Go Back   Science Forums Biology Forum Molecular Biology Forum Physics Chemistry Forum > General Science Forums > Physics Forum
Register Search Today's Posts Mark Forums Read

Physics Forum Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


What am I missing?

What am I missing? - Physics Forum

What am I missing? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 07-11-2005, 10:34 PM
odin
Guest
 
Posts: n/a
Default What am I missing?



OK... observed redshift of the galaxies shows galaxies receding from each
other. So they must have been closer together in the past. By extrapolation
that means they were at higher density and temperature. Big deal. That does
not mean that all galaxies are receding, just the ones we can see from here.
It does not imply any singularity in the past, just a higher density. It
says nothing about space itself expanding even if more distant objects are
flying away faster, since other explanations could fit that. So what am I
missing?


Reply With Quote
  #2  
Old 07-12-2005, 01:41 AM
N:dlzc D:aol T:com \(dlzc\)
Guest
 
Posts: n/a
Default What am I missing?

Dear odin:

"odin" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

No. "Receding" from the *observer*. Galaxies with equal
redshifts have relatively low net velocities wrt each other.
Probably on the order of our net velocity wrt the Universe at
large (~300 km/sec)


Hence the term "expansion". Not that expansion is *not* kinetic
motion, as if the matter were blown away from a cental point.
The center is currently located in every direction around us, as
evidenced by the CMBR.


Actually their spectra indicate they are about the same
temperature as stars we see now (black body curve).


Hopefully that these objects aren't "flying away", and that
objects at equal distances have roughly equal red shifts. And we
have detected objects up to about 700,000 years after the source
of the CMBR stopped emitting light.

Always a good resource:
URL:[Only registered users see links. ]
.... skim it first for what is interesting. Be sure and glance at
the topics in the FAQ.

David A. Smith


Reply With Quote
  #3  
Old 07-12-2005, 09:14 PM
tadchem
Guest
 
Posts: n/a
Default What am I missing?


"odin" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

<snip>


Entropy.

The universe is finite, so the *entropy* of the universe is finite.

Entropy is always increasing. Quite predictably so.

The entropy *used* to be less than what it is now. Quite predictably so.

Entropy cannot be negative.

The entropy of a one-particle universe is zero.

The entropy of a two-particle universe is greater than zero.

You are missing the inference that the entropy of the universe must have
been zero at some time in the past. At that time the universe must have
consisted of one particle.


Tom Davidson
Richmond, VA


Reply With Quote
  #4  
Old 07-12-2005, 09:52 PM
odin
Guest
 
Posts: n/a
Default What am I missing?

> The universe is finite, so the *entropy* of the universe is finite.

Is the universe is finite? How can we tell?


We see entropy increasing now, at least globally. Does it always increase?
Even if it does, how can we see the difference between *a* big bang and
*the* big bang? How can we tell local versus global?


Hmmm... never thought about that. But now you make me wonder if it can be
negative! Some think that mass and energy can be negative, bit hard to
imagine. I must admit that I cannot imagine entropy as negative. Can it be
imaginary, as disorder traded with other dimensions? My brane is starting to
hurt.



Reply With Quote
  #5  
Old 07-13-2005, 01:19 AM
N:dlzc D:aol T:com \(dlzc\)
Guest
 
Posts: n/a
Default What am I missing?

Dear odin:

"odin" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

Everywhere we look, look far enough, we see the CMBR. This is
only ~300,000 years after the Big Bang. New stuff isn't "popping
in", only older and older stuff is being discovered.


It has done so since the time of the CMBR. And it is
monotonically increasing.


We can only see the effects of one. The global one.


;>)

David A. Smith


Reply With Quote
  #6  
Old 07-13-2005, 09:02 PM
tadchem
Guest
 
Posts: n/a
Default What am I missing?


"odin" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

*Everything* we see is within 14 Gly of us.


The entropy of any *closed* system must increase. Entropy can decrease
*ONLY* if there is energy input from an outside source (like the sun's input
of energy to the earth, combined with the availability of a major
constituent that ca change phase [driving chemical processes that sergregate
components of mixtures, decreasing entropy]).

When your subject is the universe, then by definition there are no 'outside'
sources. Anything that can be a source of energy is *within* the universe.


No outside sources. The entropy of the UNIVERSE must have been zero at one
time.

to

Entropy is (by definition) proportional to the logarithm of the number of
states that a system can possibly possess - i.e. the logarithm of a positive
integer:
[Only registered users see links. ]
(equation 1)...

A 'negative' entropy implies that there is *less than one* state available
to the system (but more than zero states).


Tom Davidson
Richmond, VA


Reply With Quote
Reply

Tags
missing


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
missing residues in pdb file ozgun.harmanci Protein Forum 1 07-07-2008 03:54 PM
Missing Galaxy cluster Shadows and Huge CMB Voids seems to reason for a new raspberry shaped multiverse. LeoVuyk@gmail.com Physics Forum 0 09-05-2007 11:18 AM
Weight i.e gravity acting on phantom (missing) limb neo Physics Forum 4 09-03-2007 08:25 AM
Weight i.e gravity acting on phantom (missing) limb neo Physics Forum 0 08-31-2007 03:55 AM
Something basic missing Zarkovic Physics Forum 6 09-24-2005 07:07 AM


All times are GMT. The time now is 01:10 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright 2005 - 2012 Molecular Station | All Rights Reserved
Page generated in 0.15724 seconds with 16 queries