One often hears how "energy and matter are interchangeable" etc ... and I understand the part where stars fuse hydrogen into energy, bombs fuse plutonium into disturbingly loud bangs, etc ...

But I'm having a brain-lock at the moment, so can someone help here?

Could anyone give me a few real-world examples of energy spontaneously becoming matter?

I started to tell someone that the Big Bang was an example of that, but then I thought: well, can anyone back that up with anything but assumption and "theory" ???

We cannot say what form of energy existed pre-Big Bang until we work out the Theory Of Everything, right? No one understands how the cosmic forces and energies were unified, so we cannot use Big Bang as an example.

Is Vacuum Energy an example of matter being created from nothing, or is it just energy (and the example demands actual matter, some "we can build something out of this and use it as a paperweight" sort of matter)

So ... are energy and matter interchangeable in the real world, or does it just work nicely on a blackboard equation ... but doesn't seem to actually happen in the real world?

Anyone gots examples of energy-becomes-matter ???