[HN Gopher] The Webb Telescope further deepens the Hubble tensio...
___________________________________________________________________
The Webb Telescope further deepens the Hubble tension controversy
in cosmology
Author : nsoonhui
Score : 214 points
Date : 2024-08-13 12:50 UTC (10 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| parkaboy wrote:
| Naive question: why should the expansion rate need to be uniform
| or constant everywhere?
|
| I'm likely misinterpreting the article, but it seems to frame
| things in a way that first assumes expansion should be constant
| and it's a question of what the right constant value is between
| the measured/theoretical discrepancies.
|
| (*yeesh, editing all those spelling errors from typing on my
| phone)
| BossingAround wrote:
| That's the first thing that occurred to me too. It could also
| not be constant even at the same place, i.e. could it not be
| speeding up and slowing down as the universe expands?
| isolli wrote:
| Indeed. Some researchers have proposed quintessence, a time-
| varying form of dark energy [0].
|
| > A group of researchers argued in 2021 that observations of
| the Hubble tension may imply that only quintessence models with
| a nonzero coupling constant are viable.
|
| [0] https://en.wikipedia.org/wiki/Quintessence_(physics)
| itishappy wrote:
| It's not constant (the early universe inflated quite quickly),
| and it doesn't need to be uniform, but it sure does appear to
| be. We measure it via redshift, pulsar timing arrays, and the
| temperature fluctuations of the CMB, and it looks pretty much
| the same in all directions.
| AnimalMuppet wrote:
| The issue here is that it's not constant _depending on the type
| of star we use to measure it_. It 's not a discrepancy in
| location in space. Or at least that's how I read the article.
| chongli wrote:
| The controversy is that we get 2 different numbers depending on
| which method (cosmic microwave background vs cosmic distance
| ladder) we use to calculate the present rate of expansion.
| These numbers used to have their error bars overlapping, so we
| assumed they would eventually converge to the true value. But
| as we get more data the opposite is happening: the numbers are
| diverging and their error bars are shrinking such that they no
| longer overlap.
|
| This tells us that either our model of the universe is wrong
| (therefore the cosmic microwave background method is giving us
| an incorrect answer) or that something is wrong with how we're
| calculating the distances along the cosmic distance ladder. The
| latter was originally the assumption that should be proven true
| with more and better data from newer telescopes. This is now
| turning out not to be the case: our cosmic distance ladder
| calculations seem to have been very good, so it now seems more
| likely that our model of the universe is wrong.
| detourdog wrote:
| Thank you for this explanation. I would like to emphasize
| that our model being wrong and not our numbers sounds like
| progress.
|
| It also sound like progress that we seem to have 2 "scales"
| to play with to try to develop a consistently measurable
| distance.
| api wrote:
| Distance ladder seems much more error prone than the CMB.
| artemonster wrote:
| there is no "seems" with provable error bars
| feoren wrote:
| ehh ... everything we measure relies on our understanding
| of the universe in some way. It's perfectly reasonable
| that our distance measurements _could_ rely on a shakier
| foundation of assumptions than our understanding of the
| CMB. I don 't know enough to say one way or the other,
| but GP's comment is not unreasonable on its face. Whereas
| talking about "provable" in cosmology, and certainly in
| this case, does seem unreasonable -- especially with
| error bars, which _by definition_ have a small chance of
| not including the real value. Normally I 'd say that we
| can generally refine our assumptions to be extremely
| good, and just take more measurements, and keep narrowing
| that error bar, until we hit a level of certainty that
| anyone reasonable would call "proven", but the entire
| point of TFA is that this isn't happening in this case.
| We seem on our way to "proving" two inconsistent things.
| db48x wrote:
| All of the cosmologists expected that too!
| shepardrtc wrote:
| > so it now seems more likely that our model of the universe
| is wrong.
|
| Whenever a scientist says that it's not possible that the
| model is wrong, then I just roll my eyes. Of course models
| can be wrong - and isn't that exciting? Good on them for
| making sure that there are no errors in the measurements -
| that's incredibly valuable and absolutely necessary - but I'm
| really excited to see creative models being thought up that
| are drastically different. My personal hell is the universe
| being consistent and boring.
| mr_mitm wrote:
| > Whenever a scientist says that it's not possible that the
| model is wrong, then I just roll my eyes.
|
| But no one said that. Im fact, scientists are known to say
| things like: all models are wrong, but some are useful.
| shepardrtc wrote:
| From the article:
|
| > That the three methods disagree "is not telling us
| about fundamental physics," Freedman said. "That's
| telling us there's some systematic [error] in one or more
| of the distance methods."
|
| Freedman is saying that the model is not wrong.
| dotnet00 wrote:
| What she means is that the bar for proving that this is
| an error in physics is much higher than that of proving
| that it's a measurement error. Like, if you're measuring
| acceleration due to gravity, and your sensor/calculation
| gives you 5m/s^2 rather than the real ~9.81m/s^2 that
| everything else measures, you can't immediately resort to
| arguing that physics is wrong, you have to rule out that
| your sensor/calculation is wrong first.
|
| To argue that the physics is wrong, you are likely to be
| arguing that very well tested theories like general
| relativity, special relativity or electromagnetism are
| off in some way. That's a much higher bar than just the
| measurements of either the ladder or CMB being wrong in
| some way.
| exe34 wrote:
| to add to this, it's equivalent to the difference between
| trying to justify that one experiment (or one class of
| experiments) is wrong vs several dozens of classes of
| thousands of experiments are all subtly wrong so that
| this one experiment can be right.
| lamontcg wrote:
| That researcher has a personal conviction that the model
| isn't wrong. That is spurring them to spend the years and
| decades necessary to assemble the experimental evidence
| to test the model. Either it'll turn out to be wrong or
| right in the end, but the conviction is what gives that
| individual researcher the impetus to keep scratching at
| the problem for a good chunk of their life.
|
| You shouldn't really roll your eyes at that. They're
| ultimately doing all the work which will prove it right
| or wrong. They might wind up not liking the answer they
| get, but the conviction is necessary to get them there
| because human emotions are weird.
| mr_mitm wrote:
| She's following a hunch, it's what scientists do. In this
| case the hunch is that the model is not wrong. That's a
| far cry from saying it's _impossible_ to be wrong.
| shepardrtc wrote:
| Where does she say she's following a hunch? She was very
| certain when she said that.
| exe34 wrote:
| when she's certain, you'll know, because she'll publish
| it.
| snarkconjecture wrote:
| She's saying that a different model -- one of the three
| disagreeing methods for distance ladder measurements --
| must be wrong, because they disagree with each other. But
| if one or more of those models are wrong, then there's
| not much evidence that the LambdaCDM model is wrong.
|
| Conversely, the hypothesis that LambdaCDM is wrong does
| nothing to explain why the distance ladder methods
| disagree.
|
| She clearly isn't saying that any model is infallible,
| she's just saying that clear flaws with one set of models
| throw into question some specific accusations that a
| different model is wrong.
|
| You actually need to pay attention to the details; the
| physicists certainly are. Glib contrarianism isn't very
| useful here.
| jfengel wrote:
| Scientists have to cope with "you just said your model is
| wrong therefore I am right about everything ever". It makes
| them sometimes shortcut their way out of conversations that
| they know will not lead anywhere useful.
| shepardrtc wrote:
| That seems like an exaggeration.
| exe34 wrote:
| which part?
| shepardrtc wrote:
| > "therefore I am right about everything ever"
|
| I'm sure scientists have to deal with people jumping on
| them about their model being wrong, but this part is
| clearly exaggeration.
| jfengel wrote:
| That is comic exaggeration, but you've almost certainly
| heard people insist that the evidence for their position
| is that some scientist was wrong at some point. It's
| particularly comic from creationists.
| immibis wrote:
| Who said it was impossible? In fact, someone just said it
| was quite likely.
| sounds wrote:
| I remember reading that the local group, Laniakea
| Supercluster and the great attractor [1] are new developments
| that helped us refine our understanding of H0 but didn't
| fundamentally remove the controversy.
|
| It's exciting to see how the question drives many new
| discoveries.
|
| [1] https://en.wikipedia.org/wiki/Great_Attractor
|
| I'll try to paraphrase what it meant: measuring H0 comes down
| to measuring the relative velocity of galaxies around us. The
| great attractor was a relatively recent discovery that the
| "closer" galaxies, the ones we can use in the distance
| ladder, all have a common component in their velocities which
| we've recently begun to understand better.
| sdenton4 wrote:
| Interesting, though, that they're getting different numbers
| using different kinds of stars, which does suggest problems
| with the distance ladder.
| pdonis wrote:
| _> our cosmic distance ladder calculations seem to have been
| very good_
|
| Not according to at least one research group described in the
| article: the Freedman group, which is only getting the higher
| answer using Cepheids, but gets a lower answer, one
| consistent with the CMBR calculations, by two other methods.
| Which raises the possibility that it's the Cepheid part of
| the cosmic distance ladder that's the problem.
| JumpCrisscross wrote:
| > _what should the expansion rate need the be uniform or
| constant everywhere?_
|
| It doesn't.
|
| "The simplest explanation for dark energy is that it is an
| intrinsic, fundamental energy of space" [1]. That's the
| cosmological constant.
|
| Dark energy is a thing because we don't assume that to be the
| case. Irrespective of your dark energy model, however, there
| will be a predicted global average.
|
| [1] https://en.wikipedia.org/wiki/Dark_energy
| tzs wrote:
| There has been some interesting recent work that may get rid
| of the need for dark energy.
|
| Briefly, recent large scale maps of the universe suggest that
| the universe might not be as uniform as we thought it was. In
| particular we appear to be in a large region (something like
| a couple billion light years across) of low density.
|
| Dark energy is needed to make the solution to Einstein's
| field equations for the whole universe match observations.
| However that solution was derived based on a universe with
| matter distributed uniformly. At the time it was first
| derived that appeared to be the case--we thought the Milky
| Way was the whole universe.
|
| When we learned that the Milky Way was just a small galaxy in
| a vastly larger universe than had thought we were in and that
| there were bazillions of other galaxies, those galaxies
| appeared to be distributed uniformly enough the the solution
| to the field equations still worked.
|
| Later we found that there is some large scale structure in
| the distribution of galaxies, like superclusters, but those
| seemed uniform enough throughout the universe that things
| still worked.
|
| If that couple of billion light year low density region turns
| out to exist (large scale mapping of the universe is hard
| enough that it may just be observational error) the universe
| may not actually be uniform enough to for the field equations
| based on uniform matter distribution to actually work.
|
| Some researchers worked out the solutions to the field
| equations for a universe that has such large low density
| bubbles big enough to invalidate the uniform universe
| solution, and found that such a universe would have an
| expansion force without the need to invoke any kind of dark
| energy.
|
| There was a recent PBS Space Time episode that covered this:
| "Can The Crisis in Cosmology be SOLVED With Cosmic Voids"
| [1]. The above is my summary of what I remember from that.
| See the episode for a better explanation and references to
| the research.
|
| [1] https://www.youtube.com/watch?v=WWqmccgf78w
| xhkkffbf wrote:
| Certainly when I look at convection currents in the ocean or
| the atmosphere, I see plenty of variation. Shoot, the earth's
| atmosphere constantly produces moving blobs of relatively high
| and low pressure.
| diob wrote:
| So a lot of astronomy is based on the principle that we are not
| in a special pocket of the universe.
|
| See https://en.wikipedia.org/wiki/Cosmological_principle
|
| Basically, if this weren't to hold true, a lot of astronomy
| would fall over, even physics.
| XorNot wrote:
| Though it is worth noting if this were the case you would
| expect to see boundaries: if the laws of physics change due
| to spatial position, the discontinuity should produce an
| effect of some sort where matter and light transitions
| between regions.
| mcswell wrote:
| I suppose there could be a gradual change over distance,
| i.e. the first derivative of this change never varies.
| hindsightbias wrote:
| Sophon is amused:
| https://en.wikipedia.org/wiki/Axis_of_evil_(cosmology)
| eikenberry wrote:
| Seems there are 2 ideas at odds. One is that the universe is
| infinite, in which case this is all localized and has no
| bearing on the universe outside of our small observable
| region. The other is that we are seeing enough of a bounded
| universe where the observations we make are of a significant
| enough chunk to make theories about it.
| beltsazar wrote:
| Yes, cosmological principle is probably the most fundamental
| assumption in astronomy.
|
| Most people don't realize that science--and even everything
| in life--has to start from some axioms/assumptions, just like
| math. I first realized this fact when I was reading the
| Relativity book written by Einstein himself, who challenges
| the assumptions in classical physics.
|
| As time goes, some of the assumptions could be proved to be
| unnecessary or even wrong. There must be still some
| assumptions left, though--because without them, we can't talk
| about science, or anything, really.
| photochemsyn wrote:
| Spacetime is apparently extremely rigid as it supports the
| transmission of gravitational waves originating billions of
| light-years away, as detected by the LIGO experiments. This
| suggests smooth and gradual uniform expansion, at least
| spatially. Temporal variation (speeding up and slowing down
| uniformly at all points) might be possible but seems hard to
| explain.
| Jeff_Brown wrote:
| Seems perfectly possible. General relativity, after all, was
| precisely the discovery that the curvature of space, well
| spacetime, is not uniform.
| seanhunter wrote:
| Some cool background about the Hubble constant here, including a
| nice explanation involving blueberry muffins
| https://news.uchicago.edu/explainer/hubble-constant-explaine...
| mcswell wrote:
| I _just_ finished off a blueberry bagel, the taste is still in
| my mouth. Maybe the universe is torus-shaped?
| readthenotes1 wrote:
| "This extrapolation predicts that the cosmos should currently be
| expanding at a rate of 67.4 km/s/Mpc, with an uncertainty that's
| less than 1%."
|
| I can't measure my own weight with an uncertainty that's less
| than 1%. I wonder what these peeps are on...
| uncivilized wrote:
| Their wallets are much bigger than yours.
| readthenotes1 wrote:
| As is what they are trying to measure. I don't believe 1%
| measurement error in any universal element except perhaps the
| speed of light...
| aidenn0 wrote:
| That's an absurd statement. For example, planck's constant
| is known to better than 1%, as is the mass of various
| particles. Heck, the Earth, which is sufficiently non-
| spherical for it to matter only differs in radius (between
| polar and equatorial) by 0.3%!
| munchler wrote:
| I suggest you take a look at this list of physical
| constants, paying special attention to the "uncertainty"
| column, and then get back to us on why you don't accept any
| of them except the speed of light.
|
| https://en.wikipedia.org/wiki/List_of_physical_constants
| bloak wrote:
| Here's a nice list:
| https://en.wikipedia.org/wiki/List_of_physical_constants
|
| G (the gravitational constant) is an interesting one: the
| value is only known to about 5 significant figures, but GM
| (the gravitational constant multiplied by the mass of the
| Earth) is known a lot more accurately, unsurprisingly,
| considering how well GPS works. Some of those constants
| seem to be known to about 12 significant figures.
| dotnet00 wrote:
| If you can measure the speed of light extremely precisely,
| you can measure a lot of constants extremely precisely.
| shagie wrote:
| Depending on which end of the scale you are interested in, the
| NIST would be an interesting place to work.
|
| How To Measure The Tiniest Forces In The Universe
| https://youtu.be/pXoZQsZP2PY and World's Heaviest Weight
| https://youtu.be/_k9egfWvb7Y - both from Veritasium.
|
| From the expanded description on the heaviest weight:
|
| > Before visiting NIST in Washington DC I had no idea machines
| like this existed. Surely there's an accurate way to measure
| forces without creating such a huge known force?! Nope. This
| appears to be the best way, with a stack of 20 x 50,000 lb
| masses creating a maximum force of 4.45 MN or 1,000,000 pounds
| of force. I also wouldn't have thought about all the
| corrections that need applying - for example buoyancy subtracts
| about 125 pounds from the weight of the stack. Plus the local
| gravitational field strength must be taken into account. And,
| the gravitational field varies below grade. All of this must be
| taken into account in order to limit uncertainty to just five
| parts per million (.0005%)
| itishappy wrote:
| Skill issue.
| gangorgasm wrote:
| What is "Mpc"., if anybody knows?
| 613style wrote:
| megaparsec (1 million parsecs)
| gangorgasm wrote:
| Thanks much
| tyfon wrote:
| It is a distance unit, megaparsecs.
|
| Or approximately 3.25 million light years.
| gangorgasm wrote:
| Appreciated. Big distance
|
| I have difficulty conceptualizing "distance over time ...
| _over_ [huge] distance "
|
| I guess it means "chunks about so [megaparsecs] large are
| moving [themselves] at a speed of so many Km. per second"
| but I could be wrong
| tyfon wrote:
| The measurement for expansion is linear with distance, so
| two spots one Mpc from another moves away front each
| other at 67.4 km/s while two spots two Mpcs from each
| other moves at 134.8km/s. This means the expansion is
| accelerating and some parts of the now visible universe
| will eventually move away from us faster than the speed
| of light resulting in them disappearing from our view.
|
| The distances, time and speeds are indeed very hard to
| comprehend from our usual references :)
| gangorgasm wrote:
| It's crazy that some parts of the universe will actually
| for all purposes vanish
|
| Thanks for taking time to break it all down
| daedrdev wrote:
| At some point there will only be the galaxies in our
| local group visible, it's interesting to imagine a future
| civilization only having such a limited universe to view.
| ryandrake wrote:
| Doesn't this mean that on a long enough time frame, an
| observer anywhere in the universe won't be able to see
| anything because everything else in the universe is too
| far away to be visible?
| shagie wrote:
| Simply - yes. Furthermore, civilizations that arise in
| that era of the universe will likely have a different
| cosmology than what we are able to understand today. If
| you could only see the galaxy that you are in, you
| wouldn't be able to see galaxies that were forming
| shortly after the Big Bang, or be able to use supernovas
| in other galaxies to measure the scale of the universe.
|
| Kurzgesagt did a video on that - TRUE Limits Of Humanity
| - The Final Border We Will Never Cross
| https://youtu.be/uzkD5SeuwzM
| gangorgasm wrote:
| >> civilizations that arise in that era of the universe
| will likely have a different cosmology than what we are
| able to understand today.
|
| That is just mind-boggling
| layer8 wrote:
| It means that a chunk of space with length 1 megaparsec
| will be 67.4 km longer a second later. If you divide that
| new length by the old length, you get the factor by which
| space expands each second. It's a very small factor (i.e.
| very close to 1), but there are also many seconds.
| halayli wrote:
| Reading your very confident response it makes me wonder the
| same about you.
| ck2 wrote:
| If you really want to overload your mind thinking about this,
| imagine this universe is only a bubble crowded into a group of
| other bubbles, like a kid blowing soap bubbles.
|
| So the pressure around our bubble is not uniform, there are more
| bubbles on one side than another, other bubbles are much larger
| and some are very tiny causing tiny "lumps" of pressure in
| various places on our bubble.
|
| Decades ago I really liked the "big collapse" theory that has now
| been abandoned, it was so "simple" in comparison to a universe
| that keeps expanding and not uniformly at that.
| turndown wrote:
| Just because we are natives of this universe does not mean its
| behavior or characteristics will be naturally sensible to us.
| There is no "real" reason it should be something "simple" or
| reasonable to us. The universe simply is; us as well.
| fartsucker69 wrote:
| when did it start that the storytelling around every piece of
| physics news was framed as a controversy? I know it's been a
| while, but I feel like it wasn't this way 20 years ago...
| ajross wrote:
| Frustrating that all the comments seem to be jumping in to talk
| about dark energy and quintessence and multiverse pontification,
| when the _actual contention_ in the linked article is that all of
| this may turn out to be a measurement error and that the Hubble
| tension may not actually exist after all.
| sdenton4 wrote:
| "researchers started using Cepheids to calibrate the distances to
| bright supernovas, enabling more accurate measurements of H0."
|
| It seems like if there were some error in the luminosity
| measurement for cepheids, it would propagate to the measurements
| with supernovas...
|
| I would expect that stacking measurement techniques (as is common
| with cosmology, where distances are vast and certainty is rare)
| would also stack error, like summing the variance in gaussians...
| FredPret wrote:
| It'd be cool if we launched several space telescopes on
| Voyager-like trajectories.
|
| In 50-100 years they'd get a much better angular fix on stars
| that are too distant for Earth-orbit-sized angular
| measurements.
|
| https://en.wikipedia.org/wiki/Stellar_parallax
| HPsquared wrote:
| That'd be a nice use for Starship.
| jvanderbot wrote:
| Well, no it wouldn't actually.
|
| It'd be a nice use for falcon heavy - to get them the
| necessary delta-v. But the constraint isn't cargo space on
| launch. This isn't a starlink constellation, the orbits are
| necessarily massively different, meaning each spacecraft
| needs its own large delta-v so a single-launch, multiple
| spacecraft option is less attractive.
|
| The constraint is budget, fuel, and ambition.
|
| Now what you could do is get a telescope out around a far
| outer planet and use the orbital parallax like we do from
| earth. A Starship _might_ have a bunch of extra cargo space
| for this. But I just don 't see how it is better than a big
| faring on falcon heavy.
|
| EDIT: You know what? I am completely mistaken here. I was
| not thinking about the diff b/w FH and starship correctly.
| HPsquared wrote:
| More lift capacity means more fuel capacity onboard the
| telescope(s).
| baq wrote:
| You can easily put a third stage bigger than the whole F9
| second stage in the payload bay of the Starship and you
| likely wouldn't need a super complicated unfolding
| deployment procedure for the payload thanks to the
| enormous volume.
|
| Once the thing becomes reliable there are zero missions
| the FH can do that starship can't with a payload equipped
| with a third stage motor.
| jvanderbot wrote:
| OK I'll bite: What does starship add here? It's a very
| large re-useable faring that carries a stage + payload
| into orbit? Why not attach to the top of FH?
|
| Why: FH + Starship w/( rocket + payload)
|
| And not: FH + (rocket + payload)
| dotnet00 wrote:
| FH is already very thin and tall, probably not practical
| to stick another stage on top even if it could work
| payload wise. Besides that, SLS and New Glenn are the
| only ones with comparable lift capacities, SLS is way too
| expensive for the capability and the massive SRBs make
| the ride pretty rough, New Glenn is probably a feasible
| alternative, although probably more expensive than
| Starship.
| baq wrote:
| Starship doesn't add anything. Starship removes
| complexity by sheer brute force, cheaply due to
| reusabilty. You can architecture a mission with
| ridiculous (before starship, that is) mass and volume per
| dollar budgets.
|
| Falcon Heavy can lift a lot of mass but unless you're
| launching tungsten into orbit you can't fit interesting
| things into the fairing.
| dotnet00 wrote:
| Starship could give a single telescope a stronger boost
| than an FH could, and depending on the mass of one
| telescope (along with all the redundancies, power sources
| and transmitters such a long term mission would need),
| the telescope could be launched with an extra boost
| stage. So, several Starship launches for several
| telescopes.
| ianburrell wrote:
| Gaia is pretty small, 710kg. It was launched on Soyuz.
|
| Falcon 9 has payload to Mars of 4 tons, and Falcon Heavy
| has 9 tons to Pluto. I bet both would work.
| AprilArcus wrote:
| They'd need some very big RTGs to last that long, and I don't
| think we manufacture plutonium at the necessary volumes for
| that anymore.
| KennyBlanken wrote:
| Last I remember, RTG manufacturing was very constrained,
| period. And that was before Russia took a massive shit in
| Ukraine and got themselves embargo'd by most of the rest of
| the developed world.
| ars wrote:
| I would use Americium-241 instead, longer half life and
| much more availability.
|
| Lower power, but a telescope like this does not need
| constant power, so some kind of short term power storage
| (capacitor I would assume, or some kind of ultra long life
| battery) could handle that.
| fsckboy wrote:
| in terms of the potential plutonium shortage, wikipedia:
| _Americium-241 is not synthesized directly from uranium -
| the most common reactor material - but from the plutonium
| isotope 239. The latter needs to be produced first_
| XorNot wrote:
| I think the problem with such a mission right now is the high
| probability we could launch a faster mission in the very near
| future - i.e. with NASA looking at spaceborne nuclear
| propulsion again, we could send much more capable telescopes
| out faster - which is not just an "I want it now" benefit:
| time in space is time you run potentially having components
| wear out or break. So getting them onto their missions ASAP
| is a huge de-risking element.
| Bluestein wrote:
| I wonder - and I am sure this has been examined to death -
| if there's some calculation that can be performed to find
| the "optimum" wait-or-release-now pattern, given a certain
| rate of technological development vs. distance/years ...
|
| I am sure there are calculations for this ...
|
| PS. Of course, the _rate_ of technological development is
| the unknown variable hete, I am sure.-
| TeMPOraL wrote:
| I imagine such calculations immediately break down when
| you make the input (funding, interest) depend on the
| output. Which is the case in reality.
|
| For example, say your calculations say that the optimal
| time for the mission is 10 years from now, once a
| currently in-development propulsion technology matures.
| You publish that, and the investors, government and the
| public, all motivated to support you by the dream of your
| ambitious mission, suddenly lose interest. Your funding
| dries out, as you're repeatedly told to call back in 10
| years. The fact that the 10 year estimate, having been
| dependent on existing funding, is now "literally never",
| escapes them.
|
| See also: "nuclear fusion is always 30 years away". It
| is, because original 30 year timeframe assumed continued
| funding that never happened, and it's not happening
| because "it's always been 30 years away".
| Bluestein wrote:
| Literally a moving target ...
|
| > You publish that, and the investors, government and the
| public, all motivated to support you
|
| Interesting how PR/culture _indeed is_ a factor - a
| tangible factor in this. Indeed optimizing for "PR
| Goodwill" might be a thing ...
| pimlottc wrote:
| As Mark Twain once said, "the best time to launch a tree
| into space was twenty years ago. The second best is now"
| mcswell wrote:
| Dunno about Mark Twain, but it appears the best time to
| launch men to the Moon was more than half a century ago.
| The second best is now...ok, a year from now...I mean a
| few years from now.
| ianburrell wrote:
| The other solution is to increase the accuracy of parallax.
| This is what the Gaia project is doing. It can measure
| distance to stars in galactic center to 20%. It will measure
| distance to 2 billion stars and be super accurate within 300
| ly.
| silverquiet wrote:
| New Horizons has taken some star pictures from the Kuiper
| Belt and you can easily spot the parallax of some nearby
| stars just by eyeball. I'm not sure that it has a good enough
| camera for any kind of precision measurement, but it was
| really cool to see that.
| jerjerjer wrote:
| Why compromise? Might as well launch a solar gravitational
| lens [1] telescope.
|
| [1] https://en.wikipedia.org/wiki/Solar_gravitational_lens
| antognini wrote:
| These uncertainties in Cepheid luminosities are accounted for
| in Type Ia distance measurements. Particularly with Gaia we can
| now calibrate the luminosities of Cepheids in our galaxy using
| parallax observations.
|
| (Knowing this field I'm sure there are some astronomers who
| argue that there are still some systematic uncertainties that
| are not fully being accounted for, but from what I understand
| it's pretty hard to account for it with the Gaia results at
| this point.)
| hindsightbias wrote:
| "But according to Freedman, the galaxies' supernovas seemed to
| be intrinsically brighter than the ones in farther galaxies.
| This is another puzzle cosmologists have yet to understand, and
| it also affects the H0 value. "
| z3t4 wrote:
| Did I read it wrong, or does the universe expand at 10% of speed
| of light!? Could that possible be why the measurements are off? A
| close object vs an object very far away might look like they are
| in different places relatively.
| mr_mitm wrote:
| Rest assured, this has been taken into account. The scientists
| who spend their life working on this topic have had the same
| thoughts you had within minutes of learning about the problem.
| It's extremely basic stuff actually.
| feoren wrote:
| The observable universe has a radius of about 14 Gigaparsecs.
| If H0 is 67.4 km/s/Mpc, then a naive calculation puts the edge
| of the observable universe expanding at 943,600 km/s, or about
| 3 times the speed of light. Of course we still observe this as
| merely "close to" the speed of light, but the point is that
| most of the universe is shooting away from us so fast that we
| will never see them as they are "now", even if we wait billions
| of years. We have no way of ever interacting with most of the
| "modern" universe, even theoretically. They might as well be in
| different universes. All we will ever see is their images from
| billions of years ago, even if we wait billions of years from
| now.
| evanb wrote:
| It's likely you read it wrong; there is no sense in which the
| universe's expansion has a fixed speed. The Hubble parameter is
| speed/distance [the figure's axis is km/s/Mpc, for example].
| That is the _natural_ unit to explain an expansion rate: things
| that are farther away ALSO move away from you faster (because
| the space between you and them _all_ grows at a fixed rate).
| eisvogel wrote:
| The opening sentence of this article is 100% wrong. Hubble was a
| good scientist and correctly made no assumptions regarding his
| observations that objects that are further away by parallax are
| more red shifted.
|
| The assumption that these observations indicated an expanding
| universe was delivered to us by LeMaitre; if you believe in an
| expanding universe with a finite age, then give credit where it
| is due...
| acyou wrote:
| The current scientific consensus is actually pretty good - the
| consensus being that standard theory, quantum theory, big bang
| theory, particle theory, universe expansion model all have as
| good a likelihood as not of going down in history the same way as
| miasma theory, phlogiston theory and Newtonian classical
| mechanics, given the apparent and vast shortcomings of basic
| science around our universe's constitution, composition and
| origins. It's a mature and constructive recognition of our
| limitations and where we can improve.
|
| One of the proximate causes around our failure to progress in
| this and other areas is the funding model of publish or perish.
| Many researchers are trying to carve out a career, but not
| necessarily to contribute to progress or advancement. An
| examination of the funding structure and incentives for
| universities and researchers appears to be in order.
|
| One suggestion would be to limit grants for private universities
| and colleges. Another would be to cap compensation for university
| and college staff. Yet another would be to add funding or tax
| breaks for technology scale up and application development in the
| private sector. And another would be cutting funding to masters',
| PhD and post-doc levels, and increasing funding for 1-, 2- and 4-
| year career oriented and skill development programs. Yet another
| suggestion would be limiting loan eligibility to 1-, 2- and 4-
| year degree or lower programs. Another would be tying university
| and college funding to the success of attached technology scale
| up and application development programs. Another would be
| requiring undergraduate and lower grants and tuition revenue to
| be spent directly on those programs and facilities, and research
| funds to be kept and spent separately.
|
| I would like to know some examples of how recent, publicly funded
| PhD, masters degree and postdoc work or research has materially
| advanced or will advance our world's knowledge and progress and
| has resulted in material benefits to society, and not just
| unreproducible studies on paper and unviable technologies and
| products.
| grishka wrote:
| What if the universe doesn't expand at all? What if we're
| completely wrong and redshift is caused by something else
| entirely, like some yet-undiscovered phenomenon that occurs to
| spacetime or electromagnetic waves? How can we be so sure it's
| space that's expanding, not time?
|
| The more I read about this, the more it feels like phlogiston
| theory[1]. Works great for describing observations at first, but
| as more observations are made, some contradict the theory, so
| exceptions are made for these cases (phlogiston must have
| negative mass sometimes/there must be extra matter or energy for
| galaxies to spin as fast as they do), and then finally someone
| discovers something (oxygen/???) that explains all observations
| much simpler and requires no weird exceptions.
|
| [1] https://en.wikipedia.org/wiki/Phlogiston_theory
| dotnet00 wrote:
| We can create and observe doppler shift by making things move
| towards/away from us. Thus it is proven that if something is
| moving away from us, it will produce a redshift. In the absence
| of evidence that something else is causing the redshift, the
| assumption should be that it is a result of things moving away
| from us.
|
| As an obvious example, doppler shift often needs to be
| accounted for to communicate with spacecraft.
| nilkn wrote:
| X causes Y does not mean that Y implies X. It's reasonable to
| _suspect_ X given Y and an absence of other such causal
| relations, but it's not necessarily reasonable to spend
| decades building layers and layers of models that assume X at
| the most basic level.
| ko27 wrote:
| You are not a making insightful point at all. Nothing in
| the world can guarantee you that "Y implies X", after all,
| we can be living in a simulation. Does that mean we should
| shutdown all scientific discussions by repeating what you
| stated? Of course not.
| nilkn wrote:
| Point out where I said we should "shutdown all scientific
| discussions." You won't be able to, and you will then
| realize how incredibly absurd what you just wrote is.
| MichaelZuo wrote:
| The parent is pointing out that the prior comment is
| literally meaningless, and self defeating too, since the
| same logic would apply to your own existence, or
| simulated existence. Including any possible words you
| could ever write.
|
| (As far as any other HN reader could ever perceive)
| nilkn wrote:
| Don't you think jumping to a complete existential crisis
| over such a simple comment is a little extreme? That
| alone is a red flag that maybe dogma has taken over. No,
| nothing I wrote suggests one must shut down all
| scientific discussion or inquiry. No, it does not mean
| you cannot investigate X and its implications. No, it
| does not mean you cannot build speculative models on top
| of X. Yes, it does mean it's important to be careful with
| language and avoid enshrining what is only an assumption
| as an unassailable fact of reality for generations.
| treflop wrote:
| Everyone knows this.
|
| But without looking at the direct rules of the system, this
| is the best you can do.
|
| It's not like you can just open the source code of the
| universe. You observe and make a theory that explains the
| observations, then the theory holds at least until a new
| observation contradicts the theory.
|
| Is the current theory wrong? Maybe. But everything can be
| wrong and the world is always welcome to hear a new theory
| that completely explains all current observations.
|
| But to just say a theory is wrong without providing a
| completely explained new one adds nothing.
| nilkn wrote:
| Everybody knows it, but the principle is selectively
| applied.
|
| For instance, our observations imply both general
| relativity and quantum field theory are necessary to
| model various aspects of the world. That's an example of
| a Y. The only known X that's ever been discovered that
| can encompass all aspects of that Y at all energy levels
| is string theory. Yet we are rightly careful to assume
| string theory is correct and enshrine it into the core
| body of scientific consensus. That does not mean we
| cannot or should not investigate it or even theory build
| on top of it, but it does mean we should refrain from
| assuming it must be true just because nobody can find
| anything better.
| bumby wrote:
| > _but it does mean we should refrain from assuming it
| must be true just because nobody can find anything
| better._
|
| The vast majority of science is not disproving a theory
| but adding nuance to it. Newtonian physics wasn't
| disproven by quantum physics, but quantum physics showed
| that Newtonian physics has limitations as a model. It's
| not unreasonable to assume our best model is true until
| there is a reasonable amount of data to the contrary.
|
| As others have said, your point adds little to the
| conversation until you bring good data to the argument.
| nilkn wrote:
| I don't accept that I owe anyone any kind of additional
| data on any of this. Just like I don't have to have a
| proven solution to the problem of finding a theory of
| everything to suggest that string theory may not be the
| truth of the universe while still acknowledging that it
| can be a worthwhile thread of inquiry and study.
|
| Suggesting that we avoid possible dogma has intrinsic
| value. Let us step back and consider the fact that the
| combination of general relativity and the Standard Model
| already cannot explain our most basic cosmological
| observations. We cannot explain the stability of even our
| own galaxy based on current models. This situation
| clearly calls for some basic caution before we enshrine
| possible unproven explanations into humanity's view of
| the universe. There's a lot of evidence, both long
| established and newly growing, which shows that our
| models can't consistently explain many of the basic
| things we see around us when we look up at the sky.
| bumby wrote:
| If you are trying to make a scientific argument, you
| should bring data since that's the cornerstone of
| science. You seem to be implying that people treat these
| models as gospel. I suspect most of those who are deep
| enough in the field understand they are models and
| respect the limitations. To that end, it's not dogma.
| Saying "this is the best model we currently have" is not
| the same as dogma. The article is specifically about
| using data to either support or reject a model so I don't
| know where you get the idea that anything is being
| "enshrined" and above reproach. Ironically, saying you
| don't need to bring data to support your point pushes
| your position closer to dogma.
|
| Your original point says very little. Yes, science
| acknowledges that you can never 100% say "X causes Y".
| Science is about getting closer and closer to that 100%
| with better models and better data while acknowledging
| it's impossible to get there completely. That's why
| people are saying your point is a nothing-burger. It's
| stating the obvious based on a strawman position.
| nilkn wrote:
| Strong reactions like yours to what should be a very mild
| and uncontroversal statement that you evidently don't
| even disagree with are exactly why these things are
| increasingly viewed by many as having elements of dogma.
|
| What I wrote needed to be said, despite evidently
| containing very little interesting content, precisely
| because of how severely it provokes certain people who
| claim not to even disagree with it. The degree of the
| provocation proves the value of the statement.
| bumby wrote:
| What makes you think I have a strong reaction?
|
| > _What I wrote needed to be said_
|
| There are apparently plenty of people who disagree
| (myself included) based on the comments. I think the
| reaction you're getting is because it's not a
| particularly fruitful comment because it adds nothing to
| the conversation, while being veiled as a profound
| statement.
|
| > _The degree of the provocation proves the value of the
| statement._
|
| Except the response isn't a response to the claim, it's
| in response to the absence of one. If a researcher
| publishes some incomprehensible word-salad and lots of
| people write to the editor saying it's a worthless
| article, it doesn't somehow translate value to the
| original work. I think what you're experiencing is people
| being protective of HN in terms of having meaningful
| debate and what you said isn't particularly meaningful
| despite the wordsmithing.
| nobody9999 wrote:
| >What I wrote needed to be said, despite evidently
| containing very little interesting content, precisely
| because of how severely it provokes certain people who
| claim not to even disagree with it. The degree of the
| provocation proves the value of the statement.
|
| The point of science isn't to punk the researchers. So
| no, what you wrote didn't need to be said.
|
| As I (and others) have repeatedly pointed out, our models
| are wrong. We know they are wrong. What they are is
| _less_ wrong than previous models. That doesn 't make
| them "right" or "dogma." Rather it makes them the model
| that _currently_ provides the best explanation for
| observed reality.
|
| That neither requires or suggests that
| research/investigation into modifications of our current
| models and/or into completely different models is
| unseemly or inappropriate.
|
| What I (and presumably others, as they've expressed
| similar thoughts) require, if you want me to accept
| modified/brand new theories/models is, at a minimum, a
| logic-based argument as to why a modified/new model
| describes the universe more completely/accurately than
| current models. Assuming you can convince me that it's
| _plausible_ , the next step is to present observational
| data that supports your logically argued hypothesis --
| and that such data is described by your model/theory more
| completely/accurately than other models. I.e., that your
| theory/model is _less wrong_ than our extant models which
| are also wrong, but _less wrong_ than previous models
| /theories.
|
| And if you can't present such data (e.g., with
| M-Theory[0]), then it's not science, it's just math,
| philosophy and/or metaphysics.
|
| That's not to say math/philosophy/metaphysics aren't
| useful. They absolutely are. However, without data (or
| the means to collect such data), it's impossible to
| falsify[1] such hypotheses and, as such, aren't science.
|
| [0] https://en.wikipedia.org/wiki/M-theory
|
| [1] https://en.wikipedia.org/wiki/Falsifiability
| mistermann wrote:
| > If you are trying to make a scientific argument, you
| should bring data since that's the cornerstone of
| science.
|
| He is making an _epistemic_ argument, and epistemology is
| a part of proper science, though not of scientism, which
| is what you are bringing.
|
| Binary is not the only form of logic available, but it is
| the most popular in discussions of the unknown.
|
| > Your original point says very little.
|
| You are _literally_ mixing up subjective and objective.
|
| > Yes, science acknowledges that you can never 100% say
| "X causes Y".
|
| Careful though: science _also does the opposite_. Do you
| know why? Because science is composed of scientists, and
| scientists are Humans, and Humans are famously unable to
| distinguish between facts and their opinion of what is a
| fact. In fact, doing so is almost always inappropriate,
| and socially punished.
|
| > Science is about...
|
| It may _intend to aspire_ to that, but what it is, _is
| what it is_. And what that is, comprehensively, is
| unknown, because it is unknowable. But we do know
| portions of what it is: there 's the part you said, but
| there is also deceit, hyperbole, delusion, etc...again,
| _because it is composed of Humans_ , and this is how
| Humans are. In my experience, all Humans oppose extreme
| correctness, I have never met a single one who does not.
| bumby wrote:
| I don't think anyone is claiming that science isn't
| biased because it's conducted by humans. Just like I
| don't think anyone is really claiming that the OP is
| incorrect in their statement. The comments I've read are
| merely pointing out "X causes Y does not mean that Y
| implies X" is a given in the context of a scientific
| discussion. It reads as if you and the OP are getting
| wrapped around the axle by treating science as an outcome
| rather than a process and, in doing so, fighting a claim
| that was never made, and one where the counterclaim is
| generally well understood in the scientific community. So
| well understood that it doesn't really need to be said.
| pdonis wrote:
| _> The only known X that's ever been discovered that can
| encompass all aspects of that Y at all energy levels is
| string theory._
|
| This is not correct; string theory is not the only
| candidate we have for a theory of quantum gravity.
| nilkn wrote:
| I didn't say it's the only theory of quantum gravity. You
| can get a theory of quantum gravity by taking standard
| QFT -- it just won't work at extremely high energies.
| Other options like loop quantum gravity do not reproduce
| the rest of our models about everything else.
|
| I said it's the only theory of gravity _and everything
| else_ at all energy levels, and that's true. In fact,
| you'll notice I did not even use the term "quantum
| gravity" to avoid the exact confusion you fell into
| anyway.
| SkyBelow wrote:
| >but it does mean we should refrain from assuming it must
| be true
|
| A good scientist will tell you that we don't assume it is
| truth. Instead, it is the closest thing to truth we can
| get at this time, but we are always seek better. But like
| a limit, we can only ever approach closer and never
| arrive at truth. As the other poster mentioned, we don't
| have a way to open up the source code of the universe.
|
| Some scientists get a bit too attached to theories and
| can move them from "closest we currently have to truth"
| to "truth", but I think the bigger issue is that the non-
| scientists involve in transmitting science too often
| present it as truth, instead of the best approximation we
| currently have. Often because fake confidence beats out
| measured modesty, and the one claiming to have truth is
| more convincing than the one saying we can't know truth
| and only better approximate it.
|
| A scientist will say science is true for the sake of
| simplifying the philosophy of science to those unfamiliar
| with it, but any scientist who thinks they have captured
| objective truth has lost the philosophical foundations of
| science.
| StanislavPetrov wrote:
| >But to just say a theory is wrong without providing a
| completely explained new one adds nothing.
|
| It certainly does. You don't have to know how something
| works to be able to know how it doesn't work. And there
| is value in knowing how something doesn't work, even if
| you don't know how it works.
| exe34 wrote:
| I think everybody would be happy if you came up with a
| different explanation! what's happened so far is that we
| have a known mechanism, and no alternative explanations
| have worked yet.
| dotnet00 wrote:
| If we can suspect X given Y, but we shouldn't build models
| on top of the assumption of X, then what are we supposed to
| do with Y?
|
| To me it seems like you're arguing that it was a bad idea
| to build on the assumption of Newton's theory of gravity
| because eventually it would be replaced by Einstein's
| theories of relativity. Which is obviously not sensible,
| since Einstein's theories were in part the result of trying
| to explain inaccurate predictions made by building on
| Newton's theory.
| SkyBelow wrote:
| >but it's not necessarily reasonable to spend decades
| building layers and layers of models that assume X at the
| most basic level.
|
| If the only option for finding out better evidence for or
| against X is by building those models and watching them
| either keep matching observations or finding a
| contradiction that can lead to the downfall of X as the
| suspect, then it is if you want to progress science any
| further.
|
| Maybe there is another area that will give results faster,
| but much of the easy and fast science has already been
| science. And if someone finds a better option we missed,
| which does happen from time to time, add some rigor to it,
| verify it with testing, and they'll likely have themselves
| a Nobel prize.
| narfay wrote:
| This is wrong on several levels:
|
| 1. As other commenter said, X causes Y does not mean that Y
| implies X. There can be another cause for the Doppler.
|
| And surprisingly, 2. There is at least one known mechanism
| that cause Doppler WITHOUT moving: when the observer is in a
| gravity well (ex: earth) and observing a stationary object
| outside the gravity well (ex: some fixed point in outer
| space)
| dotnet00 wrote:
| As I've mentioned in another post, that leads to
| questioning one of the most well tested theories in
| physics, so you need extraordinary evidence to prove it
| over something as elementary as doppler shift. Like, if
| it's Earth's gravity well causing us to see things
| differently, then things that are further from Earth should
| observe things differently.
| narfay wrote:
| There is already extraordinary evidence that something in
| physics is behaving differently at larger scales: the
| behavior of galaxies (spin, gravity pull) doesn't match
| their mass. Any mass. There is no single mass value that
| predicts their entire behavior correctly. Thus dark
| matter, dark energy etc competing theories, which are so
| far untestable.
|
| It wouldn't surprise me if we discover someday another
| Doppler mechanism that occurs at those same large scales
| pdonis wrote:
| _> There is at least one known mechanism that cause Doppler
| WITHOUT moving: when the observer is in a gravity well_
|
| This is gravitational redshift, not Doppler shift. Doppler
| shift specifically _means_ redshift due to an object moving
| away--but to really be correct that definition has to be
| limited to flat spacetime, or to a small enough region in a
| curved spacetime that the curvature can be ignored.
| pdonis wrote:
| _> In the absence of evidence that something else is causing
| the redshift, the assumption should be that it is a result of
| things moving away from us._
|
| But that is _not_ what our best current model of the universe
| actually says. Our best current model of the universe says
| that the observed redshift of a distant object tells us by
| what factor the universe expanded between the time the light
| was emitted and now (when we see the light). Viewing it as a
| Doppler shift is an approximation that only works for small
| redshifts (much less than 1).
| mr_mitm wrote:
| How would you explain the CMB? We can literally see that the
| universe used to be much denser.
| grishka wrote:
| And if the universe was much denser, doesn't that imply that
| all that matter affected its surroundings gravitationally?
| And as we know, time runs slower near large masses. And when
| something falls into a black hole, according to our very own
| theories, it would _also_ red-shift because of the black hole
| 's gravitational pull without anything having to expand.
| mr_mitm wrote:
| No, it implies it expanded in the meantime. We can see that
| it was a hot plasma up until 300k years after the big bang.
| This isn't some redshifted illusion, the matter was
| literally packed so densely and thus so hot that it was in
| another aggregate state.
|
| Don't get hung up on redshifts for evidence of the big
| bang. The CMB is the real smoking gun. Read up on it, it's
| entirely worth it. I can recommend Simon Singh's book "Big
| Bang".
|
| There is also a plethora of other probes that in
| concordance all point to the same thing: that the universe
| is almost 14 billion years old and expanded from a very
| hot, dense state. It's settled science, really.
| grishka wrote:
| Speaking of the big bang, how did time work back then? :)
|
| It's cool to say "in the first milliseconds of the
| existence of the universe X and Y happened", but how did
| time supposedly run as usual while everything else was on
| the fringe of our understanding of reality? There don't
| seem to be any answers to this (or I haven't looked
| thoroughly enough) but it feels like a very important
| question that's always overlooked by everyone talking
| about this.
| Balgair wrote:
| Yeah, it is overlooked because the real answers are
| 'hidden' behind a _lot_ of graduate level math. And most
| people don 't really want to learn a bookcase worth of
| math first to talk about it, but they talk all the same.
|
| Like, if you'd like to really dive into it then you're
| going to need to go through a lot of textbooks first.
|
| If you are moderately familiar with multi-variable calc,
| then here is a good book to get started down the GR hole:
| https://www.amazon.com/Mathematical-Methods-Physicists-
| Compr...
|
| Suffice to say, yes, there have been a lot of grad
| students that have the exact same questions and issue
| that you currently have. Further, once they have reached
| the end of the mathematical education required to
| understand how space time works in the first few minutes
| of the universe, they focus those questions into the
| issues we have with inflation. Those issues mostly come
| from our lack of understanding about how GR and QM
| interact, so the first 10e-43 seconds or so. At least,
| that is my understanding. Physicists are welcome to tell
| me how dumb I am right now!
| mr_mitm wrote:
| (former) Physicist with focus on cosmology here. Your
| reply is one of the sanest in this thread.
| artimaeis wrote:
| There's a lot of attempts at investigating those
| questions. Here's a couple of pages I'd recommend to
| peruse:
|
| https://en.wikipedia.org/wiki/Cosmic_time
|
| https://en.wikipedia.org/wiki/Chronology_of_the_universe
|
| If you're into podcasts at all, I'd strongly recommend
| Crash Course Pods: The Universe. The first (full) episode
| goes into detail on that first fraction of a second in
| our universe and it's pretty enlightening without being
| to thick on the math.
| hughesjj wrote:
| It's really trippy to think about how hawking radiation
| becomes 'real' once its sufficiently 'far' away from a
| 'strong' gravitational well, and how this can be thought of
| as a Doppler shift giving real physical presence (in that
| we can interact and be affected by ) to what was once a
| 'virtual' particle
|
| I think scienceclic does a good job visualizing this, but
| end of the day I can't see a way to distinguish event
| horizons regardless if they're a black hole or the distant
| past/big bang.
|
| https://youtu.be/isezfMo8kWQ?si=9wGliV-Qo1bXCTRy
|
| Specifically look at the relativity of the vacuum section,
| which builds to a great insight at around 5:45
| pdonis wrote:
| _> doesn 't that imply that all that matter affected its
| surroundings gravitationally?_
|
| It did; it caused the expansion to decelerate. That was
| true until a few billion years ago, when the matter density
| became smaller than the dark energy density and dark energy
| started to dominate the dynamics.
| mwbajor wrote:
| The observation of the Hubble constant requires us to measure
| distance to an object in space. This is very hard to do at the
| extreme distances required
| (https://en.wikipedia.org/wiki/Parallax). In the end, the
| variation in the Hubble constant might be only due to our
| limited accuracy in measurement.
| antognini wrote:
| There is a very old theory called the "Tired Light Hypothesis"
| which supposes that for some unknown reason light loses energy
| as it travels over cosmological distances. This would reproduce
| the observed redshifts, but it has issues predicting pretty
| much every other cosmological observation.
|
| In particular it doesn't explain observed reductions in surface
| brightness (expansion has the effect of "defocusing" collimated
| light). And it doesn't explain observed time dilation effects.
| rvnx wrote:
| I like your theory more than the current setup.
|
| I have an interesting addition to it:
|
| Time dilation could be that going very fast in the space
| makes you relatively faster in one direction.
|
| The thing is, atoms also have to travel; so the atoms (and
| matter in general) have a slightly longer distance to travel,
| to achieve the same chemical reaction. Which means
| interactions between atoms is slower, giving illusion of a
| slower time due to slower inter-atoms reactions.
| drdeca wrote:
| I don't think this would match the observations that can be
| made from earth of things on earth?
|
| Though the phrasing seems a bit ambiguous. Could you put
| some math behind those words?
| pdonis wrote:
| _> This would reproduce the observed redshifts, but it has
| issues predicting pretty much every other cosmological
| observation._
|
| Not to mention contradicting the laws of conservation of
| energy and momentum.
| antognini wrote:
| To be fair we do already know that energy is not globally
| conserved over cosmological timescales. (Energy
| conservation is a consequence of time invariance, but
| cosmological expansion breaks that symmetry.)
|
| Fritz Zwicky attempted to propose a mechanism of tired
| light that was caused by Compton scattering off of the
| intergalactic medium. But these kinds of scattering
| mechanisms produce far too much blurring in the expected
| images of distant galaxies and galaxy clusters.
| pdonis wrote:
| _> To be fair we do already know that energy is not
| globally conserved over cosmological timescales._
|
| No, what we know is that there is no invariant global
| concept of "energy" at all except in a special class of
| spacetimes (the ones with a timelike Killing vector
| field), to which the spacetime that describes our
| universe as a whole does not belong.
|
| However, "tired light" (at least the versions of it that
| aren't ruled out the way the Zwicky model you describe
| was) violates _local_ energy-momentum conservation, which
| _is_ a valid conservation law in GR (the covariant
| divergence of the stress-energy tensor is zero).
| antognini wrote:
| That is a good clarification.
| mithametacs wrote:
| I've always wanted to play a game based on defunct theories.
| I'm a fan of luminiferous aether myself. What are the impacts
| on a spacefaring civilization?
|
| Sci-fi already grants alternative physics to enable FTL and
| other magic. What about hard sci-fi, but _wrong-hard_ sci-fi?
|
| Extra credit: go back to Zeno and all motion is paradoxical,
| what would you even do in the game?
| matthewdgreen wrote:
| If you haven't read Greg Egan's Orthogonal Trilogy, you
| might like it.
| https://en.m.wikipedia.org/wiki/The_Clockwork_Rocket
| macintux wrote:
| It feels like all space combat games I've seen rely on
| Aristotle's theory that objects prefer to be at rest.
| NovemberWhiskey wrote:
| Try _Frontier: Elite II_ if you want to try a
| "realistically modeled" view of space combat - things are
| pretty much strictly Newtonian.
| Dylan16807 wrote:
| Luminiferous aether in what sense, what physics? Relativity
| doesn't exactly disprove it, it shows that everything
| distorts in a way that would make any aether unmeasurable.
| So if you just say aether:yes by itself I don't think
| anything happens.
| nobody9999 wrote:
| >What if the universe doesn't expand at all? What if we're
| completely wrong and redshift is caused by something else
| entirely, like some yet-undiscovered phenomenon that occurs to
| spacetime or electromagnetic waves? How can we be so sure it's
| space that's expanding, not time?
|
| I suppose that's possible. Does that hypothesis adequately
| explain our observations?
|
| Is the model we currently have completely "correct"? Almost
| certainly not. But it appears to be less wrong[0] than earlier
| models.
|
| If you (or anyone) can show how the above describes our
| observations better and more completely than our current
| models, then it's likely "less wrong."
|
| But you offer no evidence or even logical argument to support
| your hypothesis. As such, it's not much more than idle
| speculation and essentially equivalent, from a scientific
| standpoint, as suggesting the universe is a raisin dropped into
| a sugar syrup solution[1] and absorbing the liquid -- hence the
| expansion of the universe.
|
| [0] https://en.wikipedia.org/wiki/The_Relativity_of_Wrong
|
| [1] https://en.wikipedia.org/wiki/Compote
| lieks wrote:
| I remember reading, a long, long time ago, a paper where the
| authors suggested if the universe was slightly hyperbolic, it
| would also cause a redshift effect. I can't seem to find it
| (and as far as I remember it was purely theoretical), but at
| the time I thought it was an neat idea.
|
| Not that I have the background to know what else they might not
| have accounted for to reach this conclusion.
| pdonis wrote:
| _> What if the universe doesn 't expand at all?_
|
| Not possible. Redshift is not the only observation we have. The
| totality of all the observations we have cannot be explained in
| any other way than an expanding universe.
|
| _> How can we be so sure it 's space that's expanding, not
| time?_
|
| Our best current model does not say "it's space that's
| expanding, not time". It says that in one particular frame (the
| comoving frame), the overall spacetime geometry can be
| described using a "time" that always corresponds to the time of
| comoving observers and a "space" whose scale factor increases
| with that time.
|
| _> The more I read about this, the more it feels like
| phlogiston theory_
|
| This is an extremely unjustified comparison. Phlogiston theory
| _never_ accounted well for actual observations.
|
| _> as more observations are made, some contradict the theory_
|
| None of the observations being discussed contradict the general
| model of an expanding universe. They only pose problems for the
| indirect methods we use to convert our direct observations into
| model parameters.
| alexey-salmin wrote:
| > The totality of all the observations we have cannot be
| explained in any other way than an expanding universe.
|
| Surely there are infinite other possible explanations that
| fit the finite number of data points available to us.
| Probably what you meant is that the expanding universe theory
| is the simplest of them all and creates less problems then
| others.
| pdonis wrote:
| _> Surely there are infinite other possible explanations_
|
| If you think there are others, please exhibit one.
|
| _> Probably what you meant is that the expanding universe
| theory is the simplest of them all and creates less
| problems then others._
|
| There are no other _theories_ that I 'm aware of that
| account for all the data we have, even approximately.
| oraphalous wrote:
| > If you think there are others, please exhibit one.
|
| If everyone like you attempts to rail road the
| imaginative process at the beginning of hypothesis
| formation, then we'll never get to the point of being
| able to exhibit one, should one be possible.
|
| The demand for rigour at this point in a discourse -
| which was pretty clearly signalled by the commenter to be
| offered at a stage prior to substantive hypotheis
| formation - just shuts down the imaginative process. It's
| not constructive.
| stoperaticless wrote:
| > Not possible. Redshift is not the only observation we have.
| The totality of all the observations we have cannot be
| explained in any other way than an expanding universe.
|
| Well..? What are those other observations that point to
| expansion?
| pdonis wrote:
| _> What are those other observations that point to
| expansion?_
|
| The apparent brightness and apparent angular size of
| distant galaxies, and more importantly, the _relationship_
| between the three observables of redshift, apparent
| brightness, and apparent angular size. No known model other
| than the expanding universe predicts the actually measured
| relationship between those three observations.
| handsclean wrote:
| That's just redshift. Redshift alone wouldn't be evidence
| of expansion, just relative speed, when people say
| redshift evidence they mean the relationship between
| redshift and brightness of a standard candle. And
| regardless of whether you call it redshift or the
| relationship between redshift and something else, it
| would be impacted by a change to redshift.
| pdonis wrote:
| _> That's just redshift._
|
| No, it isn't. I explicitly described two other direct
| observations that are _not_ redshift.
|
| _> when people say redshift evidence they mean the
| relationship between redshift and brightness of a
| standard candle._
|
| No, they don't. Redshifts of distant objects are directly
| observed. We don't need a "standard candle" to measure
| them.
|
| Observations of _apparent brightness_ are used to
| estimate _distances_ to objects by comparing apparent
| brightness to the absolute brightness of a "standard
| candle" that is the same kind of object. However, such
| distance estimates are model-dependent; before they can
| even be made, the model parameters first have to be
| estimated using the observed relationship between
| redshift, apparent brightness, and apparent angular size.
|
| _> And regardless of whether you call it redshift or the
| relationship between redshift and something else, it
| would be impacted by a change to redshift._
|
| I have no idea what you mean here.
| eigenket wrote:
| Its not just redshift. If you look at very distant
| galaxies you see their apparent angular size is larger
| than you expect.
|
| https://en.wikipedia.org/wiki/Angular_diameter_distance
|
| You know how distant objects appear smaller, well in an
| expanding universe that isn't completely true, very
| distant objects start looking bigger again. Roughly
| speaking this happens because the distance between paths
| different photons take to get to us gets stretched by the
| expansion.
|
| Theres also the very obvious observation of the cosmic
| microwave background, which isn't explained by any non-
| expanding universe model.
| handsclean wrote:
| It's not just phlogiston, it's the lifecycle of all
| scientific theories that they're used for as long as they
| make accurate predictions, then we start seeing things they
| mis-predict, then they're revised or replaced. You seem to
| think the expanding universe theory can still be saved by
| some data artifact or parameter tweaking, but that's been
| hunted for years and we're still at "we just can't make it
| match everything we're seeing". Historically, that's what
| precedes significant revision or replacement.
|
| > Redshift is not the only observation we have.
|
| What else is there?
| pdonis wrote:
| _> it's the lifecycle of all scientific theories that
| they're used for as long as they make accurate predictions,
| then we start seeing things they mis-predict, then they're
| revised or replaced._
|
| No, that's not what always happens with scientific
| theories. For example, Newtonian mechanics is still used,
| even though we now know it's not exactly correct; it's an
| approximation to relativity that works reasonably well for
| weak gravitational fields and relative speeds that are
| small compared to the speed of light.
|
| The "mechanics" that Newtonian theory (and its
| predecessors, Galilean mechanics and Kepler's model of the
| solar system) replaced _were_ indeed replaced--nobody uses
| Aristotelian physics or Ptolemaic cosmology any more, not
| even as approximations. But that does not always happen.
| cristianpascu wrote:
| The _conclusion_ that the Universe is expanding is based on the
| long accepted premise that the Universe is _flat_. And this
| premise can not be proven or disproved unless we travel great
| distances to actually _observe_ if the Universe does, in fact,
| look the same from any point you look.
|
| The Copernican principle is, indeed, attractive to the modern
| mind because its neutrality. But it's not neutral. It's just as
| loaded as any other principle, no matter how crazy it may sound
| today, philosophical, religious, or merely personal.
| SkyBelow wrote:
| My guess is that scientists are considering this, but until now
| no better theory has been presented.
|
| Part of this is the distinction between what is happening and
| why the model says is happening. Does any physicist believe
| they have the perfect model? Or is it that they use the model
| that best fits the observations and are open to any other
| model, as long as it is either simpler or produces fewer
| contradictions than the current model (and is just as
| testable).
|
| I think too often we hear reports of "science says X is what
| happens" when the reality is more like "science says that the
| current model based on X happening is what best describes
| current data and observations".
| while_true_ wrote:
| Expanding universe and Big Bang Theory go hand-in-hand. There
| are multiple independent observations besides the red shift
| that make it nearly certain there had to be a BBT event to
| explain what we see. The universe is too hot, chaotic and
| clumpy for there not to have been a massive explosion to kick
| it all into motion. Since there is good confidence BBT
| happened, transitioning from that event to a steady-state non-
| expanding universe would require some sort of mechanism to slow
| then freeze the expansion. Not aware of any support for that
| model.
| batch12 wrote:
| I'm going to make myself sound stupid, but these are the things
| I think about and try to picture while falling asleep. My most
| recent entertaining session was to imagine that the force
| pushing the galaxies apart was an inverse to all the gravity of
| the galaxies. Like the classic picture of the marble on a
| rubber sheet, but instead of a flat spacetime outside of the
| gravity well, it buckled upwards and outwards and the other
| galaxies kind of rolled away seeking equilibrium. Then I
| imagined the lensing that would happen with the gravity and
| time distortions. It helped me fall asleep anyway...
| inciampati wrote:
| Does quanta magazine manage to reach this level of detail in
| other fields?
| refibrillator wrote:
| If you're interested in learning more about the rich human
| history and ingenuity underpinning the Hubble "constant", please
| do yourself a favor and scroll through The Cosmic Distance Ladder
| by Terence Tao of UCLA: https://terrytao.wordpress.com/wp-
| content/uploads/2010/10/co...
|
| The slides are delightfully visual and comprehensive yet terse,
| walking you up the rungs of the cosmic ladder from the Earth
| through the moon, sun, and beyond. I can almost guarantee you'll
| learn something new and fascinating.
| causality0 wrote:
| _Everyone expected the sharp vision of the James Webb Space
| Telescope to bring the answer into focus._
|
| I think people forget that, due to the longer wavelengths to
| which it's sensitive, Webb actually has a poorer angular
| resolution than Hubble.
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