The scientific evidence
One area where we can test the two religions is in the area of cosmology. What does each religion claim about cosmology?
First, let’s take a look at what the founder of Mormonism, Joseph Smith, believes about the origin of the universe:
“The elements are eternal. That which had a beggining will surely have an end; take a ring, it is without beggining or end – cut it for a beggining place and at the same time you have an ending place.” (“Scriptural Teachings of the Prophet Joseph Smith”, p. 205)
“Now, the word create came from the word baurau which does not mean to create out of nothing; it means to organize; the same as a man would organize materials and build a ship. Hence, we infer that God had materials to organize the world out of chaos – chaotic matter, which is element, and in which dwells all the glory. Element had an existance from the time he had. The pure principles of element are principles which can never be destroyed; they may be organized and re-organized, but not destroyed. They had no beggining, and can have no end.”
(“Scriptural Teachings of the Prophet Joseph Smith”, p. 395)
A Mormon scholar named Blake Ostler summarizes the Mormon view in a Mormon theological journal:
“In contrast to the self-sufficient and solitary absolute who creates ex nihilo (out of nothing), the Mormon God did not bring into being the ultimate constituents of the cosmos — neither its fundamental matter nor the space/time matrix which defines it. Hence, unlike the Necessary Being of classical theology who alone could not not exist and on which all else is contingent for existence, the personal God of Mormonism confronts uncreated realities which exist of metaphysical necessity. Such realities include inherently self-directing selves (intelligences), primordial elements (mass/energy), the natural laws which structure reality, and moral principles grounded in the intrinsic value of selves and the requirements for growth and happiness.” (Blake Ostler, “The Mormon Concept of God,” Dialogue: A Journal of Mormon Thought 17 (Summer 1984):65-93)
So, Mormons believe in an eternally existing universe, such that matter was never created out of nothing, and will never be destroyed.
What do the best Christian theologians believe about the origin of the universe?
“By what means did you make heaven and earth? What tool did you use for this vast work? You did not work as a human craftsman does, making one thing out of something else as his mind directs… Nor did you have in your hand any matter from which you could make heaven and earth, for where could you have obtained matter which you had not yet created, in order to use it as material for making something else? It must therefore be that you spoke and they were made. In your Word you created them.” (Augustine, Confessions 11.5.7.)
“As said above (Question 44, Article 2), we must consider not only the emanation of a particular being from a particular agent, but also the emanation of all being from the universal cause, which is God; and this emanation we designate by the name of creation. Now what proceeds by particular emanation, is not presupposed to that emanation; as when a man is generated, he was not before, but man is made from “not-man,” and white from “not-white.” Hence if the emanation of the whole universal being from the first principle be considered, it is impossible that any being should be presupposed before this emanation. For nothing is the same as no being. Therefore as the generation of a man is from the “not-being” which is “not-man,” so creation, which is the emanation of all being, is from the “not-being” which is “nothing”.” (Summa Theologica, part 1, question 45)
“Let this, then, be maintained in the first place, that the world is not eternal, but was created by God.” (John Calvin, Genesis)
“We firmly believe and simply confess that there is only one true God … the Creator of all things visible and invisible, spiritual and corporeal; who from the very beginning of time by His omnipotent power created out of nothing both the spiritual beings and the corporeal.” (The Fourth Lateran Council of 1215)
So who is right? Has the universe always existed or did it come into being out of nothing?
Breaking the tie
To break the tie, we must use the ordinary tools of investigation – logic, science, historical methods, and so on. Let’s use science this time.
The Big Bang cosmology is the most widely accepted cosmology of the day. It is based on several lines of evidence, and is broadly compatible with Genesis. It denies the past eternality of the universe. This peer-reviewed paper in an astrophysics journal explains. (full text here)
The standard Big Bang model thus describes a universe which is not eternal in the past, but which came into being a finite time ago. Moreover,–and this deserves underscoring–the origin it posits is an absolute origin ex nihilo. For not only all matter and energy, but space and time themselves come into being at the initial cosmological singularity. As Barrow and Tipler emphasize, “At this singularity, space and time came into existence; literally nothing existed before the singularity, so, if the Universe originated at such a singularity, we would truly have a creation ex nihilo.“
[...]On such a model the universe originates ex nihilo in the sense that at the initial singularity it is true that There is no earlier space-time point or it is false that Something existed prior to the singularity.
Christian cosmology requires such a creation out of nothing, but this is clearly incompatible with what Mormons believe about the universe. The claims about the universe made by the two religions are in disagreement, and we can test empirically to see who is right, using science.
The historical evidence
You can find other disagreements between Christianity and Mormonism, if you are not so busy putting on make-up like politicians and journalists are. For example, Christianity is monotheistic (one God) and Mormonism is polytheistic (many gods). That means Mormonism is more like Hinduism than it is like Christianity – Mormonism and Hinduism even agree on the eternally oscillating universe. You can read all about it, with citations from Mormon scholars, in this article, authored by Baylor University professor Francis J. Beckwith. Or you could take a look at the history of Mormonism, and see if the claims made in the religious texts of Mormonism are historical. Or you could take a look at the prophetic claims of the founder of Mormonism and see if they were accurate.
Here’s an examination of the historical basis for the Mormon Scriptures, for example:
This is how responsible people evaluate religions to see whether they are all the same as the others, and, more importantly, if one is true. The point of religion is not to make people feel good, or to make them have a sense of community. The point of religion is to know how we got here, where we are going, and what we are supposed to be doing – as matters of fact.
As long as you don’t assume, before doing any research, that all religions are the same, and that all of their claims are equally untestable, then you can actually investigate things and come to some conclusions. Investigating is good, but watching debates with different views that feature public, testable evidence is also a good idea. The important thing is that you are serious about evaluating the testable claims of different religions, and that you don’t assume that choosing a religion is just like taste in clothes or taste in food, which varies by time and place and is really not making objective propositional claims about reality, instead of subjective claims about individual tastes and preferences. Just because you were born into a country that believed that the Earth was flat (or round) that wouldn’t take away the obligation on you to test those views and go looking at other views using the tools of logic, science and historical analysis.