[chadcmulligan]

So does that mean the idea of a "multiverse" is in the same box?

Edit: I'll rephrase (I'm serious) - isn't the idea of the multiverse based on the schrodinger's cat in a box idea, and the need for an observer? Or is the whole multiverse idea just sci fi? Or is there another physical basis for the idea of a multiverse?

[bawolff]

The paralell universe thingy or the "multiple worlds" interpretation (which is what i assume you mean) is one of the competing philosophical explanations for what is going on during quantum mechanics. Like most topics in metaphysics, there is no evidence either way, and there are competiting interpretations that are just as good (but don't capture the imagination in the same way). Its based off the cat experiment in that its trying to explain what is happening there metaphysically, but the parallel universe interpretation doesn't make any testable predictions beyond those made by quantum mechanics, so neither the experiment nor any other experiment, proves it.

Any sort of visiting paralell universes stuff is pure sf.

[JohnStrangeII]

The Everett interpretation of quantum mechanics is not "metaphysics", the theory is principally testable and falsifiable by empirical data. The experiments needed to test it are just not yet feasible. Sean Caroll has written a nice blog post about this in 2015 [1].

[1] https://www.preposterousuniverse.com/blog/2015/02/19/the-wro...

[chadcmulligan]

yes, thanks, thats what I meant. While I'm here, something I've always wondered about the multiple worlds interpretation is where does the energy come from for all these parallel universes? Like if each possible event causes a split then haven't we just doubled the energy we started with? since we've created a whole new universe.

[rcxdude]

I don't think there's new energy: the 'new universe' is just a part of the evolving wavefunction, which conserves energy.

[hartator]

Yes, and there is billon of quantum events happening right now in each cubic inches of air around you. So billions of universe literally from thin air. Multiverse is fun but absurd.

[pa7x1]

You seem to argue from an economic point of view, as if it was too "expensive" or "wasteful" to have all those universes. But MWI doesn't add any postulates to QM, in fact it is the simplest of the interpretations and a direct translation of what the math of QM says. All those universes are as "expensive" as the quantum mechanical state superposition they represent, and the superposition is a central tenet of QM and thoroughly tested. Your conclusion could be rephrased as "quantum superposition is fun but absurd".

[yk]

There are several different "multiverse" ideas, from the top of my head the many worlds interpretation of QM, the string landscape, the multiverse of general relativity, the multiple branes in Randall-Sudrum models.

Thing is, multiverse ideas are not testable and therefore not physics. Theorists like to entertain ourselves with them to a certain degree, but they are just that, a kind of Science Fiction. For that reason, theorists never bother to distinguish between the different kinds of multiverses, that is a tedious and ultimately not important task.

Now science writers love to write about the multiverse, because they are good entertainment, however they lack the technical sophistication to actually distinguish between the different kinds of multiverse.

[fsflover]

https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec...

[chadcmulligan]

Yes thanks, I've looked at all these from time to time, but the schrodinger's cat interpretation presented here (lets call it (1) and the many worlds interpretation (2) seems contradictory to me (or perhaps the same fallacy). So in (1) schrodinger's experiment says that you can't regard the observer as being some intelligent entity, the observer is just other particles - the wave form collapses in a small delta of time, and provides the continuity we see in the macroscopic world (a lot of my interpretation here I suppose). Now in (2) isn't this the same as the problem with (1)? the collapse happens near instantaneously and so these other worlds are fleeting possibilities that never really existed, its the same fallacy as the cat in the box never really being dead and alive.

[ShamelessC]

>in (1)..., the observer is just other particles.

It has been proven that non-concious observers can trigger a wavefunction collapse through variations of the dual slit experiment. What we don't necessarily know is exactly how the chain of wavefunction collapse occurs from e.g. the "opening of the box" to e.g. the human eye. This is known as "the measurement problem".

Also, fwiw, in both the Copenhagen interpretation (1) and the Many Worlds Interpretation (2), the observer is simply any particle which measures the event. It may be more intuitive to say that as soon as particle/s depend on knowing the answer to the wavefunction collapse, it will collapse.

This may be "fuzzy" as well meaning that if the particles don't need a precise answer only the amount of wavefunction collapse needed to give that level of precision will occur.

>Now in (2) isn't this the same as the problem with (1)? the collapse happens near instantaneously and so these other worlds are fleeting possibilities that never really existed, its the same fallacy as the cat in the box never really being dead

Many Worlds Interpretation posits that the _all_ other worlds absolutely exist before and after the collapse. After wavefunction collapse, each possible outcome occurs in a separate world. The one that "we see" is merely one outcome being experienced. Indeed, the reason this may be confusing is that you have to realize that other versions of yourself will see the different outcomes, each one convinced that they're the only version.

It can sound kind of crazy and we have no way of proving the existence of these other worlds but the interpretation is still taken seriously by many in part due to it being the most literal interpretation of the Schrodinger Equations.

>the wave form collapses in a small delta of time, and provides the continuity we see in the macroscopic world

You refer to this as a "problem" i.e. that these collapses are vanishingly small and so we never encounter them. But we can in fact encounter them!

Imagine shooting thousands of bullets through two slits with some degree of known error in aiming. The wall on the other side of the two slits will likely have holes in two vertical lines.

    |    |

This is also what happens when we measure a photon before it enters the slits. It behaves as a particle would.

Now imagine you push liquid water through the slits instead. The water forms waves as it passes through the slits. The peaks of the waves when they hit the wall on the other side form something different that looks like this instead.

| | | | | | | |

This is what happens (after shooting multiple photons) when we make no such measurement of the photons.

Now, to us, each photon comes out in different spots instead of all at once like with the wave. The first might be

   |

And then

   |.    |

But sure enough, with enough photons it will eventually appear as

| | | | | | | |

This means that either:

Copenhagen:

A pretty literal wave of possibilities travels through the slits. When it hits the wall, this so-called wavefunction collapses into a single point. That point will be statistically likely to land somewhere on the many-lined diffraction pattern.

Many Worlds:

Multiple worlds exist in which each of the single points follow the different trajectories we see. They still form a diffraction pattern because these worlds are defined by the same Schrodinger Equations that may also define the wavefunction collapse.

There's a lot more that I'm skipping over such as Pilot Wave Theory which posits that each particle was in fact always a particle that instead is guided by a "pilot wave" that can sort of see the future, or travel faster than light in order to determine where it should land. Ultimately what I'm trying to say though is that there is no way around quantum mechanics. Yes, the timeframes are tiny and the cat probably isn't alive and dead at the same time due to decoherence occuring well before you open the box; but reality is still very much quantum and there are ways to observe that.

It's weird af, but it's absolutely happening.

[chadcmulligan]

Many thanks, I don't doubt its how things are, almost thought I had a handle on it :-). Will have to take a year or two sometime and do some reading, don't think I really understand what a 'collapse' is, amongst many other things.

Edit: is a collapse a measurement? Before the measurement all the possible states are there, then a measurement occurs, and we then know the result (within uncertainty).

[ShamelessC]

I believe it to be fundamentally at odds with how we evolved to understand the universe, so don't feel bad. Even Einstein was conflicted by some of it while he worked to prove it.

The collapse is a measurement. It is also the instantaneous moment that a particle such as a photon goes from being a wave-like to being particle-like. In many ways it is just a name given to the phenomenon that we know occurs - that particles act as waves until we need them to be more "real" so to speak.

In Copenhagen, the "wavefunction collapse" is when the particle "picks a spot to land" inside of its wave. The spots it is likely to land are defined by the peaks and valleys of the wave.

Imagine liquid waves in the ocean again. They go up and down with fairly predictable heights of waves. Wavefunction collapse is when those waves decide to collapse into a small rock instead. But where should the small rock wind up? Well the highest wave of course. The wavefunction collapse is when the decision occurs to _place_ the rock; when the universe says "throw a dart somewhere along this path of likely positions".

That's a bit more metaphorical and philosophical but maybe it puts it into perspective a bit better? To be honest, I don't understand it very well and certainly couldn't tell you why it happens from more basic principles. This is part of the reason there are competing interpretations which is that even Copenhagen style wavefunction collapse _feels_ weird.

[chadcmulligan]

Thanks again, there seems to be a lot of then thats what happens :-), hopefully some bright young fellow figures it out one day.