The Great Stretch: The Ultimate Red Shift Quiz

If the source of light is moving away from the observer, then the light waves are stretched out. If light waves are stretched, then their wavelength increases. If the wavelength increases, then the light shifts toward the red end of the spectrum. Therefore, redshift indicates the galaxy is moving away.

If the universe is expanding uniformly, then the space between objects grows at a consistent rate. If there is more space between Earth and a distant galaxy than a close one, then there is more "expanding space" to push them apart. Therefore, the further a galaxy is, the faster it appears to move away.

If space itself expands while light is traveling through it, then the light waves must stretch along with the fabric of space. If the waves stretch, then their wavelength increases. If the wavelength increases due to the metric expansion of the universe, then this is defined as cosmological redshift.

If a star is moving toward the observer, then the light waves are compressed. If waves are compressed, then more wave crests reach the observer per second. If more crests arrive per second, then the frequency increases.

If we observe that velocity is proportional to distance (v=H0​d), then we need a constant of proportionality to represent that rate. If this relationship was discovered by Edwin Hubble, then the value is named the Hubble Constant.

If the Big Bang happened, then the early universe was extremely hot and dense. If the universe expanded and cooled, then that initial high-energy radiation would have stretched into longer wavelengths. If we detect a faint, uniform glow of microwaves across the sky, then it represents this cooled remnant radiation.

If a galaxy has a high redshift, then its light has been stretched significantly by the expansion of the universe. If the light has been stretched significantly, then it must have been traveling through expanding space for a vast period. Therefore, high redshift implies the light is from the very distant past.

If the expansion of the universe is the expansion of space itself between all points, then every point is moving away from every other point. If no point is the center of expansion, then an observer anywhere would see the same pattern of galaxies receding.

If the universe began at a single point and expanded, then we should see receding motion (Redshift), a leftover heat signature (CMB), and a specific ratio of hydrogen to helium formed in the early heat. If these three observations are verified, then they serve as primary evidence for the theory.

If a car moves away, the sound shifts due to its motion through air. If a distant galaxy "moves" away, the light shifts because the space between us and the galaxy is physically growing. Therefore, cosmological redshift is a property of space-time expansion, not just local motion.

If light passes through a cool gas, then the atoms in the gas will take up energy at specific frequencies. If that energy is removed from the continuous spectrum, then dark gaps appear. If these gaps represent missing light, then they are called absorption lines.

If the rate of expansion increases, then space is stretching faster than before. If space stretches faster, then light traveling through it is pulled to even longer wavelengths. Therefore, an accelerating universe results in higher observed redshifts for distant objects.

If redshift moves light toward the "redder" end of the spectrum, then it is moving toward longer wavelengths. If we look past visible red light on the electromagnetic spectrum, then the next region of longer wavelengths is the Infrared.

If the Big Bang was the origin of space and time themselves, then there was no "outside" space for it to explode into. If space itself is what started expanding, then the Big Bang happened everywhere at once. Therefore, it was an expansion of space, not an explosion in space.

If two galaxies are very close, then their mutual gravitational attraction is strong. If gravity is stronger than the relatively weak expansion of space at that small scale, then the galaxies can move toward each other. Therefore, Andromeda shows a blueshift because it is physically falling toward the Milky Way.

If the Hubble Constant is larger, then the universe is expanding at a faster rate. If the universe is expanding faster, then it would have taken less time to reach its current size from its starting point. Therefore, a faster expansion implies a younger universe.

If gravity can warp the fabric of space-time, then light traveling through that space must follow a curved path. If the path is curved like it is through a glass lens, then the effect acts as a magnifier or distorter. Therefore, this is called gravitational lensing.

If the wavelength of light increases due to expansion, then the frequency must decrease to compensate (c=fλ). If the frequency decreases, then the energy of the photon (E=hf) also decreases. Therefore, wavelength, frequency, and energy all change, while the speed (c) remains constant.

If the universe is expanding on a large scale, then the distance between most galaxies is increasing. If the distance is increasing, then their light must be stretched toward longer wavelengths. Therefore, the vast majority of distant galaxies exhibit redshift.

If gravity should pull matter together and slow down expansion, but observations show expansion is actually speeding up, then there must be an unknown force pushing outward. If this force acts as a repulsive pressure in the vacuum of space, then we label it "Dark Energy."