# Understanding the many worlds interpretation

I have a question regarding the quantum event when a wave live photon transforms into a particle like photon. In the many worlds interpretation there is a split into multiple worlds. My question is this: Do all the multiple worlds supposed to see the photon transform into a particle like photon, but just in difference positions? Or are some or all of the alternate worlds still see a wave like photon?

Isn't the central question just this: Where did the particle like photon come from if not a transformation of the wave like photon (in this world)? Whether or not it is explained by a wave collapse or some other process, before the event there was a wave like photon and after the event there was a particle like photon.

I am trying to get my head around the exact meaning of the many worlds interpretation.

Thanks,
John

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#### Martin0001

My non expert go on the subject is as follows:

One who dared to upset serene, wavy photon by obscene act of observation have caused it to become a particle.

In many worlds interpretation it is an act of observation what is causing world to split.
This very act is causing photon to become particle.

Hence in all new worlds which had been (quite recklessly :D) created photons were caught as particles found in different locations.

#### bhobba

Mentor
Do all the multiple worlds supposed to see the photon transform into a particle like photon, but just in difference positions? Or are some or all of the alternate worlds still see a wave like photon?
Each world doesn't 'see' the other.

Technically here is all that is happening. Due to a process called decoherence you have what is called a mixed state where each outcome is not in a superposition but have a probability of being the outcome of an observation. Normally what happens is you consider one outcome actually happening and the rest not happening. Its like throwing a dice - each face has a sixth chance of coming up. When that happens the other outcomes simply don't occur and are ignored. MW adds a twist to this. Each outcome is considered a world and no observation actually occurs. That's all there is too it really - nothing mystical with worlds looking at other worlds etc. Its just 'weird'.

Thanks
Bill

So every outcome but one (our world's outcome) creates a new world where the outcome is a particle like photon, but in slightly different positions alone the probability wave function, correct? So, is there an infinite number, each one being an infinitesimal distance apart? Also, since some positions are less likely to occur because of the shape of the probability wave function, but each possible outcome happens, then in affect all possible outcomes occur even for very low probability outcomes.
None of this seems reasonable. This interpretation must be favored by many for some reason.

Is there a paper that describes exactly how many outcomes occur and why does the probability wave function have any importance if all outcomes are to happen, one in our world and infinite number of other worlds.

Thanks,
John

#### bhobba

Mentor
Reasonable is in the eye of the beholder. Its appeal is its mathematically very elegant an beautiful. I don't hold to it personally, but that means diddley squat. For me its just a little too weird.

We also have the so called Decoherent Histories (also called Consistent Histories) interpretation which is basically many worlds without the many worlds:
http://quantum.phys.cmu.edu/CHS/histories.html

I don't hold to that either - for me its a bit too much like defining your way out of problems - but its a very good interpretation some call Copenhagen done right - it resolves a subtle issue with Copenhagen no need to go into here - start a new thread if you are interested.

In QM in dealing with QM foundational issues best to consider only discreet outcomes with continuum's introduced for mathematical convenience. This naturally leads to the so called Rigged Hilbert Space formulation of QM the technicalities of which are very advanced mathematically, but does resolve certain subtle mathematical issues to do with things like the Dirac Delta Function.

This means the number of worlds is very large and exponentially getting larger, but not actually infinite.

Thanks
Bill

Thanks for your insights, Bill. I joined the forum to see if I could ask specific questions that did not seem clear to me. Your comments have been very helpful.

What I noticed with both string theory and with quantum mechanics is that for some the mathematics may be what makes them chose one theory or interpretation over others. I think science if a noble pursuit because, in part, it is self doubting and wants to get it right. For me, I think it is fine to say "We can't answer that, but what if...".

I have no strong bias against theories, or in this case, interpretations that seem weird. I just want to understand them better so I am not dismissing them out of hand. I think the many worlds interpretation is fascinating. I am impressed that many scientists that think it is likely correct. But until some experiment weighs the scale in one direction or another, I think it is just a "what if" speculation.

Thanks,
John

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