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If you believe in the Everett Interpretation, then he is wrong. The Everett Interpretation, aka Many Worlds, holds that both observer and observed are quantum
by btilly 3y ago
If you believe in the Everett Interpretation, then he is wrong.
The Everett Interpretation, aka Many Worlds, holds that both observer and observed are quantum mechanical systems. From this it follows that the act of observation does not produce a "collapse", but it does separate the observer into multiple observers that can't interact with each other again.
So Schrödinger's cat is in a superposition of alive and dead before the box is opened, and after it is opened the observer is in a superposition of one who saw the cat alive, and the other who saw the cat dead. It feels bizarre, but there are no contradictions. And it is what quantum mechanics predicts.
For those who believe in this interpretation, there is a simple test of quantum gravity. Set up 2 Cavendish experiments to measure gravity. Based on whether there is a click in a Geiger counter, choose which one to put a cannon ball next to. Measure both.
This has been done, and we only see the gravity from the cannon ball that we placed, and not the alternate location it might have been placed at.
But believers in other interpretations of quantum mechanics will disagree that this experiment tests anything at all.
- fallingfrog 3y agoThis is a good summary. I like to put it the following way as an alternative: instead of imagining that you are the researcher, imagine that you are the cat.
- treeman79 3y agoWhere would energy come from for creating each universe?
- arethuza 3y agoMaybe the implementation uses copy-on-write to minimise the amount of work required? ;-)
- tgv 3y agoAmong other problems. It's just bollocks on the level of "but you didn't say it couldn't be this, nanananana."
- captainclam 3y agoI think because of the abuse of "many worlds" in science fiction media (especially as of late) as a convenient plot device, people develop this idea that it's an unserious proposal wrt the foundations of physics. As far as I have read, it strikes me as perhaps the most parsimonious interpretation of QM out there. Genuinely curious, what do you mean by "but you didn't say it couldn't be this, nanananana...?" The Everett interpretation isn't some fantastical notion spun up by a scifi writer...it is simply the consequence of removing collapse of the wavefunction as an objective event from the picture. And if it turns out our observations wouldn't be changed by removing this feature, then perhaps it was an extraneous feature in the first place!
- kgwgk 3y ago> it is simply the consequence of removing collapse of the wavefunction as an objective event from the picture. And if it turns out our observations wouldn't be changed by removing this feature, then perhaps it was an extraneous feature in the first place! > What we observe as the collapse of a function is simply an artifact of being a conscious being that can only observe one value of the of the wavefunction at any particular moment. If we simply assume that our observations are as if a wave function happened we can indeed have our Schrödinger cake and eat it too.
- tgv 3y agoAssuming many worlds, and many here means: enormous amounts, far exceeding the number of particles in the universe, is everything but parsimonious. There happens to be a model that fits some data, but that's it. It's a grotesque assumption to avoid a conflict in a man-made theory. It's a funny thought, but no more than that. There's also nothing special about observing. Our consciousness isn't super-natural, so the idea is in desperate need of some other underpinning. And probabilities: if this is one of many, many worlds, the distribution of events as we can observe them is heavily skewed. The next observations should follow a radically different pattern, unless you also assume that each split influences the probabilities of future events.
- 3y ago
- MattPalmer1086 3y agoWhy would it necessarily require any energy? Energy is what we have to expend to effect change within a universe. There may be no requirement for energy to split into a branching multiverse.
- lavelganzu 3y agoThe question is a misunderstanding. In the pure wave (Everett) interpretation, there are no universes being created when the wave function branches. Rather, different regions of the wave function become separated (decohered) from each other. https://physics.stackexchange.com/questions/41588/many-worlds-where-does-the-energy-come-from https://physics.stackexchange.com/questions/41588/many-world...
- captainclam 3y agoI think this question stems from a fundamental misunderstanding of the Everett interpretation...the idea of "many worlds" (a phrase I do not favor specifically because of this very misunderstanding!) evokes this imagery of an entirely new universe BURSTING forth dramatically upon the collapse of the wave function, and as an entirely new universe is "created," the amount of extent energy is literally doubled (or multiplied by many times more). Indeed, where does this energy come from? What the Everett interpretation suggests is that in the same way you are comfortable with the function f(x)=y having (infinitely) many values (you don't HAVE TO choose an x, ie the function doesn't collapse), the wavefunction simply is what it is and doesn't collapse either. What we observe as the collapse of a function is simply an artifact of being a conscious being that can only observe one value of the of the wavefunction at any particular moment. None of these unique values (observables) of the wave function can interact with each other (in the same way the value of x=2 doesn't "interact" with the value of x=8 for f(x)=y), so energy cannot be gathered or duplicated at any particular point of the wave function, so this energy creation/duplication is no issue.
- FollowingTheDao 3y ago"Where would energy come from for creating each universe?" Why does it have to come from somewhere? What if it just is?
- ly3xqhl8g9 3y agoSean Carroll, following Everett, puts it in the most concise form: (i) systems are described by wave functions, (ii) wave functions obey the Schrödinger equation [1]. "Many-worlds", universes, observations, observers, and so on become just entia multiplicanda [2], superfluities. [1] https://www.youtube.com/watch?v=nOgalPdfHxM https://www.youtube.com/watch?v=nOgalPdfHxM, one set of rules in quantum mechanics at 36:00; at 1:13:14 where does the energy come from? energy of the set of all universes is conserved. [2] https://en.wikipedia.org/wiki/Occam%27s_razor https://en.wikipedia.org/wiki/Occam%27s_razor
- Mizza 3y agoWhere do the eggs come from when you cut a cake?
- x3n0ph3n3 3y ago> This has been done, and we only see the gravity from the cannon ball that we placed, and not the alternate location it might have been placed at. Doesn't this presume that your brain deciding where to place the cannon ball was an uncertain quantum event? Doesn't it also presume quantum gravity does not exist?
- lavelganzu 3y agoNo: > Based on whether there is a click in a Geiger counter, choose which one to put a cannon ball next to.
- FollowingTheDao 3y agoYour brain is not deciding where the cannon ball is, it is predicting where it is and them making that prediction a certainty. That is the collapse of the wave function, turning a probability into a certainty.
- AnimalMuppet 3y ago> If you believe in the Everett Interpretation, then he is wrong. If. > And it is what quantum mechanics predicts. It is an interpretation of what the equations predict. It is very much not the only possible interpretation, so it is not "what quantum mechanics predicts". > But believers in other interpretations of quantum mechanics will disagree that this experiment tests anything at all. Within other interpretations of quantum mechanics, this does test nothing at all.
- edgyquant 3y agoWhy would anyone believe such a thing?
- bowsamic 3y agoBecause it’s very straightforward and has less assumptions and weird features than most other interpretations, and it has seen the most advancements in quantum fundamentals research
- Scarblac 3y agoComplete layman here -- does that theory say that every time a quantum effect does or does not occur, in fact both possibilities happen but in different worlds? The entire universe instantly splits up in two for every quantum event anywhere in it? Edit: I read more comments and no, it's not literally that.
- bowsamic 3y agoYes, it does mean that
- edgyquant 3y agoThese are just mathematical tools we use to make predictions. Assuming they represent objective reality and somehow prove an infinite number of universes doesn’t seem very scientific to me.
- bowsamic 3y agoI mean, that's obviously a huge matter of debate, but most of us physicists at least hope that our theories reflect objective reality in some way. Also, there are of course explicitly ontological aspects of quantum mechanics, such as PBR theorem and Bell's inequalities
- goatlover 3y agoThat's way too instrumentalist. The math also describes how atoms work and many other things. Modern physical understanding is based on those descriptions. Cosmology and nuclear physics would be useless without an understanding. How do the predictions work if they aren't in some way modeling the way reality is? Why does the technology based on them work? Instrumentalism gives no answers to those questions. Science is about understanding the world, and using that to make predictions.
- rvcdbn 3y agoI’m a “believer” in the Everett Interpretation (on the grounds that it’s the simplest interpretation) but I can’t see how such an experiment could prove anything. This experiment seems to assume we can keep the whole apparatus including the Geiger counter and the mechanism to move the cannon ball from becoming entangled with the environment (decohering). This seems very far outside the realm of current technology.
- btilly 3y agoIt shows that when there is a superposition of quantum mechanical states, you also get a superposition of two different space-time structures. The reason why the Everett Interpretation is needed for the experiment to be valid is that according to it decoherence results is a superposition of quantum mechanical states, and not a collapse. If you believe in another interpretation, there has been a collapse, and so the experiment demonstrated nothing.
- rvcdbn 3y agoOnce decoherence has occurred I don’t think it’s meaningful to say that the system exists in a superposition of states. The multiple decohered branches of the wave function can no longer interfere with each other and so there’s no way for them to affect each other, which is why we call them separate worlds. Within each decohered branch there’s an experimental apparatus and a human that sees one specific outcome. This was Everett’s main insight that each observer in each branch experiences what looks like a collapse but is really just their brain becoming entangled with one or other of the measurements.
- btilly 3y agoAccording to quantum mechanics, they can no longer interfere with each other. But we are bringing gravity into the mix. Gravity works differently than the other forces. Do space-time structures also exist in a superposition of states? Or does QM work against an essentially classical gravitational space-time background? Without a theory combining quantum mechanics and gravity, the answer is not obvious. The fact that the superpositions do NOT interfere gravitationally means that either there was no quantum mechanical superposition (collapse actually happened) or that gravity can also exist in superimposed states. If you believe in the Everett interpretation, then there must have been a quantum mechanical superposition, and this tells us something non-trivial about a quantum theory of gravity.
- slowmovintarget 3y agoIn Everettian Mechanics, decoherence occurs long before the box is opened. The photons in the box interact with the cat. That entanglement with the environment which causes the branching of the wave function occurs then. The observer that opens the box is already either in a branch where the cat is asleep (to borrow from Sean Carroll) or awake. The interesting thing to come to understand is that probability doesn't actually seem to exist as a real feature in the universe. Rather, probability is a measure of what observers believe they will or are seeing. Probability, in Everettian Mechanics, is about perception of the universe, not a feature of the universe itself.
- VirusNewbie 3y agoBut the observer is in all “probabilities” no?
- goatlover 3y agoThere are observers in all probabilities of the experiment, but each observer only observes their world because decoherence interferes with the superposition of the other worlds. Worlds being the entanglement of the entire experimental setup spreading to everything else.
- fallingfrog 3y agoThe cat is all entangled with the other stuff in the box, but by assumption the stuff inside the box is not entangled with the stuff outside the box.