Future under the magnifying glass, part 1.
by Mani Samani & Nahid Taheri
Dr. George Jones, a senior lab instructor in UNBC’s physics department, sat down with two Over the Edge volunteers to answer our questions about the future.
Question: Can we travel to the future?
Answer: In theory, yes. According to the theory of relativity, one can suppose an astronaut leaves Earth, travels at 99.9% the speed of light, and returns to Earth. If the astronaut ages ten years during the trip, the Earth and the people on it will have aged 224 years, so the astronaut will have traveled into the future! I might be dead and my grandchildren might be alive. That is clearly allowed with the laws of physics and we have measured it small amounts of time travel. In fact, this is taken into account whenever we use GPS. GPS satellites orbit about 20,000 kilometers above the earth. Due to their orbital speed and height, clocks on these satellites run at different rates than identical clocks on the Earth. If this were not taken into account, large errors (11 kilometers per day!) in positions predicted by GPS devices would accumulate.
Question: How about travel to the past?
Answer: We just do not know. Stephen Hawking wrote a famous paper in 1992 in which he called the “Chronology Protection Conjecture,” what he said would make the world safe for the historian. History would not be screwed up as long as there is no time machine. This is a standard paradox; what if one goes back in time, and one kills your grandmother before your parents were born? How is that possible? If we do not have time machines we do not have paradoxes like that. So Stephen Hawking’s 1992 conjecture proves that we do not have time machines. However, using space-time wormholes, backwards time travel may be possible. In Einstein’s theory of general of relativity, space-time is warped. Space-time wormholes first generated substantial interest in the physics community in 1988. Physicists soon realized that if space-time wormholes exist, then they could be used to create time machines. We, however, currently have zero experimental evidence for space-time wormholes. In 1992, Stephen Hawking showed that quantum theory might prevent the formation of time machines by creating a burst of very high energy radiation just before any time machine forms, thus destroying the apparatus. In 1997, further work suggested that a full quantum theory of gravity is needed to resolve these questions.
Question: Is there any investigation into travelling to the future?
Answer: One has to travel very fast in order to do this. We have not travelled nearly fast enough to verify this. You have to travel near to the speed of light which is 300,000 km/s. What is the fastest speed a human being has ever gone with respect to the earth? I think it is 11 km/s, which is not very much compared to the speed of light, and this was the speed achieved by the humans when they went to the moon. We really have not travelled fast enough with humans. We just have not done that, and there is not anyone even close to doing that; not in the next fifty years, or even in the next five hundred years. I do not think we can get to the future like that. However we have some very accurate clocks, such as atomic clocks. In 1971, scientists put an atomic clock in two airplanes, and flew them in different directions around the world. The clocks were synchronized, and when the planes landed, there was a measurable difference in the readings!
Question: If we had the ability to travel into the future, what destination should we travel to?
Answer: Destination is not important. Just the fact that you can go and come back; the speed related to us on the earth is important.
Question: When you look at the sky you look at the history, so is it possible to look at the past?
Answer: It is possible to look at the history of stars, but not the history of humans. For example when you look at the sun we are looking at it as it was eight minutes ago; when we look at the next near star we see it as it was four years ago; when we look at a star from another galaxy we see it as it was millions or billions of years ago. We cannot see ourselves in the same context. Going back to the question: in theory, in some universes, yes. If the universe is closed, and if the universe expands not too slowly and not too quickly, we can see all the way in the universe, and can observe an image of the Earth in the distant past. There are no paradoxes associated with this. We do not know if our universe is closed, and our universe seems to be expanding too quickly for this to happen. We cannot be completely sure that the universe’s rate of expansion will not slow down in the future.
Question: Could you please introduce some more references for if anyone would like to read more about this topic?
Answer: There are two books which are not just for physicists; everybody can read them. They are Time Machines by Paul J.Nahin and Time Travel and Warp Drives by Allen Everett and Thomas Roman. There is also a less accessible book titled Lorentzian Wormholes by Matt Visser.