How do we know galaxies are moving away from us

Because their light is red-shifted

Explanation:

Doppler effect is a phenomenon that occurs when the source of a wave is moving relative to an observed. In particular, two situations are possible:

- The wave source is moving towards the observer --> in this case, the frequency of the waves appear to be higher than the original one; as a consequence, the wavelength of the waves appears to be shorter

- The wave source is moving away from the observer --> in this case, the frequency of the waves appear to be lower than the original one; as a consequence, the wavelength of the waves appears to be longer

This phenomenon occurs also for light waves. In particular, the light coming from distance galaxies undergoes Doppler effect as well, since those galaxies are moving relative to us. We have again two possible situations:

- The galaxy is moving towards the Earth --> in this case, the frequency of the light appear to be higher than the original one; as a consequence, the wavelength of the light emitted appears shorter (so, it shifts towards the blue color --> this is known as blue-shift)

- The galaxy is moving away from the Earth --> in this case, the frequency of the light emitted appears to be lower than the original one; as a consequence, the wavelength of the light appears to be longer (so, it shifts towards the red color --> this is known as red-shift)

Since the Universe is expanding, almost all galaxies are moving away from us: therefore, we notice a red-shift for the light coming from nearly all of them, and this is how we know they are moving away from us.

relativism, roughly put, is the view that truth and falsity, right and wrong, standards of reasoning, and procedures of justification are products of differing conventions and frameworks of assessment and that their authority is confined to the context giving rise to them. more precisely, “relativism” covers views which maintain that—at a high level of abstraction—at least some class of things have the properties they have (e.g., beautiful, morally good, epistemically justified) not simpliciter, but only relative to a given framework of assessment (e.g., local cultural norms, individual standards), and correspondingly, that the truth of claims attributing these properties holds only once the relevant framework of assessment is specified or supplied. relativists characteristically insist, furthermore, that if something is only relatively so, then there can be no framework-independent vantage point from which the matter of whether the thing in question is so can be established.

relativism has been, in its various guises, both one of the most popular and most reviled philosophical doctrines of our time. defenders see it as a harbinger of tolerance and the only ethical and epistemic stance worthy of the open-minded and tolerant. detractors dismiss it for its alleged incoherence and uncritical intellectual permissiveness. debates about relativism permeate the whole spectrum of philosophical sub-disciplines. from ethics to epistemology, science to religion, political theory to ontology, theories of meaning and even logic, philosophy has felt the need to respond to this heady and seemingly subversive idea. discussions of relativism often also invoke considerations relevant to the very nature and methodology of philosophy and to the division between the so-called “analytic and continental” camps in philosophy. and yet, despite a long history of debate going back to plato and an increasingly large body of writing, it is still difficult to come to an agreed definition of what, at its core, relativism is, and what philosophical import it has. this entry attempts to provide a broad account of the many ways in which “relativism” has been defined, explained, defended and criticized.

explanation:

answer: b.

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