Re: The Laws of Intelligence Examined

Zoe <muze10@xxxxxxx> wrote:
On Mon, 20 Mar 2006 00:11:23 +0000 (UTC),
carlip-nospam@xxxxxxxxxxxxxxxxxxx wrote:

[...]
Now consider a large cloud of hydrogen in interstellar space, far from
any disturbing influences. Your version of thermodynamics says it
should spread out and become more disorganized. But your version of
gravity (slightly extended to go past the "ground") says it should
fall together, becoming less spread out.

where have I said it should fall together? "Fall," yes, if there is a
mass for it to be attracted to. If there is no nearby mass, it's
going to stay right where it is, isn't it?

But there *is* a nearby mass -- the hydrogen itself.

When an apple (say) falls toward the Earth, the Earth also falls toward
the apple. The Earth is much bigger, so its motion isn't nearly as
noticeable. But we've understood since Newton that any two masses
attract each other. In particular hydrogen atoms have mass (this is
measured), and attract each other. So if you start with a big enough
cloud of hydrogen, it will fall in on itself. ("Big enough" here means
big enough that the gravitational attraction can overcome pressure.)

And it should certainly
not become less spread out if 2LoT is in operation.

No. The fact that you think this merely shows that you don't understand
what the second law of thermodynamics really says. There's nothing in
this process that even remotely contradicts the second law.

(Trust me on this. I'm a physicist, and a large part of my research is
on the thermodynamics of self-gravitating systems. There is absolutely
no scientific question here.)

What really happens? Well, if the cloud is big enough, it will start
to collapse under its own gravity. The center will heat up, the
pressure will increase, and eventually you will have a star, happily
generating energy by fusing hydrogen atoms.

this is not making sense to my sandy little mind. If the cloud is
spreading out, it won't ever become dense enough to collapse under any
accumulated gravity of its own making, would it? So how will it
develop a center to heat up?

The cloud isn't spreading out. It's being pulled together by its own
gravity.

And you made a HUGE leap there, without giving the steps in between.
The center heats up, pressure increases, and......eventually.....you
will have a star? What is it about heat and pressure that will cause
a star to form,

Simple nuclear physics, of a type that's been tested all too well. It's
the way a hydrogen bomb works -- by providing enough heat and pressure
that atomic nuclei fuse.

especially if its gases continue to expand, according
to the theory of what goes on out there?

Once again, they don't.

[...]
Can you trace the steps beyond heat and pressure, where, eventually,
the star happily springs into existence?

You don't need anything beyond heat and pressure. An ordinary star is
just a ball of gas, mainly hydrogen, that's held together by gravity,
with a center that is hot and dense enough that hydrogen nuclei fuse
to form helium, releasing energy in the process. Once gravity has
squeezed the center of a ball of hydrogen enough, fusion will begin
automatically. That's all you need.

And can you please explain
how thermodynamics will allow this kind of increasing density?

It involves nothing beyond
the "laws of the physical world" you've described (and a few other
equally "physical" processes, like electromagnetic radiation and
fusion). But it gets us from a cold, formless cloud of gas to a star.

by whose say-so?

Well, mine, to start with. I'm a professor of physics, with a BA from
Harvard and a Ph.D. from the University of Texas at Austin. I have
about 65 papers published in refereed journals, a book published by
Cambridge University Press, and a grant from the Department of Energy.
I'm on the Editorial Board of two top physics journals. My main area
of expertise is gravity, and much of my recent research has been on
gravity and thermodynamics (particularly in the context of black holes).

But if you don't want to take my word for it, here are a couple of
places to start:
http://www.aoc.nrao.edu/~smyers/courses/astro12/L14.html
http://en.wikipedia.org/wiki/Star_formation (which has a nice link to
Jeans' original paper from 1902 -- this is old news)
http://www.ph.surrey.ac.uk/astrophysics/files/how_stars_form.html

If you want to understand the thermodynamics in particular, get a copy
of Zeh's book _The Physical Basis of the Direction of Time_ and look
at the first few pages of chapter 5.

Steve Carlip

.

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