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Bewildering Stories

Challenge 364 Response


by Peter Cawdron

A discussion of the questions on “Serengeti” in Challenge 364.

What is “Fermi’s paradox”?

Don Webb: Fermi’s paradox can be summed up as: “If there is intelligent life in the universe beyond Earth, why have we no evidence of it? It’s had plenty of time to make itself known.”

Peter Cawdron points to his story’s long title, which rightly implies that the story proposes a solution. It’s one of the “life is difficult” variety. A succinct list of possible solutions can be found at a University of Oregon website:

Imagine Eskimo — or, in Canadian, “Inuit” — explorers transported suddenly and without preparation to the Serengeti desert or any tropical or subtropical environment. What would you expect to happen to them?

Peter Cawdron: The point of the story is that they would be overwhelmed by the sheer abundance and diversity of life they would find as for them “normal” has been defined by a vast, sparse habitat. Point being, the reason we don’t see aliens could simply be that our galaxy is not the norm, but is below par and lacks the abundance and diversity of other galaxies.

Don Webb.: A very interesting premise. Something similar has already happened in Earth’s history — in reverse. Europeans acquired full or partial immunity to many diseases in hundreds of generations’ contact with livestock. Their explorers carried those diseases with them, and they were deadly to the inhabitants of the New World and elsewhere. Interplanetary and interstellar explorers will have to be very careful lest they catch something really bad, hence Michael Crichton’s Andromeda Strain.

“The distances were so immense that a lifetime of travel at almost the exact speed of light would barely make any perceptible difference at all.” Assume that the Andromeda galaxy is about 2.5 x 106 light-years distant from the Milky Way. Assume that the Serengeti travels, impossibly, at exactly the speed of light. Disregard time spent in acceleration and deceleration. It will take the Serengeti about 2.5 million years to reach Andromeda.

Assume that the crew members are all 30 years old upon departure. How much will they have aged when they arrive?

Peter C.: The unwritten assumption in the story is that the original crew are all dead and that nine generations of clones from the original crew have continued the journey.

Don W.: Right... and that makes the Serengeti effectively a generation ship.

If the crew are all 30 years old when they depart, how much will they have aged when they arrive at Andromeda? Answer: none. They’ll be the same age as when they left.

It all depends on relativistic points of view. From the perspective of the Milky Way and Andromeda, the Serengeti will have been traveling for 2.5 million years. For the crew members, no time at all will have passed. Discounting acceleration and decleration, they won’t have had time to make themselves a pot of coffee.

Consider it in everyday terms. If you look at the Andromeda galaxy with the naked eye or through a telescope, the photons — the light particles — that you perceive have taken 2.5 million years or so to reach you. But to the photon itself, the trip is instantaneous.

Assume that the Serengeti travels at 99.9% of the speed of light. About how long will it take to reach Andromeda? Again, how much will the crew members have aged upon arrival?

Peter C.: Also, Andromeda is the target for observation. The premise is that to observe the Serengeti effect, observations need to be made outside of our galaxy, beyond any interference from our galaxy. That has been the Serengeti’s mission.

At the end of the story, seeing there is life blossoming throughout all the galaxies, the clones realise they would never personally make it back to Earth and so they transmit their results and continue on, knowing that it would take hundreds of thousands of clone generations over millions of years before they make landfall in Andromeda. No discussion is made as to whether the ship could be space-worthy for that time, or what the braking procedure would be at the other end, but they could coast that far.

Don W.: Understood, and the premise is interesting. However, I’m not sure, myself, what the answer to the question is; we need a physicist to calculate it. I estimate the trip would take 2,500 years. At a fraction below the speed of light, the Serengeti would indeed become a true generation ship, as it is in your story. I expect but can’t say for sure that the crew members would age proportionally during that time.

Assume any arbitrary rest mass for the Serengeti. What mass would it have when traveling at the speed of light? At 99.9% of light-speed? At a relativistic velocity, how might the ship affect an interstellar environment?

Peter C.: The story assumes that technical objections like this have been overcome through one advanced means or another, but that breaking the speed of light is not possible.

Don W.: I’m afraid a technical solution is impossible. At the speed of light, the Serengeti would have infinite mass. And a difference of 0.1% in velocity is negligible; mass increases asymptotically as an object approaches light-speed. In effect, the Serengeti would become a rogue black hole.

Since gravity apparently propagates at the speed of light, I doubt the Serengeti’s effect in intergalactic space would be immediately noticeable; within a galaxy I expect it would generate gravity waves strong enough to destroy any solar system it approached.

But not to worry: it seems highly unlikely that anything of the sort can occur. To reach the speed of light, the Serengeti or anything else possessing mass would need infinite energy; even CERN’s enormous power can’t accelerate protons quite to light-speed. The Serengeti might have to pump the entire space-time continuum into its gas tank — recreate the Big Bang — to go that fast. And, thank God, the speed of light would put a stop to that anyway.

The Fermi paradox seems to contain hidden assumptions: any extraterrestrial intelligence will be like us and it will use our technology. That strikes me as a double fallacy:

Copyright © 2009 by Peter Cawdron
and Don Webb

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