NeitherRuleNorBeRuled on December 09, 2011, 08:01:07 pm
[...] as Carl Sagan said "Absence of evidence is not evidence of absence"

When Carl Sagan said this, he was wrong.  Absence of evidence is evidence of absence.  The key word is evidence.  It is, for example, valid to say that the absence of any evidence of pink unicorns is evidence that pink unicorns do not exist.  What it is not is proof.  It would be a correct statement to say "Absence of proof is not proof of absence."  Evidence is merely an indication; proof indicates certitude.

Proof of absence (sometimes stated as "proving a negative") can certainly be accomplished in some cases; for example, Kurt Goedel has nicely proven that there does not exist any consistent system of logic that includes numbers (more technically that contains the Peano Postulates) in which every true statement in that system can be derived from that system; this is known as Goedel's Incompleteness Theorem. This has huge ramifications for Mathematics and all Sciences and Technologies that incorporate Mathematics.

<SideAnecdote>:  There is a close cognate of this in Computer Science, known as the "Insolubility of the Halting Problem"; this very roughly says that there are some problems that seem to be reasonably solvable with computer programs, but no such computer program can be written to do so.  I took a Computer Science Theory course in grad school where over several lectures this proof was developed.  The day it was completed, I looked around the class and everyone else in the class was visibly angry at the result; I was the only one who was impressed at the beauty and elegance of the proof.  </SideAnecdote>

mellyrn on December 09, 2011, 08:13:12 pm
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Parmenides problem was that he believed in a smallest positive number

Was it?  Then I completely misunderstood him -- not that I could say I completely understood him before, mind you.  Can't quote it exactly, but his conclusion was something a whole lot like, "Anything that can exist, does exist and it is impossible for it not to exist" -- thus, if it could be, then it is, thus impossible for anything to either become or cease to be, i.e. change. 

Perhaps you're meaning his student Zeno and his paradoxes, Achilles and the tortoise, the arrow that can never reach its target, and the like?  That, I can apply "smallest positive number" to.

NeitherRuleNorBeRuled on December 09, 2011, 08:49:12 pm
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Parmenides problem was that he believed in a smallest positive number

Was it?  Then I completely misunderstood him -- not that I could say I completely understood him before, mind you.  Can't quote it exactly, but his conclusion was something a whole lot like, "Anything that can exist, does exist and it is impossible for it not to exist" -- thus, if it could be, then it is, thus impossible for anything to either become or cease to be, i.e. change. 

Perhaps you're meaning his student Zeno and his paradoxes, Achilles and the tortoise, the arrow that can never reach its target, and the like?  That, I can apply "smallest positive number" to.

Zeno's paradoxes is what killydd was referring to; the confusion, I suspect, comes from Plato's Parmenides, which as I recall included Zeno's paradoxes.

Parminedes' argument centers more around the the notion of "is"; he uses the term in a way that transcends time; he treats it more like a more traditional spatial dimension in terms that allow temporal position -- past, present, and future -- to already exist.

Parminedes seems to touch on a further, deeper concept, although I may be reading into it.  To explain that, I need to create a specialized term.

Think of what is often referred to as "the universe" as in fact being the single 3-Space/1-Time "hypercube" (4 dimensions) that we perceive in part (in part, since we do not perceive which specific future this represents).  Rather than using the word "universe", let's call it a 3S1T.

Parminides then seems to touch on the notion of Universe consisting of  an infinite number of 3S1Ts across a separate dimension (or dimensions) of possibility. This dimension (or dimensions) of "possibility" would encompass such things as the collapse of a quantum wave form and "free will".  If this is the case, then Parmenides' use of the word "is" transcends not only the dimension of time, but also the dimension(s) of possibility.

Welcome to the Twilight Zone.

« Last Edit: December 09, 2011, 08:52:05 pm by NeitherRuleNorBeRuled »

Killydd on December 10, 2011, 12:19:01 pm
Yes, my mistake for mixing up old Greeks.

Rereading some things, it seems almost that what he was saying is that anything you can think of must exist somewhere, because the idea could not have arrived to you from nowhere?

mellyrn on December 10, 2011, 06:27:26 pm
It would be interesting to compare translations.

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it seems almost that what he was saying is that anything you can think of must exist somewhere, because the idea could not have arrived to you from nowhere?

If a thing did not exist and could not exist, we couldn't think it (the sound of one hand clapping?)  But it doesn't follow that, say, Pegasus must physically exist somewhere.  We humans have the ability, as Tolkien says, to look upon green grass and see that it is 'green' as well as being 'grass' and then apply 'green' elsewhere -- say, to the sun.  A deep green sun may or may not exist; the relevant bit is that both 'green' and 'sun' do.  Wings exist; horses exist; seems to me that is all the physical existence needed for "Pegasus".

My source says this about Parmenides' cosmos:

"Either .. a conceptual world with which we have no sensory contact at all, or ... the material universe taken together with its history, sub specie aeternitatis, the medieval idea of God's view of it."

He thinks the former is Plato's view but for himself thinks Parmenides went with the latter.  Fwiw, the physicist who reconciled QM with relativity by doing away with "time" also seemed to have rather the latter view of existence -- pastpresentfuture together as one indivisible whole.

My source said one other thing which I've always treasured: 

"He [Parmenides] was the first to warn us that the worlds of sense and of discourse may be different."

It's thus amusing to me that we don't consider that we've really understood the world of sense until we've mapped it in discourse -- until we've represented a 3S1T in a 1T format.


enemyofthestate on December 11, 2011, 10:48:39 am
Interestingly, Parmenides (ca. 500 BCE) proved, logically proved, that change is impossible.  To the best of my knowledge, no one has ever successfully disproved him; it just gets ignored as a paradox, since, whatever logic might say, we do have to deal with change.  Seems that, for photons at least, he was right.  Heh.
Once you understand the idea of the limit, Parmenides' (and Zeno's) paradoxes disappear.  What they really demonstrated is that logic alone is not guaranteed to produce meaningful knowledge and that reasoning is only as sound as the premises it rests on.  This, in a way, helped lead to the "scientific method" with its empirical verify-then-trust approach some 2000 years later.

Re the OP, I brought this up, tangentially, a while back but decided to just let it rest.  Very few science fiction authors really take advantage of their plot devices -- especially those involving FTL --  but can be good story-tellers nevertheless.  Besides,  if the surveys are to be believed, scientific literacy is in a pretty sad state so how many readers will even understand much less see the implications?  How many people realized the Ringworld was unstable?

sam on December 13, 2011, 02:11:06 am
Re the OP, I brought this up, tangentially, a while back but decided to just let it rest.  Very few science fiction authors really take advantage of their plot devices -- especially those involving FTL --  but can be good story-tellers nevertheless.  Besides,  if the surveys are to be believed, scientific literacy is in a pretty sad state so how many readers will even understand much less see the implications?  How many people realized the Ringworld was unstable?

I did. 

But hell, you need to ignore that to have a story set on a ringworld with a fallen civilization.   It irritated so many people, that Niven retconned it away in the sequels - turned out that the ringworld had a few tiny fragments of its ancient civilization keeping it from falling apart.

It is science fiction.  You violate physics as needed for story.  So I have no objections when mortals travel between the stars faster than light.  But for a story set within the solar system, you don't need faster than light.

quadibloc on December 16, 2011, 03:28:19 pm
For it to be instantaneous, and not allow time travelling information, it has to be instantaneous with respect to one, and only one, rest frame.

Name that rest frame and tell us why it is special.
It didn't look special. Until the day that faster-than-light communications was discovered.

It's special because it's the rest frame with respect to which Tanglenet communications are instantaneous in all directions.

Killydd on December 19, 2011, 01:00:23 pm
We have actually found one "special" frame of reference:  the frame in which the cosmic microwave background radiation is most symmetric.  Unfortunately, so far it appears to have no practical significance.

Damocles on December 21, 2011, 04:08:15 am
We have actually found one "special" frame of reference:  the frame in which the cosmic microwave background radiation is most symmetric.  Unfortunately, so far it appears to have no practical significance.

I'll freely admit that the math and physics are beyond me but I've always thought about the problem of instant communications in terms of transmitting a video feed.  I would argue that the frame of reference would always be that of the party that is "transmitting" using the instantaneous communication device.  To put it one way, special relativity would affect the "speed" one perceives of the video playback but not the time it takes to transmit it.  So if you're traveling very fast, you might perceive the video playing very fast, whereas your response would be perceived to be playing very slowly. 

Wouldn't that solve the time travelling paradoxes?

Killydd on December 21, 2011, 12:39:04 pm

I'll freely admit that the math and physics are beyond me but I've always thought about the problem of instant communications in terms of transmitting a video feed.  I would argue that the frame of reference would always be that of the party that is "transmitting" using the instantaneous communication device.  To put it one way, special relativity would affect the "speed" one perceives of the video playback but not the time it takes to transmit it.  So if you're traveling very fast, you might perceive the video playing very fast, whereas your response would be perceived to be playing very slowly. 

Wouldn't that solve the time travelling paradoxes?

The problem is that both people are "transmitting."  And of course, changing the speed of transmission changes the time it takes to transmit:  if you transmit the same number of frames in your video at twice the speed, it only takes half as long to transmit.  Roughly speaking, what happens is this:  http://xkcd.com/265/, except that yes, she does mirror the observations, including the same time dilation.

Slamlander on December 28, 2011, 06:02:11 pm
<SideAnecdote>:  There is a close cognate of this in Computer Science, known as the "Insolubility of the Halting Problem"; this very roughly says that there are some problems that seem to be reasonably solvable with computer programs, but no such computer program can be written to do so.  I took a Computer Science Theory course in grad school where over several lectures this proof was developed.  The day it was completed, I looked around the class and everyone else in the class was visibly angry at the result; I was the only one who was impressed at the beauty and elegance of the proof.  </SideAnecdote>

FWIW: There was a paper by Dijkstra, in the 60's, about the seven non-computable tasks. The halting problem was only one of them. I don't know whether Dijkstra is still being taught. The seven non-computable tasks remain non-computable. Dijkstra's arguments had the beauty, elegance, and inevitability of a steamroller.
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NeitherRuleNorBeRuled on December 30, 2011, 02:10:02 pm
FWIW: There was a paper by Dijkstra, in the 60's, about the seven non-computable tasks. The halting problem was only one of them.

Any chance that you could cite the paper?  I'm a "fan" of EWD, and have read many of his papers (and also worked with one of his former PhD students), but I've never come across that paper, and my (admittedly brief) attempt to track it down yielded nothing.

BTW, there are an infinite number of such tasks; the general approach to their proofs is to demonstrate that a solution, should it exist, could be used to solve the halting problem (therefore such a solution does not exist - proof by contradiction).

customdesigned on March 03, 2012, 08:55:19 pm
While the description of "tanglenet" talks about quantum entanglement, the picture in my mind was one of a tangled network of wormholes.  Then I thought about recipes for artificial macroscopic wormholes using relativity.  They all involve creating a pair of endpoints using planet sized energy in a suitable geometry,  then transporting the endpoints apart at sublight speed.  There is no violation of causality, but the geometry of space-time becomes tangled.  (And certain paths could be time-like loops, depending on the relative motion of the endpoints.  See "How to Build a Time Machine: the Real Science of Time Travel".)

Obviously, the world of EFT doesn't have planet sized chunks of energy to throw around, so the tanglenet must be a way to create stable quantum sized wormholes, and transport the endpoints to desired locations. 

Entangled particles can't transmit information.  If the entanglement involves some kind of quantum wormhole, then it collapses on first use.  Which is the key property that makes them useful today - they enable communication (at sub-light speed) that is immune from eavesdropping at a fundamental physical level.   

BUT, maybe our brilliant inventor found a way to make a reusable quantum wormhole, perhaps entangling stable configurations of positive and negative energy particles.  (Negative energy is the key to keeping macroscopic wormholes stable while ordinary matter travels through them.)

Andreas on March 04, 2012, 07:28:15 am
Wow... two of my peeves in one thread: 1) Zeno's paradoxes - I hate it that people don't get that Zeno's "paradoxes" are merely examples of how one can obfuscate the truth with words, to make the nonsensical seem plausible. As such examples they are useful, as anything else - useless and harmful.
2) "time travel" arising from instantaneous comms. There is no way to disprove absolute time (even though it doesn't exist). There is no way to make a message arrive at its origo before it was sent. Therefore, there is no time travel (save forward, the direction we ALL travel).
We can go forward at 1sec(subjective)/sec(default frame), or we can go slower or faster. None of these can effect time travel, as there IS NO absolute time.
In other words, aging faster than time in your home world would allow doesn't constitute time travel, even when you return. There isn't a magical "present time" after all, only "time lapsed". That's important: There are no "time stamps" on matter in the universe, and there is no absolute "time frame" for such stamps to relate to, or to make sense in. To use the generally more accessible physical-travel metaphor; there are no landmarks in time. It is a flow, like a river we're all rafting on. No amount of paddling will make us go upstream, although we can with extreme exertion come to a near-halt (a complete halt, in theory - although that would be a one-way trip). We can also paddle our way forward, advancing downstream more quickly than without exertion, but seeing as how this river has no banks, no end, and no non-floating landmarks, we have no other frame of reference than our position relative to other items going downstream. And then, consider this: We don't have access to the "experienced time-flow" of other items.
To see this, notice that photons don't move downstream: moving at the speed of light, a photon doesn't experience the passage of time... but this doesn't seem to be relevant to our experience, does it? It's a feature of the photon experience, and it doesn't leak out in any way.
Not moving with respects to time has the opposite observable effect; it moves as fast as is possible, seen from the outside, nobody cares about how it feels for the photon, after all. Least of all the photon, which even were it sentient, would have no time in which to experience.
« Last Edit: April 03, 2012, 05:59:37 am by Andreas »