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

41–50 of 103 posts

Re: Is Spacetime Real?

#41

Post by randallsquared »

thisiscorrect wrote: post #28
sailingparrot wrote: post #21

Earlier quoted context omitted.

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 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…

> 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?

Re: Is Spacetime Real?

#42

Post by codeulike »

thisiscorrect wrote: post #14
codeulike wrote: post #10

Earlier quoted context omitted.

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 ca…

"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 radiatio…

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

Re: Is Spacetime Real?

#43

Post by sailingparrot »

AnIdiotOnTheNet wrote: post #37
sailingparrot wrote: post #30

Earlier quoted context omitted.

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.

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.

Re: Is Spacetime Real?

#44

Post by drewcoo »

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…

A scientific theory is a body of knowledge. The special use of the term seems like a false monocotomy.

Re: Is Spacetime Real?

#47

Post by AnIdiotOnTheNet »

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.

> 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.

Re: Is Spacetime Real?

#48

Post by cletus »

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).

Re: Is Spacetime Real?

#49

Post by headsupernova »

jakelazaroff wrote: post #40
bobcostas55 wrote: post #17

Earlier quoted context omitted.

>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.

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?

Re: Is Spacetime Real?

#50

Post by jodrellblank »

AnIdiotOnTheNet wrote: post #37
sailingparrot wrote: post #30

Earlier quoted context omitted.

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.

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.

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?
Post reply on HN