Final answer:
The statement is true; in the quark era of the early universe, extremely high temperatures and densities allowed for the conversion between matter and energy, embodying Einstein's famous equation E=mc².
Step-by-step explanation:
The statement that in the quark era, it was so hot that matter and energy were practically the same stuff is true. During the early universe, specifically in the quark era, the temperature was so high that the average kinetic energy was enough to create particles out of the radiant energy, demonstrating the equivalence of mass and energy as described by Einstein's formula E = mc². At temperatures around 10ⁱ⁵ K or energies reaching 1 TeV, phenomena such as W and Z° production occurred, marking the limits of what we currently understand about particle physics. This equivalence is a cornerstone of modern physics and is particularly evident under extreme conditions, like those during the quark era, where energy and mass interconverted with ease. This is part of the underlying principles that guide our understanding of the Big Bang and the subsequent evolution of the universe.