Comments on: OO’s and BB’s http://cosmicvariance.com/2007/02/21/oos-and-bbs/ Random samplings from a universe of ideas Sun, 20 Jul 2008 05:14:53 +0000 http://wordpress.org/?v=2.5.1 By: A Glimpse Into Boltzmann’s Actual Brain | Cosmic Variance http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-257058 A Glimpse Into Boltzmann’s Actual Brain | Cosmic Variance Fri, 04 May 2007 05:04:20 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-257058 [...] You’ve heard the “Boltzmann’s Brain” argument (here and here, for example). It’s a simple idea, which is put forward as an argument against the notion that our universe is just a thermal fluctuation. If the universe is an ordinary thermodynamic system in equilibrium, there will be occasional fluctuations into low-entropy states. One of these might look like the Big Bang, and you might be tempted to conclude that such a process explains the arrow of time in our universe. But it doesn’t work, because you don’t need anything like such a huge fluctuation. There will be many smaller fluctuations that do just as well; the minimal one you might imagine would be a single brain-sized collection of particles that just has time to look around and go Aaaaaagggghhhhhhh before dissolving back into equilibrium. (These days a related argument is being thrown around in the context of eternal inflation — not exactly the same, because we’re not assuming the ensemble is in equilibrium, but similar in spirit.) [...] [...] You’ve heard the “Boltzmann’s Brain” argument (here and here, for example). It’s a simple idea, which is put forward as an argument against the notion that our universe is just a thermal fluctuation. If the universe is an ordinary thermodynamic system in equilibrium, there will be occasional fluctuations into low-entropy states. One of these might look like the Big Bang, and you might be tempted to conclude that such a process explains the arrow of time in our universe. But it doesn’t work, because you don’t need anything like such a huge fluctuation. There will be many smaller fluctuations that do just as well; the minimal one you might imagine would be a single brain-sized collection of particles that just has time to look around and go Aaaaaagggghhhhhhh before dissolving back into equilibrium. (These days a related argument is being thrown around in the context of eternal inflation — not exactly the same, because we’re not assuming the ensemble is in equilibrium, but similar in spirit.) [...]

]]> By: What I Believe But Cannot Prove | Cosmic Variance http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-245298 What I Believe But Cannot Prove | Cosmic Variance Wed, 11 Apr 2007 20:51:02 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-245298 [...] The search for certainty in empirical knowledge is a chimera. I could always be a brain in a vat, or teased by an evil demon, or simply an AI program running on somebody else’s computer — fed consistently misleading “sense data” that led me to incorrect conclusions about the true nature of reality. Or, to put a more modern spin on things, I could be a one of Boltzmann’s Brains — a thermal fluctuation, born spontaneously out of a thermal bath with convincing (but thoroughly incorrect) memories of the past. But — here is the punchline — it makes no sense to act as if any of those is the case. By “makes no sense” we don’t mean “can’t possibly be true,” because any one of those certainly could be true. Instead, we mean that it’s a cognitive dead end. Maybe you are a brain in a vat. What are you going to do about it? You could try to live your life in a state of rigorous epistemological skepticism, but I guarantee that you will fail. You have to believe something, and you have to act in some way, even if your belief is that we have no reliable empirical knowledge about the world and your action is to never climb out of bed. On the other hand, putting aside the various solipsistic scenarios and deciding to take the evidence of our senses (more or less) at face value does lead somewhere; we can make sense of the world, act within it and see it respond in accordance with our understanding. That’s both the best we can hope for, and what the world does as a matter of fact grant us; that’s why science works! [...] [...] The search for certainty in empirical knowledge is a chimera. I could always be a brain in a vat, or teased by an evil demon, or simply an AI program running on somebody else’s computer — fed consistently misleading “sense data” that led me to incorrect conclusions about the true nature of reality. Or, to put a more modern spin on things, I could be a one of Boltzmann’s Brains — a thermal fluctuation, born spontaneously out of a thermal bath with convincing (but thoroughly incorrect) memories of the past. But — here is the punchline — it makes no sense to act as if any of those is the case. By “makes no sense” we don’t mean “can’t possibly be true,” because any one of those certainly could be true. Instead, we mean that it’s a cognitive dead end. Maybe you are a brain in a vat. What are you going to do about it? You could try to live your life in a state of rigorous epistemological skepticism, but I guarantee that you will fail. You have to believe something, and you have to act in some way, even if your belief is that we have no reliable empirical knowledge about the world and your action is to never climb out of bed. On the other hand, putting aside the various solipsistic scenarios and deciding to take the evidence of our senses (more or less) at face value does lead somewhere; we can make sense of the world, act within it and see it respond in accordance with our understanding. That’s both the best we can hope for, and what the world does as a matter of fact grant us; that’s why science works! [...]

]]> By: Stathis Papaioannou http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-212999 Stathis Papaioannou Mon, 05 Mar 2007 11:47:32 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-212999 Torbjörn> This is exactly my point - without the possibility of an external observer no one will know if the copying succeeded. The clone will only know of themselves, and they can’t tell if they were successfully copied or not. And how would you know you were the same person if you were kidnapped and taken to a distant place in your sleep tonight? Would you need to check with someone else? Torbjörn> This is exactly my point - without the possibility of an external observer no one will know if the copying succeeded. The clone will only know of themselves, and they can’t tell if they were successfully copied or not.

And how would you know you were the same person if you were kidnapped and taken to a distant place in your sleep tonight? Would you need to check with someone else?

]]> By: Torbjörn Larsson http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-212642 Torbjörn Larsson Sun, 04 Mar 2007 23:45:06 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-212642 Stathis: <blockquote> Moreover, we do know that our consciousness can survive copying because it happens all the time: most of the atoms in your brain are replaced over a matter of weeks to months. </blockquote> Well, not exactly. Many of our molecules are replaced by being broken down and reused. Metabolism supplies and removes some atoms when this happens. But much of our brain is static on the working cellular level, i.e. synapses and gate channels are added and removed but the neurons may not be replaced. But all that is besides the point, You have not explained how you will copy a brain close enough to be functionally equivalent with the original while <i>continuing with the same state</i> as when cloned. You are just claiming that it is possible. But that is not a demonstration. <blockquote> it isn’t a problem from your point of view if you are the one being copied </blockquote> This is exactly my point - without the possibility of an external observer no one will know if the copying succeeded. The clone will only know of themselves, and they can't tell if they were successfully copied or not. But I think the problem with our communication is solved, if there ever was one. You are repeating your claims without addressing my arguments. I don't think it is meaningful to continue. Stathis:

Moreover, we do know that our consciousness can survive copying because it happens all the time: most of the atoms in your brain are replaced over a matter of weeks to months.

Well, not exactly. Many of our molecules are replaced by being broken down and reused. Metabolism supplies and removes some atoms when this happens.

But much of our brain is static on the working cellular level, i.e. synapses and gate channels are added and removed but the neurons may not be replaced.

But all that is besides the point, You have not explained how you will copy a brain close enough to be functionally equivalent with the original while continuing with the same state as when cloned.

You are just claiming that it is possible. But that is not a demonstration.

it isn’t a problem from your point of view if you are the one being copied

This is exactly my point - without the possibility of an external observer no one will know if the copying succeeded. The clone will only know of themselves, and they can’t tell if they were successfully copied or not.

But I think the problem with our communication is solved, if there ever was one. You are repeating your claims without addressing my arguments. I don’t think it is meaningful to continue.

]]> By: island http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-212041 island Sat, 03 Mar 2007 20:12:03 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-212041 Elliot, I think that Lee's idea about an inherent time asymmetry necessitates "an underlying principle or law that favors the emergence of complexity", in terms of an energy conservation law that guarantees that the second law of thermodynamics never be violated, such as the one that is discussed here, in context with Richard Dawkins' own ideas about the "anti-chance mechanism of natural selection": http://pespmc1.vub.ac.be/ASYMTRANS.html ... and as it is illustrated, here: http://pespmc1.vub.ac.be/ASYMILL.html ... and on my blog, where my own ideas about <a href="http://evolutionarydesign.blogspot.com/2007/02/our-darwinian-universe.html" rel="nofollow">"Our Darwinian Universe"</a> are nearly identical, although less complex by orders of magnitude. The high energy physics mechanism for this is discussed in the following linked article, and many other places on <a href="http://evolutionarydesign.blogspot.com/" rel="nofollow">my website</a>. This is the same mehanism that is used in inflationary models, where mass can be created at the expense of a large negative gravitational energy following from expansion, except that the universe is held flat and stable as expansion accelerates toward the next big bang: http://www.lns.cornell.edu/spr/2006-02/msg0073320.html Elliot, I think that Lee’s idea about an inherent time asymmetry necessitates “an underlying principle or law that favors the emergence of complexity”, in terms of an energy conservation law that guarantees that the second law of thermodynamics never be violated, such as the one that is discussed here, in context with Richard Dawkins’ own ideas about the “anti-chance mechanism of natural selection”:

http://pespmc1.vub.ac.be/ASYMTRANS.html

… and as it is illustrated, here:

http://pespmc1.vub.ac.be/ASYMILL.html

… and on my blog, where my own ideas about “Our Darwinian Universe” are nearly identical, although less complex by orders of magnitude.

The high energy physics mechanism for this is discussed in the following linked article, and many other places on my website. This is the same mehanism that is used in inflationary models, where mass can be created at the expense of a large negative gravitational energy following from expansion, except that the universe is held flat and stable as expansion accelerates toward the next big bang:

http://www.lns.cornell.edu/spr/2006-02/msg0073320.html

]]> By: Stathis Papaioannou http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-211705 Stathis Papaioannou Sat, 03 Mar 2007 01:48:01 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-211705 Torbjörn Larsson >Therefore you must demonstrate that the deviations will still make a close enough copy to be a mind clone. It may be possible, since the we seem robust enough. But we don’t know. So you can’t claim ad hoc that it is possible, it isn’t exactly like copying a brick by dimension but it is like copying every sand particle and their binding forces in every detail. The brick has a particular function and a particular engineering tolerance for that function; you don't need to specify it down to the quantum level. If the brain had an engineering tolerance of zero, random thermal motion in our heads would kill us instantly. Moreover, we do know that our consciousness can survive copying because it happens all the time: most of the atoms in your brain are replaced over a matter of weeks to months. Torbjörn Larsson >What I mean is that even if it would be impossible of making a constructed copy, it would not preclude us or the universe to build bounded or unbounded many different brains. By chance someone might (will, in the later case) be a perfect copy of you and your thoughts from some moment and forward. >But we can’t tell which one, because if it is impossible to make an exact enough copy, we can’t compare them either. This seems to preclude any possibility of you (being in the bounded category) making an exact copy and be certain of it, ie observe it. That would be a censorship principle. For an external observer that is so, but it isn't a problem from your point of view if you are the one being copied. If you are instantaneously disintegrated and a sufficiently close copy of you is made within the event horizon of a black hole, no-one will ever be able to find the copy but you will suddenly find yourself as if magically transported there. Torbjörn Larsson >Therefore you must demonstrate that the deviations will still make a close enough copy to be a mind clone. It may be possible, since the we seem robust enough. But we don’t know. So you can’t claim ad hoc that it is possible, it isn’t exactly like copying a brick by dimension but it is like copying every sand particle and their binding forces in every detail.

The brick has a particular function and a particular engineering tolerance for that function; you don’t need to specify it down to the quantum level. If the brain had an engineering tolerance of zero, random thermal motion in our heads would kill us instantly. Moreover, we do know that our consciousness can survive copying because it happens all the time: most of the atoms in your brain are replaced over a matter of weeks to months.

Torbjörn Larsson >What I mean is that even if it would be impossible of making a constructed copy, it would not preclude us or the universe to build bounded or unbounded many different brains. By chance someone might (will, in the later case) be a perfect copy of you and your thoughts from some moment and forward.

>But we can’t tell which one, because if it is impossible to make an exact enough copy, we can’t compare them either. This seems to preclude any possibility of you (being in the bounded category) making an exact copy and be certain of it, ie observe it. That would be a censorship principle.

For an external observer that is so, but it isn’t a problem from your point of view if you are the one being copied. If you are instantaneously disintegrated and a sufficiently close copy of you is made within the event horizon of a black hole, no-one will ever be able to find the copy but you will suddenly find yourself as if magically transported there.

]]> By: Torbjörn Larsson http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-211009 Torbjörn Larsson Thu, 01 Mar 2007 21:15:21 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-211009 <blockquote> Wow, what a complicated sentence that was! </blockquote> I'm sorry, we do seem to have a communication problem which I cause, not least because I'm too tired when I have time to answer. <blockquote> Certainly it would be very difficult, like simulating the weather, but how is it possible that a neuron will do something that is uncomputable? </blockquote> My point here is that it seems to be (even classically) impossible in theory to copy a systems Hamiltonian perfectly. So it isn't only the terribly difficult matter of copying the systems biochemical wetware and current state, or the even worse difficulty of copying into another type of system, but it is impossible to make a perfect copy. Therefore you must demonstrate that the deviations will still make a close enough copy to be a mind clone. It may be possible, since the we seem robust enough. But we don't know. So you can't claim ad hoc that it is possible, it isn't exactly like copying a brick by dimension but it is like copying every sand particle <b>and their binding forces in every detail</b>. <blockquote> since the possible improbability of deterministically copying a brain doesn’t preclude the stochastic probability of doing it. </blockquote> What I mean is that even if it would be impossible of making a constructed copy, it would not preclude us or the universe to build bounded or unbounded many different brains. By chance someone might (will, in the later case) be a perfect copy of you and your thoughts from some moment and forward. But we can't tell which one, because if it is impossible to make an exact enough copy, we can't compare them either. This seems to preclude any possibility of you (being in the bounded category) making an exact copy and be certain of it, ie observe it. That would be a censorship principle.

Wow, what a complicated sentence that was!

I’m sorry, we do seem to have a communication problem which I cause, not least because I’m too tired when I have time to answer.

Certainly it would be very difficult, like simulating the weather, but how is it possible that a neuron will do something that is uncomputable?

My point here is that it seems to be (even classically) impossible in theory to copy a systems Hamiltonian perfectly. So it isn’t only the terribly difficult matter of copying the systems biochemical wetware and current state, or the even worse difficulty of copying into another type of system, but it is impossible to make a perfect copy.

Therefore you must demonstrate that the deviations will still make a close enough copy to be a mind clone. It may be possible, since the we seem robust enough. But we don’t know. So you can’t claim ad hoc that it is possible, it isn’t exactly like copying a brick by dimension but it is like copying every sand particle and their binding forces in every detail.

since the possible improbability of deterministically copying a brain doesn’t preclude the stochastic probability of doing it.

What I mean is that even if it would be impossible of making a constructed copy, it would not preclude us or the universe to build bounded or unbounded many different brains. By chance someone might (will, in the later case) be a perfect copy of you and your thoughts from some moment and forward.

But we can’t tell which one, because if it is impossible to make an exact enough copy, we can’t compare them either. This seems to preclude any possibility of you (being in the bounded category) making an exact copy and be certain of it, ie observe it. That would be a censorship principle.

]]> By: Stathis Papaioannou http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-208828 Stathis Papaioannou Tue, 27 Feb 2007 13:54:38 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-208828 SP> If it is possible in theory to preserve brain function by replacing each neuron with a computer chip, that is if the brain is Turing emulable, then a particular brain program could run on an infinite number of general purpose computers. Torbjörn Larsson> But this possibility is what I claimed earlier what you must establish. I can’t see that you have moved your argument. Brains are made of matter which follows the well-understood laws of chemistry. Certainly it would be very difficult, like simulating the weather, but how is it possible that a neuron will do something that is uncomputable? Roger Penrose has had to speculate on an uncomputable theory of quantum gravity just to keep the brain special, but he is almost alone in his position. Torbjörn Larsson> I think there is some confusion here, possibly on my part, since the possible improbability of deterministically copying a brain doesn’t preclude the stochastic probability of doing it. Wow, what a complicated sentence that was! stathisp@gmail.com SP> If it is possible in theory to preserve brain function by replacing each neuron with a computer chip, that is if the brain is Turing emulable, then a particular brain program could run on an infinite number of general purpose computers.

Torbjörn Larsson> But this possibility is what I claimed earlier what you must establish. I can’t see that you have moved your argument.

Brains are made of matter which follows the well-understood laws of chemistry. Certainly it would be very difficult, like simulating the weather, but how is it possible that a neuron will do something that is uncomputable? Roger Penrose has had to speculate on an uncomputable theory of quantum gravity just to keep the brain special, but he is almost alone in his position.

Torbjörn Larsson> I think there is some confusion here, possibly on my part, since the possible improbability of deterministically copying a brain doesn’t preclude the stochastic probability of doing it.

Wow, what a complicated sentence that was!

stathisp@gmail.com

]]> By: Torbjörn Larsson http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-208036 Torbjörn Larsson Mon, 26 Feb 2007 11:16:28 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-208036 Stathis: Sorry for not answering timely. <blockquote> If it is possible in theory to preserve brain function by replacing each neuron with a computer chip, that is if the brain is Turing emulable, then a particular brain program could run on an infinite number of general purpose computers. </blockquote> But this possibility is what I claimed earlier what you must establish. I can't see that you have moved your argument. <blockquote> If the BB is to reproduce the function of a particular brain, it need only chance upon the configuration of one of these machines, actual or (infinitely larger set) possible. </blockquote> I think there is some confusion here, possibly on my part, since the possible improbability of deterministically copying a brain doesn't preclude the stochastic probability of doing it. Stathis:

Sorry for not answering timely.

If it is possible in theory to preserve brain function by replacing each neuron with a computer chip, that is if the brain is Turing emulable, then a particular brain program could run on an infinite number of general purpose computers.

But this possibility is what I claimed earlier what you must establish. I can’t see that you have moved your argument.

If the BB is to reproduce the function of a particular brain, it need only chance upon the configuration of one of these machines, actual or (infinitely larger set) possible.

I think there is some confusion here, possibly on my part, since the possible improbability of deterministically copying a brain doesn’t preclude the stochastic probability of doing it.

]]> By: Plato http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207383 Plato Sun, 25 Feb 2007 18:57:52 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207383 Sorry! The correct link can be found <a href="http://www.santafe.edu/~mgm/" rel="nofollow">here</a>. Sorry! The correct link can be found here.

]]> By: Plato http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207380 Plato Sun, 25 Feb 2007 18:52:20 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207380 Just refer back to Plectics. One can then assume all kinds of things? :) <b>Murray Gellman</b>: <a href="http://www.santafe.edu/sfi/People/mgm/plectics.pdf" rel="nofollow"><blockquote>The name that I propose for our subject is "plectics," derived, like mathematics, ethics, politics, economics, and so on, from the Greek. Since plektos with no prefix comes from *plek- , but without any commitment to the notion of "once" as in "simple" or to the notion of "together" as in "complex," the derived word "plectics" can cover both simplicity and complexity.</blockquote></a> Just refer back to Plectics. One can then assume all kinds of things? :)

Murray Gellman:


The name that I propose for our subject is “plectics,” derived, like mathematics, ethics, politics, economics, and so on, from the Greek. Since plektos with no prefix comes from *plek- , but without any commitment to the notion of “once” as in “simple” or to the notion of “together” as in “complex,” the derived word “plectics” can cover both simplicity and complexity.

]]> By: Elliot http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207337 Elliot Sun, 25 Feb 2007 16:30:17 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207337 Going back to my comment of #12 it still seems to me that the assumption that there is not an underlying principle or law that favors the emergence of complexity leads to this conundrum. I think I should amend that comment and say emergence and persistence of complexity. The other assumption is that we OOs or our successors or other OOs may not affect or alter the far future of the universe in radical and unimagined ways to ensure our own survival or that of our "offspring". (baby universe or otherwise) To paraphrase Freeman Dyson we are already "disturbing the universe". Elliot Going back to my comment of #12 it still seems to me that the assumption that there is not an underlying principle or law that favors the emergence of complexity leads to this conundrum. I think I should amend that comment and say emergence and persistence of complexity. The other assumption is that we OOs or our successors or other OOs may not affect or alter the far future of the universe in radical and unimagined ways to ensure our own survival or that of our “offspring”. (baby universe or otherwise) To paraphrase Freeman Dyson we are already “disturbing the universe”.

Elliot

]]> By: Stathis Papaioannou http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207229 Stathis Papaioannou Sun, 25 Feb 2007 10:06:09 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207229 Tom Banks: "This model definitely predicts most intelligent observers should be BBs rather than OOs. So the model is definitely wrong... It's a fiendishly difficult area when the observer self-samples. Is the Doomsday Argument right? Should I conclude that the number of non-human intelligences in the universe is relatively small because I'm not one of them? Tom Banks:
“This model definitely predicts most intelligent observers should be BBs rather than OOs. So the model is definitely wrong…

It’s a fiendishly difficult area when the observer self-samples. Is the Doomsday Argument right? Should I conclude that the number of non-human intelligences in the universe is relatively small because I’m not one of them?

]]> By: Jack http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207119 Jack Sun, 25 Feb 2007 02:42:34 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207119 Tom Banks writes: "I hate myself for wasting any more time on this subject" Thereby giving a powerful boost to the notion that the entire subject is not to be taken seriously. Gee, thanks Tom. Tom Banks writes:

“I hate myself for wasting any more time on this subject”

Thereby giving a powerful boost to the notion that the entire subject is not to be taken seriously. Gee, thanks Tom.

]]> By: Plato http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207087 Plato Sun, 25 Feb 2007 00:52:29 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207087 Wow! Interesting points being made here. :) I believe there may have been a misuse of the term "sensorium" above in <a href="http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-204859" rel="nofollow">post #21?</a> That is can be used in "other contexts" as well. I give info on that for further inspection on my name if interested. What would "activate" the DNA in individuals that lies dormant now. I could not escape either the comment of Aaron's about what was metaphysical. Has this then been relegated to a "philosophical difference" or was it always thus? Wow! Interesting points being made here. :)

I believe there may have been a misuse of the term “sensorium” above in post #21? That is can be used in “other contexts” as well. I give info on that for further inspection on my name if interested.

What would “activate” the DNA in individuals that lies dormant now. I could not escape either the comment of Aaron’s about what was metaphysical. Has this then been relegated to a “philosophical difference” or was it always thus?

]]> By: Sean http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207025 Sean Sat, 24 Feb 2007 21:26:45 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207025 Fair enough, I won't follow up! (Although I was thinking about fluctuating into our current universe, not into BBN.) But I will think about time-dependent Hamiltonians, which I admit I don't have much intuition about. Fair enough, I won’t follow up! (Although I was thinking about fluctuating into our current universe, not into BBN.) But I will think about time-dependent Hamiltonians, which I admit I don’t have much intuition about.

]]> By: Tom Banks http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207022 Tom Banks Sat, 24 Feb 2007 21:11:36 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207022 Sean, Since it's you, I'll respond just this once. You're wrong about BU. What fluctuates is states. The Hamiltonian is fixed and TIME DEPENDENT. There is nothing about the action of the asymptotic dS Hamiltonian in the future that resembles the time dependent hamiltonian that described cosmology (it's EASY to prove this if you accept a few plausible things about the dS Hamiltonian). If you fluctuate a state, which corresponds to the state of our universe at say the time of nucleosynthesis, and act on it with the dS Hamiltonian, you won't get anything like the normal history of the universe. Nothing will happen for a time of order the dS Hubble time, and on time scales much longer than that the evolution will have nothing to do with the cosmological history we've seen. This claim depends only on my picture of the QM of dS space. If you follow the full rules of holographic cosmology it's even worse. The state of the universe at nucleosynthesis is a product of the state of things that could have been observed inside the particle horizon at that time, and a state of everything else. The holographic time dependent Hamiltonian slowly allows outside degrees of freedom to interact with inside ones. But the dS Hamiltonian does not respect this separation of the Hilbert space into a tensor product. It has big matrix elements mixing up all of the inside states with all of the outside ones: just as big as the inside inside and outside outside matrix elements (think of it as a random matrix on the whole hilbert space, with a few constraints on its spectrum). Your final comment about initial and final conditions also reflects a prejudice which comes from thinking too much about systems with time independent Hamiltonians and or time reversal invariance. And too much QFT in curved space time. It's my belief that we won't make progress on these questions until people smarter than I throw off these prejudices. I promise, NO MORE! tom Sean,

Since it’s you, I’ll respond just this once. You’re wrong about BU. What fluctuates is states. The Hamiltonian is fixed and TIME DEPENDENT. There is nothing about the action of the asymptotic dS Hamiltonian in the future that resembles the time dependent hamiltonian that described cosmology (it’s EASY to prove this if you accept a few plausible things about the dS Hamiltonian). If you fluctuate a state, which corresponds to the state of our universe at say the time of nucleosynthesis, and act on it with the dS Hamiltonian, you won’t get anything like the normal history of the universe. Nothing will happen for a time of order the dS Hubble time, and on time scales much longer than that the evolution will have nothing to do with the cosmological history we’ve seen. This claim depends only on my picture of the QM of dS space. If you follow the full rules of holographic cosmology it’s even worse. The state of the universe at nucleosynthesis is a product of the state of things that could have been observed inside the particle horizon at that time, and a state of everything else. The holographic time dependent Hamiltonian slowly allows outside degrees of freedom to interact with inside ones. But the dS Hamiltonian does not respect this separation of the Hilbert space into a tensor product. It has big matrix elements mixing up all of the inside states with all of the outside ones: just as big as the inside inside and outside outside matrix elements (think of it as a random matrix on the whole hilbert space, with a few constraints on its spectrum).

Your final comment about initial and final conditions also reflects a prejudice which comes from thinking too much about systems with time independent Hamiltonians and or time reversal invariance. And too much QFT in curved space time. It’s my belief that we won’t make progress on these questions until people smarter than I throw off these prejudices.

I promise, NO MORE!

tom

]]> By: Sean http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207004 Sean Sat, 24 Feb 2007 20:28:51 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207004 Tom, thanks for chiming in. Knowing that you won't respond, let me just remark that there is something fundamentally unsatisfying with the claim that "this scenario predicts both OO's and BB's, but so what, observation tells us that we are an OO." I think you really do have to worry about the counting. In particular, if you have a universe in which BB's can arise, it's probably also true that BU's can arise -- Boltzmann's Universes, giant configurations which look indistinguishable from our current universe, except that they are really fluctuations from a higher-entropy past, not thermodynamically-sensible evolutions from a low-entropy Big Bang. In that case, there is no conceivable anthropic argument that would put us in the ordinary universe rather than the fluctuation; but nobody thinks we live in a BU, for good reason. Also I think that boundary conditions in the asymptotic past that are very different from those in the asymptotic future are wildly ad hoc, but that's another argument. Tom, thanks for chiming in. Knowing that you won’t respond, let me just remark that there is something fundamentally unsatisfying with the claim that “this scenario predicts both OO’s and BB’s, but so what, observation tells us that we are an OO.” I think you really do have to worry about the counting. In particular, if you have a universe in which BB’s can arise, it’s probably also true that BU’s can arise — Boltzmann’s Universes, giant configurations which look indistinguishable from our current universe, except that they are really fluctuations from a higher-entropy past, not thermodynamically-sensible evolutions from a low-entropy Big Bang. In that case, there is no conceivable anthropic argument that would put us in the ordinary universe rather than the fluctuation; but nobody thinks we live in a BU, for good reason.

Also I think that boundary conditions in the asymptotic past that are very different from those in the asymptotic future are wildly ad hoc, but that’s another argument.

]]> By: Tom Banks http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207000 Tom Banks Sat, 24 Feb 2007 20:14:43 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-207000 I hate myself for wasting any more time on this subject (having recently posted a paper on hep-th and then swearing I would stop thinking about it), but I see a lot of confusion and conflation of different things in the discussion. It should be admitted by everyone at the outset that they only have religious opinions on this subject, because we have neither experimental data, nor an agreed upon mathematical framework for discussing these issues. That said, here are my principles of faith: 1)There is a particular model where Boltzmann's Brains are definitely a problem. This is the Dyson Kleban Susskind (DKS) model, which is a modern version of Boltzmann's old idea of explaining the low entropy initial conditions of cosmology as a random fluctuation in a finite system. In this model the log of the probability of getting an intelligent observer by normal cosmological and biological evolution is proportional to - R^2 , while that of thermally fluctuating an intelligent observer of mass m is - mR . I'm using natural units hbar = c = G = 1 here, and leaving out constants of order one. This model definitely predicts most intelligent observers should be BBs rather than OOs. So the model is definitely wrong, since its only excuse for focusing on the rather improbable history in the model which led to ordinary cosmology was that this was the way to get observers (Lenny S tells me that I should always emphasize that the DKS model was a straw man that DKS used to criticize the idea of eternal dS space). 2)Time is emergent in quantum gravity. It is tied to particular observers, where here observer just means a large quantum system with many semiclassical variables (modeled in all known examples by cutoff local field theory). In general, as we see from Wheeler De Witt quantization (which I regard as a rough semi-classical guide rather than the basis for a rigorous quantization of gravity), the Hamiltonian is time dependent. One can conceive of a class of systems with the following properties: the set of initial conditions for the time dependent Hamiltonian, which describes our model for cosmology, splits into two subsets. In the first everything is constantly in equilibrium. In the second there is a long period of non-equilibrium in which intelligent life can arise through the usual cosmological/biological evolutionary route we all believe we have taken. It is possible but not proven that the holographic cosmology that Willy Fischler and I invented has this property. I claim that in such models it really doesn't matter if the evolutionary period is followed by a much longer (if the whole system is finite, it doesn't really make sense to talk about its behavior over recurrence time scales - see my nightmare paper with Fischler and Paban) equilibrium period where BBs abound. So what? Every history which gives rise to a BB also had a period when OOs were alive. The model doesn't predict anything contradictory. It predicts two kinds of observers and our observations tell us which kind we are. If we invent strategies to live long enough (as a culture) we might even observe the other kind. In such models the BB is an interesting oddity like the fact that if we watch an undisturbed room full of air long enough, the air will all collect in a corner. It's crucial here that the Big Bang is NOT just a random fluctuation in an equilibrium system, and that the Hamiltonian is time dependent. So, I believe there is a scientific issue here, that it can only be resolved by a theory of initial conditions and the Big Bang, and that there is a kind of behavior compatible with the rules of quantum mechanics of a time dependent Hamiltonian, which could explain what we see. In that context, a theory which ends in "eternal de Sitter space" will have BBs in it, but there is nothing contradictory about them and they don't require us to assume the universe will decay on a time of order its current lifetime. I am unlikely to respond to comments on this, however provocative, for the reason outlined in the first sentence. Tom Banks I hate myself for wasting any more time on this subject (having recently posted a paper on hep-th and then swearing I would stop thinking about it), but I see a lot of confusion and conflation of different things in the discussion. It should be admitted by everyone at the outset that they only have religious opinions on this subject, because we have neither experimental data, nor an agreed upon mathematical framework for discussing these issues. That said, here are my principles of faith:

1)There is a particular model where Boltzmann’s Brains are definitely a problem.
This is the Dyson Kleban Susskind (DKS) model, which is a modern version of Boltzmann’s old idea of explaining the low entropy initial conditions of cosmology as
a random fluctuation in a finite system. In this model the log of the probability of getting an intelligent observer by normal cosmological and biological evolution
is proportional to - R^2 , while that of thermally fluctuating an intelligent observer of mass m is - mR . I’m using natural units hbar = c = G = 1 here, and leaving out constants of order one. This model definitely predicts most intelligent observers should be BBs rather than OOs. So the model is definitely wrong, since its only excuse for focusing on the rather improbable history in the model which led to ordinary cosmology was that this was the way to get observers (Lenny S tells me that I should always emphasize that the DKS model was a straw man that DKS used to criticize the idea of eternal dS space).

2)Time is emergent in quantum gravity. It is tied to particular observers, where here observer just means a large quantum system with many semiclassical variables (modeled in all known examples by cutoff local field theory). In general, as we see from Wheeler De Witt quantization (which I regard as a rough semi-classical guide rather than the basis for a rigorous quantization of gravity), the Hamiltonian is time dependent. One can conceive of a class of systems with the following properties: the set of initial conditions for the time dependent Hamiltonian, which describes our model for cosmology,
splits into two subsets. In the first everything is constantly in equilibrium. In the second there is a long period of non-equilibrium in which intelligent life can arise through the usual cosmological/biological evolutionary route we all believe we have taken. It is possible but not proven that the holographic cosmology that Willy Fischler and I invented has this property. I claim that in such models it really doesn’t matter if the evolutionary period is followed by a much longer (if the whole system is finite, it doesn’t really make sense to talk about its behavior over recurrence time scales - see my nightmare paper with Fischler and Paban) equilibrium period where BBs abound. So what? Every history which gives rise to a BB also had a period when OOs were alive. The model doesn’t predict anything contradictory. It predicts two kinds of observers and our observations tell us which kind we are. If we invent strategies to live long enough (as a culture) we might even observe the other kind. In such models the BB is an interesting oddity like the fact that if we watch an undisturbed room full of air long enough, the air will all collect in a corner.
It’s crucial here that the Big Bang is NOT just a random fluctuation in an equilibrium system, and that the Hamiltonian is time dependent.

So, I believe there is a scientific issue here, that it can only be resolved by a theory of initial conditions and the Big Bang, and that there is a kind of behavior compatible with the rules of quantum mechanics of a time dependent Hamiltonian, which could explain what we see. In that context, a theory which ends in “eternal de Sitter space” will have BBs in it, but there is nothing contradictory about them and they don’t require us to assume the universe will decay on a time of order its current lifetime.

I am unlikely to respond to comments on this, however provocative, for the reason outlined in the first sentence.

Tom Banks

]]> By: Gene Poole http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-206996 Gene Poole Sat, 24 Feb 2007 19:52:45 +0000 http://cosmicvariance.com/2007/02/21/oos-and-bbs/#comment-206996 Hmmm... The assumptions which devolve from the current concept of the 'big bang' seem to be taken as true. Has anyone considered (yes I am really asking) that the 'big bang' is still 'banging', and is in fact the reason why the 'universe' (as a large pattern of standing waves) does not suddenly collapse to 'zero'? We assume that the 'big bang' was a one-time event which created space/time, eh? In other words, space (an 'expanse' which seems to be expanding) and time, which is signaled by movement (known by us as 'events'). A rough analogy: Just as we so-fragile Beings are able to survive the existence of our life-giving sun Sol, due to the distance and vacuum-insulation between us and it; so also our 'universe' survives because the energy of the bang-engine is at a safe remove (however defined) from our observed universe. What event precedes the collapse of a standing wave? And why does such a wave keep standing, absent that event? ==GP== Hmmm…

The assumptions which devolve from the current concept of the ‘big bang’ seem to be taken as true.

Has anyone considered (yes I am really asking) that the ‘big bang’ is still ‘banging’, and is in fact the reason why the ‘universe’ (as a large pattern of standing waves) does not suddenly collapse to ‘zero’?

We assume that the ‘big bang’ was a one-time event which created space/time, eh? In other words, space (an ‘expanse’ which seems to be expanding) and time, which is signaled by movement (known by us as ‘events’).

A rough analogy: Just as we so-fragile Beings are able to survive the existence of our life-giving sun Sol, due to the distance and vacuum-insulation between us and it; so also our ‘universe’ survives because the energy of the bang-engine is at a safe remove (however defined) from our observed universe.

What event precedes the collapse of a standing wave?

And why does such a wave keep standing, absent that event?

==GP==

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