ACTIVITIES: Myearbot Albert Einstein S Simultaneity

ACTIVITIES: MyEarbot — Albert Einstein’s simultaneity

Imagine two observers, one seated in the center of a speeding train car, and another standing on the platform ………. the train races by. As the center of the car passes the observer on the platform, he sees two ………. of lightning strike the car - one on the front, and one on the rear. The flashes of light from ………. strike reach him at the same time, so he concludes that the bolts were simultaneous, since he knows that ………. light from both strikes traveled the same distance at the same speed, the speed of light. He also predicts ………. his friend on the train will notice the front strike before the rear strike, because from her perspective on the platform the train is moving to meet the flash ………. the front, and moving away from the flash from the rear. But what does the passenger see? As her ………. on the platform predicted, the passenger does notice the flash from the front before the flash from the rear. ………. her conclusion is very different. As Einstein showed, the ...... of the flashes as measured in the reference frame of the train must also be the speed of light. So, because each light pulse travels the same distance from each end of the train to the passenger, she can only conclude one thing: if she sees the front strike ...... , it actually happened first. Whose interpretation is correct - the observer on the platform, who ...... that the strikes happened simultaneously, or the observer on the train, who claims that the front strike happened before the rear strike? Einstein tells ..... that both are correct, within their own frame of ...... This is a fundamental result of special relativity: from different reference frames, there can never be agreement on the ...... of events.

ACTIVITIES: MyEarbot — Albert Einstein’s dilation of time

Cloze test 2.

Two spaceships are traveling together through the galaxy at ………. to the speed of light. Mounted on one ship is a laser that can fire pulses of light, and on the other, a mirror. The pilot of the first ………. fires a pulse at the mirror, and watches as it is reflected back. A clock on board measures how ………. the round trip takes. But now suppose that he does this as the ships are passing an observer on a nearby asteroid. According to relativity theory, this observer sees the …………. moving through space at exactly the same speed that the pilot does -- namely, the speed of light. But he also sees the pulse traveling a longer distance, because ………. his perspective, he must add the forward motion of the ships to the motion of the pulse between them. So he measures a longer time interval for the round ………. than the pilot does, because he is watching the pulse go farther without going any faster. This effect is called time …………….: if one observer is moving with respect ………. another, each perceives that the other's time is flowing ………. slowly. National Science Foundation