yldoi: simple elements complete the following table using either your periodic table or your...
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YLDOI: Simple Elements
Complete the following table using either your Periodic Table or your enormous brain …
NAME SYMBOLATOMICNUMBER
ATOMICMASS
PROTONS NEUTRONS
Hydrogen H
Helium He
Lithium Li
YLDOI: Simple Elements
Complete the following table using either your Periodic Table or your enormous brain …
NAME SYMBOLATOMICNUMBER
ATOMICMASS
PROTONS NEUTRONS
Hydrogen H 1 1 1 0
Helium He 2 4 2 2
Lithium Li 3 7 3 4
Hot or Not?
The observations that all galaxies are moving away from us and the farthest galaxies are moving fastest lead to only one possible conclusion: the Universe is expanding — like a band of cats.
That means the Universe was smaller, hotter and denser in the past. Maybe even extremely so.
So, is there any EVIDENCE that we can see now that supports a hot & dense Universe in the past?
Hot or Not?CLUE 1: Nucleosynthesis
A big word that means atomic nuclei are made from protons and neutrons.
But I did all the work !
But I did all the work !
The Universe was NOT hot enough to make ALL elements, but WAS hot enough to make H, He and Li.
It was my idea.It was
my idea.
Hot or Not?Prediction:
Early on, the Universe would have been hot enough so there were only photons, electrons, protons and neutrons. Of these, we can make atomic nuclei out of the protons and neutrons.
But, what atoms would we make?
Hot or Not?Exercise:
How much hydrogen and helium would we have in the Universe NOW if we started with different ratios of protons and neutrons THEN?
Method:
• Get the number of pennies listed in the table (next slide) for your assigned ratio.
• Let “heads” be protons, and “tails” be neutrons.
• Construct as many hydrogen and helium nuclei that you can. AVOID LOOSE NEUTRONS if possible! (Nature doesn’t allow them.)
Hot or Not?
Method (continued):
• Enter your results in the table.
• We’ll do the calculations as a class.
Proton
Neutron
Hydrogen Nucleus
HeliumNucleus
Hot or Not?You’ll be assigned one of these …
Then, you’ll get these …and build these …
without leaving these (if possible)
Hot or Not?
Enter your results …
Hot or Not?
Hot or Not?
Proton:Neutron
Ratiop n H He Free
n MassH
MassHe
Mass%He
7:1 14 2 12 1 0 16 12 4 25The hot universe theory predicts that U started with 7 protons for every neutron …
Which DEMANDS that 25% of the U must be helium …
Hot or Not?
Proton:Neutron
Ratiop n H He Free
n MassH
MassHe
Mass%He
7:1 14 2 12 1 0 16 12 4 25
Which turns out to be EXACTLY RIGHT.
Hot or Not?
Bottom Line:
The Universe is made of 75% hydrogen and 25% helium (plus traces of other stuff like us) which requires a 7:1 proton-to-neutron ratio, which is exactly what would’ve been made in a hot dense Universe.
Hot or Not?
Bottomer Line:
A hot dense Universe would’ve produced exactly the right amountsof deuterium and helium-3, too.
(The theory is off a bit on the lithium …)
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Hot or Not?
Bottomest Line:
A hot dense Universe is also the ONLY known way to produce deuterium (heavy hydrogen). It’s not a product of Nature as we know it — yet it exists !!!
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