Re: CMBR and neutron stars
- From: "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T:net@xxxxxxxxxx>
- Date: Thu, 11 Aug 2005 19:05:44 -0700
Dear Steve Willner:
"Steve Willner" <willner@xxxxxxxxxxxxxxx> wrote in message
news:42fb9d94$1@xxxxxxxxxxxxxxxxxxxxxxxxxx
> In article <AvzKe.6008$E95.4317@fed1read01>,
> "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T:net@xxxxxxxxxx>
> writes:
>> *Integrated over time*. Is the integral light history of our
>> Universe from formation of a BH, until it evaporates,
>> isothermal? I think it is *to a close approximation*.
>
> I'm not sure what you mean here or what time period you are
> considering, but the spectral energy distribution of light in
> the
> Universe has changed a great deal over time, and not since
> recombination has it been anything like a blackbody.
The dominant light source in our Universe is the CMBR. Even here
in the middle of the Milky Way, our nightside transfers heat to a
~5K source. I think it is a whole lot like a black body, if you
integrate light infall over the "lifespan" of a BH. It might not
be if the BH is a close companion to a donor star...
>> No one currently believes the Universe started out "the
>> size of a grapefruit", unless they also posit "c_BB >>
>> c_now".
>
> Note he wrote "observable Universe." Size of a grapefruit (6
> cm)
> corresponds to z=10^27.
And you get from cm to tens of Mly in only ~300,000 years... how
exactly?
>> You "helped
>> establish" the CMBRM was many tens of million light years
>> thick,
>> only ~300,000 years after the BB, based on the (lack of)
>> spectra.
>
> I don't know who "helped establish" any such thing, but it's
> wrong.
> Let's put in some numbers. The critical density today is about
> 5E-6
> protons cm^-2, and baryon density is about 4% of this. So at
> z=1000,
> the baryon density was about 200 protons cm^-3. The Thomson
> scattering cross section is 6.7E-25 cm^2, so optical depth 1
> was
> 7E21 cm or about 1E4 light years, not tens of millions. (I've
> just
> done all these calculations in the past few minutes, so it's
> possible
> I've made a mistake somewhere. Corrections are welcome.)
Google.groups. Thread "Olber's paradox", George Dishman, dated
2003jan05
<QUOTE>
This java applet lets you plot the general shape of the
blackbody curve. Note that it has a clear peak:
http://csep10.phys.utk.edu/guidry/java/planck/planck.html
Click new once, then adjust the bottom slider a couple
of pixels. Repeat that with similar shifts ten times
representing CBR from a set of 10 shells of stars at some
large distance. You get a family of overlapping curves and
if you add the contributions you get a much broader peak.
The CMB spectrum follows the blackbody curve to within
about 1 part in 10^5 which means the source must be a
thin shell.
<END QUOTE>
In later followups, the thickness is estimated.
> If you want to claim any electromagnetic radiation from
> before that epoch is visible now, I think you are going to
> have a hard time explaining how. That doesn't preclude
> seeing density or temperature fluctuations in the
> microwave background, which are the result of density
> fluctuations that originated well before z=1000. That's what
> WMAP and a host of other CMBR projects are all about.
> Nor does it preclude neutrino observations, though they
> will be technically challenging (to say the least). And we
> have other remnants from the pre-recombination epoch,
> notably the light nuclide abundances.
You have to posit an opaque medium, to say that we cannot see
before/through it. That is the standard interpretation. Now
what if the CMBRM is the inside of an event horizon? A horizon
that opens into our Universe, which is properly described by
Kruskal coordinates...
>> Structures can infall into large black holes and survive...
>> probably not gravitationally bound ones, but who knows.
>
> For a large black hole, tidal forces at the event horizon
> are small. No reason an object couldn't survive there. It
> just couldn't get out, once it crossed the event horizon.
.... except by evaporation, which won't involve the object so much
as its constituents.
> Of course small black holes
> will have large tidal forces when you get close to them,
> but that's a property of being close to a large mass. Tidal
> forces will be about the same just inside and just outside
> the event horizon. As George keeps writing, there is
> nothing special happening _locally_ at the event horizon.
Now, look at the event horizon form the *inside*. I am proposing
that it would look *exactly* like the CMBR, without need for
Universe filling gas and allowing structures right up to the
CMBR. *Without* any embarrassing questions about how structures
could have formed so quickly after having been "spread across the
Universe".
I'm not trying to wear George down. I hope that is not what I am
accomplishing...
And I'm not trying to irritate you, FWIW.
David A. Smith
.
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