# Re: Two Schrodinger cats

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On 17 Jan 2013, at 20:08, meekerdb wrote:```
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```On 1/17/2013 4:32 AM, Telmo Menezes wrote:
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```Hi all,

Naive question...

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Not being a physicists, I only have a pop-science level of understanding of the MWI. I imagine the multi-verse as a tree, where each time there is more than one possible quantum state we get a branch. I imagine my consciousness moving down the tree.
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Suppose Mary performs the Schrodinger's cat experiment in her house and Joe does the same in his house. They both keep the animals in the boxes and don't take a peak. Don't tell PETA. They meet for a coffe in a nearby coffeeshop.
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So now we have four possible universes where Mary and Joe can meet. But from the double slit experiment we know that the cats are both still dead+alive in the current universe. Right? So are Mary and Joe meeting in the fours universes at the same time?
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Cheers
Telmo.
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The short answer is yes. But it's not four universes, it's one universe that is a superposition of four states. The idealization is that the cats are isolated so that it is only when a live/dead measurement is made the universe splits. But a problem with MWI is that this depends on the basis. Choosing a live/dead basis is possible (in the idealization) but mathematically any other basis is equally valid and in those other bases there are still superpositions. So really the problem of the live/dead cat is pushed off onto the problem of selecting the basis: why is the live/ dead basis priveleged?
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In this case because we are interested in the live or dead observable property of the cat. In all bases, all relative states exists, and with the correct proportion. Of course, as long as Mary and Joe does not look at the cat, they could say, we are in the universe where the cat as the definite d+a state, as they can test with a (d+a, d-a) analyser. In that case Mary and Joe are in the fungible state, that you can interpret bot as being in the d+a "unique world" or in both a- world and d-world. I don't really believe in that "base" problem. Imo, Everett solved it at the start. Obviously we have a long past history, explaining why *we* prefer some bases among others.
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Bruno

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Brent

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