If you read up on zero-point energy (sometimes called 'vacuum' energy) you'll see that matter can actually appear as if from 'nothing'- subatomic particles and their anti-particle partners are continuously appearing from the quantum substrate of vacuum space - they exist for a infintessimally short period of time before annihilating each other, and thus appearing, then disappearing from the total sum of mass/energy of the universe (i.e. zero net gain) - however, sometimes the annihilations do not occur: a good example is Hawking radiation; around the event horizon (or Swarzchild radius) of a black hole (right on the very edge) matter and anti-matter particles 'pop' out of the quantum substrate, and sometimes the anti-particle of the pair crosses the event-horizon of the black hole and is lost (nothing can escape from a black hole once it has crossed the event horizon) - this leaves the matter particle of the matter/anti-matter pair un-annihilated and left to lead an existence as a 'real' particle in space (there is no matching anti-matter particle to annihilate it) - this effect has been observed as radiation energy escaping a black-hole - and is why black-holes are theorised to 'cool' over a very long period, eventually leading to their ultimate demise - black-holes 'lose' energy by swallowing anti-matter, and the 'real' matter appears as if it emanates from the black holes event boundary in the form of radiation energy (energy and matter are intrinsically linked - at extremely high temperatures they are actually the same thing)They cannot say that the matter made itself because this would be a direct violation of the 1st law of thermodynamics. We know matter cannot make itself, so where did it come from.
Physicists used to say "there's no such thing as a free lunch" (in line with the 1st law of thermodynamics) .... nowadays they know that there actually can be!
The world of quantum mechanics and quantum electro-dynamics which underpins our entire universe is a very strange world indeed!