[HN Gopher] Scientists say they may have detected dark energy
___________________________________________________________________
Scientists say they may have detected dark energy
Author : Osiris30
Score : 124 points
Date : 2021-09-16 11:25 UTC (1 days ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| mabbo wrote:
| This is neat, but I would take it with so many grains of salt.
|
| We don't know what dark matter is. We have some ideas. XENON1T
| was/is testing some of those theories about dark matter.
|
| We know next to nothing at all about dark energy. We're pretty
| sure it's a thing, or else our model of the universe is just
| completely wrong and it's not anything at all.
|
| So if XENON1T finds something that doesn't fit their model of
| dark matter, going on a limb and saying "I dunno, maybe it's dark
| energy?" is a fun thought experiment and model, but at best it
| might lead to further experiments to see how likely that model is
| to be true. And from what I'm reading, that's the attitude the
| scientists behind XENON1T are taking here.
|
| But alas, we all know that tomorrow we can expect pop-sci
| articles saying "DARK ENERGY HAS BEEN SOLVED".
| scrumbledober wrote:
| I only skimmed your comment and all I saw was "DARK ENERGY HAS
| BEEN SOLVED"
| raattgift wrote:
| Sunny Vagnozzi can't really be said to be suddenly coming up
| with the idea - there are several obviously related preprints
| at https://arxiv.org/a/vagnozzi_s_1.html
|
| I'd like to give some broad background on the link at the top
| of this discussion.
|
| If one substitutes "dark energy" with "quintessence field
| driving the accelerated expansion" one gets closer to what the
| press release (and associated paper, found at
| https://journals.aps.org/prd/abstract/10.1103/PhysRevD.104.0...
| ) discusses. The "quint" in "quintessence" refers to a "fifth
| fundamental force", which I'll get to below.
|
| As early as the 1920s (per https://arxiv.org/abs/1211.6338
| which is _really_ good history of science) relativists were
| discussing whether some long-range force could stabilize a
| universe filled with dense matter, which would otherwise have a
| tendency to collapse over surprisingly short timescales (e.g.,
| attempts to measure the age of the Earth by studying
| radioisotope ratios and coming up with billions of years of
| planetary age meant Earth should already be squashed into the
| remains of a collapsed universe). Einstein preferred a
| geometrical solution, the cosmological constant, to model the
| obvious non-collapse.
|
| With the 1990s discovery of the accelerating expansion (
| https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_...
| ) this preference has been vindicated in the effectiveness of
| the standard cosmology, \Lambda-CDM, where \Lambda is the
| cosmological constant. It captures in one variable the measured
| value of the accelerated expansion, even taking into account
| disputes over the exact value of the Hubble constant.
|
| The bulk scatter of redshifting luminous matter in universe is
| best approximated by the Friedmann-Lemaitre-Robertson-Walker
| equations, with the Robertson-Walker term being a metric
| describing a universe that, if one considers 2d-plane-slicing
| of space, is like a stack of plates, where each plate is
| stacked upon an earlier plate, and in turn supports a stack of
| later plates. The Robertson-Walker metric has parameters which
| define how flat each plate is -- typical dinner plates, tea
| saucers, and so on tend to be curved so that liquids don't roll
| off the edges. (We observe distant galaxies "rolling out of
| sight", growing too dim and too red to see). The R-W metric
| also has parameters which define the evolution in size from one
| plate to the next. Plates may get bigger towards the future;
| stay the same size; decrease; or even oscillate; depending on
| the parameter function. Bigger here means that we consider the
| radius from the centre of the plate to the edge. When we add
| the Copernican Principle, which says our model should not
| require that Earth be at or even very close to the exact centre
| of the cosmos (if there even is such a centre), we take this to
| mean the distance from us (or any comparable observer) to the
| observer-centred cosmological horizon.
|
| In our universe, we have exceptionally flat "plates" stacked in
| such a way that earlier plates are much smaller than larger
| plates. The "plates" at this age of the universe have a
| diameter of nearly a hundred billion light-years. The
| accelerated expansion means that the growth in the future
| direction is superlinear. And of course, we extend the 2-d
| planar plates to a 3-d volume.
|
| However, we can go the route that Einstein did not prefer,
| namely that something non-geometrical is at work driving the
| accelerated expansion of the universe. In that case, we
| probably retain the ideas from Robertson-Walker and stack up
| "plates", but choose a function where either all the plates are
| the same size, or where the plates grow purely linearly -- no
| acceleration of the expansion. (The latter approach is how
| cosmology was modelled when the expansion was believed to be
| _inertial_ , driven by some early-time impulse that went away
| around the time of the hot big bang).
|
| To this non-accelerating universe, we have to add something to
| make galaxies continue to accelerate apart, rather than
| drifting apart inertially, or recollapsing in the distant
| future. We add nonzeros to the _tension_ (aka pressure, but
| negative) components of the stress-energy tensor. That tensor
| is really a tensor-field where each point in spacetime has a
| tensorial value which describes the flow of energy-momentum in
| and out of a point, including in the timelike-direction. In
| general the tension term must be very small, or the accelerated
| expansion would look very different, and galaxies would look
| even more different. In general the tension must vanish inside
| stable gravitationally bound structures. Moreover, the tension
| term must also appear _in vacuum_ in deep inter-galaxy-cluster
| space.
|
| When we study mechanisms that can plausibly generate such
| stress-energy, we'd tend to be drawn towards our best
| fundamental theories for known forms of matter, namely the
| Standard Model of particle physics. We'd want to _extend_ the
| Standard Model by introducing some particles which give rise to
| interpretation as carrying and feeling a new _fundamental_
| matter force to go with electromagnetism and the nuclear
| forces. This is usually called a _fifth_ force, but maybe
| better to be just called yet another long (as in practically
| infinite) distance force comparable to electromagnetism or
| Newtonian gravitation.
|
| Now, an aside. Manhattan is not undergoing cosmic expansion.
| The Earth-Moon system is not expanding. Neither is our solar
| system to the best of our ability to measure. Our galaxy and
| the cluster that it's in do not appear to be expanding. Distant
| galaxy clusters appear to be bound together against the
| cosmological accelerated expansion.
|
| In the standard cosmology we are forced to say that the cosmos
| _in bulk_ is best described by the Friedmann-Lemaitre-
| Robertson-Walker model, but that local systems, like Earth, are
| best described with exterior Kerr metrics, or a Lemaitre-
| Tolman-Bondi collapsing metric, which we can stitch together
| through an annoying process called the Israel-Darmois Junction,
| or alternatively we can use something inhomogeneous that
| captures a set of these Kerr /Schwarzschild-like metrics all at
| once. This is no big deal; general-relativists do this all the
| time at much smaller scales with good results. Cosmologically,
| for instance, "swiss-cheese" models are reasonably powerful,
| where the "cheese" is the increasingly sparse expanding space
| and the "holes" are voids where the matter is collapsing into
| ever denser arrangements.
|
| A fifth force model _also_ has to avoid an expanding solar
| system. It can do this in at least two ways. Firstly, one can
| distribute the sources of the fifth force carefully in such a
| way that they are almost exclusively found outside galaxy
| clusters. (We take a similar approach with Dark Matter, which
| is found mainly inside galaxy clusters; the exclusiveness of
| Dark Matter is less strict than what would have to apply to a
| fifth force particle family). Alternatively, one could create
| an interaction with matter which turns the fifth-force charge
| into something else, like a low-mass particle such as the
| axion. This process is called "screening" when a large object
| like the sun (or its magnetic field) encourages this
| conversion. One could then compare the environment around the
| sun and Jupiter to see a mass-dependence or magnetic-field-
| strength dependence on such screening, or even look to more
| extreme objects like magnetars.
|
| This paper by Vagnozzi chases a small deviation from expected
| results towards this type of fifth-force screening by the sun
| driven by theoretical particles which [a] seek to solve a
| problem in the Standard Model of Particle physics, [b] are
| decent candidates for at least some of the dark matter energy-
| density, and [c] are still as far as I know theoretical rather
| than discovered. https://en.wikipedia.org/wiki/Axion
|
| At this stage, this idea is a more complicated way of capturing
| the results we have from many astrophysical observations in a
| way that must practically completely reproduce what we get from
| the FLRW equations of \Lambda-CDM. More complicated because it
| adds parameters to the energy-density of the standard
| cosmology. It also almost certainly would require additional
| parameters in the Standard Model of Particle Physics. These are
| not impossible demands, but will be difficult enough to do in
| practice that few people will make realistic attempts without
| more compelling results than those reported by Vagnozzi et al.
| mindcrime wrote:
| This may be one of the best HN comments I've ever read.
| Thanks for posting. I do have a question though. Probably a
| stupid one, as IANAP(hysicist).
|
| Regarding this:
|
| _Now, an aside. Manhattan is not undergoing cosmic
| expansion. The Earth-Moon system is not expanding. Neither is
| our solar system to the best of our ability to measure. Our
| galaxy and the cluster that it 's in do not appear to be
| expanding. Distant galaxy clusters appear to be bound
| together against the cosmological accelerated expansion._
|
| Do you mean that Manhattan (and the Earth-Moon system, etc.)
| literally _are not expanding_ even one smidgen, or do you
| mean that at that scale the expansion is just too small to
| (notice|measure|care about)? I ask, as I 'd always
| interpreted "expansion" as being space itself expanding, and
| thought that it happened at all scales (including now that I
| think about it, inside of atoms, which could cause some weird
| stuff???). But are we saying that expansion isn't something
| that happens at all scales then? Eg, that only the space
| between galaxies (or between galaxy clusters) is expanding?
| If so, that makes the whole expansion issue feel even weirder
| than ever to me, and it felt weird enough before!
| thechao wrote:
| IANAP, but I've been through early courses in QM & GR. The
| negative value of the tensor (could be) dependent upon the
| local curvature, such that in the region of massive objects
| the tensor is 0 or positive (which means "regular" GR
| dominates); and, "very far away" (in the cheese), the
| tensor is negative, and causes expansion.
| zardo wrote:
| >(including now that I think about it, inside of atoms,
| which could cause some weird stuff???).
|
| If the distance between electrons and protons were
| expanding over time, that would be hard to square with
| quantitized energy levels for electron orbitals. Not sure
| if you could get around having material and chemical
| properties changing over time.
| raattgift wrote:
| Thank you.
|
| This is not a stupid question:
|
| > Do you mean that Manhattan (and the Earth-Moon system,
| etc.) literally are not expanding even one smidgen, or do
| you mean that at that scale the expansion is just too small
| to (notice|measure|care about)?
|
| More the former.
|
| In General Relativity, we have several exact solutions of
| the Einstein Field Equations, which basically means we have
| a lot of standard spacetime metrics. The Schwarzschild
| metric for a central spherically symmetrical non-rotating
| mass is one. The Kerr metric, which is essentially an
| axisymmetric deformation of Schwarzschild is another. There
| are related metrics which incorporate gravitationally
| collapsing matter into a spacetime like these.
|
| Many such solutions are _asymptotically flat_. Very
| roughly, the inverse square law for gravity means that at a
| large distance you can ignore the gravitation of a central
| mass (which grows more and more pointlike in gravitational
| behaviour with increasing distance). Eventually you 're in
| an area where the gravitational contribution can be
| ignored. In the language of General Relativity you are in
| _effectively_ flat spacetime. The function of distance goes
| asymptotically to flat. There are obvious analogies with
| electromagnetism: distant stars are dim and pointlike, and
| really distant ones can be clumped together in larger
| structures with their clumped-together light curves being
| an example of an aggregated observable. (Indeed even at the
| level of a single star we are aggregating lots of tiny
| events into one spectrum equipped with emission and
| absorption lines, both for close-up stars and for distant
| ones).
|
| We have some procedures available that let us stitch
| together asymptotically flat spacetimes with a "thin shell"
| mathematical boundary used to translate values from one
| side of the stitching to another. We can thus build up our
| solar system as a hierarchical stitching-together of Kerr-
| like metrics (one for each rotating body) each of which can
| "meet" another at some relatively flat-space point.
|
| We can even stitch in Kerr-like metrics into a broader
| spacetime. The swiss cheese cosmology approach does this,
| and that technique traces back to the 1930s: https://en.wik
| ipedia.org/wiki/Einstein%E2%80%93de_Sitter_uni... (it has
| of course been refined over the decades).
|
| Careful observation of our solar system supports this
| hierarchical stitching method reasonably well, but only if
| the far regions away from bodies are asymptotically flat.
| If we generate almost any amount of metric expansion --
| much less than \Lambda -- to the otherwise asymptotically
| flat areas around the Earth, the moon's orbit changes
| dramatically. Likewise, if we change it within our solar
| system, things look very different in fairly short order.
| The same so far holds remarkably well for larger structures
| that are gravitationally bound, up to galaxy clusters.
|
| A couple of decades ago, there were good astrophysical-
| observation reasons to think the hierarchical "stitching"
| process was broken enough that either an inhomogeneous
| metric would be needed from the start (throwing away lots
| of useful symmetries). These have faded with subsequent
| observation.
|
| There is still some small wiggle room that allows for
| things like fifth-force screening to be taken seriously,
| however one has to do headstands to keep Manhattan (or
| Earth-Moon or Earth-Sun) from expanding measurably.
|
| Measurability here is very tight. Laser lunar ranging, very
| long baseline interferometry, and even GPS and friends keep
| tightening the bounds on how much expansion the "true"
| metric Earth sources can allow compared to its approximate
| Kerr metric.
|
| This is why I think it is safer to say that it's not
| expanding at all, rather than that we will find expansion
| if we look closer and closer.
|
| As a sibling comment has noted, there are also constraints
| from particle physics and chemistry. Those constraints also
| arise in astrophysical systems like megamasers, planetary
| nebulae, stellar deflagrations, supernovae, binary+
| millisecond pulsars, and so forth. The wiggle room for a
| suppression rather than extinction of cosmological
| expansion keeps tightening, and the constraints are from a
| diversity of lines of evidence.
|
| However, it is _reasonable_ to qualify the "it's not
| expanding" with "all our measurements to date are
| consistent with exactly no expansion in the solar system,
| and we have lots of rather different types of measurements
| all saying the same thing". I'm not sure that's as helpful
| for understanding the physical neighbourhood around here,
| or in galaxies and star systems generally, though.
|
| > I'd always interpreted "expansion" as being space itself
| expanding, and thought that it happened at all scales
|
| Observations are consistent with expansion happening only
| in really good extragalactic (extra-galaxy-cluster, even)
| vacuum.
|
| This is really easy to explain with a non-accelerating
| expanding universe.
|
| The mechanism for the (actually accelerated!) expansion is
| not known, but is usually what is meant by "dark energy".
|
| This is a highly conventional take on the matter. I'm not
| offering up any sort of pet hypotheses, and I generally
| avoid doing so anywhere like HN as explaining the standard
| theory is more interesting (even to me) anyway.
|
| Here is Ethan Siegel making similar points in somewhat
| different ways, with the benefit of editing and images: htt
| ps://www.forbes.com/sites/startswithabang/2019/02/19/this..
| .
|
| > even weirder
|
| Yep!
|
| The sky is full of weird stuff that _can_ be seen. Check
| out the "variable universe" -- astronomers like
| https://asas-sn.osu.edu/atlas/visualizations#star-map-panel
| keep finding bizarro things to think about even far away
| (in a theory-space sense) from the dark matter / dark
| energy sectors, that may test theories about those sectors.
|
| You'd expect that as visible matter gets weirder, the
| invisible stuff must get weirder still in proportion.
| Oddly, that is not really the case.
| hnuser123456 wrote:
| Thank you, you're a fantastic writer and clearly have
| some expertise. I am not on your level but do spend a
| decent amount of time trying to deepen my understanding
| of physics.
|
| This got me thinking, would one way to explain expansion
| possibly be gravity is slowly getting stronger on shorter
| distances, or that the fabric of spacetime itself is not
| perfectly rigid, not only in the "depth" component like
| the classic trampoline analogy, but also in the
| "length/width" component? Galaxy filaments are thinning,
| so if you think of the center of a supervoid surrounded
| by filaments on all sides, that void is being stretched
| apart in every direction, at some level that is so
| fundamental that it "creates more space". Then again,
| everything everywhere is surrounded by filaments and all
| space is being pulled apart by the same reasoning, but if
| there is anisotropic mass close enough, this overrides
| the creation of new space.
| arbitrage wrote:
| > But are we saying that expansion isn't something that
| happens at all scales then? Eg, that only the space between
| galaxies (or between galaxy clusters) is expanding?
|
| Yes, that's what is being said here. The space inside you
| and me and our atoms don't expand, but the empty spaces
| between galaxies do.
|
| It is very weird, and non-intuitive.
| junon wrote:
| I understood about 50% of this but wow, what a great writeup.
| Thank you.
| noobermin wrote:
| With all due respect to theorists, everyone in particle theory
| and cosmology is doing this sort of thing. I remember in grad
| school, cohort-mates down the hall whenever the LHC announced
| any sort of blip would rush to get a preprint from nothing in a
| week for the chance to be _the one_ to have made a discovery
| that fits the discrepancy. One theorist even told me the lack
| of experiment was "good" because they had space to keep
| churning nice theory papers without having to worry about being
| shot down.
|
| Occam's razor suggests to look at explanations that are mundane
| first. Even beyond dark energy candidates, it looks like Axions
| are another explanation which is more well established in the
| theory world (for what that's worth...), so absent more data
| it's hard to say it's an observation yet without elimination of
| alternatives.
| phkahler wrote:
| >> One theorist even told me the lack of experiment was
| "good" because they had space to keep churning nice theory
| papers without having to worry about being shot down.
|
| "Scientists" are forgetting the distinction between
| hypothesis and theory. They're also constantly looking for
| "new physics" and using the word "novel". Nobody seems to
| care about using what we have to explain what they see.
| TheOtherHobbes wrote:
| The grain of salt part is needed because it's a speculation
| about some data that isn't even confirmed yet.
|
| Presumably the point is to put the speculation at the head of
| the queue just in case it is.
|
| Which is fair enough, but until there's confirmation of an
| anomaly the speculation is just... speculative.
| verytrivial wrote:
| "detected dark energy" Ooo! This could be really interes--
|
| "(phys.org)" .... Oh. Expectations adjusted accordingly.
| jug wrote:
| I don't see anything wrong done here by Phys.org. It's the
| world's most sensitive dark matter detector so I'm happy
| they're reporting on its findings. This isn't some tabloid-
| level news but making its rounds at universities.
| cozzyd wrote:
| To be clear, they're reporting on an interpretation of a not-
| understood part of Xenon1T results (a low-energy excess in
| electronic recoil event rate). Here is the original paper by
| Xenon1T reporting on the excess: https://journals.aps.org/prd
| /abstract/10.1103/PhysRevD.102.0...
|
| And no, there's nothing wrong with it, but there are many
| many such interpretation papers any time an experiment
| reports something unusual and at most one of them (but
| probably zero!) might be true :).
| mcguire wrote:
| I haven't been following cosmology very closely in a while; could
| someone update my knowledge a bit?
|
| * The only evidence for dark matter is that galaxies and galactic
| clusters are moving faster than they should be; i.e. they are
| acting like there is more gravitational mass around.
|
| * The only evidence for dark energy is that the redshift of
| distant objects is higher than it should be; i.e. they seem to be
| accelerating away rather than decelerating.
|
| * All of the other properties of dark matter and dark energy are
| negative: we have not been able to observe anything, so we know
| what it's not.
| jasonwatkinspdx wrote:
| > The only evidence for dark matter is that galaxies and
| galactic clusters are moving faster than they should be; i.e.
| they are acting like there is more gravitational mass around.
|
| There's more than that:
| https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...
|
| Likewise for dark energy:
| https://en.wikipedia.org/wiki/Dark_energy#Evidence_of_existe...
| mcguire wrote:
| Thanks!
| nerfhammer wrote:
| I believe another piece of evidence is there is more
| gravitational lensing than expected in various places
| skohan wrote:
| I'm pretty far from this stuff, so I am sure the people
| studying it know far more than I do.
|
| However when I read about dark matter/energy, and quantum
| physics, it sometimes reminds me of stories of the geocentric
| model, where the scientists of the day derived this incredibly
| complex clockwork geometry of the solar system, to account for
| the strange curves the other planets seemed to take to cross
| the night's sky.
|
| I wonder if we're similarly missing a key insight which will
| make these "strange results" fall into place.
|
| On the other hand, it's entirely possible that we've just
| reached the limits of what can be found intuitive to our
| primitive ape brains.
| isaiahg wrote:
| In the present it seems like we've discovered so much but
| modern science is still such a young concept in the timeline
| of humanity. I'd wager we still have many wrong answers and
| much of how the universe works is still undiscovered
| aszantu wrote:
| I just thought: if fusion makes heavier elements, it makes sense
| that the universe expands faster... And I don't even know how I
| got there...
|
| fusion makes elements heavier.
|
| Heavier collections of elements make more gravity.
|
| (is the creation of matter limited in our universe?) In bucket
| with limited supply of new matter, through fusion the existing
| matter makes clumps which get heavier and heavier. But the
| substrate will thin everywhere else.
|
| Supermassive black holes make more gravity.
|
| The more compression there is, the more heat is generated,
|
| And matter switches state at some point. (solid -> gaseous ->
| plasma -> another step -> another step?)
|
| If the matter "becomes" dark energy as a new sort of state, it
| could get "flung" out like two electrons with the same poles.
|
| Since Energy doesn't get lost, there's no other way than to
| "collect" at the fringes of the universe
|
| If the universe was like a baloon in the universe it would push
| the boundaries of the bucket indefinitely.
|
| Gravity is kinda like our substrate, not sure if fish are aware
| about their water being "heavier or less heavy", not sure if this
| analogy will ever hold up...
|
| can someone let me know if I got some of it right?
| tsimionescu wrote:
| First of all, while fusion makes elements heavier, gravity does
| not increase this way, since the total energy of the system
| remains constant, and E=mc^2. It could be that the radius the
| mass/energy is contained in does decrease, but not all stars
| end up as black holes, while ack holes have no more or less
| gravity than any other object with the same mass/energy.
|
| Then, most of your explanation is carried by the solid ->
| liquid -> gas -> plasma ->... -> dark energy idea, which makes
| no sense. Dark energy is not matter - none of the observations
| are consistent with any kind of matter in intergalactic space.
| And matter of any kind will always have gravity, so it can't be
| responsible for the expansion of space time.
| aszantu wrote:
| unless it goes from matter to something else (like two
| particles with oposite poles) when being cooked up inside the
| black that tries to get away from each other
| tsimionescu wrote:
| Matter inside a black hole, by definition, can never leave
| the are of the black hole. The shape of space beyond the
| event horizon is simply such that there is no path outside.
|
| And there is no 'something else' beyond matter, except
| energy, which is not a thing per se, but the potential for
| other things to move or happen.
| raattgift wrote:
| The original text which the link at the top simply duplicates
| _minus_ the hyperlinks is at :
|
| https://www.cam.ac.uk/research/news/have-we-detected-dark-en...
|
| which links to the open access paper at Phys.Rev.D :
|
| https://journals.aps.org/prd/abstract/10.1103/PhysRevD.104.0...
| carbocation wrote:
| That's very helpful. Based on the paper, which seems to state
| that they have a 2s significance level, this seems very
| preliminary (I am absolutely not a physicist!)
|
| > _As an example, we examine whether the electron recoil excess
| recently reported by the XENON1T collaboration can be explained
| by chameleon-screened dark energy, and find that such a model
| is preferred over the background-only hypothesis at the 2.0s
| level, in a large range of parameter space not excluded by
| stellar (or other) probes._
| jug wrote:
| Yes - the Phys.org article also states they need to replicate
| these results and the kind of projects that are underway that
| can assist with this sort of science.
| raattgift wrote:
| > That's very helpful.
|
| Thank you.
|
| > seems very preliminary
|
| Agreed.
|
| I made a further comment in reply to another commenter at
| https://news.ycombinator.com/item?id=28566823
| carbocation wrote:
| Your other reply feels like it could be packaged up a bit
| and published somewhere!
| [deleted]
| mancy00 wrote:
| Isn't dark energy the aura that surrounds politicians?
| jjtheblunt wrote:
| "may" -> subjunctive mood verb -> usually turns out false when in
| headlines, it seems
| canjobear wrote:
| There is no subjunctive mood in the title
| [deleted]
| dirtbag__dad wrote:
| This article was a breeze to read. (As opposed to the complicated
| scientific abstracts I usually give up on after a few
| paragraphs.)
|
| Anyone have recommendations for approachable coverage of science
| journals and news?
| sanxiyn wrote:
| I actually found both Nature and Science to be excellent at
| covering science news. They are famous for science journal, but
| they also have science news department.
|
| https://www.nature.com/news
|
| https://www.science.org/news
| mcguire wrote:
| Both of which have excellent weekly podcasts covering their
| articles and other science news of the week.
|
| Oh, and speaking of Science News, that is (was?) an excellent
| weekly with short articles on recent results. I just haven't
| subscribed in a number of years.
| snambi wrote:
| Are the scientists not sure?
| tiborsaas wrote:
| Only the good ones.
| eterevsky wrote:
| I would bet at 10 to 1 rate that this will turn out not to be
| dark energy. We haven't observed any dark energy effects with
| scales less than billions light years. I would've been much less
| skeptical if they announced that they found dark matter.
| peter_retief wrote:
| Right, I wouldnt hold my breath about the dark matter theory. It
| is up there with alien space ships and santa.
| tppiotrowski wrote:
| > About 27% is dark matter--the invisible force holding galaxies
| and the cosmic web together--while 68% is dark energy, which
| causes the universe to expand at an accelerated rate.
|
| I understand that matter slows and energy accelerates the
| expansion of the universe but how is this ratio calculated? It
| seems like we would need to know the strength of dark energy to
| arrive at this reasoning.
| LegitShady wrote:
| It's based on actual observations, with some assumptions on the
| nature of the universe. As you said - dark matter is detected
| by extra "holds stuff together" force than observed masses
| would indicate exists from a host of phenomena (find the
| Wikipedia article on dark matter for more detail), and dark
| energy which is the energy required to make the universe expand
| at an accelerated rate is based on on distance-redshift
| relation, measurements of the cosmic background radiation, and
| theoretical additional non matter or dark matter energy
| required to form an 'observationally flat universe'.
|
| The basics for both of these are discussed on the Wikipedia for
| both subjects.
|
| Disclaimer - I am not a physicist but I did stay at the holiday
| inn express last night and I do watch a lot of PBS Spacetime on
| youtube.
| LegitShady wrote:
| cant edit but "accelerated rate" should be "accelerating
| rate" and "dark matter energy" should be "non dark matter
| energy"
| [deleted]
| paulpauper wrote:
| This is why I don't belive there is scientific stagnation. New
| discoveries and theories are constant being made and proposed.
| Its only because the problems have gotten harder that progress
| seems slower.
| BiteCode_dev wrote:
| Honestly progress doesn't seems slower at all. I hear news of
| scientific discovery every week. Science is large, and it's not
| just physics.
| 3pt14159 wrote:
| Also what people consider science is a bit of a continuum.
| There is what is universally objective scientific
| breakthrough (like discovery of quarks) on the one end, and
| universally objective non-breakthrough (like the construction
| of a simple bridge) on the other but where does the progress
| of iPhone 1 to iPhone 13 fit?
|
| So much advancement is going on in or around computing right
| now I think that in the future we'll sorta look back and
| consider that closer to science than mere engineering.
| adtac wrote:
| No, I disagree. Science is something that's well
| established and has been around for centuries. Engineering
| is also well established and has been around for centuries.
| The iPhone is an engineering advancement and will always be
| viewed that way; it'll always be in the same category as
| building the aqueducts. There was nothing scientifically
| groundbreaking about it, unlike discovering gravity or
| radiation.
| andrew_eit wrote:
| This is not how I understood the argument of scientific
| stagnation though, wasn't it more to do with 'breakthrough'
| discoveries that somehow radically disrupted / changed our way
| of life?
|
| In that regard I'm inclined to believe there is some sort of
| stagnation. Though not necessarily at the fault of the
| community or researchers. It could very well be a mix of what
| you said about problems being harder that we have, between 1900
| - 2000 picked all the 'low hanging fruit' in physics, and that
| we now need lots of patient, 'baby step' type improvements to
| get to a new era where the technology is powerful enough to
| make big leaps again.
|
| Kind of like how Deep Learning research stagnated due to lack
| of data volume and processing power.
|
| This is my perspective, but I think it's totally up for debate
| and I'm keen to hear different opinions.
| NineStarPoint wrote:
| Whether its the fault of the community or just natural
| consequences of the low hanging fruit being picked away will
| only be possible to know in retrospect, really. Is the issue
| that we don't have the technology to figure things out, or
| that the community was too stuck in a local maximum of
| explainability to find the summit where everything ti
| explained? Until the next major breakthrough actually
| happens, it's hard to know which is the case.
|
| Although in general, I'd say it's possible a big leap never
| happens again. Given that physics will ultimately be a finite
| set of rules, if we can explain the vast majority of
| phenomenon accurately, slotting the last few pieces into
| place might not grant us much. It will feel great for
| humanity to know of course, but it's entirely plausible that
| the reason we have so much trouble figuring these these out
| is that they're almost completely separate from the human
| experience. We might figure out quantum gravity, go "that's
| nice", but if it's only relevant when there are stellar
| masses involved not be able to use it to change our way of
| life. Big changes to how humanity lives going forward could
| be entirely reliant on human invention/ingenuity, not us
| learning new facts about the universe we live in.
| skulk wrote:
| There are still poorly understood physical phenomena that
| could prove to be tremendously useful, like
| superconductors. If quantum gravity leads us to room-
| temperature superconductors (for example), that would be
| absolutely earth-shattering for humanity.
| mcguire wrote:
| Between ~1880 and ~1920, the physical sciences made huge,
| crazypants leaps both in theory and experimentally. The rest
| of the 20th century was spent catching up with all the
| implications of those leaps. Now, the sciences have a set of
| very powerful ideas that have a bad habit of producing the
| right answers as far as anyone can see, but which have very
| visible holes and don't fit together. Thus, stagnation.
|
| On the other hand, it may just be a return to the normal
| status quo.
| BurningFrog wrote:
| Under my Dark Stagnation theory, scientific stagnation varies a
| lot between different scientific fields.
| [deleted]
| tengbretson wrote:
| My model for determining the number of scientific discoveries
| indicates that visible, understandable scientific discoveries
| only account for about 10% of the scientific discoveries out
| there. I theorize that there must be a remaining 90% of
| scientific discoveries that are undetectable, unknowable "dark
| discoveries."
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