Our Premium and Ultimate plans guarantee up to 90+ points score increase or your money back.
We cover every section of the GMAT with in-depth lessons, 5000+ practice questions and realistic practice tests.
Study whenever and wherever you want with our iOS and Android mobile apps.
Adaptive learning technology focuses on your academic weaknesses.
Which of the following is suggested about redshifts?
We know that we can learn about an object's velocity and direction from the Doppler Effect, which produces apparent sensory effects, in this case a light which appears more red from the observer's perspective than it normally is, i.e. a redshift.
Since Hubble used these redshifts to argue that the universe is constantly expanding, we may infer that if an object indicates a redshift (as opposed to a blueshift) it is moving away from the observer. We may also infer that the more redshifted an object is, the faster away it is moving from the observer.
The author uses redshifts as an example of the Doppler Effect, which only tells us about the velocity of an object and its direction, not the distance between an object and an observer. While more distant objects are more redshifted than close objects, there is no indication that the distance can be determined from the redshift itself.
Redshifts were used by Hubble to argue that the universe is expanding, and therefore a redshift must be an indicator of objects' motion away from the observer. We know from the fourth sentence that when objects move away from each other, the frequency becomes lower, not higher.
A redshift is a a sensory effect produced by the Doppler Effect, which may occur between a moving source of waves and a moving (as well as stationary) observer.
Although a redshift is not an indication of distance, this statement happens to be true for objects outside the galaxy of the observer. However, it is not true for objects within the observer's galaxy, and therefore cannot be the correct answer.