[ExI] The Great Silence again

spike spike66 at att.net
Tue Apr 26 22:09:07 UTC 2011

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-----Original Message-----
From: extropy-chat-bounces at lists.extropy.org
[mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of Anders Sandberg
Sent: Tuesday, April 26, 2011 2:37 PM
To: ExI chat list
Subject: Re: [ExI] The Great Silence again

spike wrote:
> If so, some of you young physics hipsters step up to the plate right
> now, for I am very busy now with some family crises.  First
> assignment: given a sunlike star, with 1 sun mass and luminosity,
> assume an MBrain reflects 99% of the momentum eastward.  What is the star
system's westward acceleration?
> I calculated this about a decade ago, and it is in my green notebooks
> somewhere, but I haven't the time to find it.  As I vaguely recall, it
> was a few meters per square year, but that seems high to me now.
> Hipsters, have it done by this time tomorrow, and I will do it
independently as a check.
>

>...Hmm, with momentum p=h/lambda and energy E=hc/lambda for each photon, if
there is I Watts of energy at that wavelength I get lambda I/hc photons with
a total momentum of I/c... great, no need to get into Planck's radiation
law...

Ja, all that stuff cancels.  You can use the wavelength formulation Anders
gives, instead of the frequency formulation I use.  Some of us are special,
others are temporal.  Both give the same answers if you do it right.

>... So the total momentum per second if the luminosity is L and we have
efficiency eta is eta L/c.

Cool huh?  {8-]

>...For the sun and 99% efficiency, that is 1.27*10^18 kg m/s^2. Putting
that into F=ma gives us the whooping acceleration 6.39*10^-13 m/s^2...

Ja, doesn't that seem high?  A square year is about 10^15 square seconds, so
I am getting about 600 meters per square year which agrees with what I
calculated a decade ago, or about 20 microns per second per year.  That
seems high, but perhaps my intuition is underdeveloped in the field of
hauling stars around.

>... It takes about 2.8 million years to move a lightyear this way...

Again in agreement with what I calculated long ago.  I am astonished that we
could get that far in a period of time comparable to that in which humans
evolved.

>...surprisingly fast, actually! This way you could get out of the galactic
plane within a galactic rotation, even if you didn't use a stellar gravity
assist... Anders Sandberg,

Anders does this result violate your intuition as much as it does mine?  Are
we missing something fundamental?  Feels like we are.

I do not think a star would want to get *out* of the galaxy, but rather
would want to go further inward in any case.

I had to agree with Robert that the signature seems missing: we don't see
stars on the galactic plane reflecting light towards us.  If quasars are
actually this phenomenon, there would be more of them visible in the
galactic plane than elsewhere.  Halton Arp argues that quasars are
associated with galaxies, but I never did find his data very convincing.

spike

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