 This talk will cover two concurrent and independent works, one by myself and the other by Cao and Zhu. These works provide a better understanding for the feasibility of secure hash functions in a quantum world. Let's start with the classical notion of collision resistance. Here we have a hash function h whose outputs are shorter than their inputs. This means that there must be many colliding inputs to h. However, classical collision resistance assumes that despite existing it is infeasible for any efficient adversary to actually find a collision. This property of compressing the input while having computationally hidden collisions has tremendous applications throughout cryptography, making collision resistance one of the core cryptographic building blocks. When moving to quantum, it turns out that the obvious way to divine security is insufficient, and that a stronger notion called collapsing is required in many use cases. The rough idea is that measuring the output of the hash function on a quantum superposition of inputs should be indistinguishable from measuring the input superposition. This is widely regarded now as the right notion of security for post-quantum hash functions. Unfortunately, very little is known about achieving collapsing, and there's a frustratingly wide gap between the non-positive and negative results. The only positive result in the standard model requires the learning with errors assumption or LWE, and uses the fact that LWE gives a lossy function. On the other hand, the negative results are all in idealized models or rely on untested computational assumptions. On one hand, it could be that the only standard model collapsing hash function are those based on LWE, or it could just as easily be that all standard model hash functions based on post-quantum tools are collapsing. This talk will be about a new technique for proving the collapsing property of hash functions as explored concurrently in these two independent works. The gist is that we can now build collapsing hashes from essentially all the same tools that are currently known to give collision resistance, as long as the tools are post-quantum. Note that while the tools are the same, in order to prove collapsing, the construction changes. Please see the talk for details.