PCS 581 Lecture Notes - Lecture 2: Cosmic Microwave Background, Ekpyrotic Universe, Big Bang
Lecture 2: Mysteries and Unknowns
What are Dark Matter and Dark Energy?
oWhich is more plentiful? Dark energy – 68% of the universe
What is the shape of the universe?
Could our universe be one of the many, in a multiverse?
What do we mean by “multiple dimensions”?
What is Dark Matter? MACHOS?
Mass that exists in galaxies
oOuter regions of the galaxy moving fast and a lot of the stuff we can’t see
oIs dark and can be large objects
Massive Compact Halo Objects
oThere are brown dwarfs and black holes – brown dwarfs are stars that are not
big enough to ignite
oThey are nice candidates for dark matter
oThere is a lot we don’t know – so we ruled it out
Dark Matter: Neutrinos?
Too-low mass, too fast!
Are very small particle – so small they are hard to detect – can pass through your hand
oCan kill you if it touches you dead
Didn’t much about them until today
Not dark matter – too fast that they can’t stick around in galaxy
When two particles fuse they shoot out neutrinos
Sun does a lot of fusion and it can expel a lot of neutrinos
How do you observe them?
oBuilt an observatory so nothing in space goes through it other than neutrinos
oFilled with water and neutrinos hit it and spark of light caught on camera –
slowly earned more and won a noble prize
Dark Matter: WIMPS? Weakly Interacting Massive Particles
How many times smaller is nucleus compared to electron cloud? – 10,000
Not neutrinos but something like them that interact weakly
Interacts weakly but massive than neutrinos
find more resources at oneclass.com
find more resources at oneclass.com
Electron cloud much bigger than the nucleus
Odds of hitting nucleus is much smaller
Dark matter is some sort of particle in the galaxy that interacts weakly
A WIMP Wind
As earth and sun orbit in galaxy, it is hit by winds of dark matter
Going through galaxy and moving all around us
They hit harder in June
Winds hit us harder in June – therefore the impacts of the wind would be harder around
that time
Detector: DM impact on gel pick up – snow does the same but never picked up DM
MOND: Modified Newtonian Dynamics
Completely different theory
Modified gravity
Stars in galaxy move quick – expected slower farther away bit not the case – so must be
more stuff that we can’t see that makes them move just as fast
Maybe we’re wrong about that?
oin reality saw the number if stars in the galaxy and how fast they moved
othey took newtons calculation and tweaked it
oConclusion: maybe gravity is stronger than we think instead of more stuff we
don’t see
Hard to disapprove
The Bullet Cluster: MOND vs. DM
Two galaxy clusters collided and went through each other
Will gas slow down when it collides with other gas? Yes – they’re not just going to
pretend they weren’t there
Will dark matter? (will dark matter feel friction?) No, it will just pass through
find more resources at oneclass.com
find more resources at oneclass.com
Finding Dark Matter
Could there be dark matter in the solar system? Yes
Could there be dark matter on/in earth? Yes
What would it “look” like? Nothing, we can’t see them
Dark Energy: A Cosmological Constant
Dark Matter is still a mystery and Dark Energy is even worse – no idea
If enough mass after Big Bang than Universe would have re-collapsed in on itself
Dark Matter may have been caught by Earth
Background Dark Matter I s smooth in the solar system therefore doesn’t affect us – but
not smooth in the galaxy with more in the centre
Dark Energy Quintessence?
If we don’t know how it works now, can we predict what it will do in the future?
Universe still expanding – accelerating by Dark Energy
If Dark energy does what it is doing, we will keep expanding forever and everything
would drift apart
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Mass that exists in galaxies: outer regions of the galaxy moving fast and a lot of the stuff we can"t see, is dark and can be large objects. Are very small particle so small they are hard to detect can pass through your hand: can kill you if it touches you dead. Not dark matter too fast that they can"t stick around in galaxy. When two particles fuse they shoot out neutrinos. Sun does a lot of fusion and it can expel a lot of neutrinos. Not neutrinos but something like them that interact weakly. Odds of hitting nucleus is much smaller. Dark matter is some sort of particle in the galaxy that interacts weakly. As earth and sun orbit in galaxy, it is hit by winds of dark matter. Going through galaxy and moving all around us. Winds hit us harder in june therefore the impacts of the wind would be harder around that time.
