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Why Understanding Space Is So Hard

nautil.us

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Re: Why Understanding Space Is So Hard

#51

Post by klank »

ratsmack wrote: post #36
kazinator wrote: post #24

The question "would space still exist if matter disappeared" is posed with an ontological bias which influences the answer. A better question is: does a universe in which there is nothing (and never has been) still contain space? (Though a better question, I wrecked it by introducing "never", which presupposes that the universe has time---even though it contains nothing, and therefore no events take place.) The quest…

Time is simply a measure of change, so if there is nothing to change how can there be time?

This isn't entirely accurate.

Think of the exact same system performing the same intra-system permutations (changes) but in two different reference frames (one relativistic and the other not). The changes are identical but the time required by each will be different due to their different reference frames. If time was simply a measure of change than you would expect the time taken by these two systems to be identical. Time then takes on a quality (or rather perhaps has a dependency) that exists beyond simply a "measure of change".

Re: Why Understanding Space Is So Hard

#52

Post by danbruc »

colordrops wrote: post #49
danbruc wrote: post #42

Earlier quoted context omitted.

I am actually not sure that this is true. I used to think exactly like you, that rotations are just piles of small translations with time varying directions, but there is a problem with this, linear momentum and angular momentum are two different conserved quantities. If it were the case that rotations are just translations then you should be able to get rid of angular momentum and its conservation and explain it in…

Angular momentum is an abstract concept, and an emergent property. It doesn't exist inherently in an object.

Spin angular momentum seems to be a pretty intrinsic property of (fundamental) particles. What do you understand as inherent properties of objects? Position? Charge? Mass? Velocity? Energy? Linear momentum? Spin? And why? What if the object is composite? What about quantum physics, e.g. superposition states?

Re: Why Understanding Space Is So Hard

#53

Post by Animats »

colordrops wrote: post #49
danbruc wrote: post #42

Earlier quoted context omitted.

I am actually not sure that this is true. I used to think exactly like you, that rotations are just piles of small translations with time varying directions, but there is a problem with this, linear momentum and angular momentum are two different conserved quantities. If it were the case that rotations are just translations then you should be able to get rid of angular momentum and its conservation and explain it in…

Angular momentum is an abstract concept, and an emergent property. It doesn't exist inherently in an object.

Centrifugal force is an abstraction, but angular momentum has physical reality at the subatomic level. See Feynman, chap. 17.[1] Photons have angular momentum, even though they don't have a meaningful size. This is strange, but it's reality.

[1] http://www.feynmanlectures.caltech.edu/III_17.html

Re: Why Understanding Space Is So Hard

#56

Post by danbruc »

jopython wrote: post #54

Space is infinite. It seems most humans cannot comprehend/accept infinity. Without understanding infinity you will have a hard time understanding space.

That is not a known fact, we have no idea whether space is finite or infinite, whether it has boundaries or not. Admittedly at least a finite universe with boundaries seems kind of a strange idea, but who knows.

Re: Why Understanding Space Is So Hard

#57

Post by hyperion2010 »

I was walking along the other day after a class about mathematical modelling of biomolecules and was suddenly struck by the thought that space doesn't really even exist. This came from the observation that when we calculate van der Waals interactions there are two terms [0] and the term raised to the 12th power is an approximation to account for the fact that down at the quantum level two electrons cannot occupy the same orbital. We can map electron orbitals onto space but then we get something funky like the Pauli exclusion principle and suddenly a force that appears to be 'spatial' in origin is now a consequence of a completely non-spatial phenomenon. We use space as a convenient intermediate in many measurements but it is not clear to me that the fundamental accounting system of the universe actually needs it (though as the article points out, general relativity seems to suggest that space-time does exist or at least provides a pretty reliable coordinate system).

0. https://en.wikipedia.org/wiki/Lennard-Jones_potential

Re: Why Understanding Space Is So Hard

#58

Post by klank »

Animats wrote: post #53
colordrops wrote: post #49

Earlier quoted context omitted.

Angular momentum is an abstract concept, and an emergent property. It doesn't exist inherently in an object.

Centrifugal force is an abstraction, but angular momentum has physical reality at the subatomic level. See Feynman, chap. 17.[1] Photons have angular momentum, even though they don't have a meaningful size. This is strange, but it's reality. [1] http://www.feynmanlectures.caltech.edu/III_17.html

Angular momentum could be encoded in the wave function.

http://arxiv.org/abs/0807.3930

Re: Why Understanding Space Is So Hard

#59

Post by laotzu »

jsprogrammer wrote: post #45
kazinator wrote: post #24

The question "would space still exist if matter disappeared" is posed with an ontological bias which influences the answer. A better question is: does a universe in which there is nothing (and never has been) still contain space? (Though a better question, I wrecked it by introducing "never", which presupposes that the universe has time---even though it contains nothing, and therefore no events take place.) The quest…

How about this question: Is there a space with no matter?

Is there matter with no space in it?

Re: Why Understanding Space Is So Hard

#60

Post by laotzu »

JTon wrote: post #55
jopython wrote: post #54

Space is infinite. It seems most humans cannot comprehend/accept infinity. Without understanding infinity you will have a hard time understanding space.

Can some humans comprehend infinite? I mean truly.

No. That would take infinite time to comprehend, right?
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