What about time ? What about their traces ? How do particles move ??? What about time ? What about their traces ? 5/23/2019 Dora Wagner HST 2001 Dora Wagner

What to measure ? What to know ? 5/23/2019 Dora Wagner HST 2001

What does velocity mean ? “How quickly an object moves from one point to another !” “The distance moved per unit of time.” “The rate of change of displacement.” 5/23/2019 Dora Wagner HST 2001

Now the formula : V = Ds ------- Dt Dt : interval of time Ds : distance traveled 5/23/2019 Dora Wagner HST 2001

… the steeper, the faster ! How fast? How slow ? distance … the steeper, the faster ! time 5/23/2019 Dora Wagner HST 2001

But nothing can go faster than light ! The speed of light is c = 300 000 000 m/s, and... … all little particles inside the bubble chambers were travelling nearly as fast as the light ! 5/23/2019 Dora Wagner HST 2001

Particles are interacting and decaying in a bubble chamber ! … are all particles recorded ? … are there some, which don’t leave traces ? 5/23/2019 Dora Wagner HST 2001

… the particles… ? … where do they come from ? … where are they going to ? … how do they move ? … what do their traces look like ? … are they going straight or curved ? … how long do they stay ? 5/23/2019 Dora Wagner HST 2001

What is the smallest interval of time you can imagine ? 5/23/2019 Dora Wagner HST 2001

Then it materialized into an electron… LOOK ! A photon travelled between the two marked points. The travelled distance was exactly 11.5 cm! Then it materialized into an electron… …and a positron. 5/23/2019 Dora Wagner HST 2001

Can you calculate the travelling time taken by the photon? Ds = 11.5 cm Dt = ? 5/23/2019 Dora Wagner HST 2001

REMEMBER ! Ds v = ------- Dt c = 300 000 000 m/s, 5/23/2019 Dora Wagner HST 2001

Unbelievable ? Dt = Check your result 5/23/2019 Dora Wagner HST 2001

… a few billionths of a second ! Dt = 383 Picoseconds … a few billionths of a second ! 5/23/2019 Dora Wagner HST 2001