Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Is Spacetime Real?

forbes.com

Post reply on HN
Print view View original

81–90 of 103 posts

Re: Is Spacetime Real?

#81

Post by drran »

sailingparrot wrote: post #43
AnIdiotOnTheNet wrote: post #37

Earlier quoted context omitted.

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.

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.

Aether is real again as Higgs field. Speed of light in vacuum is variable again (gravitational waves). Vacuum is no longer an empty space.

Re: Is Spacetime Real?

#82

Post by drran »

headsupernova wrote: post #49
jakelazaroff wrote: post #40

Earlier quoted context omitted.

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.

Why not?

Mathematics is too powerful. It can express anything, both real and unreal things. Physical world has limitations.

Re: Is Spacetime Real?

#83

Post by drran »

thisiscorrect wrote: post #19
jakelazaroff wrote: post #11

Earlier quoted context omitted.

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.

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.

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.

Re: Is Spacetime Real?

#84

Post by drran »

taylodl wrote: post #56

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 univers…

> 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?

Re: Is Spacetime Real?

#85

Post by sfifs »

sailingparrot wrote: post #36
thisiscorrect wrote: post #28

Earlier quoted context omitted.

"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 t…

> 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 theor…

> 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...

Re: Is Spacetime Real?

#86

Post by umvi »

ncann wrote: post #6
thisiscorrect wrote: post #5

“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 a…

While not a perfect definition of "real", don't we already have images of atoms?

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.

Re: Is Spacetime Real?

#87

Post by marshmallow_12 »

in 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?'”

Re: Is Spacetime Real?

#88

Post by drran »

jaybrendansmith wrote: post #76
jodrellblank wrote: post #55

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 b…

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…

> 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

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-aft...

Re: Is Spacetime Real?

#89

Post by contravariant »

akvadrako wrote: post #65
JumpCrisscross wrote: post #35

Earlier quoted context omitted.

> 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…

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.

Well you can visualize them well enough for basic chemistry if you just view them as spheres with a certain fixed number of lines (bonds) sticking in or out of them. I don't think anyone would call this model real, but it's arguably more relevant to daily life than more fundamental descriptions.

Re: Is Spacetime Real?

#90

Post by unanswered »

sailingparrot wrote: post #36
thisiscorrect wrote: post #28

Earlier quoted context omitted.

"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 t…

> 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 theor…

> I would add however, that you can reach out and touch an atom with a certain definition of touch

And unfortunately for your argument, the bit you elided here is the critical bit. If we understand "touch" meaning to interact with something "physically" rather than "chemically" or indirectly (light, sound), then "touch" refers essentially to electromagnetic force and the Pauli exclusion principle. Since the latter can only be defined in terms of yet more "matter", in fact we have no way to observe matter in any way but electromagnetism in its various forms, viz. "light" in a wide sense, chemical interaction, and via magnetic repulsion on macroscopic or microscopic scales. Given this, I would say it's largely correct to understand atomic theory as useful abstraction; indeed, an abstraction which dates back hundreds of years which has been refined and found still useful. That said, something being an abstraction doesn't make it not real! Indeed I'm not entirely sure I know what else "real" is supposed to be.

Post reply on HN