From <a href="https://www.schneier.com/blog/archives/2009/09/the_doghouse_cr.html" rel="nofollow">https://www.schneier.com/blog/archives/2009/09/the_doghouse_...</a><p>On brute forcing cryptographic keys using an ideal computer that uses the absolute minimum energy possible:<p><i>A typical supernova releases something like 1051 ergs. (About a hundred times as much energy would be released in the form of neutrinos, but let them go for now.) If all of this energy could be channeled into a single orgy of computation, a 219-bit counter could be cycled through all of its states.</i><p>Quantum computers won't help break cryptography because they must still consume energy to work, and even a supernova's worth of energy won't even let you <i>count</i> to 2^256, let alone actually do that many hashes.<p>The only real problem that could occur is if some weakness is found in current cryptographic standards... which while possible, seems unlikely given the massive amount of attention they've already received from incredibly smart people.<p>But, even if something like that did happen, all bitcoin would have to do is roll out a new client that fixes the problem.
No one can guarantee it. There can always be a major breakthrough that breaks the fundamental assumptions on that bitcoin is build.
For example: Quantum computers getting a main stream thing and growing exponentially in power.