During the last century and into this, we humans have traveled into outer space. This achieved a dream held by humans probably since humans evolved. Is time travel next on the horizon? If so, just as we needed to build a space ship to travel through space, we need a time machine to travel through time. Is building a time machine possible?

The surprising answer is yes, according to some astrophysicists. They suggest that there may even be more than one way to travel forwards or backwards through time. A time machine is possible--at least in theory.

Dr. John Macvey, as a fellow of the Royal Astronomical Society in Britain, the owner of his own observatory, and the author of a classic book on time travel entitled TIME TRAVEL: A GUIDE TO JOURNEYS IN THE FOURTH DIMENSIONS first published in 1990. Dr. Macvey argued that time travel is possible either through what is called the "time dilation" method or through what is called the "black hole/white hole" method.

Time travel through time dilation is based upon Albert Einstein's theory of relativity. According to one aspect of this theory, a consequence of traveling at a speed near that of the speed of light (186,281.7 miles per second) is the slowing down of time. It is probably impossible to travel at exactly the speed of light or beyond it, but traveling just under the speed of light is possible. Nevertheless, a space craft moving slightly slower than the speed of light would still be moving fast enough to become a time machine into the future. For example, such an ultra-fast space craft could complete the 4.5 million light-year journey from the Earth to the Great Galaxy in Andromeda and back again in about 55 years. But it would be the Earth, not 55 years in the future, but some 4.7 million years in the future.

The only impediment to the time dilation method of time travel is the technological obstacle of finding a fast enough space craft. Thus, if the theory holds, then a space craft traveling fast enough would, in fact, become a time machine.

Time travel through black hole/white hole usage is based upon our incomplete knowledge of black holes. A black hole in space is formed when a star "collapses" in upon itself in a particular way. The remaining "space" is the black hole, but it is really the absence of "space" in the usual sense. Much mystery surrounds black holes. And it seems that the normal rules of physics simply do not apply to them. For instance, the normal space-time relationship is greatly altered.

Dr. Macvey maintained that any space craft approaching a black hole would experience even greater time dilation than otherwise. This warping of time would allow a space craft to travel forwards as well as backwards in time. According to Dr. Macvey, a black hole is actually the doorway to a tunnel connecting our universe with something else, perhaps even another universe. Furthermore, on the other end of the tunnel is a white hole, serving as the doorway to whatever it is that is on the other side of the tunnel. Thus, a space craft entering through a black hole, moving through the tunnel, and exiting through the white hole could emerge in another part of the universe, in another universe altogether, or in another time--either past or present. In any case, again, if the theory holds, then this space craft too would, in fact, become a time machine.

Dr. Macvey points out that such black hole tunnels--our portals to the past--are so far away that we would still have to travel at almost the speed of light in order to reach one. And, since the time dilation principle would apply, in doing so, ironically, we would have to travel into the future in order to travel into the past.

Is it possible to build a time machine? The answer to this is surprising as well. In 1987, Dr. Kip Thorne, a theoretical physicist at the California Institute of Technology in Pasadena, caused controversy among fellow astrophysicists by actually suggesting that building a time machine was possible. Dr. Thorne and two colleagues published their calculations first in PHYSICAL REVIEW LETTERS. He has published further calculations on the subject.

In Dr. Thorne's time machine, metal plates would define the ends of the time tunnel. One of the two plates would then be shot through a loop in space at nearly the speed of light--returning to the place at which it started. Hence, again applying Einstein's theory of relativity, the returning plate would have passed less time than the stationary plate. This would create the time tunnel doorway into which the first time traveler could step.

Of course, there is the objection to the possibility of time travel of the presentists. Presentism is the view that neither the past nor the future exists. The only thing that exists is the present. Most presentists argue that time travel is impossible because there is no place to travel to, either past or present. However, some presentists, such as Craig Bourne in THE FUTURE OF PRESENTISM (2007) indicate that time travel still could be possible because we definitely know that certain things happened in the past. Thus, the past must have existed even if it does not now.

It is all very interesting. You never know. When it comes to time travel someday we may witness "That's one small step for man...."

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