[tt] [megascale] Fwd: Re: <snip> re; communication

[Eugen Leitl]

----- Forwarded message from Bryan Bishop <kanzure at gmail.com> -----

From: Bryan Bishop <kanzure at gmail.com>
Date: Mon, 28 Jan 2008 22:00:42 -0600
To: megascale at heybryan.org
Subject: [megascale] Fwd: Re: <snip> re; communication
User-Agent: KMail/1.9.7


----------  Forwarded Message  ----------

Ok, let me give you guys some numbers to indicate how far-fetched the
neutrino (or some other new particle that we discover) would be for
communication:

>From 
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html:
"A fairly common qualitative statement in physics texts is that the
mean free path of a neutrino is about a light-year of lead. Griffiths
makes the statement "a neutrino of moderate energy could easily
penetrate a thousand light-years(!) of lead." This cross section can
also be used to estimate the number of events which can be expected in
a given size of detector."

So, the average distance a neutrino travels through solid lead before
interacting at all is on the order of lightyears.  If it has a higher
energy, this length will decrease some... but it's not going to get
down to a realistic length.  So yes... sometimes civilizations have
inefficient technologies, but do you really think there is going to be
a civilization that figures out how to build a detector that is 1
cubic lightyear of lead big... just to receive a signal that is from a
beam which is extremely hard to direct or focus (since the only way to
focus a beam is to get it to interact with other matter or energy
fields)?  Basically, in order to believe there were civilizations out
there using neutrinos to communicate, you'd need to believe that they
were so primative that they'd never even found out that light
exists... yet somehow they can build this artificial structure that is
thousands of times the size of our solar system... just to capture one
communication signal?  Alternatively, they could build in a huge
amount of redundency and get by with a smaller structure... let's say
they used something equal in size to our solar system.  Then they
would lose nearly all of the neutrinos that were sent... needing an
amount of energy that is thousands of times larger than what would be
needed if they just used simple light to communicate.  Given that
light (electromagnetism) is pretty much everywhere, and the basis of
all of chemistry, I find it very hard to believe there are
civilizations out there this advanced who have not discovered it.

Jeff

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Bryan Bishop
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Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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