Intertemporal Communication Systems between Time Travel Agents/Offices/etc.

If you went back to, I would guess, 1946, and worked to prevent your parents’ marriage in 1947, you would still have existed in that year; you would not go out of existence just because you had influenced events. The same would apply even if you had only been in 1946 one microsecond before shooting the man who would otherwise have become your father.

Events are the result of a complex. There are no single causes. That’s why it’s so hard to change history. If I went back to, say, the Middle Ages, and shot one of FDR’s Dutch forebears, he’ll still be born in the late nineteenth century—because he and his genes resulted fom the entire world of his ancestors, and there’d have been compensation. But evey so often, a really key event does occur. Some one happening is a nexus of so many world lines that its outcome is decisive for the whole future.

The Mediterranean floor lay ten thousand feet below sea level. The inflow took most of that drop within a fifty-mile strait. Its volume amounted to ten thousand cubic miles a year, a hundred Victoria Falls or a thousand Niagaras.

This was the message received by a dozen or so experts in the "time attempters" field:

"I have succeeded in establishing a creeping time-satellite or time-shuttle at my estate of Moonwick near Lunel in the Herault Department of the Peoples Republic of France. If you are really experts in your field, you will appreciate the importance of this. From this time-shuttle, which is just beyond the ‘shoal’ of all of you to whom I am sending this message, it will be possible for you to launch genuine time probes. I am sending this to a dozen or so and I hope for acceptance from at least five. I must have a matched set of at least five. Some soon. A very little bit after ‘soon’ will be too late for me to transmit the shuttle to you. Bring ideas only. Everything else for frugal and break-through living is provided. You will receive various transportation chits and enabling papers. Peter Luna.”

The World Courier Service (“No questions asked. Messages carried anywhere or anywhen in the world”) delivered these messages to the dozen or so persons who were experts in the time field. And some of the people gave assent and some didn’t. So, the next day, the Courier Service delivered airline tickets, train tickets, and International Taxi Coupons to five of the experts who had agreed to go to Moonwick.

You’re right. We’ve got to help them, even if we are stuck in the Ice Age.