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Fine-tuning of constants in the standard model is an acknowledged mainstream physical question and not an eccentric one.

Looking at this carefully what one is saying is why do the parameters of this model the values they are. The anthropic principle says that they are what they are so that life can evolve. Of course they may not be a unique point in parameter space where this happens.

But why restrict change to constants? Are other parts of the model not changeable?

There is at least two that are mainstream: The dimension of space, the nature of point particles - perhaps they are not points and have either length or volume. Both of these changes are seen in string theory.

The jury is still out as to whether string theory was a credible alternative to the standard model. But it certainly did have the credibility to keep a lot of physicists working for sometime to make the theory fully credible.

But why stop there - are there not other parts of the theory we can change? That is we are fundamentally changing the nature of the laws themselves.

Purely speculatively, we could envisage a whole class of theories of modified physical laws forming a geometry with curvature, and our theory are extremal point of the curvature.

This means that the range of possible theories is incredibly vast.

Is it possible to envisage a universe whose laws are completely different to ours (where life does arise)? It seems to me that in theory this is possible, but in practise we can only consider deformations of our current laws only - as we could never theorise about the consequences of those laws. Is this correct.

  • You can definitely reason about universes with entirely different physical constants, at least and then make evolutionary arguments to explain why ours has the constants it does. However, it is easy to confuse your model of the world with the world when you do this and physicists are prone to this mistake. – Artem Kaznatcheev May 29 '13 at 15:55
  • If we define "life" only in terms of our models that describe our universe as we theorise it, than by definition, we cannot have any other universes that would host "life". If you can come up with a flexible definition of life, then, the task would be to prove that, despite its general definition, only our universe's laws would allow life. If, at least, uniqueness would be proven to be not-provable, then there is room for other universes hosting life. On the positive side, one can prove existence by giving examples (via,say, withsimulation) of alternate laws leading to "defined" forms of life. – mami May 29 '13 at 22:40
  • You should consult this book: John D. Barrow, Frank J. Tipler: The Anthropic Cosmological Principle, which contains a wealth of relevant (also quantitative) information. – Drux Sep 22 '13 at 17:32
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That's a big question.

I've asked tough questions that required 'soft' [read: speculative; non-quantitative] answers on physics.se, and I received helpful replies.

That aside, I recently wondered whether it were feasible for a human to conceive of a universe with a set of natural laws that were completely and essentially different than our universe's natural laws. Presently, I lean toward believing that it is not feasible for a human to do so:

  • Hume postulated that a human's imagination is his ability to combine things he has observed. If that's true, then it may not be possible for us to think of a universe guided by different natural laws. Although, if we assume that our reasonable [read: mathematical / logical] methods of thinking can be applied to at least one other universe, then I can imagine how we might come across a set of self-consistent rules that could govern another universe (a very long session of trial and error, for instance).
  • If you conceive of self consistent sets as a way to model possible universes, then I think you could also conceive of Euclid's axioms of geometry as a model of the forms that are possible in our universe. Then, consider that mathematicians have discovered sets of self-consistent non-euclidean geometric axioms that allow for different forms than Euclid's axioms allowed. The existence of these non-euclidean sets suggests that it is possible that another universe contains a set of natural laws that are different than the set of natural laws our universe contains.
  • It's also worth considering hyperbolic geometry, the first non-euclidean geometry. At first, (I believe) it was thought (by Gauss and other cognitive powerhouses) that hyperbolic geometry represented a discrete non-euclidean set of geometric axioms. However, it was later proven that the axioms of hyperbolic geometry were 'equiconsistent' with the axioms of euclidean geometry. More specifically, the axioms of hyperbolic geometry just described how forms would look to an observer positioned within a sphere, observing forms cast on the inner surface of the sphere. We know that such a scenario is consistent with the axioms of euclidean geometry because we know that, in our universe, shapes can be cast on the inner surface of spheres. Therefore, the axioms of hyperbolic geometry and Euclidean geometry are not necessarily discrete. So, hyperbolic geometry serves as evidence that, to even the most powerful minds, a distinct self-consistent set can appear to be a logically possible discrete universe, when, in fact, it is not truly discrete.
  • it's axiomatic that as one reduces the number of constraints in a consideration, its number of possibilities increases. If you went as far as to say that the laws that govern the other universe do not need to be compatible with our faculties of reason, then you will have cast away all conceivable constraints - including the requirement of conceivability itself. But if you did that, and if you had to do that to allow for the existence of a universe that contained a discrete set of natural laws, then you could say nothing of that universe, since (meaningfully) speaking of a thing requires conceiving of it, and if you could conceive of it, then you wouldn't have needed to shed the requirement that it must be conceivable.

In sum, I tend toward believing that it is not feasible to conceive of a universe that has a set of natural laws that are different than the natural laws our universe has.

Then again, Stephen Hawking, once speculated that the universe was created by another universe that had universe-creating properties and whose properties did not require it be created. So I'm hesitant to say that my take is more likely to be right than his is.

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    Thanks Gugg. I was hoping someone would ask me to defend my honesty today. – Hal May 29 '13 at 18:45
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The answer to your question is "yes we can" develop or conceive of universes with completely separate laws. However, any such speculations are limited in our understanding of how the fine details would work out.

Just look at how bad we are, generally, of understanding even the effects of our own universe most of the time without oodles of data and years, if not generations, of research. For example, look at the historical question of what would happen to man in zero-gravity and space. The vast majority of scientists (who were not science-fiction writers, anyway) believed that man could not survive space. These were the top scientific minds of the time. We had to actually experience it and get some data before we were able to fine-tune our understanding of all the effects.


Some possible examples of alternate universes

Consider all the science-fiction and fantasy literature that's been written. There must be hundreds, if not thousands, of alternate and parallel universes that have been imagined by humankind and recorded in one adventure story or another. Now, granted, the vast majority of those are a 'subtle variation' on our existing universe - typically with some kind of magic possible, different kind of intelligent lifeforms (think Middle-earth, Star Trek, etc.). But I have run across some truly unique ideas of alternate realities - for example the fractal universe created by Piers Anthony (the book is Fractal Mode). While life is roughly the same, the entire geometry of the universe is based on fractals rather than normal 3-d geometry.

I believe that the most unique alternate realties are based on mathematical discoveries. For example, non-euclidean geometry was completely developed prior to understanding that it is, indeed applicable to our world (it can be used to determine the shortest flight on a globe rather than on a flat surface, as an example). The point is not that it ended up being an alternate universe, but it was a set of rules that we were able to develop without any understanding of how it applied to our known reality. Mathematical reasoning and logic can allow us a starting point of being able to prove or disprove how things might work under an alternate set of laws without having to experience it first.

Another example would be the many different multiverse theories that have arisen from mathematical modeling. For example, take string theory - it may or may not exist in reality, but we can explore what the extra 6 or 7 dimensions are without having to empirically test or understand them through using a purely mathematical/logical approach.

And I actually like the example from Bulat's answer - the worlds that can be (and, in fact, are) created within a PC - not virtual reality worlds, per se, which just model our universe, but at world of information with no true 3-D space - perhaps with time though. Other dimensions are certainly present if you devel into it, and life is certainly conceivable (if not already proven to be possible) within that realm.


Final Thoughts

I think the core of your question though is whether we can ever have a true understanding of how such a theoretical universe would truly operate. My answer would be mostly no. We would primarily just be guessing and many guesses would be miles off the mark if history is any guide.

Could we have true insights about some of them, some of the time - sure! But just as we can interpolate data much more accurately than extrapolate data - when we have a completely new theory there are often huge disagreements on the real ramifications because we don't even have enough data to even extrapolate! So in that sense, I would say you are partially correct - with no experimental basis to gather any kind of empirical data on a newly conceived universe, we might guess correctly in some aspects how it works, but we could never know for sure. We might be able to simulate some of them - but then simulations always are only as good as their base assumptions and rules for building the simulation.

I would say that as our computational capabilities expand through technology, we gain more and more ability to simulate complex multi-variate systems, and that can only increase our ability to truly "create" such alternate universes, at least in a small-scale, model form. This may give us some basis for real experimentation/investigation into some such alternate realities. This is especially true if they arise from purely mathematical constructs.

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i think that we are already have Artificial Universe - one existing inside computers. this universe is all about processing information so it's very dissimilar to the physical one. it's easy to prove that Life can exist there - as far as you believe in Physics that describes "Nature laws", you can emulate them inside computers too (of course emulation will just recreate physical universe inside computer, but it's just "worst case" proof)

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