Claims require evidence, but how to evaluate WHO is making the claim?

Inspired by a dialogue in Getting Off the Space Elevator, wherein:


Is "It can’t be done’ a claim in any meaningful sense?

How can one be expected to support a statement to the effect ‘it can’t be done’?

Invariably in debates like this, assumptions are made about technological advances overcoming every barrier; is it accpetable to make these assumptions? is it up to the “it can’t be done” side to prove that such technological advances aren’t possible?
PS…I don’t want this thread to turn into another space elevator debate, thanks.

Sorry, I forgot to attribute that second quote, which was from AndrewL.

Well, I think it depends at least somewhat on which side of the debate is, for lack of a better words, “unpopular” or “most hotly contested.”

If the vast majority of people discussing an issue have decided that technological advances to surmount whatever obstacles will occur, then it’s up to the dissenting parties to provide a rationale [if not proof] of why they find it unlikely that such technology will develop. [“Scientists have been working on <insert central issue> with little progress for 20 years” or “<Important component> violates <basic law of physics>.”]

If, however, “prevailing wisdom” is that technological advances to solve problem X are unlikely, then it’s up to the dissenting party to motivate the likelihood of such advances. [“A thingy that would do this <important function> would require only small variations on <current technology>.”]

So if you’d like to come in and contradict everyone in the thread / conversation / what have you, you need to be able to support your position, even if your position can’t be proved.

Either that or try to help the majority understand that an unpopular or new claim is not necessarily “extreme”, amidst cries of “extraordinary claims require extraordinary evidence” - where “extraordinary” is judged by rigorous methods similar to those used in Miss America Pageants.

It is not reasonable to assume that technology will eventually conquerer everything. Many, many people participant in these threads don’t even have basic training in physics, which makes the whole thing so much more ironic.

For people who proposes a certain technological advance, it is up to them to illustrate how that can be achieved with today’s understanding of nature. Otherwise, it’s just silly bald assertion that nobody should pay attention to.