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  •  Love the essay, but disagree with the idea (0+ / 0-)

    that we're all alone.  The idea that aliens in galactic empires are out there waiting to contact us supposes that they actually do want to contact us and mess up their observations.  

    If an alien probe was here, would you know it?  Imagine a probe that looked like a human being.  Just a guy in normal clothes, walking the streets of New York, riding the subway.  Not going anywhere in particular, just wandering and recording.  He never stops, never sleeps, never eats.  Just walks and rides and records.  Everybody sees him, but no one knows him, and this is fine because no one knows that no one knows him.  There could be thousands of them out there.  How would we know?  

    If an alien civilization was out there, among the stars, would you know  it?  Maybe they have the technology to mask their signals.  Or maybe we're not listening at the right time or in the right place.  

    The folks who say that tripping across the galaxy to study us is too energy-intensive or not worth the effort need to look hard at their own species.  Say hello to Bob.  Bob is an animal researcher who lives in Chicago.  Today, he gets up, takes a plane to Frankfurt and on to Tanzania, where he bumps overland in a 4x4 until he meets a waiting helicopter that takes him up so he can dart an antelope, weigh it, take a blood sample and study the condition of its genitals.  Just 120 years ago such a scenario would have seemed impossible.  But we invented the airplane and the automobile and while these are not the primary purposes of these technologies, they do allow us to get anywhere in the world in a day.  So now think about a species 500 or 1000 (or a million) years ahead of us, having discovered technologies beyond our ken-  why shouldn't such a study trip be easy for them?  Why wouldn't it be interesting?  The antelope that sees the weird bird and then wakes up with a tag in his ear cannot even conceive of a 747 or how it works.  Why should we be able to conceive of a technology similarly advanced from our own point of view?  

    The failure of a lot of scientists in considering these questions seems to be one of imagination.  What do you all think?

    Odds and ends about life in Japan: 1971wolfie.wordpress.com

    by Hatrax on Mon Jul 15, 2013 at 02:55:56 AM PDT

    •  If it's a failure of imagination (0+ / 0-)

      It's not with scientists.

      The idea of Bob the itinerant zoologist's journey by air and land would certainly have required plenty of imagination 120 years ago.  But it's not as if gliders didn't exist at that time: grounded doubts about the possibility of moving people intercontinentally by similar aerodynamic principles were based upon the difficulty of getting sufficient thrust into a small enough weight profile, not about breaking any laws of physics.

      What science can tell us is the minimum energy requirements to get a mass M from point A to point B in time T using technology limited by the laws of physics: in particular, the highest specific impulse achievable is with a photon rocket, i.e. point a very, very powerful laser in some direction to produce thrust.  If you want to get to 99% of the speed of light this way, then slow down again you need a mass ratio of about 200.  In this case we're talking about a mass (including fuel, tanking, engine, capsule) that will turn itself into photons at an efficiency better than 99.5%.  You can't use hydrogen and antihydrogen: apart from the mass ratio being out of reach for storing those, proton-antiproton annihilation produces a bunch of pions as well as gamma rays.  There's only the electron-positron reaction available that don't have this or another loss path (muons have a very short half-life), you'd have to keep them stored apart and at this point electrostatic forces will destroy any fuel tank made of matter (a fuel tank made of a magnetic field wouldn't hold for long owing to cyclotronic radiation).  Also here I'm taking for granted that something will be invented to reflect gamma rays (which isn't going to happen with atomic isotopes that actually exist or can exist).

      Going back to hydrogen-antihydrogen reactions, let's presume that some speculative future material allows a mass ratio of 50 without the hydrogen squeezing out and allows the containment of the antihydrogen equally well (it had better or else it'll explode).  In that case the maximum speed that such a rocket could achieve and then decelerate from would be about 57% the speed of light.  The thrust would be very low, but even presuming it could be made arbitrarily large (along with all the other lack of materials and engineering limits I've assumed) you'd be limited to destinations within about 20 light years before an original human crew have all died of old age.

      The upper limit of the density of civilizations in our own galaxy originally estimated at the first SETI meeting would put the nearest one more than 70 light years away.

      Given a magic engineering wand to push materials and designs right up to and even perhaps beyond the laws of physics, then, it would be a commitment of 250 years to make such a journey - or 500 if they wish to ever return home.  That's a part of why a study trip would not be easy for them (there's also the energy cost of creating the fuel).

      You sound like you might enjoy perusing Project Rho.

      Fake candidates nominated by the GOP for the recalls: 6 out of 7. Fake signatures on the recall petitions: 4 out of 1,860,283.

      by GeoffT on Mon Jul 15, 2013 at 02:19:17 PM PDT

      [ Parent ]

      •  In the box (0+ / 0-)

        I thank you for your long and well-researched reply.  But it just reinforces what I'm talking about.  

        Maybe I shouldn't have said 120 years.  Maybe I should have said 500.  Because then, the idea of Bob's journey wouldn't call to mind experimental gliders, it would call to mind things like witchcraft.  So let's go with that.  Five hundred years ago, Bob's journey would have been nothing but fancy.

        ...similar aerodynamic principles were based upon the difficulty of getting sufficient thrust into a small enough weight profile, not about breaking any laws of physics.
        Yes, and my only counter is that we haven't discovered all the laws of physics.  Back in Newton's time, quantum mechanics was inconceivable.  What will we discover about wormholes in the future, about other means of travel we can't even conceive of now?  Are hydrogen and antihydrogen really the best we'll ever have?  Are we really going to talk about crossing the Atlantic in a Sopwith Camel?  Let's cross the English Channel first, and see where engineering goes from there.

        Yeah, I'm a dreamer.  Go ahead and tell me I have a soft head.  But I've learned never to underestimate human cleverness or intelligence, or dreams.

        Odds and ends about life in Japan: 1971wolfie.wordpress.com

        by Hatrax on Mon Jul 15, 2013 at 03:11:59 PM PDT

        [ Parent ]

        •  That's why I concentrated on the laws of physics (0+ / 0-)

          ...rather than of engineering, because while materials scientists can change the laws of engineering, ye cannae change the laws of physics.

          Are hydrogen and antihydrogen really the best we'll ever have?  Let's cross the English Channel first, and see where engineering goes from there.
          That's my point: the engineering cannot take us further than that: new physics would be required before it's even a consideration.  The laws of physics, unfortunately, are under no obligation to play ball with human wishes.

          By all means dream, but where science can help is it can tell us what barriers stand between dreams and reality: the same math with which one can describe a wormhole also shows that you can't traverse it before it collapses unless you have so-called "exotic matter" - which requires properties unseen in any particles, observed or even theorized.

          Frankly, getting anywhere outside the solar system within a human lifetime is asking a lot more than getting the sci-fi staples of e.g. human cryogenics or building ark ships working - at least in these cases no new physics is required.

          Fake candidates nominated by the GOP for the recalls: 6 out of 7. Fake signatures on the recall petitions: 4 out of 1,860,283.

          by GeoffT on Mon Jul 15, 2013 at 05:56:40 PM PDT

          [ Parent ]

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