Relativistic time dilation formula:
, where tS is Stationary Time, t' is relativistic time, v = subject's velocity, c = speed of light = 3 x 108 m/s
The theory of special relativity states that time is not fixed but rather relative to the speed of light. As an object moves closer to the speed of light, time slows down from their perspective, alongside other interesting effects. For example, someone traveling at the 0.8 times the speed of light for 180 seconds (from his perspective) will find that 300 seconds has passed in real life (i.e. the stationary observer). Time around him seems to slow down such that 1 of his seconds is longer than the 1 second of the observer. If he moves even faster, time around him will slow more and more. When he accelerates to 2.999 x 108 m/s, more than 0.99 times the speed of light, only about 7.7 seconds has passed while 300 seconds have passed for the observer.
Albert Einstein's theories of relativity (both special and general) show that time is not a fixed quality. Furthermore, if time is not a fixed quality, then perhaps time is a dimension just like our three-dimensional space (thus 4-dimensional space-time). Regardless of whether time is a dimension or not, I would like to look here at the implications of Special Relativity on the issue of eternity.
According to the relativistic formula of time dilation, the faster the speed of the object, the slower time flows around the object. Due to the Lorentz transformation, it is impossible for any object with mass to reach light speed, since any object approaching light speed will approach infinite mass and will require infinite energy to do so. But suppose an object were to reach light speed. What happens then? Well, the object will have infinite mass so it will collapse into a black hole. But as the object reaches light speed, the flow of time around the object stops. The object at the speed of light has reached timelessness, where t' equals 0. Time as perceived by the object has essentially stopped, and he can "travel" whatever distance he desires without time moving at all.
What does this have to do with movement and eternity? Well, actions involves movements, which means there is change over time. Timelessness and spontaneity in the physical world occurs for objects at the speed of light. However, if the object is timeless, then the object is stuck at that time (frozen in time). For any action done to take effect, the object has to exit the state of timelessness.
To speak of God as being "timeless" therefore is to create a deistic god, where the world is wound up and all the actions began at the singularity that is the beginning of the world. Something that is eternally timeless can only interact with time at the point of singularity, and anything that becomes timeless at time t1 can only interact with the world at time t1. Surely a god who is timeless, if he is to preserve timelessness, cannot cease being timeless even for an instant. Therefore, the only logical conclusion for a god who is timeless is that he does not interact with the world except to wind it up. Providence in this model is merely the unfolding of the decrees inbuilt within creation. There cannot be miracles, except the miracles that have been decreed to be worked out from creation. God cannot hear prayers, for a timeless god cannot be in time.
Needless to say, this is not the God of the Bible. Thus, the biblical God cannot be timeless, or at least he cannot be timeless in his interaction with the world. Timelessness can only be attributed to God's essence since His essence does not deal with us, but it cannot be attributed to God in His three persons, since Father, Son, and Spirit interacts with the world and with us. It is because of this that we must reject the classical theistic view of timelessness. God is eternal yes, and eternal time in his essence can be said to be "timeless." But God in His persons is not timeless neither does that even make sense. We are not supposed to be deists after all! The God of the Bible is portrayed as one who hears our prayers and acts on behalf of His people, whereas in a deistic system one can only say that this god began a process at creation to seemingly answer prayer even before the prayer has been uttered, and thus give an illusion that prayer has been answered.
It is because of this that God's eternity in His persons is everlasting "time," and not "timelessness." The Son in everlasting "time," in eternity past, submits to the Father in the Pactum Salutis to save His people. "Time" did not begin for God with the Incarnation, but it has always been present, as long and as eternal as the persons of the Trinity have their fellowship one with another.