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Many worlds in a single infinite universe

  1. Jul 31, 2011 #1
    First of all I want to apologize for any incorrect/non-physical terminology. Theoretical physics is not my field (which is neuroscience) and I only have some very basic knowledge in the mathematics of modern physics. Recently I read a couple of popular physics books by Brain Greene and Leonard Susskind that made me come up with a thought experiment that comes to rather strange conclusions, but which I cannot seem to debunk.

    The setting of the thought experiment is a single infinite universe (infinite inflation) with a limit in the information a region of space can hold (holographic principle). In principle in such a universe there would be an infinite number of exact copies of our universe.

    As a thought experiment, I imagine that while I am asleep, technically highly advanced aliens land near my house. They are feeling funny that night, so they decide to pull my leg. They scan me (my body) with the maximal possible precision. After that, they instantly vaporize me, so fast that I don’t notice a thing. After that, they reconstruct my body with different atoms and put me back in the bed The joke is that they film the whole thing and leave the DVD on my night table (their sense of humor is not so advanced). When I wake up in the morning I will not feel anything special (until I watch the video of course). In fact, the aliens could have chosen to rematerialize me anywhere. They could have made a copy of bedroom on the surface of mars (a pressurized version), and rematerialized me there. Only after I open the curtains things start to look rather strange.

    My description on what I would experience when I am instantly vaporized and then reconstructed is actually the mainstream view in neuroscience. What defines me is not related to specific matter or a specific location, but is determined by the information that is contained in my brain. I could replace all the atoms in my body one by one and remain the same person.
    However, who needs aliens when we have an infinite universe. When there is e.g. infinite inflation and therefore an infinite universe, there are an infinite number of exact copies of me now writing this email. This however poses a puzzling question. When I wake up in the morning, how do I know I am not waking up in a distant universe far beyond the cosmic horizon of the universe I was in before I went to sleep? The distance seems to be unimportant as no information needs to travel. As neither matter nor location binds me to one copy in one universe, all of them must be equally likely. In my atheistic worldview there is no soul occupying any of these versions of me that prevents this. Why would I only change location during sleep, why not all the time? If they are all equally likely, is there a way to choose?

    Actually the only consistent conclusion that I could come with is that all these versions would be me. In other words, all brains in an infinite universe that contain the exact same information are really me and produce my conscious experiences. This view on reality seems to have some similarities with the ‘many worlds’ interpretation of quantum physics (although I am not certain), only that it takes place in a single world/universe. When we actually are many versions of identical brains, we can be surrounded by different physical states as long as they do not influence our senses and make the information content of the brains dissimilar infinite single universe, but we humans would just be poor observers of that.

    I was wondering if there is a flaw in this line of reasoning and if it is consistent with known physical law.
  2. jcsd
  3. Jul 31, 2011 #2


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    Just two weak points in your reasoning:

    1. Our Universe is rather finite, so it is pretty unlikely that an exact copy of you exists somewhere, even behind Hubble's horizon. Even if the Universe is infinite, only some finite part of it (up to Hubble's horizon) may interact with us. Everything below the horizon is separated from us, so it is fundamentally not possible to meet your twin.

    2. No, even most advanced, technology may allow to scan your brain and reconstruct it again somewhere else, as it is a quantum object, which cannot be fully described in terms of any measurement results. However, if aliens took a bunch of qubits, having their entangled counterparts left on Mars, they may destructively scan you, send information to Mars, and there reconstruct fully your quantum state - that is quantum teleportation. Anyway, teleportation is non-cloning: scanning process is destructive, and only one copy may be restored.

    Even if you have two identical (with regard to any measurement outcome, not meaning identical wavefunctions) copies of brain and surroundings, the future history of both you must split to different paths due to fundamental quantum nondeterminability. Everett's worlds must split, and split, and split again...

    I would definitely not like to go into speculations "what if both you are identical with regard to wavefunction", as that is something fundamentally impossible.

    I may recommend some readings on multiverses, their classification and philosophical implactions. You may want to start from (quite easy) article by Max Tegmark "Parallel universes" preparred as a chapter to the book "Science and Ultimate Reality", available online: http://lanl.arxiv.org/abs/astro-ph/0302131v1.
    Last edited: Jul 31, 2011
  4. Jul 31, 2011 #3
    Incidentally, there have been a few papers recently suggesting the cosmological multiverse in a fundamentally quantum mechanical world is actually equivalent to the many worlds interpretation of quantum mechanics due to the holographic principle. Sean Carroll discusses the idea here and provides links to the papers.
  5. Aug 1, 2011 #4
  6. Aug 1, 2011 #5


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    What Nickthrop says is an Everett's many worlds view.
    As Parlyne said a bit earlier, there are some voices claiming that Everett's worlds are equivalent to multiverses. However, if you follow the references (Nomura, Bousso & Susskind) quoted in the popular article, cited by Parlyne, authors do not claim any relation to particular cosmological multiverses, especially to other Hubble bubbles. Nomura (as I understand him...) points on equivalence (not identity) between Everett's words and post-inflation bubbles in eternally inflating word.

    The question: what 'equivalent' means in such context comes back. And, of course, ontological question: what 'existence' means when is applied to objects fundamentally unreacheable (like other multiverses).

    My personal common-sense-rationalism grown in cave times allows to use the word 'existence' regarding rabbits, stones, women, Moon and stars. I don't feel extremely bad if it is used about parts of our Universe lying just behind Hubble's horizon, but I definitely don't like it if applied to more 'distant' worlds (multiverses II,III and IV kind in Tegmark's classification).

    What I said was just that it is unlikely to find a copy of Klaasje in other Hubble's bubble of our Universe, just spatially separated from us.
    And I really don't like ideas about infinite Universe. As an advocate of Occam I won't take them seriously until some proof that our Universe is not finite.
    Last edited: Aug 1, 2011
  7. Aug 2, 2011 #6
    Thank you all for the very useful comments and suggested readings. I will try (with a lot of wikipedia consulting) to get through them. As a result of some of the comments I rephrased the thought experiment to make certain aspects hopefully less of an issue. As I am not really certain on how quantum uncertainty plays a role in the information content of the brain, so I switched to computers instead of brains. Also, I reduced the setting of an infinite universe to four small rooms which may handle some doubts on infinity.
    Let's imagine I am a brilliant man and manage to develop a computer with dedicated software that can generate self-awareness, or at least can be said to have a first order perspective. Actually, I am building let's say four exact copies of these computers, and put them in four separate rooms which are from the inside also identical. Although the four computers all have digital visual sensors, these sensors are too crude to detect any microstructural differences between the rooms. Only on the outside of the door of each room there is a tag with the room number, but this tag is invisible from the inside.
    Then I switch on the computer in the first room, provide him with the information that he is in room 1, and keep it running for some time. After 30 minutes I switch off the computer in the first room and switch on the computer in the second room and run the program from the exact position were the program in room one stopped. Now if I place myself in the experience of the computer, nothing really happened. From his perspective he is just still up and running in room number 1, totally unaware of any switches. I can repeat this process and make multiple switches between the rooms without anything special happening from the perspective of the computer.
    Now in a second experiment I switch on all the computers simultaneously and run the exact same program on all computers simultaneously. All computers are provided with the information that they are in room 1 (which is of course false information for the computers in room 2-4). Also all computers are periodically switched off so that the pauses are the same as in the first experiment. From the perspective of the computers again nothing special will happen. However, from the first experiment it seems that switches between rooms can occur without awareness. Therefore I must conclude that none of the computers can from their perspective be certain in which room they are located. Could it not be argued that in fact the first order perspective of the computer is in all four rooms simultaneously? And if so, have I not in fact created four parallel universes for the computer(s)?
  8. Aug 2, 2011 #7


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    Many databases (having large memory and records of own history) work this way - just database state is transferred between multiple servers. Ant this is still the same database, regardless where the physical server is located.
    All computers are certain they are in the Room no.1, as that is a Revelation you passed to them and they have no way verify that knowledge experimentally (door labels are only outside the rooms). In the first order perspective they are in a single (only existing!) Room no.1
    As long as you wont tell him(them) about other rooms - he won't be aware of their existence. If he believes you - his first person perspective of existence of other rooms will be of the same kind, as Christians' knowledge about existence of Heaven. You may even convince him than after he is switched off in the earthy room.1 his self-awareness will be resurrected in Room.2 (Heaven) or Room.3 (Hell) depending on your judgement of his behaviour.
    As long as copies of the computer cannot communicate, existence of other copies and rooms is nothing more than religion from their epistemological point of view.

    Of course, you may call it parallel universes. You may even go further (in Everett's style) - you may run two copies of the same computer, in two rooms, but providing him with a lottery: ability to perform some truly random experiment, affecting his life. Just be sure the experiment is truly random, not based on algorithmic pseudo-random generator... Or, rather to stay at Everett's position, you should ensure that lottery gives different result in different rooms.
    After his history splits you should rather start using plural: they will be two different persons, rather than one.

    The difference between computers and human brain is that computers are fully deterministic, while brain is a quantum mechanism. So it is impossible to clone brain, while you may clone computers. It is also interesting (open) question, if self-awareness is possible to be based on fully deterministic machine.

    You may want to read something on this issue, e.g. really good popular book by Henry Stapp: "Mind, Matter and Quantum Mechanics".
    Last edited: Aug 2, 2011
  9. Aug 5, 2011 #8
    Thanks again for your comments. Now although I believe that the computer is a bad metaphor for the human brain, still the basic components of the brain are neurons, which are in essence binary units. Now free will is a hot topic with philosophers and actually most believe that the human brain is governed by physical laws just like any other object, and free will must thus be an illusion. Anyway, for the moment let’s assume robot-like humans as observers.
    So you already addressed the core of my question. What it boils down to is whether the following statement is conflicting with physical laws:
    Quantum-behavior is random/non-deterministic, but all particles do have definite positions and speeds etc.. However, observers do not have a unique perspective in space (perhaps even time), so that all histories that lead to the same particular state of the (memory of the) observer are simultaneously true.
  10. Aug 5, 2011 #9
    A slight correction I would like to point out since what you have just said is self-contradicting.

    Unless, I am greatly mistaken in Q.M particles aren't in a definite position in fact things seem to be particle like only when the wavefunction is made to collapse upon participation/observation.

    Going by what HUP tell's us we cannot know both parameters of a particle in this case: Momentum and position for if either of them is measured(the more better measurement taken [precision] the greater is the uncertainty of the other parameter.

    I am a little confused about your last paragraph.Can you please rephrase.
    P.S: I have just started reading on Q.M[Sir Feynman's lecture on physics,vol. I] so whatever I have just said may not be right I apologize if that happens and would like to be corrected if it comes to that.

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