Anthropic principle

[Perpetual Student]

To be more explicit about what I meant, for the constants to be fine tuned it must be that they could have been something else. Otherwise there is no meaning to saying they are tuned.
Then, if it is possible for them to be something else, you have to assume that that isn't the case somewhere else; that alternative universes don't exist. Otherwise the anthropic principle provides the answer.Then, and only then, does the fine tuning argument make any sense. But to back it up "you" really need to show that of all the possible sets of constants that describe theoretical universes, only a very tiny fraction of them could harbour intelligent life. But people don't do that. They just pick a single constant in our Universe and change it slightly. And go "ooh look, no more us".

What?

 

[Tubbythin]

What?

For any argument of fine-tuning to make sense you have to assume that the constants could have been other than what they are, but at the same time that there are no other Universes. Because, if there are multiple universes its hardly surprising that we find ourselves in one in which human life is possible.

 

[sol invictus]

For any argument of fine-tuning to make sense you have to assume that the constants could have been other than what they are, but at the same time that there are no other Universes. Because, if there are multiple universes its hardly surprising that we find ourselves in one in which human life is possible.

I'm not sure the rest of us know what you mean by "argument of fine-tuning". In models in which other regions of the universe with different values of the constants exist, one can observe that ours is fine-tuned for our form of life, and then explain that tuning with the anthropic principle. When this is discussed in the physics literature that's generally the idea.

 

[Tubbythin]

I'm not sure the rest of us know what you mean by "argument of fine-tuning". In models in which other regions of the universe with different values of the constants exist, one can observe that ours is fine-tuned for our form of life, and then explain that tuning with the anthropic principle. When this is discussed in the physics literature that's generally the idea.

I think I agree with the above, although I only realised there was quite so many versions of the anthropic principle recently.
The problem may be that I'm used to fine-tuning arguments coming from creationists. Along the lines of "if things were slightly different we wouldn't be here, therefore God must have selected the constants so that we could exist".
To me, saying the universe is fine-tuned is at least partly backwards but also rather selective. A hypothetical universe is created in which one (and usually only one) of the constants is changed (usually only slightly) and everything falls apart. But if we can change one constant, why can we not change a second to compensate, or all of them, or add a new one? Its a hypothetical alternative universe after all.
I guess I'm saying that the argument to show the Universe is finely tuned has to be tuned itself otherwise it falls apart.

Any clearer yet?

 

[sol invictus]

To me, saying the universe is fine-tuned is at least partly backwards but also rather selective. A hypothetical universe is created in which one (and usually only one) of the constants is changed (usually only slightly) and everything falls apart. But if we can change one constant, why can we not change a second to compensate, or all of them, or add a new one? Its a hypothetical alternative universe after all.

Sure - that's a significant problem. And even if one could do better, e.g. by varying over all known constants, there's the problem of measure: if you want to compute the fraction of those universes which could sustain life, how do you define volume? Is it the fine structure constant that's the right thing to vary, or its square, or its log, or its exponential?

So it's very tricky - but problems on the forefront of physics are always like that, or they would already be understood.