medium · GMAT Verbal

Passage: The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. In the context of astronomy, this effect manifests as 'redshift' or 'blueshift.' When a celestial object moves away from the Earth, the light it emits is stretched, shifting toward the longer, redder wavelengths of the electromagnetic spectrum. Conversely, an object moving toward Earth exhibits a blueshift as its light waves are compressed. By measuring these shifts, astronomers can determine the radial velocity of stars and galaxies. Perhaps the most profound application of this principle was Edwin Hubble's observation that almost all distant galaxies are redshifted, and that their redshift is proportional to their distance from us. This finding provided the first empirical evidence that the universe is expanding, a cornerstone of the Big Bang theory. However, it is important to distinguish between the 'cosmological redshift' caused by the expansion of space itself and the 'Doppler redshift' caused by the local motion of objects through space. The author's attitude toward Hubble's observation can best be described as:

1. Critical of Hubble for failing to account for the local motion of galaxies.
2. Unbiased and purely descriptive, avoiding any evaluative language regarding the Big Bang theory.
3. Skeptical of the evidence used to distinguish between cosmological and Doppler redshifts.
4. Appreciative of its fundamental importance to modern cosmological models.
5. Dismissive of the expansion theory in favor of a more localized explanation of redshift.

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