CMB seems not counterfactual. The discovers did have to notice it and remain confused about how it was unexplained by problems with their equipment, and then be receptive to being told about a paper about how there might be radiation from the early universe. But the discovers were just looking at a sensitive radio detector meant to detect radio waves reflecting off hot air balloons. Anyone that developed sensitive equipment and then try to see faint signals would’ve noticed the mysterious noise.
Given the sheer importance of radio technology, I think there’d be many instances of people developing a similarly sensitive device and noticing the noise. It surprised me to learn that already at the time there was a paper about the possibility of radiation from the early universe, which plausibly sped up discovery. Note also that some astrophysicists nearby were (independently of the first discoverers, not independently of the paper as some of the people wrote the paper) about to look for a signal in the right region with the explicit intent of looking for background radiation.
So, if anything here is counterfactual, it would be Dicke and Peebles predicting the CMB. But I still don’t buy it, because even if nobody predicted it, people would’ve seen it not that long in the future. In fact before the main discovery in 1964, McKellar in 1941 observed a background appearing like a blackbody with the right temperature while observing the spectra of a star. He even guessed it had some significance.
CMB seems not counterfactual. The discovers did have to notice it and remain confused about how it was unexplained by problems with their equipment, and then be receptive to being told about a paper about how there might be radiation from the early universe. But the discovers were just looking at a sensitive radio detector meant to detect radio waves reflecting off hot air balloons. Anyone that developed sensitive equipment and then try to see faint signals would’ve noticed the mysterious noise.
Given the sheer importance of radio technology, I think there’d be many instances of people developing a similarly sensitive device and noticing the noise. It surprised me to learn that already at the time there was a paper about the possibility of radiation from the early universe, which plausibly sped up discovery. Note also that some astrophysicists nearby were (independently of the first discoverers, not independently of the paper as some of the people wrote the paper) about to look for a signal in the right region with the explicit intent of looking for background radiation.
So, if anything here is counterfactual, it would be Dicke and Peebles predicting the CMB. But I still don’t buy it, because even if nobody predicted it, people would’ve seen it not that long in the future. In fact before the main discovery in 1964, McKellar in 1941 observed a background appearing like a blackbody with the right temperature while observing the spectra of a star. He even guessed it had some significance.