[HN Gopher] The cosmological constant is physics' most embarrass...
___________________________________________________________________
The cosmological constant is physics' most embarrassing problem
Author : samizdis
Score : 71 points
Date : 2021-02-01 20:34 UTC (1 days ago)
(HTM) web link (www.scientificamerican.com)
(TXT) w3m dump (www.scientificamerican.com)
| ridaj wrote:
| "The universe is under no obligation to make sense to you" --
| Neil DeGrasse Tyson
|
| IMO the most embarrassing problem in physics is people pushing
| non-falsifiable, unscientific theories (multiverse). The fact
| that some futzing constant needs or doesn't need to be added in
| order to bring a model in line with empirical observation, in
| comparison, is quite benign.
| jw1224 wrote:
| > IMO the most embarrassing problem in physics is people
| pushing non-falsifiable, unscientific theories (multiverse)
|
| The Big Bang itself is a non-falsifiable, unscientific theory.
| We cannot prove it happened in the way we think it might have.
| The Big Bang created a universe of cause and effect, yet has no
| cause itself. All known laws of physics fail to work in the
| early moments of our existence.
|
| "Give me one free miracle, and science will explain the rest"
| (-- maybe Terrence McKenna? I can't remember)
| simonh wrote:
| We can literally see the big bang happening, in the form of
| the CMB. That's the actual light from the big bang.
|
| Just because we don't understand it's cause yet doesn't mean
| we won't, and doesn't mean it didn't have a cause.
| Daho0n wrote:
| This is a tad disingenuous IMO. We can't "literally see the
| big bang happening". That's is like saying we can see the
| explosion of a stick of dynamite that exploded inside a
| mine because we see a dust-cloud and hear a boom a split
| second later at the mine entrance. We are standing outside
| the mine, talking about the effect of the dynamite. We see
| the effect (electromagnetic radiation or "the dust-wave"),
| not the cause or the event itself.
| simonh wrote:
| I don't see how it's disingenuous, that's literally what
| it is. It was even predicted well in advance of
| measurement. If you see the flash and hear the boom, how
| can you credibly say that was not witnessing the event?
| [deleted]
| Tenoke wrote:
| The CMB is an observation well matching what you'd expect
| with a Big Bang but it is not the Big Bang itself and one
| can make other theories to try and explain it.
| simonh wrote:
| It's photons emitted by the plasma of the big bang, that
| have been propagating continuously through vaccuum since
| they were emitted. It's just as much seeing the big bang
| as the flash from an explosion is seeing it go off.
| canjobear wrote:
| The real "one free miracle" is that the universe started in
| an anomalously low-entropy state, lower than could be
| explained by random fluctuations.
| JimBlackwood wrote:
| What you said is very true, it doesn't apply to the
| cosmological constant though.
|
| It is not so much that we need it for a model to be in line
| with empirical observation, it's that empirical observation
| gives one value and our models predict another value.
|
| The discrepancy is big and if we can't make our models work
| empirical observations, that is really embarrassing.
|
| Regarding non-falsifiable theories; there's not a physicist
| that thinks theories should not be tested. A lot of work is
| done to make these theories testable. Unfortunately, they are
| often only testsble on open problems since the limit of these
| theories just reduces to GR for instance.
| Tenoke wrote:
| If you had added the right constant or few you could've proven
| geocentrism in the 1600s and said that "The fact that some
| futzing constant needs or doesn't need to be added" doesn't
| prove the model is wrong.
| garaetjjte wrote:
| I'm not a physicist and I don't really have an opinion there,
| but that's funny. One side argues that pushing multiverse is
| unscientific, while other side argues exactly the opposite,
| that pushing Copenhagen is unscientific.
|
| https://www.lesswrong.com/s/Kqs6GR7F5xziuSyGZ/p/xsZnufn3cQw7...
| JesseMReeves wrote:
| ,,During March and April 1959, at Wheeler's request, Everett
| visited Copenhagen, on vacation with his wife and baby
| daughter, in order to meet with Niels Bohr, the "father of the
| Copenhagen interpretation of quantum mechanics". The visit was
| a complete disaster; Everett was unable to communicate the main
| idea that the universe is describable, in theory, by an
| objectively existing universal wave function (which does not
| "collapse"); this was simply heresy to Bohr and the others at
| Copenhagen. The conceptual gulf between their positions was too
| wide to allow any meeting of minds; Leon Rosenfeld, one of
| Bohr's devotees, talking about Everett's visit, described
| Everett as being "undescribably [sic] stupid and could not
| understand the simplest things in quantum mechanics". " Source
| and original source here: https://en.wikipedia.org/wiki/Many-
| worlds_interpretation
|
| Everett spent 4 years doing graduate studies, taking his first
| physics courses then and coming up with his many-worlds
| dissertation within a single year (137 pages 'typed' (according
| to current historical records) by his later wife Nancy Gordon).
| He pretty much left physics afterwards, for doing weapons
| research(!) for the Pentagon.
|
| Many-worlds sounds like what an overconfident ,pragmatic'
| college graduate would come up with even to those who don't do
| physics.
|
| Is it just my impression or is it mostly US-Americans who are
| pushing many worlds into physics?
| simonh wrote:
| Not at all, Stephen Hawking was a proponent of the idea, as
| is David Deutch, another British physicist. It has plenty of
| proponents, or at least those unwilling to discount it, on
| both sides of the Atlantic.
| jMyles wrote:
| > IMO the most embarrassing problem in physics is people
| pushing non-falsifiable, unscientific theories (multiverse).
|
| Is this a not-so-subtle dig at Beacham and other
| experimentalists who make room for multiverse? Or do I jump to
| the wrong conclusion?
|
| Two questions for you:
|
| 1) Does 'falsifiable' in this context per se mean that there
| needs to be some particle physics experiment that can be
| designed to test the theory? Is there no room for theoretical
| physics? Is Rovelli, for example, per se barking up the wrong
| tree by this measure?
|
| 2) Aren't these theories reasonably falsifiable insofar as
| they'll eventually result in experiments designed to map out
| the possible domains of the space? eg, what if we build a much
| higher energy collider and finally find real evidence of the
| super-symmetry particles?
| lmm wrote:
| > 2) Aren't these theories reasonably falsifiable insofar as
| they'll eventually result in experiments designed to map out
| the possible domains of the space? eg, what if we build a
| much higher energy collider and finally find real evidence of
| the super-symmetry particles?
|
| Would you treat _not_ finding super-symmetry particles as
| falsifying those theories? AIUI those theories admit the
| possibility of such particles but also the possibility of
| such particles not existing, so they 're not actually
| falsifiable that way.
| l33tman wrote:
| Most theories' predictions are not open ended. It's
| possible to exhaustively search the prediction space to
| falsify them (up to an experimental standard that you need
| to agree on). I'm by far not an expert on super-symmetry
| but from what I've seen the prediction space of the most
| common SUSY models is getting continuously boxed in.
| andi999 wrote:
| I think super symmetry is almost falsified. People just
| cling to it because there is (almost) nothing else. If any
| new theory comes around without supersymmetry (but other
| predictions) people will jump ship.
| throwaway3699 wrote:
| Science is defined by testability. A theory that can't be
| tested is just pseudoscience, unlike a theory that just can't
| be tested _right now_ due to technological limitations.
| JimBlackwood wrote:
| It would be pseudoscience if it were to be seen as or
| communicated as fact. It's not.
|
| Any newly observed fact can falsify these theories. It just
| takes a long time. There's still tons of open issues on
| General Relativity too. So far though, it seems to have
| passed every test.
|
| Would you call GR pseudoscience too then? Since it'll
| likely never be fully verified.
| boomboomsubban wrote:
| > would be pseudoscience if it were to be seen as or
| communicated as fact. It's not.
|
| Pseudoscience is something labelling itself as science
| while not adhering to scientific standards. Claiming it's
| a fact would be a dead giveaway though.
|
| Relativity has been experimentally tested and made
| accurate predictions, it is impossible for it to be
| "fully verified."
| piokoch wrote:
| So very true. The ideas mentioned in the article does not sound
| appealing to me:
|
| "In this picture, the curvature of space would constantly
| fluctuate on extremely small scales, well beyond anything we
| could hope to measure"
|
| "Her model is based on the idea that extra dimensions, beyond
| the three of space and one of time that we witness, might be
| hidden out of sight."
|
| Instead of cosmological constant "novel" approaches relay on
| something that could not be observed, even in principle. That
| does not sound like a good approach.
|
| My guess is that they try to make some assumptions, figure out
| math around it, hope that it will somehow stick nicely, which
| would give hope that there is something in it.
|
| Indeed, it seems that math "likes" to describe our universe,
| some mathematical theories (Riemannian geometry, group theory)
| fit physics wonderfully. The problem is that for physics math
| is just a language, it is unlikely that language alone will
| give us answers without understanding physical phenomena
| itself.
| lmm wrote:
| How surprised would you be if it turned out we really did live
| in a multiverse? Would you expect things to look different if
| we did? Do you think it's extremely implausible a priori?
|
| I find multiverses far more plausible than futzing constants,
| because the universe in general seems to be absurdly big but
| simple and consistent physics-wise. Smaller but more
| fiddly/complicated models seem much less plausible, just
| judging by history.
| boomboomsubban wrote:
| How would one develop an experiment that would result in
| evidence we live in a multiverse? Demonstrating observable
| phenomena is a result of something outside this universe
| seems like a logical impossibility currently.
|
| Philosophically I find the idea of the multiverse probable,
| but making it science is a separate thing.
|
| _edit_ poor word usage.
| l33tman wrote:
| Does it provide predictions that can be falsifiable? That's
| what we search for. In this context (anthropomorphic
| principle and multiverses to explain physical constants) I
| do think there are some statistical predictions possible
| that could be checked (after all this is why the multiverse
| theory got popular in the first place, the seemingly weird
| finetuning of constants).
|
| Though, the outlook of getting an answer to "is there
| _really_ a multiverse out there or is the multiverse just a
| sequence of simulation runs on some future teenagers
| quantum computer simulator trying to find the best set of
| meta-parameters " is probably bleak...
| RobertoG wrote:
| >>"How would one develop an experiment that would result in
| evidence we live in a multiverse? [..]"
|
| I don't understand this criticism. It's my understanding,
| the double slit experiment shows interference between
| universes. What is the alternative? decoherence?, but how
| do you develop an experiment that result in evidence that
| decoherence is real?
|
| From a experimental point of view, multiverse have the same
| evidence that the alternative. From an epistemological
| point of view, multiverse is a more simple theory. Ergo,
| until we have more data, we have to prefer the multiverse
| theory.
| boomboomsubban wrote:
| >decoherence
|
| Yes, the alternative is that classical mechanics is
| incomplete and quantum mechanics is necessary. And there
| has been plenty of experiments supporting this
| conclusion.
| akvadrako wrote:
| Science doesn't prove anything so it's not really relevant
| to the question of the demarcation line.
|
| A theory involving a multiverse can make observable
| predictions even if the other regions are not accessible.
| boomboomsubban wrote:
| >Science doesn't prove anything
|
| I should have said evidence rather than proof, my
| mistake.
|
| >theory involving a multiverse can make observable
| predictions even if the other regions are not accessible
|
| All those predictions would serve as evidence for the
| same theory without involving a multiverse.
| akvadrako wrote:
| The multiverse is not some addon that can be removed
| easily; it's just another prediction of the theory.
| boomboomsubban wrote:
| Without an experiment that can show a multiverse, it is
| just a way to explain the unexplainable. It can be
| completely discarded and replaced with "for some reason"
| and any experimental evidence would support the same
| conclusion.
| akvadrako wrote:
| It's not unexplainable if there is an explanation,
| obviously.
|
| "For some reason" is not a theory and it makes no
| testable predictions.
| boomboomsubban wrote:
| > if there is an explanation, obviously
|
| One with the same evidence as "god did it."
|
| > is not a theory and it makes no testable predictions.
|
| This is true of the multiverse too. It is an attempt to
| explain why things are like they are rather than a
| testable theory.
| akvadrako wrote:
| _> This is true of the multiverse too._
|
| Okay, this is just going in circles. Up above you
| accepted that multiverse theories did make testable
| predictions. And they do, which is what makes them
| science.
| boomboomsubban wrote:
| No, I did not. A theory may have includes the idea that
| the multiverse caused whatever it predicted, but that is
| not based on anything except the authors fantasy. It is
| exactly the same as arbitrarily saying god caused
| something in a theory, an unobserved event we can say has
| whatever impact on this universe we want without any
| proof.
|
| _edit_ let 's use a concrete example. This thread is
| about the cosmological constant. I could easily say that
| concept is causes by multiverse influence on this
| universe, just as rightly I could say it's god's finger
| on the scales. Neither now have experimental data because
| I can say that.
| [deleted]
| lmm wrote:
| > All those predictions would serve as evidence for the
| same theory without involving a multiverse.
|
| The prediction that objects continue to exist when we're
| not looking at them is not testable in the same sense
| (you could even say it's unfalsifiable and therefore not
| scientific); nevertheless most of us tend to believe in
| it.
| boomboomsubban wrote:
| Believing something and it being science are unrelated,
| my first post mentions I find a multiverse idea likely
| philosophically.
| simonh wrote:
| Sexy exciting SF theories like the Everett Multiverse get a lot
| of press, but they are sideshows when it comes to bread and
| butter physics. No actual enquiries into physics or our
| understanding of the universe are being obstructed by it, so I
| don't really see how it's a problem.
| atoav wrote:
| I see these multiverse theories more as a philosophical idea
| than anything empirical. To explore the different variations of
| our own world can also be intersting to understand what's going
| on (e.g. what if $variable in the beginning of the universe
| would have been slightly altered).
|
| But yeah more in the world of thoughts than anything else.
| DavidSJ wrote:
| If you're referring to the Everett multiverse (although the OP
| was not, so maybe you're not), then its status is not so
| different from that of the unobservable portion of our own
| universe.
|
| That is, if we take the simplest known cosmological model
| consistent with our evidence, its equations predict space and
| matter outside our observable universe. That cosmological model
| is falsifiable in that it makes other predictions besides this
| one, many of which can be (and have been) tested, but this
| specific prediction cannot be directly tested.
|
| Similarly, the equations of quantum mechanics predict multiple
| "worlds" (although I find this term unfortunate: the state of
| the "multiverse" is always just a single point in Hilbert
| space, and it only seems like there are multiple "worlds" when
| we imperfectly try to map that physical state onto the
| intuitive level of everyday experience). That specific
| prediction cannot be directly tested, but other predictions of
| the equations can be, and have been. There is essentially no
| dispute about the math. The dispute is whether to deny the
| reality of something which is right there in that math, akin to
| denying the reality of a universe beyond that which is
| observable.
| boublepop wrote:
| > Similarly, the equations of quantum mechanics predict
| multiple "worlds"
|
| No they don't. If I roll a dice it'll land on one of 6 faces.
| That's a model, in that model I might assume equal
| probability due to the geometrical symmetry, that's an
| assumption. So now I have a problem if all outcomes are
| equally likely how do I resolve that only one occurs? Well
| obviously every dice roll must spawn 6 parallel universes...
| Now nowhere in that model or that assumption does "so there
| must be 6 parallel worlds spawned when you roll the dice" get
| predicted by my model. The multiverse/many world is an
| interpretation, not an outcome of, or even prediction from
| the model.
|
| There is nothing "right there in the math". QM makes
| predictions about probabilistic outcomes, accurate
| predictions, but there is no requirement for those accurate
| predictions to be right that there must be multiple parallel
| worlds.
| simiones wrote:
| > There is nothing "right there in the math". QM makes
| predictions about probabilistic outcomes, accurate
| predictions, but there is no requirement for those accurate
| predictions to be right that there must be multiple
| parallel worlds.
|
| While I mostly agree with you, the discussion is much more
| complex than this.
|
| First of all, most of QM is completely deterministic, just
| like classical and relativistic mechanics. The Schrodinger
| equation is a linear partial differential equation, it
| gives you an exact prediction of the state of any system of
| particles.
|
| However, that prediction turns out to be so wrong on the
| face of it, it's almost meaningless: the Schrodinger
| equation predicts that "particles" (wave-packets) have some
| complex amplitudes of many different mutually-exclusive
| states, such as being here with amplitude 1+i and being
| there with amplitude 1-i.
|
| BUT, it turns out that if we interpret these amplitudes of
| the wave function (well, the squares of their absolute
| values) as being probabilities of the particle being in
| those states when measured, then you get extremely accurate
| predictions.
|
| The final problem then is that the amplitudes ->
| probabilities step is only correct when predicting the
| result of a measurement. At the particle level (before the
| measurement) the particles actually exist in all those
| states at the same time, and interact with each other in
| all those states (e.g. particle A may interact with
| particles B and C at the same time in two different places,
| modifying both their trajectories).
|
| So, the laws of motion for QM that you need to use are:
|
| 1. Particles move and interact according to the Schrodinger
| equation (e.g. causing interference patterns, interacting
| in multiple places at the same time), fully
| deterministically and linearly
|
| 2. When you want to predict the outcome of a measurement on
| a system that has evolved according to 1, you will get a
| single value with some probability computed as the square
| of the absolute values of the amplitudes of the possible
| states. After the measurement, the amplitude of any other
| state than the one measured will be 0, and this can be
| plugged in to make further predictions about how it will
| interact with other particles.
|
| It is this 2nd postulate that feels very artificial, the
| main subject of the measurement problem. MWI seeks to
| explain QM without the 2nd postulate - that is why people
| say that it "derives from the math" (the 2nd postulate can
| obviously not be derived from the first, as it is a
| nonlinear change to the system).
| simiones wrote:
| The multiverse usually refers to multiple universes each with
| their own big bang, existing in regular space, but outside
| our light cone. It is a completely unscientific theory, in
| the sense that there is no chance of ever proving or denying
| it, by its very construction.
|
| The many worlds interpretation is completely unrelated, and
| it doesn't suffer from this problem of being unfalsifiable
| even in principle. However, I would also not say that the MWI
| is a straightforward deduction from the laws of QM. It
| rejects the most visible effect of those laws (the Born rule,
| i.e. that they predict probabilities of classical events and
| not certainties) and replaces it with an infinity of
| "worlds". Even worse, it still doesn't explain WHY we can
| only "see" one such "world", while elementary particles can
| "see" all of them (i.e. it doesn't solve the measurement
| problem any more than Copenhagen interpretation). And there
| is also debate on how plausible it is to even define the
| "probability of a world", so whether MWI is actually
| consistent with the Born rule is somewhat in doubt.
| onethought wrote:
| I thought the multiverse as you describe it has been
| falsified, logically: if you could observe it then it's
| part of our universe, therefore not a multiverse. If it
| cannot be observed, then it's not a thing.
|
| Perhaps that is just playing with the meaning of words or
| semantics to some, but it's compelling enough for me.
|
| The other description of quantum equations predicting many
| "worlds" I think is a different and more acceptable
| proposition. Like we've observed the shadow of an object,
| but can't figure out how to observe the object directly.
| canjobear wrote:
| > it still doesn't explain WHY we can only "see" one such
| "world", while elementary particles can "see" all of them
|
| For that you need quantum decoherence. Big creatures like
| us only ever see one or the other outcome of a two-outcome
| experiment because we get entangled with the outcome.
| DavidSJ wrote:
| _it still doesn 't explain WHY we can only "see" one such
| "world"_
|
| It's just that there's one of us in each world. The one in
| this world sees this one. The one in that world sees that
| one.
| simiones wrote:
| Why doesn't that apply to photons and electrons, then? At
| what scale do things stop interacting with the other
| worlds and stay in their own world only?
|
| This is exactly the measurement problem, essentially
| identical between Copenhagen and MWI.
| im3w1l wrote:
| Different worlds interact by interference. To interfere
| they must be in some sense "adjacent" so that they can
| both evolve into the exact same world - but with opposite
| phase. If you have a huge object like a human it's very
| hard to get every single atom to line up with those of
| the other world.
| DavidSJ wrote:
| It does apply to photons and electrons.
|
| As I understand it, it becomes ever more difficult to
| maintain a coherent quantum state among larger and larger
| collections of particles (this is why making large
| quantum computers is difficult), so for most practical
| purposes large aggregates of particles behave like a
| single "world". But there is no sharp dividing line, and
| the same math applies at all scales.
|
| Unfortunately, this is where the imperfect mapping to
| which I referred above -- between the math and our
| intuition -- becomes misleading, and why I don't like the
| term "world" to begin with.
| simiones wrote:
| MWI actually postulates that coherence of the system is
| always preserved, even up to the level of the entire
| universe. It's only locally that decoherence seeps in, at
| some scales.
|
| But still, the problem I was questioning was different:
| you are saying "there is one of us in each world". In
| fact, that is not what QM predicts: in QM, there is only
| one of us in the entire system described by the wave
| function, with different amplitudes in different states.
| A system with 1 electron with some amplitude < 1 in state
| A and some amplitude < 1 in state B is not the same as a
| system with 2 electrons, one with amplitude 1 in state A
| and another with amplitude 1 in state B.
|
| So, if we took a detector that could measure state A or
| state B, we should expect that it detects state A with
| some amplitude and, simultaneously, state B with some
| other amplitude. Instead, MWI postulates that there are 2
| detectors, one which measures state A with amplitude 1,
| and the other state B with amplitude 1 (in fact, it
| postulates an infinity of detectors, out of which some
| number measure state A and some measure state B, such
| that the Born rule predictions by "counting" detectors).
|
| This is the part that remains unexplained.
| DavidSJ wrote:
| "One of us in each world" is shorthand for "one of us in
| the entire system described by the wave function, with
| different amplitudes in different states".
|
| There is only 1 detector, and it, along with the detected
| particle, is in a superposition of states.
|
| Again, this is where the language of "worlds" becomes
| misleading, and why I don't like it.
| TheOtherHobbes wrote:
| Define "sees."
|
| That's just one of the many problems that MWI fails to
| solve.
| DavidSJ wrote:
| In MWI, the problem doesn't exist to begin with.
|
| In e.g. the Copenhagen interpretation, observation plays
| a special role, because it's the moment of wave function
| collapse.
|
| In MWI, there is no wave function collapse, so there's no
| need to identify certain special events called
| "observations" which are somehow different from the rest
| of physics. It's just our eyes, and brains, and
| instruments, interacting and becoming entangled with the
| other things in the world.
|
| When we "observe" Schrodinger's cat, we entangle
| ourselves with the cat just as the cat was already
| entangled with the cesium atom. Now the world is in a
| superposition of two states: in one, the cat is alive and
| we see it as alive; in the other, the cat is dead and we
| see it as dead. This is exactly what the equations say
| should happen. Nothing special.
| simiones wrote:
| And yet, photons can keep interacting with both versions,
| while we are forever unable to see the other version of
| the cat. The problem doesn't go away.
|
| Even more interestingly, say you want to predict the
| outcome of a quantum experiment. In the MWI, that outcome
| is deterministic, and it is a superposition in Hilbert
| space. However, in your own space, you still need to
| compute a probability for that outcome.
|
| What is this _a probability of_ in the MWI? The concept
| of probability across worlds is not really rigorously
| defined, especially since you need to arrive at very
| specific results to be consistent with observations.
| DavidSJ wrote:
| I address your first point here:
| https://news.ycombinator.com/item?id=25999766 (in brief,
| photons are treated no differently than people).
|
| I agree that the meaning of probability in the MWI
| context is an interesting open question. Mathematically,
| it's the squared amplitude of part of the wave function.
| But why this corresponds to our personal experience of
| frequency is something I'm unclear on.
| ummonk wrote:
| The local wavefunction part corresponding to each world
| has a configuration in it that involves a human being
| with eyes and optical nerves and a brain registering
| neural impulses in response to light stimuli to perceive
| its world.
| RobertoG wrote:
| Reading Sean Carroll (1) and David Deutsch convinced me
| that Everett is the straightforward interpretation of what
| the data is saying.
|
| Copenhagen is adding unnecessary concepts to the
| interpretation and making it more complex, so, if we are
| using the scientific method, the burden of proof should be
| with the backers of Copenhagen.
|
| (1) - https://www.youtube.com/watch?v=F6FR08VylO4
| AnHonestComment wrote:
| To concur:
|
| Copenhagen made a choice to try and preserve locality
| when faced with two different solutions to quantum.
|
| Unfortunately, it looks like reality is non-Euclidean
| instead.
|
| At this point, we actually know Copenhagen represents an
| extraneous assumption -- but it's deeply baked into the
| work of the past century.
| simiones wrote:
| I dislike both interpretations, because they both throw
| in the towel and consider that the measurement problem is
| not resolvable. Even in MWI, you still to compute
| probabilities (of what is actually much harder to say) if
| you want to actually use it for predictions.
|
| Instead, the more interesting thing is to stop ignoring
| the measurement problem and find a theory that actually
| solves it somehow; until such a thing exists, waxing
| philosophically about many worlds or un-reality is not
| really interesting.
| slowmovintarget wrote:
| Everettianism does not ignore the measurement problem. It
| fully acknowledges it as decoherence. The problem you
| have instead is the location identification problem, and
| for that you need to calculate probabilities.
|
| Objective Collapse theories, and Bohmian Mechanics
| (hidden variables / pilot waves) are the only other games
| in town for being actual working theories. (Copenhagen is
| not a theory, it is an assertion that one should stop
| trying.)
|
| Of these, Everettianism is actually the simplest.
|
| That said, the multiverse, often referred to as the Bulk
| is a horse of different color. It has nothing to do with
| branches of the wave function in Everettian mechanics.
| Instead it seems to be a way to explain the fine-tuning
| problem. If there is no Bulk, and our comoving patch of
| the universe is representative of the whole shebang, then
| the conditions at the time of the Big Bang were
| unimaginably improbable, extraordinarily special, just
| exactly right to produce the stars in the sky, and us. A
| single solar mass black hole has more entropy than the
| entirety of the universe did at the time of the Big Bang.
|
| One way to explain that "problem" is to think that the
| universe in which our comoving patch exists is a small
| pocket arising from quantum fluctuations in a much more
| vast "bulk" of true vacuum that exists at high entropy.
|
| It does seem like a lot of mental gymnastics, and mostly
| it seems to be directed at elimination of every whiff of
| the idea that a creator was required for the improbable
| conditions in the early universe that give us the arrow
| of time. I'm not sure it's at all useful, nor would it
| have any predictive power were the idea to be true. Our
| comoving patch still expands to an infinite nothingness
| where even the black holes have evaporated away.
| posix_me_less wrote:
| _"I think most people in the cosmology and astrophysics community
| believe it 's a problem because they've been told that for a long
| time."_
|
| This. Quantum theory does not necessarily predict big
| cosmological constant. All big terms can be cancelled /
| regularized by some modification of the theory that keeps the
| results intact. The only problem here is that there is no
| agreement in how to properly quantize fields and some people
| think zero point fluctuations are real and necessary to explain
| some phenomena. However others point out there isn't single rock-
| solid example of such a need. Not even Casimir effect needs
| vacuum fluctuations to be explained. But these facts didn't
| penetrate into mainstream cosmology yet.
| dr-detroit wrote:
| red shift/blue misunderstandings and a broken model of an
| expanding universe are what our time period will be mocked for
| jhoechtl wrote:
| I recently raised a question in the Physics Stackexchange about
| cosmological constants, especially the fine structure constant
| (which is already said to be not-so constant) and the relation to
| gravitaional force:
|
| https://physics.stackexchange.com/questions/603669/are-gravi...
| politelemon wrote:
| I've read many accounts (in popular-science articles and books,
| so never at source) of Einstein's "blunder" the cosmological
| constant. Was it really a case of him second-guessing himself as
| it's often portrayed, or was there more history and thinking
| behind him dropping it?
| mhh__ wrote:
| Although the "history" in physics pedagogy is often made up,
| IIRC it is just a case of him trying to enforce a static
| universe.
| pa7x1 wrote:
| He added it to enforce a static universe, which was the
| predominant viewpoint at the time (more rooted on theology
| than experimental evidence). Then he dropped it and called it
| "his most embarrassing mistake" when Hubble showed the
| expansion of the universe.
|
| Finally, our current models put it back in to explain the
| accelerated expansion of the universe.
|
| Einstein definitely made a mistake but his mistake was not
| adding the cosmological constant, it was adding it for the
| wrong reasons. He should have added it as a free parameter to
| be fitted against empirical data.
| mhh__ wrote:
| Think of the accolades if he'd correctly predicted
| expansion
| kreeben wrote:
| To this day we would still be talking about him.
| simonh wrote:
| He dropped it when Edwin Hubble showed that the galaxies are
| moving away from us and that the universe is expanding. At that
| point the notion of a constant value that imposes a static
| universe became untenable.
|
| Note that it wasn't so much that the constant as such became
| untenable, but if the purpose of introducing it is to create a
| static situation and the situation is showed not to be static,
| then the reason for selecting the given value goes away. If you
| no longer have a reason to set any given value, you have to
| consider whether you need it at all.
| ike77 wrote:
| If the vacuum is producing a force, why would it push outward
| from us and not in every directions, including toward us,
| canceling itself out in the process?
| cambalache wrote:
| Same way as the pressure only pushes "inward". The sign is
| reversed.
| ike77 wrote:
| I don't get it?
|
| If there is vacuum everywhere:
|
| vacuum --- us --- vacuum --- galaxy --- vacuum
|
| Why would galaxy go away from us? I expect that the vacuum on
| the left of the galaxy applies the same force on it as the
| vacuum on its right and thus should have a null net effect on
| its movement?
| sanxiyn wrote:
| I am not sure why the anthropic principle is not accepted as a
| solution to this problem. The principle is obviously true, and
| the problem is solved by the application of the principle.
| akvadrako wrote:
| Because it's too powerful and can be used to explain almost
| anything. A good theory should make specific and rigid
| predictions with few free parameters.
| physicsguy wrote:
| Because in science we tend to use "Occam's razor" approach - we
| don't make assumptions that are more than necessary to explain
| the behaviour of something. Most adherents of the anthropic
| principle assumes "Oh hey, we probably live in a multiverse" to
| justify it, but we have no strong evidence that that is true.
| So making that assumption is difficult to justify. It may be
| true! But we don't know it is, and until it can be proved, the
| theory rests on shaky ground. It might be that another, simpler
| theory can explain the same behaviour. Should we assume that a
| simpler theory is true? No, not necessarily. But it lies on the
| adherents of a more complex theory to come up with reasons why
| that theory is right, by making predictions that can be tested.
| whatisthiseven wrote:
| As an analogy, I think everyone here would be quite upset if
| someone made the claim, "why shouldn't we trust Musk, Gates,
| Jobs, etc at their word when they say what caused them success?
| Obviously it is true because they are successful"!
|
| If you reject the premise I proposed, but not the anthropic
| principle, then you have just moved the goal posts on when to
| accept blind tautologies without further examination.
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