VACETS Regular Technical Column

"Science for Everyone"

"Science for Everyone" was a technical column posted regularly on the VACETS forum. The author of the following articles is Dr. Vo Ta Duc. For more publications produced by other VACETS  members, please visit the VACETS Member Publications page or Technical Columns page.

The VACETS Technical Column is contributed by various members , especially those of the VACETS Technical Affairs Committe. Articles are posted regulary on [email protected] forum. Please send questions, comments and suggestions to [email protected]

Mon, 22 May 1995

Spacetime-Travel & Relativity (Part 2)

Kirk: Mister Sulu, set the course for What-The-Heck star system, warp five.

Sulu: aye aye, captain... The course is set. The What-The-Heck star system is five hundred light-years away and we will get there in about one week.

Kirk: That's not fast enough. Mister Scott, how much more power can you give?

Scott: Captain, we have plenty of power to blow up the Enterprise if you like.

Kirk: Mister Sulu, warp nine and up.

Spock: Captain, according to my calculations, the ship may not be able to withstand the warp nine speed. There is a probability of 0.0511010342 that the ship will blow up.

Kirk: That's enough, Spock. Go ahead, Mister Sulu.

(Excerpt from a Star-Trek episode extracted from D.T.Vo's memory.)



My empty head friend has always been a sore loser. This evening, however, he seems quite different. Even after losing three consecutive arguments, he was smiling. I think he has some tricks hidden somewhere in his hollow brain that I don't know and he is going to dump it on me soon.

-Duc: Alright, spit what's in your brain out now, my friend.

-Nobrain: Do you believe in time travel, that is, going backward as well as forward in time?

-Duc: No way, Jose. And don't tell me that you believe in that kind of stuff. Those are science fictions, man.

-Nobrain: You know that good science fiction has to have its idea somewhat scientifically acceptable. The warp space and time travel in science fictional movies like Star-Trek may have some truth in them. What if I can prove time travel can be made real? Would you believe then?

-Duc: What? You mean that you believe the Star-Trek garbage stuff where it takes one week for the Enterprise to travel thousands of light year distance... I can understand if the Enterprise can travel very near the speed of light then it may take them only one week to travel, while for the rest of the universe, thousands of year has gone by. But in the show, the people on earth or on the far-away planet also record only one week passing by for them. Relativity does not allow that, man. How are you going to explain that? If you can prove it, scientifically, then I will believe.

I think my friend is bluffing. Maybe he has had one beer too many. I'll get him a glass of water the next time he ask for a drink. My friend does not waste much time. He seems happy to start the discussion.

-Nobrain: You know that the faster you travel, the slower you will see the time passing by and when you get to the light speed, the time will stand still for you. So if you can move faster than light speed, what do you suppose will happen then?

-Duc: No way can any one or any thing move faster than the speed of light. Albert Einstein said so. So the IF you said can never happen.

-Nobrain: O.K., so nothing can ever go faster than light. But that does not mean faster than light travel is impossible.

-Duc: What the hell are you talking about? Relativity says that the time it takes to go from place to place can not be less than the time it takes light to pass between them.

-Nobrain: Agree! But do you know that Albert Einstein's relativity theories have a hole in it... I mean a loophole, where the conventional rules break down. That loophole is given the name black hole, inside which anything impossible is possible. A black hole is a hole in space-time which gives birth to another kind of holes, the wormholes, which in turns can form shortcuts connecting different regions of space together. So if you can find a short cut like a wormhole to go from place to place then you may be able to travel faster than light. And faster than light (FTL) travel means time travel, that is, you can go back in time.

-Duc: Alright, slow down. One thing at a time, and don't try to confuse me. If you are really knowledgeable about this stuff, then answer these questions one by one so I can understand them. 1/ Tell me what is warp speed and how scientific it is about the time experienced by the people in Star-Trek when it really contradicts the theories of relativity. 2/ What are wormholes? Are they what you see in the yard in the morning after a heavy rain? 3/ How can a wormhole be used for FTL travel? 4/ And how FTL can be used for time travel?

-Nobrain: That's easy, my man. The answer to your first question about Star-Trek is somewhat complicated so I'll leave it to the end. To answer the second question, what are wormholes, I have to start with an other kind of holes, the black holes. There are four kinds of black holes which are named for after the ones who worked out the mathematical descriptions of them. They are the Schwarzschild black hole which has no electrical charge and no spin, the Reissner-Nordstrom black hole which has charge but no spin, the Kerr black hole which has spin but no charge, and the Kerr-Newman black hole which has both charge and spin. Each kind of black hole has a slightly different internal structure and affects particles and light in different fashions...

This guy said all those things in one breath. I think he just memorized the whole thing, word by word, from a text book and then recited the whole thing trying to impress me. It's nothing. Any first grade kid can recite any thing from any text book just like him.

-Nobrain: ... The Schwarzschild black hole is the simplest form of black hole. It has one "event horizon" within it nothing, including light, can escape. This type of black hole, no spin and no charge, is not likely to exist. One particular property of this black hole is that it has a connection, called the Einstein-Rosen bridge or wormhole, connects this universe with another universe. The problem is that you can not use this kind of wormhole to travel because whatever enters beyond the event horizon can travel only in one direction heading toward the singularity and be annihilated. The second kind of black holes is called the Reissner-Nordstrom black hole. This kind of black hole has charge but no spin and is even less likely to exist than the Schwarzschild black hole. A Schwarzschild black hole has one event horizon. If a small electrical charge is added to the black hole, the event horizon begins to shrink inward and a second event horizon appears near the singularity. As the amount of charge in the black hole increases, the outer event horizon continues to shrink, and the inner event horizon begins to expand outward. With enough electrical charge, the two event horizons will merge into one. Keep adding more charge now, the now-single event horizon will shrink more and more and eventually will vanish into the singularity. The result: a naked singularity.

Two other kinds of black holes that are more likely to exist than the just mentioned two are the Kerr and Kerr-Newman black holes which have spins. A spinning black hole has two event horizons like the Reissner-Nordstrom black hole. Also, the singularity of a spinning black hole would have the form of a ring instead of a point. One characteristic of a spinning black hole, which is different than the Schwarzschild black hole, is that, the inside of the inner event horizon is traversable and you can steer your spaceship to avoid the singularity and the annihilating death. This property enable the possibility of building a traversable wormhole via a spinning black hole connecting this universe with another one or this part of the universe with another part thousand or million light years away.

-Duc: Do you mean a traversable wormhole exists inside a spinning black hole? Is the wormhole inside the event horizons or is it outside?

-Nobrain: Inside, of-course. It is inside the inner event horizon.

-Duc: Then if you get through a wormhole and travel to the other side, how are you going to get out? Isn't the other end of the wormhole also buried inside the event horizon? So with your traversable wormhole, you may be able to avoid the singularity and can travel back and forth between the two ends of the wormhole, but you can never get pass the event horizons to get out to see the other universe. Your wormhole shortcut idea is cut short and it doesn't work, my friend.

-Nobrain: Ooooppps... Get me another bud, man.

(to be continued)

Duc Ta Vo, Ph.D.
[email protected]

For discussion on this column, join [email protected]

Copyright © 1996 by VACETS and Duc Ta Vo


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