THE RESULT: A traveler would move in "hops", naturally. But there would come a point where an airplane is cheaper and more convenient, or both, than a succession of teleport booths. Thus, cars would go, but airplanes and shipping would remain.

Change the limiting distance and, again, you change the society. At a mile a jump only the cars go. At a thousand miles a jump, only spacecraft remain.

THE ASSUMPTION: Teleportation is limited by the Laws of Conservation of energy and Momentum.

THE RESULT: Not very different from above. Cars would go, airplanes would remain. By teleportation we could not travel long distance north and south; we would have to do it on short hops. The longer the hop, the harder momentum would jerk the passenger sideways each time.

Traveling east, our momentum would lift us a few inches from the chair of the receiver booth on each hop. (Yes, I said chair. You might try it standing up, but I wouldn't.) Traveling west would be worse: momentum would slam you down hard. A New Yorker might prefer to reach San Francisco via the western route, in a line of booths crossing the Atlantic and Pacific Oceans.

(Assume a passenger is at the equator, teleporting straight east a distance of X miles.

Then X/4000 is the angle $ of his jump in radians. For X small, we take sine$=$ and get:

X *1000/4000=X/4 [We multiplied the sine of the angle, equal to the angle itself for small angles given in radians, by the rotational velocity of the Earth.]

X/4 is the velocity at which the passenger gets lifted off his feet. Going west, he gets slammed down, same equation. For small angles, the equation holds elsewhere than at the equator. Decreasing the distance from the Earth's axis of rotation decreases the speed of rotation, but increases the angle of shift.)

Notice one important exception. We can travel from the northern hemisphere to the southern in perfect comfort, provided the departure point and destination are at corresponding latitudes.

Elevators become more important than ever. In Earth's gravitational field, at ground level, we lose-seven degrees Fahrenheit for every mile we teleport upward and we gain as much going downhill. Elevators are more comfortable.

So: you want to go skiing in the Swiss Alps, at St. Moritz. From the United States your best bet is to take a plane to someplace with a big landing field, ride an elevator half a mile up to a teleportation booth, then teleport to St. Moritz. Do it any other way and you wind up sick for a couple of days. But from New York you can reach Angol, Chile in one jump!

So much for booths. They still look like our best attempt at prophecy; but let's try some wilder ideas and see what we get.

THE ASSUMPTION: Open teleport discs. You step on a disc, it teleports you to another disc. Cost, pennies per thousand trips.

THE RESULTS: All present transportation disappears. With the proper setup, you can walk anywhere on the planet. Figure 2 is a design for intercity transportation, but it can easily be adapted for longer distances. The blocks shown could be lines of longitude and latitude; their length is optional.

For the rectangular city layout shown, we simply walk in the direction we wish to go. The distance between the receiver plate, at the center of the intersection, and the next transmitter disc is about three paces. In three paces one covers a block, whose length, I repeat, is optional. Perhaps there would be faster lanes through the center of town, and faster still between towns: intersections a mile or ten miles apart. To get out of the system one walks around the final disc and goes window shopping or whatever.

The biggest advantage is that we can give up all the endless dialing!

THE ASSUMPTION: Our transmitter is hand sized. We can hang it from our belt. It has (oh, well) a telephone-type dial on it. The receiver is bigger: an open platform, either a small plate at home, in vestibule, or a community receiver the size of a public square. Cost is equivalent to the cost of using a telephone. There are (if necessary) compensators for momentum-and heat-transfer in the receiver plates.

THE RESULT: Bester's THE STARS MY DESTINATION, with minor changes. No mazes behind the doors; simply unlisted receiver numbers.

VI

Shall we design a few spacecraft? Limited teleportation might not make spacecraft obsolete. It might even be used to improve the spacecraft themselves.

THE ASSUMPTIONS: Teleportation requires both a transmitter and a receiver. Conservation holds. Teleportation is instantaneous, and does not involve beaming.

THE RESULT: See Figure 3. The ship consists mainly of a couple of rocket motors, fuel tanks, and an open-ended teleportation receiver open to the rear. You can leave it open because, in vacuum, you don't need to worry about air getting in the receiver.

The ship, unmanned, is fired from Earth orbit or from further out. Probably it should be fired in the direction of the galactic core, where we anticipate more traffic. By firing the ship from, say, Jupiter orbit, we can pack quite a lot of fuel-water, for reaction mass-outside the ship. (See Isaac Asimov, THE MARTIAN WAY.)

We use all the fuel except a reserve for steering. The ship coasts.

It passes through a star system. Let it be about the size of the solar system; then we have ten hours (assuming our ship is near lightspeed) to shove an entire prefab colony into the Earth-based transmitter. If all ten hours are used, then the colony building materials are strewn across the entire system. Each piece of equipment arrives at rest with respect to Earth, and thus leaves the receiver at a speed approaching lightspeed. (Now you know why we put a hole in the receiver.)

Last through the receiver are the ships designed to collect all this crap. Since they are manned, we had better not send them from Earth. Conservation of energy would freeze the pilots to ice in an instant. Consider the irony: to keep them from freezing, we must ship them from Pluto orbit!

It might be more efficient to send through the teleport system only a few ships and another prefab teleport receiver. The rest of the colony comes through the second receiver.

In any case, notice four advantages. You don't have to carry the entire cargo, or waste fuel accelerating it. You don't decelerate the ship, so none of your limited fuel supply need be reserved for that purpose.

The colonists need not twiddle their thumbs for decades. And the ship can be re-used.

Can and will. You just let it coast. Every time it comes near a star system, you have another colony. In eighty thousand years we leave a line of colonies clear across the galaxy, before we finally run out of stars.

Less peaceful societies would shove war fleets through the teleport system. It is hard to imagine a safer way to make war. The fleet is strewn all across the system, with all the warships at rest with respect to the universe at large. And how could the target system counterattack? To reach the invading system, they would have to catch a ship which has had years to accelerate to its tremendous velocity, and which is long gone into interstellar space before the attack can even begin.

During the Boston speech, a member of the audience suggested that teleportation be used to fuel the above craft. Specifically: the motor is a receiver, Open, with a flared nozzle attached. We drop a transmitter on Jupiter. Presto! Hellishly dense high-pressure gas expands explosively into the vacuum of space, driving the ship forward. Fuel supply: inefficient compared to ion drives or the like, but almost literally unlimited.