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https://arxiv.org/abs/1301.1069
Effectively there is no current consensus on the issue, though Many Worlds and String Theory are widely regarded outside their adherents as non-falsifiable and therefore not legitimate theories.
Essentially the proponents of the theory have created beautiful math that fit their view, but absolutely nothing in the real world that can show that it is a more valid theory than any of the other theories which have equally elegant math to back them.
though Many Worlds and String Theory
String Theory has nothing to do with interpretations of quantum mechanics.
are widely regarded outside their adherents as non-falsifiable and therefore not legitimate theories.
Only by people who don't understand them.
Essentially the proponents of the theory have created beautiful math that fit their view
No? Many Worlds has nothing to do with math. You seem to be getting your criticisms mixed up. To be blunt: if you can't even remember what your criticism is actually meant to apply to, you should probably read into it more before commenting.
If you want to go into depth on this, I recommend you look up Sean Carrol talking about the subject - or read his book Something Deeply Hidden, if you're up for it - he's one of the best science communicators I've heard and a strong proponent of many worlds.
But to try to summarize it in very short: the "multiversal" behavior is already baked into quantum mechanics - a particle can be in two places at once, as in the double slit experiment - just at a very small scale. Traditional quantum physics postulates that there's some mechanism by which this behavior is cut off before it reaches the macroscopic scale (wave function collapse). Many Worlds just asks "Do we actually need this postulate? What would it look like if we didn't have it?" And the answer is, it would look like the universe we experience, just with a multiverse along side it.
Doesn't Carrol have a reputation for being rather crass or am I thinking of someone else?
Not that I know of.
[H]ow does one look at atoms and say "My God! There must be many worlds than just our one?"
Electrons. You've seen the model of the atom, right? Cluster of balls in the middle (protons and neutrons) and the electrons are little balls that whizz around like little planets around a Sun?
That model is a simplification of the truth. It turns out that it is impossible to pin down where an electron is and also know what it is doing. And if you know what it's doing (you can see its effects), you'll have no idea where it is.
Where they are has to be measured by probability. "It's bound to this nucleus / taking part in a chemical bond so it's likely to be in this vicinity", is about as close as you can get.
There is literally nothing excluding that electron from temporarily being a billion miles away. That's astronomically unlikely, but it's not impossible.
And by some measurement methods, when you do try to pinpoint where the electron is, it can appear to be in multiple places at once.
This can be interpreted as bleed-through from nearby quantum realms, maybe even other universes, where the electron is in one place per nearby universe. One of those places is ours, but we cannot tell which. And by the time we've made any kind of determination, the electron has moved. They never stop.
Photons - particles of light - also do this. All subatomic particles do this.
The more subatomic particles you have in some combined state (as an atomic nucleus, or even a molecule), the lower the probability is that that bound state can be in multiple places at once, but again, it is not ruled out.
But it does mean that the more bound particles an object is made from, the more definite its position appears to be, which is what we're used to at our human-sized scale.
I'm trying to follow, how can an electron be a billion miles away? Aren't the attractive forces keeping the atom together?
In quantum physics the position of an electron is defined by a wave function. This wave function or rather it's square modulus is the probability distribution of the position of the electron. In more simple terms, the electron doesn't have a precise position but rather a high probability to be somewhere.
One example of an electron being able to be billion miles away is the following: Think of a probability in the shape of a bell. Where the center of the bell has a value between 0 and 1 and to each side the function tends to 0. The likeliest region for the electron to be is the center of the bell, but since the function never takes the value 0, it is not impossible for the electron to be a billion miles away.
If you apply a force to the electron, like an electrical field, you will simply shift and modulate the probability distribution moving the maximum probability towards the positive side of the electrical field. But the electron being in the place you expect it to be is still nothing but a very likely event. The event of the electron being a billion miles away is still of probability not 0.
Draw a graph by flipping a coin. Start at (0,0). Assume a fair coin and fair flips. Move one unit right each time, but go up (+1) for heads and down (-1) for tails. The line drawn can go arbitrarily far vertically from 0, but the average vertical position necessarily remains 0.
The average position of an electron is slightly more nebulous than the line x=0, and depends on what, if anything, the electron bound to, but for each state an electron can be in there is a group, or a locus, of possible positions that represent that bound state and the whole locus is a mean of sorts. An electron can go on a journey wherever as long as it continues to regress to that locus.
And in the exceptionally rare instance where a subatomic particle goes on an indefinite journey, we call that quantum tunnelling.
Quantum tunneling is actually a problem in integrated circuit design: https://medium.com/@markveerasingam/quantum-tunneling-the-semiconductors-struggle-in-the-miniaturization-race-7ef2df8f9e48
I heard about that too. Its absolutely mind blowing when you realise, that we are able to build chips on such a small scale (and not just for special chips but for relatively common chips), that we are dipping into the realm of quantum physics causing all sorts of problems.
There isn't any "proof"; in fact, Many Worlds is what's called "unfalsifiable", which means we don't have a way through the scientific method to show Many Worlds to be false.
Also, it's not really
My God! There must be many worlds than just our one?
But more
There are moments in time where one path is taken and not another... but what if all paths are taken, somewhere?
It's not meant to be a valid theory, it's just a possible outcome of having a spacetime continuum; because it's not falsifiable though, it's not worth pursuing right now, only worth keeping in mind in case we come across new evidence to evaluate.
Many Worlds is what’s called “unfalsifiable”, which means we don’t have a way through the scientific method to show Many Worlds to be false.
For one thing, any experiment which demonstrated objective collapse (which aren't just possible in theory, they've actually been performed) would falsify MW.
I'm aware of the double slit experiment and its variations, but I probably do misunderstand Many Worlds to at least some degree; how does wave collapse prove Many Worlds to be false?
Well, under Many Worlds, wave function collapse isn't a real "thing"; it's just an illusion caused by the observer becoming entangled with the wave function. Objective Collapse theories, however, propose a real physical mechanism of wave function collapse. If that's true, and there was found to be a real mechanism of collapse, then MW would be impossible, because the wave function would collapse before any "branching" could happen.
And what is there to stop the collapse from being the branch point? In one world, it collapses one way; in another, another. There doesn't seem to be any inconsistency there.
Well, because under Many Worlds, the wave-function not collapsing is the reason there are multiple branches; the wave function is the multiverse. So if the wave function has collapsed into a single, definitive state, then there is only a single, definitive universe.
I don't understand how it's any more outlandish than thinking that we can be aware of everything that exists, or that everything exists in a straight line through time, never branching. Maybe it's a lack of understanding on my part, but it seems the sum total of what we have discovered through science, or even through imagination, only illuminates a very small subset of reality. We can only measure with the instruments we can imagine and build, and with our own limited senses. So I wouldn't jump to believe, nor to label unbelievable.
I admit that I might be dumb, but, how does one look at atoms and say "My God! There must be many worlds than just our one?"
Well, we looked at atoms and found out that the only meaningful way to describe them is with quantum mechanics. This is the most precise and possibly best tested physical theory ever developed. And it says that if an atom starts out in state A, it will then naturally evolve into a state A+B.
Now, A and B are mutually exclusive. So what does that mean? One reasonable way to view it is that it is indeed physically in both states A and B as the theory says. That's ultimately what leads to the many worlds interpretation. The atom is both in state A and state B, and the universe accepts both of the different trajectories of reality that leads to.
This view is equivalent to a number of other ways of view things, all of which lead to the same prediction of physical behaviour for now, so essentially you can just pick your favourite.
Multiverse and many worlds interpretation are two different things.
The idea of multiverse is that there are many other universes existing in parallel with ours. Either the universes are created through different big bangs, or maybe the universe is constantly splitting into many other universes. This is mostly science fiction.
MWI is one of many competing ideas to help coming to terms with the counterintuitive nature of quantum physics. A particle can be in many places at once when not observed. Once it’s observed, it chooses to stick in one place. MWI is one interpretation of why this is happening.
I'm pretty sure the multiverse theory is baked into the big bang theory and cosmological theories, so I wouldn't necessarily call it mostly science fiction.
Cosmological hypotheses suggest universes with different initial conditions are possible (different space-time geometries, different elementary particle masses, etc.). The big bang theory suggests multiple universes (not just ours) with different initial conditions were formed due to eternal inflation. As the multiverse continues to undergo this eternal inflation, there forms pockets where the inflation has ended and is "hospitable". Our observable universe would be an example of such pockets, but since inflation is eternal, there should be many of these pockets.
I call it science fiction because there’s no real evidence for it. Not yet at least.
Most ideas of multiverse comes from making educated extrapolations of currently known science. But that’s not enough. Scientists must also design experiments which confirms the extrapolation to be correct. This hasn’t been done.
Maybe it’s harsh to call it science fiction. Correct wording is theoretical physics.
Hehe, yeah, it's a bit harsh to call it science fiction, especially this day in age when a lot of new physics lives in theoretical physics.
Cosmological models are very difficult to test given their nature. In many cases they are tested in massive physics simulations. The general test is to simulate the cosmological theory and see if it produces a universe that has the same observable qualities as our current universe once the simulation reaches our present epoch.
Nevertheless, Hawkins had his own reserves regarding his theory due to it not being experimentally falsifiable; but one must understand that rejecting the multiverse theory = rejecting the big bang theory since they are currently coupled.
If you want to know why it's taken seriously:
https://m.youtube.com/watch?v=kTXTPe3wahc
Tl;dr: you need to actually understand the physics at play that lead to serious consideration of the many worlds theory. It's not the pop-sci it gets painted as. It's much more specific.
This was mentioned (not fully, but enough to get some of the ideas) recently in an episode of PBS Space Time
As far as MWI itself, my understanding is that it comes from simply taking the same math that works for atoms (as you say) and applying it to everything - the observers of a quantum system, the earth, the whole universe. I think it really comes down to the question: If Everything is a wave function, what would it look like from the inside? And MWI pops out of trying to answer that.
And the other interpretations of quantum mechanics don't even seem better to me, requiring arbitrary conditions for a state to collapse to a single value for example. That feels to me like an entity of the type Occam meant.
Two points:
The MWI/Everett interpetation is the simplest interpretation of quantum mechanics—other interpretations have to add additional assumptions to prevent it from happening.
The most common version of the MWI is actually an interpretation of an interpretation (i.e., Bryce deWitt’s reinterpretation of Hugh Everett's 1957 thesis), but many of those who subscribe to deWitt’s interpretation (including deWitt himself) don’t seem to grasp how it differs from Everett’s. Everett’s thesis makes no explicit reference to multiple worlds—just a single wave function that can be measured in different bases to produce multiple versions of each observer, each of which perceives a different version of the universe. For Everett, the wave function was ontologically prior to the material world, so his universal wave function was a complete explanation as-is. But for deWitt (and for most people), the material world is ontologically prior, while the wave function is just a tool for describing its behavior. So by their reasoning, those multiple perceived worlds must all really exist as parts of the wave function in some sense.
I had a though experience years ago on mushrooms, that our universe lives in a blackhole. Just think about it, when stars big enough implodes it creates a black hole in the fabric of space, where nothing can escape (not even light).
The beginning of our universe is somehow related to a condensed hot/light that explodes and creates the actual expansion we see right now... Kinda curious right?
Also there's somehow a limit how far we can see through our universe, that's also odd... It's impossible at the moment to see outside our own universe, because remember nothing can escape outside a blackhole, not even light !! Soo yeaah that's why I think we live in a multiverse.
Also on a final note, Rick&Morty said so 🤷♂️
This theory is called Schwarzschild Cosmology, and has actually gained some traction recently based on some new experiments.
https://journals.aps.org/prd/abstract/10.1103/PhysRevD.111.103537
As a youth this made intuitive sense to me as I first learned about different cosmological theorems. A black hole is essentially a pocket of mass on which a set of physical properties exist that are different from its containing universe, with the boundary between different physics being the event horizon and the "Big Bang" being the initial collapse of the singularity.
Just a correction, there isn't anything limiting how "far" we can see our into the universe except our limited technology. And even then we are very close. We're only limited by how old our universe is, as it takes light that long to travel to us from the edge of the expanding universe. The furthest we can possibly see would be about 300,000 years after the big bang, when light was finally able to travel unimpeded throughout the universe.
Thats way I said "for the moment", because I know we are limited by our technology. However, even If our technology evolves to a degree so large we can not comprehend, I'm pretty sure we wouldn't be able to "see" outside our own universe.
Sorry If my wording is a bit janky and not very scientific. Following your guts is also not very scientific in anyway, but that's how I feel when seeing all those strange coincidence that cross each other strangely enough !
But thanks for the clarification !
Edit: Even if we can't see outside our own bubblrle, we will still be able to travel from one universe to another :p
If we take the Schwartzchild Cosmology at face value we would only ever be able to "pierce the veil" through the boundaries of our cosmos with information/radiation through the Hawking Radiation, at least if the universe containing our local singularity has similar physics at play regarding singularities and the force of gravity.
That said, you could always go "down-well" into a singularity in our universe, but surviving the event horizon as more than particle soup spaghetti is quite a challenge.
You're kinda right, but not really. Based on a reductionist definition of a black hole, our universe is inside one.
However, that's strictly based on some of the characteristics of a black hole, and our universe.
However, if we're talking about black holes with more nuance, the answer becomes "no".
I'm not qualified to answer this, but I happen to know someone with a PhD in astrophysics, who has published multiple articles about black holes. We've talked about this before and long story short: we don't live inside a black hole.
The big bang theory disproves it. The existence of background cosmic radiation doesn't match the interior of a black hole; it's geometrically impossible.
Our universes ever growing horizon is out of limits, and we can't escape from it. That's not the sane thing as an event horizon though.