[HN Gopher] New theory claims to unite Einstein's gravity with q...
___________________________________________________________________
New theory claims to unite Einstein's gravity with quantum
mechanics
Author : dotnet00
Score : 308 points
Date : 2023-12-05 03:47 UTC (19 hours ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| hn_throwaway_99 wrote:
| > A second paper, published simultaneously in Nature
| Communications and led by Professor Oppenheim's former Ph.D.
| students, looks at some of the consequences of the theory, and
| proposes an experiment to test it: to measure a mass very
| precisely to see if its weight appears to fluctuate over time.
|
| Definitely don't know enough to comment about the overall
| proposal, but given how many grand physics theories over the past
| couple decades have been untestable, it's really nice to see the
| proponents proposing a test.
| dotnet00 wrote:
| Yeah, since untestable proposals for this kind of theory are
| basically the norm, the fact that they have a proposed test
| made me think it was worth sharing.
| Animats wrote:
| It's good that it's testable. This is one of those ideas which
| either wins a Nobel Prize or is totally bogus. So what does it
| take to test it?
| stjohnswarts wrote:
| Bogus usually implies something meant as a fake or
| counterfeit, I think a better way to describe it would be
| "incorrect", I don't think these scientists are trying to
| fake anything.
| szundi wrote:
| Untestable theories are not theories - I mean, for what purpose
| and why care?
| colordrops wrote:
| Path finding
| dotnet00 wrote:
| The other big theories aren't completely untestable, the
| issue is basically that the models have a lot of parameters
| which can often be tuned in a way that leaves a possibility
| for the general theory to still work, and testing them to the
| point that any corrections seem too unreasonable is even more
| difficult and expensive.
| dragoncrab wrote:
| Not reflecting to this particular theory, but in general
| history is full of theories which were not testable at their
| birth, but both engineering and the evolution of the theory
| eventually found a way to do so, even if it took a century.
|
| Black holes, Higgs bozon and neutrinos are a few popular
| examples.
| mr_mitm wrote:
| Some theories are only untestable for practical reasons, like
| needing a particle accelerator the size of the solar system.
| That doesn't make them unscientific or "not theories". That
| is not the kind of falsifiability that Karl Popper had in
| mind.
| leptons wrote:
| Yes, it does. The word "theory" has a specific meaning.
| What this article is about is really a _hypothesis_ , not a
| theory. I saw no evidence or data to back up what they
| think might be happening, thus not a theory.
|
| _" In scientific reasoning, a hypothesis is constructed
| before any applicable research has been done. A theory, on
| the other hand, is supported by evidence: it's a principle
| formed as an attempt to explain things that have already
| been substantiated by data."_
|
| Most people in this thread, as well as the writers of the
| article seem to be confused about the meaning of the word
| theory.
| mr_mitm wrote:
| Maybe that should give you a hint that professional
| working scientists don't care much for definitions from
| wordbooks.
|
| Besides, I was commenting on the topic of falsifiability.
| To be a scientific _hypothesis or theory_ it must be
| falsifiable - in principle, not practically. At least
| that 's my claim in the context of Popper. Evidence
| didn't even enter the discussion.
| j-krieger wrote:
| Do you have any examples? I'd to read up!
| Cthulhu_ wrote:
| Yeah they are, they just cannot be verified - or cannot be
| verified yet.
|
| The higgs boson theory was theorised in 1964 and it was
| untestable at the time, but that theory got the funding
| together to create one of the largest and most expensive
| scientific instruments built to prove the theory.
|
| Nuclear fusion was theorised in 1915, again untestable at the
| time, and look how far we've come.
|
| The above comment is an anti-science comment if I've ever
| seen one.
| thereddaikon wrote:
| Usually when people say something is untestable they don't
| mean like the Higgs Boson. It was testable, they just
| needed the proper tools. This was always known and was
| being actively worked towards. An untestable theory is one
| that cannot be tested regardless of the tools due to the
| nature of the theory. Multiverse is an example of an
| untestable theory. There is no way we know of to actually
| prove or disprove it. And its fair to question their
| legitimacy as theories. As testing a hypothesis is the core
| action of the scientific method, it logically follows that
| anything untestable is fundamentally not science and
| therefore not a theory.
| snewman wrote:
| Isn't the term for this "unfalsifiable"?
| defgeneric wrote:
| A theory can be untestable but also falsifiable. For
| example, while the multiverse theory/interpretation may
| be untestable, it could be immediately falsified if QM
| were falsified.
|
| Popper's falsifiability criterion was more aimed at
| theories like Marxism, where it seemed that within the
| theory there was always something available to account
| for an exception or challenge.
| thereddaikon wrote:
| In this case I think multiverse is both. Testability and
| falsifiability are closely related. But its possible to
| make a testable statement that can't be falsified in most
| examples I can think of the test can't be exhaustive.
| guenthert wrote:
| > it's really nice to see the proponents proposing a test.
|
| Is it feasible though? I wonder whether that test is not just
| outside of what can be technically realized today, but
| Heisenberg's uncertainty principle gets in the way.
| mikro2nd wrote:
| Well,... measuring gravity waves was outside of the
| technically realisable for a long time, but a couple of
| decades of trial and refinement and it _got_ realised.
| nojvek wrote:
| Love that there is a test.
|
| Some of the theories like gravity waves and Higgs boson took
| almost half a century to be confirmed by experimentation.
|
| The hard part about this is building tools that can precisely
| measure mass fluctuations with extremely low error bars at
| picosecond timescales.
|
| Because we need to both validate the theory and that the device
| is correctly measuring.
|
| So much of science became only possible because of better
| instruments. Be it microscopes to see the tiniest phenomena or
| telescopes to observe the furthest phenomena.
| edgefield wrote:
| I'm not a physicist much less an astrophysicist and so take
| what I'm about to say with a hefty grain of salt. But I
| wonder if this new approach can also explain observations of
| distant galaxies. Distant galaxies either redshift because
| they're moving away faster over time due to dark energy or
| redshift because their mass is changing. Can this new theory
| help explain why older galaxies might lose increasing mass
| over time?
| jakubmazanec wrote:
| > So much of science became only possible because of better
| instruments.
|
| I would argue a stronger claim: experimental confirmation of
| theories and better measurements must always bootstrap each
| other. The history of temperature has many examples [1].
|
| [1] https://psychology.okstate.edu/faculty/jgrice/psyc4333/Th
| erm...
| rhelz wrote:
| The various standard kilograms held by the national bodies, and
| the prototype standard kilogram in paris, were measured very
| precisely over the past hundred years, and their weights did seem
| to diverge mysteriously.
| dataflow wrote:
| What made them mysterious? Aren't there always some fraction of
| atoms or molecules with sufficiently high energy to escape the
| object?
| mvdtnz wrote:
| The fact that you, a random internet guy, knows this makes me
| believe that the world's top experts on measuring this exact
| thing probably thought of it, and if there is a mysterious
| divergence this probably doesn't account for it.
| dataflow wrote:
| I figure as much, but that's kinda why I'm asking what made
| it mysterious. I actually hadn't heard of it being seen as
| mysterious until today - that comment is the first time
| I've seen that. Until today I thought it had been was
| unsurprising for scientists.
| yetihehe wrote:
| > I figure as much, but that's kinda why I'm asking what
| made it mysterious.
|
| You expect simple explanations to VERY complex problems
| from random internet commenters. I think you expect too
| much.
| quickthrower2 wrote:
| Not on HN sometimes some gems of comments are made by
| experts
| yetihehe wrote:
| Sometimes: when you least expect them. Not expecting them
| is a good strategy here.
| quietbritishjim wrote:
| I think the real question is: where is the evidence that
| scientists find it mysterious? That doesn't need any sort
| of explanation, just a reference for a claim made by a
| commenter. As with the other commenter, I've heard about
| the mass divergence before, but never that anyone found
| it surprising.
| gumby wrote:
| As has even been discussed on HN over the years (!), the
| cause is unknown.* This is one of the motivations to
| replace the official kilogram with a definition based on
| measurable natural quantities, as had been done with the
| second and the meter. It took until 2018 to do so:
| https://www.nist.gov/si-redefinition/kilogram-
| introduction
|
| * it's not like there aren't good theories but you can't
| experiment directly on "the" kg because you can't risk
| changing it!
| dataflow wrote:
| I'm neither seeing the cause being mentioned as unknown
| in that link, nor would the cause being unknown imply
| anything being mysterious?
|
| Like if you find that your car has broken down after 200k
| miles, you might not be able to determine the cause, but
| it wouldn't exactly be some kind of mysterious physical
| phenomenon that would puzzle scientists. Obviously,
| something wore out. Why/how is this any different?
| gumby wrote:
| Did you click on the other kilogram links (or other
| metric links which are also interesting?)
|
| A useful paragraph is the following: "The trend during
| the past century had been for most of BIPM's official
| copies to gain mass relative to the IPK, although by
| somewhat different amounts, averaging around 50
| micrograms (millionths of a gram) over 100 years. But an
| alternative explanation is that the IPK was losing mass
| relative to its copies. Even more likely, it was a
| combination of both."
|
| Those pages are for the lay audience but you can do your
| own web search (probably even an algolia search of HN) to
| know more.
|
| In general, it's often easy to come up with an
| explanation of some new phenomenon, but to answer the
| question you still have to do science...which often
| simply confirms intuition but not always. My comment was
| less on the reason and more on the difficulty of doing
| experiments on what was literally the kg, no matter how
| it fluctuated.
| DFHippie wrote:
| My theory: People are treating them with different
| degrees of reverence. They are careful to polish anything
| off the IPK, causing it to lose weight gradually through
| abrasion. The others gain wait through random adhesions,
| perhaps oils picked up by gloves used to handle them.
|
| I'm just some random guy on the internet, I know. It's
| fun to have theories!
| vanderZwan wrote:
| I don't disagree with you, but on the other hand: if
| people claim something in a discussion thread we need to
| be able to ask them to back those claims up. Otherwise
| anyone can just assert anything.
|
| Sure, the explanation might not fit in the margins here,
| but then a link to a source that does attempt to explain
| it would be fine too.
| gcr wrote:
| One reason why questions like this are important is
| because it gives the audience around the asker an
| opportunity to learn something new. Isn't it important to
| be able to express curiosity, especially for the benefit
| of others?
| Guvante wrote:
| 50 ug over 130 years is way too fast
|
| > The reason for this drift has eluded physicists who
| have dedicated their careers to the SI unit of mass. No
| plausible mechanism has been proposed to explain either a
| steady decrease in the mass of the IPK, or an increase in
| that of its replicas dispersed throughout the world
|
| https://en.m.wikipedia.org/wiki/International_Prototype_o
| f_t...
| satvikpendem wrote:
| They're not being arrogant, as it seems like the parent is
| genuinely curious as to why such weights diverged, as am I.
| It is still a good question to ask, since I also have not
| heard a good answer to that question.
| iainmerrick wrote:
| Right -- and they're not even asking for the answer,
| they're just asking what the interesting mysterious
| phenomenon is.
| ramblerman wrote:
| I've heard of an appeal to authority, but an appeal to
| ignorance is new.
|
| OPs question is not ridiculous, nor does he suggest it to
| counter the "mysterious" claims
| lordnacho wrote:
| Not new, Efficient Markets Hypothesis is like this. "I
| haven't heard of a way to make money from trading so
| there isn't one" is my caricature of it.
| cnity wrote:
| Isn't it more like: "exploitation of a market
| inefficiency renders the market efficient over time", or
| something to that effect? Or rather, (others) making
| money from trading is what makes it hard (for you) to
| make money from trading.
| lordnacho wrote:
| Sure, depends on how you encounter it. Most often on
| forums someone will show up wanting to hear about how to
| write a strategy, and they are rebuffed with "nobody
| would ever publish that".
| cnity wrote:
| I love encountering nay-sayers because it means either:
|
| 1. I am wrong and could learn something new.
|
| 2. They are wrong and their opposition fills me with
| defiant determination.
|
| The difficulty comes when you view something as case 2
| but it is actually case 1 and you embarrass yourself. I
| do this all the time.
| sam0x17 wrote:
| I find that it saves time to just start by assuming the
| experts haven't thought of X because of how many times I've
| seen assuming that they _have_ thought of X turn out to be
| a poor assumption, across many domains.
| bookmark1231 wrote:
| That's incredibly specious reasoning.
| justinclift wrote:
| Probably gets a better result than the alternative
| though. ;)
| Widdershin wrote:
| Can you give any examples of times you've easily
| anticipated X when a whole field of subject matter
| experts have demonstrably overlooked it?
| simiones wrote:
| I don't really agree with the OP, but I do think there is
| at least one, possibly two such examples. The pretty
| clear one is nutrition: the vast majority of studies and
| recommendations made over the years are pure bullshit,
| and quite transparently so. They either study a handful
| of people in detail, or a huge swathe of population in
| aggregate, and get so many confounding variables that
| there is 0 explanatory power in any of them. This is
| quite obvious to anyone, but the field keeps churning out
| papers and making official recommendations as if they
| know anything more about nutrition than "missing certain
| key nutrients can cause certain disease, like scurvy for
| missing vitamin C".
| digging wrote:
| Is that an example of "the experts didn't actually think
| of [simple explanation]" though?
| dataflow wrote:
| This isn't to agree with the parent comment, but wouldn't
| this situation itself be an answer to your question
| (assuming the claim is true)? Laymen like me easily
| anticipated mass divergence, but purportedly scientists
| have been surprised by it.
| cwillu wrote:
| The procedure of multiple weights being calibrated
| against a single standard is _predicated_ on anticipated
| mass divergence.
|
| The mystery being discussed is that, even after the
| obvious sources of error are allowed for, there is still
| a discrepancy, and it's not easy to determine how much of
| that discrepancy is with the weights being recalibrated
| vs the test standard they're being calibrated to. None of
| which is shocking to anyone involved, just puzzling.
| monktastic1 wrote:
| This comment chain is getting circular. We can't use this
| as an example for itself by assuming that it is true.
| sumtechguy wrote:
| I think that they do not have an exact reason and
| measured it and seen it happen is the surprising bit.
| Anything else is a good guess. Of those, people have
| plenty.
| anymouse123456 wrote:
| Can't speak for OP, but I've had more than a few similar
| experiences (from both sides of the fence FWIW).
|
| I can think of one example in software deployment
| frequency. The observation (many years ago), was that
| it's painful and risky (therefore, expensive) to deploy
| software, so we should do it as infrequently as the
| market will allow.
|
| Many companies used to be on annual release schedules,
| some even longer. Many organizations still resist
| deploying software more than every couple/few weeks.
|
| ~15 years ago, I was working alongside the other
| (obviously ignorant) people who believed that when
| something is painful, slow and repetitive, it should be
| automated. We believed that software deployment should
| happen continuously as a total non-event.
|
| I've had to debate this subject with "experts" over and
| over and over again, and I've never met a single person
| who, once migrated, wanted to go back to the nightmare of
| slow, periodic software deployments.
| ndriscoll wrote:
| I don't see why a slow deployment cadence is a nightmare.
| When I've worked in that setting, it mostly didn't matter
| to me when something got deployed. When it did (e.g.
| because something was broken), we had a process in place
| to deploy only high priority fixes between normal
| releases.
|
| Computers mostly just continue to work when you don't
| change anything, so that meant after the first week or so
| after a release, the chance of getting paged dropped
| dramatically for 3 months.
| rtsil wrote:
| That's more "the experts had a (wrong) opinion on
| something" than "the experts overlooked something
| obvious". They didn't overlook it, they thought about it
| and came to a conclusion.
|
| And if by "many years ago" you refer to a period where
| software deployment was mostly offline and through
| physical media, then it was indeed painful and risky (and
| therefore expensive). The experts weren't wrong back
| then.
| NoLsAfterMid wrote:
| Did you ever pause to think "is this comment worth
| posting"? Maybe you should.
| notjoemama wrote:
| Can they perform the calculations to estimate the
| fluctuations? Can they write an informal explanation about
| what happens to the gluons? I think the experience of
| seeing a factoid on the internet is being given too much
| weight here.
| dotnet00 wrote:
| If it were simply a matter of losing particles, I'd expect
| that one of the many very capable metrology labs around the
| world would've devised an appropriate experiment, e.g.
| storing two exact same masses at slightly different
| temperatures near absolute zero and characterizing the
| difference in mass (since presumably the higher temperature
| sample would lose slightly more mass if it were down to high
| energy particles).
|
| A test for this theory would have to involve a means of
| accounting for these kinds of fluctuations.
| dataflow wrote:
| I mean I just gave one example of how it might lose mass.
| There are other obvious ways (like when they're picked up
| etc.). My point wasn't to present a hypothesis for people
| like myself here to rebut. I can do that just fine myself.
| I was trying to understand what about this has been
| confusing for scientists.
| chasd00 wrote:
| > like when they're picked up etc.
|
| Wouldn't just moving an object change its mass? Any
| change in potential energy would mean a change in mass
| from good old e=mc^2
| mcpackieh wrote:
| Make sure to store them very deep underground down a
| mineshaft, so random cosmic rays don't ever knock a few
| atoms loose.
| analog31 wrote:
| Look for material condensed on the inside of the jar.
| irjustin wrote:
| > Aren't there always some fraction of atoms or molecules
| with sufficiently high energy to escape the object?
|
| Can someone help me understand this? I thought that things
| were supposed to be stable given the elements used for le
| grand k. That they don't decay on their own and it would have
| to be another mechanism to explain the divergence?
|
| [0] https://en.wikipedia.org/wiki/International_Prototype_of_
| the...
| pants2 wrote:
| In a system of particles, due to random Brownian motion and
| the nature of Gaussian energy distributions, a small number
| of particles occasionally gain significantly higher energy
| than average through statistical fluctuations. Maybe enough
| to escape the binding energy of le grand k. However I would
| think this is a very very small effect in platinum.
| irjustin wrote:
| Sure, radioactivity.
|
| But, Le grand K is made of naturally occurring platinum
| of which most of the isotopes are observationally
| stable[0] and the one isotope that isn't has a half-life
| of 6.5x10^11 and only makes up 0.012% [1].
|
| So yeah I don't buy the unstable explanation to even
| begin to show the divergence, let alone "weight gain".
|
| [0] https://en.wikipedia.org/wiki/Stable_nuclide#Still-
| unobserve...
|
| [1] https://en.wikipedia.org/wiki/Isotopes_of_platinum
|
| [Edit] Wait are you describing evaporation?
| shwouchk wrote:
| Edit: yes
| bowsamic wrote:
| Yes, he's describing evaporation. Here's a thread about
| it, basically the answer is "we don't know"
| https://physics.stackexchange.com/questions/77130/why-
| does-p...
| dataflow wrote:
| Thank you, that link (particularly [1]) is basically the
| kind of explanation I was looking for in my initial
| comment.
|
| [1] https://physics.stackexchange.com/a/784886
| imglorp wrote:
| There's so many variables there! What kind of purity
| could 1889 achieve? What kind of uniformity between the N
| samples? How do they know the different cleaning
| procedures (!) are not adding mass by leaving something
| behind? If the samples are known to be oxidizing, why
| leave them in air? Why are there multiple elbows in that
| graph around 1950 -- surely another procedural change but
| again not uniformly applied?
|
| Maybe these aren't the best sources of historic mass
| data.
| Y_Y wrote:
| Perhaps you mean Boltzmann distributions?
| marcosdumay wrote:
| It's well known that they tend to gain weight, not lose it.
|
| And yeah, the mystery is just what mechanism exactly affected
| each one. (AKA, not much of a mystery.) The possibilities are
| very well understood.
| dataflow wrote:
| > And yeah, the mystery is just what mechanism exactly
| affected each one. (AKA, not much of a mystery.) The
| possibilities are very well understood.
|
| Ahh, that makes more sense. Thanks!
| analog31 wrote:
| If the object is evaporating, look for material condensed on
| the inside of the jar.
| pegasus wrote:
| I'm sure that if they suspected that variance in mass could
| support their theory, they would have investigated that
| possibility instead of proposing a new test.
| pavon wrote:
| If I understand correctly this theory would manifest itself as
| variation in measuring the same standard kilogram over and over
| (to a precision beyond what we are currently capable of),
| whereas divergence between different standard kilograms could
| have other unrelated causes.
| dang wrote:
| (We detached this subthread from
| https://news.ycombinator.com/item?id=38527238.)
| lostdog wrote:
| Is there a decent explanation of what the conflict is about, that
| is understandable with a non-physics-major college level maths
| background?
| whatshisface wrote:
| Gravitons don't work as force carriers in quantum field theory
| because the sums describing them diverge even worse than other
| sums describing the three other forces; sums which also diverge
| but can be corrected.
| mvdtnz wrote:
| Depends how much time you want to spend on it. I first learned
| about this topic in Brian Green's book The Elegant Universe
| back in 2005 or so. At the time there was a glut of popular
| science books on the topic (Lee Smolin had an excellent book
| titled The Trouble with Physics which made an excellent counter
| argument to Green's string theory-heavy title).
|
| If you want to go much deeper, Roger Penrose wrote The Road to
| Reality which is a much much harder read (I was never able to
| complete it after 3 separate attempts).
| selecsosi wrote:
| Being _hyper_ reductionist, the standard model of physics,
| which describes, to an extremely high degree, the interaction
| (creation, elimination, and chance of one thing turning into
| another) of particles that constitute "stuff" (matter / energy)
| does not account for the interaction of matter via gravitation.
|
| Most things interact with each other, they create "particles"
| to exchange force / energy (actually in the case here much of
| this is actually virtual particle interaction / creation). An
| example of this is when two magnets are interacting with each
| other, the repulsion/attraction that the magnets / and magnetic
| fields, the force carriers there actually described by best by
| "virtual photons" https://en.wikipedia.org/wiki/Virtual_photon#
| :~:text=Virtual....
|
| The whole standard model is like this (protons/neutrons
| exchange gluons via the strong nuclear force).
|
| For gravity, there isn't a good "particle" we've found that can
| accurately describe how gravity behave. It's good to note here
| a "particle" is what is used to "quantize" something, and so
| quantum mechanics is the study of how these subatomic particles
| interact and are created when things like protons are smashed
| together in a particle accelerator.
|
| Gravity, on the other hand, behaves more like a classical
| theory (in the sense that it is a field, rather than a discrete
| quantized energy exchange). In the parlance of the field, mass,
| appears to cause a curvature in space time according to the
| rules (quite accurately predicted) in general relativity.
|
| This appears to be some sort of more reconciliation by
| acknowledgment of the different aspects of the behaviors of the
| models (GR vs QM), and chooses a path to verify this by looking
| at the breakdown of matter (in this case, entangled quantum
| particles) in a asomtomic limit that might be imposed on a
| quantized theory when that is subatomically reconciled against
| a continuous field like gravity.
|
| (My own notes) This might be indicating that there is a
| continuous nature (or at least continuous at the scales that
| these subatomic particles experience) such that when the
| particles interact with the continuous field, their movement
| creates some snapback of the field (thinking how movement in
| water creates microscopic cavitation) which disrupts what would
| be a continuous laminar flow in the water case, creating
| macroscopic turbulence (in this case disturbing the entangled
| particles)
|
| * Edit: a little clarity / notes on the SM/QM/GR overlap
| sroussey wrote:
| Coming from an engineering background, is there something
| about this that might prove useful?
|
| Like electron tunneling that made a good amplifier
| (transistor)?
|
| Could this "snapback" be utilized in interesting ways?
| loosak wrote:
| One day, Sir, you may tax it...
| junon wrote:
| Wow, thank you for this very clear explanation. :)
| tsimionescu wrote:
| User selecosi gave a beautiful explanation, but perhaps it's a
| bit too detailed.
|
| Trying to give a slightly more high level idea, the conflict is
| simply that if you introduce the gravitational effects
| (spacetime bending) from general relativity into the equations
| of quantum mechanics you get infinities all over the place.
| This happens because in QM particles are not localized, they
| exist as a probability wave with certain values at any space
| and time, but the effects of their mass at all those spaces and
| times adds up to infinity if you just apply the calculations
| from relativity, in a way that we haven't been able to solve.
|
| This is all very roughly speaking - the exact reasons are quite
| technical and I don't understand them myself. Electromagnetism
| and other interactions had similar issues, but we found
| mathematical solutions to fix them, and those solutions we know
| just don't work with the equations for gravitational
| interactions.
| GoblinSlayer wrote:
| Infinities appear if particles are assumed to be zero size:
| they become black holes with infinities at the event horizon.
| psc wrote:
| ScienceClic on youtube has some really great videos, the first
| half of the string theory video [1] does a good job framing the
| conflict at a high level, string theory being one attempt to
| resolve the problem.
|
| It doesn't go into math but mentions that in the standard
| model, interactions are local, which for example means
| something like photon emission is instantaneous. When applied
| to gravity/gravitons, you get infinities in the math. This sort
| of makes sense to me, but I have yet to find anything that does
| an understandable job explaining how/why exactly the math
| breaks down.
|
| There's a series on the maths of general relativity [2] which I
| haven't completed but I'm hoping will provide a bit more
| background to understand the math.
|
| Also, the article mentions that the new theory was motivated by
| solving the black hole information paradox [3], which there's a
| good video [4] about as well
|
| [1] https://www.youtube.com/watch?v=n7cOlBxtKSo
|
| [2]
| https://www.youtube.com/watch?v=xodtfM1r9FA&list=PLu7cY2CPiR...
|
| [3]
| https://en.wikipedia.org/wiki/Black_hole_information_paradox
|
| [4] https://www.youtube.com/watch?v=isezfMo8kWQ
| empath-nirvana wrote:
| The curvature of space time depends on the distribution of mass
| and energy within that space time. If you're modeling general
| relativity classically with quantized mass and energy at very
| small scales, stuff gets "weird". If a particle isn't in a
| well-defined location with a well-defined energy, then what is
| its effect on the curvature of space time around it?
| inasio wrote:
| I was really hoping to find concrete details of what the
| experiment that they proposed to validate or refute their theory
| is. I hope it's something achievable, or at least not
| ridiculously far from what we can currently measure
| fgoesbrrr wrote:
| They mention 20 years in the article.
| pmontra wrote:
| The experiments are described in the second paper, at
| https://www.nature.com/articles/s41467-023-43348-2
| defrost wrote:
| Jonathan Oppenheim: If you'd like to attend a
| public lecture (virtual or in London) about the postquantum
| theory of classical gravity, or contribute a donation to the
| group's research program, click "Donate" to add your email
| address to our list.
|
| https://www.ucl.ac.uk/oppenheim/
|
| https://www.ucl.ac.uk/oppenheim/research.html
|
| See Also:
|
| _Gravitationally induced decoherence vs space-time diffusion:
| testing the quantum nature of gravity_ (March 2022)
| https://arxiv.org/pdf/2203.01982.pdf
|
| _Is it time to rethink quantum gravity?_ (March 2023)
| https://arxiv.org/pdf/2310.12221.pdf
| Certhas wrote:
| This is all surprisingly substantative.
|
| That said, there are many results that connect gravitational
| and thermodynamic phenomena. It would be good to understand how
| these look from the perspective of this theory.
|
| Edit: just started reading, so if this is explained somewhere
| would love to get a pointer.
| maaaaattttt wrote:
| This is a question I've been asking myself (probably due to a
| lack of understanding and knowledge) and this theory seems to
| hint at something similar: why do we assume spacetime to be
| homogenous in its nature? Here they seem to say that on some
| quantum level spacetime could vary drastically. Couldn't then
| dark matter be explained by some variations on a large scale?
| Like giant "wrinkles" in spacetime? They would then behave as
| pseudo black holes, or more like "black trenches", that lead to
| the structures we see today in the universe. The structures seem
| to have more mass than what we can actually see, but are in fact
| just placed in locations that behave differently gravity wise?
| samus wrote:
| Science had fared quite well so far with the assumption that
| the laws of physics are largely the same no matter where and
| when we are. There would have to be very strong evidence to
| throw that out. And the immediate next problem is that it
| actually wouldn't explain much. The immediate next question
| would be "why is spacetime behaving this way".
| maaaaattttt wrote:
| Ultimately it's just a way to say, "well, there is simply
| more gravity there". I was also thinking of the "why" and I'd
| say because when the universe expends, or initially expended,
| it didn't happen homogeneously. In my opinion it's more
| realistic that spacetime isn't homogeneous than that it is.
| psc wrote:
| I've had the same question and I don't have the answer, but
| what you're asking about might be referred to as the
| cosmological principle
|
| https://en.wikipedia.org/wiki/Cosmological_principle
|
| Seems like so far our observations are that the universe is
| pretty homogeneous. Cosmological principle being the default
| position, my best understanding is that it's just a lack of
| evidence otherwise:
|
| > The End of Greatness is an observational scale discovered at
| roughly 100 Mpc (roughly 300 million light-years) where the
| lumpiness seen in the large-scale structure of the universe is
| homogenized and isotropized in accordance with the Cosmological
| Principle. At this scale, no pseudo-random fractalness is
| apparent.
|
| https://en.wikipedia.org/wiki/Observable_universe#End_of_Gre...
| colechristensen wrote:
| If there is some reason over here isn't the same as over there
| then there will be a mechanism as to why that is the case and
| you will want an explanation.
|
| You want your physics to apply everywhere and that's why you
| start with the assumption that the same laws, constants, etc
| apply everywhere.
|
| There's no "ope stuff is just different over there" in physics,
| you look for those inconsistencies and then you try to explain
| them.
| Root_Denied wrote:
| Small nitpick on choice of words here - homogenous probably
| isn't the right word to use, instead the correct term is
| probably invariant.
|
| The universe appears homogenous at various scales, meaning it's
| self-same within some amount of tolerance across itself. The
| distribution is homogenous. That's different from invariance,
| the assumption that a variable (in this case an intrinsic
| property such as mass) remains unchanged over time for a given
| subject of study, such as a particle.
|
| Even if a given property can vary from subject to subject (even
| wildly), the sum of all subjects could still appear homogeneous
| in their distribution.
|
| >why do we assume spacetime to be homogenous in its nature?
|
| Because it's distribution appears to be consistent, at least as
| far as we can measure. That's not the same thing as objects at
| the quantum scale being invariant (or variable) in some way
| that we currently think is the opposite.
|
| >Couldn't then dark matter be explained by some variations on a
| large scale? Like giant "wrinkles" in spacetime?
|
| Considering the scales at which these fluctuations would have
| to occur for us to have not already measured them I'm doubtful
| they could build up to anything like that, even in aggregate
| and random patterns.
|
| >They would then behave as pseudo black holes, or more like
| "black trenches", that lead to the structures we see today in
| the universe. The structures seem to have more mass than what
| we can actually see, but are in fact just placed in locations
| that behave differently gravity wise?
|
| I don't think I'm really qualified to answer on how possible
| this interpretation is, but with the confirmation of
| gravitational waves a few years back we confirmed another piece
| of Einstein's theories and seem to have a good grasp on the
| observational effects of gravity at least. There was a recent
| announcement about mapping of the Gravitational Wave Background
| [0] using pulsars spread across the galaxy that was super cool
| too you might be interested in that I would say is related to
| this question.
|
| The real answer is that theories like this require quite a bit
| of work to manipulate existing and complex math, and that you'd
| need someone who can translate an idea like yours into a
| mathematical model that fits with our observational data.
| That's an exceedingly difficult thing to do, as evidenced by
| the last 70ish years of physics.
|
| [0]: https://www.space.com/gravitational-wave-background-
| universe...
| zmgsabst wrote:
| I have a similar question:
|
| What happens to quantum tangles[0] that get inflated? -- do
| they melt or is it possible for them to absorb energy in a hard
| to interact with state?
|
| Eg, is the reason dark matter looks like a braid that it is? --
| and inflated foam turned into a foamy-web?
|
| [0] - https://en.wikipedia.org/wiki/Anyon
| vanderZwan wrote:
| If you look at the various ways people have tried to interpret
| thermodynamics and the observation that our local universe
| started in a state of low entropy (not exactly spacetime, I
| know, but it's related to the problem), then you'll see that a
| variation of your question has been very thoroughly considered
| already.
|
| Namely, the possibility of the low-entropy start of our
| observable universe being merely a local statistical fluke on a
| cosmic scale across infinite time and space.
|
| The problem is that this often leads to weird paradoxes, like
| the Boltzmann brain universe[0], and from what I understand
| it's still not entirely clear if that's just a sign we're doing
| statistics wrong or if there's something missing in the theory
| of cosmology.
|
| Personally, I'm wondering if the issue isn't that these
| theories are assuming randomness, but in reality the next
| "state" of the universe depends on the previous state, so it's
| actually pseudo-random. But that sounds like too obvious an
| explanation so that has probably been ruled out somehow.
|
| Anyway, just to be explicit about it again: what I'm talking
| about relates to thermodynamics and entropy. You're question is
| about spacetime and the laws of physics, which is something
| else.
|
| [0] https://en.wikipedia.org/wiki/Boltzmann_brain
| jerf wrote:
| "Here they seem to say that on some quantum level spacetime
| could vary drastically."
|
| This is not a result of this theory. Our best current theories
| say this too: https://en.wikipedia.org/wiki/Quantum_foam
| Spacetime getting distinctly different at very small scales is
| a vital part of all modern theories and I doubt it's going
| away. Even if spacetime is shown to be continuous itself, which
| I tend to personally doubt [1], getting close to the scales
| where the uncertainty principle becomes a major influence
| rather than an almost academic curiosity will inevitably have
| major impacts on the behavior of things.
|
| "Like giant "wrinkles" in spacetime?"
|
| Giant wrinkles in space time don't act like dark matter. They
| either smooth themselves out basically instantly (on
| cosmological scales) or form something other than a giant
| wrinkle, such as a cosmic string:
| https://en.wikipedia.org/wiki/Cosmic_string
|
| In fact one of the low-key mysteries extant in the universe
| today is that our best theories say cosmic strings really ought
| to exist, but we don't see them. Though I think the confidence
| in our theories being pushed to that extent is low enough that
| this is not generally considered the biggest problem, and very
| unlikely to be the thing that cracks the mystery, so it isn't
| something that gets talked about a lot. So you could say that
| we actually _don 't_ "expect" space time to be homogeneous and
| one of the mysteries is why it observationally is!
|
| [1]: https://news.ycombinator.com/item?id=38433917
| maaaaattttt wrote:
| Thank you for the link to cosmic strings! This is actually
| exactly what I had in mind when, as you quoted, I was
| mentioning wrinkles and "black trenches".
|
| So, you don't think structures like galaxy superclusters are
| a second hand visualization of the existence of cosmic
| strings? I know these formations could be explained by the
| effect of gravity of just visible matter. But maybe it's
| both. Like a valley could exist because of a river and a
| river could exist because of a valley.
|
| Since this concept has been around for so long I have some
| reading to do to understand why cosmic strings are not a
| possible explanation for dark matter. To me high density and
| invisible fit the bill for dark matter quite well.
|
| Edit: never mind, continued reading the article and saw this
|
| > in the past it was thought that their gravity could have
| been responsible for the original clumping of matter into
| galactic superclusters. It is now calculated that their
| contribution to the structure formation in the universe is
| less than 10%.
| I_am_tiberius wrote:
| So in summary, if right, it means that spacetime is not as
| predictable as we thought.
| quickthrower2 wrote:
| Almost as if it is a machine learning simulation :-)
| yathaid wrote:
| The article mentions the 5000:1 odds bet, but reading the text of
| the bet itself is hilarious:
|
| >>> Whereas Carlo Rovelli and Geoff Penington firmly believe that
| gravity is better described by a quantum theory.
|
| >>> And whereas Jonathan Oppenheim is more sympathetic to other
| possibilities (i.e. doesn't have a clue) ...
|
| [1] -
| https://www.ucl.ac.uk/oppenheim/pub/quantum_vs_classical_bet...
| bilekas wrote:
| > a small amount of olive oil, balsamic vinegar, or wine
|
| I think we can guess who write up the contract!
| DrBazza wrote:
| Crisps though!
|
| > Should space-time be shown to be quantum, the loser will
| give to each of the winners, one ITEM* of their choice. If
| the alternative hypothesis is deemed to be correct, the
| losers will each give 5,000 ITEMS to the winner.
|
| > * ITEM is defined to be a object of the winner's choice,
| worth no more than 20 British pence on January 21st, 2021.
| Examples include some crisps, a bazinga ball, a small amount
| of olive oil, balsamic vinegar, or wine
| denton-scratch wrote:
| The contract doesn't specify what kind of balsamic vinegar.
| Supermarket balsamic is just a mixture of colourings and
| flavourings. Proper solera balsamic is sipped as an aperitif,
| and is much too expensive for me to have ever tasted.
| GuB-42 wrote:
| It doesn't say the amount either, just that each item must
| be worth less than 20 british pence.
|
| So it can be one drop of "Aceto Balsamico Tradizionale di
| Modena DOP", which is the real deal. Prices start at around
| 50EUR for 100mL, but it can easily go into the 100s if you
| want the more premium ones (25 years). A single drop would
| fit the 20 pence bill.
| dash2 wrote:
| Why not have both: salt 'n' vinegar flavour crisps?
| 3cats-in-a-coat wrote:
| It's heartwarming to see these people have fun while still
| sticking to serious work. Everything should be like that.
| trinsic2 wrote:
| When it comes to science, only the British seem to be able do
| that.
| n4r9 wrote:
| Rovelli is Italian, and I think Pennington is American and
| Oppenheim is Canadian.
| bjornsing wrote:
| Interesting that three so obviously intelligent people could
| get the odds of the bet wrong: it's not a 1:5000 bet, it's a
| 2:5000 bet a.k.a. a 1:2500 bet.
| jessriedel wrote:
| I mean clearly if it's a mistake this is a matter of
| terminology not intelligence, but could you explain how it's
| wrong?
|
| If A wins, B pays A $1. If B wins, A pays B $N. For the bet
| to be fair (zero expectation value), the probability that A
| wins needs to be p=N/(N+1) and that B wins needs to be
| 1-p=1/(N+1). My understanding of what "odds" are is the ratio
| of the outcome probabilities: p:(1-p) = p/(1-p) = N/1 = N:1.
| (This is why the "log odds" are log(p/(1-p)).)
|
| Do they use a different notion of "odds" in sports gambling?
| bjornsing wrote:
| Turns out the only interesting thing is how sloppy my
| reading is (and how quick I am to blame others for that
| sloppiness...).
|
| I simply missed the second "each" below:
|
| > Should space-time be shown to be quantum, the loser will
| give to each of the winners, one ITEM of their choice. If
| the alternative hypothesis is deemed to be correct, the
| losers will _each_ give 5,000 ITEMS to the winner.
| seeknotfind wrote:
| Given this each, I'm surprised the headline isn't
| 10,000:1 bet.
|
| Also, who wants 10,000 <$20 items? It's a cool payout,
| but if I wanted to spend ~$200,000, I wouldn't do it in
| 10,000 pieces.
| sgt101 wrote:
| I think, reading it, it could be PS1000 worth of wine.
| For example two cases of decent Gevrey Chambertin, I
| myself could bring myself to accept such a thing.
| dash2 wrote:
| It's not $20. It's 20 British pence - about 25 cents....
| "Examples include some crisps, a bazinga ball, a small
| amount of olive oil, balsamic vinegar, or wine."
| hoseja wrote:
| What awful AI-generated illustrations.
|
| Anyway, is there any justification for treating spacetime as a
| smooth manifold, except for mathematical tractability?
| staunton wrote:
| Yes. GR does it and GR gives good descriptions for a lot of
| observed phenomena.
| hoseja wrote:
| Except, you know, all the elementary particles. I have this
| intrusive thought those are just bits of non-smoothly
| kinked/knotted spacetime but have neither the physics
| background or sense where to even start to look further into
| that.
| fsckboy wrote:
| >> _Yes. GR does it and GR gives good descriptions for a
| lot of observed phenomena._
|
| > _Except, you know, all the elementary particles._
|
| except, you know, all the elementary particles don't do a
| good job of explaining what GR explains
| TheOtherHobbes wrote:
| Hardly an expert, but it seems more likely to me that GR
| is the smoothed-out limit of a lot of much smaller stuff
| happening, than QM is somehow low-level wrinkles in an
| otherwise perfectly smooth spacetime.
|
| I don't think a smooth anything is physically tractable.
| You need infinite resolution for perfect smoothness -
| essentially an infinite amount of information at every
| point.
|
| Except there are no points. So somehow you have equations
| that define curvature floating in some kind of
| metaphysical space which somehow gets mapped to
| observable phenomena.
|
| And if it's a noisy smoothness - where does the noise
| come from?
| showlife wrote:
| Maybe what you're looking for is a "geon"?
|
| https://en.wikipedia.org/wiki/Geon_(physics)
| vore wrote:
| They're not AI generated, there's literally artist credits in
| the picture captions.
| hoseja wrote:
| Perhaps they're post-edited somewhat but there isn't a way
| you're convincing me those are fully handmade. Look at the
| nonsensically warped tiles. Look at the rods suspending some
| of the globes but not others in a random fashion, look at the
| illegible "writing".
| jug wrote:
| Yeah and the style has the default DALLE-3 style written
| all over them. Isaac Young may be credited but I think
| Isaac is using DALLE-3 and I hope they are aware they have
| hired a "prompt wizard". :)
| fl7305 wrote:
| I think they even put the prompt as the image caption?
| spuz wrote:
| I think you're right. I don't really have a problem with AI
| generated art being used in articles like this. After all,
| what kind of alternative visual can you put alongside an
| article about fundamental theories of nature? If AI art
| helps to reduce the cost of scientific journalism (without
| decreasing the quality) then I'm ok with it.
|
| Having said that, to produce art that actually works is
| clearly not easy. If you've ever used Midjourney or DALL-E,
| you'll know it's a challenge to get the tool to output
| exactly what you have in mind. It's also clearly hard to
| produce images that physically realistic. If mismatched
| tiles and unrealistic perspectives are noticeable then
| they'll be a distraction and detract from the reader's
| experience.
| hoseja wrote:
| But these add nothing to the article but confusion.
| That's not how doing interference works. That's not any
| sort of weighting device. Could have been a generic
| galaxy-brain stock art and I'd be less annoyed.
| CaptainFever wrote:
| Oof yeah, I just saw the article pics. I don't have an
| issue with AI assistance, but the final output here was
| just kind of incoherent and confusing. Like an unrelated
| stock photo. I understand that it is hard to control but
| that just means that the artist needed to do a better job
| to make something more coherent, more informative and
| less generic.
|
| Unless yeah as you said, it's just too abstract to put
| anything coherent, in which case I guess it works (though
| the mass weighing image surely could have been better
| than some generic sci fi thing)?
| fl7305 wrote:
| Doesn't the image caption contain a prompt?
|
| When i use it in DALL-E 3, I get similar images.
|
| "The image depicts an experiment in which heavy
| particles(illustrated as the moon), cause an interference
| pattern (a quantum effect), while also bendingspacetime. The
| hanging pendulums depict the measurement of spacetime. The
| actual experiment istypically performed using Carbon-60, one
| of the largest known molecules. The UCL calculationindicates
| that the experiment should also be performed using higher
| density atoms such as gold. The other two images represent
| the two experiments proposed by the UCL group, both of
| whichconstrain any theory where spacetime is treated
| classically. One is the weighing of a mass, the otheris an
| interference experiment."
| ben_w wrote:
| I'm more annoyed with the captions.
|
| > ... Carbon-60, one of the largest known molecules.
| hoseja wrote:
| Eh, C60, one of the largest molecules with observed quantum
| interference, close enough.
| denton-scratch wrote:
| The illustrations looked like some sort of steampunk drawings
| from a fantasy book.
| 8bitsrule wrote:
| A wonderful, bold, and colorful idea, already thought through
| carefully. And 5000:1 odds! It'll be more interesting how many
| more dozens of minds will find more testable consequences. Is it
| too much to hope that some untestable ideas will deservedly die?
| hallway_monitor wrote:
| That which can be destroyed by the truth should be.
| jeisc wrote:
| Our present day understanding of the universe is rudimentary at
| best and will be rocked with each new device invented to reveal
| its nature to us. When we explode a nuclear bomb here how far
| away in the universe would it be visible or detectable? If there
| were a highly developed civilization would they not be listening
| for this background noise to detect when a civilization had
| reached the nuclear point and used it for exploding a bomb?
| tsimionescu wrote:
| Nuclear explosions on Earth, while very powerful, are not even
| a blip compared to the random noise in the amount of energy
| that the Sun gives out. You would have to very very carefully
| measure the Earth itself in particular to notice them in any
| way.
| bawolff wrote:
| > and this scale can be determined by another experiment where we
| test how long we can put a heavy atom in superposition of being
| in two different locations."
|
| Im a physics noob, but does this imply the theory helps explain
| why we usually only see quantum effects on the mucroscopic scale,
| since it says something about how heavy objects cant be put in
| superposition?
| bheadmaster wrote:
| I'm a physics noob too, but from what I understand, the quantum
| effects don't happen on macroscopic scale because of high
| temperature and lack of "structure". Every interaction of
| particles seems to change the state ("collapse the wave
| function") of the particles, so such a chaotic environment
| makes things start behaving in a predictable way. Sort of how
| balls falling in a Galton board seem to converge to Gauss
| normal distribution: https://en.wikipedia.org/wiki/Galton_board
|
| In low enough temperature and regular enough structure, even
| macroscopic objects can be entangled (or, I assume, show other
| quantum effects):
| https://www.scientificamerican.com/article/scientists-supers...
| jug wrote:
| Honestly at this point, who knows. Let's find out. This is even a
| testable theory so that already puts it ahead of a host of
| others.
| netfortius wrote:
| I am a huge fan of Carlo Rovelli, and read all his books to date,
| so I am siding with him on this one.
| eterevsky wrote:
| Previous discussion on HN:
| https://news.ycombinator.com/item?id=36667278
| amai wrote:
| See also https://www.quantamagazine.org/the-physicist-who-bets-
| that-g...
| maho wrote:
| After skimming the second paper, I still don't understand how
| precision mass measurements come into play here. They mention
| Cavendish-type measurements, but they are used for measuring the
| gravitational constant. Of course, you can turn the formula
| around, plug an unknown mass into the apparatus and then call it
| a mass measurement, but it's going to be a very imprecise
| measurement. A Penning trap can give you 11 to 12 significant
| digits -- a Canvendish-type measurement could give you maybe 5 or
| so, I think.
|
| Or is it because the Penning trap measures "inertial mass" but
| they really want a measurement of "gravitational mass"? But
| wouldn't inertial mass fluctuate the same way?
| Timeroot wrote:
| (I went to a talk by Oppenheim author a couple weeks ago on
| this topic.) The idea is that gravity, as a force, only
| operates classically. More precisely: there is a classical
| state describing the curvature of space time, and then a
| quantum state describing the configuration of particles on that
| spacetime. But then, that quantum state needs to affect the
| classical state again (mass bends space), which would usually
| lead to the classical half becoming quantum and entangled with
| the other half.
|
| You can keep the classical half (the shape of spacetime)
| classical, if the effect of the quantum part is partially
| stochastic. There's a minimum amount of random noise you need
| for it to be mathematically consistent. So, you set up an
| experiment where a particle is acting on another via gravity.
| There's a quantity of noise you should expect to see in the
| gravitational force.
|
| "Inertial Mass=Gravitational Mass" now only holds on average.
| The gravitational mass will effectively have a Brownian noise
| term added in.
| Workaccount2 wrote:
| So if I am understanding this correctly:
|
| Quantum particles can effect change (curve) spacetime without
| direct quantum action if you sprinkle a bit of randomness
| into the (quantum acting on spacetime) effect?
| a_cardboard_box wrote:
| If this hypothesis is true, would it give us a way to
| distinguish many-worlds vs. wave function collapse? If the
| many "worlds" are all interacting with a single classical
| spacetime, we should be able to measure the gravity of other
| worlds, right? I'm not a physicist, but that sounds a lot
| like dark matter to me.
| layer8 wrote:
| There is no implication that the classical spacetime
| wouldn't still split into branches, possibly with different
| variations in the stochastic effect from each other.
| codethief wrote:
| Wouldn't it be enough to measure the (fluctuation of the) total
| gravitation force ( = gravitational constant times mass)
| exerted on the second particle, in order to draw conclusions
| about the nature of the gravitational force at small scales?
| kristov wrote:
| I wonder: does this theory explain any currently unexplained
| phenomenon? It may be testable, but that doesn't guarantee it to
| be correct. There could be another undescovered theory that also
| passes these tests. It feels weird to make up a theory, and then
| make up some tests to validate it, without mentioning the actual
| problem the theory is trying to resolve. It seems physicists just
| don't like there being two separate models, one for large things
| and one for small things, but it could be the universe is just
| like that, right?
| naijaboiler wrote:
| Theories like that are never "correct". They just explain
| things and fit data better than other/previous theories.
| Correct is not what I would go for. "Best we currently have"
| sounds more like it
| mettamage wrote:
| Disclaimer: not a physicist.
|
| It seems to me that one issue with falsification is that: if
| you're _exactly right_ on how the universe works, then it 's
| hard to know that you are exactly right. So I imagine that we'd
| be infinitely putting resources in it (to some extent) to see
| if anything is unexplained. So if the universe is just like
| that, then we'd have a long way to go to find out.
|
| I do think that physicists are bothered by the idea that
| current theories can't explain everything they're observing. So
| whether the universe is or isn't like that, more research is
| definitely needed.
| simiones wrote:
| > It seems physicists just don't like there being two separate
| models, one for large things and one for small things, but it
| could be the universe is just like that, right?
|
| No, it couldn't be just like that. There could exist a common
| umbrella theory that uses GR for certain objects and QM for
| others, but it would have to be a new theory that introduces a
| very important new info: the nature of the separation between
| the two.
|
| Right now, all of the laws of QM say that it applies just as
| much to the motion of the Sun as to the motion of an electron.
| GR says the same. And yet, GR's predictions for how an electron
| behaves are clearly wrong. QM's predictions for how the Sun
| moves are closer to being correct (that is, QM + SR + Newtonian
| gravity), but it is hard to measure.
|
| A unified theory has to either correct the equations of QM, GR,
| or both; or to add explicit boundaries to each of them. A
| theory that would say "an object moves according to the laws of
| QM if it's 0.00000001g or lower, and according to the laws of
| GR if it's any higher" (or any other distinguishing
| characteristic) would be an entirely new theory.
|
| Interestingly, this new theory being proposed in the articles
| actually does something slightly in this vein: it says "QM
| applies to the electromagnetic, weak, and strong interactions,
| and GR applies to the mass/gravity interaction". It then finds
| a new way to account for the known inconsistencies between the
| math of each, apparently by getting rid of the assumption that
| a particle has a fixed mass (and thus fixed space-time
| curvature in GR).
| kristov wrote:
| Thank you!
| FrustratedMonky wrote:
| Any physicist here that can tell if this is the big breakthrough
| to a theory of everything?
|
| Or just hype? Sorry, gun shy about believing big breakthroughs
| this year.
|
| Quantum Gravity and Testable? Seems huge on the surface.
|
| If it can be tested, then this is already worlds ahead of string
| theory.
| throwaway4PP wrote:
| Exciting times! Any physicist here aware of how these two papers
| would impact the applicability or validity of Modified Newtonian
| Dynamics (MOND)?
|
| background: my lay understanding of MOND is that it modifies the
| gravitational interaction parameter over cosmological distances.
| the force exerted on objects due to gravity is currently accepted
| to scale with distance in a certain manner (ex. 1/distance^2)
| while MOND postulates a different scaling relation (ex.
| 1/distance^3). Those are just examples, not actual values. The
| currently accepted gravitational interaction force scaling is
| what gives rise for the need for dark matter, and the
| corresponding lambda cold dark matter (LCDM) theory. Of course,
| we have not been able to observe dark matter, which is a problem
| for a theory. That is what has given rise to MOND, amongst other
| things. There are prominent, esteemed physicists who have
| recognized many issues with LCDM, some of which are addressed by
| MOND (https://astro.uni-bonn.de/~pavel/kroupa_SciLogs.html)
|
| previous HN posts with interesting discussions / links re: MOND
|
| https://news.ycombinator.com/item?id=37012052
|
| https://news.ycombinator.com/item?id=33261981
|
| https://news.ycombinator.com/item?id=23982814
| Timeroot wrote:
| It's of no relevance to MOND, at least none that I can see.
|
| MOND gives a different scaling relation, and is therefore
| contradicting general relativity. Its goal is to explain the
| effects we associate with dark matter, without the need for
| dark matter.
|
| General relativity is (we are pretty sure) inconsistent with
| quantum field theory. String theory tries to fix the issue by
| replacing the particles in field theory with strings. Oppenheim
| is trying to fix it by putting general relativity as a
| classical phenomenon that lives "outside" of quantum field
| theory.
|
| They're trying to solve different problems. And, Oppenheim's
| classical gravity picture could be used just as well with MOND
| instead of standard general relativity, if that's what you
| wanted.
|
| MOND is getting less popular every year as evidence for dark
| matter piles up. The Bullet Cluster is a particular instance
| where we can actually "see" the dark matter flying around, in a
| way MOND couldn't hope to explain. LIGO has also given us a lot
| of confidence we have the right theory of gravity, at least up
| to the quantum scale.
| naasking wrote:
| > The Bullet Cluster is a particular instance where we can
| actually "see" the dark matter flying around, in a way MOND
| couldn't hope to explain
|
| This is not correct. In fact, LCDM can't even explain the
| Bullet Cluster [1]. The evidence is not so favourable to LCDM
| over MOND [2] when taken as a whole.
|
| More recent observations on wide binary stars disfavour MOND
| more strongly, but the classic reasons you cite are not valid
| reasons.
|
| [1] https://arxiv.org/abs/0704.0381
|
| [2] https://arxiv.org/abs/2110.06936
|
| Edit: See for instance what Milgrom said about the Bullet
| Cluster back in 2006:
|
| http://astroweb.case.edu/ssm/mond/moti_bullet.html
| zehaeva wrote:
| I am pretty sure that MOND has been completely ruled out[0]
| given some recent evidence. And by more than 5 sigma.
|
| [0]https://bigthink.com/hard-science/dark-matter-alternative-
| mo...
| curation wrote:
| What if universality is a name for a kind of antagonism? What
| comes first is not a wholeness that is disturbed, but difference
| itself. Reality itself is unfinished and built in parallax. This
| new theory alongside current metaphysical theories of everything
| is inspiring.
| VHRanger wrote:
| Why is this comment at the top of the discussion thread?
|
| We're talking about the validity of the mathematical theory,
| not new age woo-woo methaphysical theories.
| stjohnswarts wrote:
| So can anyone explain why this will possibly take 20 years to
| prove/disprove? We don't have the current level of accuracy
| necessary to test it, but might if we work through issues over
| the next 20 years or so?
| qwertywert_ wrote:
| So to unify the theories they are actually keeping them separate?
| zehaeva wrote:
| Holy hell, talk about burying the lede here! The last sentence of
| the whole article is:
|
| _The new theory allows for information to be destroyed, due to a
| fundamental breakdown in predictability._
|
| Are you kidding me?!
| nine_k wrote:
| Is there something fundamental that breaks when information is
| allowed to be destroyed?
| mackman wrote:
| Wouldn't that prevent time from going in reverse?
| nine_k wrote:
| Isn't the growth of entropy preventing this already at the
| macro scale? Isn't it similar to the loss of information,
| because it's a transition from a less-probable state to a
| more-probable state?
| digging wrote:
| I mean essentially, quantum physics only works if information
| can't be destroyed.
| amai wrote:
| I believe gravity can be both quantizable and non quantizable.
| Gravitons could be like phonons (quantized sound waves) and only
| exist in the solid state of space time. In the fluid state of
| space time gravitons don't exist ( Similar to the fact that
| phonons can only exist in solids, but not in fluids).
| digging wrote:
| What are the solid and fluid states of spacetime?
| amai wrote:
| One could imagine that for a very low Unruh temperature
| spacetime changes the phase and becomes ,,solid". A low Unruh
| temperature means very low acceleration/gravitation. This
| might explain dark matter.
|
| Similar things are discussed in the literature under
| https://en.wikipedia.org/wiki/Superfluid_vacuum_theory and
| https://penntoday.upenn.edu/news/physicist-theorizes-dark-
| ma...
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