Help with correct description of Everettian QM

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Help with correct description of Everettian QM

#1  Postby crank » Apr 19, 2016 9:58 am

I hope this is a quick one. I've read/heard many many descriptions of the Everett interpretation of QM, virtually every one was that every time a quantum system 'decides' which of two paths is taken, the universe branches into separate universes one for each possible path taken, etc etc. I just watched a talk [see below, t=1h12m39s] where a speaker gave a different slant, the second time I've heard this but can't remember where first, that all the different branches of the universal wave function exist simultaneously in these parallel universes.

Is this a difference with no difference? Is it in how you look at time? Or is it a very different way to see it? The common description seems to create universes as you progress through time, the second posits they all exist from the beginning [whatever that means]. The second version somehow seems far more intuitive/believable, somewhat more comprehensible, at least for me, though I couldn't articulate why. Thanks to anyone who takes the time to try to enlighten me.

Very interesting overall:
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Re: Help with correct description of Everettian QM

#2  Postby John Platko » Apr 19, 2016 1:23 pm

:popcorn:
I like to imagine ...
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Re: Help with correct description of Everettian QM

#3  Postby DavidMcC » Apr 22, 2016 1:21 pm

crank wrote:I hope this is a quick one. I've read/heard many many descriptions of the Everett interpretation of QM, virtually every one was that every time a quantum system 'decides' which of two paths is taken, the universe branches into separate universes one for each possible path taken, etc etc. I just watched a talk [see below, t=1h12m39s] where a speaker gave a different slant, the second time I've heard this but can't remember where first, that all the different branches of the universal wave function exist simultaneously in these parallel universes.

Is this a difference with no difference? Is it in how you look at time? Or is it a very different way to see it? The common description seems to create universes as you progress through time, the second posits they all exist from the beginning [whatever that means]. The second version somehow seems far more intuitive/believable, somewhat more comprehensible, at least for me, though I couldn't articulate why. Thanks to anyone who takes the time to try to enlighten me.
...

Neither version is meaningful, because they are both based on Everett's false belief that the entire universe can be described by a single quantum state in the first place. The reality is that QM is inappropriate to large, massive systems. It is only appropriate for very small, very low mass systems, such as atoms and molecules, unless the temperature is below a critical value. Once the energy difference between states of the whole system becomes less than thermal fluctuations, the model breaks down.

LATE EDIT: Having said that, mass quantum effects do occur at achievable temperatures, for certain aspects of certain bulk systems, such as a body of liquid He4.
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Re: Help with correct description of Everettian QM

#4  Postby crank » Apr 22, 2016 2:43 pm

The Everett interpretation is gaining support amongst physicists. There is at least 1 video with Max Tegmark discussing his informal polling he's been doing, I'm pretty sure it's one of these two. Plus, it's my understanding that QM, meaning the Standard Model IS the theory for everything but the regimes requiring GR. It's not that QM doesn't apply to macro systems, it's just not feasible to do so, and Newtonian mechanics, classical mechanics, is more than adequate. At least is what I've understood for a long time. I'm obviously no physicist.

I appreciate the reply, but whether Everett is correct, or wrong, or both simultaneously, I would still like to know the answer to the question. I'm pretty sure Sean Carroll supports Everettian interpretation, and voiced something similar to Tegmark's remarks about it gaining ground. Most physicists I think still will say Copenhagen, but if pressed say they really don't think about it, said it because that's what they were exposed to in school. And in reality [haha] few physicists think Copenhagen is the right way to go.





I'm watching shit while trying to respond, this has some interesting info, the audio really sucks, and the white board he is using is really really white to where you can seldom see the slide, but it's worth a watch if you like this stuff
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Re: Help with correct description of Everettian QM

#5  Postby DavidMcC » Apr 30, 2016 12:36 pm

crank wrote:The Everett interpretation is gaining support amongst physicists. There is at least 1 video with Max Tegmark discussing his informal polling he's been doing, I'm pretty sure it's one of these two. ...]

It doesn't surprise me at all that that Tegmark (of "all mathematics is physics for some universe somewhere" fame) should support Everett (whose MWI theory is so nutty that he was derided by physicists until he took the hint, and dropped out of the subject.
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Re: Help with correct description of Everettian QM

#6  Postby surreptitious57 » Apr 30, 2016 1:50 pm


When I give talks I like to know what the people in my audience think. When I asked them which interpretation of quantum mechanics they identified most closely with here is what they said first at a 1997 quantum mechanics conference at UMBC in Maryland then at a 2010 talk I gave at the Harvard Physics Department:

Interpretation

Maryland 1997


Copenhagen 13
Everett 8
Bohm 4
Consistent histories 4
Modified dynamics 1
None of the above/undecided 18

Total votes 48

Harvard 2010

Copenhagen 0
Everett 16
Bohm 0
Consistent histories 2
Modified dynamics 1
None of the above/undecided 16

Total votes 35

Although these polls were highly informal and unscientific and clearly do not survey a representative sample of all
physicists they nonetheless indicate a rather striking shift in opinion: after reigning supreme for decades the Copenhagen interpretation saw its approval rating drop below 30 per cent in 1997 to 0 (!) in 2010. In contrast after being proposed in 1957 and going virtually unnoticed for about a decade Everetts Many-Worlds interpretation survived twenty five years of fierce criticism and occasional ridicule to top the 2010 poll. Its also worth noting that theres a large fraction of undecided voters suggesting that the quantum-mechanics debate is in full swing

P 228 / Our Mathematical Universe My Quest For The Ultimate Reality Of Nature / Max Tegmark
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Re: Help with correct description of Everettian QM

#7  Postby DavidMcC » Apr 30, 2016 2:04 pm

... I forgot to mention that there are two vesions of MWI: onle in which the many worlds are just a mathematical construct, and one in which they arre considered to be real univereses, popping up willy-nilly. I guess it was the latter version that drew most of the derision. I could be wrong, but I think Everrett himself was in the latter camp.
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Re: Help with correct description of Everettian QM

#8  Postby surreptitious57 » Apr 30, 2016 3:01 pm


The Quantum Cards thought experiment. At 10 00 am you balance a card on its edge bet S100 on it falling face up and you
close your eyes. Ten seconds later the card has fallen down both to the left and the right in quantum superposition so the wavefunction describes the card being in two places at once. Another ten seconds later you have opened your eyes and
looked at the card so the wavefunction describes your being happy and sad at once. Although there is still only one wave function and one quantum reality ( within which particles making up both the card and you are in two places at once )
Everett realized that this is in practice as if our Universe has split into two parallel universes with a definitive outcome
in each of them

Page 188 / Our Mathematical Universe My Quest For The Ultimate Nature Of Reality / Max Tegmark
A MIND IS LIKE A PARACHUTE : IT DOES NOT WORK UNLESS IT IS OPEN
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Re: Help with correct description of Everettian QM

#9  Postby DavidMcC » Apr 30, 2016 3:18 pm

surreptitious57 wrote:
The Quantum Cards thought experiment. At 10 00 am you balance a card on its edge bet S100 on it falling face up and you
close your eyes. Ten seconds later the card has fallen down both to the left and the right in quantum superposition so the wavefunction describes the card being in two places at once. Another ten seconds later you have opened your eyes and
looked at the card so the wavefunction describes your being happy and sad at once. Although there is still only one wave function and one quantum reality ( within which particles making up both the card and you are in two places at once )
Everett realized that this is in practice as if our Universe has split into two parallel universes with a definitive outcome
in each of them

Page 188 / Our Mathematical Universe My Quest For The Ultimate Nature Of Reality / Max Tegmark

Just remember that "cards" shoud be interpretted as quantum particles, NOT playing cards, which are way to big for QM to apply.
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Re: Help with correct description of Everettian QM

#10  Postby crank » Apr 30, 2016 6:24 pm

And you have Max Tegmark using the 'popping into existence' description here, but I don't think that is correct, the right way to think of it is all the possible branched universes exist. There's already going to be some vast number 'behind' you, it's more accessible to my mind to have them all existing, the branching idea is too confusing if you really think about it. Just try to imagine how many branchings occur in a second universe-wide.

I also kind of laugh when you hear people pondering the 'copies' of themselves, even Tegmark's musings seem to be ridiculously lacking in imagination. It's an incredibly small subset of the yous that will be all that similar to you, and you won't exist in but a tiny tiny tiny insignificant fraction of the universes. And yet, there will be an astounding array of yous that you could never figure out what the difference was.
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Re: Help with correct description of Everettian QM

#11  Postby DavidMcC » May 01, 2016 1:00 pm

crank wrote:And you have Max Tegmark using the 'popping into existence' description here, but I don't think that is correct, the right way to think of it is all the possible branched universes exist. There's already going to be some vast number 'behind' you, it's more accessible to my mind to have them all existing, the branching idea is too confusing if you really think about it. Just try to imagine how many branchings occur in a second universe-wide.

I also kind of laugh when you hear people pondering the 'copies' of themselves, even Tegmark's musings seem to be ridiculously lacking in imagination. It's an incredibly small subset of the yous that will be all that similar to you, and you won't exist in but a tiny tiny tiny insignificant fraction of the universes. And yet, there will be an astounding array of yous that you could never figure out what the difference was.

Crank, I disagree. I think only one of the branches actually happens - the one we are in. All the others are just failed possibilities, that don't really exist. They are the product of a probability distribution for what could have happened, but didn't, as it turned out. Years ago, there was a sci-fi series based on them being real, but I've forgotten what it was called. It was basically a vehicle for speculating on what the world might have been like if something turned out differently from actual history - eg, if the Nazis had won WWII. The heroes of the program had invented a gizmo that enabled them to travel between these alternate versions of history.
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Re: Help with correct description of Everettian QM

#12  Postby crank » May 01, 2016 1:12 pm

OK, I think I've seen enough, the video below has Mex Tegmark saying, @5:13 "According to Everett, the beauty is there is nothing that triggers it, because there really is no split, there's only one universe where all these things are happening..."

Tegmark mentions 'quantum suicide' as a way to prove Everett is right, we just need to find someone to do the experiment. That is something you really should watch, v v interesting.

Edit, forgot link to video.

Last edited by crank on May 01, 2016 1:47 pm, edited 1 time in total.
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Re: Help with correct description of Everettian QM

#13  Postby DavidMcC » May 01, 2016 1:25 pm

crank wrote:OK, I think I've seen enough, the video below has Mex Tegmark saying, @5:13 "According to Everett, the beauty is there is nothing that triggers it, because there really is no split, there's only one universe where all these things are happening..."

Tegmark mentions 'quantum suicide' as a way to prove Everett is right, we just need to find someone to do the experiment. That is something you really should watch, v v interesting.

That could be Tegmark putting words into Everrett's mouth to save his credibility.
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Re: Help with correct description of Everettian QM

#14  Postby crank » May 01, 2016 1:26 pm

DavidMcC wrote:
crank wrote:And you have Max Tegmark using the 'popping into existence' description here, but I don't think that is correct, the right way to think of it is all the possible branched universes exist. There's already going to be some vast number 'behind' you, it's more accessible to my mind to have them all existing, the branching idea is too confusing if you really think about it. Just try to imagine how many branchings occur in a second universe-wide.

I also kind of laugh when you hear people pondering the 'copies' of themselves, even Tegmark's musings seem to be ridiculously lacking in imagination. It's an incredibly small subset of the yous that will be all that similar to you, and you won't exist in but a tiny tiny tiny insignificant fraction of the universes. And yet, there will be an astounding array of yous that you could never figure out what the difference was.

Crank, I disagree. I think only one of the branches actually happens - the one we are in. All the others are just failed possibilities, that don't really exist. They are the product of a probability distribution for what could have happened, but didn't, as it turned out. Years ago, there was a sci-fi series based on them being real, but I've forgotten what it was called. It was basically a vehicle for speculating on what the world might have been like if something turned out differently from actual history - eg, if the Nazis had won WWII. The heroes of the program had invented a gizmo that enabled them to travel between these alternate versions of history.

I'll let you argue with the physicist, see below, Tegmark was using 'splitting' more as a aid in explaining, that isn't the right way to think about it. You might want to try the experiment suggested in the video, get back with us when you're done. :coffee:

I think maybe you mean Sliders? I watched a bunch of those just recently, it was marginally watchable, severely lacking in consistency, utter disregard for logic, etc. As I said above, it surprises me how poorly people think about the implications. Like if Hitler won the war to use an example NO ONE would ever pick... How many people alive today would actually exist in that world, even given great leeway in saying this person in our world, is that person in Hitler's world? Just think of how many people's marriage came out of the war, and what a huge difference the mix of survivors would be, forget about the rest of the massive differences in the post-war years.
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Re: Help with correct description of Everettian QM

#15  Postby crank » May 01, 2016 1:30 pm

DavidMcC wrote:
crank wrote:OK, I think I've seen enough, the video below has Mex Tegmark saying, @5:13 "According to Everett, the beauty is there is nothing that triggers it, because there really is no split, there's only one universe where all these things are happening..."

Tegmark mentions 'quantum suicide' as a way to prove Everett is right, we just need to find someone to do the experiment. That is something you really should watch, v v interesting.

That could be Tegmark putting words into Everrett's mouth to save his credibility.

What the fuck are you talking about? How is Tegmark's credibility even an issue? He's not some schlub trying to do science vblogs, Tegmark is a highly respected physicist FFS, you might not like his ideas, but he's not going to be lying about Everett's work, there are a few other physicists around the world would shred him if he misrepresented such an important issue. What are you thinking?
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Re: Help with correct description of Everettian QM

#16  Postby DavidMcC » May 01, 2016 1:35 pm

crank wrote:
DavidMcC wrote:
crank wrote:OK, I think I've seen enough, the video below has Mex Tegmark saying, @5:13 "According to Everett, the beauty is there is nothing that triggers it, because there really is no split, there's only one universe where all these things are happening..."

Tegmark mentions 'quantum suicide' as a way to prove Everett is right, we just need to find someone to do the experiment. That is something you really should watch, v v interesting.

That could be Tegmark putting words into Everrett's mouth to save his credibility.

What the fuck are you talking about? How is Tegmark's credibility even an issue? He's not some schlub trying to do science vblogs, Tegmark is a highly respected physicist FFS, you might not like his ideas, but he's not going to be lying about Everett's work, there are a few other physicists around the world would shred him if he misrepresented such an important issue. What are you thinking?

A. It was Everrett's credibility that my post was about. He was laughed out of court over MWI with real universes.
B. Tegmark damaged his own credibilty by claiming that there was a universe for every math, as opposed to a math for every universe.
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Re: Help with correct description of Everettian QM

#17  Postby crank » May 01, 2016 1:54 pm

DavidMcC wrote:
crank wrote:
DavidMcC wrote:
crank wrote:OK, I think I've seen enough, the video below has Mex Tegmark saying, @5:13 "According to Everett, the beauty is there is nothing that triggers it, because there really is no split, there's only one universe where all these things are happening..."

Tegmark mentions 'quantum suicide' as a way to prove Everett is right, we just need to find someone to do the experiment. That is something you really should watch, v v interesting.

That could be Tegmark putting words into Everrett's mouth to save his credibility.

What the fuck are you talking about? How is Tegmark's credibility even an issue? He's not some schlub trying to do science vblogs, Tegmark is a highly respected physicist FFS, you might not like his ideas, but he's not going to be lying about Everett's work, there are a few other physicists around the world would shred him if he misrepresented such an important issue. What are you thinking?

A. It was Everrett's credibility that my post was about. He was laughed out of court over MWI with real universes.
B. Tegmark damaged his own credibilty by claiming that there was a universe for every math, as opposed to a math for every universe.


None of that is relevant, his ideas on the maths subject and whether or not a bunch of physicist disagree with him say nothing about Everett's work or whether Tegmark knows its basics. My question was about the basic concept behind Everett.
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Re: Help with correct description of Everettian QM

#18  Postby crank » May 01, 2016 1:58 pm

And I can't believe my memory is so shoddy. I knew I had seen this video before, but hadn't remembered the 'splitting' comment, but right under the video is a comment I made 9 months ago bitching about that very thing. I need a better brain, or at least better RAM.
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Re: Help with correct description of Everettian QM

#19  Postby DavidMcC » May 01, 2016 2:03 pm

crank wrote:... My question was about the basic concept behind Everett.

You mean you aren't interested in whether or not it's nonsense?
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Re: Help with correct description of Everettian QM

#20  Postby DavidMcC » May 01, 2016 2:10 pm

crank wrote:
DavidMcC wrote:
crank wrote:
DavidMcC wrote:
That could be Tegmark putting words into Everrett's mouth to save his credibility.

What the fuck are you talking about? How is Tegmark's credibility even an issue? He's not some schlub trying to do science vblogs, Tegmark is a highly respected physicist FFS, you might not like his ideas, but he's not going to be lying about Everett's work, there are a few other physicists around the world would shred him if he misrepresented such an important issue. What are you thinking?

A. It was Everrett's credibility that my post was about. He was laughed out of court over MWI with real universes.
B. Tegmark damaged his own credibilty by claiming that there was a universe for every math, as opposed to a math for every universe.


None of that is relevant, his ideas on the maths subject and whether or not a bunch of physicist disagree with him say nothing about Everett's work or whether Tegmark knows its basics. My question was about the basic concept behind Everett.

It wasn't merely "a bunch of physicists disagreeing with him". If that was all it was, he surely wouldn't have given up the subject (which he did, on the basis that he was getting too much ridicule from the physics community).
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