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The Question

(Submitted September 02, 1997)

My husband and I both have Applied Physics degrees and studied the theory of relativity in college. We went to see "Contact" the other day in which Jodi Foster discovers plans for a space transport. The theory of relativity states that a person in space will age less than a person on earth; in other words, time moves slower in space, relative to earth.

In this movie, based on Carl Sagan's book, Foster's trans- port capsule drops through a gyroscope-like accelerator and is enclosed for approximately a half a second. Her experience is that she travels through a series of "worm holes" and is gone for about 18 hours. Her recording device recorded 18 hours of static in spite or her only being out of reach for a split second. This story line is backwards to Einstein's theory of relativity.

Our question for you is: could you please explain the theoretical "worm holes" and if they would account for the longer time spent in space relative to the time that passed on earth.

The Answer

I am sorry that I didn't make contact with you sooner, however your question spurred a flood of diverse comments from our Ask an Astrophysicist Team. I will not inundate you with the raw data, however I will attempt to put them together into some sort of answer. So here it goes:

I did not see the movie Contact, but from what you said, I would agree with you that the movie got the relativity wrong. I do not know if the plot device had Jodi Foster's character fly away fast (thus accelerating greatly to start, stop and turn around) or if she went close to a black hole (thus entering a very strong gravitational field) or both. Either way the effect is basically the same -- time appears to slow down from the point of view of someone in an inertial reference frame. So, I agree, the clock should have shown less time than the observers from the mother-ship (or however the story went) would have seen.

On the other hand, strange gravitational field structures can do strange things. This was pointed out by one member of my team who wrote:


From: David Palmer

Worm holes can be time machines as well as space machines. Thus you can go through a series of wormholes and end up wherever and whenever the wormholes are set up to take you (within limits).

Carl Sagan, when writing Contact, asked Kip Thorne (one of the world's leading relativists) how to transport a person to distant stars, have her come back to find that no time had passed on Earth (which is in both the book and the movie).

From this question, Kip Thorne revitalized the whole modern field of the study of wormholes, a field which had lain dormant for a few decades until Thorne figured out how to make a wormhole people could actually travel through.

A good book on wormholes is:
Black holes and Timewarps, Einstein's Outrageous Legacy, Kip Thorne, ISBN 0393312763


In addition, another member of our team wrote a really nice letter in response, which I will include verbatim here.


Thank you for writing us with your question about the crucial plot element in the movie (and novel) 'Contact' with regards to an observed time difference. Although it is realized in slightly different ways in the novel and the movie, the essential point that, to Earth observers, nothing happened while the cosmonauts (there were several in the book rather than just Dr. Arroway in the movie) traveled for some time and arrived at a destination which they were also at for some time. I don't recall the time they thought they were gone in the book (the danger of borrowing books from friends is you can't go back and check details five years later!), but certainly it was comparable to the movie's depiction of eighteen hours. In both cases, it is a crucial plot. Considering that Dr. Sagan is a knowledgeable and accomplished astronomer, my own reaction without resorting to equations is to assume he has something quite specific and physically correct in mind.

You are, however, correct about the interpretation of relativity. The essential concept is that objects in motion with respect to each other will observe different time frames. This was measured experimentally some years ago when two identical high-precision atomic clocks were synchronized and then one was flown on a high-speed plane and the synchronization of the clocks checked. The flying clock observed less time had passed in exact accordance with relativity (though the difference is very minor: pilots are not getting a significant boost on life by their choice of profession!). There are a number of other types of high speed clocks which so the same temporal effects (relativistic muons generated at the top of the Earth's atmosphere by cosmic ray collisions can be observed at the surface of the Earth, even though their decay life time is so short they should not be observed save for the time dilation effect they experience due to their near-light-speed velocity). Thus if the idea of relativistic motion was intended in 'Contact', your point is correct: a speeding Dr. Arroway (and recording gadgets she might be carrying) would record less time as passing than observers on Earth.

However, the plot element which allows Dr. Arroway to travel to distant destinations in the Galaxy is not a speeding spaceship, but something that bears a strong resemblance to some modern physics ideas about worm holes. Worm holes are hypothesized as possible consequences of certain well-regarded contemporary high energy physics theories. There is a good deal of literature on the subject of worm holes, including some very readable resources such as Steven Hawking's 'A Brief History of Time' and Lawrence Krauss' 'The Physics of Star Trek' (which addresses the theory behind the worm hole used in Deep Space Nine). Temporal flow in a worm hole need not necessarily match that outside the worm hole, although I must admit worm hole theory is well outside my field of study. Thus it might be possible for considerable time to pass in the worm hole while less observed time occurs external to it. Thus the Contact plot might seem to be intact scientifically.

Or maybe not: Ellie Arroway also talks to a projection/simulation of her father at the terminus of the worm hole network that brought her there. This was not in the worm hole and appreciable time passed while she was there, so unless the worm hole actually functioned as a short-range time machine sending her back to a time perhaps eighteen hours earlier, the same problem of time remains. One very weak speculation on this point might be that this is what happened. Some physics does seem to actually allow the possibility of time travel. Perhaps this is what Dr. Sagan had in mind. It should be noted that he was heavily involved in the production of the movie and it was in post-production editing prior to his death. His wife, who is also well versed in science, also worked very closely with the movie production. I (personally) suspect that Dr. Sagan did have some very specific physics ideas in mind to explain, or at least make possible, the temporal paradox you noted.

Alas, ultimately, though, the movie and novel are interesting pieces of entertainment. Some contortions might make the physics of the plot work, but at the same time: 1/ The canyon at the end of the movie in which Ellie Arroway dangles her feet with VLA in the background exists... but it is several hundred miles away from the VLA, and 2/ There is no straight road in front of the U.S. Capitol also depicted near the end of 'Contact'. Now THAT'S a physics error!

Jesse Allen


Thank you again for you insightful question that gave us something fun to think about and debate.

Sincerely,

Jonathan Keohane
for the entire Ask an Astrophysicist team

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