Chainoth, my assertion is based on history of science, more than science per se.
Just a couple of decades ago we all knew that the universe's expansion was slowing down. My old GR textbook devotes one sentence to the cosmological constant: assumes it's 0, admits it might not be. It then examines the 3 possibilities, k=-1, 0 or 1, for many pages: closed, asymptotically flat or open universe. The last, leading to heat death; the first, to the big crunch.
Then in 1998 studies of Type 1 Supernovae led to the current view that expansion is accelerating, as we all know. Don't get me wrong: I accept this finding; but feel it's provisional. It depends on hard-to-know assumptions: that the supernovae have the same light curve in early universe and that distance / age estimates are correct, within something like 5%; and others. I know that the astronomers involved give it 5 sigma confidence (or so) - and they're right, given their assumptions. But such results can easily change in the light of new information.
Some examples:
Just 3 days ago astronomers decided that a class of spiral galaxies (the "outrageously" luminous spirals) are at only 4 billion LY, not twice that! What are the chances that the supernovae estimated distances / ages are off by a few percent?
Recently LUX failed to find DM. The best physicist I ever knew - at the top of the field - told me in 2011, "If there's Dark Matter to find, LUX will find it!" (He was in charge of the North American effort). Admittedly if he were alive today he wouldn't actually give up on DM, just admit he was wrong about LUX. Still, I remember when we thought DM was probably brown dwarfs (undetectable by the technology of that era). 40 years of watching absolute certainty in physics turn into admission of defeat prompts me to take a wait-and-see attitude. If DM doesn't exist (remember aether!) all these expansion-of-the-universe calculations are thrown off.
Then there's galactic formation: everyone knew it must have taken 4 billion years, not long ago. Every time a new telescope sees deeper, they see more galaxies: now we're down to 400 million. What will the James Webb find? I'm certain of only one thing: it will find surprises.
Going back farther, Lord Kelvin - remembered today as a fool, for not seeing radioactivity, relavitity, and QM when it was right under his nose - was, in fact, one of the most brilliant physicists ever. If a man like that can miss things, so can we.
On the other hand, there have been great triumphs recently like the Higgs boson and gravitational waves. Higgs was very much against my expectations (I bet against it one year before it was found.) I remember when it was respectable to doubt Black Holes; that's no longer the case. The accuracy of physicists' theoretical predictions has often amazed me; it's incredibly gratifying to watch the steady accumulation of knowledge, much of it science-fiction just 4 decades ago, beyond doubt today. But I don't, yet, put accelerated expansion in that category.
But - let's assume it's perfectly correct. Alright, for 7 billion years expansion decelerated, then accelerated. What will happen 7 billion years from now? Might it decelerate again? Who knows? I can't believe that in that distant future, whatever strange intergalactic beings the human race has become will say to each other: "Darn it, those guys in the 21st century knew everything! Nothing left for us to discover!"
We don't even have a complete quantum gravity, and yet we're certain we know what happens 7 billion years, even 100 billion, from now - When not 20 years ago our ideas were upended.
We've gotten a very obscure look at MWBR from one point in space-time (here, today). Those future beings will have viewed it with resolution 10^whatever, from different galaxies over billions of years. Any possibility they come to different conclusions, when their database is something like 10^30 greater than ours? We're comparable to cavemen striking flint to make fire, and "knowing" how the sun works.
NOTE - I wrote the above, put it aside. Then, found talk in another post about MWBR strangely aligning with our solar system! May mean nothing at all; may mean we misunderstand MWBR. Unwarranted faith in tenuous theories can cause more problems than it solves. Have theories; but don't have faith.
"It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” - A. Conan Doyle
As I say: this is not about science per se, but science history, and common sense. It's not about denying new discoveries, but rejecting hubris and keeping an open mind.
Thanks for the opportunity to clarify my statement!
