
Solution to the Problem of Intergalactic Travel - Kinnard
http://www.chabad.org/library/article_cdo/aid/3170867/jewish/The-Problems-of-Intergalactic-Travel-and-Jewish-Continuity.htm
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dalke
To start with, the article it titled "The Problems of Intergalactic Travel and
Jewish Continuity", not "Solution to the Problem of Intergalactic Travel".

Then whoever gave the title (which is often the editor and not the author)
doesn't have a sense of scale. Travel to Alpha Centauri is _intersteller_
travel, not _intergalactic_ travel, that is, 4 light years compared to 70,000.

The piece considers that the only solution is a generation ship, which leads
to a new set of problems.

Food is one. It says "There’s sunlight in most of outer space, so algae could
be grown on the collected sweat and urine from the humans." That rang alarm
bells. Outside of the solar system, the "sunlight" is really "starlight". It's
not possible to support people on sun/starlight at that distance.

Back of the envelope calculation: "Average annual solar radiation arriving at
the top of the Earth's atmosphere is roughly 1366 W/m2." Which means at 1
light year away (63,241 AU), or 1/4th of the way to Alpha Centauri, the energy
density is 1366/63241/63241 = 0.34 µW/m2.

Basal metabolism is 100 W, so assuming impossible pure energy conversion, each
person needs about 300 sq. _kilometers_ of collection area to provide enough
energy.

The second one is, how do can it have a stable social system across multiple
generations? One professor made the observation "So far as I know, they’re the
only group of people who, for thousands of years, have managed to hand down
their traditions intact to each new generation."

That's another alarm bell. An astrobiologist likely knows little about
anthropology. Buddhism, Confucianism, and Zoroastrianism also have passed down
traditions 'intact to each new generation', even to the present. Parts of the
Vedas are 3,000 years old. Surely we need to look at multiple such systems to
see what they have in common, rather than doing what the author of this piece
does and examine only the Jewish rabbinic tradition.

It then correctly points out that a stable culture isn't enough. But it does
so with at best a lay understanding of gravity. "The real problem is that
after the first two hours, after the ship leaves the gravitational pull of the
earth from that moment on, everyone, for all generations, will live in a
weightless environment."

Why "two hours"? Will the ship boost for two hours? The most meaningful
definition for the 'gravitational pull of the earth' is to be within the Hill
sphere of ~1.5 million km. Basic physics says that ship needs to pull about 6
gravities to do that. And why won't the generation ship spin in order to
maintain gravity? We know that long-term zero gee is not good for the body.

Since this piece isn't meaningfully about the science, I conclude it's more
likely written to promote or at least maintain a sort of exceptionalism about
the Jewish faith.

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whoopdedo
So let me see if I have this correct. Did Prof. Greene essentially propose
creating a new religion for the preservation of scientific knowledge?

