In the early 1960's, the previous co-contender for the title of "The most successful explanation of everything" by a theory of the universe would have been the Steady State theory. This theory, proposed by Fred Hoyle, declared that the universe was constantly expanding. To compensate, it was continually adding the necessary hydrogen through spontaneous creation. Using this steady-state method, the relative size and appearance of the universe would have remained constant. The steady state theory assumed that the universe always looked the same as it does today, and it would always continue to look the same in the future.
The steady state theory did successfully explain the observed expansion of the universe. From the standpoint of the law of conservation of energy, it was not esoterically pleasing to think that matter had to be created from nothing, continuously, to expand and fill the vacuum or void created by the expansion. The steady state theory required that only a very small amount of extra matter would be needed each year, something on the order of one hydrogen atom per cubic light year, to maintain the current appearance of the universe.
In the early to mid '60's, the steady state theory was considered to be in contention for the "Best theory", competing with the Big-Bang. One of the most attractive of the proposed benefits was that the universe would not have need for a theoretically complicated ending or a beginning. The portion of the Big-Bang theory that made some scientists cringe was the requirement that everything we see now, somehow came instantly into being, without any prior existence.
The Steady State theory met it's doom, however, when the very smooth, and extremely redshifted remnant of what was thought to be the Big Bang radiation was detected. This "black body" type of radiation was detected by Arno and Penzias, two employees of Bell Telephone.
Arno and Penzias were investigating microwave transmission and reception. When a very large, and very sensitive antenna was aimed anywhere in the sky, they were surprised to learn that there was a uniform source of microwave noise coming from every direction. After resoldering and recalibrating all of their equipment, and with no improvement in the amount of noise they encountered, Arno & Penzias at last accepted that this noise was extraterrestrial in origin.
When a team of astronomers searched for just this type of radiation, they were surprised that it had been detected several years prior to their search by someone who wasn't looking for it. This radiation, which occurs with it's peak at about 2.7 K was later suspected of being the time-weakened, long-sought, theoretically-predicted remnant of the Big Bang explosion.
Once this radiation from the sky was verified by other teams of astronomers; scientists and theorists also took note of it. This one observation of the red-shifted, incredibly smooth background energy effectively knocked out the Steady State theory from cosmological contention.
The universe was not so kind or considerate to allow an explanation of the universe to be so simple. On the other hand, now we do not have to contend with the universe sneaking hydrogen atoms into existence throughout all of eternity. This would have proved frightfully demeaning and demoralizing to the rule of Conservation of Energy.