Hi Ben,

Thank you so much for your encouraging and insightful comments. I'm so glad you share my interest in the profound significance of covariance and observer-dependence/independence. The history of physics seems to suggest that separating the invariant from the observer-dependent is the key to getting at the true reality beneath, and I'm fascinated by the ways in which quantum gravity undermines invariances that even relativity and quantum mechanics had left intact.

With regard to your comments:

1. I agree that the question of how to define global or even local observables in quantum gravity is extremely important and mysterious. Personally I am intrigued by the notion that while for AdS or asymptotically flat spacetimes you can retain some kind of invariant boundary observables, you can't seem to do so in de Sitter space, precisely because the de Sitter boundary is observer-dependent. This to me is suggestive that reality is far more observer-dependent than it seems.

I've just read and greatly enjoyed your eloquent essay - though I think I'll have to read it a few more times to understand it! (That's a reflection of my nonexistent mathematical background, not of your essay!) I'm curious if it is in any way related to Tom Banks's work on holographic spacetime? As I understand it, he argues that the causal structure of spacetime can be reconstructed from quantum commutation relations up to a rescaling of lengths and times, and then you can use the holographic principle (because it gives you an area as a function of the number of quantum states) to include scale and now you've got spacetime structure. I believe in his work the observables are noncommutative matrices on the boundary of each "reference frame". Sorry if that's totally irrelevant. In any case, I'm in full agreement that the manifold won't survive quantum gravity - the dualities of string/M-theory certainly point in the direction of a kind of emergent spacetime. In your model, with its basis in binary elements, would you say that the world is "made of information"? And is that information observer-dependent?

2. You're absolutely right - I probably should have mentioned that there is disagreement about how much we can extrapolate the lessons of black hole horizons to cosmic horizons; even Susskind himself has gone back and forth over whether horizon complementarity applies to the de Sitter horizon. Personally, however, I'm unconvinced by arguments that they shouldn't be treated equally. They are mathematically equivalent, they share the same properties of entropy, temperature, etc... yes, there are physical differences (the dS space doesn't "evaporate away", etc) but it just seems to be telling us something general and profound and as a structural realist I see every reason to treat them as equivalent - not least of all because of the equivalence principle!

Thanks again for your comments and for your fascinating contribution, which I will now go and re-read :)

All best,

Amanda

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What is your opinion about my essay?

http://fqxi.org/community/forum/topic/1413

  • [deleted]

Amanda

i think you are reincarnation from George Berkeley

http://en.wikipedia.org/wiki/George_Berkeley

Hi Yuri,

Thanks - I take that as a compliment! However, the solipsism I'm talking about is not a kind of Berkeleyean idealism. I'm not arguing that everything exists only in the mind; in fact, I'm not talking about "minds" at all, but merely reference frames or causal patches. The "solipsism" lies in the fact that, according to some exciting new ideas in theoretical physics, each reference frame defines its own unique yet objectively existing universe. Covariance demands that we can talk about reality equally well from any frame, but the holographic principle and horizon complementarity demands that we restrict our description to a single frame at a time.

All best,

Amanda

  • [deleted]

Thank you. Very interesting comment.

Have you read my essay?

http://fqxi.org/community/forum/topic/1413

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    Dear Amanda,

    you may have a look to my essay (and rate it). It is related to many aspects with yours.

    Ioannis

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      Hi Amanda,

      I thought your essay was very well written and clearly argued.

      I have two questions: What is an observer - a particle, an atom, a molecule, a cell or a larger living thing like a human being? If a particle is a type of observer with its own reference frame, would a molecule or a cell etc. be viewed as a type of composite reference frame?

      Lorraine

        Hi Yuri,

        I enjoyed reading your essay. I must admit I did not fully understand it, but you seem to be drawing some interesting connections.

        All best,

        Amanda

        Hi Lorraine,

        Thanks very much for reading my essay and for your comment.

        I define an observer as a frame of reference. That is, a coordinate frame (to put it in the language of relativity), a causal patch (cosmology), or even a Boolean lattice (quantum logic). I would not consider a particle (or any group of particles up to and including living creatures) as an observer precisely because, once gravity is involved, the very definition of a particle depends on the reference frame (hence, for example, the accelerated observer sees Hawking radiation while the inertial observer does not).

        All best,

        Amanda

        Dear Amanda,

        (Replying down here because the subthread above got a bit long.)

        I think Tom Banks starts with a lot more structure than I do... which might, incidentally, be necessary. The most obvious criticism of my ideas is that they may be too parsimonious to achieve sufficient explanatory power, but I do have some reasons to be hopeful that I can get somewhere worthwhile from this direction.

        "Made of information" is a good description of my approach, although I wouldn't choose that terminology myself simply because it's already been used to describe a lot of theories that really involve a lot of auxiliary structures. The information is observer dependent, but not the laws of physics.

        I have my doubts about a lot of aspects of recent black hole physics, simply because we know that it resides near the horizons of validity of the theories involved (no pun intended). I view it as worth taking seriously, and it's certainly worthwhile to explore the consequences, but I would not be surprised if certain aspects of it turn out to be artifacts of theory stretched beyond its bounds. Take care,

        Ben

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        Dear Amanda,

        If you have found the time to read my essays you would note that our thoughts coincide apart from the different way of expression (due of my amateur education in physics). Each observer has his own reference frame and we can not examine any phenomenon taking two (or more) reference frames at the same time. However I propose that the deviating views by different observers is resemblance of their different frames and it does not mean a difference in Reality. It is like a view from an open window. Every observer has his own view that depends from his position and not to another Reality out of the window. Each observer can see a different part of the only one Reality because of his own position in relation to the window and the Reality out there.

        The expression inside and outside of a Black Hole (BH) resembles mine real and virtual part in any universe. It is evidence that real observers can realize only the real part of their universe while the virtual observers only the virtual part. It is time however to try to resolve the rules of the virtual part of our Universe (if we consider ourselves as real observers).

        During the BH's inhalation the information "lost" is transferred to a new universe which may be of different or the same dimensionality (hence the black holes' jets).

        The quantum part of your essay can be related to World Line (WL) individuality of each event through spacetime that for many instances there are equivalent different paths close to the WL of events (see fig. 1).

        Thank you for the "Experimental evidence of solipsism?" that is a straight evidence of NCS as well.

        Best wishes, Ioannis

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        Amanda -- Wow! I've read a lot of FQXi essays over the years, and this is one of the most interesting I've seen. One thing I didn't notice you tackling, though, was an explanation for the consistency among observations. I have an idea on that: The kinds of observers familiar to us -- biological and technological ones -- share a topological connection which makes inconsistent observations impossible. That idea is central to my essay, "Toward an Informational Mechanics," as is Rovelli's relational quantum mechanics (which I was thrilled to see you mention -- Rovelli just doesn't get enough love).

        In my essay's comments section, there is some discussion about solipsism. I explained my thought that collective reality is a kind of "collective solipsism," but you're absolutely right that each observer frame corresponds to its own universe. It's just that topologically connected observers necessarily observe common informational features of the universe, and I think it is precisely this commonality and consistency that creates the appearance of a single universe. I hope you have a moment to check it out.

        Great work again, and best of luck in the competition.

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          Hello Ms Gefter,

          I beleive that you speak about the interpretations of this Universe. You know the Universe is the same for all.That said we perceive it with our own emotions correlated with our education. The universe is the same sphere for all. In fact I beleive that you cannot say so your conclusion about the universe. We cannot confound an interpretation with a pure determinism.

          Let's take a simple example.Imagine that you like the color of the planet mars, red. and that a friend , him does not like the red color of this planet. It does not mean that this planet mars does not exist or that it exists two planets mars for example.

          1+3+5+7+11+13=40 I don't see an other number :)

          Best Regards

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            Dear Amanda

            in last issue of Russian magazine

            http://ufn.ru/en/articles/2012/9/

            you can read

            Letters to the editors

            "Einstein Moon"

            http://ufn.ru/en/articles/2012/9/h/

            It seems to me soliptic view.

            Dear Amanda.

            Your thesis first sounds shocking, as intended, but; 'the truth will first look wrong as it will be unfamiliar.' (Feynman) so it's in with a shout. I think you find much of the path to truth, but suggest you then drift off to hypothesise and question. I hope you may read my essay which suggests a direct mechanistic and deterministic path in a similar direction, and some causal answers to co-variance. This nevertheless agrees or has analogies with your views;

            "...we must never speak of more than one observer or universe at a time."

            the "...observer-dependence of the vacuum."

            "...multiverse cosmology will have to give way to a new kind of cosmology, one that is radically frame-dependent."

            "...it is equally valid to describe reality from any one of an infinite number of possible reference frames."

            "...each observer's reference frame defines a complete universe, and anything outside the frame is considered merely a redundant description"

            I agree your identification of the low quadrupole, 'axis of evil' and the other CMB anisotropies, to which a solution emerges (consistent with electron twin vortex spin). A consequential recycling mechanism is more referred in the end notes, last years essay and elsewhere. ("...the black hole evaporates and eventually blinks out of existence, presumably taking all internal information with it."). But then returns.

            A very well written, courageous and well argued essay. I really do look forward to your comments on the 'hard reality' analogies underlying the theatrical surface of mine.

            Very best wishes

            Peter

              Hi Karl,

              Thanks so much for your kind comment! I'm so glad you enjoyed the essay.

              The question of consistency among observations is a fascinating one. For me, the key insight comes from Rovelli and from the lessons of horizon complementarity: there is no view from outside the universe, no superobserver who can see across reference frames. That means that any time two observers "compare notes", the comparison is itself an ordinary quantum mechanical interaction. That is, if I compare my observations with yours, the act of comparison takes place within a single reference frame - mine or yours but never both simultaneously. There's no "view from nowhere" from which we can compare two observers' perspectives independent of a reference frame.

              I just had the chance to read your essay and I thought it was fantastic. I'll post some thoughts over on your page.

              Thanks again!

              All best,

              Amanda

              Hi Steve,

              Thanks for reading my essay and for your comment. I appreciate your view; however, the point that I was trying to make in my essay is that while common sense would suggest that we all live in a single universe and that different observers' perspectives are merely different descriptions of one and the same reality, the latest advances in theoretical physics suggest otherwise. That is, we can assume, as you do, that there is one single reality occupied by several observers, but in doing so we actually violate the laws of physics (we clone information, for instance). Put another way, the laws of physics only make sense within a single reference frame at a time. This, to me, is both shocking and profound.

              Best,

              Amanda

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              Amanda,

              Your thesis vitally depends on miraculous theoretical results like this one:

              "...Hawking particles objectively exist according to observers outside the black hole and objectively do not exist according to the unlucky observers who fall in."

              In my view, juggling with such results, without questioning the underlying assumptions, leads you nowhere. The miraculous results may simply be absurd consequences of false assumptions. Let me give examples of an opposite approach:

              Lee Smolin, The Trouble With Physics: "Einstein's special theory of relativity is based on two postulates: One is the relativity of motion, and the second is the constancy and universality of the speed of light. Could the first postulate be true and the other false? If that was not possible, Einstein would not have had to make two postulates. But I don't think many people realized until recently that you could have a consistent theory in which you changed only the second postulate."

              Joao Magueijo, Faster Than the Speed of Light: "Lee [Smolin] and I discussed these paradoxes at great length for many months, starting in January 2001. We would meet in cafés in South Kensington or Holland Park to mull over the problem. THE ROOT OF ALL THE EVIL WAS CLEARLY SPECIAL RELATIVITY. All these paradoxes resulted from well known effects such as length contraction, time dilation, or E=mc^2, all basic predictions of special relativity. And all denied the possibility of establishing a well-defined border, common to all observers, capable of containing new quantum gravitational effects."

              Pentcho Valev

                Hi Pentcho,

                I wholeheartedly agree that questioning our assumptions is crucial to make progress in physics - and of course that is the whole point of this essay contest!

                The "miraculous theoretical result" you refer to is very well accepted in the physics community. I have yet to come across any legit disproof of Hawking's calculation, which itself is based on the extremely well-tested equations of quantum mechanics and general relativity. Could Hawking turn out to be wrong? Of course. In the meantime, I think it's important to follow these profound theoretical discoveries to their logical limits and see where they lead. As I explain in my essay, I am further convinced by the convergence coming from physics as wide-ranging as quantum logic and the cosmic microwave background data.

                Thanks for your comment.

                Best,

                Amanda

                Hi Peter,

                Thanks very much for your comment. I look forward to reading your essay.

                Best,

                Amanda