Short office hours today

The Barn Door Paradox

Lorentz transform

Lorentz Transformation

                     

The primed frame moves with velocity v in the x direction with respect to the fixed reference frame. The reference frames coincide at t=t'=0.

Galilean Transformations

The Lorentz Transformations

)(' vtxx

)/(' 2cvxtt

yy '

zz '

4-vector

Faster than LightBlah blah blah

Captain Kirk, at the edge of the galaxy but at rest with respect to the earth, receives an instantaneous message from earth. How fast must I be going (relative to earth) in order to observe that the message was received before it was sent?

A : a very tiny velocityB : 0.5 cC : cD : I cannot see it received before it was

sent.

Velocity Transformations

21'

cvu

vuu

x

xx

)1('

2cvu

uu

x

yy

)1('

2cvu

uu

x

zz

What two velocities can two people in two different inertial reference frames agree on?

Two spaceships leave Earth traveling at a velocity of 0.5 c in opposite directions . . .

Achilles and the Trailer BedLike the fabled Achilles, who was immune to every lethal blow except to his heel, many of us have a special weakness that can be exploited to our spiritual downfall. For some, that weakness may be a taste for liquor, an unusual vulnerability to sexual temptation, or a susceptibility to compulsive gambling or reckless speculation. For others, it may be a craving for money or power. If we are wise, we will know our weaknesses, our spiritual Achilles' heels, and fortify ourselves against temptations in those areas.BY ELDER DALLIN H. OAKS - Ensign Oct. 1994

Relativistic Momentum

According to the special theory of relativity, if a 30-year old astronaut is sent on a space mission is accelerated to speeds close to that of light, and then returns to earth after 20 years as measured on earth, what would be his biological age upon returning?1. Less than 50 years2. 50 years3. More than 50 years

Individual question: We see a spaceship flying past at 0.9c. The captain of the spaceship launches a missile, which she sees leaving her ship at 0.9c out the front. We see the missile traveling at

1. A speed less than c2. A speed equal to c.3. A speed greater than

c.

Discussion question: The observed relativistic length of a super rocket moving by the observer at 0.70 c will be what factor times that of the measured rocket length if it were at rest?

A. 0.45B. 0.71C. 0.82D. 1.4E. 1.9

Discussion question: The crew of a spaceship watches a movie that is two hours long in a spacecraft that is moving at high speed through space. An Earthbound observer, who is watching the movie through a powerful telescope, measures the duration of the movie to be . . .A. Less than 2

hoursB. 2 hoursC. More than 2

hours

Notice I wrote “measure the duration” rather than “see the movie.”

According to the special theory of relativity, if a 30-year old astronaut is sent on a space mission is accelerated to speeds close to that of light, and then returns to earth after 20 years as measured on earth, what would be his biological age upon returning?A. Less than 50 yearsB. 50 yearsC. More than 50 years

Thought question: We see a spaceship flying past at 0.9c. The captain of the spaceship launches a missile, which she sees leaving her ship at 0.9c out the front. We see the missile traveling at

A. A speed less than cB. A speed equal to c.C. A speed greater than

c.