# Re: Two Schrodinger cats

`On Thu, Jan 17, 2013 at 3:01 PM, Bruno Marchal <marc...@ulb.ac.be> wrote:`
```
>
> On 17 Jan 2013, at 13:32, Telmo Menezes wrote:
>
>  Hi all,
>>
>> Naive question...
>>
>> 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.
>>
>> 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.
>>
>> 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?
>>
>
> Let a = alive, d = dead, and the subscript 1 and 2 distinguishes the two
> cats, which are independent. Both cats are in a superposed state dead +
> alive:
>
> (a1 + d1) and (a2 + d2),
>
> so the two cats configuration is given by (a1 + d1) * (a2 + d2), with "*"
> the tensor product.
> This products is linear and so this give a1*a2 + a1*d2 + d1*a2 + d2*a2.
> Mary and Joe don't interact with any cats, so the global state is also a
> direct tensor product M * J * (a1*a2 + a1*d2 + d1*a2 + d2*a2), which gives:
>
>
> M * J *a1*a2 + M * J *a1*d2 + M * J *d1*a2 + M * J *d2*a2
>
> You can add the "normalization" constant, which are 1/sqrt(2) times
> 1/sqrt(2) = 1/2=
>
> 1/2 M * J *a1*a2 + 1/2 M * J *a1*d2 + 1/2 M * J *d1*a2 + 1/2 M * J *d2*a2
>
>

Nice. Thanks Bruno!

>
> To be sure, the normalizing factor does not mean there are four universes,
> but most plausibly an infinity of universes, only partitioned in four parts
> with identical quantum relative measure.

Sure, I get that.

Am I a set of universes?

> To get the exact "number" of universes, we should first solve the marriage
> of gravity with the quantum. And with comp, we should also derive the
> Quantum from arithmetic (but that's not true, actually: with comp we have
> directly the infinities of "universes").
>

Ok, sounds good but I have to dig deeper. (moving my own understanding of
what you're saying beyond the mushiness that it currently is)

>
> Best,
>
> Bruno
>
>
> http://iridia.ulb.ac.be/~**marchal/ <http://iridia.ulb.ac.be/~marchal/>
>
>
>
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