What well-established theoretical argument concludes that intelligent life exists elsewhere in the galaxy that isn't speculative like those based on Drake's equation?
Uniformitarianism.
"If it happened this way once, it's likely to happen this way again."
Arguably the most fundamental and well-established scientific argument in existence.
Perhaps, but then if both are irrational then the example doesn't support your argument that theoretical support is the "difference between the two" that would allow one to be labeled irrational while another is rational, as you implied here:
I never claimed that belief in Bigfoot is rational. I claimed that belief in Galadriel is MORE irrational than belief in Bigfoot.
Yet both are irrational beliefs.
Yes. An argument can fail to be contradictory while nevertheless remaning implausible to the point that belief is irrational. Similarly, a theoretical argument may be sufficiently far-fetched that it demands little credence.
It's theoretically possible that I might have flown to Monte Carlo last weekend and won fifty billion Euros. It violates no law of physics. It is immensely implausible, to the point where any rational observer would dismiss it out of hand without further supporting evidence.
Which means that even with "theoretical support" a belief can be irrational.
Yes. So what?
That seems to rule out theoretical support or lack thereof as a criteria by which one can label one belief irrational and another belief rational since Bigfoot would be a counter-example rather than an example.
Yes, if you're looking for a
single criterion by which to label all beliefs as rational or irrational, you will fail to find one. Similarly, if you are looking for a
single criterion to distinguish a good job application from a poor one, you will fail to find one. That's because beliefs, like job applications, can fail in a number of different ways.
However, it's fairly safe to say that a belief for which no credible empirical evidence can be cited
and for which no theoretical support can be given is irrational.
You'll have to define "well-founded" I think. Nearly all scientific theories are considered "well-founded" until they are proven wrong.
Er, no, although it wouldn't surprise me if all the theories which which you are familiar are the well-founded ones. Read some of the cutting-edge journals and see some of the wild speculations that scientists feel free to indulge in in exactly those cases where there is little experimental evidence. Physics is a good discipline for that.
An example of an ill-founded scientific theory -- as I said, it's really little more than a hypothesis -- is the idea (popularized by Arthur C. Clarke, among others) that there is
life on Europa. There's no "firm evidentiary basis" for Dr. Greenberg's speculations, and he would no doubt be among the first to admit that. As a working theory, he's perfectly free to speculate about what kind of life it might be, and more importantly, about what traces it might leave so that we can find it. But I don't think I would characterize anyone as irrational who didn't believe in Europan life, despite Dr. Greenberg.
Any scientific theory that has been refuted would be a valid example.
No.
Scientific theories are only refuted when new evidence comes along. It is rational to reject an old belief in favor of new evidence, almost by definition. One of the major intellectual hurdles to the acceptance of Darwin's theory of evolution was the lack of evidence for the process of heritance and genetic variability. The rediscovery of Gregor Mendel's experiments filled in that hole. It would have been rational for one of Darwin's contemporaries to reject Darwin's theories on the basis that the evidence just wasn't there.... not so today.
The "plum pudding model" of the atom was rejected when Rutherford ran his experiments. It was not irrational to believe in the plum pudding model beforehand, because we didn't know any better. Learning that the atomic nucleus exists makes belief in the plum pudding model irrational.
How about causation? Wasn't that a "well-founded" scientific theory until quantum theory contradicted it?
Er, no. Quantum theory has not contradicted causation.
Don't some scientists still hold the opinion that causation is true
Most of them, I should think. All the ones that don't wear underpants on their heads....
and that the "well-founded" quantum theory is wrong?
No. Because quantum theory doesn't contradict causation.
If so, are they irrational?
Any "scientist" who believes tha quantum theory contradicts causation is at best ill-informed.