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Physics of creating a deliver-to-Earth-in-future signal

  1. Apr 12, 2010 #1
    Physics of creating a "deliver-to-Earth-in-future" signal

    Assume we had to send a signal to space so that it is automatically bounced back to earth at some point in the future (~a few thousand years),
    i.e a space based signal-time-capsule.
    How could this be done hypothetically?

    I am assuming we can use some form of Time Dilation or leverage Black Holes in some sort, but I am stumped as to how it could be done.

    Any suggestions, no matter how wild would be greatly appreciated.
  2. jcsd
  3. Apr 13, 2010 #2
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Sure, just stick your message in a rocket and send it on a round trip. You don't even need to invoke exotics for that. Ever see the movie Star Trek 1? That was essentially the plot! :wink:

    If you're talking about shooting some form of EM radiation out, I can't imagine how you would protect the signal, or WHY you'd want to invoke differential aging or time dilation.
  4. Apr 13, 2010 #3


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    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    you could just shoot the beam at something really far away...and wait for it to reflect (if at all).

    If you shoot a beam at a "reflective object" 500ly away, the light beam should return to Earth in 1000ly...
  5. Apr 13, 2010 #4
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Hmmmm, but could you do that, maintain signal integrity AND assure that the reflection will return to where Earth WILL be? I'm not even sure that's possible given recession speeds. This is a lot more than bouncing a laser off our moon...
  6. Apr 13, 2010 #5


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    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    lol, I'm speaking very hypothetically. I don't think there are any reflective surfaces in space (non-man made) which are nearly reflective enough. Dissipation of the signal would be a huge problem (just from the light spreading out). Red-shift/blue shift would also have to factor in.

    Predicting where the Earth will be shouldn't be too bad in comparison imo. Recession speeds are not significant in comparison to the speed of light for distances such as 1000ly which is still well within our galaxy. If you wanted to shoot a laser beam 13.7Gly to a distant galaxy however.......
  7. Apr 13, 2010 #6
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Oh I know, I didn't think you were making a case for perfect space-mirrors! Thanks for clarifying the recession speed issue, I really wasn't sure about that at all.

    Given all of this, I think it's fair to ask the OP: What made you think of this? It's an interesting concept; a REAL time-capsule so to speak... but why a 'signal' rather than a 'rocket'?
  8. Apr 13, 2010 #7
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Thanks for your replies. Although I was really hoping there would be a way :-(

    As to the reason for this question
    > What made you think of this?
    A plot-device for a sci-fi story. Imagine this scenario,
    'Earth has suffered a catastrophic disaster. Population reduced to a few million, forced to live in a technologically backward culture.
    Human knowledge is in danger of being lost forever. Worse, as expected, this gives rise to a totalitarian regime which seeks to hoard all knowledge for itself to remain in power. Thus this regime is actively destroying all other forms of information in public hands.
    A set of people work on a time-capsule which is the sum total of all knowledge.
    It should have these characteristics

    a) It should be available to earth after a few 100 to a few 1000 years when mankind can make better use of it
    b) It should be indestructible. Should not decay.
    c) It should not be capturable by the evil-powers
    d) Should be widely available to all in all parts of the globe when it is opened
    e) Should be able to be read with simple technological devices. Not DVD drives or disk drives.
    f) Multiple such time-capsules should be creatable with different "open-dates."

    The space-based signal-time-capsule fits the bill.
    It's better than a rocket in many ways
    a) Evades capture. Once sent, it's hard to be caught by someone else
    b) Indestructible in space. Cannot collide with space debris. (Assuming we can solve the dissipation problem)
    c) Multiple signals can be sent. One will return after 500 years, another after 600 years and so on.
    d) Once the signal comes back to earth, a simple radio reciever can be built which can read this signal at many parts of the globe.
    So it's hard for a regime to enforce a total black out.

    I thought of a simple satellite sent to a Lagrange point, L1 or L2, that will just beam signals back. But this can be destroyed by an evil regime(assuming they have some rockets left)

    Another wild-idea was to have the signal rotate near the Event horizon near a black hole. Thus travelling forward to the future due to time dilation.
    Not sure whether it was possible, hence the post.

  9. Apr 14, 2010 #8


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    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Gravitational time-dilation of your signal will just red-shift it, and would have nothing to do with when you receive that signal. Time-dilation to a photon is simply a red-shift.

    I don't think there are any currently conceivable devices that would fit all 6 of your points...there may be certain extremely complicated devices which can fit a,b,c,d, and f; however, I don't see point e being fulfilled.

    Any signal can always be intercepted...there is no way to create something that cannot be intercept-able at this time. The best bet at the moment involves quantum encryption which is in principle unbeatable...however, that doesn't mean someone can't intercept the signal...it just means that the receiver will KNOW someone has intercepted the signal.

    I think your best bet is a really fast rocket...with enough of a head start, the current "regime" wouldn't be able to catch up. You could fill the rocket with thousands of leaflets or w/e you want to leave information on, and at command return to Earth and disperse that information everywhere.

    E-M wave signals will be dispersed by the ISM, and very little will reflect back to you after traveling such distances.

    Some ideas I have which may fit some of the criteria, but not all:

    1) Encode the information in the genetic code of your species (or other species with complicated DNA). There's a lot of our DNA that's, as far as we know, not used (called non-coding DNA). I could imagine people encoding information in these sections of DNA and waiting for a future advanced civilization to decode it.

    Advantages are that with enough offspring from the original person who's DNA was spliced, the spread of information would be large and very hard to control. Coding the DNA wouldn't be too tough, although, one could not do it with primitive technology. There is pretty good capacity for information in the billions of non-coding codons. However, with this method, there will be degradation of the "signal" due to random mutations in the DNA...which should be manageable if the time-scales are not too long (e.g. <1000 generations). I don't have any math to back this up haha. I like this option the best.

    2) Beam the information to multiple satellites with stable orbits. The satellites would beam the information from one to another in a non-predictable fashion which would make interception of the signal difficult. However, this method doesn't guarantee against the "regime" simply destroying ALL satellites.

    That's about all I can think of...
  10. Apr 14, 2010 #9
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Essentially what you are speaking about is an instance of a class of delay-line storage. The options for variations on the theme are immense. The practical complications vary vastly depending on the details. For instance, if the recipients are likely to be re-emerging from barbarianism there is no point to hiding the signal in technology-dependent media such as space-transmission of photons, or encoding it into Nuclear DNA. Also, remember that if the signal is something transient, it needs to be regenerated so that it does not simply pass by and vanish on its return.
    Human DNA would not be able to contain a great deal of data by modern storage standards. Firstly, there is not a great deal of capacity, only a GB or so total. How much of that is significant is grossly unclear, the very term "junk DNA" has become Non-PC. "Non-coding DNA" simply means that it is not transcribed, not that you could survive without it, or even without a great deal of its functional information. Watch this space!
    A more viable approach might be to design a class of microbes, say something like a strain of beneficial cyanobacteria, that could quietly live in every mud puddle without harm, possibly being of great food value to a large range of organisms. It could house segments of data, say a few MB per cell, possibly as plasmids, together with a really serious error-correcting function, plus a sequence marker so that segments could be fitted together intelligibly. The organism should be strongly spore-forming so that soil, blown dust, and marine ooze all could store huge repositories of data, formatted for easy and reliable interpretation.

    Similarly, some of the spores could be sent into space. You never know...

    Last edited: Apr 14, 2010
  11. Apr 14, 2010 #10
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    I would use a VERY powerful gun, probably using compressed hydrogen, to shoot very hardy modules set to "sleep" for 10, 20, 100, etc.. years. Each would be set for a relatively short period of transmission, and would otherwise be dark. Fire these in some large asterois, or lodge them in periodic comets.

    Rely on the celestial body to return periodically, and embed transmitters all over the world, or have those probes triggered by some passive means unique to earth (can't be magnetic field, that fluctuates). Then, you conserve power, don't open a signal to interception (the probes can be hardy and made to self-destruct upon ANY tampering). Use that swarm, and only ONE needs to survive the current 'evil regime', and you also avoid the need to extremely energy-intensive means of launch, or ones that would be easier to trace.

    I would then combine that with every other method concievable... including Jon's. In fact, I might insert the relevant code into E. Coli, and have it live in our own guts. That should protect against some mutation due to UV spectrum, and you could program them to express information through... say... transformation of a person when they die. A dead person is still a vat of chemical energy, that could be used, and apoptosis on a large scale could also trigger secondary function in bacteria, or disparate sequences.

    To expand on Matterwave's #2, and what Jon Richfield have said: The "fantasy-sci-fi" would be to use something like Herpes to encode the information in our DNA, maybe as introns. The hardcore fantasy would be to use a retrovirus to make that information "appear" in one's brain. In that case, cashes of inert viruses in their 'crystalline' formation would last 100-1000 yrs without even NOTICING, and even barbaric humans just need to open the vessel and become infected.

    If the people of that time have drifted so far from 'human', or so deeply into barbarism that none of these means are effective, I think that civilation would need to follow a natural course anyway, or they would no longer be people you wish to impart knowledge to. That brings up the final issue: what motivates such a complex plan for the 'opressed' in this regime? Human nature is not to preserve knowledge in that fashion, but to fight and die.
  12. Apr 14, 2010 #11
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Fascinating info on genetic encoding. Didn't think of that.
    Going back to the drawing-board!

    Many thanks for the insightful replies.
  13. Apr 15, 2010 #12
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    One thing that I'd do if I were in this sort of situation is to try *everything*. If you do one method, there may be a flaw in it that causes it not to work, but if you end up trying 20 or 30 different methods, then maybe one of them will end up working.

    Also there is an interesting problem which you should be aware of....

    In 221 BC, the Emperor Qin Shi Huang unified China (which from the point of view of the people living there was the entire civilized world). He then proceeded to burn any book he could find in order to destroy any trace of history from before he was was Emperor. Now he lived only about 20 years before his dynasty collapsed.

    After the Qin dynasty collapsed, there was a great effort to reconstruct the missing texts. One thing that they did was to interview scholars that had escape death and write down what they remembered of the books, This created what was known as the "new script texts." Now while all of the books where being burned, some people managed to hide some books and so over time fragments of the old books appeared, and people put them together to form the "old script texts."

    Now the interesting part is that for the last several thousand years, Chinese scholars have debated which set of texts were the better texts. The 'new script" texts were reconstructed from memories, but the 'old script" texts were created from fragments of books.

    The other interesting thing about this happened in the 19th century. When the Europeans first arrived, Chinese scholars were under the mistaken impression that the science and mathematics that the Europeans were using had actually started in China, and if people could piece together the ancient texts that they would get some of the lost knowledge that would allow China to fight off the Europeans. Now it turned out that this wasn't the situation at all, and after a few decades it became obvious to everyone that this there was no secret lost knowledge in the ancient texts, but this caused China to lose some time in mounting a defense against Europe in the 19th century.

    (Replace the Europeans with space aliens, and you have a story.)
  14. Apr 16, 2010 #13
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Here is a not so scientific idea. Everyone in the world (or those who are trying to keep the knowledge) gets a tattoo with certain letters on thier body. By itself the letters mean nothing but when you take the letters and add them to other letters from the same family you get words...the family makes small "pages" of the knowledge to be passed on..and then extended family makes up a larger version of the message and by doing the whole 6 degrees thing you get the whole picture when you put the whole world together.

    Just an idea.
  15. Apr 16, 2010 #14
    Re: Physics of creating a "deliver-to-Earth-in-future" signal


    Though it doesn't offhand strike me as practical in the context of the question, I like the 6 (or is it 7... or 9...? No matter) degrees aspect of the idea. Mmmm... I wonder. I can't think of a story or a scheme that it would fit into, but it is worth thinking about.

    Anyway, the tattoo aspect reminds me of the Saki (H.H. Munro) short story "The Background". In case anyone online has never read it, it is at:
    http://www.readbookonline.net/readOnLine/501/ [Broken]
    Enjoy. Saki is read too seldom nowadays, much to many people's loss.
    Last edited by a moderator: May 4, 2017
  16. Apr 16, 2010 #15
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Actually FD, I have on occasion mulled over the idea of hiding serious amounts of information that intelligent survivors of a nearly-terminal civilisation crash could use and read, not really millions, but certainly thousands of years into the future. I was thinking of something low-tech, like a building that savages could not easily damage (how about walls of SiC with imprinted pictures etc, say?) It is quite an interesting line of speculation. You need something durable, not obviously valuable, with tricks for teaching reading, writing, pronunciation, maths, science ... the whole tutti. Anyone bright enough to realise that there is something to learn, should be bright enough to learn it. I have roughed out some technology and future history, but not the politics, nor a satisfying plot as yet.
    But the general idea hath its attractions...

  17. Apr 16, 2010 #16


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    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Larry Niven used this idea in "Footfall": Take huge granite blocks and etch them with lasers all the way through. (this prevents anyone from chiseling away the writing or it eroding away). Scatter these blocks over the planet, with the simplest information in places easy to find and the more advanced in more and more remote spots.
  18. Apr 16, 2010 #17
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    That was the inspiration for my idea (using periodic comets/orbits in the place of scattering)... :biggrin: I even read the man-kzin wars (and YES, I am ashamed of that!) when I was younger...

    To be fair, I also thought of the Code of Hammurabi, which relied on little more than placement, materials, and really REALLY nasty threats.
    Last edited: Apr 16, 2010
  19. Apr 16, 2010 #18
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Also, it would be interesting to imagine a society in which advances in knowledge involved decode semi-secret messages from the past, it would be a *very* different society than the one we live in.
  20. Apr 16, 2010 #19
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    Ahhh, but then the Evil Regime could destroy that. I suppose the best way would be to follow the lead of the Sumerians and Akkadians, use clay, and follow the Niven-"pollen" model.
  21. Apr 16, 2010 #20
    Re: Physics of creating a "deliver-to-Earth-in-future" signal

    That might be the idea however... knowledge along with warnings... a kind of reversed "Star Trek" Prime Directive. If you've properly seeded the world, you could actually accept the rise and fall of petty dictators using that knowledge, until eventually it fell into better hands.

    That brings me back to: "Why?" Why do dying people want to share the information that led in some way to their destruction? Why would people exert their final (but not inconsiderable) effort to something OTHER than immidiate survival? That ALREADY sounds like a very different society.
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