Word for a topic with an unreachable conclusion

What would I call a topic or question with an unreachable (or almost so) conclusion? Example:

It is difficult to write a paper about the meaning of life because the topic is so _______.

or:

Political discussions at the Thanksgiving table are ________.

A similar term is a metaphysical question, but I am looking for a word/short phrase that more conveys the unlikelihood of coming to a definitive answer/conclusion. I searched Google and came up with nothing.

You can borrow the term for unsolvable mathematical problems which are said to be intractable

Not able to be solved (of a mathematical problem)

-- Wiktionary

1. It is futile to write a paper about the meaning of life because the topic is so unfathomable
2. Political discussions at the Thanksgiving table are futile

(OD) unfathomable, Incapable of being fully explored or understood.

inconclusive (although you might have to reword your sentences slightly for them to sound right)

Google's definition:

not leading to a firm conclusion or result; not ending doubt or dispute.[1]

Cambridge Dictionary's definition:

not giving or having a result or decision[2]

The usual descriptor, at least for your second example, is interminable.

RHK Webster's gives

interminable adj.

1. having no apparent limit or end; unending: an interminable job.

CED lists the hyperbolic usage as being the most usual:

interminable continuing for too long and therefore boring or annoying

For your first sentence, "It is difficult to write a paper about the meaning of life because the topic is so broad."

ODD 2 Covering a large number and wide scope of subjects. ‘the company has a broad range of experience’

In this specific example, unless one is discussing Douglas Adams, the scope of the topic is too large to lead to a reachable conclusion.

For your second, "Political discussions at the Thanksgiving table are interminable."

ODD Endless or apparently endless (often used hyperbolically) ‘we got bogged down in interminable discussions’

The two topics that I avoid at Thanksgiving are Religion and Politics. In both cases, a right conclusion depends on your beliefs. I find that when someone's core beliefs differ from my own we tend to talk past each other leading to no conclusion. So when anyone brings up Politics or Religion at Thanksgiving my response is, "Can you please pass the stuffing?"