From there one can go several places. You can take the existence of your favoured god on pure faith and be a theistic agnostic, you can simply say “who cares” and drop the whole debate, or you can defer to Occam’s Razor and be an atheistic agnostic.

Agnosticism in the other context you mention doesn’t seem appropriate to me.

1) It doesn’t interact via the electromagnetic force. (we know this because, well, it’s *dark*, and because CMB power spectrum results show that it interacted with the photon-baryon fluid only through gravitation)

2) It’s stable (as in, it has existed through the entire lifespan of the universe without decaying, which lets out such particles as free neutrons, which meet the first criteria)

3) It’s not neutrinos. There just aren’t enough and they don’t weigh enough.

4) Based on 1-3, it isn’t any particle which has yet been observed.

5) It clumps on large scales, and forms a much greater proportion of overall mass at large scales (e.g. galaxies, or clusters of galaxies) than at small scales (e.g. stars and solar systems). This is also likely a result of 1-3.

6) It’s at least fairly massive and “cool” (i.e. not relativistic), or it would have smoothed out the structure in the universe much more than it has. Whether it’s “cold” or “warm” is as yet undetermined.

For example, it is the current position of quantum physics that the position and momentum of a particle can not both be known simultaneously (the Heisenberg Uncertainty Principle). That’s a kind of agnosticism, although perhaps it isn’t the most natural word to use. Granted, it might be the case (as with all scientific theories) that quantum physics itself might be wrong, but that doesn’t affect what the theory says in the meantime.

Further, in mathematics it can be proved that some things are unproveable. I’m having trouble thinking of an exact example now though… some ideas about algorithms with infinite run times come to mind but I’ll have to look it up.

But of course these are fields which depend on their precision of language. In our everyday lives and social sciences, it’s much more difficult to use the word agnostic and actually mean it. People often accuse (religious) agnostics about being wishy washy in their beliefs, but to be truly agnostic requires a conviction at least as strong as the most devout athiest. Defeatist it most certaintly is not.

The solution is not to redefine what agnostic means (i.e. to indicate a weaker position of mere indecisiveness or ignorance rather than fundamental unknowability) but rather just admit what we don’t know (or haven’t decided) and get back to figuring out what the answers are.

The stuff we know and the stuff we can do now would seem positively godlike to a medieval peasant. Who knows what we will be able to achieve and what new evidence we will uncover in the coming centuries? To say that something is forever unknowable seems short-sighted and defeatist.

It seems that when you hear “agnostic” you immediately assume the temporary case, whereas I think by default (and by definition) it is the permanent one. To be agnostic means you believe something to be fundamentally unknowable, which is an epistemologically different sort of problem from whether or not we currently know (or can conclude) something.

To say you are agnostic about dark matter means you think it’s impossible to prove or disprove its existence.

That’s not entirely true. In The God Delusion, Dawkins differentiates between what he calls TAP and PAP. That is temporary agnosticism and permanent agnosticism. Permanent agnosticism says something can never be proven/disproved. Temporary agnosticism says that based on current evidence we cannot be sure either way.

I’m agnostic about dark matter until enough evidence is available to confirm it (and to explain what it actually is). I’m agnostic about life on other planets until we have better numbers. As the probability increases in scale and accuracy, my agnosticism decreases.

Having said that, the press release you quoted pushes my dark matter agnosticism from 50% to about 40%.

I always get this problem when I tell people that I don’t believe in God but I also believe it’s impossible to disprove his existence. They always ask, “doesn’t that mean you’re agnostic?” It doesn’t, since if God exists, then there’s no reason it would be impossible to prove it. Disprove is different since you can always redefine God to be just outside what we do know. But that’s a theological problem.

As a matter of fact, I would say it is actually impossible to be
agnostic about certain things, such as life on other planets. All you have to do is either make contact or go visit other planets to find them. It may be impractical, but there is no fundamental reason why that knowledge (whether aliens exist or not) is unattainable.

As a sidenote, dark matter has actually been directly observed recently: http://home.slac.stanford.edu/pressreleases/2006/20060821.htm