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A type I parallel Universe (according to Max Tegmark) is a universe that is infinite and looks everywhere more or less like our universe does (it's homogeneous). Tegmark claims that within this infinity there are regions say with a diameter of 100 000 lightyears that are indistinguishable from each other. Just by chance. Or take a Hubble volume, a volume as big as our visible universe, of which there are many (in fact infinitly many) exact copies of one another. So you and me are doing exactly the same thing in all those volumes.

Isn´t Tegmark forgetting that beyond the borders of all these exactly equal volumes, by definition, things are different? For example, no two balls of volume with a radius of 100 000 light years can be the same, because if I (and my presupposed copies) find myself (and my copies) somewhere near the border in one of those infinite amounts of exact copies and look with a telescope beyond the boundary of these copies all my copies see different things outside the ball, implying that all my copies are different and thus also the 100 000 light years sized balls. In other words doesn´t he overlook the interaction (via photons) between a volume and it´s surroundings?

Deschele Schilder
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  • here, if I understand, he says only obvious things that may occur in an ordinary infinite universe. According to what he seems to claim, if the universe is infinite, anything happens an infinity of times with small or no changes. But, it is obviously false to claim it like that ( because many people understand the same ) , you may also have an infinity of completely different locations and what he says is an unlikely solution of this kind of multiverses. Are you reading a scientific publication or a pop-sci book ? –  Feb 04 '16 at 13:27

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Well, you are supposed to think about a volume of 100000 light years radius around the solar system. If at a given instant, two volumes are exactly the same, even if there is a significant difference outside this volume, we will not be able to see this difference during 100000 years.

Even if you are at 1 meter from the ball border, to be able to see outside means you have to wait from light to reach your eye. The ball are identical now, that doesn't mean they will stay identical 3 nanoseconds later.

ch7kor
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  • But the point is that from the start of such a universe, if there are big pieces exactly the same, fotons from outside these regions (wich are different from eachother, otherwise they would belong to the similar regions) will change the similarity between the regions, so no two similar regions can develop in an infinite universe (because of the interaction that´s already there from the start). – Deschele Schilder Feb 05 '16 at 08:54
  • The whole point is that such identical region exists because the universe is infinite. If something happen somewhere, that means probability for it to happen is strictly above zero. Has universe is huge, it will also happen elsewhere. – ch7kor Feb 05 '16 at 09:22
  • Also, if you consider two strictly identical balls of 100000 light year radius, the neighborhood of these balls will be very similar. Photons from a galaxy 1 billion light years away will be distributed in the whole ball area. So near the two identical balls, there will have similar galaxies, not completely identical, but identical enough from far away. – ch7kor Feb 05 '16 at 09:27
  • Suppose I sit in the middle off a ball with a radius of 100 000 lightyears. Now this ball can never be the same as any other 100 000 lightyear radius ball filled with particles, since photons emitted from a region around the ball (these regions outside the ball, are all different from eachother, otherwise they would belong to the ball), 100 101 years ago make me see a different picture as the alleged copy of me in the centre of the other ball 100 000 lightyears in radius. If I see other things (happened over 100 000 years ago), this makes me and my copy differ, so likewise the entire ball. – Deschele Schilder Feb 05 '16 at 14:35
  • Take the game of life automaton. Imagine is it run on an infinite grid, starting from a pure random 50% initial grid. After a given number of steps, you select a given 10000x10000 square. As the grid is infinite and initially pure random, you know there exist other 10000x10000 squares with same content. That's it. The next step, theses square will be probably be identical only in their 9998x9998 interior. But there will be still other identical 10000x10000 squares elsewhere. – ch7kor Feb 05 '16 at 15:08