Geek44 & I must have had a Vulcan mind meld in the "All-American nose
art thread & we started discussing astronomy. I thought I better move
our discussion here in case there is people interested that didn't check
out the other thread & to keep from totally hijacking the other thead ...
Anyway, here is relevant quotes:
Quote:
Originally Posted by Geek44
Quote:
Originally Posted by Brett
Totally off topic, it reminds me of when I 1st heard the
question “Why is it dark at night”? If the universe was
infinitely vast with infinitely many stars, wouldn’t the
night sky be just as bright as day?
I had encountered many dark nights, but had never
thought to ask why …
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I've often wondered the same thing about the darkness of the universe at night. I can add a question and two points here.
Question; Why can't we see the massive black hole at the centre of the galaxy? It must have the mass of a million suns. As matter falls into it, it flares with all kinds of wavelengths as it crosses the event horizon which must be huge.
Point 1; Photons from stars further than the sun are scattering in all directions...maybe they hit our eyes in small numbers compared to the concentrations we get from the sun which is closer, or even an electric light.
Point 2; The universe is only 'dark' to one's photon sensitive eyes. If we could see x-ray or radio waves, it would be very 'bright'.
I'm a bit of an armchair physicist/astronomer. Currently trying to understand 'string theory'. Now...if you'll excuse me, I'm needed in an alternative dimension.  |
(Bright non visible - Point 2) Good Point. I had never
thought of that or read it. It just goes to show
why I love the subject so much, the more you
learn, the more you realize there is much more
to learn.
I’m not sure of your math background, so forgive
me if I repeat something obvious to you below.
(photons hit eye - Point 1) I’m not sure I understand this.
One thing I thought of later after hearing the night
sky paradox was – Wait a minute … infinite sums
don’t necessary add up to infinity (for instance
PI = 3 + 0.1 + 0.04 + 0.001 + … = 3.1415 ... & adds up to
less than 3.2).
I asked about this on an astronomy forum
& the reply I got was that you can do a calculus
integration (a generalization of addition for
infinite sums) and if there is infinite time + stars
the integration will add up to a bright night sky.
I have a college Math degree but haven’t used anything but HS algebra for
years, so I got lost on their answer, but its on my list …
(see center galaxy - question) From what I understand
there is dark clouds between us & the center.
I forgot to add that infinite time + stars &
vastness is hard to reconcile with a dark night
sky. If the universe was infinitely old, the
dark clouds would have time to be heated
to visibility.
(string) Have you read “The Elegant Universe”
by Brian Greene? It’s the best book on string theory
I have read (well, it’s the only, but I thought
it was very good). One thing I mean to explore
is the theory says each point in 3-D space is actually
rolled up 10-D points (much as a 3-D pipe looks
2-D if seen from far enough away).
The picture in the book (& try showing 10-D in 2-D!),
reminds me of fractal dimension objects. For instance,
a coastline has a bigger D than a 1D line, but less than
a 2D plane. So it might have a dimension of 1.4. Similarly
mountains has a bigger D than a 2D plane, but less than
ordinary 3D space. So it might have a dimension of 2.36.
What I want to ask is: Could the universe have a fractal
dimension - for instance 6.3 or 5.8?