6 ms·
What is spacetime made of?
- ivansavz 4y agoI couple of weeks ago, I watched a really good talk by Nima Arkani-Hamed on the same topic: https://www.youtube.com/watch?v=GL77oOnrPzY https://www.youtube.com/watch?v=GL77oOnrPzY that I discovered via https://news.ycombinator.com/item?id=33229614 https://news.ycombinator.com/item?id=33229614 I found Nima's lecture to be a masterclass on how to explain very advanced physics topics without using unnecessary jargon, or math. Highly recommended for anyone interested in this topic.
- ThinkBeat 4y agoI wonder if we will bump into something that we are just not able to figure out. Something beyond human comprehension. I have a highly unpopular opinion that time might be that thing. I also think that fully comprehending it and being able to influence it is a universal key to how it all works™. And if we did figure it out, we would cease to exist in a recursive manner before we could do much damage.
- signalToNose 4y agoSite down?
- mikewarot 4y agoNon-majority opinion/Guestimate of reality follows: I think that spacetime is an emergent phenomenon of something that has no dimensions. Imagine RAM in your computer, inherently there's an address dimension when the CPU needs to read/write data, but the actual physical location doesn't matter (other than latency). How correlated two bits of matter/energy/spacetime are is a good proxy for distance, except when it isn't. A photon leaves a star, then strikes your eye a billion years later, and those events could be entangled, as far as the photon is concerned, they happened at the same instant in time. However the laws of physics work, I don't see how there can be any direct mapping between what we see, and the underlying quantum phenomenon, as long as light and quantum superpositions / entanglement, are things.
- colechristensen 4y agoThis kind of terminology soup speculation isn’t helpful. Don’t muddy the waters when you don’t know enough to add anything of value.
- Koshkin 4y agoThe article itself isn’t much better: If space is made of entanglement, then the puzzle of quantum gravity seems much easier to solve: instead of trying to account for the warping of space in a quantum way, space itself emerges out of a fundamentally quantum phenomenon.
- zachf 4y agoI have a PhD in a closely related field and I'm not sure what you mean--this sentence is well-formed and basically correct, if slightly simplified to appeal to laymen.
- wrycoder 4y ago“If space is made of entanglement, then it emerges out of a fundamentally quantum phenomenon.” This makes sense to you?
- zachf 4y agoIts the part that you omitted from your summary that makes the statement nontrivial—the idea that the metric theory (poetically, the warping of space) is only valid as a low energy effective description, and the general case does not have a classical interpretation even in a limit. To put it another way: the quantum theories that are best understood are the ones that are similar to a classical field theory, but that’s not the case here.
- wrycoder 4y agoIt appears that when I eliminated inessential verbiage, what remained was a tautology.
- satvikpendem 4y agoWhy, luminiferous aether of course!
- akomtu 4y agoIf we're talking about aether, then it's worth mentioning that the seven elements have been traditionally earth, water, fire, air, aether (magnetic field), space (aka the emptiness) and consciousness.
- dimensionc132 4y ago
- ogogmad 4y agoScientific American's reputation is in the toilet: https://www.math.columbia.edu/~woit/wordpress/?p=13152 https://www.math.columbia.edu/~woit/wordpress/?p=13152 I don't recommend wasting your time.
- butMebbe 4y agoMiddle management idiocracy has taken over to “create jobs” everywhere.
- Akronymus 4y agoDont they kinda have to, to avoid falling into problems with the DEI crowd?
- TEP_Kim_Il_Sung 4y agoad majorem Dei gloriam
- butMebbe 4y agoExactly. There’s no law forcing me me to chip into healthcare. Tacit admission in the US I don’t have to care any other meat bag exists; why should I care what they have to say?
- zachf 4y agoPeter Woit has strong opinions but they're often not representative of the physics community as a whole. In my opinion, which as a physicist myself I think matters as much as Woit's (i.e. not much), Scientific American is variable in quality, but I wouldn't dismiss the article before reading it. This article does a pretty good job of summarizing a range of modern ideas about spacetime. I see that it introduces laymen to some of the important names in the field, including van Raamsdonk and Maldacena, and presents their important and influential work in an accessible way. No paywall version: https://web.archive.org/web/20221124171006/https://www.scientificamerican.com/article/what-is-spacetime-really-made-of/ https://web.archive.org/web/20221124171006/https://www.scien...
- WastingMyTime89 4y agoThis article is framed in a way I find epistemologically suspect. It confuses observations, models and truth. Some of its intertitles are meaningless like "Will we ever know the real nature of space and time?". The article is actually about models in which spacetime is an emergent property of more fundamental structures: string theory and loop quantum gravity. Both face a lack of experimental evidences validating their predictions.
- Koshkin 4y agoBut the question, then, is: is there reality behind the model (or, rather, how close to reality the model is)? The answer lies in how accurate the model is. This is all we can know in this regard.
- WastingMyTime89 4y agoBut knowing if there is reality behind the model is not a scientific question. There is no tool in science which can answer that. The only thing that matters is how well the model predicts what we observe. One can believe that’s a form of truth but people should be conscious that it is merely a belief.
- hnews_account_1 4y agoThis is not strictly true. The recent Nobel was such an expedition which was ignored by scientists in the 40s-70s as an esoteric philosophical question that cannot be answered. It is still not “answered” per se but Bell’s formulations leave very few choices for the base reality of the model. Observe that the model itself worked quite well regardless of the base reality. Knowing that truth doesn’t change any current applications. But who knows where it’ll lead. So knowing which model is successful and which model is real is a very important question that we must try our best to answer. Only in the natural sciences can such a question even be answered.
- pyinstallwoes 4y agoNo matter how good a model is, a simulacrum is still a simulacrum.
- thriftwy 4y agoAre there any formulas supporting this or that composition of spacetime? Until there's math it's a simple handwaving.
- zachf 4y agoOne of the most important papers in this field is [0]. (As is common in science, it built on a long history of nearby ideas, e.g. [1].) An important calculation done around this idea is presented in [2], in which remarkable progress is made on Hawking's black hole information paradox. All of these papers have some amount of mathematical backing, but you'll find plenty of formulas and calculations in [2]! [0] https://arxiv.org/abs/1306.0533 https://arxiv.org/abs/1306.0533 [1] https://arxiv.org/abs/1005.3035 https://arxiv.org/abs/1005.3035 [2] https://arxiv.org/abs/1908.10996 https://arxiv.org/abs/1908.10996
- thriftwy 4y ago> General relativity contains solutions in which two distant black holes are connected I can see these as artifacts of insisting to work in 3D coordinates and dealing with artifacts of projection where it breaks down, instead of working in honest 4D coordinates where formulas are much simpler and everything is smooth. How would two connected black holes look like in Kruskal–Szekeres coordinates? Where's the firewall in case of Kruskal–Szekeres coordinates? Where's the firewall at all if the event horizon seemingly moves away from you as you approach the wormhole?
- deleted 4y ago[deleted]
- zachf 4y agoThe existence of those solutions is independent of a choice of coordinates. (Nothing in GR is ever allowed to depend on coordinates, in the end!) The existence of the second asymptotic region is easiest to see from the Penrose diagram of the Schwarzschild black hole. A derivation of this that uses Kruskal coordinates is in [0], see Figure 3.3 for the result. [0] https://scholar.harvard.edu/files/yshi/files/physics_211r_-_black_holes_final.pdf https://scholar.harvard.edu/files/yshi/files/physics_211r_-_...
- kordlessagain 4y agoSpacetime is the Ether, in my opinion. This was tested, but never proved/disproved: https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_exper... Here's a paper on it: https://www.researchgate.net/publication/283669822_Connection_between_Gravity_and_Electromagnetism https://www.researchgate.net/publication/283669822_Connectio... The upshot is a charged shell will modify the acceleration/inertia of particles inside the shell, according to Weber's Electrodynamics: https://en.wikipedia.org/wiki/Weber_electrodynamics https://en.wikipedia.org/wiki/Weber_electrodynamics
- hdjjhhvvhga 4y agoWell, the concept of ether/aether had many forms and some of them were definitely disproved. The wiki link you gave basically confirms the absence of aether at increasingly smaller scales.
- deleted 4y ago[deleted]
- duozerk 4y ago> Spacetime is the Ether, in my opinion. This was tested, but never proved/disproved Am I missing something ? because you just linked an article that clearly disproves your first assertion. ... and followed it by what looks like a poorly written research article by a self described "independent physicist" (https://nitter.net/tavi_balaci https://nitter.net/tavi_balaci) with only three published articles and all kinds of red flags.
- kordlessagain 4y agoYeah, I hear you. > After all this thought and preparation, the experiment became what has been called the most famous failed experiment in history. We accept Maxwell's equations as the truth, not Weber. I'm not saying this alternate approach is true, it's just my opinion we missed something, collectively. The paper is likely poorly written, but it's something I found while researching this a few years ago. Just sharing it for others to see. Again, my comment isn't claiming one way or the other...
- Razengan 4y agoMemory addresses?
- swayvil 4y agoProbably emotions. An endless torrent of the stuff. Like your favorite song, minus the words and notes. Which is then interpreted as sights, sounds, smells, thoughts (we love those), feelings, time, space, things, pizza, money, etc.
- college_physics 4y agothese folks are doing their best to combine and extrapolate mathematical principles to extremes (an approach which, nota bene, did prove spectacularly successful in explaining huge parts of the universe earlier on) but the results of this exercise has been exceedingly poor for almost half a century now. at some point we must give up or admit that the nature of the game has changed. In a sense even the tiniest piece of experimental evidence that probes (or at least remotely reflects) the actual inner workings of "quantum" spacetime would be worth more than this enormous cumulative effort to infer what is happening on the basis of abstract symmetries and what not.
- awinter-py 4y agothere were cool things that came from pure math in the early quantum + relativistic era -- lasers + black holes were math constructs before we thought to build them / look for them in the sky I think (as an outsider to this field) the 'probing' now has fallen to the quantum computing people. their day job is basically making houses of cards out of entangled particles; if there are tricks to be learned about entanglement, they may be the ones to find them
- ngcc_hk 4y agoAnd superposition. The other part like quantization of field and the wave function … decoherence.
- zachf 4y agoYou might be excited by [0]. The idea there is to study a novel phenomenon in strongly-coupled quantum systems that is very complex to see ordinarily, but becomes easy to understand when you look at the same physics from the gravitational perspective. That would be a nontrivial experimental check of AdS/CFT duality. It's effectively a novel form of "quantum teleportation" wherein an excitation is transmitted between systems using the quantum equivalent of a gravitational wormhole [1]. [0] https://arxiv.org/abs/1911.06314 https://arxiv.org/abs/1911.06314 [1] https://arxiv.org/abs/1608.05687 https://arxiv.org/abs/1608.05687
- awinter-py 4y agosigh not sure why you'd try explaining LQG to a layperson without 'background independence' as a motivating concept would rather see pop sci invest in explaining the actual concepts to laypeople, rather than their philosophical implications like give me an interactive intro to witten diagrams as a way into ads-cft + holography or like make lie groups interesting somehow please the theoretical physicist they interview in the first paragraph has videos about her specific work (kozsul duality) which go deeper into the concepts https://www.youtube.com/watch?v=VW87-4t-Fsg https://www.youtube.com/watch?v=VW87-4t-Fsg