Total energy=1/2E+1/2E=E
— Andrew M

So at every branching, the total energy of the universe is divided by 2? And likewise with its mass, I suppose. Since there is a gigamongous number of branching per nanosecond, it follows that if the MWI was true, our universe would become empty of all matter and energy quite rapidly, like in a few seconds. — Olivier5

Here's a possible way to think about it.

Consider a superimposed photo. The number of times that the photo is superimposed doesn't change the amount of material in the photo. There is still only one photo, but it can be described from different points of view. Further, a filter could potentially be applied such that you see one definite picture (or slice).

This idea reflects the math of superposition. Suppose I have a vector (which can be visualized as an arrow) that points north-east. It's just one thing. But I can also consider it as a linear combination of one vector pointing north and another vector pointing east. Now there are two things. But nothing has really changed. I'm just describing the original vector in a different way.

Now suppose that you have a quantum coin that is in a superposition of heads and tails. In MWI, whether it is one coin (like the north-east vector) or two coins (like the north vector and east vector) is just a matter of how you want to describe it.

What MWI says is that you, the observer, are a quantum system just like the quantum coin. From an isolated observer's viewpoint (see Wigner's Friend), you become entangled with the quantum coin when you measure it. The universe still contains the same energy that it did before, but it now looks different from your point of view compared to the isolated observer's point of view (where they describe you as in a superposition of measuring heads and measuring tails).

What MWI says is that you, the observer, are a quantum system just like the quantum coin. From an isolated observer's viewpoint (see Wigner's Friend), you become entangled with the quantum coin when you measure it — Andrew M

Thought experiments mean very little, especially when poorly thought through.

E.g. what Schrödinger forgot in his famous mind experiment is that the cat is just as valid an observer as his master. And the Schrödinger equation of the Schrödinger cat (or of any other cat) remains unknown so even if we assume that the cat can be described with QM formalism, we have no idea how.

A cat, or a human being for that matter, is not just an observer. She is also a biological system. Nobody has ever solved the Schrödinger equation for biological systems, it's far too complicated. We can barely compute it for simple molecules, like water. If you want to apply QM to life, you got a lot of very very hard "shut up and calculate" to do.

So before you can speak of me getting "entangled" with my coin, you would have to show that QM applies to me, as a whole, and that my holistic Schrödinger equation accepts such a possibility.

Thought experiments mean very little, especially when poorly thought through.

E.g. what Schrödinger forgot in his famous mind experiment is that the cat is just as valid an observer as his master. — Olivier5

I'm pretty sure Schrödinger and Wigner had carefully thought their ideas through. What is relevant are the implications of those thought experiments for differentiating and testing various interpretations and theories.

A cat, or a human being for that matter, is not just an observer. She is also a biological system. Nobody has ever solved the Schrödinger equation for biological systems, it's far too complicated. We can barely compute it for simple molecules, like water. If you want to apply QM to life, you got a lot of very very hard "shut up and calculate" to do. — Olivier5

Perhaps Schrodinger's Bacterium?

In essence, it appears certain photons were simultaneously hitting and missing photosynthetic molecules within the bacteria—a hallmark of entanglement. “Our models show that this phenomenon being recorded is a signature of entanglement between light and certain degrees of freedom inside the bacteria,” [Marletto] says. — 'Schrödinger's Bacterium' Could Be a Quantum Biology Milestone

I'm pretty sure Schrödinger and Wigner had carefully thought their ideas through. — Andrew M

How come Schrödinger did not see that his cat was just as good an observer as he was, pray tell?

How come Schrödinger did not see that his cat was just as good an observer as he was, pray tell? — Olivier5

I'm sure he did. But the thought experiment is not about what the cat observes, it's about where the line is drawn (if at all) for when a system stops being in a superposition of states.

Actually Schrödinger's cat was an attempt to prove that observers cannot be the cause of anything quantic happening.

But the thought experiment is not about what the cat observes, it's about where the line is drawn (if at all) for when a system stops being in a superposition of states. — Andrew M

The line is my consciousness at the latest, because I experience only one world.

Actually Schrödinger's cat was an attempt to prove that observers cannot be the cause of anything quantic happening. — Olivier5

Sorry, I'm not sure what you're saying. Can you clarify?

The line is my consciousness at the latest, because I experience only one world. — SolarWind

OK, so consciousness causes collapse, on your view? Or something else?

Can you clarify? — Andrew M

The Schrödinger cat thought experiment was conceived in order to refute the Copenhagen interpretation, specifically the idea that the act of "observation" or "measurement" reduces or "collapses" the wavefunction. I am sympathetic to the attempt, I don't believe in the magic of observation either. But to me, it seems Schrödinger forgot a tiny little detail, which is that his cat was an observer too and therefore (according to said Copenhagen interpretation) could collapse the wavefunction inside his box, all by himself.

Edit: I've read your "Schrödinger bacterium" article. As often the case, the title widely overstates the finding that

"Our models show that this phenomenon being recorded is a signature of entanglement between light and certain degrees of freedom inside the bacteria,”.

Namely, the analysis points to a quantic interaction between photons and the bacterium's chlorophyll. What happens when a photon is "captured" by a chlorophyll molecule has been the subject of countless studies and many of them call upon QM to explain how photosynthesis works. For instance, chlorophyll is known to be fluorescent. It releases photons in a certain precise wave length (red). You can see it for yourself here, or you can just put a nice green solution of chlorophyll under the sun, and you will notice like a faint red light shimmering inside the green liquid.

Now, fluorescence is considered a quantic phenomenon, so this finding above that chlorophyll can "entangle" with photons doesn't seem so new to me.

OK, so consciousness causes collapse, on your view? Or something else? — Andrew M

"Latest" I wrote. But the truth is a combination of Bohmian Mechanics and the Schrödinger–Newton equation causing the collaps. It depends in the mass of the measuring apparatus. The cat is heavy enough.

The Schrödinger cat thought experiment was conceived in order to refute the Copenhagen interpretation, specifically the idea that the act of "observation" or "measurement" reduces or "collapses" the wavefunction. I am sympathetic to the attempt, I don't believe in the magic of observation either. But to me, it seems Schrödinger forgot a tiny little detail, which is that his cat was an observer too and therefore (according to said Copenhagen interpretation) could collapse the wavefunction inside his box, all by himself. — Olivier5

OK, but the basic point of Schrodinger's thought experiment was that if it doesn't make sense to imagine macroscopic phenomena being indeterminate, then it shouldn't make sense to imagine atomic phenomena being indeterminate either. After presenting his thought experiment, Schrödinger says:

It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a "blurred model" for representing reality. In itself it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks. — The Present Situation in Quantum Mechanics - Erwin Schrödinger, 1935

...

Now, fluorescence is considered a quantic phenomenon, so this finding above that chlorophyll can "entangle" with photons doesn't seem so new to me. — Olivier5

From the article, "According to study co-author Tristan Farrow, also of Oxford, this is the first time such an effect has been glimpsed in a living organism."

And regarding future experiments, "Several research groups, including those led by Gröblacher and Farrow, are hoping to take these ideas even further. Gröblacher has designed an experiment that could place a tiny aquatic animal called a tardigrade in superposition—a proposition much more difficult than entangling bacteria with light owing to a tardigrade’s hundreds-fold–larger size."

"Latest" I wrote. But the truth is a combination of Bohmian Mechanics and the Schrödinger–Newton equation causing the collaps. It depends in the mass of the measuring apparatus. The cat is heavy enough. — SolarWind

Fair enough. Is that different to the Penrose interpretation?

OK, but the basic point of Schrodinger's thought experiment was that if it doesn't make sense to imagine macroscopic phenomena being indeterminate, then it shouldn't make sense to imagine atomic phenomena being indeterminate either. — Andrew M

Not really. The scales of reality are a view of the mind. Nature is one. The basic point Schrödinger was trying to make is that observers are not magic; they don't collapse wave functions just by "observing".

About your paper, it may indeed be the first time such an effect is evidence in vivo, as opposed to in vitro. But they haven't "entangled" a whole bacterium yet, only its chlorophyll.

Note that in the double slit experiment, you can replace photons by whole molecules, and it will still work. You will get interferences... So molecules behave as waves too, including medium size molecules such as chlorophyll. But I don't think the double slit experiment works with entire bacteria.

As I understand it, via Sean Carroll's work, if you die here, you may well be alive in many other universes, but that would not matter in the sense that you are closed off from causal interaction with the other "you's". The problem with Many Worlds, is that, there is no evidence that could be gathered that offers proof of its validity. It's a speculation based on a scientific equation that seeks to establish determinacy. It could be false, in that the universe may be indeterminate deep down.

"Latest" I wrote. But the truth is a combination of Bohmian Mechanics and the Schrödinger–Newton equation causing the collaps. It depends in the mass of the measuring apparatus. The cat is heavy enough.
— SolarWind

Fair enough. Is that different to the Penrose interpretation? — Andrew M

Yes. The Bohm-Schrödinger-Newton interpretation does not need the general relativity. The particles move according to Bohm, entangle with the measuring apparatus, this localizes itself over its own gravity and acts back over the entanglement, which causes the collapse. At 10^10 atomic mass units, the transition is quantum mechanical-classical according to SN equation.