suminha wrote:
Quasars---celestial objects so far away that their light takes at least 500 million years to reach Earth---have been seen since 1963. For anything that far away to appear from Earth the way quasars do, it would have to burn steadily at a rate that produces more light than 90 billion suns would produce. But nothing that burns at a rate that produces that much light could exist for more than about 100 million years.
If the statements above are true, which one of the following must also be true on the basis of them?
A. Instruments in use before 1963 were not sensitive enough to permit quasars to be seen.
B. Light from quasars first began reaching Earth in 1963.
C. Anything that from Earth appears as bright as a quasar does must produce more light than would be produced by 90 billion suns.
D. Nothing that is as far from Earth as quasars are can continue to exist for more than about 100 million years.
E. No quasar that has ever been seen from Earth exists any longer.
Posted from my mobile device
Question type : Infer, Must Be True
<Information from the statement>
1) Quasars is at least 500 million light years away from the Earth.
2) Quasars started to be seen since 1963.
3)
Any celestrial obects at least 500 million light years away from Earth like Quasars burn steadily at a rate that produces more light than suns would produce to be seen from the Earth.4) But
they can not exist for more tham 100 million years.
Now, let’s evaluate the options below.
A. Instruments in use before 1963 were not sensitive enough to permit quasars to be seen.
-> No infos about the instruments in unse before 1963 was mentioned above. Therefore we can’t even judge the validity of this option. Pass.
B. Light from quasars first began reaching Earth in 1963.
-> We only can find the information about when the light from quasars first started to be seen, not when the light started to go towards to the Earth. Pass.C. Anything that from Earth appears as bright as a quasar does must produce more light than would be produced by 90 billion suns.
-> Not only this option is “meh” using extreme expression such as <<must>>, but also the statement does not offers any infos to generalize like this option. We are given with the RATE that produces more light tha 90 billion suns would produce, not brightness. As you must, it can be Can Be True, not Must Be True. Pass.D. Nothing that is as far from Earth as quasars are can continue to exist for more than about 100 million years.
-> Same trick as option C above. The statement says that nothing that burns at a RATE that produces that much light could exist for more than about 100 million years. This option is talking about distance. Pass.E. No quasar that has ever been seen from Earth exists any longer.
-> This option needs little bit of math. So since the birth of quasars, its light started to travel to earth, or every where cuz the light doesn’t have a path, it spreads. Its light arrived on Earth at 1963, and at that point, it was 500 million years old. But wait, the statement says that quasars’ life expectancy is 100 million years old. Therefore, quasars was already dead when its light arrived to Earth. And only its light, which had been radiated from quasars will travel until it fades away. Therefore, quasar extists any longer. E must be true.Hope it helps