The Planck Era At the grand unified scale, gravity is weaker than the other forces But getting stronger as energy increases! At a temperature of about 1031 K, it is as strong as the others Maybe all forces are unified! This scale is called the “Planck Scale” A theory unifying all forces is called a “Theory of Everything” We don’t know what it would look like We have lots of candidates String theory, Loop quantum gravity, etc. t = 10-43 s T = 1031 K Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today

What Came Before the Big Bang? t < 10-43 s T ~ 1031 K No one knows One possibility: Eternal/Chaotic Inflation Inflation went on forever, and is still going on One small pocket escaped and became “our universe” Other pockets escaped and became others My guess: Space and time was created in the big bang Time becomes quantum uncertain “Before” becomes meaningless Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today

What is the Nature of Dark Matter? We don’t know, but there are always kooks who try to guess

What is the Nature of Dark Energy? We don’t know, but there are always kooks who try to guess

Multiple Universes What Do We Mean? Scientific Speculation! Some of these ideas are unproven or controversial But they are taken seriously by at least some scientists What do we mean by multiple Universes? The Universe is the totality of existence that we are aware of or can be aware of us If there are places that are real, but we can’t see them, they are other Universes

Reasons to Believe in Multiple Universes Universe might be infinite or very large In a big enough universe, anything can happen Completely separate universes may appear spontaneously If our universe came from nothing, why not others? Many Worlds Interpretation of quantum mechanics If correct, then everything happens

The Horizon 90 Gly Q. 115: Horizon Size The Universe has, apparently, a finite age: 13.8 Gy Nothing moves faster than light Naively, nothing can affect us more than 13.8 Gly away Because it was travelling in a smaller universe, it can actually go farther, about 45 Gly The volume of space withing 45 Gly is our horizon Sometimes called the visible universe Effectively, it’s our universe 90 Gly Q. 115: Horizon Size

A Big Universe is Many Universes Different parts of the Universe are cut off from each other If the Universe is infinite, there are infinitely many Universes

Spontaneous Creation of the Universe The universe we see could be created out of nothingness Quantum Cosmology The universe could be a bubble of order amidst a Universe of chaos Chaotic Inflation Not all bubbles need have the same properties Different physical laws Different numbers of dimensions?

Quantum Mechanics and Probability In the everyday world, we think of probability as expressing our ignorance ? 5

Copenhagen Interpretation of Q. M. Some processes are inherently quantum uncertain All possibilities actually occur Until a measurement occurs ? Q. 116: Copenhagen Interpretation of Quantum Mechanics 5

Many Worlds Interpretation of Q. M. All possibilities actually occur Even after a measurement occurs In many cases, the different possibilities become so disconnected, they effectively become separated universes ? We are only cognizant of one 1 2 3 4 5 6

Do People Take This Seriously? Many famous physicists, and a lot of obscure ones, believe in the Many Worlds Interpretation Murray Gell-Mann Steven Weinberg Stephen Hawking Richard Feynman That One

Life in the Universe What We Want to Know There is intelligent life on Earth Could it have happened elsewhere? Alien Spacecraft/UFO’s? Evidence is unconvincing Can we calculate probabilities? No Drake’s Equation is a way to estimate how many intelligent civilizations (besides ours) are in the galaxy

Q. 117: What Life Doesn’t Need Drake’s Equation N = R* fP nPM fl fi L N = number of civilizations in our galaxy R* = rate at which solar-type stars form fP = fraction of those stars with planets nPM= number of suitable planets and moons fl = probability of getting life fi = probability of life evolving intelligence L = lifetime of intelligent species Q. 117: What Life Doesn’t Need