The first law of thermodynamics states that energy cannot be created. If that's the case, how did the universe come into existence? I mean, doesn't that require energy to be created?
Excuse my ignorance if this question seems a bit idiotic. I haven't read much in thermodynamics, hence my lack of understanding.
It is not obvious that the universe did not exist before some moment in time.
Stephen Hawking tried to answer that question in his book "A Brief History of Time". His answer is based on the uncertainty principle:
$$\Delta E\Delta t\geq \frac{\hbar}{2}$$
If you take that the total variance of energy of the universe to be $\Delta E=0$, then, according to this principle, you can have $\Delta t\rightarrow\infty$ and then, the universe can exist for an indefinite amount of time. The stated fact is that the total amount of energy of the universe is exactly $0$. The reason is that matter has "positive" energy from it's mass ($E=mc^2$) which is exactly balanced by "negative" binding energy (electrons in an atom, atoms in molecules, planet orbiting stars, stars clusters, galaxies, galaxies clusters, superclusters, etc.). Thus, the universe would have a total amount of energy equals to $0$.
To answer your question about the "creation of energy": it is sufficient to say that in the quantum mechanics realm, it is perfectly allowed to "borrow" energy from nothing. As long as the time when the energy is borrowed does not violate the uncertainty principle. This is a real effect that leads to spontaneous creation of particle-antiparticle pairs which have (or may have) a measurable effect (lamb shift, Hawking radiation, casimir effect, spontaneous emissions, etc.). These particles are also called "virtual particles" as they do not exist freely and cannot be measured directly. Thus, according to Hawking, the Universe could have spawned from such a quantum fluctuation as long as the total energy borrowed is $0$.
