Cloudscape

There can be no ultimate limits in the universe, because those limits would themselves need to have a reason to be what they are. Everything has a cause, and therefore so do physical constants; if they had not, then why could they not just as well have another value? Why do physical constants have one value rather than another, if they are purely random? There is a reason, for instance, that the speed of light is 300.000 kilometers per second, rather than 400.000 or 200.000; the same counts for every other physical constant.
The fact that physical constants are fine-tuned to life means that they cannot have been predetermined before existence; they must have been determined by existing factors. If they do have a cause, however, then that cause must be changeable. We cannot assume constants to be fully constant without dispensing with causality.
Since it would be too coincidental that there would be only one universe which is fine-tuned to life, there must be many other universes, most of which are not fine-tuned; ours merely continued to evolve because of natural selection. Something must have fine-tuned its constants. If we can find out how this happened, we might change these constants within a closed system, and so even these may not pose ultimate limits.
If all things have causes, and those causes themselves have causes, then this must essentially go on in infinity; this means that causation occurs in an infinite series. Thus, throughout this series, as everything will have random causal connections with other things, it must follow that all things are causally connected in infinitely many ways, throughout the infinite series of causations.
This means that all causes can themselves be changed; this also means that with sufficient science, all things can be observed, and that with the right technology, all things can be influenced. There can simply be no one-way causation if all things are causally interconnected, and so all causes can themselves be changed.
If everything has a cause, including physical constants, this may also mean that the universe cannot be finite. If the universe would be finite, this would mean that it possesses a certain finite amount of energy.
As this amount of energy would be specific, however, it would again be the question why it would be the specific amount it is: why one amount rather than another? If there is any such finite amount, we can only suppose that this amount would be random. Even if there were a reason that it is this specific amount, that reason would itself have been determined by other specific parameters and so forth. However, if this amount is ultimately random, it follows that its determination is acausal.
All limits, like anything else, must have a cause. If a system is limited, there must be something that limits the system; but the Universe itself cannot be limited as there is nothing to limit it. There is nothing outside the Universe to limit it, neither was there anything before the Universe to limit it, as the Universe is all that exists.