[HN Gopher] Four years on, new experiment sees no sign of 'cosmi...
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Four years on, new experiment sees no sign of 'cosmic dawn'
Author : _Microft
Score : 100 points
Date : 2022-03-09 17:08 UTC (5 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| 9wzYQbTYsAIc wrote:
| Seems like cosmologists, astronomers, and physicists might now
| have enough new food for thought to fill in their boredom with
| quantum mechanics.
|
| Apparently, this result implies new information about dark
| matter.
| 77pt77 wrote:
| > to fill in their boredom with quantum mechanics
|
| What does this even mean?
| SiempreViernes wrote:
| No, this is rather a case of the old models probably being the
| more correct ones: the EDGES result itself was quite unexpected
| and hard to explain in the existing framework as it was much
| stronger than expected.
|
| Now that EDGES looks to be dead, the old predictions of a
| weaker effect are validated.
| 9wzYQbTYsAIc wrote:
| from the article:
|
| "a radio astronomer at McGill University in Montreal who
| wasn't involved in either experiment, says that both EDGES
| and SARAS were extremely thorough in their calibration and
| analysis procedures, and that it's too soon to say which
| result is correct. "The level of disagreement is enough to
| make people uncomfortable, but I think it's far from the end
| of the story," she said. "From my perspective, it adds to the
| excitement."
|
| And
|
| "Stranger still, the dip was very pronounced, suggesting that
| hydrogen in the early universe was colder than theoretical
| models predicted, possibly because of exotic interactions
| with the dark matter that fills the cosmos. Or perhaps the
| EDGES dip had a more mundane origin."
|
| The article seems to imply that the EDGES dip may be due to
| mundane, faulty experiment design, instead.
|
| In any case, a little bit of excitement for those scientists.
| djohnston wrote:
| Great to see the scientific method at work! I am a layman but
| curious to see the next report here.
| [deleted]
| deanCommie wrote:
| For any physicists reading, I have a question about the Big Bang:
| Is the standard consensus that the specific physical description
| is literal or just the closest approximation/visual model we have
| that matches the data?
|
| I ask because I was in my 30s before I learned that Dark Matter
| and Dark Energy are effectively metaphors. There is something
| that contributes more gravity in the universe than our
| understanding of the it predicts. And there is something that
| contributes energy to accelerating the expansion of the universe,
| and we have no idea what. So we call them "matter" and "energy"
| but TECHNICALLY they don't have to be right? It could also be
| that something exists that is completely beyond our bounds of
| understanding.
|
| I ask because this feels very much the situation with the Big
| Bang. Even if all the data shows the universe rapidly expanding
| in fractions of a second, it is incomprehensible to understand
| where the energy for it came from, or what happened "before". And
| the answer "nothing happened before because that's when time
| started" feels like an acknowledgement of the limitations of our
| human understanding.
|
| So here's my follow-up question: Obviously we build an
| understanding of the universe based on observations of the data.
| And sometimes the data doesn't match and we have to upgrade
| Newtonian Physics to Einsteinian, or introduce Quantum Mechanics,
| etc. So are there comparable/equivalent
| investigations/experiments going on today that reveal
| numbers/observations that are basically fundamentally
| unexplainable without looking beyond the realms of our
| understanding of the limitations of our universe?
| arcadi7 wrote:
| Not metaphors . We know these are out there -- we just don't
| know a lot about them. The situation is similar to atoms in
| second half of 19th century : we knew they are there , we knew
| some of their properties but only it the first quarter of 20th
| century we learned how much more there is to learn about atoms
| caymanjim wrote:
| Metaphor probably isn't the right word, but it's not really
| wrong either. "Placeholder" is also sorta correct but not
| entirely. Dark matter is a placeholder for an as-yet-unknown
| thing that interacts with gravity, in the most popular
| theories. There are less-popular ideas--still given serious
| study and consideration--like MOND that may some day explain
| the effects currently labeled as "dark matter". I don't think
| it's accurate to say "we know these are out there", and if it
| turns out that MOND or some other alternative explains
| observations, "dark matter" will turn out to have been fairly
| metaphorical (or just plain wrong).
| simonh wrote:
| The idea that the universe rapidly expanded in a fraction of a
| second right at the beginning is called inflation theory, it's
| a supplemental modification of the big bang theory and not all
| physicists that accept the big bang theory also accept
| inflation theory. There are also some theories that try to
| explain what there might have been 'before' the big bang,
| conformal cyclic cosmology for example. Then there's zero
| energy universe hypothesis, which suggests the universe may
| have arisen from a random quantum fluctuation - though a
| fluctuation of what is unclear.
|
| So there are quite a few alternative variations on big bang
| theories. The observation that the universe is expanding seems
| solid, and the detection of the cosmic microwave background
| means something must have happened long ago that blasted out
| all that energy, seemingly everywhere at once. When you go
| beyond those though things start to get less certain.
| Zenst wrote:
| Fascinating image and reminded me momentarily of Frogspawn, which
| is kind of fitting as they are looking at the Frogspawn of time
| itself.
| strainer wrote:
| The big image in the article is just an illustration of the
| subject, alas.
| overthemoon wrote:
| The photos of the EDGES antennas are beautiful. Tools used to
| study something so remote, set in remote places.
| eisvogel wrote:
| I've never heard it mentioned, but I strongly suspect that
| cosmological redshift is simply the result of photons losing
| energy over vast distances due to some as-of-yet-undiscovered
| interaction with the quantum vacuum. It was a couple of vatican-
| sponsored jesuits with an obvious creationist agenda who turned
| the observation of redshift into an assumption of spatial
| expansion to support the theory of a single-point-of-origin
| universe with a finite age and a finite size. I think western
| science is predisposed, due to religious cultural influence, to
| being uncomfortable with an infinite universe, because it implies
| our own ultimate insignificance.
| jl6 wrote:
| Science does not suppose a finite or infinite universe, but
| rather an observable universe of finite size plus an
| unobservable universe which may or may not be finite in size.
| Science is a lot more comfortable and accepting of uncertainty
| and unknowns that you give it credit for here.
| SiempreViernes wrote:
| I think that EDGES probably didn't see a real signal is more or
| less the expectation of the field. I remember that the feelings
| towards the result at the time was quite sceptical, and it seems
| it didn't take long before someone discovered that the published
| result wasn't very robust:
| https://telescoper.wordpress.com/2018/09/03/edges-and-foregr...
|
| The people from the follow up instruments are very polite about
| all this, which I guess makes sense if you've used the EDGES
| result to get money for your own antenna.
| wolverine876 wrote:
| Which critics have funding that depends on the EDGES result
| holding up (rather than, for example, finding something new
| themselves)?
|
| Do you work in that field? I've always read that competition is
| pretty brutal in natural sciences.
| simonh wrote:
| They don't necessarily depend on the EDGES result holding up,
| but may be to confirm/refute it. Even if your experiment
| refutes EDGES, you don't want to imply EDGES was utter bunk
| from the start, because if that was so why did you spend so
| much money bothering to test it? Your funding and project
| still depends on it having some credibility.
| akeck wrote:
| Maybe we can get one of these experiments onto the side of the
| moon not facing us...
| [deleted]
| willis936 wrote:
| I'm so excited for JWST's data. Observations from the
| inflationary period have the potential to completely upend
| cosmological dogma. Findings like this are the precursor. I'm
| sure theorists are furiously working on alternative models. This
| is an exciting period to watch.
| astro123 wrote:
| Inflation happened during the first tiniest fractions of a
| second post big bang. No telescope is going to make direct
| observations of the inflationary period so I'm not sure what
| you mean by this.
| jazzkingrt wrote:
| Well, I guess measurements of the early universe (100-250
| million years after the big bang) can test predictions made
| by models of the inflationary period.
| astro123 wrote:
| Measurements of pretty much any time in the universe can
| test predictions made by models of the early universe. One
| of the main reasons we think there was inflation is from
| late time (near today) observations of matter density (see
| https://en.wikipedia.org/wiki/Flatness_problem).
| throwawaycities wrote:
| > No telescope is going to make direct observations of the
| inflationary period so I'm not sure what you mean by this.
|
| Isn't this an engineering problem and what we are attempting
| to do with gravitational wave detectors?
|
| I know at one time it was believed gravitational waves were
| detected that provided direct evidence for inflationary
| theory but then the data was determined to be dust from the
| Milky Way. I thought this was still one of the major ongoing
| efforts in gravitational wave detection, was this ruled out?
| slowmovintarget wrote:
| This isn't just an engineering problem. Photons couldn't
| move around for the first 380K years or so. Space was
| nearly uniform, hot, and dense. The CMB is literally the
| heat wave left over from the point where the heavy soup
| thinned out just enough to allow photons to fly away in all
| directions.
|
| The gravitational waves from those events would have
| already warped space, and the ones just now reaching us
| would be from the edge of the observable universe, and so
| too weak for any instruments we could conceivably build in
| the next few decades. Not that we shouldn't try, mind you.
| There are new frontiers in quasimatter and time crystals
| that could yield far more accurate gravitational wave
| detectors.
|
| Also fascinating would be to attempt to decipher the
| deformations left in the metric already. There are some
| theories that basically say gravity waves permanently
| "crumple" spacetime, and it might be possible to read
| signatures of such events if this is so.
| dataflow wrote:
| > There are some theories that basically say gravity
| waves permanently "crumple" spacetime
|
| Does that mean those theories predict you can achieve
| permanent gravitational effects (locally) without any
| matter or energy to cause it? Wouldn't that violate
| relativity?
| simonh wrote:
| No, you still need something to create the gravity waves.
| The idea is that once a gravity wave has passed through a
| region of spacetime it leaves a permanent deformation. In
| the case of a detector like LIGO this means rather than
| the mirrors wobbling relative to each other and then
| settling down to their previous configuration, in fact
| they are left in a (very slightly) permanently altered
| configuration. The difference is probably way too small
| to detect though, for now anyway.
| dataflow wrote:
| I understand what you're writing (I think), but I don't
| think I understand how the implications would be
| consistent with relativity unfortunately. I thought
| gravity is (supposedly) caused by the deformation of
| space. If your space isn't flat, then you're going to
| experience acceleration (aka gravity) at that point,
| right? And if this deformation is permanent, then its
| source is already long gone - meaning that when you look
| down to see why you're falling, you see that there's no
| matter or energy causing you to fall. Which seems weird
| to me because I thought you need some kind of
| matter/energy to cause space to curve (and hence feel
| gravity/acceleration). Is that not the case?
| metalliqaz wrote:
| But those aren't really "telescopes", are they? :)
| throwawaycities wrote:
| Yes gravitational wave telescopes is commonly used along
| with gravitational wave detectors, gravitational wave
| instruments and gravitational wave observatories.
| willis936 wrote:
| I'm referring to the earliest era of transparent space, when
| conventional matter supposedly coalesced. If we look back to
| that period and still see red-shifted mature galaxies then
| something is very wrong with the current models. I'm under
| the impression that we don't have good observations of the
| period 375k-400M years after inflation and that infant galaxy
| observations have not been confirmed.
| metalliqaz wrote:
| The earliest moment of transparent space is the CMB. I know
| JWST can't detect Pop3 stars, but is there even
| expectations that it could detect proto galaxies with those
| stars? I thought it was still much later, like the early
| Pop2 generation.
| jxoxsknd wrote:
| digitcatphd wrote:
| Wouldn't the James Webb telescope be the optimal device for
| collecting and deciphering this data?
|
| Seems like we're on the brink of potentially the most significant
| scientific discovery since Copernicus, or are about to feel
| awfully stupid.
| adrian_b wrote:
| No, these signals are at a low frequency of around 1.4 GHz, not
| at the high frequencies of infrared or visible light.
|
| For such radio signals, much larger antennas are needed than
| what we can expect to have on space telescopes in the near
| future.
|
| A much more likely improvement, compared to what can be done on
| Earth, could be obtained by building a large radiotelescope on
| the Moon (i.e. with a large array of antennas), on its hidden
| face.
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