What an experience it would be to have a time machine! Just imagine traveling into the future, seeing technological marvels that have yet to be invented, and meeting our distant descendants. What will the world be like in 50 years? Or 100? Consider visiting the earth before the global Flood or encountering a living dinosaur. What would it be like to meet the apostle Paul, Moses, Noah, or Adam? And what Christian could pass up the opportunity to talk with Christ during His earthly ministry?
Science fiction abounds with time-travel stories. This perhaps reveals a fundamental aspect of human nature: We are fascinated with time. Animals live in the moment, but humans are made in God’s image. We have a sense of eternity that God has placed in our hearts (Ecclesiastes 3:11), so it’s not surprising that adventures through time captivate our imaginations. But is time travel really possible?
As is often the case, truth turns out to be stranger than fiction. Scientists have discovered that time travel is indeed possible. Furthermore, time travel has even been documented. But lest anyone have fanciful hopes of traveling through time in a flying DeLorean, we must understand that real time travel is far more limited than the unrestrained freedom enjoyed by characters of science fiction.
First, it is limited in direction. It seems that time travel into the future is permitted, whereas time travel into the past is not. In principle, it’s possible to send a person forward 100 years or more to see his distant descendants. However, he could not come back.
Second, time travel into the future is limited in degree by our current technological level. While it is theoretically possible to send a human into the distant future by traveling close to the speed of light, such speeds are far beyond the limits of our current technology. The velocity necessary for noticeable time travel requires energy that drastically exceeds what we can currently produce. For the moment, we can only accelerate subatomic particles through time in any noticeable way. So, how does this work?
The Physics of Einstein
In a very real sense, all of us travel through time. Simply observing the ticks of a clock shows that we move from one second to the next. We cannot stop or reverse our passage. It would seem at first glance that we cannot accelerate our passage by any means. We might subjectively feel that time passes faster or slower, leading to the expression “time flies when you’re having fun,” but our watch confirms that the actual passage of time is utterly unaffected by our emotional state. Our intuition suggests that the forward progression of time is absolute and unaffected by anything we do. But our intuition is utterly wrong.
The famous physicist Albert Einstein discovered that the passage of time is affected by motion. A moving clock does not tick at exactly the same rate as a stationary clock of identical construction. We don’t notice this effect in our everyday lives because the effect is miniscule at the velocities we ordinarily experience. But imagine an astronaut traveling through space at 99% the speed of light—over 660 million miles per hour. He would experience one year for every seven Earth years! That is, he would be moving through time seven times faster than observers on Earth. If he were to return in 70 (Earth) years, he would have perceived and aged only 10 years. This effect is called time dilation. It’s strange but true.
Einstein discovered this effect—but not by doing any physical experiments. He discovered it with logic and geometry. By his day, it was known that the round-trip average speed of light is the same for all observers, regardless of their motion. The only way to account for this counterintuitive phenomenon is to recognize that observers with different velocities have different measurements of time.1 Their clocks tick at different rates.2 Using logic and basic geometry, Einstein calculated how velocity affects these rates.
Physical experiments have confirmed his calculations. Moving clocks tick slower than stationary ones by exactly the rate that Einstein computed. The effect is miniscule at ordinary speeds but becomes noticeable when velocities approach the speed of light. Matter must accelerate to 14% the speed of light for a meager 1% time dilation. No wonder we don’t observe it in our everyday lives! Nonetheless, the effect has been measured by atomic clocks on airplanes.3 Furthermore, physicists have accelerated subatomic particles to nearly the speed of light, at which the effects of time dilation become quite pronounced and are easily observed.
Back in Time
If we could achieve a sufficiently high velocity, we could send a person into the distant future. However, three reasons cause us to think that time travel into the past is impossible. One is a physics reason, one is a logical reason, and one is a biblical reason.
Einstein’s equations show that if a person traveled faster than the speed of light, then he could travel back in time. The problem is that it would take an infinite amount of energy to reach the speed of light. As a mass is accelerated, it becomes more massive (“heavier”) and increasingly more difficult to accelerate. Since it takes an infinite amount of energy to accelerate a mass to the speed of light, a mass can obviously never go faster. Hence, anything with positive mass cannot go faster than light and therefore cannot go back in time.4
From logic, we expect that time travel into the past is impossible for any information-bearing system. The reason is that it could lead to contradictions—situations in which something must exist and not exist at the same time. An important rule of logic is this: Since contradictions cannot occur in reality, whatever leads to a contradiction must be false. The possibility of time travel into the past can lead to a contradiction, and thus we conclude that the possibility of time travel into the past must be false.
Several such examples have been conceived, such as the “grandfather paradox” or the “logically pernicious self-inhibitor.”5 With the first, we imagine being able to send a person back to a time before his grandparents met. It would then be possible for him to prevent his grandparents from ever meeting each other, thereby preventing their marriage and any subsequent descendants, including himself. But if he were never born, then how could he possibly travel back in time to prevent his own birth? In this situation, the man must both exist in the present (to travel back and prevent his grandparents from meeting) and not exist in the present (since his grandparents never met) at the same time and in the same way—a contradiction. And it will not solve the problem to have the man simply vanish when he prevents his grandparents from meeting. After all, if they never met, then the man could never have existed, in which case he could not have prevented them from meeting.
The Bible also seems to indicate that time travel into the past is not possible for human beings. God alone is beyond time, and hence He alone knows the future. In Isaiah 46:9-10 the Lord says, “I am God, and there is none like Me, declaring the end from the beginning, and from ancient times things that are not yet done.” Only God can say at a given time what will certainly happen at a later time. Humans can only make educated guesses. But if time travel into the past were possible, then we could simply jump back to 1970 and know with certainty what will happen over the next four-and-a-half decades. This contradicts God’s claim that He alone can declare those things that have not yet happened.
Also, in regard to His coming, Jesus said, “But of that day and hour no one knows…but My Father only.”6 But if we could travel through time, we could jump ahead to the moment of His return and then come back to the present. Then we too could know the day and hour. Of course, God is beyond time and could move a person forward or backward through time in a self-consistent way without any paradoxes. He has full knowledge of the past, present, and future. But our human ability to time travel is quite limited.
Although we cannot travel back in time, God knew that we would be curious about the past, how the universe came to be, and where it is headed. So He graciously gave us His written Word, providing us the most important details of history and glimpses of the future as well. In this respect, the Bible is much like a time machine. When we read God’s Word we are virtually transported to another time. We experience history in light of God’s plan of redemption. And the Bible even gives us a taste of the wondrous eternal state to come. We see how all of time—past, present, and future—is under God’s sovereign control.
- Einstein realized that they also have different measurements of length. Moving rulers are shorter in the direction of motion than stationary ones of identical construction. This effect is called length contraction.
- Some people have suggested that only clocks are slowed by motion, not time itself. But this seems to be a distinction without a difference. After all, what do clocks measure but the passage of time?
- Time dilation was confirmed by the Hafele-Keating experiment in 1971. Atomic clocks were placed on aircraft and flown around the world in opposite directions. When compared with each other and atomic clocks on the ground, the difference in time matched the predictions of Einstein’s theory of relativity.
Although mass cannot be accelerated to the speed of light, Einsteinian physics theoretically allows for particles to be “born” that are already moving faster than light. These hypothetical particles, called tachyons, would have an “imaginary” rest mass—the square root of a negative number. (The rest mass of a particle refers to the mass it would have if it were stationary.) This explains the particle’s seemingly strange behavior. Ordinary matter speeds up when we add kinetic energy, but tachyons would slow down. As ordinary matter would require infinite energy to be accelerated up to the speed of light, tachyons would require infinite energy to be slowed down to the speed of light. Thus, tachyons must travel faster than light, just as ordinary matter must travel slower. Although they may be theoretically permitted by Einstein, no tachyons have been discovered, and other branches of physics give us reasons to think they do not exist.
An imaginary rest mass poses no problem because tachyons are never at rest. Like time, mass is affected by motion. The faster-than-light motion of tachyons causes their total mass to always be a real number. Physics predicts that particles with a positive rest mass must travel slower than light, particles with imaginary rest mass must travel faster than light, and particles with zero rest mass must travel at the speed of light.
In addition to tachyons, physics has a few other faster-than-light “loopholes.” Phase waves in plasma can move faster than light. And there is a strange phenomenon called quantum entanglement that involves an instantaneous effect over large distances. However, in all cases these superluminal phenomena cannot be used to transmit useful information. Apparently, the laws of nature are such that anything bearing information cannot move faster than light. Thus, information cannot travel back in time. This prevents causal paradoxes.
- While time travel into the past wouldn’t necessarily invoke a change that causes a contradiction, it seems at least possible to cause a contradiction. That is, a time traveler wouldn’t necessarily prevent his grandparents from meeting, but the fact that he could would imply that contradictions would be possible if time travel into the past were possible. Since contradictions are not possible, the premise—time travel into the past—is falsified.
- Matthew 24:36.
* Dr. Lisle is Director of Physical Sciences at the Institute for Creation Research and received his Ph.D. in astrophysics from the University of Colorado.