Testing the Holographic Principle

Adrian Cho at Science magazine this week has an article about Craig Hogan’s project to build a “holometer” and somehow test the “holographic principle”. Since this promises some sort of experimental test of fashionable ideas about quantum gravity, it has gotten a lot of attention, including a cover story in the February Scientific American (also available here and maybe elsewhere).

This kind of thing often gets promoted as a “test of string theory”, but in this case, at least from certain quarters, that definitely isn’t happening. Cho quotes Raphael Bousso:

But some experts on the holographic principle think the experiment is completely off-target. “There is no relationship between the argument [Hogan] is making and the holographic principle,” Bousso says. “None whatsoever. Zero.” The problem lies not in Hogan’s interpretation of the uncertainty relationship, but rather in “the first step of his analysis,” Bousso contends.

Bousso notes that a premise of special relativity called Lorentz invariance says the rules of physics should be the same for all observers, regardless of how they are moving relative to one another. The holographic principle maintains Lorentz invariance, Bousso says. But Hogan’s uncertainty formula does not, he argues: An observer standing in the lab and another zipping past would not agree on how much an interferometer’s beam splitter jitters. So Hogan’s uncertainty relationship cannot follow from the holographic principle, Bousso argues.

The experiment can do no good in testing the holographic principle, Bousso says, but running it could do plenty of harm. The holometer has garnered an inordinate amount of attention in the blogosphere and in press accounts, he says, raising unrealistic expectations. “They’re not going to have a signal and then there is going to be a backlash saying that the holographic principle isn’t valid, and we’ll look like we’re on the defensive,” Bousso says. “That’s why I’m trying to get the word out [that the experiment won't test the principle] without appearing to make excuses.”

There’s also the following from Lenny Susskind:

Not everyone cheers the effort, however. In fact, Leonard Susskind, a theorist at Stanford University in Palo Alto, California, and co-inventor of the holographic principle, says the experiment has nothing to do with his brainchild. “The idea that this tests anything of interest is silly,” he says, before refusing to elaborate and abruptly hanging up the phone.

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13 Responses to Testing the Holographic Principle

  1. Shantanu says:

    Peter, two swallows don’t make a summer. am sure you will find some string theorists who will claim this as evidence for string theory.
    Over the years I have found that string theory agrees with even contradictory facts.
    o string theory is consistent with both equivalence principle and violations of equivalence principle
    o string theory predicts supersymmetric dark matter as well as MOND.
    o string theory agrees with superluminal neutrino as well as neutrinos moving at c.
    someone should add more such examples.

  2. Dan Winslow says:

    Well, hype aside; whether it tests the holographic principle or not it does seem to me ( as a layman ) to be an interesting test. Wouldn’t having some quantization of space time affect things like renormalization and other infinity-plagued calculations? Forgive me in advance if I;m not making sense.

  3. Peter Woit says:

    Shantanu,

    If Hogan’s experiment actually sees something, I have no doubt it will be claimed as “evidence for string theory”.

    Dan,
    A quantization of space/time is a holy grail for many theorists, with the fact that it would provide a natural cut-off for QFT calculations just one of many reasons to be interested. The argument here is over whether Hogan’s experiment actually is sensitive to such a quantization. It seems overwhelmingly likely that it won’t see anything, so Bousso/Susskind are sensibly trying to distance themselves from having their favorite theoretical idea associated with it.

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  5. Bee says:

    I explained the issue with Lorentz-invariance years ago here. One has to be grateful, I think, to Bousso and Susskind to speak at least a few clear words before hanging up the phone.

  6. Sesh says:

    Peter, your first link is missing a semicolon.

  7. Sesh says:

    Sorry, I meant a colon.

  8. Rhys says:

    I think it’s important to emphasise that the holographic principle is independent of string theory; AdS/CFT (of the ‘hard’ variety) is just the most concrete realisation that has been found. If there is one thing which is thought to be ‘known’ about quantum gravity, it is the relationship between horizons and entropy.

    But as Bousso said, there doesn’t appear to be any link between what Hogan is doing and the holographic principle. The “Scientific Bibliography” on the holometer website is extraordinary, by the way:
    http://holometer.fnal.gov/scientific-bibliography.html

  9. Peter Woit says:

    Sesh,

    Thanks, fixed.

  10. Visitor says:

    “In fact, Leonard Susskind, a theorist at Stanford University in Palo Alto, California, and co-inventor of the holographic principle, says the experiment has nothing to do with his brainchild. ‘The idea that this tests anything of interest is silly,’ he says, before refusing to elaborate and abruptly hanging up the phone. ”

    Considering how much of his time and effort is spent in creating and proselytizing for baseless speculations that masquerade as theory, and his appeals to their utility as a philosophical foundation of atheism as a reason to support those speculations, Susskind seems to me to be pretty nearly the last person to be making such a criticism, and this would have severely diminished my opinion of him, had I any positive opinion of him in the first place.

  11. Owen Patterson says:

    While I am sure that Dr. Susskind is a very busy and important man, perhaps if he had taken a few moments to explain things a bit to the interested pleibians huddled outside his door, perhaps we would all be better enlightened and then would not bother the great man with so many such puny questions and theories in the future.

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