2 The Technique

Even if there is only one pos­sible uni­fied theory, it is just a set of rules and equa­tions. What is it that breathes fire into the equa­tions and makes a uni­verse for them to describe? The usual approach of sci­ence of con­structing a math­e­mat­ical model cannot answer the ques­tions of why there should be a uni­verse for the model to describe. — Stephen Hawking

1 Begin­nings

“It was almost as incred­ible as if you fired a 15-​​​​inch shell at a piece of tissue paper and it came back and hit you.” — Ernest Rutherford

2 Com­plex numbers

“The ulti­mate goal of math­e­matics is to elim­i­nate any need for intel­li­gent thought.” — Alfred N. Whitehead

3 The Schrödinger equation

“I do not like [quantum mechanics], and I am sorry I ever had any­thing to do with it.” — Erwin Schrödinger

4 The fuzzi­ness relation

“If we want to describe what hap­pens in an atomic event, we have to realize that the word ‘hap­pens’ can apply only to the obser­va­tion, not to the state of affairs between two obser­va­tions.” — Werner Heisenberg

5 Quan­ti­za­tion of energy

“While I am describing to you how nature works, you won’t under­stand why nature works that way. But you see, nobody under­stands that.” — Richard Feynman

6 The hydrogen atom

“The paradox is only a con­flict between reality and your feeling what reality ought to be.” — Richard Feynman

7 Clas­sical mechanics in a nutshell

8 From clas­sical to quantum

“The most exciting phrase to hear in sci­ence, the one that her­alds the most dis­cov­eries, is not ‘Eureka!’ (I found it!) but ‘That’s funny…’” — Isaac Asimov

9 Beyond “either-​​​​or”

“The appear­ance of a def­i­nite posi­tion x during an obser­va­tion … is then regarded as a cre­ation existing out­side the laws of nature.” — Wolf­gang Pauli

10 Com­pat­i­bility

“Of all the the­o­ries pro­posed in the 20th cen­tury, the sil­liest is quantum theory… The only thing quantum theory has going for it is that it is unques­tion­ably cor­rect.” — Michio Kaku

11 Quantum states (output)

12 Quantum states (input)

“Who­ever endows the wave func­tion with more meaning than is needed for com­puting observ­able phe­nomena is respon­sible for the con­se­quences.” — Nico van Kampen

13 Whence those “rules of the game”?

“Quantum mechanics makes absolutely no sense.” — Roger Penrose

14 The meaning of mass

“Elec­trons seem to have modes of being, or modes of moving, avail­able to them which are quite unlike what we know how to think about.” — David Z. Albert

15 Why spe­cial rel­a­tivity? (I)

16 Why spe­cial rel­a­tivity? (II)

“The essence of sci­ence: ask an imper­ti­nent ques­tion, and you are on the way to a per­ti­nent answer.” — Jacob Bronowski

17 The prin­ciple of least action

18 From quantum to clas­sical (effects)

19 From quantum to clas­sical (causes)

“Matter is not made of matter.” — Hans-​​Peter Dűrr.

20 Spin, Zeno, and the sta­bility of matter

“Ein­stein said that if quantum mechanics is right, then the world is crazy. Well, Ein­stein was right. The world is crazy.” — Daniel Greenberger

21 Entan­gle­ment, Bell revisited

“Unper­formed exper­i­ments have no results.” — Asher Peres

22 Going rel­a­tivistic

“Physics is math­e­mat­ical not because we know so much about the phys­ical world, but because we know so little; it is only its math­e­mat­ical prop­er­ties that we can dis­cover.” — Bertrand Russell

23 The Stan­dard Model

“I think sci­ence has enjoyed an extra­or­di­nary suc­cess because it has such a lim­ited and narrow realm in which to focus its efforts. Namely, the phys­ical uni­verse.” — Ken Jenkins