7) Interstellar hydrogen would be swept up by the moving ship. Aboard an end-teleport drive there would be absolutely no smoking. Drinking, yes...
8) As for meteors and larger bodies... we'll use a trick.
Let's say we're going toward the galactic core, i.e. toward Sagitarius. Okay: Before we leave the system, we take our ship to within a few million miles of the Sun, on the Sagitarius side; and we hover.
We hover by end-teleporting outward as the Sun's gravity draws us inward. Half an hour of this should give us a respectable intrinsic velocity Sunward. Now we take off toward Sagitarius.
So we ram something en route. It can happen.
But... it takes energy to make two solid masses occupy the same space. Chances are we cannot teleport into what we've rammed. A fuse blows and the motor stops. That leaves the ship with its intrinsic velocity, which we have built up hugely in a direction opposite to the direction of travel.
So the ship backs up at hundreds of miles per second!
Even if we ram a planet, our intrinsic velocity is higher than escape velocity, and we're safe.
9) Conservation of energy rears its head once more. The ship becomes fiendishly cold as it leaves the solar system, and body temperature drops simultaneously.
The reverse occurs as we enter a system. It's a good thing we built a heavy air conditioning system to get rid of all that dust. We'll need it for temperature control.
VII
Why do I persist in assuming that the conservation laws hold?
This question caused a series of soapbox speeches, mostly in my defense (thanks, friends), along the back wall of my Boston audience. The assumptions are important, and I'm going to try to justify them.
1) The behavior of the universe does not change. In all known cases the laws of conservation of energy and momentum hold rigorously. Now we use them for prediction. The existence and most of the properties of the neutrino were predicted by use of these and other conservation laws. Later the neutrino itself was detected through judicious use of its own proposed properties.
If today's physicists can use conservation to predict ghost particles, I can use- them to predict the behavior of a teleport system.
2) In any case, I'm entitled to make any assumptions I like, if they are internally consistent. This is an exercise in speculation, remember? Speculation starts with assumptions. If you don't like mine, try your own; you might get some interesting results.
3) A passenger teleporting downhill must lose potential energy. Some equivalent gain in energy must appear. But why heat?
Good question. I myself generally assume that the energy will appear as a jump in electron orbits. Then the electrons drop back, releasing photons. The photons are absorbed before they reach the passenger's skin, giving heat. But almost any reasonable process will ultimately end in heat. Heat is the most general, most randomized form of energy.
Could the released energy appear as neutrinos? That would not give heat. But it would upset some of the obscure parity laws of nuclear physics (thus upsetting Isaac Asimov, Hal Clement, and thousands of reactionary physicists) and it would make uphill teleportation impossible, for the process would have to destroy neutrinos which weren't there in the first place.
VIII
How about a perpetual motion machine?
See Figure 5 (page 107). The idea is to use open transmitter and receiver booths. The cargo, thirty gallous of water, is teleported to the receiver. It immediately pours out into the open transmitter, which teleports it back to the receiver, et cetera. Put a water wheel in the system and we get power.
Obviously there's a flaw. If conservation holds, the water freezes pretty quick. Furthermore, thermodynamics says that the energy to run the system will be greater than the maximum energy to be obtained from the continuously falling water.
But the system is interesting in other ways.
Let's replace the water with a ton of iron filings. That way we can enclose the whole system in a vacuum chamber and stop worrying about atmospheric friction, water evaporation, and freezing of the water. We let the filings fail under gravity until the mass is a black stream, near absolute zero, moving at seven miles per second. That's nineteen minutes of operation.
Now we let it go another nineteen minutes. The velocity doubles, and we've let the filings fail the equivalent of twice the distance from infinity to the Earth's surface.
We could maintain this acceleration forever, provided we do one thing. We will have to build our system at the North (or South) Pole. Otherwise the stream of filings will seem to bend away from the transmitter door as the Earth turns. (BOOM!) So we're at the North Pole...
In thirty days the mass of the filings has doubled. In sixty days it has quadrupled. Note that while Earth pulls the filings, the filings pull the Earth. Minutely, at first. But the filings aren't really going anywhere, so we have the equivalent of a reactionless drive. Every month the thrust doubles. If we run the system long enough the filings will weigh as much as a star. Obviously we don't want that. Tides! But in its present state, turning off the system would destroy the Earth. So we set up a second receiver at the South Pole.
The stream of filings goes tearing off through the Earth's atmosphere, a blue flash of iron vapor ramming air. Even the gamma rays are going upward! What a show! Listen to that applause! But all the teevee cameras have melted…
Well, this is where I quit. But try a few postulates yourself, and see what you get.
THE THEORY AND PRACTICE OF TIME TRAVEL
Speculate : (2) To ponder a subject in its different aspects and relations; meditate; esp. to theorise from conjectures without sufficient evidence.
-Webster's New Collegiate Dictionary, 1959
Once upon a time a man was given three wishes. He blew the first two, getting himself in such deep trouble that if he let either wish stand, he would suffer terribly.
Now desperate, he cried, "I wish I'd never had a fairy godmother!" And the past healed to cancel both wishes.
The first time-travel story was a fairy tale-here drastically condensed.
Its theme is buried deep in the literature. L. Frank Baum used it in THE WONDERFUL LAND OF OZ. Cabell borrowed it for THE SILVER STALLION. Traditionally the protagonist may change the past without actually moving backward in time.
H. G. Wells, one of the fathers of modern science fiction, also fathered the time traveling vehicle. This may be the reason Well's spiritual sons tend to treat time travel as science fiction rather than fantasy. But Wells wrote only of travel into the future. He missed the Grandfather Paradox and all the other derivative paradoxes of travel into the past. His time machine was a mere vehicle, no more remarkable than the gravity shielding material, Cavorite.* (*Both were mere philosophical vehicles. Wells liked to preach.)
Wells also missed the most important aspect of time traveclass="underline" wish fulfillment. When a child prays, "Please, God, make it didn't happen," he is inventing time travel in its essence. (He will probably give up the idea when he learns good English. More about that later.) The prime purpose of time travel is to change the past; and the prime danger is that the Traveler might change the past. The man who first thought of travel into the past combined the Wells machine with the fairy tale to produce time travel in its present form.