Dear Courtney Seligman,
Is it true that the Universe (rather, all the matter in the Universe) used to be, at its early epochs, litteraly a cloud of smoke?
I suppose it would depend upon what you mean by a cloud of smoke. Very early on, the 'matter' in the Universe consisted of particles of such high energy that we can't imagine what they were like, or what their properties were (there are various theories, but I wouldn't count on any of them being correct, without better information than we currently have). As the Universe (very rapidly) expanded, it cooled off, and those high-energy particles transformed into quarks and similar sub-atomic particles, with which we are more familiar. And at a (very slightly) later date, and a still lower temperature, those particles combined into the nuclei of hydrogen atoms, and similar "normal" sub-atomic particles.
All of this took place in a very short time -- perhaps just a few seconds -- but there was then a longer period, during which a small fraction of the hydrogen nuclei combined to form helium nuclei. As a result, about 1/4 of the mass (and about 10% of the nuclear particles) were turned into helium, while about 3/4 of the mass (and about 90% of the nuclear particles) remained as hydrogen.
It took a long time after the end of this period of nucleosynthesis before the matter was cool enough to form normal atoms. And it was quite a while longer (several hundred thousand years), before temperatures were low enough for gravitational and electromagnetic forces to start pulling things into clumps, which eventually became stars and galaxies.
So, for quite a while, early on, there was a "sea" of relatively simple particles, of very high energy, with no atoms, molecules, or any other complex structures. And if this satisfies your definition of smoke, then yes, that is what the Universe would have been like. But it wasn't smoke in any sense that we would normally mean that nowadays, as the molecules which make up normal smoke are relatively complex, and involve atoms which did not exist until after the first generation of stars lived out their lives, died, and blew themselves to smithereens.