According to Evgeny Morozov, there are two kinds of walls: stone walls and virtual firewalls (The Net Delusion, 2011, p. 45.). Regarding the previous one, it is hard to build, but relatively easy to destroy. A house of cards is an extreme example of it: difficult to create and easy to ruin. Opposite to it, it is relatively simple to build (to write) a firewall, but it is impossible (or, at least, almost impossible) to destroy if you don’t have a physical access to the computer which runs it. This is because both the stone wall builder and invader act on the same level: on the level where the wall itself exist. Opposite to it, a firewall attacker has to work on the level of the actual system, while the programmer creator constructs the firewall from a “higher level” or, if you prefer, from an external point. Notice that some there are “harder to ruin than to build” systems can exist in the physical reality, as well: e.g. the pro WWII French Maginot Line of a concrete fortification system is such a construction. But the two level nature of firewalls is more important from our point of view, so it shall be used as a metaphor. Applying this wall approach to our Universe, it is obvious that a house of cards world unsuitable either for life or intelligence since it is too sensitive to any disturbance: We can imagine a multiverse with continuously appearing and promptly disappearing cosmoi. This multiverse differs from ours: Edward Teller was afraid during the WWII that an exploding hydrogen bomb, because of the extremely high temperatures, would destroy the whole Earth, but we don’t have neither weapons to ruin our planet, nor our Universe even today (opposite to the alarm bells in connection with the possible dangers of the CERN’s supposed miniature, artificial black holes). Namely, the physical system of our world seems to be both intelligence and technology proof (and at least to a certain level seem to be even foolproof). It can be imaginable a universe which is vulnerable even to a relative low level technology. It was a popular belief in the cold war era that the answer for the Fermi paradox was that every alien civilization perished because of the nuclear weapons. This scenario is adaptable in a slightly modified form for a cosmic level supposing that the stability of the physics of different universes are different. Traditionally the end of a universe is interpreted as a “matter of fact” question, but from our point of view it, can be interpreted as a version of Anthropic Principle where the level of technical development is correlated with the physical laws’ strength to determine the whole universe’s fate. Of course, it is not known whether our world’s relative long existence is a result of only a stone wall style stability and it wouldn’t be too difficult to ruin this using a near-future technology. Or, we live in a firewall style world where we can act only under the level of physics. In this case we can destroy the physically existing Universe at most: Writing about Global Catastrophic Risks, Nick Bostrom and Milan Cirkovic discuss “only” the possibility of a disaster destroying “the potential of our future light cone of universe to produce intelligent… beings" (2008, p. 2–3.).
It would be even more fatal to create a super bomb–e.g. an artificial black hole–which can destroy everything but keeps intact the laws of physics. But this not the end of the possibilieties since it is imaginable that we could destroy somehow not only the physically existing Universe but the physical laws themselves too.