MadSci Network: Astronomy

Re: How does the Big Bang Theory go with Newtons Laws and Einsteins theories?

Date: Sun Apr 4 16:17:17 2004
Posted By: Steve Nelson, research physicist
Area of science: Astronomy
ID: 1080765835.As

First, Newton's laws fall underneath Einstein's relativity.  They may be 
derived from relativistic equations of motion, but are valid only where 
the speeds of objects under discussion are much less than the speed of 
light and gravitational acceleration (or other acceleration) is low.  But 
Newton's laws were important in the historical development of cosmology, 
as was relativity.  So your real question may take one of two flavors, 
historical and scientific.

1)  Historical...  Many books on the history of science exist which 
chronicle the development of physics.  Newton developed laws of motion 
which gave us a much more accurate framework in which to analyze 
observations of the stars.  Eventually, accurate measurements led to the 
discovery of small inconsistencies between Newton's theories and 
measurements.  Einstein's theory of relatvitiy resolves these
discrepancies, although that wasn't necessarily what he was trying to do when
he first came up with relativity.

Astronomer Edwin Hubble, observing that galaxies which 
were further away were moving away faster than galaxies closer to us (by 
looking at this very red-shift) was able to determine that the universe 
was expanding.  What caused the expansion, and where was the universe 15 
billion years ago?  Projecting the expanding universe back billions of 
years, we can calculate that the universe must have been hotter and
denser in the past.  This Big Bang theory was created to explain the 
evolution of the universe from that point to what we see today.  A google 
search, or any book on the history of science in the library would tell 
you a more exhaustively detailed story.  Page 500-501 of the book "An 
Incomplete Education" tells a shorter version, and any astronomy book 
should have a thorough account.

2)  Scientific...  There are an equally dizzying number of references to 
approach this from, and the above references are a good place to start, as 
is Brian Greene's "Elegant Universe" if you want to know more about more 
modern physics, cosmology, and how they are all related.  As I said 
before, Newton's laws (scientifically) are a special case of Einstein's 
relativity.  And Einstein's relativity is the language and framework in 
which we can get an overall picture of the universe, including the theory of 
the Big Bang, and how we derive its existence from current observations.  There 
are other theories involved, you should particularly look up information on 
blackbody radiation and the cosmic microwave background...Gingio Segre's 
book "A Matter of Degrees" is an excellent popular reference on this subject, 
as well as a good book on how science depends on and advances which are driven 
by the measurement of temperature and our understanding of thermal physics. 

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