#23 - Quasars—celestial objects so far away that their

[nvesti]

The stimulus in this question gives facts about Quasars and the question stem asks what must be true. However, I am unable to figure out why E is correct. Does it have to do with the difference between the 500 Million years and the 100 Million years in the stimulus?

Thanks in advance.

[Dave Killoran]

Hi Nvesti,

Yes, exactly, it does center around the 500 vs 100 time periods!

Think about it this way: the quasars burn so brightly that they only last 100 million years. Yet, it takes 500 million years for the light to reach the Earth. So, by the time the light reaches here, the quasar has already been burned out for 400 million years. It's a like a live TV program that lasts an hour, but the signal takes a week to reach us: by the time the signal reaches us, the live program has already ended.

Please let me know if that helps. Thanks!

[nvesti]

This makes perfect sense. I was looking at it complete wrong. I thought that since it can only last 100 Million yrs, the light would never make it to earth since that takes 500 Million yrs, but now that you clarified these to time frames are not mutually exculsive it makes perfect sense. Thanks!

[SherryZ]

Thank you very much for your patience and time!

Oct 1999 LSAT, Sec 4, Q23:

I picked D but the correct answer is E. Could you explain E is right but D is wrong???? They are so similar to me.

Thanks again!

---Sherry

[Dave Killoran]

Hi Sherry,

The essence of (D) and (E) can be reduced to:

• Answer choice (D) says nothing really far away from earth can last more than 100 million years.
  
  Answer choice (E) says the quasars that we see, which are really far from earth, don't exist anymore.

Right away I'd be a bit suspicious of (D) because it is so broad and powerful: nothing far away can last more than 100 million years. Is there evidence in the stimulus that supports a statement that sweeping? There isn't.

Answer choice (E), on the other hand, is supported. What the stimulus is describing is a "radio effect" situation where the signal is sent out, and keeps traveling through space until it reaches us. When we finally receive the signal, the source "program" is over.

With the quasars, we know they are really far away, and according to the stimulus they burn so brightly that they last a relatively short amount of time (in the grand scheme of things). So, when a quasar first comes into being, it burns really brightly for a 100 million years then flames out. But, that light continues traveling across space, and after 500 million light years, it reaches earth. So, if we see a quasar pop into existence, what we are witnessing is an event that happened long ago, but the light from the event is only reaching us now. And, it took so long to reach us, that not only are what we seeing is very old, the quasar itself has already burned out. Hence, if we can see a quasar from earth, it is no longer in existence, and answer choice (E) is correct.

Please let me know if that helps. Thanks!

[LSAT2018]

So is the scope of the stimulus limited to anything that is far away to appear from Earth the way quasars do AND anything that burns steadily at a rate that produces more light than 90 billion suns would produce? So based on the scope, answers (C) and (D) can immediately be eliminated because they aren't sufficient?

[Dave Killoran]

So is the scope of the stimulus limited to anything that is far away to appear from Earth the way quasars do AND anything that burns steadily at a rate that produces more light than 90 billion suns would produce? So based on the scope, answers (C) and (D) can immediately be eliminated because they aren't sufficient?

Well, the scope of the stimulus is more than those statements, because you have things in there about 1963 and distances. But, more specifically to your point, (C) goes outside the scope by stating "anything" and (D) does so by stating "nothing." Those are, as you note, claims that are too broad to meet the limitations within the argument.

Thanks!