Assertion 1.2: Big Bang theory violates the first law of thermodynamics.
Analysis:
The first law of thermodynamics says that the total energy of a closed system must remain constant over time. Thus, for a theory about the universe to violate the first law of thermodynamics, the theory must stipulate two points in time (call them T and T*) such that the total energy of the universe at T and the total energy of the universe at T* do not match one another. The creationist argument implicitly assumed that Big Bang theory stipulates a time t < prior to the origin of the universe, at which time there was no energy at all (because the universe did not exist).
We can consider this problem from both the perspective of general relativity alone and the perspective of quantum gravity. Readers are advised that the discussion in section 1.1 will provide a good background.
(i) If we use general relativity alone, then the origin of the universe is also the origin of spacetime. That means that on this view there can be no such thing as a time t < 0. But if there is no time t < 0 when there was no energy, then the presence of any amount of energy at t = 0 cannot violate the first law of thermodynamics.
On a personal note, I want to interject that it is very odd that creationists would think that virtually the entire physics community would unwittingly come to accept a theory that violates a fundamental law of nature they would all obviously be very familiar with. This is one of those instances in which creationist arrogance comes to fore, when they actually believe themselves to be the only ones who have managed to avoid such an elementary error. Unfortunately, such arrogance appears to be an ongoing theme in the world of creationism. Is it any wonder that scientists so easily lose their patience?
(ii) If we add quantum mechanics to the picture, then we are faced with Lee Smolin's three options covered in section 1.1: (A) there is still a first moment in time; (B) the universe continues indefinitely into the past; (C) time breaks down in the very early universe. Scenario A does not violate the first law of thermodynamics for the reasons discussed above. Scenario B does not violate the first law of thermodynamics as long as the total energy of the universe remains constant at all times; unsurprisingly, models that actually fall under scenario B respect the first law of thermodynamics. I am still unclear about exactly how scenario C is supposed to work, but if there is no succession of time in the early the universe, then it would seem that the first law of thermodynamics cannot apply to the early universe, either.
(iii) If the universe came from something else (if, for instance, it started as a region of spacetime pinching off from a black hole in another spacetime, as proposed by Smolin 1997) then there is still no conflict with the first law of thermodynamics, since the universe was not always a closed system, and would have inherited its initial energy from whatever it came from.
(iv) Even proposals like that of Tryon (1973), that has the universe appearing spontaneously in an empty spacetime, would not violate the first law of thermodynamics if the universe has an overall energy of zero. Strange as it may sound for the universe to have zero total energy, it may be true: the gravitational energy of the universe is a negative quantity, which some cosmologists believe may turn out to balance the rest of the energy in the universe, leaving a net balance of zero energy.
References
Leslie J (ed). 1998. Modern Cosmology and Philosophy. Amherst, NY: Prometheus.
Smolin L. 1997. The Life of the Cosmos. Oxford: Oxford University Press.
Tryon EP. 1973. Is the universe a vacuum fluctuation? pp. 222-225 in Leslie 1998.