Many Little Dimensions or One Big One?

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Walden2
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Many Little Dimensions or One Big One?

Postby Walden2 » Wed Mar 07, 2007 12:00 am

Adapted from two articles originally published in the newspaper
Tompkins Weekly (http://www.tompkinsweekly.com).

In the early months of 2007, the college town of Ithaca, New York was visited by two giants in the field of physics.

Dr. Lisa Randall, a Professor of Theoretical Physics at Harvard, went to Cornell University to talk about her theory concerning gravity, namely why is it that of the four fundamental forces of nature – strong, electromagnetic, weak, and gravity – the force of gravity is so weak compared to the other three sets of interactions between particles and the large-scale behavior of matter throughout the Universe?

Randall’s explanation for this conundrum was explained in two science papers she wrote in 1999 with Raman Sundrum, now a Professor in the Department of Physics and Astronomy at Johns Hopkins University in Baltimore, Maryland. Randall also explained her theory at a popular level in her book Warped Passages: Unraveling the Mysteries of the Universe’s Hidden Dimensions (HarperCollins Publishers, New York, 2005). The book’s official Web site is http://www.warpedpassages.com/.

Randall and Sundrum conceived of a theory that has our three-dimensional (four if you count time) Universe residing in an “infinite extra dimension that warps spacetime so much that gravity [in the form of particles called gravitons] is concentrated near another brane [a three dimensional hypersurface embedded in a higher dimensional bulk],” says Randall.  “There are actual physical consequences because of this extreme warping of spacetime.”

In essence, certain parts of the Cosmos may have stronger concentrations of gravity than what we experience due to these higher dimensions, thus explaining why gravity is the weakest of the four forces of nature – at least for us in this Universe.

Randall and her colleagues may be able to prove their theory later this year when the Large Hadron Collider (LHC) becomes operational at CERN laboratory near Geneva, Switzerland.

The giant particle accelerator and collider may be powerful enough to produce and detect what are known as Kaluza-Klein particles that move through those extra dimensions.  The physicists could then determine their properties and potentially prove that we do exist in a world of higher dimensions that obey different physical laws.

“If the theory is true, it will affect many other sciences such as cosmology and string theory,” says Randall.  “The scientists in those fields will have to explain their theories and the phenomena they detect in relation to those extra dimensions that interact with our Universe.”

Several months later, Dr. Sylvester James Gates, Jr., the director of the University of Maryland Center for String and Particle Theory, came to Ithaca College to explain the concept of strings.

Imagine the smallest thing you can possibly imagine.

Now scrap that thought, because you cannot imagine just how small a string really is.

Not the kind of string you tie to a kite or around your finger, but a strand of vibrating energy that many physicists think is the fundamental building block of everything in the Cosmos, the thing that even atoms are ultimately made of.

How small is one of these strings? If an atom were expanded to the size of our Solar System, roughly ten billion miles across if you include the orbit of Pluto, a string inside that atom would be the size of your average tree.

On the real world scale, about 5 sextillion (a five followed by 22 zeroes) atoms are contained in a single drop of water. The strings inside the nucleus of all those atoms are 100 billion billion times smaller than the protons and neutrons that make up every atomic core.

Strings are seventeen orders of magnitude smaller than the smallest objects that current science can actually observe. Physicists estimate that in order to actually detect a string, they would need a particle accelerator the size of the Milky Way galaxy, 100,000 light years across, to create the energy buildup required to smash apart atoms enough to find the presumed strings within them. Such a device is just a bit beyond current science budget plans.

Yet diminutive as they are, if strings actually exist as scientists have predicted mathematically since the 1960s, they could be the basis for all that exists in the Cosmos.

Gates, the John S. Toll Professor of Physics at the College Park institution, explained to his listeners how the different ways strings oscillate “create” the particles that make up the atoms that are part of every object we know. Beyond this, the theory requires there to be extra dimensions beyond the ones we experience with our senses, perhaps as many as 11 in total.

Gates and others think that superstrings, a concept which combines all of the current separate theories on string particles into one unified whole, could also explain gravity, the only member of the four fundamental forces of nature whose existence and actions cannot be fully explained at the quantum level.

Gates was one of the physicists featured in the Nova science series on PBS television in a 2003 adaptation of the 2000 book The Elegant Universe, a popular exposition of superstring theory written by Columbia University physicist and mathematician Brian Greene. You can read Gates’ complete interview from that program here: http://www.pbs.org/wgbh/nova/elegant/view-gates.html.

Gates’ presentation on strings is a generalization of his college lectures on the subject, which can be purchased either as a DVD set or a transcript through this Web site: http://www.teach12.com/ttcx/coursedesclong2.aspx?cid=1284

Strings of another sort accompanied and framed Randall’s lesson in physics, courtesy of musicians Stephen Andrew Taylor from the University of Illinois at Urbana-Champaign and Wendy Herbener Mehne and Pablo Cohen, both of Ithaca College.

Using a combination of flute, guitar, and live electronics, the trio performed Taylor’s piece titled seven microworlds, which premiered in 2000 in Toronto. The piece can be heard on Taylor’s Web site here: http://www.stephenandrewtaylor.net/

Taylor earned his Ph.D. in music composition from Cornell.  Over the last two decades, he has composed a number of pieces honoring science, including one dedicated to Dr. Carl Sagan called Pale Blue Dot, after the late Cornell astronomer’s evocative description of our planet Earth as seen from the edge of the Solar System by the Voyager 1 space probe in 1990.

Taylor explains what brought him to create music based on particle physics.

“I was inspired to compose seven microworlds by learning about string theory, a recent branch of physics in which fundamental particles such as quarks and photons are thought to consist of unimaginably small, vibrating strings. By vibrating in different ways, these strings account for all currently known particles, just as you can play many different notes on a single guitar string.

“But nobody knows whether or not the theory is true, and in some ways it is quite bizarre.  In addition to our three familiar spatial dimensions, strings inhabit several other ultra-microscopic dimensions curled into complex knots.  We don't notice these microdimensions, even though the theory says we move through them constantly.

“In my piece, the electronics are intended to act as a bridge between the ‘real world’ of the flute and guitar and these hidden microworlds that permeate us all.  Of the seven movements (played without pause), the first, fourth, and seventh for both flute and guitar loosely represent the three macrodimensions. The others are solo movements inspired by various twisting microdimensions.  ‘Collision Focus’, the first movement, zooms into microscopic chaos; the fourth, ‘Verticality’ (the only movement without electronics), plays with ascents and wide leaps; ‘Flatland’ is a meditation on a plane curving into itself, just as the seemingly flat surface of Earth wraps into a sphere.”
 
Which theory is right about what lies beyond the reality we can see, or think we know? The answers may come sooner than we think, perhaps even in ways and with results we did not anticipate. But that is half the fun.
Last edited by Walden2 on Wed Mar 07, 2007 12:51 am, edited 1 time in total.

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Celestial music

Postby Windwalker » Wed Mar 07, 2007 12:40 am

Dear Larry, welcome to the forum!

I met Larry (Walden2) when I gave a talk about my Star Trek book to the Boston Chapter of the National Space Society. As you can tell from the article he just posted, Larry is very knowledgeable about physics, astrophysics and, like all of us here, in love with space exploration.

I will comment on the article itself soon. In an interesting synchrony, I am presently reading Lisa Randall's book Warped Passages, in which she elaborates the theory that Larry describes. Calvin will be the first to tell you that string theory, elegant and beguiling as it is, has some serious problems (testability, for one). The problem of uniting gravity with the other three fundamental forces is still very much with us.
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Re: Celestial music

Postby caliban » Wed Mar 07, 2007 10:46 am

Windwalker wrote:Calvin will be the first to tell you that string theory, elegant and beguiling as it is, has some serious problems (testability, for one).


Part of the reason Lisa Randall's brane theory became very popular--and she shot to a professorship at Harvard--is that it has more directly testable consequences than string theory, namely, that gravity ought to be modified at short distances. Experiments have already ruled out modifications down to about 1 mm, but further clever experiments are being planned.

String theory, unlike the Big Bang, evolution, global warming, relativity, and quantum mechanics, is indeed worthy of the phrase "just a theory": it's beautiful mathematics, but it has (almost) no experimental evidence for, or against, it. The only real hint that superstring theory might be right is non-baryonic dark matter, which composes about 25% of the mass-energy budget of the cosmos. We have no idea what it is, and the best candidate is one of the particles predicted by supersymmetry. But that's a rather big stretch... String theory is proving itself extremely difficult to test.

If you want to amuse yourself with debates on string theory, try the "Not Even Wrong" blog : www.math.columbia.edu/~woit/wordpress/

(For the unintiated, "Not even wrong" was a famous put-down Wolfgang Pauli: an idea so far off it couldn't even be given credit as being merely wrong.)

Also: if you read in the paper that "string theory" is now being tested at places like RHIC (the Relativistic Heavy Ion Collider at Brookhaven National Lab on Long Island), that's not really true. What has happened is some of the mathematical tricks of superstring theory are being applied to heavy-ion collisions, which is very interesting, but have nothing to do with superstrings as fundamental constituents of the universe.
"Results! Why, man, I have gotten a lot of results. I know several thousand things that won't work." --Thomas A. Edison

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Re: Celestial music

Postby Windwalker » Wed Mar 07, 2007 9:24 pm

caliban wrote:Part of the reason Lisa Randall's brane theory became very popular--and she shot to a professorship at Harvard--is that it has more directly testable consequences than string theory, namely, that gravity ought to be modified at short distances.

I must confess a fondness for string theory, although I'm fully aware of its very real limitations. At the same time, Randall's concepts, if verified by experiments, may well help set limits on the string model that we should investigate (depending on which of her brane models prove correct).

caliban wrote:Also: if you read in the paper that "string theory" is now being tested at places like the Relativistic Heavy Ion Collider at Brookhaven National Lab on Long Island, that's not really true.

Indeed. Larry McLerran, who's a friend and a senior theoretical physicist at Brookhaven, is as doubtful as you are about string theory. He has evolved his own theory, the colored glass condensate, for matter at high energies.
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Re: Celestial music

Postby caliban » Wed Mar 07, 2007 10:07 pm

Windwalker wrote:Indeed. Larry McLerran, who's a friend and a senior theoretical physicist at Brookhaven, is as doubtful as you are about string theory. He has evolved his own theory, the colored glass condensate, for matter at high energies.


Yes, but it is important to keep in mind that we are mixing up "string theory" in two different contexts. One is superstrings as the fundamental constituents of matter, in an attempt to marry quantum mechanics with gravity, which is the subject of Brian Greene's "The Elegant Universe." The other is mapping QCD at high temperatures, found at RHIC, onto the mathematics of string theory. It is the latter that McLerran's theory competes with, not with "superstrings as ultimate particles." (McLerran may also have reasonable doubts regarding string theory as the Theory of Everything, but the colored glass condensate is not a Theory Of Everything, nor does it claim to be.)
"Results! Why, man, I have gotten a lot of results. I know several thousand things that won't work." --Thomas A. Edison

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Re: Celestial music

Postby caliban » Wed Mar 07, 2007 10:55 pm

Windwalker wrote: At the same time, Randall's concepts, if verified by experiments, may well help set limits on the string model that we should investigate (depending on which of her brane models prove correct).


Personally, I am tired of string theory. For one, I have students walking into my office saying they want to do string theory, and having not a clue as to the whole landscape of particle physics. (They also generally do not have the math skills to do it, although they insist they do.) String theory is the end of a long series of developments in quantum field theory that began with Feynman's path integrals in quantum electrodynamics, only taken to a much more advanced level. I personally suspect that paradigm may be reaching its limits. (That's not to say its wrong--whatever theory we eventually do find, may see superstrings as an approach that is ultimately not very fruitful. An analogy is Einstein's geometric theory of gravity. Works great for gravity. Can be extended to electromagnetism through a rolled-up fifth dimension, in a Kaluza-Klein theory. But after that, it was a dead-end...until some of the ideas got reborn in superstring theory. If I were writing an SF story--oh, wait, I am, I would hint that the Theory of Everything was based on something else, but cannabalized some of the ideas from superstrings.)

Randall's brane theory--actually a whole class of theories--have reinvigorated the field in a way that has not happened with superstrings for a long time. Not only is it more immediately testable, it also explains the mystery of why gravity is much weaker than other forces, and also, through a variant called the ekpyrotic theory, may explain the origin of the universe itself. She is thinking outside the box, literally, and particle physics desperately needs that.
"Results! Why, man, I have gotten a lot of results. I know several thousand things that won't work." --Thomas A. Edison

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Re: Celestial music

Postby Windwalker » Wed Mar 07, 2007 11:00 pm

caliban wrote:Randall's brane theory--actually a whole class of theories--have reinvigorated the field in a way that has not happened with superstrings for a long time. Not only is it more immediately testable, it also explains the mystery of why gravity is much weaker than other forces, and also, through a variant called the ekpyrotic theory, may explain the origin of the universe itself. She is thinking outside the box, literally, and particle physics desperately needs that.

I have only started Warped Passages, so I will be in a better position to comment on this when I finish it. Why did it take so long to come up with the ideas that she and her collaborator articulated? From my reading so far, it seems all the facts had been there for a while.
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How small does one get before it no longer affects us?

Postby Walden2 » Thu Mar 08, 2007 12:32 am

One of the things I emphasized in my article is how utterly
small strings are supposed to be. Anything 100 billion billion
times smaller than a neutron that would requre a particle
accelerator the size of our galaxy to detect is going to be
difficult to prove for a very long time, to put it mildly.

If Randall's theory does not pass muster, what is next?
If strings remain just a theory because of their untestability,
what's next?

Athena, could you tell us more about McLerran's theory?
Thanks.


High Energy Physics - Theory, abstract
hep-th/0703055

From: Maurizio Gasperini [view email]

Date: Tue, 6 Mar 2007 18:43:39 GMT (176kb)

String Theory and Pre-big bang Cosmology

Authors: M. Gasperini, G. Veneziano

Comments: 29 pages, three figures. Contribution to the book: "Beyond the Big Bang", ed. by Ruediger Vaas (Frontier Collection Series, Springer-Verlag, Heidelberg, 2007)

Report-no: CERN-PH-TH/2007-026

In string theory, the traditional picture of a Universe that emerges from the inflation of a very small and highly curved space-time patch is a possibility, not a necessity: quite different initial conditions are possible, and not necessarily unlikely. In particular, the duality symmetries of string theory suggest scenarios in which the Universe starts inflating from an initial state characterized by very small curvature and interactions. Such a state, being gravitationally unstable, will evolve towards higher curvature and coupling, until string-size effects and loop corrections make the Universe "bounce" into a standard, decreasing-curvature regime. In such a context, the hot big bang of conventional cosmology is replaced by a "hot big bounce" in which the bouncing and heating mechanisms originate from the quantum production of particles in the high-curvature, large-coupling pre-bounce phase. Thanks to the strong coupling there is also an associate production of higher-dimensional branes, which could prepare (and provide the initial conditions for) a subsequent phase of brane-dominated inflation.

http://arxiv.org/abs/hep-th/0703055

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Re: Celestial music

Postby caliban » Thu Mar 08, 2007 1:20 am

Windwalker wrote:I have only started Warped Passages, so I will be in a better position to comment on this when I finish it. Why did it take so long to come up with the ideas that she and her collaborator articulated? From my reading so far, it seems all the facts had been there for a while.

I'm afraid I don't read popular physics books, because they inevitably devolve to baby talk, and it's better to tease out the primary literature. I did read A Brief History of Time because so many people asked me about it; I'm pretty sure I know what Hawking was saying, but I can't imagine anyone without a degree in maths having the faintest idea. So I don't know what Randall says in her popular book...

...but the history of science is full of ideas that were obvious once someone pointed them out. Hell, I've even come up with one or two.

And to jump ahead and answer walden2's question to Athena regarding McLerran's "colored glass condensate" -- it has NOTHING to do with the tiny superstrings in your article. Repeat after me: NOTHING. It is a theory to describe what happens in a relativistic collision between nuclei, in an attempt to produce the fabled quark-gluon plasma. Some other competitors of McLerran use the MATH of superstring theory to model the quark-gluon plasma, but it's not the same thing at all. Really. Please stop confusing them. It hurts.
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Colored glass condensate

Postby Windwalker » Thu Mar 08, 2007 1:47 am

Here's the initial Brookhaven link about colored glass condensate. As Calvin said, the terms describe what may happen in a very high-energy collision. Each of the three terms (colored, glass, condensate) has a specific meaning.

http://www.bnl.gov/bnlweb/pubaf/pr/2003/colorglasscondensate-background.htm

Calvin has a valid point about popular physics books -- but the mathematics requirement is too steep for most people. So physicists who want to make these complex, non-intuitive concepts accessible are stuck between suboptimal choices of presentation.
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Re: Colored glass condensate

Postby caliban » Thu Mar 08, 2007 2:22 am

Windwalker wrote:Calvin has a valid point about popular physics books -- but the mathematics requirement is too steep for most people. So physicists who want to make these complex, non-intuitive concepts accessible are stuck between suboptimal choices of presentation.


Of course. I was just being a snob. :) Actually, these books are heroic, but people--my mother, my neighbor--will often ask me about a particular popular science book, usually one by Hawking, and I have to explain that I haven't read it, and why I haven't read it.

And I don't read the primary literature in biology, either--I have to ask Athena, or my wife. :)

I am reminded, however, of Roger "I'm just as smart as Hawking but I'm not in a wheelchair so no one pays attention to me" Penrose and his desperate cry for attention, The Emperor's New Mind which is just as awful in its cognitive pscyhology as it is in his biology, as Athena has alluded to elsewhere. *Shudder.* The books purports to explain how consciousness cannot be algorithmic in nature, i.e., computers cannot think like you or me. He spends page after page explaining complex numbers, quantum mechanics, Goedel's theorem, and so on, only to conclude, Well, obviously computers can't think real thoughts! He drags the reader through all that, all to end with a shaggy maths tale. Doug Hofstadter had already demolished that argument decades before in Goedel, Escher, Bach: An Eternal Book no one will Get through. Which still is far better than Penrose's book.

Sorry. Athena's right, the math is beyond the average person in the street, so popularizations have to muddle through. Unfortunately many people then mistake the metaphor for the actuality. If I had a nickle every time I had to explain about how quantum mechanics does not say a particle can be in two places at once, well, I could at least buy a nice latte.
"Results! Why, man, I have gotten a lot of results. I know several thousand things that won't work." --Thomas A. Edison

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Re: Colored glass condensate

Postby Windwalker » Thu Mar 08, 2007 1:48 pm

caliban wrote:I am reminded, however, of Roger "I'm just as smart as Hawking but I'm not in a wheelchair so no one pays attention to me" Penrose and his desperate cry for attention, The Emperor's New Mind which is just as awful in its cognitive pscyhology as it is in his biology, as Athena has alluded to elsewhere. *Shudder.*

Doug Hofstadter had already demolished that argument decades before in Goedel, Escher, Bach: An Eternal Book no one will Get through. Which still is far better than Penrose's book.

The fable from which Penrose borrowed the title fit his book depressingly well. Not only did he get most of his biology blatantly wrong (Quantum microtubules? Ouch, ouch! Get thee to an introductory textbook, go!) but also the style was so turgid and boring that I wondered if it was a Sokal-like hoax expanded to book size. Hofstadter's book, on the other hand, is a unique gem. He succeeded in explaining complicated ideas and his style was absolutely brilliant, a virtuoso performance.

A propos of mathematics: I have grave reservations about Robert Heinlein's politics (and sanity) but I agree with at least one of his pronouncements -- increasingly difficult to follow in today's bizarre lifestyle, that leaves little time and no incentive for general knowledge and contemplation.

A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.

-- Lazarus Long, Time Enough for Love

You can find more Heinlein soundbites here. Be warned, he's as nuanced as Ayn Rand (*laughs*):
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Postby sanscardinality » Thu Mar 08, 2007 2:03 pm

You touched on a subject that I've read a fair bit about and have some expertise in - AI. My expertise is mostly in the expert systems part of AI (generally in the areas of sensor data analysis and user behavior prediction). I've also dabbled in neural nets and other approaches such as genetic algorithms, but I'm no expert on any of the above. I have spent enough time with them to have a fairly well-informed opinion.

It seems premature to say whether or not we can make a human-like mind in a computer, but we can say that many have tried and all have failed. We can make things that kinda-sorta act like thinking machines, but they have never shown anything close to parity with organic minds. And perhaps even more interestingly, they've never shown any sign whatever of self awareness. AI as it stands is more like building a model of a mind based on its behaviors rather than building a mind up structurally. The attempts to do the latter end up looking a lot more like a new kind of model than progress towards the real thing (neural nets for example).

The problem, I suspect, is the same one that physics is wrestling with in the form of a GUT and strings - we really don't know what the fundamental structures are of intelligence or of energy and matter. Having read both Godel Escher Bach and Metamagical Themas (Hofstaeder's other book I could find) I didn't find anything in what he said that gave evidence for the ability to manifest a mind algorithmically other than logical games, which have been used to "prove" all manner of nonsense. That said, I loved both books and found them very clever and interesting.

Perhaps the best test of an actual AI is its arbitrariness, or put another way, whether it makes some decisions because it "wants to" for inobvious reasons rather than a pre-programmed reason. This is different than a decision derived from pre-programming, and may be difficult to differentiate from a fraud. The Turing test strikes me as being akin to the anthropic principle in that it makes an assertion sans evidence, and is generally employed without stating clearly the unproven a priori assumptions that are required for it to have value. Please ignore the philosopher behind the curtain!

I suspect that true AI is possible using computer hardware and software, but we are so very far from it that this is akin to an ancient Egyptian imagining space flight.

SC
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Postby Windwalker » Thu Mar 08, 2007 2:29 pm

sanscardinality wrote:It seems premature to say whether or not we can make a human-like mind in a computer, but we can say that many have tried and all have failed.

I suspect that true AI is possible using computer hardware and software, but we are so very far from it that this is akin to an ancient Egyptian imagining space flight.

I agree with all your points. In my opinion, the most useful outcome of the AI models has been that they created a feedback loop: they furnished salient questions that biologists (broadly defined) could ask about the brain/mind.

Building a model of the nervous system that attains self-awareness poses intriguing questions of scale. Single neurons are not intelligent; also, self-awareness may be a matter of degree in live organisms. It is also contested how much of human perceived free will (the "arbitrariness" that you mention) is real, versus being a complex but nevertheless hard-wired response.
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Postby caliban » Thu Mar 08, 2007 2:57 pm

sanscardinality wrote:I suspect that true AI is possible using computer hardware and software, but we are so very far from it that this is akin to an ancient Egyptian imagining space flight.

Like Athena, I agree with this. My/our objection to Penrose is not so much his conclusion but his lousy arguments. Although Penrose quotes lots of physics and math, it comes down to more or less "By definition a computer cannot think."

I mentioned Hofstadter because he satirized this argument, which predates Penrose, as being the equivalent of "By definition a woman cannot think." The philosopher John Searle is a big proponent of this line of thought, introducing several non sequitur arguments.

We are very far away from true AI, and I think it is because we do not really understand how our own minds work. I don't know that it is possible, or at least practical, but I bristle at stupid arguments, like Penrose's, against AI. I also think that if we ever do create "true" AI it will be very different from human, simply because our body and our chemistry affect us far more than we allow ourselves to realize.
"Results! Why, man, I have gotten a lot of results. I know several thousand things that won't work." --Thomas A. Edison


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