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Is Spacetime Real?
- bondarchuk 6y agoDefine "real"
- dimitrios1 6y agodefine "define"
- ejolto 6y agoIf 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 6y agoSo my DMT trips were real?
- Aeronwen 6y ago"Reality is that which, when you stop believing in it, doesn't go away." --PKD
- deleted 6y ago[deleted]
- RichardCA 6y agoIf 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.
- yesenadam 6y agoTLDR: Article ends with > whether it’s “real” or not — that’s not a question that science has yet discovered the answer to.
- tim333 6y agoNot sure that's even a question of science. It's a question of how you define real.
- thisiscorrect 6y ago“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.
- ncann 6y agoWhile not a perfect definition of "real", don't we already have images of atoms?
- thisiscorrect 6y agoWe 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_eclipse_of_May_29,_1919#Observations https://en.wikipedia.org/wiki/Solar_eclipse_of_May_29,_1919#... and https://en.wikipedia.org/wiki/Gravitational_lens#Gallery https://en.wikipedia.org/wiki/Gravitational_lens#Gallery.
- jakelazaroff 6y agoAtoms 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 6y agoI 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?
- Jeff_Brown 6y agoThe question is meaningless.
- smitty1e 6y agoThe 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.
- gmuslera 6y agoI feels like explaining an old greek that the air that he doesn't see exists because it inflates a balloon.
- invalidtaxonomy 6y agoThis 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.
- chris-orgmenta 6y agoCome on now, that's facetious and you know it. I'm on your side but hyperbole like that isn't going to get us anywhere. Let's just invoke Hanlon's razor and accept that these decisions are mostly just made without much thought or understanding.
- invalidtaxonomy 6y agoTo be honest I did hesitate on hitting the reply button because I knew it was a rage-fueled comment at the time. Yet, now that I calmed down I still don’t see how this could not have been 1. made poorly by design 2. approved by someone that have no clue why it was designed this way So yes, my comment may seem hyperbolic but I still think that mixing with such people is a bad idea as long as they show no remorse knowingly doing damaging deeds. That said, this is clearly off-topic and I regret starting this discussion here.
- mmcconnell1618 6y agoDoes 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 6y agoThose aren't explanations, they are analogies to help the human mind picture the effect.
- acd 6y agoYes but you can warp space time with gravity according to Einstein. https://en.wikipedia.org/wiki/Spacetime 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.html 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 6y agoI 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.
- tim333 6y agoWell to quote Adams, Time is an illusion. Lunchtime doubly so.
- slowmovintarget 6y agoSpacetime 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 6y ago> Entanglement yields locality Could you please expand on that?
- slowmovintarget 6y agoIn 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-emerging-from-quantum-mechanics/ http://www.preposterousuniverse.com/blog/2016/07/18/space-em...
- cletus 6y agoModern 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).
- richardjennings 6y agoI have come to accept that I do not and almost certainly cannot understand spacetime. I cannot fathom the consequences of the passage of light through circumstances. I do not see how the concept of 1 Billion years can be thought to apply universally; how the Universe can have an age when as I understand it, time is circumstantial and potentially as meaningless as speed without a point of reference.
- jodrellblank 6y agoAlways 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 6y agoIt'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.
- drran 6y ago> It's nice to think there must be a missing field that brings it all together Higgs field? https://simple.wikipedia.org/wiki/Higgs_field https://simple.wikipedia.org/wiki/Higgs_field Quantum vacuum energy is just noise. Superposition is for waves only. Dark matter can be explained by "SISO" principle. Wave-paticle duality is boring simple: https://dotwave.org/single-particle-creates-interference-after-double-slit/ https://dotwave.org/single-particle-creates-interference-aft...
- taylodl 6y agoIs 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 6y ago> 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?
- m0llusk 6y agoOne of the more interesting potential answers to this question is quantized spacetime: http://einsteinsintuition.com/what-is-qst/overview/ http://einsteinsintuition.com/what-is-qst/overview/
- m4r35n357 6y agoTerrible article, terrible comments!
- goodlifeodyssey 6y agoI enjoyed reading everybody's comments. I've been in a long conversation with a friend about the Mūlamadhyamakakārikā---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 https://goodlifeodyssey.com/nothing-inherently-exists
- marshmallow_12 6y agoin 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?'”
- tobmlt 6y agoJudging by the comments I think there might be a good amount of interest in reading Gavin Bascom’s “On the Inside of a Marble” As for the actual question of spacetime, I like the author’s conclusion for the time being: “ But despite all the things that spacetime enables us to predict and know, it isn’t real in the same way that an atom is real. There’s nothing you can do to “detect” spacetime directly; you can only detect the individual quanta of matter and energy that exist within your spacetime.” For the future, I think ...“it’d be really cool if”.... holography stitched spacetime from entanglement/entropy such that we could measure directly... something quantum... and believe it to be a real measurement of spacetime itself, right here in good ol’ de Sitter (or wherever we are, should experiment find things afresh;). Is there any hope there I wonder.
- 8bitsrule 6y agoThis kind of question goes round and round. I'm tempted to say there's no time, only space and matter. But then, someone once asked me 'what is energy?' So I rattled through the whole orthodox list, mechanical, kinetic, potential, electrical, heat, audio - and how each form may be transformed into another form. But then, the question was repeated 'So ... what is energy?' 'Ummm, matter moving in space, relative to some other matter.' Doesn't apply to potential, that's an object in a field. That snow and those boulders up the hill aren't moving relative to me ... but could be, any minute now. In the end, there's matter moving (or not, relative to me) in space. The rest of what's 'real' is in our minds - each of which is different.