PCS 581 Lecture Notes - Lecture 1: Planck Units, Atomic Nucleus, Super Force
Lecture 1: The Big Bang
Course Philosophy
We live in a big, mysterious Universe
Humanity has found a way to figure out the rules: the scientific method
oScientific method is a way of problem solving
We want to describe the things we observe
We want to explain and understand those things
We must appreciate our place in the Universe, and our ability to discover, explore and
learn
Looking Back
The Andromeda Galaxy is 2.5 million light-years from us
If we see a supernova going off inside it, when did that star actually explode? – 2.5
billion years ago – light takes 2.5 years to travel to earth
Light is a natural time machine into our past
The farther away it is the longer it takes light to reach us
The farther away we look, the farther back we are looking in time
The Observable Universe
Age of the universe: 13.7 billion years ago
Observe using light, which travels at 300,000 km/s
Can we see past 13 billion light-years? No
Can there be a galaxy 100 billion light-year away from us? Yes
oWe can look back 14 billion light years into the past – it is just how far we can
see. The world doesn’t just end there. It is just the observable universe. There is
more that we can’t see
We see back in time. Only Limit: we can’t see beyond 14 billion years
Universe was born 13.7 billion years ago, and we can’t see anything beyond that
Can only see up to 14 billion lights years ago – we see the big bang
The Motions of Galaxy
Distant galaxies are moving away from us
The universe is moving
There is no centre of the universe – we’re not in the centre even though it may look like
that
Expansion of the Universe and the Big Bang
The farther away they are, the faster they are moving away
Looked at light from different galaxies
When something is moving away from us, it will be red shifted (doppler effect)
When something is moving towards us, it will be blue shifted
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50/50 – some blue, and some red
The farther away the more red shifted meaning moving faster
Galaxies are set in place, only space is expanding – that’s why it looks like galaxies are
moving
Raisin bread example – everything is moving away
The Everywhere Stretch
The Big Bang should be called the Everywhere stretch
Just space stretching out, nothing exploded
Hit rewind on the big bang – everything comes closer – we call it the singularity: the very
beginning
The universe started as a single small tiny point – singularity – it is at that point where
we get stuck and know nothing beyond
We are an infinite piece of raisin bread moving in all direction – the bread is carrying the
raisins away
We’re moving twice as far and twice as fast – no change in speed, just the space in
between
Everything is isolating with time
The stuff farther away is moving away faster
The Big Bang
The Big Bang was an event that happened everywhere in space
Everything in space is expanding
It was a smaller point and our observable universe stretched and expanded –
everywhere and in every direction
Hubble’s law: the farther away things are the faster they are moving away – not exactly
moving but are being carried away
“Just a theory” is very dismissing
Theory is never proven wrong – a model that works very well – and the model thus far
works very well
So, saying “just a theory” is very wrong
The Big Bang or Everywhere Stretch?
What do you picture when you hear:
oThe Big Bang – an explosion
oEverywhere Stretch – raisin bread
The big bang was a derogatory term – too evocative of something that isn’t right
Raisin bread example is a better way to understand a picture the everywhere stretch
not the big bang
There are still universes beyond our observable universe
Calculating Backwards
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find more resources at oneclass.com
Forget “picturing” this stuff, rely on physics
oDensity, pressure, temperature, knowledge of particles and how they interact,
etc.
We can work backwards with the law of physics to within one ten-billionth of a second
of the Big Bang
But earlier than that, the laws of physics change
oAt best, with the most cutting-edge physics theories, we can push to within 10-43s
after the Big Bang
What does it look like when everything overlaps in space? We can picture 1/10 billionth
of a second after the Big Bang – can’t look at anything beyond that – earlier than that
the law of physics starts to get weird and hard to understand
The Laws of Physics: Four Fundamental Forces
Strong forces hols nucleus together
EM is stronger than gravity – EM is a lot stronger
Why does everyone talk about gravity and not electro magnetism? We are normally
neutral – protons and neutrons are balanced. And EM doesn’t matter because
everything cancels out – but not gravity
Which is important in large scales?
Small scale: strong and weak forces win out
oStrong binds atomic nuclei
oWeak plays a role in nuclei reactions, and it’s the only force that affects
neutrinos and WIMPS
The strong and the weak balance each other
Forces in the Universe
Maybe the “four forces” are just aspects of one or two fundamental forces
Water example
oUnder different conditions it takes different forms – water becomes steam in hot
environment
Universe is very hot and very dense – and everything is the same thing
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
We live in a big, mysterious universe. Humanity has found a way to figure out the rules: the scientific method: scientific method is a way of problem solving. We want to describe the things we observe. We want to explain and understand those things. We must appreciate our place in the universe, and our ability to discover, explore and learn. The andromeda galaxy is 2. 5 million light-years from us. 2. 5 billion years ago light takes 2. 5 years to travel to earth. Light is a natural time machine into our past. The farther away it is the longer it takes light to reach us. The farther away we look, the farther back we are looking in time. Age of the universe: 13. 7 billion years ago. Observe using light, which travels at 300,000 km/s. Yes: we can look back 14 billion light years into the past it is just how far we can see.
