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by thx-2718 1109 days ago
Obviously the thought experiment requires energy that doesn't 'exist' or doesn't have meaning in the sense that it could happen literally. It's a what-if and that does have a number and that does have meaning.

So there is meaning to the previous persons question which is what the thought experiments were meant to show but obviously that's something you can't imagine.
1 comments
pdonis 1109 days ago
> Obviously the thought experiment requires energy that doesn't 'exist'

No, it requires energy to be added to the system from outside the system. Which is precisely what you cannot do with the universe as a whole. That's what makes such thought experiments meaningless for the universe as a whole.

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thx-2718 1109 days ago
> it requires energy to be added to the system from outside the system.

Yes that is exactly what energy that doesn't 'exist' means.

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pdonis 1109 days ago
But you can't do that for the universe as a whole. Asking what would be the case if you could is meaningless; it's like asking what would be the case if 2 + 2 were 5. No consistent model exists of such a situation, so the question is meaningless.
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thx-2718 1109 days ago
> you can't do that for the universe as a whole.

Yes correct, that's why that energy doesn't 'exist' because it's outside of the universe.

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pdonis 1109 days ago
There is no such thing as "outside of the universe".

If you disagree, please show me the consistent model on which your scenario is based.

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thx-2718 1109 days ago
> There is no such thing as "outside of the universe".

Yes that's correct in the general accepted sense for the term 'universe'.

Edit: question if the initial thought experiment was posed as 'observable universe' would it make a difference to you?

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faangsticle 1109 days ago
Now take off your nitpick hat and ignore that detail. Its what makes it a thought experiment.
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pdonis 1109 days ago
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.
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faangsticle 1109 days ago
Yes, that's what a thought experiment is. A cat can't be alive and death at the same time, either.
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pdonis 1109 days ago
> 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.

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faangsticle 1109 days ago
> "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 :-)

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