Notices
Results 1 to 37 of 37

Thread: the universe as a quantum computer

  1. #1 the universe as a quantum computer 
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    Has anyone read this book?

    Programming the Universe: A Quantum Computer
    by Seth Lloyd

    It describes how the universe is a quantum computer and I had a question concerning entropy and how it was described in the book. I believe it was stated that entropy was information that was hidden from the ongoing computation. I just would like your input on this and entropy in general. Also I would like to know your thoughts on whether or not information can ever be destroyed.


    Reply With Quote  
     

  2.  
     

  3. #2  
    Forum Sophomore
    Join Date
    May 2009
    Location
    Beverly Hills, NSW, Australia
    Posts
    140
    no... sorry... i havent read the book.

    and i (personally) think that 'NO' information cannot be destroyed.... because once you release it into the public, it becomes public knowledge.... and to get rid of that 'information' you would have to impose corporal punishment or make freedom of speech illegal or something.

    btw im kinda new to the forums.... but no i think that once information is seen or discovered that it canNOT be 'destroyed' as such...


    "Give Your Soul to me For Eternity, and take Your place Inside The Fire in my Life" "Inside The Fire" by Disturbed

    'Asprin' Apply Directly To The Forehead =P
    Reply With Quote  
     

  4. #3  
    Administrator KALSTER's Avatar
    Join Date
    Sep 2007
    Location
    South Africa
    Posts
    8,231
    Quote Originally Posted by Spaceman34
    no... sorry... i havent read the book.

    and i (personally) think that 'NO' information cannot be destroyed.... because once you release it into the public, it becomes public knowledge.... and to get rid of that 'information' you would have to impose corporal punishment or make freedom of speech illegal or something.

    btw im kinda new to the forums.... but no i think that once information is seen or discovered that it canNOT be 'destroyed' as such...
    He was more speeking from a physics perspective. And yeah it can, AFAIK, by black holes. I haven't read the book either though.

    Information paradox
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
    Reply With Quote  
     

  5. #4  
    Forum Freshman
    Join Date
    May 2009
    Posts
    23
    I've not read the book, but I've read that the universe may have been created by a computer programmer in another universe, using no doubt a quantum computer.
    The earth, by the way, is merely a quarantine for a nasty computer virus.
    Reply With Quote  
     

  6. #5  
    Forum Ph.D. Leszek Luchowski's Avatar
    Join Date
    Jun 2008
    Location
    Gliwice, Poland
    Posts
    807
    I have yet to see a proof that we aren't all characters in a caveman's science-fiction book (or rather, an s-f saga spread by word of mouth).
    Leszek. Pronounced [LEH-sheck]. The wondering Slav.
    History teaches us that we don't learn from history.
    Reply With Quote  
     

  7. #6  
    Forum Freshman
    Join Date
    May 2009
    Posts
    23
    In the beginning was the Word. What do you think the chances of a fine tuned universe for life really is? The answer must be a truly mind blowing number.
    Unless of course it was programmed that way. Apparently it only takes 4 lines.
    All life is purely an information flow of genes (and memes) over a vast time scale.

    "I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image". (Stephen Hawking).
    Reply With Quote  
     

  8. #7  
    Forum Sophomore
    Join Date
    May 2009
    Location
    Beverly Hills, NSW, Australia
    Posts
    140
    Quote Originally Posted by KALSTER
    Quote Originally Posted by Spaceman34
    no... sorry... i havent read the book.

    and i (personally) think that 'NO' information cannot be destroyed.... because once you release it into the public, it becomes public knowledge.... and to get rid of that 'information' you would have to impose corporal punishment or make freedom of speech illegal or something.

    btw im kinda new to the forums.... but no i think that once information is seen or discovered that it canNOT be 'destroyed' as such...
    He was more speeking from a physics perspective. And yeah it can, AFAIK, by black holes. I haven't read the book either though.

    Information paradox
    ok thanks dude,
    black holes? how can energy be destroyed by black holes??
    what about the theory that says "energy cannot be gained or destroyed... it only changes from you form to another"??
    plz help me out.... im new to physics....
    "Give Your Soul to me For Eternity, and take Your place Inside The Fire in my Life" "Inside The Fire" by Disturbed

    'Asprin' Apply Directly To The Forehead =P
    Reply With Quote  
     

  9. #8  
    . DrRocket's Avatar
    Join Date
    Aug 2008
    Posts
    5,486
    Quote Originally Posted by Spaceman34
    Quote Originally Posted by KALSTER
    Quote Originally Posted by Spaceman34
    no... sorry... i havent read the book.

    and i (personally) think that 'NO' information cannot be destroyed.... because once you release it into the public, it becomes public knowledge.... and to get rid of that 'information' you would have to impose corporal punishment or make freedom of speech illegal or something.

    btw im kinda new to the forums.... but no i think that once information is seen or discovered that it canNOT be 'destroyed' as such...
    He was more speeking from a physics perspective. And yeah it can, AFAIK, by black holes. I haven't read the book either though.

    Information paradox
    ok thanks dude,
    black holes? how can energy be destroyed by black holes??
    what about the theory that says "energy cannot be gained or destroyed... it only changes from you form to another"??
    plz help me out.... im new to physics....
    The question is not whether energy is created or destroyed by a black hole. The question is whether, as a black hole evaporates due to Hawking radiation, the information that was contained in the quantum states of the matter that was consumed by a black hole is destroyed or whether there is a mechanism by which it is released to the universe at large.

    The general feeling is that the information is not permanently destroyed, but there is not a solid consensus. Hawking one held that the information would be irretrievable lost, but he changed his position and conceded a bet with John Preskill, who took the opposite stance. But Kip Thorne who was also a party to the bet has not conceded.

    You might want to read Leonard Susskind's book on the subject, The Black Hole War for one perspective on the problem.
    Reply With Quote  
     

  10. #9  
    Forum Sophomore
    Join Date
    May 2009
    Location
    Beverly Hills, NSW, Australia
    Posts
    140
    ok then thanks dude...
    btw my friend said, when i asked him for his thoughts on the subject "light in the black hole" theory we were on about...

    he said:
    "it would do irreverisbly lost to us, but the energy would not be destroyed just that the particles containing our energy would be contained within the highly dense environment of the black hole, but the energy would still remain."
    "Give Your Soul to me For Eternity, and take Your place Inside The Fire in my Life" "Inside The Fire" by Disturbed

    'Asprin' Apply Directly To The Forehead =P
    Reply With Quote  
     

  11. #10  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    One thing I'd like to point out is that a black hole definitely doesn't destroy mass/energy. The question is whether or not it can destroy information. Information, in this case, probably doesn't mean what you think it means.
    Reply With Quote  
     

  12. #11  
    Forum Sophomore
    Join Date
    May 2009
    Location
    Beverly Hills, NSW, Australia
    Posts
    140
    thanks dude

    i didnt know what he meant when i first posted but i do now
    'information' is just a real sciency way of saying 'energy'
    "Give Your Soul to me For Eternity, and take Your place Inside The Fire in my Life" "Inside The Fire" by Disturbed

    'Asprin' Apply Directly To The Forehead =P
    Reply With Quote  
     

  13. #12  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    Reply With Quote  
     

  14. #13  
    . DrRocket's Avatar
    Join Date
    Aug 2008
    Posts
    5,486
    Quote Originally Posted by Spaceman34
    thanks dude

    i didnt know what he meant when i first posted but i do now
    'information' is just a real sciency way of saying 'energy'
    No.

    Information in the context of black holes is basically entropy, and the connection dates to Shannon's classic paper on information theory.

    http://cm.bell-labs.com/cm/ms/what/s...hannon1948.pdf
    Reply With Quote  
     

  15. #14  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    I don't know I've heard Michi Kaku saying that if we threw the encyclopedia into a black hole, is the information lost? I don't if he meant literally the information in the book is lost or if that's just an analogy. It may just mean the spin and various other properties of the particles that went in. There is an Idea that if it is true on one scale it may be true on others. I don't know. So when you say information is not destroyed it applies to all information everywhere, not just to particle properties.
    Reply With Quote  
     

  16. #15  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    That would be an analogy. After all, it's fairly easy to destroy that kind of information. Just burn the book. The pile of ashes would be (practically) the same no matter what was written before hand.

    BTW, a random jumble of letters contains more information than meaningful text (of approximately the same length, at least).
    Reply With Quote  
     

  17. #16  
    Forum Isotope
    Join Date
    Feb 2009
    Location
    Transient
    Posts
    2,914
    He meant it literally, just not how you think. He meant the information that IS the book. The information that is the particles and how they are arranged.
    Wise men speak because they have something to say; Fools, because they have to say something.
    -Plato

    Reply With Quote  
     

  18. #17  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    How can a random set of letters have more information than written text?
    Reply With Quote  
     

  19. #18  
    Forum Isotope
    Join Date
    Feb 2009
    Location
    Transient
    Posts
    2,914
    it simply means that there will, on average, by more letters in the jumble than in that text. Think information as in the information stored on a hard drive. The jumble of letters contains as much or more information than a document of equal length, simply because there are more letters physically contained therein
    Wise men speak because they have something to say; Fools, because they have to say something.
    -Plato

    Reply With Quote  
     

  20. #19  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    ok i see. So do you think that any information is preserved. for example human consciousness or memories?
    Reply With Quote  
     

  21. #20  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    Quote Originally Posted by Arcane_Mathematician
    it simply means that there will, on average, by more letters in the jumble than in that text. Think information as in the information stored on a hard drive. The jumble of letters contains as much or more information than a document of equal length, simply because there are more letters physically contained therein
    Well, no. Even for the same amount of letters and spaces, there's more information in a random collection of letters than in meaningful text. This is more of a math question than a physics question, so I don't want to go too deep into it here. Also, this isn't the same kind of information as is being discussed here. (Well, not exactly, but it is related.)

    Anyway, the reason that random letters have more information is because meaningful text is full of redundancies, and redundancies don't add to the information content. That's how compression works, by removing redundancies. The size of a compressed file is a rough estimation of the information contents of whatever was compressed, and random text is much harder to compress than plain text.
    Reply With Quote  
     

  22. #21  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    What information does the random text represent. Bit's on a computer is a traslation of information into bits. Random bits have no information.
    Reply With Quote  
     

  23. #22  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    You're talking about the wrong kind of information. Actually, what you're talking about isn't information in any technical sense at all, but meaning. Meaning is something imposed on one system by another. We agree these bits represent letters, and these letters make words, and these words mean these things, etc., but none of that is information in the technical sense.

    Information mean, roughly, "how much effort does it take to reproduce this datum." (Can't think of a better word at the moment.) Something with structure is easier to reproduce than something that's completely random, regardless of meaning (or lack thereof).
    Reply With Quote  
     

  24. #23  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    What usable information is there in random letters. Maybe in the quantum world what you say make sense for a particles spin or whatever but in the macroscopic world information IS meaning. I don't understand you explanation.
    Reply With Quote  
     

  25. #24  
    Administrator KALSTER's Avatar
    Join Date
    Sep 2007
    Location
    South Africa
    Posts
    8,231
    Anyway, the reason that random letters have more information is because meaningful text is full of redundancies
    How does this work? Take these two lines:

    ilikewalkingintheparkwithmydog

    jkdkfcnkdkfjklleiieeoopofejjvlety

    Are the redundancies the formatting of the text, or what do you mean?
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
    Reply With Quote  
     

  26. #25  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    Quote Originally Posted by Wildstar
    What usable information is there in random letters. ... but in the macroscopic world information IS meaning.
    No, information is not meaning, and no, information has nothing to do with usability. You're using a completely different definition of information (an informal, intuitive, non-rigorous one). That is not the kind of information being talked about here.

    Quote Originally Posted by KALSTER
    How does this work? Take these two lines:

    ilikewalkingintheparkwithmydog

    jkdkfcnkdkfjklleiieeoopofejjvlety

    Are the redundancies the formatting of the text, or what do you mean?
    I'm not sure those two strings are really long enough to make a good demonstration, but I'll try. (BTW, if you hand typed that second one, it's not random. Humans are terrible at producing randomness. There are sites that will test your input to see how random it is.)

    Since actually measuring the information of those two strings is really tricky, I'll go with a closely related idea, compression. Basically, a string with more information is harder to compress.

    Well, I wanted to try and demonstrate this using some method with just letters and numbers, but the strings are too short, so I'll go with bits instead. The first string is 30 characters long, and the second is 33. The goal is the find some way of representing those strings in as few bits as possible and in such a way that the original can be recovered. I'll use Huffman coding and assume that what I'm compressing is, for the most part, English text. (Note that these assumptions matter. That's why there are so many different compression programs, for example, and this is where information and meaning are closest though they're still not the same.)

    I looked up the English letter frequencies:
    e - 0.12702
    t - 0.09056
    a - 0.08167
    o - 0.07507
    i - 0.06966
    n - 0.06749
    s - 0.06327
    h - 0.06094
    r - 0.05987
    d - 0.04253
    l - 0.04025
    c - 0.02782
    u - 0.02758
    m - 0.02406
    w - 0.02360
    f - 0.02228
    g - 0.02015
    y - 0.01974
    p - 0.01929
    b - 0.01492
    v - 0.00978
    k - 0.00772
    j - 0.00153
    x - 0.00150
    q - 0.00095
    z - 0.00074

    Turning this into a Huffman tree becomes... a big mess. I'll try and type it out if you want, but for now, I'll just show the resulting code. Besides, if you go look up Huffman trees or Huffman coding, it's not hard to do it yourself. Anyway, the final code is:

    e - 000
    t - 100
    a - 0100
    o - 0110
    i - 0010
    n - 0011
    s - 1100
    h - 1101
    r - 1110
    d - 01010
    l - 01011
    c - 11110
    u - 11111
    m - 10100
    w - 10101
    f - 10110
    g - 011100
    y - 011101
    p - 011110
    b - 011111
    v - 101110
    k - 1011110
    j - 101111100
    x - 101111101
    q - 101111110
    z - 101111111

    Phew. Anyway, you'll notice that the more common characters get shorter codes. Also, since no whole code is the beginning of another code, it's pretty easy to get the original back. Well, on to those strings:

    ilikewalkingintheparkwithmydog becomes:
    0010 01011 0010 1011110 000 10101 0100 01011 1011110 0010 0011 011100 0010 0011 100 1101 000 011110 0100 1110 1011110 10101 0010 100 1101 10100 011101 01010 0110 011100

    jkdkfcnkdkfjklleiieeoopofejjvlety becomes:
    101111100 1011110 01010 1011110 10110 11110 0011 1011110 01010 1011110 10110 101111100 1011110 01011 01011 000 0010 0010 000 000 0110 0110 011110 0110 10110 000 101111100 101111100 101110 01011 000 100 011101

    The first is 139 bits for 30 characters or about 4.633 bits per character. (BTW, ASCII uses 8 bits per character, but it has more than just lowercase letters.) The second is 176 bits for 33 characters or about 5.333 bits per character. That means that the if you're expecting Huffman-coded English text, the first string contains less information than the second. It's important to note that if you were expecting something else, the results might be different. After all, there's a lot of redundancies in that second string too. (It's not very random.)

    Edit: Oh. I should mention that the theoretical limit for compressing random lowercase letters would be or about 4.700. The calculation isn't as simple, but for English letters it'd be more like 4.176. Huffman coding can get close, but there are other methods that can get closer.
    Reply With Quote  
     

  27. #26  
    Forum Isotope
    Join Date
    Feb 2009
    Location
    Transient
    Posts
    2,914
    redundancies happen all the time in random strings, especially long ones. either way, I'd rather code it in straight binary.

    a=00001
    b=00010
    c=00011
    d=00100
    e=00101
    f=00110
    g=00111
    h=01000
    i=01001
    j=01010
    k=01011
    l=01100
    m=01101
    n=01110
    o=01111
    p=10000
    q=10001
    r=10010
    s=10011
    t=10100
    u=10101
    v=10110
    w=10111
    x=11000
    y=11001
    z=11010

    using this, it's irrelevant how long the string is and in accordance with random strings, the frequency is irrelevant, it will always be 5bits per character, and either way, how would you deal with redundancies.
    Wise men speak because they have something to say; Fools, because they have to say something.
    -Plato

    Reply With Quote  
     

  28. #27  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    Okay I can kinda see that now. Thank you.
    Reply With Quote  
     

  29. #28  
    . DrRocket's Avatar
    Join Date
    Aug 2008
    Posts
    5,486
    Quote Originally Posted by MagiMaster
    That would be an analogy. After all, it's fairly easy to destroy that kind of information. Just burn the book. The pile of ashes would be (practically) the same no matter what was written before hand.

    BTW, a random jumble of letters contains more information than meaningful text (of approximately the same length, at least).
    Actually that doesn't do it. I don't understand the mechanism, but supposedly even if you burn the book the original quantum states are, in principle, recoverable.

    I get the impression that there is some looseness among the physicists as to precisely how entropy is defined in this very general setting. But they seem to be convinced that "information" cannot be destroyed by any physical process, now including black hole consumption.

    If you want to get a flavor for this you might try Leonard Susskind's book The Black Hole War, my battle with Stephen Hawking to make the world safe for quantum mechanics. It is a pretty interesting read, but Susskind does some hand waving and makes unstated assumptions (for instance the validity of the AdS/CFT correspondence which is widely believed by string theorists but is in truth an unproved conjecture).
    Reply With Quote  
     

  30. #29  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    Sorry, in that post I was referring to the intuitive, informal definition of information (IIRC).
    Reply With Quote  
     

  31. #30  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    I've heard the physicists talking about information loss. they say that if information is lost in a black hole then all of physics would be undermined and one could not trust memories and so on. they seem to speak in analogy in regards to complex mathematics. but seem to address the problem of information loss ion terms of the intuitive analogy description as if it applies not only to abstract mathematics but also to everyday notions of information. Michio Kaku explains that (approximate quote)) "what if we threw the encyclopedia into a black hole? Would the information survive"?
    Is this just an analogy of the quantum mechanical process of entropy and spin and position and momentum. or does it also mean in macroscopic terms everyday existence. If you thew the book into the fire the information of t5he book, not in a quantum mechanical sense, would lost? Or would the information contain in the macroscopic arrangement of the ink and the position of all of the particles involved in the book be preserved if burned? In the book programming the universe by Seth Lloyd, he explains how the universe is a quantum computer, and entropy is information no longer accessible to the ongoing computation. I think. I don't have the book to reference but it is an extremely illuminating book. So if entropy is a transformation of information that is in the processing of quantum Qbits, in reality, into a hidden form, perhaps a black hole is a similar phenomenal. What do you think of this?
    Reply With Quote  
     

  32. #31  
    . DrRocket's Avatar
    Join Date
    Aug 2008
    Posts
    5,486
    Quote Originally Posted by Wildstar
    I've heard the physicists talking about information loss. they say that if information is lost in a black hole then all of physics would be undermined and one could not trust memories and so on. they seem to speak in analogy in regards to complex mathematics. but seem to address the problem of information loss ion terms of the intuitive analogy description as if it applies not only to abstract mathematics but also to everyday notions of information. Michio Kaku explains that (approximate quote)) "what if we threw the encyclopedia into a black hole? Would the information survive"?
    Is this just an analogy of the quantum mechanical process of entropy and spin and position and momentum. or does it also mean in macroscopic terms everyday existence. If you thew the book into the fire the information of t5he book, not in a quantum mechanical sense, would lost? Or would the information contain in the macroscopic arrangement of the ink and the position of all of the particles involved in the book be preserved if burned? In the book programming the universe by Seth Lloyd, he explains how the universe is a quantum computer, and entropy is information no longer accessible to the ongoing computation. I think. I don't have the book to reference but it is an extremely illuminating book. So if entropy is a transformation of information that is in the processing of quantum Qbits, in reality, into a hidden form, perhaps a black hole is a similar phenomenal. What do you think of this?
    I think Kaku's main concern is book royalties rather than physics.
    Reply With Quote  
     

  33. #32  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    I don't know about that. He co wrote sting field theory.
    Reply With Quote  
     

  34. #33  
    . DrRocket's Avatar
    Join Date
    Aug 2008
    Posts
    5,486
    Quote Originally Posted by Wildstar
    I don't know about that. He co wrote sting field theory.
    Not really. IMO he is at best a bit player.

    The guys who get the lions share of the credit for strings are Leonard Susskind (in the beginning as a model for the strong force), Ed Witten, Michael Green, John Schwarz, Polchinski, Maldecena and a few others.

    IMO Kaku's strength is self-promotion.

    The "Big Guy" in string theory, very clearly, is Ed Witten. He is far and away the best. He could also come in 2,3,4, and 5 if he wanted to. After that the next biggest influence is probably Maldecena, who is pretty young but already a big gun with a permanent position at the Institute for Advanced Study with Witten.

    There are not many books on the subject. The original was a 2-vol set,Superstrings by Witten, Green and Schwartz, which is probably a bit dated now, but these three guys shaped the initial theory, so it is a book by masters of the field. Then there is another 2-vol set,String Theory by Polchinski, also a "big gun". After that there are some introductory books, notably String Theory and M Theory: A Modern Introduction[/u] by Katrin Becker, Melanie Becker and John Schwarz (same Schwarz as the first book).

    Kaku was a co-writer of a couple of introductory books, but that is all. Lots of people have written books, but only a few have really shaped the field.
    Reply With Quote  
     

  35. #34  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    Really. I've read both of Greenes books. I like them. The other books you discussed are layman books or textbooks? I've heard that Witten may be the greatest living physicist, and he was the one that came up with the translation from one of the five string theory's in to a cohesive whole called M-theory. but since that time I have not read about any progress in the field.
    Reply With Quote  
     

  36. #35  
    . DrRocket's Avatar
    Join Date
    Aug 2008
    Posts
    5,486
    Quote Originally Posted by Wildstar
    Really. I've read both of Greenes books. I like them. The other books you discussed are layman books or textbooks? I've heard that Witten may be the greatest living physicist, and he was the one that came up with the translation from one of the five string theory's in to a cohesive whole called M-theory. but since that time I have not read about any progress in the field.
    Wrong Green.

    Michael Green, along with Ed Witten and John Schwarz was one of the early pioneers of modern string theory.

    Brian Greene is a physicist who has written a couple of good popularizations and done some original research as well. I actually think rather highly of those books -- The Elegant Universe and The Fabric of the Cosmos. They are especially good if you pay attention to the footnotes that talk more about the real physics that is involved. But Brian Greene is of somewhat lesser stature than Michael Green -- he is just better known because of his popularizations.

    Ed Witten is the driving force behind string theory. He is the recipient of the Fields Medal in mathematics.

    But the case for M-theory is overstated. In 1995 string theory was on the ropes. There were several promising competing string theories, and no indication if any of them were valid physics. Witten gave a talk and wrote a paper that made a plausibility argument that these string theories were actually equivalent and part of one larger theory that was dubbed M-theory. The key to the explanation, and even the existence of M-theory would be a "dictionary" that would allow one to translate back and forth among the relevant set of string theories, and Witten's talk/paper served to state the conjecture that such a dictionary exists and make it plausible that a proof might be found. That dictionary has never been produced, and there is no firm definition of what "M-theory" really is.

    So M-theory fails to be a "cohesive whole" by simply failing to be clearly defined. The same problem actually exists with the constituent string theories --they are not well-defined either. The major open problem in string theory and M-theory is "what is it ?" While you don't hear that from the string community very often (they don't deny it) you do hear it from people like 'tHooft, who is one of the very best theoretical physicists on the planet -- he received the Nobel prize for contributions to quantum field theory (his PhD dissertation showed that the electroweak theory is renormalizable).

    While there is no doubt that Witten is very good, the statement that he is the "greatest living physicist" sounds like it is coming from the string community "Taliban". I doubt that Witten himself would support that statement, as he is generally fairly honest. His contributions thus far have been to mathematics rather than to physics -- since string theory is rather short of physical predictions. My personal picks for theoretical physicists would include 'tHooft and Weinberg, Witten would jump to the head of the line if and when string theory started producing correct and testable physical predictions, but not before.
    Reply With Quote  
     

  37. #36  
    Forum Sophomore
    Join Date
    May 2009
    Posts
    144
    Have Witten, green and Schwarz writen books?
    Reply With Quote  
     

  38. #37  
    . DrRocket's Avatar
    Join Date
    Aug 2008
    Posts
    5,486
    Quote Originally Posted by Wildstar
    Have Witten, green and Schwarz writen books?
    They wrote the books that I listed earlier. Those are not for aeneral audience though.

    I don't know of any books that they have written for a general audience.

    But at least Witten has written some articles that are accessible. You can find some on his web site. http://www.sns.ias.edu/~witten/
    Reply With Quote  
     

Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •