio, but difficult to understand the audio? Is it because one can assume image representation would tend towards mathematical efficiency, but spoken languages do not? >While compression formats may reveal a few hints that there is some structured information present, encrypted data will be all but impossible to distinguish from random transmissions. We may be picking up transmissions from alien life but be unaware simply because the data is encrypted. I would think that encrypted transmissions would be easily distinguishable from background white noise, no? My thinking is, you have the general random noise of space, and then you would have something obviously different, is that totally not the case?
- deleted 14y ago
  [deleted]
- lusr 14y ago
  Yes, I believe that images (encodings of electromagnetic radiation of particular wavelengths) and audio (encodings of mechanical waves of pressure) are universal concepts aliens are also likely to be familiar with, whereas understanding the information encoded within the transmission requires interpretation within a context we are highly unlikely to have here on Earth. This is just my intuition and speculation but I would guess somebody could formalise some support in terms of Kolmogorov complexity (http://en.wikipedia.org/wiki/Kolmogorov_complexity http://en.wikipedia.org/wiki/Kolmogorov_complexity): there are only so many ways to represent an image or audio, and over time an intelligent race will discover the least complex method and use it. Therefore, alien races of equivalent levels of technical advancement in a given field should be able to decode raw (uncompressed and unencrypted) transmissions of common types of information (images, audio). Any additional complexity on top of this method will probably be quite structured, e.g. with television signals we have portions of the signal that are blank because during that time the CRT of old televisions would be retracing and not displaying data. (Actually, I believe these "dead" portions of the video signal are sometimes used to send additional structured data, e.g. Teletext, which would make the structure of the signal even more apparent.) I suspect it'll be much easier to look at alien video transmissions and figure out what they're about than trying to listen do the same with audio transmissions because video would provide objective context (assuming it's not just a video of talking alien heads, or whatever the equivalent of a "head" for them would be). With respect to encrypted transmissions, if the entire protocol is encrypted from start to finish, and you're using the right cipher* then no, you can't distinguish encrypted data from random noise. This is the principle behind TrueCrypt's hidden volumes (http://www.truecrypt.org/docs/?s=hidden-volume http://www.truecrypt.org/docs/?s=hidden-volume). * What's the right cipher? So far no nobody has found a distinguisher for AES, and that's in common use, so that's probably good enough to make an alien race blind to us; i.e. we could be picking up signals from a race as sophisticated as c. 1998 humans (http://en.wikipedia.org/wiki/Advanced_Encryption_Standard http://en.wikipedia.org/wiki/Advanced_Encryption_Standard) without realising it.
  - mistermann 14y ago
    > then no, you can't distinguish encrypted data from random noise. But, would there not be a noticeable difference between random noise in space, and that same space PLUS someone broadcasting random noise? (And would it depend on whether or not they cared about being heard, even if they still wished their transmission to be encrypted). It just seems to me that if there is a particular point that is continuously broadcasting randomness, would it not be noticeable? Or is what you are saying that that is essentially what stars are doing is broadcasting randomness, across a broad spectrum, and we can't distinguish between a star and an intelligent race....they are literally indistinguishable.
ithkuil 14y ago
some encodings are virtually indistinguishable from background noise,. e.g. spread spectrum like CDMA used in GPS. It's already difficult to decode them here on earth if you don't know the sequence key, let alone picking faint signals from distant civilizations.
- lusr 14y ago
  I was not aware of that. This is an interesting counter-point to caf's observation: http://news.ycombinator.com/item?id=4188432 http://news.ycombinator.com/item?id=4188432
orp 14y ago
Mandatory XKCD reference: http://xkcd.com/638/ http://xkcd.com/638/
- vibrunazo 14y ago
  Woa, I had never seen that one before. It puts together every criticism I have about SETI in much more clear and obvious language. I could never be so eloquent. Randall Munroe is an absolute genius.

by lusr 14y ago

mistermann 14y ago

> While tricky without context, decoding extraterrestrial signals will inevitably produce something of interest (images, audio) even if understanding e.g. the audio itself will be tricky. Serious question: How is it presumably simple to decode images and audio, but difficult to understand the audio? Is it because one can assume image representation would tend towards mathematical efficiency, but spoken languages do not? >While compression formats may reveal a few hints that there is some structured information present, encrypted data will be all but impossible to distinguish from random transmissions. We may be picking up transmissions from alien life but be unaware simply because the data is encrypted. I would think that encrypted transmissions would be easily distinguishable from background white noise, no? My thinking is, you have the general random noise of space, and then you would have something obviously different, is that totally not the case?

deleted 14y ago
[deleted]
lusr 14y ago
Yes, I believe that images (encodings of electromagnetic radiation of particular wavelengths) and audio (encodings of mechanical waves of pressure) are universal concepts aliens are also likely to be familiar with, whereas understanding the information encoded within the transmission requires interpretation within a context we are highly unlikely to have here on Earth. This is just my intuition and speculation but I would guess somebody could formalise some support in terms of Kolmogorov complexity (http://en.wikipedia.org/wiki/Kolmogorov_complexity http://en.wikipedia.org/wiki/Kolmogorov_complexity): there are only so many ways to represent an image or audio, and over time an intelligent race will discover the least complex method and use it. Therefore, alien races of equivalent levels of technical advancement in a given field should be able to decode raw (uncompressed and unencrypted) transmissions of common types of information (images, audio). Any additional complexity on top of this method will probably be quite structured, e.g. with television signals we have portions of the signal that are blank because during that time the CRT of old televisions would be retracing and not displaying data. (Actually, I believe these "dead" portions of the video signal are sometimes used to send additional structured data, e.g. Teletext, which would make the structure of the signal even more apparent.) I suspect it'll be much easier to look at alien video transmissions and figure out what they're about than trying to listen do the same with audio transmissions because video would provide objective context (assuming it's not just a video of talking alien heads, or whatever the equivalent of a "head" for them would be). With respect to encrypted transmissions, if the entire protocol is encrypted from start to finish, and you're using the right cipher* then no, you can't distinguish encrypted data from random noise. This is the principle behind TrueCrypt's hidden volumes (http://www.truecrypt.org/docs/?s=hidden-volume http://www.truecrypt.org/docs/?s=hidden-volume). * What's the right cipher? So far no nobody has found a distinguisher for AES, and that's in common use, so that's probably good enough to make an alien race blind to us; i.e. we could be picking up signals from a race as sophisticated as c. 1998 humans (http://en.wikipedia.org/wiki/Advanced_Encryption_Standard http://en.wikipedia.org/wiki/Advanced_Encryption_Standard) without realising it.
- mistermann 14y ago
  > then no, you can't distinguish encrypted data from random noise. But, would there not be a noticeable difference between random noise in space, and that same space PLUS someone broadcasting random noise? (And would it depend on whether or not they cared about being heard, even if they still wished their transmission to be encrypted). It just seems to me that if there is a particular point that is continuously broadcasting randomness, would it not be noticeable? Or is what you are saying that that is essentially what stars are doing is broadcasting randomness, across a broad spectrum, and we can't distinguish between a star and an intelligent race....they are literally indistinguishable.

ithkuil 14y ago

some encodings are virtually indistinguishable from background noise,. e.g. spread spectrum like CDMA used in GPS. It's already difficult to decode them here on earth if you don't know the sequence key, let alone picking faint signals from distant civilizations.

lusr 14y ago
I was not aware of that. This is an interesting counter-point to caf's observation: http://news.ycombinator.com/item?id=4188432 http://news.ycombinator.com/item?id=4188432

orp 14y ago

Mandatory XKCD reference: http://xkcd.com/638/ http://xkcd.com/638/

vibrunazo 14y ago
Woa, I had never seen that one before. It puts together every criticism I have about SETI in much more clear and obvious language. I could never be so eloquent. Randall Munroe is an absolute genius.