Professor: Many scientists hypothesize that there is an invisible "light-absorbing medium" in outer space.
Conclusion
There is no reason to believe that the hypothesis is correct.
rephrase: There is no reason to believe that an invisible "light-absorbing medium" in outer space explains our low visibility of other star systems.
Evidence (since)
The low visibility is already completely explained by the general theory of relativity.
Evaluate
This argument seems to think that if Eddie has already offered a convincing explanation for X, then there's no reason to believe Laura's explanation for X.
Couldn't more than one explanation be valid?
It seems like the author is thinking,
if X is completely no good reason to explained by relativity → believe any other explanation for X
If we wanted to try debating this argument to think of possible objections, we could think,
Given that ... Relativity completely explains why we can't see lots of other star systems,
How could we argue that ... There is still some reason to believe that an invisible light-absorbing medium in why we we can't see lots of other star systems?
Maybe we could say that they actually agree on important parts of the explanation. Like if Eddie and Laura were both witnesses to the same event, we wouldn't think, . After all, maybe they both have the same explanation for X.
Goal
Look for an answer reflecting the reasoning move of, .
Or look for an answer ruling out the objection that maybe these scientists and relativity agree / overlap a lot in terms of how they're explaining the low visibility of other star systems.