There is no particular reason to assume that if the stars are moving away from each other right now, then they must always have done so. They could be expanding and contracting in a sort of sine wave, or something more complicated.
The key is there at the end of your quote. From the first set of observations (of relatively close galaxies), the simplest behavior that explained the observations was that everything was flying apart fast enough to overcome gravity. This predicted that when they had the technology to look at more distant galaxies, these too should be flying away from us, and at certain rates depending on their distance.
When we actually could observe those more distant galaxies, we did in fact see them red-shifted as predicted. This alone should be enough to put the “sine wave” theory in the epistemic category of “because the Dark Lords of the Matrix like red shifts”, because the light left these galaxies at all different times! It would take a vast conspiracy for them all to line up as red-shifted right now, from our perspective.
With strong evidence in hand that the galaxies had been flying apart for billions and billions of years, the scientists then noticed an irregularity: the velocities of those distant galaxies were different from the extrapolation made on the early data! However, they differed in a patterned way, and the simplest way to account for this discrepancy was a variant of Einstein’s “cosmological constant” idea.
Additional support for the Big Bang:
Stephen Hawking calculated that there would have been no way for matter to fly towards a point, “miss” colliding with itself, and fly apart in an apparent expansion without a singularity and Big Bang. (This is somewhere in A Brief History of Time, but Google Books won’t let me find it.)
We can roughly estimate our galaxy’s age by other means (i.e. how much hydrogen has been used up in stars, how much is left). Have you looked into this, to see whether the estimates thus derived are consistent with the estimate of about 10 billion years that the Big Bang theory implies?
ETA: Also, this seems like exactly the sort of issue where the “physicist-test” applies, as described above. For example, being critical of QM on common-sense grounds (of course the electron has to go through one slit or the other!) doesn’t make for discriminating skepticism, since one should assign high probability to physicists having strong evidence to this effect if they’re claiming something weird, or else one should have strong evidence that common sense usually beats the consensus of the physics community. Needless to say, I wouldn’t hold my breath on the second claim.
You win. I did not realize that we knew that galaxies have been flying apart for billions and billions of years, as opposed to just right now. If something has been going on for so long, I agree that the simplest explanation is that it has always been going on, and this is precisely the conclusion which I thought popular science books took for granted.
Your other arguments only hammer the nail deeper, of course. But I notice that they have a much smaller impact on my unofficial beliefs, even thought they should have a bigger impact. I mean, the fact that the expansion has been going on for at least a billion years is a weaker evidence for the Big Bang than the fact that it predicts the cosmic background radiation and the age of the universe.
I take this as an opportunity to improve the art of rationality, by suggesting that in the case where an unofficial belief contradicts an official belief, one should attempt to find what originally caused the unofficial belief to settle in. If this original internal argument can be shown to be bogus, the mind should be less reluctant to give up and align with the official belief.
Of course, I’m forced to generalize from the sole example I’ve noticed so far, so for the time being, please take this suggestion with a grain of salt.
I prefer the meme where you’ve just won by learning something new; you now know more than most people about the justifications for Big Bang cosmology, in addition to (going meta) the sort of standards for evidence in physics, and (most meta and most importantly) how your own mind works when dealing with counterintuitive claims. I won too, because I had to look up (for the first time) some claims I’d taken for granted in order to respond adequately to your critique.
I take this as an opportunity to improve the art of rationality
Good idea! It’s especially helpful, I think, that you’re writing out your reactions and your analysis of how it feels to update on new evidence. We haven’t recorded nearly as much in-the-moment data as we ought on what it’s like to change one’s mind...
When two people argue, and they both realize who is actually right, without drama or flaring tempers, then everybody wins. Even people down the block who weren’t participating at all, a bit; they don’t know it yet, but their world has become slightly awesomer.
The key is there at the end of your quote. From the first set of observations (of relatively close galaxies), the simplest behavior that explained the observations was that everything was flying apart fast enough to overcome gravity. This predicted that when they had the technology to look at more distant galaxies, these too should be flying away from us, and at certain rates depending on their distance.
When we actually could observe those more distant galaxies, we did in fact see them red-shifted as predicted. This alone should be enough to put the “sine wave” theory in the epistemic category of “because the Dark Lords of the Matrix like red shifts”, because the light left these galaxies at all different times! It would take a vast conspiracy for them all to line up as red-shifted right now, from our perspective.
With strong evidence in hand that the galaxies had been flying apart for billions and billions of years, the scientists then noticed an irregularity: the velocities of those distant galaxies were different from the extrapolation made on the early data! However, they differed in a patterned way, and the simplest way to account for this discrepancy was a variant of Einstein’s “cosmological constant” idea.
Additional support for the Big Bang:
Stephen Hawking calculated that there would have been no way for matter to fly towards a point, “miss” colliding with itself, and fly apart in an apparent expansion without a singularity and Big Bang. (This is somewhere in A Brief History of Time, but Google Books won’t let me find it.)
We can roughly estimate our galaxy’s age by other means (i.e. how much hydrogen has been used up in stars, how much is left). Have you looked into this, to see whether the estimates thus derived are consistent with the estimate of about 10 billion years that the Big Bang theory implies?
Finally, the cosmic background radiation gives us way more than one bit of data; its spectrum is precisely the black-body radiation one expects from a Big Bang.
ETA: Also, this seems like exactly the sort of issue where the “physicist-test” applies, as described above. For example, being critical of QM on common-sense grounds (of course the electron has to go through one slit or the other!) doesn’t make for discriminating skepticism, since one should assign high probability to physicists having strong evidence to this effect if they’re claiming something weird, or else one should have strong evidence that common sense usually beats the consensus of the physics community. Needless to say, I wouldn’t hold my breath on the second claim.
You win. I did not realize that we knew that galaxies have been flying apart for billions and billions of years, as opposed to just right now. If something has been going on for so long, I agree that the simplest explanation is that it has always been going on, and this is precisely the conclusion which I thought popular science books took for granted.
Your other arguments only hammer the nail deeper, of course. But I notice that they have a much smaller impact on my unofficial beliefs, even thought they should have a bigger impact. I mean, the fact that the expansion has been going on for at least a billion years is a weaker evidence for the Big Bang than the fact that it predicts the cosmic background radiation and the age of the universe.
I take this as an opportunity to improve the art of rationality, by suggesting that in the case where an unofficial belief contradicts an official belief, one should attempt to find what originally caused the unofficial belief to settle in. If this original internal argument can be shown to be bogus, the mind should be less reluctant to give up and align with the official belief.
Of course, I’m forced to generalize from the sole example I’ve noticed so far, so for the time being, please take this suggestion with a grain of salt.
I prefer the meme where you’ve just won by learning something new; you now know more than most people about the justifications for Big Bang cosmology, in addition to (going meta) the sort of standards for evidence in physics, and (most meta and most importantly) how your own mind works when dealing with counterintuitive claims. I won too, because I had to look up (for the first time) some claims I’d taken for granted in order to respond adequately to your critique.
Good idea! It’s especially helpful, I think, that you’re writing out your reactions and your analysis of how it feels to update on new evidence. We haven’t recorded nearly as much in-the-moment data as we ought on what it’s like to change one’s mind...
When two people argue, and they both realize who is actually right, without drama or flaring tempers, then everybody wins. Even people down the block who weren’t participating at all, a bit; they don’t know it yet, but their world has become slightly awesomer.