Re: Many Fermis Revisited
Title: Re: Many Fermis Revisited At 22:47 +0100 13/01/2003, scerir wrote: [George Levy] Here is a (white) hared brained idea on how to build a time machine. You need a very good recording device and a Quantum Suicide (QS) machine. For a simpler device see: http://www.fourmilab.ch/rpkp/chan-evid.html [Tim May] I am quite strongly persuaded that "many pasts for a particular present" is not a reality. I think GL is following Einstein (1931) and Wheeler (1978) here. The past has no evidence except as it is recorded at present. Hence, you can choose 'how' to observe this recorded past. By means of which set-up. And you can get different 'pasts'. Indeed. Something quite similar appears also in Bell "one-world" interpretation of Everett's relative state theory. This is discussed with some detailed in Barrett's book, mentioned recently by Tim, "The quantum mechanics of Mind and Worlds". (Oxford Press 1999) (I have read that book quickly but my first feeling is that Barrett did not understand the Everett's subjective /objective distinction (akin to 1/3 person distinction). I would follow GL (George Levy or Godel-Lob as you wish!) on the many pasts, although I am not sure Bell's many past are so coherent with Everett. Interesting matter anyway. Bruno
Re: Many Fermis Revisited
[George Levy] Here is a (white) hared brained idea on how to build a time machine. You need a very good recording device and a Quantum Suicide (QS) machine. For a simpler device see:http://www.fourmilab.ch/rpkp/chan-evid.html [Tim May] I am quite strongly persuaded that "many pasts for a particular present" is not a reality.I think GL is following Einstein (1931) and Wheeler (1978) here. The past has no evidence except as it is recorded at present. Hence, you can choose 'how' to observe this recorded past. By means of which set-up. And you can get different 'pasts'.
Re: Many Fermis Revisited
Tim May wrote If you mean that "many presents" have "many pasts," yes. But the current present only has a limited number of pasts, possibly just one. (The origin of this asymmetry in the lattice of events is related to our being in one present.) I mean one (many?) present has many pasts as well as many futures. Many pasts are fundamentally caused by quantum uncertainty in memory devices; many presents are caused by uncertainty in observation devices; many futures are caused by uncertainty in the controlling devices. The past cannot be ascertained precisely just as the future cannot be predicted precisely. Our consciousness is a fuzzy point in the many world. It has an infinite number of pasts and an infinite number of futures, an everbranching tree toward the past and an everbranching tree toward the future. Taking many observer moments together, I view the many world more as a lattice then as a tree. Thus navigation in the many-world makes sense. George
Re: Many Fermis Revisited
On Monday, January 13, 2003, at 10:47 AM, George Levy wrote:
Tim, Hal, Russell
Since we have several futures ( and several pasts), time travel is
just a particular case of many-world travel.
I somewhat agree...and we are not the first to make this point.
However, we need to be careful about saying we have "several pasts" (I
assume by "several" you mean "many").
The usual modal operators are needed. We have many possible futures,
but our possible pasts are limited by the events which are "necessary"
to produce the world we are actually in. The square operator for "that
which necessarily may be" and the diamond operator for "that which may
be."
If you mean that "many presents" have "many pasts," yes. But the
current present only has a limited number of pasts, possibly just one.
(The origin of this asymmetry in the lattice of events is related to
our being in one present.)
...interesting theory elided...
If there is only a single sequence of events ("a past") which produces
the actual world we are in today, then your time machine will not work,
as one cannot go back to a world where the past was different from what
"actually happened."
(And if one did, then of course one would be an actor in a past that
never happened, a la the usual grandfather paradox in all of its usual
variants. So "returning to the present" would be to a different
present.)
If this idea has any merit this is why space travelers are not
observable either. It provides a form of cosmic censorship. By
reducing their measure through QS and the likes, advanced aliens just
evolve out of existence in our world!
You ought to read "Finity," by John Barnes. He explores a very similar
idea.
--Tim May
"They played all kinds of games, kept the House in session all night,
and it was a very complicated bill. Maybe a handful of staffers
actually read it, but the bill definitely was not available to members
before the vote." --Rep. Ron Paul, TX, on how few Congresscritters saw
the USA-PATRIOT Bill before voting overwhelmingly to impose a police
state
Re: Many Fermis Revisited
Tim, Hal, Russell Since we have several futures ( and several pasts), time travel is just a particular case of many-world travel. Here is a (white) hared brained idea on how to build a time machine. You need a very good recording device and a Quantum Suicide (QS) machine. 1) You allow the recorder to operate for a prolonged period of time and record everything in the universe within an given degree of resolution. 2) You select a past where you would like to go and send the corresponding data to a QS machine. 3) The QS machine then restricts your consciousness to follow a path in the manyworld leading to the reconstruction of the selected past within the tolerance provided by the recording machine. This path must go through a series of worlds logically consistent with your consciousness to eventually reach the world you desire. This is navigation in the manyworld! (it reminds me of the sci-fi author Zelazny). Result of the time travel is the *extreme* reduction in relative measure of the time traveler. This is why time travelers are not observable. Time travel can only work if there is a recording already in existence. Thus, time travelers cannot go before the recording machine was turned on. Of course, beside time travel, several other forms of manyworld travel are possible, ie., going to alternate pasts, alternate presents, improbable futures, fantasy worlds, etc... If this idea has any merit this is why space travelers are not observable either. It provides a form of cosmic censorship. By reducing their measure through QS and the likes, advanced aliens just evolve out of existence in our world! George
Re: Many Fermis Revisited
Tim May wrote:
>
>
> Imagine what will happen if strong MWI communication happens in our
> universe, our branch:
>
> -- presumably access to all of the manifold knowledge from every
> universe which has done science, engineering, etc.
>
> -- vast amounts of technology (as some universes are "ahead" because
> the Newtonian revolution happened in 535 A.D., etc.)
>
> -- like a quantum computer, every calculation run a bunch of times,
> answers already known
I grant this, but nevertheless trying to extrapolate possible
technologies out a billion years or so in the conventional Fermi
Paradox is also a tad meaningless. About all we can say is that from
energetic reasons, civilisations are unlikely to expand much faster
than 1 order of magnitude slower than the speed of light, hence your
bound of 100 million light years away.
Of course if exotic technologies like warping spacetime were
possible... but then this is probably about as unlikely as time travel
or MWI communication, and just as subject to Hal Finney's argument,
namely that information on how to effect a wormhole must travel at
subluminal between the two end...
Cheers
A/Prof Russell Standish Director
High Performance Computing Support Unit, Phone 9385 6967, 8308 3119 (mobile)
UNSW SYDNEY 2052 Fax 9385 6965, 0425 253119 (")
Australia[EMAIL PROTECTED]
Room 2075, Red Centrehttp://parallel.hpc.unsw.edu.au/rks
International prefix +612, Interstate prefix 02
Re: Many Fermis Revisited
On Sunday, January 12, 2003, at 06:54 PM, Russell Standish wrote: (I'll limit myself to only commenting on the last, and most interesting, point.) This is where I lose your argument. I can't see why an MWI communication capable civilisation should be able to spread throughout our universe any faster than a non-MWI communication capable one. And even if its true, all it does is place tighter bounds on how difficult it is to create such civilisations. I agree that I didn't spend as much time as I could have on this point. Consider what would happen if MWI communication/travel happened in our timeline. First, let's distinguish between what I'll "weak MWI communications" and "strong MWI communications" (or travel, which is essentially isomorphic to communication): * Weak MWI communication. Strange, cryptic, ghostly sorts of communications, somewhat like the "I Ching" pentagrams and fleeting glimpses of "close" worlds in Dick's "The Man in the High Castle," Echoed in the James Hogan novel from 1997, "Paths to Otherwhere, and in a time travel version in Greg Benford's "Timescape," where a future/branch a century in the future attempts to communicate via particle physics with the "present" to stop/alter an outcome. * Strong MWI communication. Full communication with other branches, including substantive exchanges of information. Heinlein's "Glory Road" is a somewhat fantasy-oriented take on this, but the notion is clear: "Queen of the Nine Billion Universes," etc. Imagine what will happen if strong MWI communication happens in our universe, our branch: -- presumably access to all of the manifold knowledge from every universe which has done science, engineering, etc. -- vast amounts of technology (as some universes are "ahead" because the Newtonian revolution happened in 535 A.D., etc.) -- like a quantum computer, every calculation run a bunch of times, answers already known A summary of the Hogan book captures a bit of the impact: "The well-worn sf notion of parallel universes receives a computer-driven update in Hogan's latest novel. Berkeley research scientists Hugh Brenner and Theo Jantowitz are just beginning to make startling progress in siphoning information from other universes by means of sophisticated computer technology when their funding disappears. Fortunately but not fortuitously, they are recruited by a secret Defense Department research arm to continue their work under the umbrella of Project Octagon. Joined by a motley team of brilliant minds, including a Buddhist philosopher, the two quickly develop the means to shift their awarenesses to other versions of themselves in the "multiverse" and to preview thereby future outcomes for their home universe ..." This is why is it seems reasonable to me that MWI communication would dramatically a civilization's technology. (Not saying this knowledge would cause them to colonize the universe...maybe they'd give up in despair, or contemplate their navels, whatever. But contact with 10^10^N other worlds sure could be a kick in the pants, a kick that puts a civilization drastically ahead of any civilization which is still evolving "unitarily.") >From Hal's reference to Mike Price's document (which I read several years ago, so I'd forgotten or had not read his bit about MWI and Fermi), it looks like Price reached the same conclusion. --Tim May
Re: Many Fermis Revisited
Tim May wrote:
> I made no assumptions of nondifficulty (to use your phrasing).
>
> This is in fact why I picked the Thogians a few hundred million
> light-years from us. Now perhaps you think advanced civilizations are
> even rarer than in this example, there have not yet been any
> civilizations reaching our level, except ourselves, anywhere within a
> billion light-years or so of us. Arguing this one way or another was
> not my point.
It probably does make a point. 10^8 light years still puts the
Throgians close enough that we would have seen their Dyson spheres
etc, regardless of whether they've achieved MWI communication.
>
> Rather, it is that the effects of MWI communication (or time travel)
> would likely be enormous and that such a civilization would be expected
> to expand and show themselves in the (likely) billion or more years
> they would have had to expand, build Dyson spheres and other cosmic
> artifacts, send signals, etc.
>
I don't see this.
>
> >
> > This also implies that such technological civilisations are also
> > rather diffuse within the Multiverse, _excepting_ of course those
> > which share part of their history with ours (eg the Nazis which won
> > WWII). We have some predictive power as to what those people would be
> > like, since they will be similar to us.
>
> I'm not following this at all. Why do you think that communication with
> (or actual travel to) worlds is dependent on our ability to _predict_
> things about them?
>
Only that we can predict they're unlikely to achieved MWI
communication (relative to a completely unknown Throgian-like civilisation).
> I can see an argument to be made that only close worlds can be
> communicated with, and some folks have argued this, but this argument
> was not made by you here.
>
True.
> >
> > So, I for one, would not discount Hal Finney's point.
> >
>
> What I said was that the point that we have not yet built a receiver or
> portal says nothing about what others have done. And if there are other
> civilizations out there and building such receivers or portals is
> possible, one would expect a fair number of them to have done so. Since
> the implications of building such portals are, I think, enormous, I
> would expect a civilization which has built such things to have
> expanded even more rapidly through their part of the universe than
> without such things.
>
This is where I lose your argument. I can't see why an MWI
communication capable civilisation should be able to spread throughout
our universe any faster than a non-MWI communication capable one. And
even if its true, all it does is place tighter bounds on how difficult
it is to create such civilisations.
> --Tim May
>
A/Prof Russell Standish Director
High Performance Computing Support Unit, Phone 9385 6967, 8308 3119 (mobile)
UNSW SYDNEY 2052 Fax 9385 6965, 0425 253119 (")
Australia[EMAIL PROTECTED]
Room 2075, Red Centrehttp://parallel.hpc.unsw.edu.au/rks
International prefix +612, Interstate prefix 02
Re: Many Fermis Revisited
On Sunday, January 12, 2003, at 05:38 PM, Russell Standish wrote: The key assumption here is whether advanced technological civilisation (such as ourselves) is easy or difficult on the timescale of the age of the universe (10^10 years). Assuming that this is difficult (contra to your comments below), solves the standard Fermi paradox (namely other advanced civilisation are too far away to have reached us yet, and probably too far away to ever reach us, unless the universe starts contracting again. So your Throgians are as good as mythical. I cannot understand why you would say "contra to your comments below" when in several places I discussed this issue of how common life is: "... estimates of likelihood of advanced civilizations elsewhere. If we are the only form of life in our timelike region of the universe, i.e., within a few billion light-years, then of course this makes the odds of another receiver-builder nil." "My hunch is that alien civilizations may well exist, but are not abundant " I made no assumptions of nondifficulty (to use your phrasing). This is in fact why I picked the Thogians a few hundred million light-years from us. Now perhaps you think advanced civilizations are even rarer than in this example, there have not yet been any civilizations reaching our level, except ourselves, anywhere within a billion light-years or so of us. Arguing this one way or another was not my point. Rather, it is that the effects of MWI communication (or time travel) would likely be enormous and that such a civilization would be expected to expand and show themselves in the (likely) billion or more years they would have had to expand, build Dyson spheres and other cosmic artifacts, send signals, etc. This also implies that such technological civilisations are also rather diffuse within the Multiverse, _excepting_ of course those which share part of their history with ours (eg the Nazis which won WWII). We have some predictive power as to what those people would be like, since they will be similar to us. I'm not following this at all. Why do you think that communication with (or actual travel to) worlds is dependent on our ability to _predict_ things about them? I can see an argument to be made that only close worlds can be communicated with, and some folks have argued this, but this argument was not made by you here. So, I for one, would not discount Hal Finney's point. What I said was that the point that we have not yet built a receiver or portal says nothing about what others have done. And if there are other civilizations out there and building such receivers or portals is possible, one would expect a fair number of them to have done so. Since the implications of building such portals are, I think, enormous, I would expect a civilization which has built such things to have expanded even more rapidly through their part of the universe than without such things. --Tim May
Re: Many Fermis Revisited
Michael Clive Price wrote and widely distributed his "Many-Worlds FAQ" back in the 90s, and he has a couple of questions that touch on this topic: http://www.hedweb.com/everett/everett.htm#linear Is physics linear? Could we ever communicate with the other worlds? http://www.hedweb.com/everett/everett.htm#exact Is linearity exact? In the first answer above, Price argues that communication between the Everett worlds is impossible if the quantum mechanics formulation is correct and the Schrodinger equation evolves in a linear fashion as is presently believed. I'm not sure he is right about this, because I was under the impression that the worlds could exert slight influences on each other. Worlds never completely split, as I understand it; but rather, as decoherence develops between two branches, the degree of influence between them declines exponentially and soon they are effectively split. In his second answer above, Price build on this to argue that physics really is linear, because if it were not, inter-world communication and possibly transportation would be possible. He then argues along similar lines as Tim May has done here, that in some world an early civilization would have arisen and colonized through world-space as well as physical space. As I said, I'm not sure that Price is 100% correct in his reasoning here, but still there is a good argument to be made that inter-world travel cannot be too easy, or else they would certainly be here by now. Hal Finney
Re: Many Fermis Revisited
The key assumption here is whether advanced technological civilisation (such as ourselves) is easy or difficult on the timescale of the age of the universe (10^10 years). Assuming that this is difficult (contra to your comments below), solves the standard Fermi paradox (namely other advanced civilisation are too far away to have reached us yet, and probably too far away to ever reach us, unless the universe starts contracting again. So your Throgians are as good as mythical. This also implies that such technological civilisations are also rather diffuse within the Multiverse, _excepting_ of course those which share part of their history with ours (eg the Nazis which won WWII). We have some predictive power as to what those people would be like, since they will be similar to us. You are no doubt aware of statistical studies of the fossil record indicating that our own evolution was rather hard won (eg Robin Hanson's "Hard Steps" paper). So, I for one, would not discount Hal Finney's point. Cheers Tim May wrote: > > > In the interests of doing wild speculation here, which some folks are > asking for more of, here's a followup to a discussion we had a few > weeks ago: > > The Fermi Paradox asks the question: "If extraterrestrial civilizations > are at all common, even at the level of a few dozen per galaxy per > galaxy life, why aren't they _here_? Or why don't we see artifacts, > relics, ringworlds, Dyson spheres, evidence of large engineering > projects, and so on?" Fermi used the succinct quip, "Why aren't they > here?," with the details about rate of spread even at slow, sublight > speeds, etc. implicitly obvious. > > The Many Fermis Paradox is a variant of this: "If the MWI theory is > correct, AND if there is any communication or movement between the > worlds that is possible, why aren't they here?" > > (Note that movement amongst branches is not part of any conventional > MWI interpretations, though it's used in novels and in some of the > wilder interpretations.) > > Hal Finney pointed out that the same kind of Fermi Paradox argument is > used to argue against time travel: "If time travel is possible, why > aren't travelers from the future here?" (Arguments that they are here > but they only talk to some people, etc., are trumped by the sheer size > of the future, and by the "defector" argument to the "Cosmic > Quarrantine" solution to the Fermi Paradox: _lots_ of defectors would > violate the quarantine, etc. > > Hal further raised the possibility that, like the time travel version, > perhaps the resolution has to do with the need for a "receiver": > neither time travelers nor MWI travelers are here, yet, because we have > not, yet, built the portals or receivers needed by them (opening up > wormholes, a la Visser, etc.). > > (The other resolution being, of course, that neither time travel nor > MWI travel is possible, which was Fermi's point about the absence of > aliens.) > > I've thought about Hal's point and have this reply: > > While we on this earth may not have built the necessary portals or > receivers for either (time travel or MWI travel), some other > civilization surely would have a billion or three billion years ago. > (Assuming the usual crude estimates of distribution of ages of stars, > non-special status of us as observers (a la Boostrum and others), and > crude estimates of likelihood of advanced civilizations elsewhere. If > we are the only form of life in our timelike region of the universe, > i.e., within a few billion light-years, then of course this makes the > odds of another receiver-builder nil. > > In this fanciful scenario, the Throgians in a small elliptical galaxy > in Coma Berenices built a MWI receiver in their approximate equivalent > of 4500 A.D., by our measures. This was 2 billion years ago. Once this > MWI receiver was built, the Throgians were the beneficiaries and > traders of vast amounts of MWI knowledge...every discovery made in any > MWI universe they had contact with, including universes filled with > other civilizations, all manner of creatures, and so on. > > Call this first construction of such a portal the "MWI Singularity." > > (A similar situation, arguably much the same situation, ensues with the > construction of the first time machine portal.) > > Steven Baxter has written a series of novels in his future history > which explore this very kind of idea. > > With nearly any nonzero chance of building either a time machine or MWI > receiver, a distribution of civilizations would have done this billions > of years ago. (By the usual argument that there is nothing which makes > our emergence about 4.5 billion years after the formation/cooling of > the earth anything special in the cosmic scheme: there should have been > planets which similarly formed and cooled as many as 12 billion years > ago, giving some of them a 6-8 billion year "head star
