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HUBBLE'S LAW...
 Now, the most amazing discovery of Hubble (which is why
we named the space telescope after him). Most of you have probably
heard of Hubble's law but it is one of the most confusing things
in astronomy and cosmology and it is frequently misunderstood,
misinterpreted, and mis-taught. Here is Hubble's law, I have
just drawn several of these galaxies; here is the Milky Way.
Here is another galaxy and then here is another one. What Hubble
discovered was that you can measure the velocity of these galaxies
through the Doppler shift. The fact that something that is traveling
away from you is admitting light at a certain frequency but since
it is traveling away it takes longer for those individual pulses
to reach you, that's the Doppler shift. It is often called a
"red shift" because many of these things are moving
away, and as they move away you look in the spectral lines and
they are at a longer wave length --- they are "red shifted".
From this we can measure the velocity of recession. He measured
this from many galaxies. He could also estimate the distance
of the galaxies, very crudely if you just take the galaxy's apparent
and assume most of the small ones and dim ones are further away.
There are many more sophisticated ways of estimating distance
now. (In fact, my up-to-date information that I got actually
last night, involves one of the ways of estimating distance.)
What Hubble determined was that the galaxies that were further
away were moving away from us, they were all moving away from
us and the ones that were further away were moving away faster.
The ones that were twice as far away moved away twice as fast.
This is disturbing to many people. Does this mean that we are
at the center of universe? Everything is moving away from us!
This is actually a very nice mathematical issue for those of
you who love to work with vectors. There is a way of demonstrating
that that is not true, but let me show you my preferred way of
explaining what is going on. This is Hubble's law.
The Universe Before
The Big Bang
(Actual Size) |
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One way you might be tempted to explain Hubble's law is
like this: assume that the universe began with all of the matter
lumped into a tiny little clump which then exploded and the earth
happened to remain at the center. In this Sidney Harris cartoon,
the universe before the big bang, actual size. Then as the thing
blew apart the objects that were moving faster are further away
and that explains Hubble's law. This is the way many people interpret
Hubble's law but not scientists who are knowledgeable about the
field. There is just an enormity of evidence that say's this
picture is not correct, and when I say there is misinformation,
there is a wonderful quote attributed to Mark Twain that I use
all the time. "The trouble with most folks isn't so much
their ignorance, it's knowing so many things that ain't so".
Actually I checked with the Mark Twain research program at UC
Berkeley and they say that is actually not his quote. It was
probably said first by Josh Billings, another humorist in the
1800's.
CONTINUE
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