4 ms·

Gravity is so many orders of magnitude weaker than electromagnetism that it is not even funny.

buildbot 4y ago
True, but you can theoretically format a gravity wave to not follow the inverse square law - these are called solitons (apparently, I just looked this up)
- jerf 4y ago
  Yes. Now look into how you construct a soliton, and try to figure out what monstrous levels of control you'd have to exert over solar-system sized quantities of degenerate matter to create them, and how much energy it would take. Now compute how much laser light you can generate for, oh, let's say, 6 orders of magnitude less energy. And how tightly you'd expect a civilization that apparently can casually wiggle dozens of solar masses at multiple Hz, in a modulated manner no less (so just a several Hz orbit is not sufficent, we are wiggling these things under power), to be able to collimate such a beam. This is the problem with gravity waves. It isn't some sort of supreme cheat code of the universe for super awesome communication. It's transparently obviously idiotic. Like, not just, "well, it's not necessarily the best way, but even if it's not great someone may have tried it", like, you're burning dozens of orders of magnitude more energy per bit. Plural dozens, of orders of magnitude. Not dozens of times, ten to the power of dozens. This is not sensible no matter how advanced the civilization. We're talking levels of stupid that would greatly exceed spending the entire output of Earth's collective industrial civilization for all of history on a single pack of Skittles. This is not a bright thing to do, and it only gets dumber the smarter you suppose the aliens are.
  - marginalia_nu 4y ago
    To be fair, because we don't know how to construct gravity waves does not mean such a means does not exist. Keep in mind, not too long ago we thought we needed to heat up a fillament surrounded by an inert gas in order to make artificial light, and our understanding of gravity is fairly poor (to the point where it's largely considered an unsolved problem quite how it fits together with other parts of physics).
    - SketchySeaBeast 4y ago
      If we make assumptions like that then the sky is the limit for other baseless assumptions, right? We're basically just picking our favourite pseudomagical science and arguing for it?
      - marginalia_nu 4y ago
        Well that is the basic posture of all science, uncertainty. We must assume we don't know until we are convinced otherwise.
        SketchySeaBeast 4y ago
        But you don't use that to suggest new unsupported ideas. In that case why can't I postulate for FTL communication by form of anti protons to be the best communication method?
        marginalia_nu 4y ago
        I've never talked about FTL communication.
        SketchySeaBeast 4y ago
        I didn't say you were. I was trying to make the point we're both suggesting science fiction now and it's not terribly helpful when trying to talk about the current science.
        misnome 4y ago
        By your argument, shouldn’t we assume that it’s possible by <literally any means you can imagine> that we just don’t know about?
        marginalia_nu 4y ago
        Not necessarily. We have no reason to assume gravity waves couldn't be produced artificially. This wouldn't really break any existing understandings of physics, it would merely require adding to them. The question is just how. We do have reason to think that information can't travel faster than the speed of light, as this would make it possible to send information to the future and then back to the past via a closed time-like curve, which would have all manner of effects that contradict what we've observed about how the universe works, and in fact are self-contradictory as well. This doesn't go to say this isn't possible, after all the Alcubierre drive seems hypothetically possible (it "only" hinges upon the ability to create negative energy density), it's just much more implausible.
all2 4y ago
Yes, but does it propagate faster than the speed of light? Even if a gravitic field is weak, it would be my preferred mode of communication if it propagated "instantly" across space/time. And it moves at the speed of light [0] so there's no speed advantage here. I see no reason a sufficiently advanced species would choose gravitic waves over any other EM wave. Does someone with a clue (not me) have any ideas why this would be the case? [0] https://en.wikipedia.org/wiki/Speed_of_gravity https://en.wikipedia.org/wiki/Speed_of_gravity
- jerf 4y ago
  It does not. The concrete evidence of this is relatively recent; theoretically nobody has expected that it would for a long time, but it has been theory. But yes, we've coordinated detections between LIGO and radar astronomy now, and there's no reason to believe gravity travels FTL. As always, there are error bars, but they're tight enough not to get excited about. That is, who cares if gravity travels at 1.00000000000001 the speed of light? (The theoreticians would go absolutely ballistic, but pragmatically that would mean nothing.)
  - nwiswell 4y ago
    > but pragmatically that would mean nothing Well except the part where you could use gravity waves to send messages to the past, I imagine that would have some pragmatic implications.
    - vecter 4y ago
      Huh? What about gravity waves allows... backwards time travel?
      - nwiswell 4y ago
        Anything that travels faster than light is a violation of causality and would be perceived to move backward in time.
        4y ago
raverbashing 4y ago
This is the answer Something like a neutrino bean sounds more plausible as a communication medium than gravitational waves

True, but you can theoretically format a gravity wave to not follow the inverse square law - these are called solitons (apparently, I just looked this up)

jerf 4y ago
Yes. Now look into how you construct a soliton, and try to figure out what monstrous levels of control you'd have to exert over solar-system sized quantities of degenerate matter to create them, and how much energy it would take. Now compute how much laser light you can generate for, oh, let's say, 6 orders of magnitude less energy. And how tightly you'd expect a civilization that apparently can casually wiggle dozens of solar masses at multiple Hz, in a modulated manner no less (so just a several Hz orbit is not sufficent, we are wiggling these things under power), to be able to collimate such a beam. This is the problem with gravity waves. It isn't some sort of supreme cheat code of the universe for super awesome communication. It's transparently obviously idiotic. Like, not just, "well, it's not necessarily the best way, but even if it's not great someone may have tried it", like, you're burning dozens of orders of magnitude more energy per bit. Plural dozens, of orders of magnitude. Not dozens of times, ten to the power of dozens. This is not sensible no matter how advanced the civilization. We're talking levels of stupid that would greatly exceed spending the entire output of Earth's collective industrial civilization for all of history on a single pack of Skittles. This is not a bright thing to do, and it only gets dumber the smarter you suppose the aliens are.
- marginalia_nu 4y ago
  To be fair, because we don't know how to construct gravity waves does not mean such a means does not exist. Keep in mind, not too long ago we thought we needed to heat up a fillament surrounded by an inert gas in order to make artificial light, and our understanding of gravity is fairly poor (to the point where it's largely considered an unsolved problem quite how it fits together with other parts of physics).
  - SketchySeaBeast 4y ago
    If we make assumptions like that then the sky is the limit for other baseless assumptions, right? We're basically just picking our favourite pseudomagical science and arguing for it?
    - marginalia_nu 4y ago
      Well that is the basic posture of all science, uncertainty. We must assume we don't know until we are convinced otherwise.
      - SketchySeaBeast 4y ago
        But you don't use that to suggest new unsupported ideas. In that case why can't I postulate for FTL communication by form of anti protons to be the best communication method?
        marginalia_nu 4y ago
        I've never talked about FTL communication.
        SketchySeaBeast 4y ago
        I didn't say you were. I was trying to make the point we're both suggesting science fiction now and it's not terribly helpful when trying to talk about the current science.
        misnome 4y ago
        By your argument, shouldn’t we assume that it’s possible by <literally any means you can imagine> that we just don’t know about?
        marginalia_nu 4y ago
        Not necessarily. We have no reason to assume gravity waves couldn't be produced artificially. This wouldn't really break any existing understandings of physics, it would merely require adding to them. The question is just how. We do have reason to think that information can't travel faster than the speed of light, as this would make it possible to send information to the future and then back to the past via a closed time-like curve, which would have all manner of effects that contradict what we've observed about how the universe works, and in fact are self-contradictory as well. This doesn't go to say this isn't possible, after all the Alcubierre drive seems hypothetically possible (it "only" hinges upon the ability to create negative energy density), it's just much more implausible.

all2 4y ago

Yes, but does it propagate faster than the speed of light? Even if a gravitic field is weak, it would be my preferred mode of communication if it propagated "instantly" across space/time. And it moves at the speed of light [0] so there's no speed advantage here. I see no reason a sufficiently advanced species would choose gravitic waves over any other EM wave. Does someone with a clue (not me) have any ideas why this would be the case? [0] https://en.wikipedia.org/wiki/Speed_of_gravity https://en.wikipedia.org/wiki/Speed_of_gravity

jerf 4y ago
It does not. The concrete evidence of this is relatively recent; theoretically nobody has expected that it would for a long time, but it has been theory. But yes, we've coordinated detections between LIGO and radar astronomy now, and there's no reason to believe gravity travels FTL. As always, there are error bars, but they're tight enough not to get excited about. That is, who cares if gravity travels at 1.00000000000001 the speed of light? (The theoreticians would go absolutely ballistic, but pragmatically that would mean nothing.)
- nwiswell 4y ago
  > but pragmatically that would mean nothing Well except the part where you could use gravity waves to send messages to the past, I imagine that would have some pragmatic implications.
  - vecter 4y ago
    Huh? What about gravity waves allows... backwards time travel?
    - nwiswell 4y ago
      Anything that travels faster than light is a violation of causality and would be perceived to move backward in time.
      - 4y ago

raverbashing 4y ago

This is the answer Something like a neutrino bean sounds more plausible as a communication medium than gravitational waves