Picture this:
The left hand end represents what can be “seen” directly from earth, relatively local and recent in red-shift terms. Look out any window. Out into space, backwards in time.
CMBR, (Cosmic Microwave “Background” Radiation) at the right end, represents the iconic echoes of the original big-bang in microwave-visible structures. So iconic, the little strip of the “heat map” already carries the whole story. Verily, a meme.
Blog post and original paper, both by Stacy McGaugh.
(Hat tip to Sabine @sdkh for tweeting links)
Blog Post on Tritonstation:
“The next cosmic frontier: 21cm absorption at high redshift.“
Paper on Arxiv:
“Predictions for the sky-averaged depth of the 21cm absorption signal at high redshift in cosmologies with and without non-baryonic cold dark matter.“
So much cosmology suffers from doubts of can it really be science? – regarding the tenuous and indirect nature of any “empirical” evidence to support speculative interpretations of what little can be observed, if anything. The CMBR heat-map originally created a stir because it appeared to show structure (very early in the history of the universe) in which our perspective, (as human observers on earth today) was reflected in the patterns of those structures.
That ought to be impossible. It suggests Copernicus was right, we, the earth, our solar system, really are somehow the centre of the universe.
To paraphrase any number of cosmologists at the time.
Of course the smart-money, philosophy, was always on the side of some observer effect. That our would-be objective model of physics is after all a human construct, probably with our perspective as observer (ie model-builder) built into the story. It’s only natural. Humans are – obviously – the center of physics. We built this city. Science can’t be as entirely objective as it would like to be. Physics is anthropic.
If that was literally true of the cosmos, not just our model of it, there is a good deal of supernatural explanation to be denied. And denial is what bad physicists did. Physics is political.
Good physicists keep looking, theoretically and empirically. Theoretically you can make a teleological (information / entropy / patterns) argument that intelligent life is in some sense an end – an objective – of cosmic evolution. Central in some grand scheme of things, even if a geometric cosmic centre in space-time is a moot concept. More denial, obviously, from bad physicists. Good theoretical physicists, those that recognise the metaphysical dependencies in their natural philosophy, are working on many fronts to explain what is going on. Many philosophers too.
But the science of this story still depends on some good physicists finding some empirical evidence to join up these extremes of cosmic evolution with some middle-ground.
The search for gravitational waves was part of that story. But when stakes are so high – the entire supernatural vs objectivity confusion – agendas are (almost) inevitably politically motivated to deny one side of the argument. As Brandon Carter pointed out many years ago – in earlier “fine-tuning” debates, long before the CMBR observations – the mere suggestion of the word Anthropic sends most physicist screaming for the hills in denial of any such possibility as a matter of policy. People stop listening.
Which is where the latest work by Stacy McGaugh (with original linked at the top) comes in. Good news is – whatever the technical, empirical detail and the statistical interpretations (eg in the significance of very small differences between mind-bogglingly large numbers for example), not to mention the physics itself- human perceptions of the boundaries of possibility are acknowledged rather than denied.
“Wonderfully, the atomic physics of the 21cm transition is such that it couples to both the radiation and gas temperatures in a way that matters in the early universe. [Me neither, but.] It didn’t have to be that way ” most transitions don’t [*]. Perhaps this is fodder for people who worry that the physics of our universe is fine-tuned.”
“In the meantime, I think we’re obliged to take their result seriously, and not just hope it goes away (which seems to be the first reaction to the impossible).”
Worth a read. Don’t worry, be happy. Keep calm and carry on. Onward and upward.
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[Post Note: (*) Transitions?
Phase-transitions – really are part of this “fluid” picture.]