
Why Understanding Space Is So Hard - dnetesn
http://nautil.us/blog/this-is-why-understanding-space-is-so-hard
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kazinator
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 question creates a bias because when we imagine matter being removed from
the universe, we firstly imagine the removal as an event unfolding in time.
Secondly, we continue to imagine the locations where pieces of matter _used_
to be, and those locations continue to be separated by the abstract space
which we continue to imagine.

~~~
grondilu
I've struggled several times to formulate this question properly. I'm not
convinced by your formulation. I'll give it an other try.

Does space have an existence per se, that is regardless of the matter it
contains, or is it just a mathematical framework for the interactions between
particles?

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gkya
This requires a definition of space. For your question to be logical, _space_
should be taken as the thing that is among and around matter. Then on it may
be researched physically. Buf if _space_ is taken to mean the thing that
exists among and around _perceivable_ matter, then your question becomes
obscure, as this means that space is matter, but just not perceivable. And
therefore it exists, also without relation.

~~~
grondilu
We know what space is, at least operationally. Or rather space-time. Space is
what can be measured with rigid rods. Time is what clocks measure. Einstein
painstakingly defined those concepts this way.

Plank's question is more metaphysical : beyond what it means experimentally,
does space have a -physical- existence per se, even in a completely empty
universe? In other words, is an empty universe different than no universe at
all? If not, one way to look at space it is to consider it as a set of
abstract rules regarding the possible interactions between particles, those
rules being very close to what we call geometry.

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CPLX
Space is big. Really big. You just won't believe how vastly, hugely, mind-
bogglingly big it is. I mean, you may think it's a long way down the road to
the chemist, but that's just peanuts to space.

~~~
danbruc
_52! is the number of different ways you can arrange a single deck of cards.
Let 's try to wrap our puny human brains around the magnitude of this number
with a fun little theoretical exercise. Start a timer that will count down the
number of seconds from 52! to 0. We're going to see how much fun we can have
before the timer counts down all the way.

Start by picking your favorite spot on the equator. You're going to walk
around the world along the equator, but take a very leisurely pace of one step
every billion years. Make sure to pack a deck of playing cards, so you can get
in a few trillion hands of solitaire between steps.

After you complete your round the world trip, remove one drop of water from
the Pacific Ocean. Now do the same thing again: walk around the world at one
billion years per step, removing one drop of water from the Pacific Ocean each
time you circle the globe. Continue until the ocean is empty.

When it is, take one sheet of paper and place it flat on the ground. Now, fill
the ocean back up and start the entire process all over again, adding a sheet
of paper to the stack each time you’ve emptied the ocean. Do this until the
stack of paper reaches from the Earth to the Sun.

Take a glance at the timer, you will see that the three left-most digits
haven’t even changed. You still have 8.063 × 10⁶⁷ more seconds to go. So, take
the stack of papers down and do it all over again. One thousand times more.
Unfortunately, that still won’t do it. There are still more than 5.385 × 10⁶⁷
seconds remaining. You’re just about a third of the way done._ [1]

Well, the volume of the visible universe is 3.4 × 10⁸⁰ m³ and therefore
another factor of 4.2 trillion larger than 52!. And then the entire universe
is estimated to be at least another 150 or 250 times larger than the visible
universe. In diameter, not volume.

[1] [http://czep.net/weblog/52cards.html](http://czep.net/weblog/52cards.html)

~~~
scoj
Wow. Thank you for sharing this. Amazing to try and wrap your head around
this.

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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](https://en.wikipedia.org/wiki/Lennard-Jones_potential)

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colordrops
Spinning motion is an illusion and doesn't exist as a fundamental form of
movement, similar to how lack of gravity in orbit is an illusion, in that you
are continuously falling downward but missing the earth.

Spinning objects are made of particles that are all actually going in straight
lines but forces against each other are causing them to change direction,
cummulatively appearing to be spinning, like an extremely coherent eddie
current or vortex. Their movement is in relation to each other, and there is
no need for an objective space in which to spin.

~~~
tarikjn
Suppose your object is the only thing in space, how do you tell that it is
spinning? How do the particles in the object can tell that the object as a
whole is spinning?

What you describe are particules going in straight lines, but over what
space/grid are they going on a straight lines? If they are going over straight
lines on something then your description is one of an objective space.

If pulling forces are still exerted on its edges in proportion to said
"spinning", then there exist a static field in space for which the object is
in static alignment when the pulling force are at minima.

Interestingly the same observation could be made of two objects in orbit or
the electrons orbiting individual atoms in the object, with the static
alignment being observed when the acceleration between the objects is at a
maxima i.e. they are falling into one another.

~~~
colordrops
They are going in straight lines in relation to the other particles in the
object. Then the force of one particle exerts on another particle as they get
closer or further from each other, causing them to change direction. This
happens for innumerable numbers of particles, appearing like a singular object
that is spinning, since the forces are too great to pull the object apart. If
you spin it fast enough, the particles will overcome the atomic forces holding
it together, and the object will break apart, with the individual pieces
continuing to move in a straight line.

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abecedarius
Julian Barbour's _The Discovery of Dynamics_ goes into great detail on
absolute vs. relative pre-Einstein. His _The End of Time_ reviews the ideas at
a more popular level and continues the story into the 20th C.

~~~
ashark
Do you have the paperback? If so, is it well-constructed? I'm interested, but
with so many pages I'm wary of the format. I'd usually buy something like this
in hardcover but the paperback's not cheap and the hardcover's far more
expensive, and seemingly out of print.

~~~
abecedarius
I'm afraid I don't know -- I read a pdf, and a library hardback for the latter
book. That one shouldn't be hard to find from a U.S. library, and would tell
you whether you want to delve into the former. (Which I found really
interesting, though it's maybe too ready to valorize Ptolemy just because we
know so little about his predecessors.)

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amelius
I'm still wondering why space is 3-dimensional.

~~~
gobbo
Doesn't need to be, but observations constrain extra spacial dimensions to be
compact and under ~1mm in size.

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donutz
Does anyone have a good way of explaining to a layman how a dimension can be
small?

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aardvark179
Consider the outside of a straw. The surface is a curved two-dimensional space
which is bounded in one direction only by the length of the straw, but is
quite small in the other (the circumference of the straw). If the straw is
very long and very thin then it may appear to be essentially 1-dimensional,
but the surface is still two dimensional.

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DubiousPusher
Nice example. Wouldn't there be easily measurable evidence of this? Imagine a
flattened caterpillar like creature living on such a straw. Unwittingly, one
day it might wrap itself round the straw many times. Looking back, seeing
itself turned round the straw in this way, wouldn't it see slices of itself
rather than a whole?

~~~
evanpw
In the caterpillar's universe, light rays wrap around the surface of the straw
too, so they won't see anything "missing".

~~~
DubiousPusher
Awww, of course.

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hownottowrite
Do not skip the comments on this post. Priceless.

~~~
gobbo
Yes, great comments, I'd pay to see the deleted one though, based on the
replies.

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Videweo
Rather illuminating. I like to think that this could open some interesting
thought experiment in centrifugal space travel.

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hashmymustache
Do objects have inertia in higher dimensions?

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

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JTon
Can some humans comprehend infinite? I mean truly.

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

~~~
yarou
To understand recursion, you must understand recursion.

