[pdonis]

You can't ignore it because it's not a "detail"--it's a crucial feature of the thought experiment that doesn't work for the universe as a whole. What you're suggesting is like saying, in my thought experiment I assume that 2 + 2 = 5, just ignore the fact that 2 + 2 is actually 4.

[faangsticle]

Yes, that's what a thought experiment is. A cat can't be alive and death at the same time, either.

[pdonis]

> that's what a thought experiment is.

No. A thought experiment cannot be based on a contradiction.

> A cat can't be alive and death at the same time, either.

And the Schrodinger's Cat thought experiment does not claim that it is, even though many pop science discussions try to claim otherwise. The Schrodinger's Cat thought experiment is based on the math of QM, i.e., on a consistent underlying model. It simply points out consequences of that model that might not be obvious to many people.

The "thought experiment" I have been objecting to in this thread, by contrast, is not based on any consistent mathematical model. The operation it is proposing to do on the universe as a whole is inconsistent with GR, which is the only consistent model we have of the universe as a whole. That means it's not a valid thought experiment. "Thought experiment" does not mean you can make up whatever you want.

[faangsticle]

> "Thought experiment" does not mean you can make up whatever you want.

The only thing we can agree on is that "thought agreement" means that you can't make up whatever you want :-)

[pdonis]

"Thought experiments" that allow you to make up whatever you want are pointless, because you can also make up whatever answer you want. So the "thought experiment" tells you nothing.

As actual physicists actually use thought experiments, they cannot make up whatever they want. Thought experiments involve taking a known consistent model and working out consequences of it that were not previously obvious or well known, and seeing where that leads. You can only do that usefully if you constrain the thought experiment by the model, i.e., if you do not allow yourself to make up whatever you want.

Since the discussion here is about an article on physics, it seems appropriate to treat proposed thought experiments the way actual physicists would treat them. That is what I have been doing.

[faangsticle]

Like I said, you can't.

[pdonis]

Anyone who wants to do physics instead of just making stuff up can't.