Quantum interpretations

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  • #51
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The occam's razor argument against CI is:

1. Quantum mechanics talks about quantum states evolving according to Schrödinger's equation (or similar)
2. CI includes another form of evolution for quantum states (collapse)
3. Collapse, as used in CI, has no observable effect
4. Therefore, CI has unnecessarily multiplied entities, a violation of Occam's razor


As far as I can tell, once you get past the silly arguments, it's just a matter of gauge freedom -- and CI tries to insist that it's choice of gauge fixing is a physical truth. MWI simply studies what happens in a 'frame' where unitary evolution holds good.

See above^. I think it is discounted by being deterministic though is it not?
 
  • #52
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MWI is deteministic from the birds view (when you observe all parralel universes at the same time) but it appears to be random in the frog's view(from the point of view of an observer)

For example, in case of S.Cat
Birds view: deterministic, there are both cats: dead and alive, and 2 experimenters saying "cat is dead/alive! nature is random!"
Frogs view: an experimenter observing one cat (dead or alive, it appears to be random for them)
 
  • #53
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Time Symmetric QM does away with the (time) asymmetry of collapse, that is one of its salient features - the other being that it posits a mechanism that respects locality (although strangely). You might be interested in looking at that more closely given your strong opinion on the subject (I think you mentioned "damnation"). :smile:

Yes, thank you, I noticed that link in the Cramers thread and already reading this!
 
  • #54
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MWI is deteministic from the birds view (when you observe all parralel universes at the same time) but it appears to be random in the frog's view(from the point of view of an observer)

For example, in case of S.Cat
Birds view: deterministic, there are both cats: dead and alive, and 2 experimenters saying "cat is dead/alive! nature is random!"
Frogs view: an experimenter observing one cat (dead or alive, it appears to be random for them)

So it appears to be exactly the same as CI from any perspective we could measure? Is that all that useful?
 
  • #55
jambaugh
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2 Do you agree that the CI definition is badly recursive, because it defines the properties of the particles based on "what we know". 'What we know' is quite a high level thing because it requires to be consciouss and intelligent.
You are making the mistake (or are you? maybe I'm misreading) of assuming the opposite of what you pretend to assume when considering CI. Quantum actuality keeps on zippin' along regardless of consciousness or intelligence. But the first assumption of QM is that you cannot separate what we know from the act of knowing. That's why the principle objects in QM are Observables and not State variables.

Measurement does not require consciousness, just an amplifying mechanism to correlate those quantum variables with a large scale observable such as where a meter needle points or where a meteor lands etc but when we speak of wave functions we must acknowledge their existence is only in conscious minds and not "out there" and thus identify them as such.

Further there is no problem invoking "what we know" about physical systems provided you are being operational... "what we know" must come from a physical observation and physical constraints placed on a system. This is how entropy gets defined. It is a measure of ignorance about a physical system said ignorance assumed by the physical definition and constraints of said system.

If it is not enough, let me ask you a question, had wavefunction ever collapsed in the first 1000 years after Big Bang? :)
Now here you are really missing the point. CI doesn't posit wave-functions exit!!!! They are not "out there" they are in our heads. Again they have the exact same status as a probability... a prediction about what may happen. They are more precise in what they predict but they are none-the-less of the same family as classical probability distributions.
And they collapse upon actualization of the coin-flip or spin-spin measurement for exactly the same reason.

As we have only invented wave-functions in the past half century I can only say for certain that some have collapsed in that period. Who knows what other beings in the past have developed the equivalent in their descriptions of nature. And update their wave-function equivalents when they learn what a quantum actually does rather than what they know it might do.
If yes, what should be used for 'WE' and 'KNOW' in your claim?
If no, then it appears that the universe had developed fine without any collapse, so we get MWI where there is no collapse :)
Again you keep trying to give wave functions reality even in pretending to adopt my point of view. Of course the universe developed fine without any collapse. Again collapse is a conceptual act and not a physical one (according to the interp. I am positing.) Again MWI only if you either mean Many conceptual worlds existing in our imagination given my interp. or many real worlds given your reification of the wave-function. The psi's we write on paper are not describing physical wave-functions they are the wave functions.
The collapse recipe is an instruction in sequential calculation not a physical process.

Adopt this position in earnest just for a moment... make sure you understand it clearly just for the sake of argument. Then revisit your counterpoints and see if they make any sense.
The inconsistencies you think you see are inconsistencies with your implicit a priori assumptions which you still hold even as you consider what CI says. You need to recognize these explicitly and de-invoke them for a moment to see what I'm saying.

It is just like asking "But which twin is really older when considering the twin's paradox in SR. One must first understand all the precepts of SR, and especially the loss of absolute simultaneity and time which we are assuming when we ask "who's older" without qualifying "as seen from what perspective?"

It would be awfully silly to invoke parallel worlds to explain the twin's paradox...

"You see in one universe twin A is older but in the other universe twin B is older"

...just so one could hold onto the absoluteness being denied by the very term relativity in SR. But further absurd is to then claim that SR predicts such parallel worlds because you can't fit your mind around what SR really does say.

As a matter of fact it is the same sort of relativization occuring in the transition from CM to QM. David Finkelstein (under whom I've had the honor to study) wrote a book "Quantum Relativity" which makes this very point. In QM we relativize the classical concept of absolute state.
3 in MWI wavefunction IS reality (from the birds view), not knowledge
As the fundamental christian also claims the bible IS reality. Again how is your belief in many worlds anything but a religious faith?

1 As a sidenote, I was always curious about that interpretation from the popular books. This claim is true... but it is only a part of the truth!

It comes from 2 extremes of HUP: we know position precisely we dont know the momentum, and vice versa.

So if we apply one of these 2 extremes to the wavefunction, we get this interpretation with the square root. But we can apply another side of HUP as well, getting another 'meaning' of a wavefunction.

I'm not sure I follow your meaning here. But let me say that HUP generalizes to any non-commuting observables. Momentum and position are not two endpoints they are two of a continuum of possible incompatible position-momentum measurements. Any one set of commuting observables defines a classical logic of "what is" just as any set of space-time coordinates defines a frame of simultaneity in SR. Once you step outside this choice of frame you can no longer speak of simultaneity in the case of SR or state of reality in the case of QM. (Actually you have a problem with "the state of reality" in SR as well given there is an implicit "now" of time in the phrase "state of reality" however it is less of a problem in a classically deterministic SR).

As I see it, the MWI is a conceptual black hole into which one can be sucked so that one need never truly understand the operational meaning of QM. If it were only a matter of sleeping better at night then that would be fine. I don't deny any person the comfort of their faith. But the noise of it confuses the new students of QM. Especially as was the case here I will strongly object to statements claiming "QM says" when it is not QM saying it but instead an article of someone's faith.

So let me ask you one question...

Do you deny that if you don't consider the wave-function a physical object then wave-function collapse is a non-issue?
 
  • #56
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So let me ask you one question...

Do you deny that if you don't consider the wave-function a physical object then wave-function collapse is a non-issue?

This is a good question.
In fact, rereading your message carefully I can 'emulate' (partly) your vision so there are less contradictions then I saw before.

In a form you formulated your question - I can not deny that.
However, then I have to ask you several questions (they are closely related):

1. Do you think that it is possible to create an axiom system for QM (or TOE) without back-references to upper-level things like 'what we know', 'our knowledge about' etc? (6th Hilberts problem)
2. Do you believe it is possible to formulate all physical laws in a pure mathematical terms?
3. If we are talking obly about the 'observables', can we define the observables without an observer?
4. How do you describe the evolution of the Universe during first 0.01s (quagma state, too hot for ANY observers or stable measurement systems)
5. Your interpretation of the Wigner's friend experiment.

Thank you in advance.
 
  • #57
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Dmitry67 said:
This is a good question.
In fact, rereading your message carefully I can 'emulate' (partly) your vision so there are less contradictions then I saw before.

In a form you formulated your question - I can not deny that.
However, then I have to ask you several questions (they are closely related):

1. Do you think that it is possible to create an axiom system for QM (or TOE) without back-references to upper-level things like 'what we know', 'our knowledge about' etc? (6th Hilberts problem)
2. Do you believe it is possible to formulate all physical laws in a pure mathematical terms?
3. If we are talking obly about the 'observables', can we define the observables without an observer?
4. How do you describe the evolution of the Universe during first 0.01s (quagma state, too hot for ANY observers or stable measurement systems)
5. Your interpretation of the Wigner's friend experiment.

Thank you in advance.




I have just one question about your favourite MWI -


If a mosquito farted, would it create a whole universe?
 
  • #58
jambaugh
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This is a good question.
In fact, rereading your message carefully I can 'emulate' (partly) your vision so there are less contradictions then I saw before.

In a form you formulated your question - I can not deny that.
However, then I have to ask you several questions (they are closely related):

1. Do you think that it is possible to create an axiom system for QM (or TOE) without back-references to upper-level things like 'what we know', 'our knowledge about' etc? (6th Hilberts problem)
I don't think we should. Science=empirical epistemology = what we know is what we see.
We start with what you call "back-references" but it is going back to the true fundamentals of science...the experiment. Get too far from this and you begin arguing about things no-one can observe and that is a theological debate, not science.
2. Do you believe it is possible to formulate all physical laws in a pure mathematical terms?
No of course not. At some point the mathematical terms must be related to the physical...that by the way is the true interpretation of the theory. How a ket or Hermitian operator relates to an actual experimental device.
3. If we are talking obly about the 'observables', can we define the observables without an observer?
How can we define anything without "we"? Science is what scientists do. This again is what "operationalism" is all about. Trying to excise reference to the epistemological foundation of a scientific theory makes it that much harder to separate the theory from the theology. But choosing this language is not a denial of the actuality independent of the observer. It is a recognition that (again) "what we know" and "what we can say" about that actuality always implies a "we".

Any declaration about the world, if it is to be made in the context of science must be prepared to face the immediate challenge of "how do you know?!!!" This is the nature of science. All the better to coach the declaration in terms of "how we know" so that the means to meet this challenge are explicit.

4. How do you describe the evolution of the Universe during first 0.01s (quagma state, too hot for ANY observers or stable measurement systems)
Again actuality is independent of the observer. Again you keep reifying the very thing that I'm trying to point out is not the reality. When you do this you are puzzled how it can continue to be real without an observer. Clearly as I posit it isn't real even with an observer.

As to how I describe the evolution of the Universe during the first 0.10s....
I will answer that I currently don't know enough to answer this question (observer or no). I find the addenda of qualifiers (hyper inflation, exotic dark matter, dark "energy" et al) to the original BB model to be quite unsatisfactory and too much like the infinite series of epicycles used to keep describing planetary motion in terms of circles prior to Newton's universal law of gravitation. I think the whole question needs revisiting. I have my own pet model but it is a long way from a full blown theory and likely is unable to incorporate known observations.

5. Your interpretation of the Wigner's friend experiment.

Thank you in advance.
Hmmm... let me look that one up, it's been a while,... Oh well first ask me about Schrodinger's cat. I can't say it any better than the wikipedia article on CI http://en.wikipedia.org/wiki/Copenhagen_interpretation" [Broken]

But I'll summarize. Again given the wave function (and its collapse) are representations of our knowledge Wigner's friend uses a different wave function given he knows different information. Remember Schrodinger's thought experiment was intended to show the absurdity of giving ontological weight to the wave function. The original resolution is the correct one. Superposition is a property of our description not of the physical system.

What's more to properly do the cat experiment you would need to first work within the density operator (which introduces more "classical" probabilities into the description) formulation to account for the thermal nature of the cat (and more importantly of the particle detector used to set off the vial of poison). The description then of the evolution of cat/poison vial/radioactive source would then very-very-very quickly devolve into a classical probabilistic description of 50% a live cat, 50% a dead cat.

Decoherence takes place almost immediately since the detector is a detector and its assumed nature is to amplify the small signal of the decay event into a big fat electrical pulse strong enough to pop open a vial of poison. Amplification is a thermodynamic process requiring an entropy dump.

So in the end all observers properly using an evolving density operator formulation would see a classical probability 50-50 for the alive cat dead cat "states" until they actually looked at the fall of the dice and updated their description.
 
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  • #59
vanesch
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I meant it was a conclusion that resulted from the experiment to be clear. But this of course discounts MWI does it not, because the wavefunction is real and the theory is thus deterministic, thus there are "hidden" variables. That means all things are not equal surely?

The way MWI, with a "real" wavefunction, and "deterministic" evolution, nevertheless gets out of Bell's theorem is simply this: in Bell's theorem, you need unique and definite outcomes at Alice and Bob for each experiment, and in MWI, that's not the case: Alice didn't see "up" or "down" ; there is AN alice which saw "up" and ANOTHER alice which saw "down". And the correlation only happens when A Bob compares his results with AN alice. But at that point, there is no distance anymore between them, and they can influence each other (that is to say, the probability to see a specific "alice and bob pair" can depend as well on the alice as on the bob under consideration).
In Bell's proof, you need a single definite outcome at both sides when they are still spacelike separated.

In other words, Bell assumes the "dice are thrown" at Alice and Bob. In MWI, the dice are never definitely thrown.
 
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  • #60
vanesch
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I have just one question about your favourite MWI -

If a mosquito farted, would it create a whole universe?

You must understand what "universe" means in MWI: it means "essentially orthogonal term in the wavefunction". So "creating a universe" comes down to "splitting a single term into two others".

If you have something like |psi> = blah ... + |moon>|sun>|earth>|filled-mosquito>|ocean>... +....

then the explicit term is "one universe". Now, if your mosquito evolves into:
|filled-mosquito> ===> |farting-mosquito> + |constipated-mosquito>

and we fill this in the original wavefunction:

|psi> = blah ... + |moon>|sun>|earth>(|farting-mosquito> + |constipated-mosquito>)|ocean>... +....

and we work this out, then:

|psi> = blah ... + |moon>|sun>|earth>|farting-mosquito>|ocean> + |moon>|sun>|earth>|constipated-mosquito>|ocean> ... +....

and lo and behold, where we had 1 term, we now have 2 terms, so we "created a universe".

Yes.
 
  • #61
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The way MWI, with a "real" wavefunction, and "deterministic" evolution, nevertheless gets out of Bell's theorem is simply this: in Bell's theorem, you need unique and definite outcomes at Alice and Bob for each experiment, and in MWI, that's not the case: Alice didn't see "up" or "down" ; there is AN alice which saw "up" and ANOTHER alice which saw "down". And the correlation only happens when A Bob compares his results with AN alice. But at that point, there is no distance anymore between them, and they can influence each other (that is to say, the probability to see a specific "alice and bob pair" can depend as well on the alice as on the bob under consideration).
In Bell's proof, you need a single definite outcome at both sides when they are still spacelike separated.

In other words, Bell assumes the "dice are thrown" at Alice and Bob. In MWI, the dice are never definitely thrown.

Yes but this is the same as CI for all practical purposes, if so what's the point of it? I mean I can dream up anything to make QM deterministic does that mean my dreams exist?

If in experiment QM is random, and in MWI which in experiment appears random where's the difference and isn't that just semantics?
 
  • #62
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You must understand what "universe" means in MWI: it means "essentially orthogonal term in the wavefunction". So "creating a universe" comes down to "splitting a single term into two others".

If you have something like |psi> = blah ... + |moon>|sun>|earth>|filled-mosquito>|ocean>... +....

then the explicit term is "one universe". Now, if your mosquito evolves into:
|filled-mosquito> ===> |farting-mosquito> + |constipated-mosquito>

and we fill this in the original wavefunction:

|psi> = blah ... + |moon>|sun>|earth>(|farting-mosquito> + |constipated-mosquito>)|ocean>... +....

and we work this out, then:

|psi> = blah ... + |moon>|sun>|earth>|farting-mosquito>|ocean> + |moon>|sun>|earth>|constipated-mosquito>|ocean> ... +....

and lo and behold, where we had 1 term, we now have 2 terms, so we "created a universe".

Yes.

Vanesch is God. :tongue2:
 
  • #63
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MWI seems to remove the randomness from the collapse, but isn't the collapse still there? In the double-slit experiment, you still register each photon at a specific location on the screen.

There is still the wave/particle duality which results in seeing a photon register at a specific location, with the wave-like interference only showing up in the statistical distribution.

So isn't MWI saying that there are many non-random collapses, rather than that there would be no collapse?
 
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  • #64
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MWI seems to remove the randomness from the collapse, but isn't the collapse still there? In the double-slit experiment, you still register each photon at a specific location on the screen.

There is still the wave/particle duality which results seeing a photon register at a specific location, with the wave-like interference only showing up in the statistical distribution.

So isn't MWI saying that there are many non-random collapses, rather than that there would be no collapse?

No because all wave functions are actualised in another universe, all you do is select one to measure, which to all appearances is random, all possible and presumably infinite wave functions except the one you measure are resolved in another universe thus random instead of the true random of CI, and thus deterministic not probabilistic, as said the die has already been rolled. This sounds like hidden variables repackaged to me though so I think its ruled out but then who am I to judge?
 
  • #66
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No because all wave functions are actualised in another universe, all you do is select one to measure, which to all appearances is random, all possible and presumably infinite wave functions except the one you measure are resolved in another universe thus random instead of the true random of CI, and thus deterministic not probabilistic, as said the die has already been rolled. This sounds like hidden variables repackaged to me though so I think its ruled out but then who am I to judge?

That's just explaining-away the randomness. To me the real paradox of quantum physics is that the probabilities of flying through either slit will interact with each other, but in the end the photon will appear only in one place, not smeared out like butter. And trying to measure the path will strangely make the interference go away. MWI doesn't seem to change that.
 
  • #67
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The Dagda said:
Vanesch is God. :tongue2:



Wait, wait... I reject decoherence/MWI mainly on the fact that it cannot explain the presence of liquid water.

The molecule of water contains three atoms in the H20 molecule. The H atom has only one electron. The molecule of water relies on this electron to be in multiple places all at once(as waves), so that a covalent bonding can take place between the atoms. Decoherence is an irreversible process, once decohered waves become particles, and that's why according to decoherence we observe a a "physical" universe(how physical is another topic). But...

If the electrons of the H atom have decohered 4.5 billion years ago into single electrons, why do we observe liquid water instead of gaseous H and oxygen? If there is no covalent bonding between the atoms in the molecule of water, the molecule H20 would fall apart and we wouldn't see homogenous liquid water. And i've just opened a beer, and it's liquid and doesn't turn into H and O(luckily).
 
  • #68
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colorSpace, check the wiki article. It explains why you detect photon in only one point.
 
  • #69
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WaveJumper, please read the articel again.
"If the electrons of the H atom have decohered 4.5 billion years ago into single electrons" - electrons never decohere until you entangle electorns with a thermodinamically irreversible system with a huge number of states.
 
  • #70
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colorSpace, check the wiki article. It explains why you detect photon in only one point.

That's a rather long article. As far as I can tell, it explains what happens to the other parts of the wavefunction after measurement. But the wave function still remains an odd thing of complex-interacting probabilities. The fact that the photon appears only in one place is an expression of that the wavefunction is still expressing a probability, rather than a continuous physical property. Or I haven't found the place in the article where this is explained otherwise.
 
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Dmitry67 said:
WaveJumper, please read the articel again.
"If the electrons of the H atom have decohered 4.5 billion years ago into single electrons" - electrons never decohere until you entangle electorns with a thermodinamically irreversible system with a huge number of states.



So? What are you saying? That electrons in the atoms of water have not decohered?? Then may i ask how do you see water? Do you think you see wavefunctions?
 
  • #72
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2 colorSpace

Decoherence shows how a macroscopic system interacting with a lot of microscopic systems (e.g. collisions with air molecules or photons) moves from being in a pure quantum state—which in general will be a coherent superposition (see Schrödinger's cat)—to being in an incoherent mixture of these states. The weighting of each outcome in the mixture in case of measurement is exactly that which gives the probabilities of the different results of such a measurement.

So after you detect a photon in a matrix of your camera, the interference is lost and you get for 1 megapixel matrix something like :

1/1000000 * (photon detected by pixel at (0,0)) + ....
 
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  • #73
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So? What are you saying? That electrons in the atoms of water have not decohered?? Then may i ask how do you see water? Do you think you see wavefunctions?

In order to decohere some electrons it is not enough to 'look' at water, you need to measure *individual* propeties of some electrons.

Until then they are not decohered.

As an example, you can make lens of water and perform all sorts of interference experiments using such lens and reflection from the surface of water. Interference is not lost in all these cases.
 
  • #74
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Dmitry67 said:
In order to decohere some electrons it is not enough to 'look' at water, you need to measure *individual* propeties of some electrons.

Until then they are not decohered.

As an example, you can make lens of water and perform all sorts of interference experiments using such lens and reflection from the surface of water. Interference is not lost in all these cases.


And very definitely i see liquid water because all the particles have already decohered. Otherwise, very definitely, i wouldn't be able to see water. No one has ever seen a wavefunction. You see physical objects because their wavefunctions have "collapsed" to a single state.

The case with water is special, because H has only 1 electron, which means that if it's decohered, water molecules would fall apart, which is very definitely not the case.
 
  • #75
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2 colorSpace

So after you detect a photon in a matrixof your camera, the interferenc eis lost and you get for 1 megapixel matrix something like :

1/1000000 * (photon detected by pixel at (0,0)) + ....

Right. Once the wavefunction is decoherent, the probabilities can't cancel each other out (interact) anymore, as they do in an interference pattern.

Let me approach it from a slightly different side:

In CI, the selection of a possible result has no mechanics which explains why that result happens, and not one of the other possible ones. The missing mechanics are called "randomness".

Now, MWI assumes that all possibilities remain real (unless they cancel each other out, which is a very strange thing), and so removes the name "randomness". But the mechanics of why things happen this way in one world, and that way in another, are still missing. How is it possible that a photon which could have been seen by one observer (if there had been one) and a photon which could have seen by an alternate observer, cancel each other out, and are not seen by anyone? In MWI, that's just two complex numbers adding up to zero, but how can two photons disappear by nothing else than mathematical addition? The mechanics for that are still missing, they just don't have the name "randomness" anymore.

Now an MWi proponent could say: that's simply what the wavefunction says will happen. However, the same thing could be said by the CI proponent: it's simply random according to the wavefunction. That's not a scientific difference or even Occam's razor, it just seems a personal preference: Would you rather believe in randomness, or in trillions alternate versions of yourself and everyone else coexisting in trillions of alternate universes.
 

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