動量
牛頓版動量守恆 u u u’ ？ u 完全非彈性碰撞 v=u O’ O 牛頓版的動量守恆遵守伽利略變換下的相對性原則
但？如果考慮相對性效應….. u u u’ ？ u v=u O’ O 牛頓的定義使動量守恆不遵守相對性原則
新的定義 以Proper Time 取代時間 動量P是4-vector 在O’座標系中的動量 如果在O座標系中，Px及Pt都守恆，在O’座標系中，P’x自然保證守恆
u u u’ u v=u O’ O
新定義與舊定義的關係 接近牛頓的定義
P0是什麼？ 可以猜 動量守恆與能量守恆便整合成一個定律。 動量與能量的分別只是表面的
E=mc2 Using the relativity principle, Einstein is able to derive that the energy of an object can be written as For v=c, the energy is infinite. Hence you are never able to push an object faster than the speed of light! Even at rest, an object still contain an energy due to its mass: It opens up the possibility to convert mass into energy or vice versa.
Even at rest, an object still contain an energy due to its mass: It opens up the possibility to convert mass into energy or vice versa. 質量是能量的一種形式，能量守恆蘊含質量可以轉換為其他形式的能量，其他形式的能量亦可轉換為質量，質量不再守恆。
u u 質量不守恆，動能轉換成質量。 反之，質量轉化為能量，也有可能
原子能
If we can smash a coin and destroy it………. This is more than a day’s output of a power plant. Smash a coin and generate power plant.
Nuclei
束縛態
原子核質量 = 質子中子總質量 – 總束縛能/c2 束縛能越大，質量越小
總質量減少，消失的質量以能量形式釋出
Count the mass difference The mass total decreases and the difference turns into energy.
Chain reaction
Atomic bomb
核融合 Fusion
Sun and fusion
deuterium
宇宙核融合
With the current rate of burning, the sun will last for another five billion years.
Tabletop fusion and the scandal