Re: Universes infinite in time
I wrote: > Paul Steinhardt, one of the original cosmic-inflation theorists and the > man who coined the term "quintessence" has a new theory of cosmology > which is described at http://arxiv.org/abs/astro-ph/020447. Sorry, the correct URL is http://arxiv.org/abs/astro-ph/0204479. Hal
Universes infinite in time
Paul Steinhardt, one of the original cosmic-inflation theorists and the man who coined the term "quintessence" has a new theory of cosmology which is described at http://arxiv.org/abs/astro-ph/020447. The abstract reads, The Cyclic Model is a radical, new cosmological scenario which proposes that the Universe undergoes an endless sequence of epochs which begin with a `big bang' and end in a `big crunch.' When the Universe bounces from contraction to re-expansion, the temperature and density remain finite. The model does not include a period of rapid inflation, yet it reproduces all of the successful predictions of standard big bang and inflationary cosmology. We point out numerous novel elements that have not been used previously which may open the door to further alternative cosmologies. Although the model is motivated by M-theory, branes and extra-dimensions, here we show that the scenario can be described almost entirely in terms of conventional 4d field theory and 4d cosmology. The theory does not actually have a "big crunch" in the traditional sense; rather, after a long period of expansion so that there is less than one particle in each visible segment of the universe, a hidden dimension contracts and suddenly the universe is full of light and energy, and it starts expanding again. There is no inflation as in the regular model, instead the long period of expansion from the previous cycle is what is responsible for the remarkable uniformity that is observed. The interesting aspect from this list's perspective is how to regard infinite-time cosmologies. Does it make sense to imagine a universe which has had an infinite past? How could we simulate that on a computer, if there were no starting point? I think Steinhardt's model also allows for a spatially infinite, flat universe as well. So we have infinities in all directions, temporal as well as spatial. We could avoid the problem by postulating that every cycle in Steinhardt's model is identical, giving the effect of a single universe, but I don't think there is any reason in the theory to suppose that would happen. Rather, each crunch is slightly different, and these small perturbations carry over into unique initial conditions for the next big bang. How could we go about modelling a universe like this? Can we rule out Steinhardt's cosmology on fundamental principles? Are infinite-time universes of zero measure compared to ones with a fixed beginning? It would be interesting if the everything-exists model could be used to constrain cosmological theorizing in this way. Hal Finney
Re: Quantum suicide without suicide
[Tim May] All indications are that there are virtually no worlds in which random guessers do well. Lev Vaidman wrote that we must care about all our 'successive' worlds in proportion to their measures of existence [Behavior Principle]. He does not agree to play the 'quantum Russian roulette' because the measure of existence of worlds with himself dead is be much larger than the measure of existence of the worlds with himself alive and rich! s.
Re: Quantum suicide without suicide
On Wednesday, January 8, 2003, at 10:58 AM, George Levy wrote: In the original verision of Quantum Suicide (QS), as understood in this list, the experimenter sets up a suicide machine that kills him if the world does not conform to his wishes. Hence, in the branching many-worlds, his consciousness is erased in those worlds, and remains intact in the worlds that do satisfy him. Is it possible to perform such a feat without suicide? What is the minimum "attrition" that is required and still get the effect of suicide? Hawking had a good line: "When I hear about Schrodinger's Cat, I reach for my gun." Slightly modify the QS conditions in another direction: instead of dying immediately, one goes onto death row to await execution. Or one is locked in a box with the air running out. And so on. This removes the security blanket of saying "Suicide is painless, and in all the worlds you have not died in, you are rich!" In 99....99% of all worlds, you sit in the box waiting for the air to run out. I don't know if there are other worlds in the DeWitt/Graham sense (there is no reason to believe Everett ever thought in these terms), but if they "exist" they appear to be either unreachable by us, or inaccessible beyond short times and distances (coherence issues). In particular, it seems to me there's a "causal decision theory" argument which says that one should make decisions based on the maximization of the payout. And based on everything we observe in the world around us, which is overwhelmingly classical at the scales we interact in, this means the QS outlook is deprecated. Consider this thought experiment: Alice is facing her quantum mechanics exam at Berkeley. She sees two main approaches to take. First, study hard and try to answer all of the questions as if they mattered. Second, take the lessons of her QS readings and simply _guess_, or write gibberish, killing herself if she fails to get an "A." (Or, as above, facing execution, torture, running out of air, etc., just to repudiate the "suicide is painless" aspect of some people's argument.) From rationality, or causal decision theory, which option should she pick? All indications are that there are virtually no worlds in which random guessers do well. (The odds are readily calcuable, given the type of exam, grading details, etc. We can fairly easily see that a random guesser in the SATs will score around 550-600 combined, but that a random guesser in a non-multiple-choice QM exam will flunk with ovewhelming likelihood.) What should one do? What did all of you actually do? What did Moravec do, what did I do, what did Tegmark do? --Tim May
Quantum suicide without suicide
In the original verision of Quantum Suicide (QS), as understood in this list, the experimenter sets up a suicide machine that kills him if the world does not conform to his wishes. Hence, in the branching many-worlds, his consciousness is erased in those worlds, and remains intact in the worlds that do satisfy him. Is it possible to perform such a feat without suicide? What is the minimum "attrition" that is required and still get the effect of suicide? Here is a thought experiment that illustrates that this may be possible. There is a cost - it is not death - just a tiny weeny lobotomy. :-) All the experimenter has to do is set up his machine to erase the portion of his memory that stores the information dealing with the machine erasing from his mind the information about the machine erasing from his mind the information about the machine erasing from his mind the portion of his memory dealing with the experiment, (phew! I thought I was going into infinite regress!) and then have the machine erase (or destroy) itself without a trace (this is important to maintain consistency). The outcome of the experiment in the many-world branches is as follows: 1) in some branches the experimenter's wishes are satisfied and he remembers the experiment. His world is consistent. 2) in the other branches the experimenter's wishes are not satisfied, and he does not recall performing the experiment. Whether he as done the experiment or not is not subjectively material to him. His world is consistent. What can we deduce from this? I don't really know for sure but I 'd like to discuss it. 1) The erasing of the memory of the quantum suicide machine seems to be the "minimum" required in terms of information deletion. Why? What does the memory of the quantum suicide machine have to do with consciousness? Is the infinite regress relevent? - this infinite regress describing this machine erasing from his mind the information about the machine erasing from his mind the information about the machine erasing from his mind the information about the machine erasing from his mind the information about the machine... ? 2) The "other" worlds in which the experimenter's wishes are not satisfied are of two kinds. A) those worlds where he did not perform the experiment, and of course have no memory of performing the experiment B) those worlds where he did perform the experiment but does not remember performing the experiment because of the lobotomy. In my opinion those worlds are equivalent because I believe in a subjective reality. But of course, many of you will disagree. 3) The lobotomy was a way to shift the experimenter subjective "frame of reference." How does the knowledge of the machine affect the frame of reference? What is the essence of the frame of reference? George Levy
