[HN Gopher] Is Spacetime Real?
___________________________________________________________________
Is Spacetime Real?
Author : RickJWagner
Score : 39 points
Date : 2021-02-16 12:51 UTC (10 hours ago)
(HTM) web link (www.forbes.com)
(TXT) w3m dump (www.forbes.com)
| marshmallow_12 wrote:
| i think nows a good time to remember the immortal words of albus
| dumbledore: "Tell me one last thing," said Harry. "Is this real?
| Or has this been happening in my head?" Dumbledore beamed at him
| and his voice sounded loud and strong in Harry's ears even though
| the bright mist was descending again, obscuring his figure. 'Of
| course it is happening inside your head Harry, but why on earth
| should that mean it is not real?'"
| gmuslera wrote:
| I feels like explaining an old greek that the air that he doesn't
| see exists because it inflates a balloon.
| tim333 wrote:
| Well to quote Adams, Time is an illusion. Lunchtime doubly so.
| cletus wrote:
| Modern physics is well beyond the point where I, as a layman, can
| really understand it.
|
| It still doesn't make sense to me how gravity is put in the same
| bucket as the other three "fundamental" forces.
|
| Since the universe is expanding, are we making more space (or
| spacetime)? If so, how does that work?
|
| I'm not even sure if the universe is finite or not. I mean the
| observable universe is but how that relate to the actual
| universe? This seems like it would be somewhat unknowable.
|
| Honestly, I'm still fuzzy on what the Higgs boson is and does and
| how it seems to be this redheaded stepchild in the Particle Zoo
| that doesn't really fit it anywhere else.
|
| Speaking of the particle zoo, why are there (generally) three
| generations of particles/
|
| The article touched on this but is space and/or time discrete or
| continuous? I'd learned that there was a concept of Planck
| distance, being the limit of how small a distance you could have.
| But is this the quanta of distance or just a limit on how low you
| can measure?
|
| Is it just me or are we in a drought of theoretical physics
| breakthroughs? When I was younger, I guess I imagine we'd not be
| in the same position we were 20+ years ago. I mean there have
| been advances of course but we have things like the LHC pretty
| much confirming everything we already knew. Even the Higgs boson
| breakthrough was confirmation of a ~50 year old theory. A bunch
| of contender theories have been disproven, which of course has
| value.
|
| But it seems like we're really no closer to reconciling quantum
| mechanics and gravity (other than eliminating candidates).
| goodlifeodyssey wrote:
| I enjoyed reading everybody's comments. I've been in a long
| conversation with a friend about the Mulamadhyamakakarika---a
| Buddhist text that argues that nothing _inherently exists_,
| including, presumably, space-time. I don't find all of the
| arguments in the text convincing, partly because it is based on a
| number of outdated metaphysical assumptions, but it is very
| interesting none-the-less.
|
| My discussion with my friend went back and forth, and we
| eventually decided that most things don't inherently exist,
| including people, chairs, and atoms. We ended up on the fence as
| to whether the "wave function of the universe" inherently exists.
| Anyway, I captured the essence of our conversation in a dialogue
| that may be of interest to other HNers:
|
| https://goodlifeodyssey.com/nothing-inherently-exists
| slowmovintarget wrote:
| Spacetime is a vector in Hilbert space.
|
| Entanglement yields locality. Space emerges. I'm not convinced
| time is emergent, though (I give the idea low credence).
|
| I'm not a scientist, I just listen to Sean Carroll's podcasts.
| bitcharmer wrote:
| > Entanglement yields locality
|
| Could you please expand on that?
| slowmovintarget wrote:
| In trying to derive spacetime from quantum field theory, some
| working theories show that minimum "energy" fields that are
| highly entangled with each other are "near" each other. That
| gives you locality, therefore space. That is, locality arises
| in the model from certain kinds of entanglement.
|
| Better explanation here:
| http://www.preposterousuniverse.com/blog/2016/07/18/space-
| em...
| jodrellblank wrote:
| Always casually wonder that as you approach the speed of light,
| Lorentz contraction shrinks distance in the direction of travel,
| and slows time. Photons travelling at the speed of light
| experience no time in the direction of travel. Therefore they
| experience no distance in the direction of travel.
|
| In some frame of reference, a photon leaving the Sun and hitting
| your retina, is a 0-distance, instantaneous connection between
| the Sun and your retina. And in another frame of reference, the
| photon "should" be stretched a hundred million miles long - or,
| not be a discrete corpuscular thing with a front and a back which
| travels through the intervening space.
|
| It would be simpler to imagine if there was a nice Aether already
| connecting the Sun and your eye, for the photon to be a
| peturbation of, and then the emission of a photon wouldn't be a
| generation of a new thing de novo, but an electron dropping down
| an orbital level and its electric charge yanking on the
| electromagnetic field Aether like shoving a compression wave down
| a slinky. :/
| jaybrendansmith wrote:
| It's nice to think there must be a missing field that brings it
| all together, knitting space-time into a consistent quantum
| reality with causality preserved, and neatly explaining things
| like quantum vacuum energy, superposition, dark matter, and
| wave-particle duality.
|
| For some reason the idea of photons stretching a hundred
| million miles long reminded me of the Asimov story 'The Dead
| Past' showing how a 'time viewer' would in reality be a Total
| Informational Awareness device.
| bondarchuk wrote:
| Define "real"
| Aeronwen wrote:
| "Reality is that which, when you stop believing in it, doesn't
| go away." --PKD
| dimitrios1 wrote:
| define "define"
| guerrilla wrote:
| Interesting[1] but off topic. Definitions were not discussed
| in the article but asking whether something is real or not
| without clear criteria is foolish.
|
| https://plato.stanford.edu/entries/definitions/
| potiuper wrote:
| From end.
| RichardCA wrote:
| If the Earth were destroyed in some sort of cataclysmic event
| and all humans were gone, what would remain? What would still
| be true about the universe?
|
| To put it another way, if we are not the only scientifically
| capable species, would a different species discover different
| physics? How different? Would there be at least some ideas that
| overlap?
|
| These topics get explored in science fiction. Carl Sagan and
| James Burke also wrote quite a bit about how humans discover
| new ideas and suddenly the universe changes.
|
| But if you think these ideas are so abstract as to be
| meaningless, then there is no question to pose, and nothing to
| discuss.
| [deleted]
| ejolto wrote:
| If you're talking about what you can feel, what you can smell,
| what you can taste and see, then real is simply electrical
| signals interpreted by your brain.
|
| - Morpheus
| dimitrios1 wrote:
| So my DMT trips were real?
| yesenadam wrote:
| TLDR: Article ends with
|
| > whether it's "real" or not -- that's not a question that
| science has yet discovered the answer to.
| tim333 wrote:
| Not sure that's even a question of science. It's a question of
| how you define real.
| thisiscorrect wrote:
| "What exactly is spacetime? Is it a real thing like an atom, or
| just a mathematical construct that is used to describe how mass
| 'generates' gravity?"
|
| This is a false dichotomy. Atoms too are "just" a mathematical
| construct used to describe how certain observable, physical
| systems behave. It's even called the atomic _theory_, and like
| all other good theories it knows its limits. At low enough
| energies, it's too fine and at high enough energies it's too
| coarse a model. Spacetime is exactly as real as any other current
| model of observable physical phenomena that physics can offer.
| f154hfds wrote:
| I think you and the author are talking about different
| concepts. To your credit, for the author's 'real thing like an
| atom' here, the term real is ambiguous.
|
| The question the author is talking about isn't whether a
| particular theory is correct, or even whether a theory contains
| explanatory power. I believe the author is assuming general
| relativity for the sake of argument, and discussing the concept
| of existence within the general relativity theory's framework.
|
| For example, take the three-body problem [1]: does the _theory_
| of general relativity require us to add initial conditions to
| the three body problem? In other words, are there more
| fundamental initial conditions not derivable that must be
| inserted as inputs into the equations when we use general
| relativity to solve the problem instead of say Newtonian
| mechanics? The answer is No. While the equations will change,
| the initial conditions (the degrees of freedom) do not.
|
| What does that mean? It demonstrates indivisible properties of
| the universe given a set of theories. With general relativity
| now 'energy' and 'mass' are interchangeable, but the existence
| of mass/energy isn't a fictitious force, it can't be explained
| away by coordinate transformations. Gravity can't either, but a
| gravity well points to an underlying reality of mass/energy,
| not the other way around. If it were the other way around, we
| would say gravity is the 'real' thing, and mass/energy are
| resulting effects.
|
| [1]: https://en.wikipedia.org/wiki/Three-body_problem
| Voloskaya wrote:
| I disagree with you. Your argument could be made about
| anything, there is no such thing as a "human" either, it's just
| a big bunch of wave-particles that does not have some clear
| limits. Yet when we talk about a human, we all know what that
| is, and when a human is seating on a chair we don't think the
| chair is part of it.
|
| The same applies to atoms, we all agree on what they are, and
| we can show pictures of them etc.
|
| The question here is whether spacetime is something like that,
| or if it is a proxy concept with no grounding whatsoever in the
| universe, but with good predictive powers?
|
| For example, for a long time we believed that Aether filled
| space, and although we now know this is not the case, the
| mathematical model provided by the Aether theory was pretty
| useful. You could very well imagine a world where we know
| Aether is not real, but continue using it for lack of a better
| theory as it is a useful framework.
|
| > It's even called the atomic _theory_
|
| Theory, in scientific theory, means the opposite of theory in
| our everyday language though. Theory does not mean a guess, it
| means a body of work accepted as valid and robustly tested.
| AnIdiotOnTheNet wrote:
| > The question here is whether spacetime is something like
| that, or if it is a proxy concept with no grounding
| whatsoever in the universe, but with good predictive powers?
|
| Consider that "human", "chair", and "atom" are also just
| concepts are minds apply to certain patters of energy. We all
| "know what that is" because it is advantageous for our minds
| to place things in these categories for the purpose of
| modeling. You may know what a "chair" is, but there are an
| infinity of gradations between "chair" and any two other
| objects, like the beanbag chair sitting between "chair" and
| "pillow".
|
| The concept of a chair has no grounding in the universe, it's
| all in the mind. There are no physics that only apply to
| chairs.
|
| > For example, for a long time we believed that Aether filled
| space, and although we now know this is not the case, the
| mathematical model provided by the Aether theory was pretty
| useful. You could very well imagine a world where we know
| Aether is not real, but continue using it for lack of a
| better theory as it is a useful framework.
|
| Yes, that's how it works. When we have a better model we use
| that unless a simpler one will do. Newtonian gravitation
| isn't "real" by your definition, but we still use it in a lot
| of circumstances even though we have more accurate models.
| Voloskaya wrote:
| Right, and that was the point I was trying to make with the
| human analogy.
|
| So the question is whether spacetime is one of those
| patterns we can point to, like a "human" a "chair" or an
| "atom", which is what we call "real" in our everyday
| language, or whether it is only a useful modelization tool,
| like the Aether. There are no pattern anywhere in the
| universe matching the Aether.
|
| It is a valid question.
| AnIdiotOnTheNet wrote:
| I'm saying the differentiation is meaningless. We have a
| model of space time that makes accurate and measurable
| predictions and that is as real as real gets.
| jodrellblank wrote:
| We have a photo of a building that makes accurate and
| measurable predictions of things like the roof being
| above the door, and how far, and which parts are
| transparent (windows) and which parts opaque (walls), and
| how many people could fit inside it. Is that picture as
| real as buildings get?
| AnIdiotOnTheNet wrote:
| Is your claim that the picture _is_ the building? Because
| that 's the equivalent of claiming that the a Penrose
| diagram _is_ spacetime, instead of a representation of
| the model.
|
| The photo of the building is an accurate diagram of the
| model of that one individual building. It _describes_ the
| building, it is not actually the building. However, your
| model (roof height, walls, location, etc) _is_ the
| building. If that building is destroyed in a fire and
| remade to those exact specs, do we not say it is still a
| building?
| jodrellblank wrote:
| > " _Is your claim that the picture is the building?_ "
|
| You said "a model which makes accurate predictions is as
| real as real gets". That the picture _is_ the building is
| _your_ claim here, that there 's nothing more real than
| an accurate model, which I'm countering by absurdum. Wind
| can turn a turbine, a weather predicting model of wind
| cannot. You say " _the differentiation [between a model
| and reality] is meaningless_ ", I say a model is a leaky
| abstraction - when you send a single atom through a
| Young's double slit experiment and it interferes with
| itself and generates a wave interference pattern, that's
| leaking a reality outside the billiard-ball model of
| atoms, that's one time when the distinction between model
| and non-model is meaningful.
|
| > " _If that building is destroyed in a fire and remade
| to those exact specs, do we not say it is still a
| building?_ "
|
| If the building is destroyed in the fire, and your model
| of it isn't, how can you say there is no difference
| between the building and the model?
| AnIdiotOnTheNet wrote:
| > You said "a model which makes accurate predictions is
| as real as real gets". That the picture is the building
| is your claim here, that there's nothing more real than
| an accurate model, which I'm countering by absurdum.
|
| My claim is that the model describes a real thing, not
| that it itself is a real thing, and the extent to which
| that thing being described is real is a matter of the
| accuracy of the model. You can model the motion of
| planets with geocentric epicycles, but that is less real
| than a model that uses heliocentric ellipses.
|
| Let me turn this around for a second:
|
| > when you send a single atom through a Young's double
| slit experiment and it interferes with itself and
| generates a wave interference pattern, that's leaking a
| reality outside the billiard-ball model of atoms, that's
| one time when the distinction between model and non-model
| is meaningful.
|
| Now ask yourself: if we have a 100% accurate model of
| physics that employs a concept of spacetime such that
| there are no leaks, no unaccounted for observations
| whatsoever, then would you say that it matters if
| spacetime is just some mathematical concept and the real
| mechanism works differently but produces exactly the same
| results?
|
| I submit that it doesn't. A model that produces perfectly
| accurate descriptions describes reality in so far as any
| description of reality can be said to. We don't have
| perfect models of reality, that is known, however lacking
| a more accurate model it is meaningless to say that our
| current ones (which are astonishingly accurate despite
| being imperfect) don't describe reality.
| cgriswald wrote:
| > You can model the motion of planets with geocentric
| epicycles, but that is less real than a model that uses
| heliocentric ellipses.
|
| This example actually weakens your argument. Heliocentric
| ellipses are chosen because they explain our _model_ well
| and importantly are _simpler_ than epicycles; but we can
| make epicycles arbitrarily accurate by piling on as many
| of them as you like.
|
| So which is real? That Earth and the other planets
| revolve around the sun or that the sun and other planets
| revolve around the Earth?
|
| > if we have a 100% accurate model of physics that
| employs a concept of spacetime such that there are no
| leaks, no unaccounted for observations whatsoever,
|
| Let's say I have a box with a green LED, a red LED, and a
| button. One of the LEDs is always lit. Whenever I press
| the button, that LED becomes unlit, and the other becomes
| lit. If I try to open the box, it explodes. My model of
| how this box works is very simple: A demon is sitting
| inside the box and touches the LED that becomes lit. When
| I press the button he gets poked with a tack and switches
| to touching the other LED. If I try to open the box, he
| gets angry and blows up.
|
| This model is 100% accurate. Every one of these boxes I
| have seen always behaves this way. Is there a demon
| sitting in the box?
| AnIdiotOnTheNet wrote:
| > This example actually weakens your argument.
| Heliocentric ellipses are chosen because they explain our
| model well and importantly are simpler than epicycles;
| but we can make epicycles arbitrarily accurate by piling
| on as many of them as you like.
|
| Epicycles allowed us to map the motions very well but
| they were incredibly complicated and didn't provide for
| explanations of how they came into being. Simpler models
| that provide the same results are considered to be
| better. Given two models that make the same predictions,
| it makes more sense to use the simpler one than the more
| complicated one (Occam's razor). The heliocentric model
| no doubt had its detractors until it was refined enough
| to make the same or better predictions, but its
| simplicity made it much more attractive as an
| explanation.
|
| > This model is 100% accurate. Every one of these boxes I
| have seen always behaves this way. Is there a demon
| sitting in the box?
|
| Typically we apply Occam's razor in this. If we know how
| we could construct such a device without a demon, a being
| for which we have no other evidence of its existence,
| then our simpler and more readily explainable solution is
| what we generally go with. However, if this box is indeed
| unopenable, and the light always changes, then it doesn't
| really matter does it? Neither the demon nor a more
| conventional explanation makes any difference to how we
| interact with the box, nor could it ever.
|
| The "reality" of what happens inside the box is not
| relevant and some would argue not even something that
| exists in the realm of scientific thought. It's like, say
| you live in Conway's Game of Life, and ask "what are
| cells made of?", it is completely unknowable and even if
| you somehow had the answer it would be meaningless since
| cells always behave in exactly the same way that is 100%
| explained by a simple model.
| cgriswald wrote:
| You said:
|
| > ... the extent to which that thing being described is
| real is a matter of the accuracy of the model. You can
| model the motion of planets with geocentric epicycles,
| but that is less real than a model that uses heliocentric
| ellipses.
|
| This statement doesn't suggest simplicity as a measure of
| realness and it is unclear why reality would necessarily
| prefer the simpler thing. We prefer it, of course.
| However, the two models on offer are mathematically
| equivalent and differ only in: (1) simplicity, and (2)
| explanation. So I'm not sure if you're modifying your
| stated position or not when you apply Occam's razor here.
|
| As for whether it matters, I think that's rather the
| point: We don't know if it matters until we find out it
| does. I don't think we _can_ know if matters until the
| moment it definitely does. A 100% accurate full-knowledge
| model is, by our own models, an impossibility. And even
| if we had such a model, how would we ever know it?
| AnIdiotOnTheNet wrote:
| > This statement doesn't suggest simplicity as a measure
| of realness and it is unclear why reality would
| necessarily prefer the simpler thing.
|
| Because it doesn't matter if the results are the same,
| and simpler things are inherently preferred. Assume that
| both of these models are 100% correct in their
| predictions: there is no reason whatsoever to believe
| that the more complicated one is a "truer" model of
| reality, nor is there a reason to believe the simpler one
| is, so we proceed on the notion that the simpler one is
| because that is more to our liking and the end results
| are the same.
|
| I guess one of the fundamental impasses here is that I am
| not convinced, on a philosophical level, that there is
| any deeper "realness" than can be modeled. If we can't
| model it, or rather if modelling it serves no purpose,
| then it may as well not exist.
|
| > As for whether it matters, I think that's rather the
| point: We don't know if it matters until we find out it
| does. I don't think we can know if matters until the
| moment it definitely does.
|
| Right. We must assume reality is what it appears to be
| until we make observations and tests that prove
| otherwise, then we construct a new model. We must assume
| that new model represents reality because we simply have
| no alternative until we build a better model.
|
| > A 100% accurate full-knowledge model is, by our own
| models, an impossibility. And even if we had such a
| model, how would we ever know it?
|
| To a certain extent we can't. No matter how many correct
| predictions we make there is always the possibility that
| we will eventually make an observation that defies our
| model. That's sorta my point. What we call reality is, by
| necessity, a product of observation, deduction, testing,
| and modelling. We have to construct our reality from
| that, and talking about whether or not an accurate model
| represents some deeper "reality" or not is pointless
| without an alternative.
|
| If right now we question the "reality" of spacetime, what
| changes? Can we even build an accurate model of reality
| as we currently know it without spacetime? Can that model
| be made simpler than the ones with spacetime? If so, no
| one has done it yet. Therefore we have no choice but to
| believe that the universe isn't deceiving us and
| spacetime actually does exist, because believing the
| opposite is completely pointless.
| Voloskaya wrote:
| So then the Aether was real for a while and stopped being
| real 200 years ago?
|
| If we discover a new model that makes better prediction
| than our current spacetime based model, just like
| relativity was to Newton's theory, will spacetime stop
| being real?
|
| The article was clearly using "real" with the definition
| we attach to it in our everyday language, not in deep
| philosphical sense.
| AnIdiotOnTheNet wrote:
| > So then the Aether was real for a while and stopped
| being real 200 years ago?
|
| Yeah, pretty much.
|
| > If we discover a new model that makes better prediction
| than our current spacetime based model, just like
| relativity was to Newton's theory, will spacetime stop
| being real?
|
| In so far as Newtonian gravitation is also not-real. We
| still use that model for a lot of things of course. I
| don't know much about Aether theory or its predictions,
| so instead I'll use another long gone theory for my
| example: People used to model the motion of "heavenly
| bodies" using epicycles, complicated circles-within-
| circles patterns that assumed the Earth was the center of
| the universe and everything was taking a very complicated
| path around it. These epicycles were actually quite good
| at predicting the motion of planets and stars, so as far
| as anyone was concerned they were real. Some clever
| people eventually came around to the idea that all of
| that could be much more easily and more accurately
| modeled if we put the sun at the center. Of course we
| know today that that isn't quite right either.
|
| We don't, and possibly cannot, ever know if the models we
| use to describe the world around us are the most accurate
| or not. They are real when they work, because we have no
| better metric to determine their reality.
| Voloskaya wrote:
| I do agree with your point, but I think we are seeing the
| limit of language: when we don't attach the exact same
| definition to words, we can misunderstand each others
| while trying to convey the same thing.
|
| The way you use "real" is the way I would use "valid": A
| theory is valid until proven otherwise.
|
| And the way I use "real" (and I think it is the same way
| the article used it), is whether something has any
| grounding in our universe (some pattern as you said
| before).
|
| For example, wormholes are possible following the theory
| of general relativity, but we don't know if they are
| "real", e.g. can there actually be a wormhole in our
| universe. If we do end up finding one, then they are
| real. If we however find conclusive evidence that they
| cannot exist in our universe, then they are not real, but
| only an artifact of our (incomplete) theory of general
| relativity.
| AnIdiotOnTheNet wrote:
| > And the way I use "real" (and I think it is the same
| way the article used it), is whether something has any
| grounding in our universe (some pattern as you said
| before).
|
| Many of the things you described as "real" don't have
| grounding in our universe, i.e. things like "chair". It's
| possible I misunderstand your usage of the term
| "grounding".
|
| > For example, wormholes are possible following the
| theory of general relativity, but we don't know if they
| are "real", e.g. can there actually be a wormhole in our
| universe. If we do end up finding one, then they are
| real. If we however find conclusive evidence that they
| cannot exist in our universe, then they are not real, but
| only an artifact of our (incomplete) theory of general
| relativity.
|
| Sure, but how does that apply to spacetime? We know, so
| far as anything can be known, that space and time are two
| different perspectives of the same thing. Relativity
| described it, and we have measured and the effects it
| predicts with startling accuracy.
|
| Here's a question: It matters if wormholes can or cannot
| exist regardless of if the current model permits them or
| not. Does it matter if spacetime fits your definition of
| "real" or not?
| drran wrote:
| Aether is real again as Higgs field. Speed of light in
| vacuum is variable again (gravitational waves). Vacuum is
| no longer an empty space.
| thisiscorrect wrote:
| "The same applies to atoms, we all agree on what they are,
| and we can show pictures of them etc."
|
| This is where you bury the lede. It's clear if you read many
| of the comments here that there is no such agreement. Some
| people _think_ of an atom as something you can reach out and
| touch, or grok in some deep sense distinct from performing
| specific experiments. Others take an approach that's more in
| line with theory in the sense I use it
| (https://en.wikipedia.org/wiki/Scientific_theory). Your
| definition of theory is too loose: it's not just a body of
| work. That sounds like a pile of experimental evidence to me.
| A theory is a robust model or family of related models that
| match the experimental evidence. Atoms exist in that sense:
| they're a well tested model of experimental phenomena.
|
| I'm certainly not claiming that atomic theory is a wild
| speculative guess which you seem to imply I've done.
| Voloskaya wrote:
| > It's clear if you read many of the comments here that
| there is no such agreement
|
| I guess I should have said "all experts agree" instead?
| Lack of knowledge about something by some people doesn't
| change the definition of that thing. I would add however,
| that you can reach out and touch an atom with a certain
| definition of touch (as touch is mostly a macroscopic
| concept).
|
| > I'm certainly not claiming that atomic theory is a wild
| speculative guess which you seem to imply I've done.
|
| You will have to explain this one to me then. You said
| "it's *even* called a theory" to reinforce your point that
| it was just a mathematical tool (and hence not real
| following your definition). This point is valid only if
| theory means guess, which it does not.
| slibhb wrote:
| Touch isn't any different than measuring radiation
| interacting with something. These are metaphysical
| questions, not scientific ones.
|
| Scientists, like everyone, have a realist perspective.
| They consider reality to correspond with appearences. But
| this is a convention or a metaphysical belief or even a
| religous belief, it's not scientific.
| sfifs wrote:
| > I would add however, that you can reach out and touch
| an atom with a certain definition of touch (as touch is
| mostly a macroscopic concept).
|
| Don't be so sure... atoms and even relatively large
| molecules definitely experimentally exhibit [1] wave
| particle duality in double slit experiments demonstrating
| they move as waves. Given that absolutely nothing is
| stationary at any temperature above absolute zero, what
| are you touching and with what?
|
| [1] see end of article
| https://arstechnica.com/science/2021/01/the-curious-
| observer...
| blablabla123 wrote:
| Theory is indeed separated into several disciplines,
| speaking about mathematization: Phenomenology, Model
| building, Mathematical Physics. FWIW I think Phenomenology
| is where a lot is going on, it's about looking what is
| there and how it compares to the models.
|
| The fully formalized ("axiomatic") mathematical
| descriptions oftentimes lag behind the theoretical models
| ("postulated") in use that are used to compare with real
| data for instance.
|
| That said, I would say Atoms are as real as it can get.
| There are so many experiments about them and applications
| as well, for instant nuclear fission. How can they not be
| real? :-) Speaking about Spacetime, of course it is real.
| There is such a crazy amount of predictions based on
| Special Relativity.
| karmakaze wrote:
| > Atoms are as real as it can get
|
| Well put, and also not any specific degree of real, if
| you accept that the simulation hypothesis can't be
| disproven. The specific 'real' discovered properties of
| atoms or spacetime are actually artifacts of simulation.
| randallsquared wrote:
| > _Some people _think_ of an atom as something you can
| reach out and touch, or grok in some deep sense distinct
| from performing specific experiments._
|
| Right, with an atomic force microscope.
|
| ...but it almost sounds like you're suggesting that atoms
| and molecules are NOT something you could individually pick
| up with an AFM?
| iand wrote:
| The parent was referring to the perceived physicality of
| atoms which you cannot touch or understand except in
| terms of the forces between your instrument and the
| bundle of quanta we call an atom.
| JumpCrisscross wrote:
| > _The question here is whether spacetime is something like
| that, or if it is a proxy concept with no grounding
| whatsoever in the universe, but with good predictive powers?_
|
| I'd add: is it something one can develop an intuition for?
|
| I don't think there is anyone who says gluons or general
| relativity are intuitive. You have to do the calculations (or
| memorize heuristics) to get something useful. Atoms, on the
| other hand, or electromagnetic radiation as another example,
| can be visualized (and mentally simulated) more or less
| correctly. (Note: atoms. Not nuclear mechanics.)
| akvadrako wrote:
| I don't believe anybody can intuitively "visualize" an atom
| which leads to accurate predictions, especially the
| electron cloud and it's collapse. Atoms which manage to
| stay isolated for long enough are not even localized in
| space.
| ncann wrote:
| While not a perfect definition of "real", don't we already have
| images of atoms?
| ordu wrote:
| Those images, as I understand, constructed by heavy
| calculations based on a theory of atoms. Isn't it? So it is
| arguable that images are not "real", they are visualizations
| of a data.
|
| At the same time not every real image is real. We could
| sometimes see two Suns in the sky, or we can see a rainbow,
| but it doesn't mean that the second Sun and the rainbow are
| real.
| mhh__ wrote:
| We have images of black holes merging too.
| yes_man wrote:
| We have devices that register electromagnetic radiation
| spectrum emitted (by "atoms") which can be visualized as an
| image. But this is at the heart of the parent comment: does
| the atom exist, or is it just a concept that describes the
| end result when strong interaction, electromagnetic force and
| gravity make particles stick together in a (usually)
| consistent way? If we call the atom real, we can call other
| aggregations like the economy or game theory real as well.
| But they are just concepts
| AnIdiotOnTheNet wrote:
| It isn't much of an argument. Everything we think of as
| "real" in the sense that you describe it is actually just a
| conceptual model we have for how certain patterns of energy
| in the universe behave. The universe has no special rules
| for apples, floors, wifi access points, cars, or
| basketballs.
| thisiscorrect wrote:
| We do. Thinking a bit about what that means, we have
| photographs showing how the physical entity we model as atoms
| interact with light, and can confirm that the theory lines up
| with experiment.
|
| If we adopt that same definition for spacetime, we also have
| photographs of it, e.g. https://en.wikipedia.org/wiki/Solar_e
| clipse_of_May_29,_1919#... and
| https://en.wikipedia.org/wiki/Gravitational_lens#Gallery.
| jakelazaroff wrote:
| Atoms aren't just something we've modeled -- they're a
| _physical thing_ , i.e. matter. We can sense them directly,
| not just infer their existence by measuring related
| phenomena. I realize when you get into theoretical physics
| the "thingness" of concepts becomes more and more abstract,
| but atoms don't fall into that bucket.
| enkid wrote:
| I don't see the distinction you're making between
| "sensing" and "measuring related phenomena." What's
| different from using a specialized microscope to take a
| picture of an atom and using a telescope to take a
| picture of black hole?
| Balgair wrote:
| The amount of grant funding! ;P
| bobcostas55 wrote:
| >We can sense them directly
|
| What does this even mean? Unless you're talking about
| some supernatural "atomic sense", there's obviously no
| way to "sense them directly" - we sense them through
| their interaction with other things combined with our
| model of those things and the interaction.
| jakelazaroff wrote:
| Okay, that's fair. But taken to its extreme, we sense
| _everything_ through its interaction with other things.
| But obviously, things exist; not everything can be just a
| mathematical model.
| headsupernova wrote:
| Why not?
| drran wrote:
| Mathematics is too powerful. It can express anything,
| both real and unreal things. Physical world has
| limitations.
| bobcostas55 wrote:
| Check out Max Tegmark's writings on the mathematical
| universe, some very interesting stuff in that direction.
| jakelazaroff wrote:
| Will do, thanks for the rec!
| thisiscorrect wrote:
| You sense spacetime directly too. It's what holds you do
| this planet we inhabit.
|
| I think atomic phenomena may feel somehow more familiar
| because it takes far less energy to make them dynamic
| than it does for gravitational phenomena. If we were
| somehow huge beings made of binary stars or something,
| gravity would probably be the very familiar force and
| atomic phenomena almost inconceivably small to you.
| drran wrote:
| Spacetime is defined as [x,y,z;t] - 4d array of data.
|
| > You sense spacetime directly too. It's what holds you
| do this planet we inhabit.
|
| Nope.
| jodrellblank wrote:
| Atomic phenomena are almost inconcievably small to me.
| There's around a hundred trillion atoms in a human body
| cell, and around a hundred trillion cells in a human
| body, plus or minus an order of magnitude or two. It's
| astonishing to me that people in the early 1900s could
| measure and calculate the charge on an electron, or that
| Marie Curie had to process tons of pitchblende to purify
| micrograms of Radium - and could, and did. Or that
| Rutherford could say where most of the mass inside an
| atom is, and split the nucleus of Nitrogen atoms -
| 1/1000th of the size of the whole atom - and tell what
| was happening down at that scale - using the technology
| of 1917.
| umvi wrote:
| Yeah but what are we actually seeing? An atom is made of
| protons, neutrons, and electrons, and 99.9% empty space. But
| you can't really look at an image of an atom and say "there's
| a proton there" so what is the image of exactly? Rinse and
| repeat with quarks.
| drewcoo wrote:
| A scientific theory is a body of knowledge. The special use of
| the term seems like a false monocotomy.
| codeulike wrote:
| I dont agree its a false dichotomy.
|
| Yes every theory is just a model to fit observations etc etc.
| But Atoms are conceivable - they work as a model, but we can
| also imagine how to fit into the reality that we experience. We
| can 'see' them to an extent with special instruments. And their
| abilities/behaviours are evident in all the physical world of
| compounds and elements around us. You can disolve salt in
| water, you can light up a neon sign.
|
| Quantum Mechanics is a model that fits experiment results very
| well, but is very hard to conceive of. Wave function collapse
| has no obvious analogue in the world as we experience it. Thats
| the point of schrodingers cat. You either have to go for the
| many worlds interpretation, or get into spooky stuff about
| observers.
|
| Spacetime/relativity is similar, we can do stuff like fly a
| clock around the world in an airplane, or observe mercury
| transitioning past the sun, but its much less conceivable based
| on our everyday world. So spacetime might just be a constuct,
| like wave function collapse, that doesnt map easily onto our
| experience of the world. Certainly its a question worth asking.
| enkid wrote:
| Our ability to conceive of something should not be in the
| definition of reality. Quantum mechanics and relativity have
| just as much, if not more experimental evidence to support
| them as atomic theory, and make even better predictions. This
| has implications in the "real world." If we base our
| definition on what is "intuitive" instead of what is
| provable, we end up with things like humour theory in
| medicine.
| thisiscorrect wrote:
| "But Atoms are conceivable - they work as a model, but we can
| also imagine how to fit into the reality that we experience."
|
| "Quantum Mechanics is a model that fits experiment results
| very well, but is very hard to conceive of."
|
| These two statements stand in contradiction. Atoms only work
| as a model if quantum mechanics holds. In a non-quantum
| world, electrons collapse into a nucleus, shedding
| electromagnetic radiation and lowering their energy as they
| do so. That's also necessary to understand why neon signs
| have their colors.
|
| More broadly, if you want to compare one scientific theory to
| another and contrast their "realness" you have to take
| quantum mechanics along with your atomic theory.
| codeulike wrote:
| I guess I'm referring to the theory of atoms as it was
| before QM came along. In the same way that newtonian
| mechanics is still useful even though its has been
| superceded by relativity.
|
| If you're saying I 'have' to take QM along with my atoms,
| then you also have to take Relativity along with your QM,
| and at the moment they are irreconcilable. Until we have a
| 'theory of everything' its ok to use simpler models within
| boundaries
| Q_is_4_Quantum wrote:
| Agree with this - the jury is still out on "reality" or
| otherwise of a wavefunction, and people expend their "real"
| research efforts differently according to their opinion!
| Saying "well everything is just mathematics" is a bit like
| advocating solipsism: people will roll their eyes and stop
| inviting you to cocktail parties, its a boring position.
|
| Another historical example would be electric and magnetic
| field lines. My impression is that even Faraday originally
| had doubts about their reality; others certainly did. They
| could have just been forever considered a useful mathematical
| construct. At some point it became clear that thinking of
| them as really existing, permeating space, and having
| physical properties akin to those of accepted real stuff
| (momentum etc) was more useful. Many years after GR was
| formulated there were arguments about similar mathematical
| objects (dynamical components of a tensor, or "gravitational
| waves") should be considered real or not. The story is that
| Feynman convinced many with a simple thought experiment about
| how they transmit energy.
| m0llusk wrote:
| One of the more interesting potential answers to this question is
| quantized spacetime: http://einsteinsintuition.com/what-is-
| qst/overview/
| taylodl wrote:
| Is spacetime real? Does mass & energy "curve" spacetime? Is
| gravity an actual force or is it a virtual force emerging from
| "curved" spacetime? Like all forces gravity can be modeled by
| geometry. Where gravity is different from the other forces is it
| applies to _everything_ - regardless of charge, regardless of
| mass, regardless of energy. Therefore the geometry, and gravity
| 's metric, applies to _everything_ in the universe. Does
| spacetime exist? Is it curved? We simply can 't tell - spacetime
| is indistinguishable from gravity's metric.
|
| I think a more interesting question then is whether spacetime
| arises as a result of the presence mass & energy?
| drran wrote:
| > I think a more interesting question then is whether spacetime
| arises as a result of the presence mass & energy?
|
| Spacetime is 4D array of data: [x,y,z;t]. Can you translate
| your question to plain English, please?
| Jeff_Brown wrote:
| The question is meaningless.
| smitty1e wrote:
| The question is a fine journey whose path as such could be
| profitable.
|
| But practically, we behave as though reality, consciousness,
| and freewill have substantial basis.
| invalidtaxonomy wrote:
| This raise a bunch of interesting questions, but the first one
| that comes to mind is "should approving such cookie popup for
| your business be considered a clear sign of mental illness?".
| This is clearly the work of a dangerous and deranged mind that I
| would not feel comfortable letting my family hang out with.
| mmcconnell1618 wrote:
| Does anyone else see a logical flaw in explaining the distortion
| of spacetime with examples like a weight on a rubber sheet or too
| many actors on a stage causing it to warp? It seems that the
| easiest way to explain how gravity is created by spacetime is to
| use a self referential example of gravity itself.
| iand wrote:
| Those aren't explanations, they are analogies to help the human
| mind picture the effect.
| acd wrote:
| Yes but you can warp space time with gravity according to
| Einstein.
|
| https://en.wikipedia.org/wiki/Spacetime
|
| But you need to warp space as in curve it. If you would fly close
| to a black hole space might be warped.
|
| https://www.space.com/1976-black-hole-puts-dent-space-time.h...
|
| You probably need to think of space in higher dimensions than
| three for example four dimensions.
| juanbyrge wrote:
| I believe it's the other way around. Objects with mass warp
| spacetime, and the resulting curvature results in gravity.
| Everything not accelerating travels in straight lines, where
| straight lines are geodesics through spacetime. This is why
| gravity is not a real force, but the result of objects
| traveling through the curvature spacetime.
| m4r35n357 wrote:
| Terrible article, terrible comments!
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